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Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Primary Total Replacement of the Dysplastic Hip*

FARES S. HADDAD, B.SC., M.CH.(ORTH), F.R.C.S.(ORTH), BASSAM A. MASRI, M.D, F.R.C.S.(C), DONALD S. GARBUZ, M.D., F.R.C.S.(C) and CLIVE P. DUNCAN, M.D., F.R.C.S.(C), VANCOUVER, BRITISH COLUMBIA, CANADA

An Instructional Course Lecture, American Academy of Orthopaedic Surgeons

	Introduction

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
Developmental abnormalities following such childhood conditions as congenital dislocation and dysplasia of the hip, Legg-Calvé-Perthes disease, and slipped capital femoral epiphysis are the most common cause of secondary osteoarthritis of the hip^3,43 and may be a cause of degeneration in a large portion of patients with so-called idiopathic osteoarthritis of the hip⁴³. Despite concerted screening programs, a large number of patients still have the sequelae of dysplasia or dislocation of the hip in adulthood^37,117.

The severity of hip dysplasia varies widely, ranging from the shallow acetabulum to the completely dislocated and so-called high-riding hip. Osteoarthritis of the hip secondary to hip dysplasia, therefore, presents a broad spectrum of reconstructive challenges. Hips that have mild anatomical abnormalities can be treated with standard primary total hip replacements, but until recently others would have been labeled unreconstructible¹⁶. Because patients who have hip dysplasia are often young and active, it is critical to understand the complexities of total hip replacement in this group and to plan any interventions meticulously. To this end, the nature and the extent of the preoperative deformities and abnormalities must be understood, and the problems that have been obstacles to obtaining satisfactory fixation with acceptable long-term function must be addressed. In this paper, we present an overview of the classification and assessment of the dysplastic hip with secondary osteoarthritis and summarize the current knowledge about total hip arthroplasty in patients who have this disorder.

	Anatomy

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
A thorough understanding of both the clinical and the radiographic anatomy of the dysplastic hip is necessary in order to plan and perform a reconstruction of the hip that will yield satisfactory long-term results. This anatomy may be distorted by the primary disorder and by the effects of previous operations.

The anatomical abnormalities that are present depend on the severity of the dysplasia^94,116. In a low subluxation, the acetabulum is shallow but may have a wide, oval opening. The anteromedial aspect of the acetabular wall may be very thin, but there is usually better bone stock posteriorly. In a high dislocation, the affected side of the pelvis is smaller and the acetabular wall is thin, soft, and, in some patients, grossly anteverted.

The abnormal anatomy of the proximal aspect of the femur includes a small femoral head with a short neck that is usually markedly anteverted^19,25,53,82, posterior displacement of the greater trochanter¹⁶, and a narrow, straight, tapered femoral canal with a tight isthmus^19,82,94. The neck-shaft angle is also often increased^38,98. The complex abnormalities of the proximal aspect of the femur in hip dysplasia have led to the inclusion of a rotational malalignment category in the American Academy of Orthopaedic Surgeons' classification system of femoral bone deficiency in primary and revision hip arthroplasty²⁰ (Figs. 1-A and 1-B).

View larger version (18K): [in this window] [in a new window]   Fig. 1-A Illustration showing the distorted anatomy of the proximal aspect of the femur, which includes excessive anteversion of the femoral neck and posterior displacement of the trochanter.

View larger version (21K): [in this window] [in a new window]   Fig. 1-B Illustration showing one method of treatment of this deformity, which can be managed in a number of ways. Here, the greater trochanter is moved laterally at the time of reattachment in order to increase the lever arm of the abductors. The femoral component is inserted in the desired version. Alternative forms of treatment include subtrochanteric rotational osteotomy and the use of modular implants and custom prostheses.

There are also a number of secondary anatomical anomalies. Most of the soft tissues, particularly the hamstring, adductor, and quadriceps muscles, are shortened. Proximal migration of the femoral head leads to a relatively horizontal orientation of the abductor muscle mass, which can easily be damaged at the time of reconstruction. Moreover, the hip capsule may have an hourglass configuration, extending from the rim of the hypoplastic acetabulum, narrowing substantially, and then enlarging to surround the dislocated femoral head. The hip capsule may be thickened, and, in association with a hypertrophic psoas tendon, may make the exposure and femoral mobilization difficult. The sciatic nerve is shortened and may be vulnerable to injury if limb-lengthening is attempted^14,26,32,73. The femoral nerve and the profunda femoris artery are both at increased risk of direct injury, as their course is altered by the high-riding femur. The femoral nerve may be forced to proceed laterally and superiorly on exiting the pelvis, rendering it very vulnerable to injury from traction when the medial structures are retracted. Likewise, the profunda femoris artery may be injured at the inferior pole of the acetabulum, which is normally a safe zone.

	Classification

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The dysplastic hip presents such a wide range of abnormalities with their own inherent difficulties that a classification system is necessary in order to compare data from different studies. A number of such systems have been described, and these will be outlined. However, there is clearly a need for a universally accepted system so that all authors can report their results in a common language. At this time, the classification system of Crowe et al. comes closest to fulfilling this need, particularly regarding stratification for the assessment of outcomes¹⁹.

In the radiographic assessment of the dysplastic hip, the height of the pelvis, the junction of the head and neck, and the teardrop can usually be identified. Crowe et al. classified dysplastic hips radiographically into four categories on the basis of the extent of proximal migration of the femoral head¹⁹. They estimated that the normal height of the femoral head is 20 percent of the height of the pelvis. They differentiated their classes on the basis of the distance from the bottom of the teardrop to the junction of the head and neck. In normal hips, these landmarks are at approximately the same level. The proximal migration of the femoral head can then be expressed as a percentage of the height of the pelvis or as a percentage of the height of the femoral head. Class I represents proximal displacement of less than 10 percent of the height of the pelvis or, in other words, proximal subluxation of the femoral head of less than 50 percent of the height of the femoral head. Class II represents proximal displacement of 10 to 15 percent of the height of the pelvis or 50 to 75 percent of the height of the femoral head. For Class III, these values are 15 to 20 percent of the height of the pelvis or 75 to 100 percent of the height of the femoral head. Class IV is assigned when the proximal migration is more than 20 percent of the height of the pelvis or more than 100 percent of the height of the femoral head.

Hartofilakidis et al. divided dysplasia and dislocation of the hip into three categories: dysplasia; low, or subtotal, dislocation; and high, or total, dislocation^44,45. In dysplasia, the femoral head is subluxated but is still contained within the original (true) acetabulum. Hartofilakidis et al. noted a superior segmental deficiency and a shallow acetabulum due to an osteophyte covering the acetabular fossa. In a low dislocation, the femoral head articulates with a false acetabulum that partially overlaps the true acetabulum. There is both an anterior and a posterior segmental deficiency, and the acetabulum has a narrow opening and is of inadequate depth. In 74 percent (thirty-two) of forty-three hips with a low dislocation, there was also excessive acetabular anteversion⁴⁵. In a high dislocation, the femoral head is superior and posterior and articulates with a hollow in the acetabular wing. The entire rim of the true acetabulum is deficient, and the acetabulum is excessively anteverted, lacks depth, and has a narrow opening. The bone stock is mainly located superoposteriorly.

Because the acetabular location and bone stock determine the type of reconstruction that is necessary, we have found it helpful to use a similar system in our preoperative planning. The height of the acetabulum and the available bone stock are assessed. If the acetabulum is in its normal location but there is some loss of coverage of the femoral head (Fig. 2), the patient can be managed with the insertion of a low-profile cup with or without added osseous support. A twenty-two-millimeter-diameter femoral head may be required to ensure an adequate polyethylene thickness of the acetabular component. If the acetabulum is at an intermediate height, with or without satisfactory bone stock for reconstruction in that position, a decision must be made regarding whether to place the acetabular component at the level of the false acetabulum or to bring it down to the true acetabulum. The final decision may be made intraoperatively in some instances (Figs. 3-A, 3-B, 4-A and 4-B). If the acetabulum is very high and markedly dysplastic, the socket usually is brought down to the level of the true acetabulum and the femur is shortened as necessary (Figs. 5-A and 5-B).

View larger version (89K): [in this window] [in a new window]   Fig. 2 Anteroposterior radiograph of the pelvis, showing a low dislocation on the left side. A standard total hip arthroplasty can be performed in this case. A twenty-two-millimeter-diameter femoral head should be available.

View larger version (93K): [in this window] [in a new window]   Figs. 3-A and 3-B: Anteroposterior radiographs of the pelvis of a patient who had an intermediate dislocation on the right side. Fig. 3-A: Preoperative radiograph.

View larger version (109K): [in this window] [in a new window]   Fig. 3-B It was possible to place a porous-coated acetabular component at the level of the true acetabulum. The component was augmented with an autogenous femoral head graft.

View larger version (107K): [in this window] [in a new window]   Figs. 4-A and 4-B: Anteroposterior radiographs of the pelvis of a patient who had bilateral dysplasia of the hip with secondary degenerative changes. Fig. 4-A: Preoperative radiograph. An acetabular osteotomy had been performed previously on the right.

View larger version (88K): [in this window] [in a new window]   Fig. 4-B Total hip arthroplasty was performed with use of a so-called high hip center with medial placement of the socket. No supplementary structural bone-grafting was used. The greater trochanter was placed laterally with so-called dynamization of the abductors.

View larger version (98K): [in this window] [in a new window]   Figs. 5-A and 5-B: Anteroposterior radiograph of the pelvis of a patient who had bilateral dislocation of the hip. Fig. 5-A: Preoperative radiograph.

View larger version (111K): [in this window] [in a new window]   Fig. 5-B A subtrochanteric shortening derotational osteotomy was necessary in order to perform a reconstruction at the level of the true acetabulum.

Kerboul et al. classified dysplastic or dislocated hips as anterior, intermediate, or posterior on the basis of the pathological femoral anatomy⁶⁶. The anterior classification is given for low subluxations; the intermediate classification, for high subluxations; and the posterior classification represents high, unstable hips.

Mendes et al. recently proposed a classification of adult congenital hip dysplasia for the planning of a total hip arthroplasty⁸³. There are two broad types, high and subluxated. Primary considerations are the bone stock, which may be adequate or deficient, and the inclination of the acetabulum, which may be normal or superior. Secondary considerations define soft-tissue abnormalities in terms of contractures and muscle weakness. Tertiary considerations address the associated problems of pelvic obliquity and lumbar curvature, valgus deformity of the knee, and limb-length inequality. This system provides a useful algorithm for the planning of a replacement of a dysplastic hip, but it is not quantitative enough to be useful for comparing results from different centers.

Of these classification systems, that of Crowe et al.¹⁹ is the most quantitative and the simplest to use, allowing for the comparison of results of operative treatments with various techniques. For these reasons, we favor this classification system over the others.

	Assessment

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The treatment of the dysplastic hip depends on the severity of the disease, the extent of the secondary osteoarthritic changes, the age and the functional goals of the patient, and the availability of bone stock. For most patients, pain in the hip is the primary symptom, although a major limb-length discrepancy, a severe limp, pain in the back, or symptoms in the knee commonly play a part. Many of these patients are first seen at a young age, and either femoral or pelvic osteotomy may be suitable for them. Judicious intervention at an early stage may delay total hip replacement for a long period; it may also facilitate the reconstruction in the long run, although there is no clear evidence for this at present.

Patients with congenital hip dysplasia often have fatigue in the hip early in adult life, may have a marked limb-length inequality, and usually have an abductor lurch. Many have no symptoms until middle age, when they have pain in the back secondary to an exaggerated compensatory lumbar lordosis. Patients with bilateral hip dysplasia have a positive Trendelenburg's test bilaterally and walk with a waddle. The symptoms and functional aims of the patient should be carefully assessed. Many patients with bilateral dislocation maintain satisfactory function into later life, with a severe limp but with little pain. As a rule, patients who have class-II or III dysplasia according to the system of Crowe et al.¹⁹ tend to have degenerative changes and symptoms earlier and to need hip replacement at a younger age than do patients who have class-I or IV dysplasia. Despite the markedly abnormal radiographic appearance in patients with bilateral class-IV disease, often these patients do not need operative intervention because they have little pain.

Pelvic tilt, lumbosacral flexibility, fixed deformities of the hip, and true and apparent limb-length discrepancy should be assessed preoperatively, as they will determine the required correction of limb length. It should also be determined whether the patient had any previous operations, as previous procedures may complicate the soft-tissue dissection and influence the choice of approach or prosthesis. Patients should be counseled regarding the increased risks of injury to the femoral and sciatic nerves, vascular injury, prosthetic failure, and infection at the site of the prosthesis. In addition, they should be made aware that, even with a successful reconstruction, they may be left with a residual limb-length discrepancy and a noticeable limp. A realistic appraisal of the long-term outcome of total hip arthroplasty should be given, as young patients have high activity levels and great expectations.

	Previous Operations

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The effect of previous interventions on the outcome of total hip arthroplasty for dysplasia is unclear. Total hip arthroplasty after a previous femoral osteotomy has been associated with higher rates of complications and revision²⁸, although this may not be the case with second-generation techniques of cementing¹¹¹. Shinar and Harris noted that intertrochanteric osteotomy did not, in general, affect the expected excellent results associated with femoral components inserted with use of modern cementing techniques¹¹¹. Severe deformity following subtrochanteric osteotomy, however, did adversely affect the outcome. Boos et al. compared the results of seventy-four total hip arthroplasties carried out after a previous osteotomy of the proximal aspect of the femur with those of seventy-four primary procedures performed in a diagnosis-matched control group during the same period⁸. They detected no significant difference in the rate of perioperative complications (p < 0.38) or the rate of revision (p < 0.28). The only significant differences were greater difficulty with exposure and a longer operating time in the osteotomy group (p < 0.0002). Boos et al. concluded that hip arthroplasty after a previous femoral osteotomy is more demanding technically but is not necessarily associated with a higher rate of complications.

Periacetabular osteotomy and other pelvic osteotomies are increasing in popularity and may improve the acetabular coverage^30,48,122. These osteotomies have the potential to alter the position of the best available bone stock; therefore, careful preoperative assessment is necessary when an arthroplasty is to be performed after such an osteotomy. Chiari believed that his osteotomy made subsequent hip replacement easier¹⁸. Other authors have also suggested that the Chiari osteotomy facilitates the implantation of an acetabular component, but we are not aware of any good long-term data to support this view^51,85,122.

Difficulties certainly arise when hardware from previous operations remains in situ¹². The morbidity associated with the removal of hardware^5,7,57, which is greatest for implants in the proximal aspect of the femur^57,65,72,121, has led some surgeons to advocate leaving the hardware in situ⁶². This view has been reinforced by economic arguments^9,10. In the setting of the dysplastic hip, in which later intervention and, particularly, hip arthroplasty are very likely, we strongly urge the removal of the hardware soon after it has achieved its aims. This approach prevents the great difficulties and complications associated with embedded hardware, which, on occasion, may even be intramedullary by the time that hip arthroplasty is indicated. The presence of any remaining metal in the proximal aspect of the femur should alert the surgeon to the need for specialized equipment such as universal screwdrivers, metal-cutting devices, high-speed burrs, and screw-extraction sets. A decision must be made preoperatively as to the best way to remove the hardware, and secondary options should be detailed, as screw heads are frequently stripped, pins are often solidly ingrown, and plates are deeply embedded. In some circumstances, a staged operation may have to be considered¹². It is sometimes possible to resect the hardware with a segment of bone at the time of femoral shortening (Figs. 6-A and 6-B), provided that this option is considered in the preoperative plan.

View larger version (70K): [in this window] [in a new window]   Figs. 6-A and 6-B: Intramedullary hardware from a previous osteotomy can be managed in one of two ways. Fig. 6-A: The hardware shown in this radiograph was removed by use of the plate as the plane for an extended trochanteric osteotomy. This approach greatly complicated the reconstruction and lengthened its duration.

View larger version (68K): [in this window] [in a new window]   Fig. 6-B: The hardware shown in this radiograph was resected with its associated segment of bone at the time of subtrochanteric shortening.

	Preoperative Planning

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
Preoperative planning is vital in order to ensure the availability of the appropriate equipment and prostheses. Standard radiographs of the pelvis and hip can be supplemented with Judet radiographs in order to assess the available acetabular bone stock. Alternatively, computerized tomographic scans can be used both to determine the available acetabular coverage and to estimate the degree of femoral anteversion (Fig. 7).

View larger version (164K): [in this window] [in a new window]   Fig. 7 Posterior view of a three-dimensional model created from high-resolution computerized tomography to help to evaluate the femoral deformity preoperatively. This model clearly shows the posterior position of the greater trochanter and the crooked proximal aspect of the femur.

Kim et al. used the frog-leg lateral radiograph to determine the reducibility of the dislocation and hence the complexity of the reconstruction needed⁶⁷. They also used preoperative magnetic resonance imaging to show laxity of the soft tissues around the hip even in high dislocations.

In the planning of a total hip arthroplasty for the treatment of osteoarthritis secondary to hip dysplasia or dislocation, detailed templating is vital, as it frequently leads to modifications of either the selection of the prosthesis that is used or the procedure that is performed. On the acetabular side, the position of the true acetabulum should be identified, and a decision should be made as to whether to attempt to restore the acetabulum to its original location. The degree of anteversion of the acetabulum should also be defined, as should the adequacy of the bone stock for satisfactory fixation and coverage. A plan should be formulated, including an estimate of the size of the component to be used, the preferred method of fixation, and the need for bone graft or for any special equipment such as universal screwdrivers, screw extractors, high-speed burrs, and metal-cutters. On the femoral side, the size of the femoral canal and the need for special or custom components should be assessed. Particular attention should be paid to the need for a twenty-two-millimeter inside cup diameter and femoral head, as these are not part of the standard armamentarium of many hospitals. A decision regarding the need for shortening with or without rotational osteotomy of the femur should be made preoperatively.

The preoperative assessment should also include decisions regarding the securing of a wide but safe exposure, the solutions to the problems posed by a hypoplastic or dysplastic acetabulum, the treatment of the distorted or hypoplastic femur, the assessment and relative equalization of any limb-length discrepancy, and the restoration of abductor function.

	Operative Approaches

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
Either the anterolateral or the posterolateral approach to the hip may be used in patients who have a less severe condition. When there is a high dislocation or when abductor retensioning is required, a transtrochanteric or subtrochanteric approach is indicated.

The transtrochanteric approach affords excellent circumferential exposure of the acetabulum, and this improved exposure is deemed by many to justify the difficulties of trochanteric reattachment^11,106. These difficulties can be reduced by careful reattachment techniques and postoperative management.

We favor the so-called trochanteric slide⁸⁰, originally described by Mercati et al.⁸⁴ and more recently popularized by Glassman et al.³⁶. The approach involves a trochanteric osteotomy, which is performed from the posterior aspect of the hip. The gluteus medius and the vastus lateralis remain attached to the trochanteric fragment, thus effectively creating a digastric muscle. The opposing pulls of the two muscles help to prevent postoperative avulsion and escape of the greater trochanter. This approach affords excellent exposure of the acetabulum and can be continued distally to provide exposure of the entire femoral shaft if necessary for the removal of previous hardware or for a corrective femoral osteotomy. The comprehensive acetabular exposure is helpful when superior acetabular allografts or autogenous grafts are needed and particularly during primary arthroplasty for the treatment of high-riding congenital dislocation. So-called dynamization of the trochanteric fragment by sliding the trochanteric fragment more distally in the case of shortening or more proximally in the case of lengthening can be used to advantage when considerable limb-lengthening or limb-shortening is anticipated.

In a similar manner, a very good exposure can be obtained at the time of subtrochanteric femoral shortening by retracting the proximal fragment superiorly or anteriorly in order to perform the acetabular reconstruction¹²⁶. After resection of the femoral head, the femoral shaft is exposed and a transverse osteotomy of the subtrochanteric portion of the femur is performed. The proximal fragment is then retracted superiorly to facilitate the acetabular exposure and reconstruction. Appropriate soft-tissue and tendon releases are performed in order to mobilize that fragment. Alternatively, after the osteotomy, a posterior approach to the hip is used and the fragment is mobilized anteriorly, which results in less stripping of the soft tissues. The subtrochanteric approach obviates the often considerable problems of trochanteric reattachment after the reconstruction, at an anatomical hip center, of a hip with a high dislocation.

Cameron et al.¹³ used an anterior Smith-Petersen approach for class-III and class-IV hips¹⁹ and reported an excellent exposure. However, they also reported a high rate of nerve palsy (two sciatic and two femoral nerve palsies in a series of sixteen hips). Kumar and Shair described an extended iliofemoral approach for total hip arthroplasty in patients with congenital dislocation of the hip⁶⁸; the approach provides a wide exposure but requires the division of a large number of muscles, which may ultimately be weakened by the procedure. Kumar and Shair described only one case and did not demonstrate any objective advantages over the previously described approaches.

Harley and Wilkinson reported a technique of soft-tissue releases of the ilium to bring the hip down before total hip arthroplasty⁴¹. It is, however, difficult to know how much releasing is necessary before the insertion of the trial components at the time of the operation, and such an approach increases the risk of weakness and instability in the postoperative period.

	The Acetabulum

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The reconstruction of the acetabulum is the most important part of the whole procedure. It determines the approach that is used; the type of bone graft (if any) that is needed; and, in many cases, the type of femoral reconstruction that should be performed. The best bone stock available for the reconstruction is usually at the site of the true acetabulum^16,25,27,83, but this may not be the case if there has been a previous acetabular osteotomy or shelf procedure. The acetabular component is optimally placed at the site of the true acetabulum^74,127, although a high, but not lateral, position can be accepted^24,100,118. Obtaining satisfactory acetabular coverage is the key step. For most patients, this necessitates only deeper reaming and use of a small-diameter acetabular component that is porous-coated or inserted with cement. Alternatives include controlled acetabular medialization^49,92, the use of cement or bone graft to augment the acetabulum^76,77, and the use of a reinforcement ring³⁴. Bipolar prostheses have also been used in patients with a dysplastic acetabulum but may lead to acetabular stress fractures and high rates of femoral loosening¹¹⁹.

Acetabular Coverage
The definition of adequate acetabular support varies among centers. We believe that 70 percent of the cup should be covered with intact host bone⁸⁸. The remaining 30 percent can be covered with morseled autogenous graft or allograft, if that is available. Linde and Jensen analyzed the results of 123 Charnley arthroplasties to determine the factors that lead to loosening⁷⁴. The main predictor was a lack of lateral osseous support, followed by the degree of preoperative dislocation and the height of the acetabular component relative to the true acetabulum. When there is deficient superolateral coverage, the stresses shift to the posterosuperior aspect of the acetabulum and to the bone-cement interface¹⁰⁵. If the anterior and posterior bone stock is sufficient to support an acetabular component, as assessed by a detailed preoperative radiographic review and by direct intraoperative inspection, 75 to 80 percent coverage of the acetabular component is acceptable and there is no need for lateral augmentation^105,123.

Small Acetabular Components
When there is only a moderate reduction of acetabular bone stock, the use of a small acetabular component may be satisfactory¹²⁴. In these situations, it is important to ensure that the apex of the acetabulum is superior to the lateral lip. This position decreases the risk of socket breakout laterally and can be achieved by moving the cup medially and preserving the lateral rim. Care should be taken to avoid overreaming, as this reduces the bone stock and provides the potential for axial migration of the cup, loss of position, and fatigue fractures of the acetabulum¹⁹. A corollary of the use of a smaller acetabular component with an outer diameter in the region of forty millimeters is the requirement for a twenty-two-millimeter-diameter femoral head in order to allow for a satisfactory polyethylene thickness.

Sochart and Porter reviewed the results for sixty hips with congenital dysplasia or dislocation, of which forty-three (72 percent) had a small or extra-small Charnley acetabular component (thirty-eight millimeters in diameter or less) inserted with cement¹¹³. At twenty years postoperatively, twenty-two acetabular components (37 percent) had been revised. The probability of survival of the acetabular component was 97 percent at ten years and 58 percent at twenty-five years.

Although acetabular components have traditionally been cemented in place, sockets inserted without cement have produced equivalent results in older patients^59,102 and better results in young patients^103,104. Bone ingrowth could lead to longer-lasting fixation, particularly because, theoretically, it resists both tensile and shear stresses at the host-prosthesis interface.

Cotyloplasty
Dunn and Hess²⁵, and then Hess and Umber⁴⁹, recommended a deliberate fracture of the medial wall of the acetabulum in order to place the acetabular component within the available iliac bone. The medial wall was sometimes augmented with mesh⁴⁹. Fifteen of seventeen hips were found to have an excellent result after a relatively short duration of follow-up (mean, thirty-seven months)⁴⁹.

Hartofilakidis et al. reported the results at a mean of seven years (range, two to fifteen years) after cotyloplasty in eighty-six hips in sixty-six patients⁴⁵. This procedure advances the acetabulum medially by the creation of a controlled, comminuted fracture of the medial acetabular wall. Once formed, the defect is then reinforced with an autogenous graft, and a small cup is inserted with cement. The weight-bearing axis is therefore shifted distal to the acetabulum while anterior and posterior coverage is also gained. Hartofilakidis et al. recommended bed rest for three to four weeks and protected weight-bearing for three to four months after this procedure. Eighty-one (94 percent) of the eighty-six hips had a good or excellent clinical result, and only two acetabular components had to be revised during the study period. The clinical survival rate, with revision of the cotyloplasty acetabular reconstruction as the end point, was 100 percent at five years and 93 percent at ten years. It should be noted, however, that obvious radiolucent lines around the acetabular component were observed on radiographs of twelve of the hips. Two of these lines were progressive, and two additional acetabular components had migrated. Symeonides et al. also reported very good results using this technique¹¹⁷, and Paavilainen et al. proposed a similar technique with use of a Lord cup (Howmedica, Rutherford, New Jersey) inserted without cement⁹².

Hartofilakidis et al. recently reviewed the results at a mean of 7.1 years after total hip replacement in eighty-four hips (sixty-seven patients) with a high dislocation⁴⁶. These replacements were performed through a transtrochanteric approach with use of a cup inserted with or without cement and, in some patients, with the cotyloplasty technique. The femoral canal was prepared with hand reamers in order to avoid cortical perforation, and the psoas tendon and the short external rotators were released to facilitate femoral mobilization. The reconstruction failed at a mean of 6.4 years in eleven hips (13 percent).

The available results associated with this technique are very promising, but careful scrutiny is necessary because the intentional violation of the medial wall may compromise later revisions.

High Hip Center
Alterations in the center of hip rotation dramatically change hip biomechanics and may influence the survival of the hip reconstruction. Johnston et al. developed a mathematical model in order to determine the optimum acetabular location⁶¹. The forces through the hip were lowest when the hip center was as far medial as possible and somewhat anterior and inferior. The greatest forces were generated when the hip center was lateral, posterior, and superior.

Delp et al. developed a three-dimensional computerized model of the hip in order to study the effects of moving the hip center and altering the length of the femoral neck on the moment arms and force-generating capabilities around the hip^22,23. They showed that superior displacement alone could easily be compensated for by increasing the length of the femoral neck, whereas the effects of superolateral placement on abductor power could not be compensated for. Likewise, Doehring et al. demonstrated that superolateral positioning of the acetabular component led to very high hip forces as measured by strain gauges in an experimental fiberglass model²⁴.

Clinical studies have provided conflicting information regarding high acetabular placement. Schutzer and Harris reviewed the results of fifty-six complex hip replacements that required a high center of rotation¹⁰⁷. At a mean of forty months postoperatively, no cups were loose, and the authors therefore recommended superior but not lateral placement of the acetabular component when anatomical placement was not possible. Russotti and Harris reviewed the results of accepting a high center of rotation of the hip¹⁰⁰. The cups in their patients were located superiorly but not laterally. Those authors were unable to establish a relationship between loosening of the cup and the height of the hip center. They reported a rate of failure of 16 percent (six of thirty-seven hips) at a mean of eleven years.

Less favorable results of high placement have been reported by many other authors^64,95,127. After a mean duration of follow-up of nine years, Yoder et al. determined the vertical and horizontal location of 116 Charnley total hip replacements inserted with cement¹²⁷. The location of the hip center did not influence the rate of acetabular loosening, but the rate of femoral loosening increased considerably when the cup was superior or superolateral. Pagnano et al. examined the effects of nonanatomical acetabular reconstruction in primary total hip arthroplasties with cement for the treatment of dysplasia⁹⁵. One hundred and forty-five hips with class-II dysplasia¹⁹ were evaluated after a mean duration of follow-up of fourteen years. Placement of the acetabular component more than fifteen millimeters superior to the normal center of rotation of the hip, even without lateral displacement, led to substantially higher rates of loosening and revision of both the femoral and the acetabular component. Stans et al.¹¹⁴ reviewed the results at a mean of 16.6 years after total hip arthroplasty in seventy hips with class-III dysplasia¹⁹. Superior and lateral location of the center of rotation were strong predictors of acetabular loosening. There were eight trochanteric nonunions, a finding that highlights the importance of placing the acetabular component as close to the true acetabulum as possible. Crowe et al. reported that the presence of a limp was related to the degree of superior displacement of the acetabular component¹⁹.

Cement Augmentation
The use of cement to fill the superior acetabular defect provided gratifying early results⁷⁷ but has not been associated with satisfactory long-term outcomes^74,76. MacKenzie et al.⁷⁶ reported the results, at a mean of sixteen years, for class-II, III, and IV hips¹⁹ (in forty-six patients) that had been reconstructed with the use of bone cement to fill any acetabular defects. Fourteen percent (eight) of the fifty-nine hips had revision of the acetabular component, and 32 percent (twelve) of the thirty-seven unrevised hips for which radiographs were available had evidence of radiographic loosening. There was a trend toward a higher rate of failure in patients who had had a previous cup arthroplasty and in those in whom a large quantity of cement had been used. Patients who were less than fifty years old also had a higher rate of failure. Linde and Jensen also reported loosening in 19 percent (twenty-three) of 123 hips in a similar series with a mean duration of follow-up of nine years⁷⁴.

Okamoto et al. studied the effects of modern techniques of acetabular fixation with cement for the treatment of mild acetabular dysplasia⁹¹. They carefully selected patients in whom the superolateral cement thickness was less than twenty millimeters when the acetabular component was placed in the true acetabulum at a 45-degree angle. The results of thirty-seven reconstructions performed with the Charnley technique were compared with those of twenty-two later Charnley hip arthroplasties in which a flanged socket and so-called modern cementing techniques had been used. In the first group, aseptic loosening was seen in ten hips (27 percent), compared with one hip (5 percent) in the second group. Okamoto et al. postulated that, for mild dysplasia (effectively class-I dysplasia according to the system of Crowe et al.¹⁹, if the criteria of Okamoto et al. are met), modern cementing techniques provide satisfactory long-term fixation.

Acetabular Augmentation
The bone stock may also be augmented by bulk bone-grafting. Either the patient's own femoral head or an allograft can be used, but the outlook is better with the use of an autogenous graft¹¹⁰. Some authors believe that, when a bulk graft is used, superior fixation may be achieved with bolts rather than screws because of the deficient superoacetabular iliac bone⁴². The graft should also provide posterior as well as superior coverage⁸⁸ and should ideally be buttressed by the most lateral part of the acetabulum⁹⁹.

Structural support with an autogenous femoral head graft in a dysplastic acetabulum and cementing of the acetabular component into the graft has provided satisfactory short-term results^{33,42,47,59,123}; some longer-term follow-up studies have shown high rates of failure of the acetabular component^33,88, although others have not^39,99.

Wolfgang reported a rate of loosening of 5 percent (two of forty-two hips) at a mean of 5.7 years¹²³. Gerber and Harris noted that 21 percent (ten) of forty-seven acetabular components failed at seven years³³. Mulroy and Harris followed the same group for a mean of twelve years and reported a rate of acetabular failure of 46 percent (twenty-one of forty-six hips)⁸⁸.

Garvin et al.³², however, reported that the six hips in which bone graft had been used to augment the acetabulum in the original series of Crowe et al.¹⁹ showed no signs of loosening at a mean of fourteen years. Stringa et al. reported the results of total hip replacement and use of a femoral head bone graft in twenty hips with congenital dysplasia or dislocation¹¹⁵. They had used a small or extra-small Charnley cup and had stabilized the graft with two screws. After a mean duration of follow-up of ten years, nineteen patients were free of pain. The graft had fused without resorption in eighteen hips. Two grafts showed severe resorption associated with loosening of the cup. In total, three cups showed radiographic signs of loosening; only one of them caused symptoms. Garvin et al. concluded that moving the hip medially and the use of a small cup are important to allow sufficient support of the prosthesis by bone so that the distribution of load on the graft is minimized.

At a mean of 10.2 years, Lee et al. reviewed the results of 102 consecutive primary and revision hip arthroplasties performed with acetabular grafting⁷¹. Of fifty-eight hips that had underlying congenital dysplasia, 3 percent (two) had acetabular revision for aseptic loosening at five years and 17 percent (ten) had such a revision at ten years. The survival rate decreased further after ten years. Loosening was not related to failure of the bone graft.

Rodriguez et al. reviewed the results for twenty-nine hips in twenty-three patients at a mean of eleven years after a primary total hip arthroplasty with cement and with reconstruction of the acetabulum with use of an autogenous femoral head bone graft⁹⁹. There was union of all of the grafts, which covered a mean of 24 percent of the component. Rodriguez et al. found no relationship between the result and fixation of the graft with lag screws, Steinmann pins, or press-fit. Loosening was seen in eleven hips (38 percent), but 90 percent (twenty-six) of the twenty-nine hips were asymptomatic. Rodriguez et al. postulated that their reconstructions were more successful than those of Mulroy and Harris⁸⁸ because the graft was used to cover a smaller portion (less than 40 percent) of the acetabular component and because the graft was protected by being buttressed by the proximal-lateral aspect of the acetabulum.

Numair et al. followed 190 patients who had had a total of 230 Charnley total hip replacements performed with use of cement for the treatment of congenital dysplasia or dislocation⁹⁰. An autogenous femoral head graft was used for acetabular augmentation. The rate of acetabular revision was 12 percent (twenty-two of 182) after a mean duration of follow-up of 9.9 years.

After a mean duration of follow-up of 8.1 years, Morsi et al. reviewed the results for thirty dysplastic hips treated with total hip arthroplasty and shelf reconstruction with insertion of an autogenous femoral head graft⁸⁷. The cup was inserted with cement in thirteen hips, and it was inserted without cement in seventeen hips. All of the autogenous grafts united to host bone, with resorption seen equally in the hips in which cement had and had not been used. In all cases, resorption was considered minor and was restricted to the lateral, non-weight-bearing part of the graft. Only three of the thirty hips had an unsuccessful acetabular reconstruction, so the rate of success was 90 percent. The same authors expanded on this series by evaluating thirty-three hips treated with a cup inserted without cement⁸⁶. Structural autogenous graft was used in seventeen hips, and allograft was used in sixteen. Those authors reported an overall rate of success of 94 percent (thirty-one of thirty-three hips) at a mean of 6.6 years. They recommended insertion of the cup without cement and use of structural allograft or autogenous graft, provided that the graft supports less than 50 percent of the cup.

Gross and Catre evaluated the results of fifteen shelf reconstructions that had been performed with use of an autogenous femoral head graft and insertion of the acetabular component with cement³⁹. After a mean duration of follow-up of ninety-nine months, all of the grafts showed radiographic evidence of union to the pelvis, although there was some resorption of the graft in eight patients. None of the grafts or acetabular components showed any signs of migration, and the Harris hip score of the patients increased a mean of 29 points compared with the preoperative score.

The weight-bearing portion of the graft tends to remodel with time as it revascularizes. This remodeling leads to resorption of the graft and the transmission of forces to the bone-cement interface. Cups inserted without cement and augmented with bone graft may have a better outcome because the transmission of force to the pelvis is improved¹. After a relatively short duration of follow-up (mean, twenty-five months), Barrack and Newland reported satisfactory results with use of autogenous femoral head graft and a component inserted without cement in ten hips in seven patients⁴. Hintermann and Morscher reported on thirty-nine hips (mostly class-III or IV¹⁹) treated with a solid autogenous femoral graft and an acetabular component inserted without cement⁵⁰. At a mean of 7.6 years, all of the grafts were well incorporated, although there was lateral resorption in twenty-two hips. Aseptic loosening occurred in two hips, one of which was revised.

Augmentation with a bulk allograft leads to satisfactory early results^42,58 but has a higher rate of late failures^69,88,110 compared with total hip arthroplasty performed without an allograft. The fundamental problem may well be late fatigue failure of the avascular corticocancellous bone. Chandler and Penenberg argued that failure of the graft may be related to the fact that the trabeculae of the allograft are not oriented in the direction of the force going through them¹⁵; however, no data have been provided to support this hypothesis. The success in some series of arthroplasties performed with acetabular allografts may be related to the fact that the grafts were used to cover the lateral 30 percent of the cup, which may not be necessary for satisfactory fixation and ingrowth.

If a considerable portion (40 percent) of the socket needs to be covered with allograft, ideally the cup should be inserted with cement, as growth into the dead bone graft is unlikely. However, Silber and Engh reported satisfactory results with use of structural allografts and porous-coated acetabular components inserted without cement in thirteen hips¹¹². It must be emphasized that this was a short-term study, with a mean duration of follow-up of only three years.

Although the long-term results of acetabular augmentation with bone graft have not met the expectations generated by the initial reports, this technique remains useful when the other options have been exhausted. It should also be noted that the longer-term outcome associated with the use of autogenous graft for the augmentation of acetabular components inserted without cement is still unknown. Moreover, the bone graft usually incorporates and may contribute to the patient's bone stock and facilitate later revision reconstructions^33,50,71.

Reinforcement Rings
Gill et al.³⁴ reported the results of the use of an acetabular reinforcement ring, designed by Müller, in eighty-seven primary acetabular reconstructions performed in seventy patients for the treatment of osteoarthritis secondary to class-II, III, or IV hip dysplasia according to the system of Crowe et al.¹⁹. After a mean duration of follow-up of 9.4 years (minimum, five years), there were only two acetabular revisions for aseptic loosening: one in a class-III hip and one in a class-IV hip. In both of these hips, cement had been used rather than bone graft. The authors advised against the use of cement to fill the osseous defects and recommended the use of autogenous graft medially and superiorly.

In a later publication with different coauthors, Gill reported on the use of the acetabular roof reinforcement ring with a hook, designed by Ganz, in thirty-three consecutive hips followed for a mean of 6.7 years³⁵. There were four failures, with two hips revised for aseptic loosening, one hip with definite radiographic evidence of loosening, and one hip with possible radiographic evidence of loosening. Although the basic designs of the two ring systems are similar, the latter has a hook that the surgeon inserts along the inferior margin of the acetabulum, enabling anatomical placement of the center of rotation of the prosthetic hip joint.

Overview
Acetabular reconstruction in the dysplastic hip still generates a great deal of controversy. The consensus at present is to aim for the insertion of a small acetabular component at the site of the true acetabulum. There is an increasing weight of evidence to support the insertion of components with screws and without cement in this situation⁹³. These components can be augmented with particulate autogenous graft from the femoral head. If more than 30 percent of the cup is uncovered, consideration should be given to the use of cement or bulk autogenous graft or allograft. Reinforcement rings, the cotyloplasty technique, and the acceptance of a high center of rotation will continue to be evaluated and will play a role in specific situations.

	The Femur

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Femoral reconstruction may be complicated by a small medullary canal, femoral hypoplasia, severe developmental distortion of femoral shape and version, and the effects of previous intertrochanteric and subtrochanteric osteotomies⁵⁶. Previous osteotomies may necessitate a repeat osteotomy so that the femoral component may be inserted safely. A narrow canal facilitates femoral plugging at the time of an arthroplasty with use of cement, but great care is necessary during femoral preparation, as there is an increased risk of reaming through the femoral cortex and causing a femoral fracture¹⁹. The problem of a very narrow femoral canal can be overcome by splitting the proximal eight to ten centimeters of the femoral shaft both anteriorly and posteriorly⁹³. Bone graft is placed in the created gaps, and the split is stabilized with lag screws at the time of trochanteric reattachment.

In many cases, the femoral anatomy demands the use of a small, short, straight component, as the prosthesis is essentially placed directly into the diaphysis rather than across the metaphysis^{2,54,58,93,124}. Use of a template helps to determine the need for a modular or custom implant. When choosing an implant, the potential for fracture of a small component inserted without cement should be considered.

For hips with class-I, II, or III dysplasia¹⁹, it may be sufficient to use a conventional femoral component, provided that the small size of the femur is taken into account. For hips with class-IV dysplasia, a straight, narrow stem with a limited medial curvature should be used, as the resection level leaves no calcar and no proximal-medial femoral curve. When there is more than 40 degrees of anteversion, a corrective rotational osteotomy^1,52,94 or a custom implant or a modular implant in which version of the femoral neck can be varied may be necessary⁵².

Woolson and Harris reported that, of fifty-five hips, 7 percent (four) had loosening of a cemented femoral component at a mean of 4.8 years¹²⁴. Stringa et al. reported the results of total hip replacement in twenty-one hips that had congenital dysplasia or dislocation; a miniature femoral component was used in fifteen¹¹⁵. All stems except one were radiographically stable and were not causing symptoms at a mean of ten years postoperatively.

Silber and Engh noted the importance of modularity of the femoral stem in the reconstruction of dysplastic hips¹¹². The wide variation in femoral size and shape and loss of the metaphyseal flare necessitated the use of a custom or modular implant in sixteen of their nineteen patients. The freedom to alter the femoral head-neck version provided by prostheses such as the S-ROM implant (Johnson and Johnson, Raynham, Massachusetts) may also help to decrease the dislocation rate.

In an effort to decrease stress-shielding and pain in the thigh, Matsui et al. used the Metal-Cancellous Cementless Lübeck prosthesis (S & G; ESKA, Lübeck, Germany) in fifty-one dysplastic hips in forty-five patients⁸¹. All forty-seven hips that were followed for a minimum of five years had a good or excellent clinical result.

Huo et al. used custom-designed femoral components in order to increase the offset of the femoral head to thirty to forty millimeters (or equal to the other side if it was normal) and to equalize limb lengths⁵⁴. A varus (swan) neck was designed in order to avoid impingement. At a mean of fifty-seven months, none of the components had been revised. However, no longer-term data have been presented.

Symeonides et al. reported on seventy-four total hip replacements in sixty-four patients who had painful, untreated congenital dislocation of the hip¹¹⁷. All of the acetabular components were placed at the site of the true acetabulum, with a cotyloplasty performed in sixty-five hips. A variety of methods were used to bring the femur down to the true acetabulum, including trochanteric osteotomy, femoral shortening distal to the level of the lesser trochanter, division of the psoas tendon, and, in one patient, progressive distraction with an external fixator. A metal plate and screws were used to secure the sites of the subtrochanteric osteotomies. At a mean of 7.2 years, seventy of the seventy-four procedures had resulted in marked pain relief as well as substantial improvements in gait and mobility. There was one infection, and three of the polyethylene cups loosened, necessitating revision.

If the acetabulum is brought down to its true level, the femur may have to be shortened in order to reduce the risk of injury to the sciatic nerve. Generally, it is unwise to try to lengthen the femur more than four centimeters, as doing so increases the risk of sciatic nerve palsy^14,32,73. A number of methods of intraoperative assessment of limb length have been described¹²⁴.

Femoral shortening may be carried out at the level of the trochanter or in the subtrochanteric region. This procedure allows for any femoral rotational correction and still effectively lengthens the limb even though the femur itself is shortened. When subtrochanteric femoral shortening is performed, the acetabular reconstruction is completed and a trial femoral component is introduced into the proximal fragment. The hip is then reduced, allowing the two femoral fragments to override. The degree of femoral shortening required can then be determined by distal traction on the extremity and by reference to the preoperative template. Another transverse femoral osteotomy is then made, with resection of the appropriate length from the distal fragment. The femoral component can be inserted either with or without cement. The resected section of femur can be used as an onlay vascularized autogenous graft at the site of the osteotomy once the definitive femoral component is in place. Strut allograft and cerclage cables may also be needed for support.

Reikeraas et al. reviewed the outcome of replacement with a subtrochanteric shortening osteotomy in twenty-five completely dislocated hips⁹⁷. A transverse osteotomy was performed with angular or rotational correction as indicated, and distal fixation was achieved by so-called press-fit. A number of different prostheses were used. The median limb-length discrepancy was five centimeters, and the median limb-lengthening was three centimeters. There was one sciatic nerve palsy, one nonunion, and one malunion. None of the hips had been revised after a minimum duration of follow-up of three years.

Yasgur et al. also described a subtrochanteric osteotomy with femoral shortening for the treatment of high hip dislocations¹²⁶. They used a transverse osteotomy as well but augmented the distal press-fit of the prosthesis with allograft struts and cables. Muirhead-Allwood et al. used a transverse osteotomy with a distally fluted custom stem in sixteen patients, with no malunions or nonunions (personal communication).

Other suggested means of femoral shortening have included step-cuts^93,92, double chevron osteotomies⁶, and oblique osteotomies². In general, subtrochanteric osteotomies are increasingly popular because they reproduce a more normal femoral morphology, may provide superior fixation in the metaphyseal region, and avoid the problem of the pencil-thin femur that is sometimes seen after a more proximal shortening (Fig. 8).

View larger version (95K): [in this window] [in a new window]   Fig. 8 Illustration of preoperative femoral planning on a radiograph of a hip with a high dislocation. In order to place the socket at the site of the true acetabulum, it is necessary to shorten the femur either by resection of the proximal aspect of the femur to a level distal to the lesser trochanter (1) or by performance of a subtrochanteric intercalary shortening while retaining the proximal aspect of the femur (2).

Other strategies that have been considered for the treatment of the dysplastic hip have included surface replacement²¹ and use of a ceramic prosthesis⁵⁵, but these techniques have met with limited success.

Femoral reconstruction does not generate as much controversy as acetabular fixation does. Most difficulties can be addressed with either a proximal or a subtrochanteric osteotomy, with or without the use of a modular or custom implant. The choice of component is generally dictated by the size and shape of the femur and by the need for an associated osteotomy or shortening.

	Abductor Function

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The treatment of congenital dysplasia of the hip may lead to osteonecrosis and trochanteric overgrowth⁶³, which results in the greater trochanter lying superior to the center of the femoral head. This situation can sometimes be addressed by the use of an appropriate femoral component so that the head of the prosthesis is restored to an appropriate level, but it may also require distal advancement of the greater trochanter. Increasing the offset of the femoral component will also help to improve abductor function^2,94.

When a trochanteric osteotomy is performed, a careful and extensive capsular release allows easier distal mobilization and reattachment. The psoas tendon may have to be released, and the gluteus maximus insertion into the femur may have to be transposed. In these instances, the trochanter is reattached in wide abduction, and the patient walks with protected weight-bearing for three months. Active abduction is also avoided during this period.

When the transfemoral subtrochanteric approach is used, the abductors and the greater trochanter are usually not disturbed, although occasionally the greater trochanter has to be transposed distally as well¹²⁶.

Alternatives that may be employed in extreme circumstances include z-plasty of the abductor tendons as they approach their point of insertion, fractional lengthening, and an abductor slide (Figs. 9-A, 9-B, and 9-C). An abductor slide involves stripping the abductor muscle mass from the ilium and advancing it on the superior gluteal neurovascular leash. It is reattached after trochanteric stabilization, but it provides no initial stability and needs to be protected in a hip spica for six weeks.

View larger version (44K): [in this window] [in a new window]   Fig. 9-A Illustration showing a number of soft-tissue abnormalities associated with hip dislocation, which must be managed at the time of reconstruction.

View larger version (41K): [in this window] [in a new window]   Fig. 9-B Illustration of the steps taken to correct soft-tissue abnormalities at the time of reconstruction, including excision of the hypertrophic capsule (large double-headed arrow), division of the psoas tendon (small double-headed arrow), trochanteric osteotomy (midsized double-headed arrow), and femoral shortening (dashed lines). The single-headed arrows indicate the direction of the reduction.

View larger version (43K): [in this window] [in a new window]   Fig. 9-C Occasionally, because of potential difficulty in mobilizing the greater trochanter distally, a so-called abductor slide (dotted arrow) may be needed, but great care must be taken to preserve the superior gluteal neurovascular bundle. The curved arrows indicate the direction of reattachment.

	Controversies

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The effect of the severity of the initial dysplasia or dislocation on the final outcome of total hip arthroplasty remains unclear.

Cameron et al.¹³ prospectively evaluated seventy-one patients who had hip dysplasia and twenty-two control patients in order to determine the influence of the class according to the system of Crowe et al.¹⁹ on the clinical outcome, functional outcome, and complications of total hip arthroplasty. A porous-coated cup was used with an S-ROM modular stem (Depuy, Warsaw, Indiana). There was no difference in any of the parameters measured between the class-I hips and the controls. The class-II (p < 0.05), III (p < 0.05), and IV (p < 0.01) hips all had significantly lower Harris hip scores. There was no difference in radiographic outcome among the groups. The class-IV hips had a substantially higher rate of complications, which included one femoral nerve palsy, two sciatic nerve palsies, one fracture, and one collapse at the site of a subtrochanteric osteotomy. The fracture and the collapse necessitated revisions.

Marti et al. reviewed the results of superolateral acetabular grafting in eighty-four hips⁷⁹. They noted a decrease in the hip score as the severity of the dysplasia increased, but they did not submit this finding to statistical analysis. Crowe et al. noted a higher rate of revision in the more severely dysplastic hips¹⁹.

In a review of the long-term results of the Charnley low-friction arthroplasty (Thackray, Leeds, United Kingdom), Sochart and Porter included sixty hips with congenital dysplasia or dislocation¹¹³. An extra-small acetabular component (outside diameter, thirty-eight millimeters or less) was used in forty-three hips (72 percent), and a miniature femoral component was used in twelve hips (20 percent). After a mean duration of follow-up of 244 months, six femoral components (10 percent) and twenty-two acetabular components (37 percent) had been revised. Both components remained in thirty-five hips (58 percent). Sochart and Porter saw no differences in outcome among the hips in different classes according to the system of Crowe et al.¹⁹. The probability of survival of both components was 97 percent at ten years and 54 percent at twenty-five years. The probability of survival of the femoral component was 97 percent at ten years and 89 percent at twenty-five years, and the probability of survival of the acetabular component was 97 percent at ten years and 58 percent at twenty-five years.

Numair et al.⁹⁰, who were from the same center as Sochart and Porter¹¹³, followed 182 Charnley total hip replacements performed with use of cement for the treatment of congenital dysplasia or dislocation in 141 patients. The mean duration of follow-up was 9.9 years. Forty-six hips were class IV according to the system of Crowe et al.¹⁹ and, of those, 17 percent (eight) were revised compared with 10 percent (fourteen) of 136 class-I, II, and III hips. The rate of acetabular revision in the dislocated hips (class IV) was twice as high as that in the subluxated hips (classes I, II, and III). There was no difference in the rate of femoral failure, however; only five stems (3 percent) were revised in total.

	Complications and Pitfalls

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
The findings in several series confirm higher rates of complications after total hip arthroplasty in patients who have dysplasia of the hip than in patients who have osteoarthritis of the hip^9,34,95. The high rate of failure of these arthroplasties has already been discussed^32,74,75 and, according to Sochart and Porter, is not entirely due to the young age of the patients involved¹¹³.

The prevalence of nerve palsy after total hip arthroplasty in general has been reported as being between 0.5 and 2 percent in series ranging from sixty-seven to 7133 hips^{17,40,60,78,89,101}. This risk increases in hips with congenital dislocation, with reported prevalences of 3 to 15 percent in series ranging from twenty-three to 172 hips^{14,19,21,29,33,47,60,73,76,101,109}. Garvin et al. recommended that limb-lengthening be limited to two centimeters to decrease the risk of nerve damage³². Lewallen suggested that this limit should be four centimeters or 6 percent of the length of the limb, depending on which is less⁷³. Cameron et al. reviewed the results of 106 replacements of dysplastic hips in ninety-two patients¹⁴. They found six nerve palsies (three femoral and three sciatic), all in patients who had limb-lengthening of more than four centimeters. Nercessian et al. believed that lengthening of as much as 10 percent of the length of the femur was safe⁸⁹. Edwards et al. suggested that lengthening of more than four centimeters greatly increased the risk of sciatic palsy²⁶. Our experience suggests that as much as four centimeters of lengthening is safe, provided that tension in the sciatic nerve is assessed intraoperatively. Others use electromyographic monitoring^1,94. A wake-up test, analogous to that used in operations for the treatment of scoliosis¹²⁰, can also be performed. When lengthening is undertaken or a very scarred hip is reexplored, the sciatic nerve should be exposed, or at least palpated, in order to assess the amount of tension in the nerve at the time of reconstruction.

To the best of our knowledge, the highest rates of dislocation after primary total hip arthroplasty (5 to 11 percent in series ranging from twenty-three to eighty arthroplasties^29,31-33,76) have been reported in patients who had congenital dysplasia or dislocation of the hip. The highest rates of trochanteric nonunion after arthroplasty (10 to 29 percent in series ranging from twenty-one to eighty arthroplasties^2,21,29,31) have also been reported in patients who had congenital dysplasia or dislocation.

Some of the dislocations after total hip arthroplasty may be related to nonunion of the trochanter or so-called trochanteric escape, while others are due to impingement, which is greatly increased with the use of a high hip center, particularly when the cup is placed medially¹¹². In such circumstances, the femoral component often impinges on the anterior acetabular column in flexion and internal rotation and impinges on the ischium and the posterior column in extension and external rotation. This can be avoided by increasing the offset of the femoral component. It may also be necessary to release the rectus femoris and occasionally to resect the anterior inferior iliac spine or ischium.

Complex deformities of the proximal aspect of the femur, particularly when associated with a narrow medullary canal (as seen in secondary degenerative joint disease following congenital dislocation of the hip), may also increase the risk of intraoperative fracture of the femur^25,108. A narrow femoral canal is also predisposed to cortical perforation during preparation of the canal. Thus, great care has to be taken when reaming a narrow femoral canal. If a perforation is recognized during the operation, it should be bypassed with either a longer stem or a cortical onlay allograft strut and cerclage-wire fixation. Total hip arthroplasty with femoral osteotomy in a patient with proximal femoral deformity is also associated with a high risk of intraoperative fracture⁹⁶; cerclage wires, with or without strut allografts, should be used when the bone stock is poor.

Young patients managed with total hip arthroplasty for treatment of hip dysplasia have been reported to have higher rates of infection^1,31,91 than patients managed with total hip arthroplasty for treatment of osteoarthritis. This difference may be related to the duration and complexity of the operations. The extensive dissection and stripping of the soft tissues and the use of bone graft may also contribute to higher rates of infection⁷⁶.

	Overview

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 
Total hip arthroplasty relieves pain and improves function for many patients with end-stage arthritis secondary to abnormalities following congenital dysplasia of the hip or other conditions seen in childhood. These patients are often young and unlikely to tolerate arthrodesis, and they have high expectations. The challenge that they pose must not be underestimated.

Our interpretation of successful outcomes in the literature must be tempered by the knowledge that reported series have mostly included patients with mild cases. Whereas a mildly dysplastic hip may not require any special expertise, a hip with a complex dislocation represents one of the most multifaceted challenges facing the reconstructive surgeon.

Hips with complex dislocation pose a broad spectrum of difficulties and present unique technical problems. Arthroplasties for the treatment of such hips are associated with higher morbidity and inferior outcomes than are primary hip arthroplasties for the treatment of osteoarthritis. It is vital to recognize the magnitude of the problem and to marshall the necessary skills and services, in specialist centers if feasible, in order to have the best possible results in the future.

The future management of these disorders may partly lie in the realms of prevention at birth, in the childhood years, and in early adulthood. We must, however, strive to ensure that arthroplasty, the ultimate end point for most of these hips, is not compromised by previous interventions.

The sequelae of the dysplastic hip will challenge us for a long time to come. Fortunately, our understanding is evolving with the availability of longer-term results. It is only with careful prospective analysis of these difficult cases and with critical appraisal of new and evolving methods, in terms of both preoperative evaluation and operative technique, that we will ultimately improve the functional outcome for these patients.

NOTE: The fellowship training of one of the authors (F. S. H.) was supported, in part, by the John Charnley and British Orthopaedic Association/Wishbone Trusts and by the Norman Capener Travelling Fellowship.

	Footnotes

 
*Printed with permission of the American Academy of Orthopaedic Surgeons. This article will appear in Instructional Course Lectures, Volume 49, American Academy of Orthopaedic Surgeons, Rosemont, Illinois, March 2000.

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

Department of Orthopaedics, Laurel Pavilion, Vancouver General Hospital, 910 West Tenth Avenue, Third Floor, Vancouver, British Columbia V5Z 4E3, Canada. The e-mail address for Dr. Masri is masri@interchange.ubc.ca, and the e-mail address for Dr. Duncan is cduncan@interchange.ubc.ca.

	References

Top Introduction Anatomy Classification Assessment Previous Operations Preoperative Planning Operative Approaches The Acetabulum The Femur Abductor Function Controversies Complications and Pitfalls Overview References

 

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