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Current Concepts Review - Acetabular and Femoral Anteversion: Relationship with Osteoarthritis of the Hip*

D. TÖNNIS, M.D., DORTMUND and A. HEINECKE, PH.D., MÜNSTER, GERMANY

*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.

	Introduction

Top Introduction Etiology of Altered Acetabular... Diagnosis of Decreased... Clinical and Radiographic Study Operative Treatment Conclusions and Recommendations References

 
Primary osteoarthritis of the hip, often referred to as idiopathic, may be secondary to mechanical causes. There have been numerous studies on the measurement of torsion of the bones of the lower extremity^{1,3,8,13,14,31,34,39,44,45,47,48,54,63,79,80,84}. Some studies have supported the hypothesis that a persistent increase in femoral anteversion predisposes to osteoarthritis of the hip^29,53,54,62, whereas others have not^35,40,61. Menke et al.⁴⁵ found an association between decreased acetabular anteversion and osteoarthritis of the hip, and Eckhoff²³ found a similar association between femoral anteversion and osteoarthritis of the knee. Increased femoral torsion also has been documented in patients who have pain or osteoarthritis of the knee and patellar instability^5,22.

There have been few reports on the potential problems that are associated with decreased femoral anteversion^{15,21,36,37,51,69}. In 1959, Crane¹⁵ noted that decreased femoral anteversion or retroversion was associated with a toeing-out gait whereas increased femoral anteversion was associated with a toeing-in gait. Decreased femoral anteversion has been consistently observed in patients who have a slipped capital femoral epiphysis^{25,28,38,52,58,59} as well as in those who have congenital hypoplasia of the femur^60,73.

	Etiology of Altered Acetabular and Femoral Anteversion

Top Introduction Etiology of Altered Acetabular... Diagnosis of Decreased... Clinical and Radiographic Study Operative Treatment Conclusions and Recommendations References

 
There is some evidence to suggest a congenital etiology for increased or decreased anteversion of the femur and acetabulum¹⁹. Watanabe⁷⁷ examined 144 embryos and stillborn fetuses between six and twenty-four weeks of gestation. At the completion of the first half of the prenatal stage (that is, by twenty weeks of gestation), the fetus is completely formed and resembles the newborn infant. Femoral anteversion was measured in specimens that were between eleven and twenty-four weeks of gestation; it was not possible to measure anteversion in younger specimens because the hip joint space had not yet formed. The femur and the tibia were dissected out, and the knee was flexed to 90 degrees and held in a vertical plane on a small platform. The angle between the upper surface of the platform and the femoral neck was then measured. Watanabe reported that, at twenty to twenty-four weeks, femoral anteversion ranged from -10 to 30 degrees. In addition, he found that marked internal rotation of the lower extremity was associated with increased femoral anteversion whereas external rotation was associated with femoral retroversion. External rotation of the lower limbs was more common in males and internal rotation was more common in females, but specific numbers were not given. Watanabe noted that femoral anteversion develops during the second half of pregnancy and reaches an average of 35 degrees by the time of birth.

Wilkinson^82,83 studied the changes in the femoral neck in young rabbits after immobilization of the hindlimb in a cast. It was first necessary to determine the normal degree of femoral anteversion in rabbits at different ages. The normal degree of femoral rotation was 10 degrees of anteversion at five days, 0 degrees at six weeks, 10 degrees of retroversion at sixteen weeks, and 15 degrees of retroversion at twenty-eight months. Immobilization of the hindlimb in a position of external rotation led to increased retroversion of the femoral neck, whereas immobilization in a position of internal rotation led to increased anteversion. In another study⁸⁴, Wilkinson documented the position of the lower extremities in 948 infants immediately after birth. Most newborns had an externally rotated position of the femur, and Wilkinson found that an intrauterine posture with the hips and knees flexed and the feet crossed was the only position that was associated with internal rotation of the hips.

Pitkow⁵¹ examined 500 children who had gait abnormalities and found that sixty-six walked with a toeing-out gait. Twenty-one of these sixty-six children had external tibial torsion, and forty-five had an external rotation contracture of the extended hip. The external rotation contracture decreased progressively with growth and typically resolved around the age of eighteen months, at which time a toeing-in gait became more prevalent. Fewer than 5 percent of the patients had a persistent external rotation contracture. Pitkow did not examine radiographs and based his observations on the results of a physical examination. He suggested that the children had a low degree of femoral anteversion until the age of eighteen months because the external rotation contracture usually did not resolve until that time. He noted that this external rotation contracture is related to the intrauterine position of flexion and external rotation of the hips. This position persists for one to two years, at which time standing appears to stimulate the child to maintain a position of internal rotation. As noted earlier, Pitkow observed a persistent external rotation contracture in a small group of patients, and it is possible that these patients went on to have decreased anteversion as adults.

Hamacher³², who evaluated 994 individuals between the ages of one and eighteen years, and Zippel⁸⁹, who evaluated 400 individuals between the ages of one and twenty years, found that the standard deviation of the angle of femoral anteversion was large and that the average angle was between 45 and 48 degrees at the age of two years and then slowly decreased over time. Those authors measured the angle of anteversion according to the method of Dunn¹⁸ as reported by Müller⁴⁶ and Rippstein⁵⁵. A number of authors^24,57,67,68 excluded children who had a toeing-in gait and reported an average angle of 26 or 27 degrees. Huguenin and Bensahel^36,37 reported retroversion of the femoral neck in ten children who were an average of ten years old. All ten children had a toeing-out gait and an imbalance between internal and external rotation of the hip. Only two children complained of pain. One of us (D. T.)⁶⁹ reported similar findings in ten children and thirteen adults with decreased femoral anteversion who were known to have walked with a toeing-out gait since early childhood.

Yoshioka and Cooke⁸⁷ studied thirty-two cadaveric specimens from adults who had been at least eighty years old at the time of death. Those authors reported femoral retroversion in four specimens. The amount of femoral rotation ranged from 10.8 degrees of retroversion to 22.1 degrees of anteversion.

Associated Conditions
Decreased femoral anteversion has been observed in association with slipped capital femoral epiphysis, even on the asymptomatic side^38,58,59. It is also seen in association with a number of other conditions, including proximal femoral focal deficiency^60,73, coxa vara, a deep acetabulum, and, occasionally, dysplasia of the hip. In most patients, decreased femoral and acetabular anteversion appears to be a congenital deformity without other pathological findings, although it has been reported in association with pistol-grip deformity³³ and subclinical slipped proximal femoral epiphysis³⁰. Decreased femoral anteversion also is seen after derotational varus osteotomy in children when the femoral anteversion, which has been reduced to 0 degrees, does not remodel. Such patients frequently have pain in adulthood. Similar findings have been reported after the treatment of fractures of the femoral shaft in patients in whom the distal fragment was left in a position of external rotation that was greater than normal femoral anteversion. Femoral rotation to a normal anteversion of 15 to 20 degrees has been reported to relieve the pain associated with an iatrogenic decrease of femoral anteversion^{7,56,69,72,86}.

Compensatory Torsional Deformities in the Lower Extremity
External torsion of the tibia is a clinical finding that is observed frequently, although not consistently, in patients with increased femoral anteversion. In one of our patients, a six-year-old girl with markedly decreased femoral anteversion and externally rotated femora characterized by the patellae pointing outward, medial rotation of the knees until the patellae were parallel brought the feet into a toeing-in position suggesting internal tibial torsion (Figs. 1-A and 1-B). In another patient, a nine-year-old girl with increased femoral anteversion and internally rotated femora characterized by the patellae pointing inward, lateral rotation of the knees until the patellae were parallel brought the feet into a toeing-out position suggesting external tibial torsion (Figs. 1-C and 1-D). Therefore, it is possible that there may be some compensatory process at the knee and leg in response to a proximal deformity, resulting in a torsional deformity of the leg. We also have noted that a change in the anteversion of the acetabulum or femur is frequently, but not always, offset by a change on the opposite side of the joint. If this compensation does not occur, the knee may adapt to the altered anteversion.

View larger version (88K): [in this window] [in a new window]   Fig. 1-A Photographs demonstrating internal torsion of the tibiae with greatly reduced femoral anteversion in a six-year-old girl. When the feet are parallel, the patellae point outward (Fig. 1-A). When the knees are placed in neutral rotation, the legs and feet show pronounced internal rotation (Fig. 1-B). An intertrochanteric rotational osteotomy was performed bilaterally to increase femoral anteversion, and a proximal tibial osteotomy was performed bilaterally to externally rotate the tibiae.

View larger version (93K): [in this window] [in a new window]   Fig. 1-B Photographs demonstrating internal torsion of the tibiae with greatly reduced femoral anteversion in a six-year-old girl. When the feet are parallel, the patellae point outward (Fig. 1-A). When the knees are placed in neutral rotation, the legs and feet show pronounced internal rotation (Fig. 1-B). An intertrochanteric rotational osteotomy was performed bilaterally to increase femoral anteversion, and a proximal tibial osteotomy was performed bilaterally to externally rotate the tibiae.

View larger version (116K): [in this window] [in a new window]   Fig. 1-C Photographs showing increased femoral anteversion in a nine-year-old girl. When the feet are placed parallel to each other, the knees are rotated inward (Fig. 1-C). When the knees are rotated so that the patellae are facing directly forward, there is evidence of external tibial torsion (Fig. 1-D).

View larger version (125K): [in this window] [in a new window]   Fig. 1-D Photographs showing increased femoral anteversion in a nine-year-old girl. When the feet are placed parallel to each other, the knees are rotated inward (Fig. 1-C). When the knees are rotated so that the patellae are facing directly forward, there is evidence of external tibial torsion (Fig. 1-D).

	Diagnosis of Decreased Anteversion

Top Introduction Etiology of Altered Acetabular... Diagnosis of Decreased... Clinical and Radiographic Study Operative Treatment Conclusions and Recommendations References

 
Swanson et al.⁶¹ identified decreased femoral anteversion as one of several potential causes of an internal or external rotational deformity of the lower extremity, which they defined as an excessive range of movement of at least 20 degrees in either direction. In a study of 111 joints in fifty-nine patients, we found that the average external rotation of the hip was at least twice the average internal rotation, and frequently more, in patients who had decreased anteversion of the femoral neck⁶⁹. The total range of internal and external rotation is normally between 80 and 90 degrees, but this range decreases with the early development of osteoarthritis of the hip. In our study, four of the fifty-nine patients complained of diffuse pain around the knee, ten complained of pain at the patellofemoral joint, and four complained of pain in the sacroiliac region⁶⁹. Pain was elicited or exacerbated by simultaneous abduction and internal rotation of the slightly flexed hip, which increases intra-articular pressure. This finding also is observed in patients who have osteoarthritis or joint irritation.

Occasionally, symptoms of impingement or a torn labrum are reported by patients who have decreased femoral anteversion. Ganz²⁷ noted tears of the anterior aspect of the acetabular labrum and signs of wear of the anterior joint cartilage in patients who had no femoral anteversion or a subclinical slipped capital femoral epiphysis. In his opinion, these changes were related to the absence of narrowing or offset of the femoral neck immediately adjacent to the femoral head.

Decreased femoral anteversion should be suspected if there is marked lateral projection of the greater trochanter and the entire length of the femoral neck can be visualized on an anteroposterior radiograph of the pelvis and hips. These findings can be visualized only if the knee joint is in a central or neutral position when radiographs are made. Careful positioning of the lower extremities is often neglected when radiographs are made.

In order to allow for an accurate assessment of acetabular anteversion, the pelvis must be in a neutral position and should not be tilted anteriorly or posteriorly. The degree of pelvic tilt can be estimated from the shape and position of the obturator foramina. Anterior tilt reduces acetabular anteversion, whereas posterior tilt increases it^1,2,75,76. Lateral rotation of the pelvis decreases acetabular anteversion on the ipsilateral side. On an anteroposterior radiograph of the pelvis, the anterior and posterior margins of the acetabulum should be approximately 1.5 centimeters apart as measured from the center of the femoral head in a plane that is vertical to the anterior aspect of the acetabular rim (Fig. 2-A). A decrease in this distance suggests a decrease in acetabular anteversion (Fig. 2-B), whereas an increase in this distance suggests an increase in acetabular anteversion (Fig. 2-C). Acetabular retroversion is present when the posterior margin ends in a more medial position than the anterior margin in relation to the superior aspect of the acetabular rim (Fig. 2-D). These findings only suggest the possibility of a change in the degree of acetabular anteversion. Femoral anteversion can be measured on a radiograph made with the hip in 90 degrees of flexion and 20 degrees of abduction according to the technique described by Dunn¹⁸, Rippstein⁵⁵, and Müller⁴⁶. This method is similar to that described by Dunlap et al.¹⁷. The simultaneous evaluation of acetabular and femoral anteversion requires computerized tomographic scans to be made with the patient in the prone position, with a summation image composed of multiple slices of the femoral neck^75,76.

View larger version (160K): [in this window] [in a new window]   Fig. 2-A through 2-D: Anteroposterior radiographs demonstrating various degrees of acetabular anteversion. The appearance of the acetabulum is altered by an anterior, posterior, or lateral pelvic tilt; thus, images made with tilting of the pelvis cannot be used to make a definitive diagnosis. Fig. 2-A: The anterior and posterior acetabular margins are normally approximately 1.5 centimeters apart as measured from the center of the head in a plane vertical to the anterior aspect of the acetabular rim. The distance shown here is at the lower limit of the normal range.

View larger version (134K): [in this window] [in a new window]   Fig. 2-B: The anterior and posterior acetabular margins appear close together, indicating approximately 0 degrees of anteversion.

View larger version (120K): [in this window] [in a new window]   Fig. 2-C: The acetabular margins appear farther apart than normal, suggesting increased anteversion.

View larger version (128K): [in this window] [in a new window]   Fig. 2-D: The posterior acetabular margin is more medial than the anterior margin in relation to the superior aspect of the acetabular rim, suggesting the presence of acetabular retroversion.

	Clinical and Radiographic Study

Top Introduction Etiology of Altered Acetabular... Diagnosis of Decreased... Clinical and Radiographic Study Operative Treatment Conclusions and Recommendations References

 

Materials and Methods
We are not aware of any studies on the relationship between acetabular and femoral anteversion and clinical and radiographic changes in the hip. Therefore, we assessed various combinations of femoral and acetabular anteversion in relation to pain, rotation of the hip, and osteoarthritis.

Data on the Patients
We evaluated the computerized tomographic scans and conventional radiographs of 356 hips in 181 patients (eighty-eight female patients and ninety-three male patients). Six hips in six patients could not be evaluated: three had been treated with a triple osteotomy, one had grade-2 osteoarthritis^9,11, one had residual changes secondary to Perthes disease, and one had idiopathic necrosis of the femoral head. The patients ranged from seven to seventy-one years old, and the greatest number of patients were between twenty and thirty years old (Fig. 3).

View larger version (15K): [in this window] [in a new window]   Fig. 3 Graph showing the age distribution of the patients in the study. (One patient [one hip] is not included.)

Imaging Studies
The computerized tomographic images were made with a Somatom Plus S scanner (Siemens, Erlangen, Germany). The images were made with the patient in the prone position, as recommended by Visser et al.^75,76, in order to keep the pelvis in an anatomical position and to avoid a pelvic tilt. The feet were slightly supported so that they were parallel. The images included the area between the superior portion of the acetabular roof and the lesser trochanter. The slice thickness was three millimeters, the table feed was four or five millimeters, and the table increment was three millimeters. Three images with a slice thickness of five millimeters were made at the level of the femoral condyles. Three-dimensional reconfigurations were not useful for the measurement of anteversion.

The computerized tomographic scans occasionally were made without reference to the femoral condyles, making it difficult to measure femoral anteversion. However, in sixteen of the patients who had such scans, both hips were evaluated with use of biplanar radiographs that were made according to the method described by Dunn¹⁸, Rippstein⁵⁵, and Müller⁴⁶, and, in two others, one hip was evaluated with such radiographs.

Measurement of Acetabular Anteversion
Acetabular anteversion, as measured on computerized tomographic scans, is the angle between the sagittal plane and a line drawn tangential to the anterior and posterior acetabular margins (Fig. 4). As mentioned previously, Visser et al.^75,76 and others^1,2 found that an anterior pelvic tilt reduces acetabular anteversion whereas a posterior pelvic tilt (an upright pelvic position) increases it. A neutral position of the pelvis is obtained by having the patient lie prone, with the anterior tips of the iliac crests and the symphysis pubis resting evenly on the table⁴³. A support placed beneath the ankles keeps the feet parallel to each other.

View larger version (85K): [in this window] [in a new window]   Fig. 4 Computerized tomographic scan demonstrating the lines used to measure acetabular anteversion. A line is drawn midway between the two halves of the pelvis; this is the best method for defining the sagittal plane when the scan cuts the hemipelves at different levels or when the pelvis is not perfectly horizontal. On each side, a parallel line is drawn in the sagittal plane, beginning at the posterior margin of the acetabulum. The angle of acetabular anteversion is measured between the line corresponding to the sagittal plane and a line drawn tangential to the anterior and posterior acetabular margins. At this level, the femoral head is in full and congruent contact with the anterior surface of the acetabulum (see Figs. 5-A, 5-B, and 5-C).

View larger version (101K): [in this window] [in a new window]   Figs. 5-A, 5-B, and 5-C: Computerized tomographic scans illustrating different levels of scanning through the femoral head. (The terms left and right refer to the sides of the images as visualized by the reader.) Figs. 5-A: Computerized tomographic scan demonstrating the optimum level of scanning through the femoral head. In both hips, the anterior part of the acetabulum covers the femoral head congruently.

View larger version (111K): [in this window] [in a new window]   Fig. 5-B On the left side, the diameter of the femoral head is greater than that shown in Fig. 5-A but the congruence is still perfect. Therefore, the measurement was made at this level. On the right side, however, there is no congruence at the anterior part of the acetabulum. Therefore, the anteversion was measured at the level shown in Fig. 5-A.

View larger version (104K): [in this window] [in a new window]   Fig. 5-C On the right side, the anterior surface of the acetabulum appears to be even smaller than that shown in Fig. 5-B and there is no congruence. The degree of anteversion would be high if measured on this image.

Measurement of Femoral Anteversion
Femoral anteversion is the angle between the transverse axis of the knee joint, which is best indicated by a line drawn tangential to the maximum posterior convexity of both femoral condyles (Fig. 6-A), and the transverse axis of the femoral neck. The femoral neck cannot be visualized in the transverse plane because of its anterior and cephalad orientation; however, images made at different levels (Fig. 6-B) can be superimposed to create a summation image^13,14,44, making it possible to draw a line through the center of the femoral head and along the central axis of the femoral neck. On proximal scans, the trochanteric fossa makes the neck appear to be more slender and more ventrally located than it appears on distal scans. On the summation image, the central axis is more dorsally located and there is increased anteversion. The lateral end of the line passing through the center of the femoral head should be located exactly between the anterior and posterior cortical margins but not in the trochanteric region (Fig. 6-C).

View larger version (63K): [in this window] [in a new window]   Figs. 6-A, 6-B, and 6-C: Computerized tomographic scans illustrating the method used to measure femoral anteversion. Fig. 6-A: The transverse axis of the knee joint is indicated by a line drawn tangential to the posterior surfaces of the femoral condyles. The scan used for the measurement should define the complete posterior convexity of the condyles. The vertical line against which the transverse axis is drawn is the line that corresponds to the midline between the iliac wings (not shown).

View larger version (70K): [in this window] [in a new window]   Fig. 6-B This image of the femoral neck is composed of a few computerized tomographic scans made at various levels. It is necessary to cover the full width of the femoral neck and to draw a correctly positioned central axis that passes through the center of the femoral head.

View larger version (112K): [in this window] [in a new window]   Fig. 6-C This image, which represents the final summation image of all of the sections of the femoral neck, is used to measure the degree of femoral anteversion. The transverse axis of the limb should form a 90-degree angle with the sagittal plane of the pelvis, which is defined by a line drawn midway between the iliac wings. The starting point of the axis of the femoral neck is drawn a bit too laterally in this example and should be in the medial part of the femoral neck and pass to the center of the femoral head.

Normal and Abnormal Ranges of Femoral and Acetabular Anteversion
Grading system: Our study was based on the assumption that the normal range of femoral and acetabular anteversion is 15 to 20 degrees (grade 1). We defined decreased anteversion as either grade -2 (10 to 14 degrees) or grade -3 (less than 10 degrees), and we defined increased anteversion as either grade +2 (21 to 25 degrees) or grade +3 (more than 25 degrees) (Table II). Our findings confirmed the validity of these ranges.

Clinical Evaluation of Rotation of the Hip
Internal and external rotation of the hip are assessed with the patient in the supine position and the hips flexed to 45 degrees. Pelvic rotation must be eliminated and the anterior superior iliac spines must be observed for any evidence of rotation. We measured all patients in the same position. With the patient in the prone position, it is possible to rotate the pelvis as well, resulting in increased rotation.

Clinical and Radiographic Findings

Pain
We evaluated 250 hips (143 patients) with regard to the relationship between pain and the instability index. Pain was most prevalent among hips that had a very high or very low instability index—that is, hips that had a very high or very low degree of acetabular and femoral anteversion (p = 0.014) (Table IV). The 95 percent confidence intervals revealed almost no overlap between the hips that had a low instability index and those that had a normal index and only a slight overlap between the hips that had a high instability index and those that had a normal index. This finding suggests that there is a relationship between pain and the degree of anteversion.

Rotation of the Hip
We evaluated 189 hips (118 patients) with regard to changes in the range of motion of the hip. In the eighty-two hips with an instability index of less than 20, the average internal rotation and external rotation measured 17 and 46 degrees, respectively (Table V). This difference was significant (p < 0.001). In the thirty-five hips with a normal instability index of 30 to 40, there was no difference between internal and external rotation, further validating these values. In the thirty-two hips with an index of more than 40, internal rotation was minimally increased, paralleling the increased femoral anteversion.

Osteoarthritis
We evaluated 275 hips (152 patients) for evidence of osteoarthritis and found no significant differences among the various groups (p = 0.154) (Table VI). However, analysis of the 95 percent confidence intervals revealed a very small overlap between the hips with the lowest instability index (less than 20) and those with a normal index (30 to 40), indicating that the prevalence of osteoarthritis was increased in hips that had a very low instability index in association with decreased femoral and acetabular anteversion. One possible reason for the relatively low percentage of patients who had osteoarthritis is that most of the patients in our series were managed for pain before signs of osteoarthritis appeared. Moreover, only a few cases of severe osteoarthritis were included in our statistical analysis because joint stiffness is often associated with decreased internal rotation and increased external rotation, findings that also are associated with decreased anteversion.

Effects of Various Combinations of Femoral and Acetabular Anteversion
The changes in rotation and the rates of pain and osteoarthritis indicated that normal or increased femoral anteversion (grade 1, +2, or +3) was often compensated for by decreased acetabular anteversion (grade -2 or -3). The reverse also was noted. The hips were subdivided into groups on the basis of various combinations of femoral and acetabular anteversion (Table VII). Hips with severe dysplasia, a deep acetabulum, or protrusio acetabuli were excluded. In the group that was studied, there was an increased percentage of hips with decreased acetabular and femoral anteversion. Normal anteversion and increased anteversion were found in a relatively small number of hips.

Dysplasia of the Hip, Deep Acetabulum, or Protrusio Acetabuli
The various grades of acetabular and femoral anteversion in patients who had dysplasia of the hip, a deep acetabulum, or protrusio acetabuli were evaluated separately on the basis of the definitions given earlier (Table I). It is commonly thought that dysplasia of the hip is associated with increased acetabular anteversion^8,10,39, but this is not necessarily the case (Table XII). Severely decreased acetabular anteversion (grade -3) was found in 29 percent (nine) of thirty-one dysplastic hips, and severely decreased femoral anteversion (grade -3) was found in 59 percent (nineteen) of thirty-two dysplastic hips. It should be remembered that this was a preselected group in which most of the dysplastic hips had a moderate deficiency of anterior acetabular coverage. Similar results were seen in hips that had a deep acetabulum, which may be considered the reverse of dysplasia. Protrusio acetabuli was predominantly associated with higher grades of acetabular and femoral anteversion; however, there were too few hips to allow any conclusions.

Slipped Capital Femoral Epiphysis, Coxa Vara, or Coxa Valga
We also assessed the relationship between decreased anteversion and slipped capital femoral epiphysis, coxa vara, and coxa valga (Tables XIII and XIV). Only moderate slips, asymptomatic slips, and pistol-grip deformities were included in the analysis. Severely decreased femoral anteversion (grade -3) was observed in 77 percent (twenty-four) of the thirty-one hips with obvious or subclinical slipped capital femoral epiphysis, and moderately decreased femoral anteversion (grade -2) was observed in 13 percent (four). Severely decreased acetabular anteversion was observed in 27 percent (nine) of thirty-three hips, and moderately decreased anteversion was observed in 21 percent (seven). Decreased femoral anteversion is a common feature of coxa vara and occurred with almost the same frequency as it did in association with slipped capital epiphysis (Table XIV). Coxa valga usually is thought to be associated with increased femoral anteversion, so it was surprising to find severely decreased femoral anteversion (grade -3) in 33 percent (seven) of twenty-one hips and moderately decreased anteversion (grade -2) in 14 percent (three). Severely and moderately decreased acetabular anteversion (grades -3 and -2) were each present in 29 percent (six) of the twenty-one hips with coxa valga.

Tibial Torsion
Computerized tomographic scans showed varying degrees of internal or external rotation of the knee joint despite the parallel position of the feet with the patient in the prone position. We attempted to determine whether this finding was due to compensatory external tibial torsion in response to a high angle of femoral anteversion with increased internal rotation of the knee or to compensatory internal tibial torsion in response to a low angle of femoral anteversion with increased external rotation of the knee. The extremities were divided into three groups on the basis of the degree of internal or external rotation of the knee with the feet parallel: 0 to 5 degrees (group 1), 6 to 10 degrees (group 2), and more than 10 degrees (group 3) (Table XV). Computerized tomography showed that, with internal rotation of the knee, the average femoral anteversion increased from approximately 9 degrees (group 1) to approximately 16 degrees (group 3); this increase apparently was due to the increasing degree of external tibial torsion. With external rotation of the knee, femoral anteversion decreased from approximately 6 degrees (group 1) to 3 degrees (group 3). Therefore, the increase in external rotation of the knee and internal rotation of the tibia was due to the decrease in femoral anteversion.

	Operative Treatment

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Selection of Patients
Operative treatment is indicated for deformities that cause pain or have already induced compensatory changes in the knee and the leg. Pain generally precedes radiographic evidence of osteoarthritis of the hip. Corrective procedures should be considered in order to correct the anatomical deformity, to decrease pain, and to avoid the development of osteoarthritis. We previously evaluated the association between age at the time of the onset of pain and the degree of deformity in patients who had dysplasia of the hip^64,68. The association became stronger with increased deformation of the hip, and two-thirds of severely dysplastic hips were associated with an onset of pain before the age of thirty-five years. All patients who had extremely dysplastic hips had the onset of pain before the age of thirty-five years. Approximately 47 percent of patients had the onset of pain or discomfort before the age of thirty years and 72 percent, before the age of forty years (Fig. 3). Patients who were less than ten years old and who had increased external rotation were hampered by this deformity. It appears that the degree of torsional deformity and the total amount of femoral and acetabular anteversion influence the age at the onset of pain.

Operative Correction of Femoral Anteversion
Decreased femoral anteversion (Figs. 7-A, 7-B, 7-C, 7-D) is corrected by means of an intertrochanteric or subtrochanteric rotational osteotomy to achieve the normal degree of anteversion⁷². Two short Kirschner wires are drilled toward the center of the femoral shaft, one proximal to and one distal to the plane of the osteotomy, parallel to each other⁷². Decreased anteversion is corrected by rotating the distal fragment internally, and increased anteversion is corrected by rotating the fragment externally; in both instances, the goal is to achieve 15 to 20 degrees of anteversion. The necessary amount of correction is determined on the basis of preoperative radiographs and computerized tomographic scans. However, this amount of rotation is not sufficient to ensure that the goal of the procedure will be achieved, as it is common for internal rotation to decrease postoperatively. Additional internal rotation therefore must be obtained. After preliminary fixation of the plate, the range of internal rotation, measured with the hip in 45 degrees of flexion and without abduction, should exceed the range of external rotation by 15 to 20 degrees when the lower limb is rotated without force. However, it should be remembered that excessive internal rotation of the distal fragment can result in painful limitation of external rotation. The presence of osteoarthritis with loss of motion necessitates an even more careful assessment of the problem and operative correction.

View larger version (102K): [in this window] [in a new window]   Figs. 7-A through 7-D: Radiographs of a twenty-year-old woman who had decreased femoral and acetabular anteversion. The patient complained of pain in the left hip. At the time that the patient was examined, in 1983, operative treatment was limited to an intertrochanteric rotational osteotomy to increase femoral anteversion. Today, we also would rotate the acetabulum to 15 to 20 degrees of anteversion. Nevertheless, the patient had only moderate pain at the time of the most recent examination. Fig. 7-A: On the anteroposterior radiograph, the femoral necks appear to show no anteversion. The pelvis shows an unusual degree of ischial torsion with marked projection of the ischial spine toward the midline. The posterior acetabular margin terminates quite medial to the anterior margin. A computerized tomographic scan (not known) demonstrated that acetabular and femoral anteversion were reduced to 0 degrees.

View larger version (123K): [in this window] [in a new window]   Fig. 7-B Dunn-Rippstein radiograph showing markedly decreased femoral anteversion.

View larger version (90K): [in this window] [in a new window]   Fig. 7-C Anteroposterior radiograph of the pelvis and hips, made after rotational osteotomy of the left femur and fixation with a 90-degree AO plate.

View larger version (108K): [in this window] [in a new window]   Fig. 7-D True lateral radiograph showing the femoral anteversion after intertrochanteric rotational osteotomy. The anteversion is substantially greater than that seen in Fig. 7-B. Intraoperatively, the degree of anteversion and the range of motion of the hip can be monitored with image intensification.

Operative Correction of Acetabular Anteversion
The correction of acetabular orientation in the axial (transverse) plane requires complete mobilization of the acetabulum by means of a triple pelvic osteotomy^67,68,70,77 or an osteotomy performed according to the technique of Ganz et al.^26,74. A Kirschner wire is inserted vertically into the acetabular fragment, from the anterior aspect, to serve as a guide for measuring and checking the correction relative to the sagittal plane and to avoid the inadvertent creation of an external rotation deformity. This step is indicated during all pelvic osteotomies that produce anterolateral rotation of the acetabulum. An additional 10 to 15 degrees of internal rotation of the acetabulum is required because simple anterior rotation also produces anterior displacement of the posterior, more laterally projecting parts of the acetabular roof, thereby reducing the degree of acetabular anteversion^2,75,76. The difference in the appearance of the acetabulum can be seen on radiographs of the pelvis that are made with a marked anterior pelvic tilt. Either a severe decrease or a severe increase in acetabular anteversion can be an indication for a corrective procedure. The principal symptom among patients with decreased anteversion is pain in the hip (Figs. 8-A, 8-B, and 8-C). The principal symptom among patients with increased anteversion is instability (Figs. 9-A, 9-B, and 9-C).

View larger version (104K): [in this window] [in a new window]   Figs. 8-A, 8-B, and 8-C: A thirty-four-year-old man who complained of severe pain in the right hip. Fig. 8-A: Anteroposterior radiograph showing evidence of early osteoarthritis of the right hip.

View larger version (106K): [in this window] [in a new window]   Fig. 8-B Computerized tomographic scan showing 2 degrees of acetabular anteversion and 4 degrees of femoral retroversion.

View larger version (140K): [in this window] [in a new window]   Fig. 8-C Anteroposterior radiograph made three years after the acetabulum was rotated to 15 degrees of anteversion by means of a triple pelvic osteotomy. The femoral neck was also corrected to 15 to 20 degrees of anteversion by means of a valgus osteotomy with slight lateral rotation of the acetabulum. The radiograph demonstrates the round femoral head and maintenance of the joint space. At the time of the most recent examination, the patient was working full-time and was playing tennis, and he complained of pain only after walking for more than three hours.

View larger version (86K): [in this window] [in a new window]   Figs. 9-A, 9-B, and 9-C: A fifteen-year-old girl who complained of repeated episodes of giving-way of the right knee into flexion and internal rotation when walking. Fig. 9-A: Radiograph of the right hip, showing no obvious abnormalities other than increased separation of the anterior and posterior acetabular margins. A Dunn-Rippstein radiograph (not shown) revealed only a moderate increase in femoral anteversion.

View larger version (99K): [in this window] [in a new window]   Fig. 9-B Computerized tomographic scan demonstrating a marked increase in acetabular anteversion (27 degrees) and a moderate increase in femoral anteversion (23 degrees). The two angles yield a McKibbin instability index43 of 50, indicating severe instability.

View larger version (87K): [in this window] [in a new window]   Fig. 9-C Radiograph made after a triple pelvic osteotomy in which the acetabulum was externally rotated by 15 degrees. The distance between the anterior and posterior acetabular margins of the right hip is within the normal range of approximately 1.5 centimeters. The range of internal rotation was no longer increased, and the episodes of instability ceased.

Treatment Considerations
Decreased femoral anteversion has a greater effect on the change in hip motion than decreased acetabular anteversion does. It is reasonable to suggest, therefore, that a rotational osteotomy to increase femoral anteversion may be sufficient in a patient who has moderately decreased acetabular anteversion. However, if acetabular anteversion approaches 0 degrees, then a rotational osteotomy of the acetabulum should be performed as well.

Decreased femoral anteversion is two to three times more common than decreased acetabular anteversion. It is only in the last few years that we have developed methods for the diagnosis and treatment of torsional deformities of the acetabulum. Until 1991, we only performed rotational osteotomies of the femur^69,72. Therefore, the total number of operations on the acetabulum is too small, and the duration of follow-up has been too short, to allow any specific conclusions or recommendations to be made.

We compiled a list of the procedures that had been performed for and recommended to our patients (Table XVI). We noted that only seven hips had had a derotational osteotomy because of increased femoral anteversion, whereas seventy-two had had a rotational osteotomy because of decreased femoral anteversion. In retrospect, we noted that we had missed the torsional deformity in a number of patients who were managed with a pelvic osteotomy for the correction of dysplasia of the hip. We also identified fourteen hips with higher grades of osteoarthritis that could not be treated with an osteotomy (Figs. 10-A and 10-B). Patients who have osteoarthritis often have severe torsional deformities that involve the femur and the acetabulum equally. It is important to remember that increased internal rotation of the hip and instability are not necessarily due to increased femoral anteversion; one of our patients, for example, had 27 degrees of acetabular anteversion and 23 degrees of femoral anteversion, resulting in a high instability index of 50 (Fig. 9-B). It also is important to note that anteversion frequently does not remodel after it has been corrected to 0 degrees by means of a varus derotational osteotomy. This phenomenon was observed in one of our patients, an eighteen-year-old woman who returned because of pain two years after a well performed triple osteotomy. Reevaluation showed that we had overlooked the absence of femoral anteversion at the time of the operation. The pain resolved once the anteversion had been corrected to 15 to 20 degrees by means of a rotational osteotomy of the femur.

View larger version (96K): [in this window] [in a new window]   Figs. 10-A and 10-B: A fifty-three-year-old man who had severe osteoarthritis of the right hip. The only treatment option was total hip replacement. Fig. 10-A: Anteroposterior radiograph of the pelvis and hips, showing evidence of severe osteoarthritis of the right hip.

View larger version (92K): [in this window] [in a new window]   Fig. 10-B Computerized tomographic scan showing both acetabular and femoral anteversion to be decreased to 0 degrees.

Treatment of Osteoarthritis
The results of treatment of osteoarthritis can be improved in patients who have external rotation contractures by performing a femoral rotational osteotomy in addition to a varus osteotomy or by performing a femoral rotational osteotomy only⁵⁰. We reviewed the results of various types of intertrochanteric osteotomies that had been performed on 136 hips in 116 patients (seventeen men and ninety-nine women) who had osteoarthritis secondary to dysplasia of the hip. The average age of the patients was thirty-nine years (range, nineteen to sixty-two years), and the average duration of follow-up was seven years (range, two to fifteen years). A hip was considered to be dysplastic when the center-edge angle⁸¹ was less than 25 degrees and the acetabular angle of Ullmann and Sharp⁶⁵ was more than 43 degrees. Rotational osteotomy led to a marked decrease in pain in nineteen (90 percent) of twenty-one hips (Tables XVII and XVIII). When varus or valgus osteotomy was performed simultaneously with rotational osteotomy, a marked decrease in pain was noted in only sixteen (64 percent) of twenty-five hips and six of eight hips, respectively, and when varus or valgus osteotomy was performed alone (without rotational osteotomy to obtain normal anteversion), a marked decrease was noted in only forty-five (62 percent) of seventy-three hips and five of nine hips, respectively. It would be easy to assume that the difference between the groups was related to the grade of osteoarthritis. However, a careful review of the data showed that higher grades of osteoarthritis were noted in the hips that were treated with rotational osteotomy (average grade, 2.2) and combined valgus and rotational osteotomy (average grade, 2.3), whereas lower grades were noted in the hips that were treated with varus osteotomy alone (average grade, 1.25) and combined varus and rotational osteotomy (average grade, 1.8). This difference may be related to the fact that, if the femoral head was well centered or there was a higher grade of osteoarthritis, only the external rotation contracture was corrected to equalize the range of motion.

Zaoussis et al.⁸⁸ reviewed the results of seventy intertrochanteric osteotomies in sixty-five patients who had osteoarthritis. In almost two-thirds of the patients, the osteoarthritis was secondary to a congenital disorder of the hip. The operation usually involved a rotational osteotomy with slight medial displacement. The average age at the time of the operation was forty-seven years, and the duration of follow-up ranged from six to fifteen years. The result was satisfactory in forty-nine hips and unsatisfactory in twenty-one.

Detenbeck et al.¹⁶ reported on fifty-nine intertrochanteric osteotomies in fifty-five patients (thirty-one women and twenty-four men) who had degenerative osteoarthritis. Those authors noted that external rotation of the femoral head for maximum relaxation of the capsule frequently was present before the operation. In such patients, only the distal fragment was rotated internally to improve the position of the leg. Those authors reported a satisfactory result after forty-seven (80 percent) of the fifty-nine procedures. Our results were better probably because we did not include any patients who had primary osteoarthritis but rather included only those who had dysplasia of the hip with decreased femoral and acetabular anteversion. Furthermore, we did not just bring the knee to a position of neutral rotation; rather, we tried to equalize internal and external rotation with a slight overcorrection for internal rotation. We found that rotational osteotomies are effective if performed accurately after a thorough evaluation of all changes and deformities in the femur and acetabulum.

	Conclusions and Recommendations

Top Introduction Etiology of Altered Acetabular... Diagnosis of Decreased... Clinical and Radiographic Study Operative Treatment Conclusions and Recommendations References

 
Our studies indicate that torsional deformities of the hip, frequently classified under the heading of idiopathic osteoarthritis, should be evaluated with radiographs and computerized tomography in order to allow for the measurement of acetabular and femoral anteversion. Operative treatment can be used to correct these deformities, decrease pain, and prevent early osteoarthritis. Since various combinations of decreased and increased acetabular and femoral anteversion in the same hip may be additive or compensatory in their effects, we assessed these combinations in relation to rotation of the hip, pain, and osteoarthritis. We estimated that 15 to 20 degrees is the normal range for both femoral and acetabular anteversion and that 30 to 40 degrees is the normal range for the McKibbin instability index. We found that a normal McKibbin instability index was associated with balanced ranges of rotation of the hip and with the lowest rates of pain and osteoarthritis. As the index approached the upper and lower limits, we found increasing degrees of rotational change, pain, and osteoarthritis.

These observations suggest that decreased acetabular and femoral anteversion associated with a McKibbin instability index of less than 20 is a major cause of altered rotation of the hip, pain, and osteoarthritis. When acetabular and femoral anteversion were increased, there was a tendency toward increased pain; however, the number of hips was too small to allow for definite conclusions. Decreased femoral anteversion was more than twice as common as increased femoral anteversion. In our study, the instability index was decreased in 181 hips (62 percent), normal in sixty-eight (23 percent), and increased in only forty-one (14 percent). These findings suggest that it is important to consider torsional deformities during the diagnostic evaluation of problems related to the hip. It is reasonable to conclude, therefore, that these deviations may account for a substantial percentage of the osteoarthritis that previously was classified as idiopathic³³.

Our findings suggest that a deep acetabulum, coxa vara, and deformities of the hip secondary to an obvious or subclinical slipped capital femoral epiphysis should be considered as precursors of osteoarthritis because of their high association with decreased femoral anteversion. Differences in the degree of anteversion of the acetabulum and femur are a congenital condition caused by various intrauterine rotational positions of the fetal limbs. In most instances, these differences regress spontaneously after birth, but an estimated 15 percent of hips have a persistent increase or decrease in anteversion. Decreased anteversion of the femur and the acetabulum may occur either in isolation (as a congenital deformity) or in combination (in association with other conditions such as slipped capital femoral epiphysis, coxa vara, a deep acetabulum, proximal femoral focal deficiency, and, quite frequently, dysplasia of the hip). The reduced femoral and acetabular anteversion could produce a deformity that results in osteoarthritis independently of the other deformities associated with the slip or hip dysplasia. Therefore, it is possible that, in the future, correction of the anteversion may be considered necessary for such patients.

A varus derotational osteotomy or a fracture of the femur may lead to a complete decrease in femoral anteversion. Decreased anteversion is suggested by decreased internal and increased external rotation of the hip as well as by radiographic changes. The computerized tomographic scan and the summation image of the femoral neck can establish the diagnosis. Treatment is necessary to reduce pain and to halt the progression of osteoarthritis. Decreased femoral anteversion is corrected by means of a rotational osteotomy in which a normal angle of femoral anteversion (15 to 20 degrees) is established. Decreased acetabular anteversion, which may be combined with decreased femoral anteversion, is corrected by means of a triple pelvic osteotomy in which the acetabulum is rotated to 15 to 20 degrees of anteversion. Increased acetabular anteversion that is associated with instability also can be corrected by means of a triple pelvic osteotomy.

	Footnotes

 
Departments of Orthopedics and Diagnostic Radiology, Städtische Kliniken, Syburger Strasse 14, D-44265, Dortmund, Germany.

Institute of Medical Informatics and Biomathematics, University of Münster, Domack Strasse 9, D-48149 Münster, Germany.

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