 |
 |
 |
|
| home | CME | help | feedback | subscriptions | archive |
|
The Journal of Bone and Joint Surgery (American). 2007;89:2508-2518. doi:10.2106/JBJS.F.01296 © 2007 The Journal of Bone and Joint Surgery, Inc.
Impingement of the Native Hip Joint1 Aditya V. Maheshwari, MD Aamer Malik, MD Lawrence D. Dorr, MD The Arthritis Institute, 501 East Hardy Street, Suite 300, Inglewood, CA 90301. E-mail address for L.D. Dorr: Patriciajpaul{at}yahoo.com
Investigation performed at The Arthritis Institute, Inglewood,
California
 Impingement at the hip
is a common cause of osteoarthritis.
Impingement of the hip joint has been a hidden disease until the current decade. Femoroacetabular impingement was identified as a dynamic cause of osteoarthritis by Ganz et al.1-22, although Murray23 and Stulberg et al.24 had identified the so-called tilt deformity and pistol-grip deformity, respectively, as probable causes. Impingement within the hip joint is an abutment conflict between the bone of the femur and that of the pelvis. Impingement in young patients is a mechanical problem caused by biological structural patterns or by overuse, particularly in athletes or in very flexible hips. Leunig et al.14 observed evidence of impingement with aging in the acetabula of patients (sixty-nine to ninety-seven years of age) with a femoral neck fracture and not uncommonly in cadavers of donors who were sixty to ninety years old at the time of death.
The cause of impingement in the osseous hip can be developmental, as a result of childhood conditions such as Legg-Calvé-Perthes disease and slipped capital femoral epiphysis; it may also result from posttraumatic or post-osteotomy morphologic changes in inclination and anteversion angles1-3,7,10,14,18-21. Extra-articular impingement of the intertrochanteric bone of a deformed proximal part of the femur can occur, but that is not the focus of this review. Instead, we will focus on the skeletal changes that have their destiny determined by the perinatal formative months. Impingement caused by structural deformities (morphologic dysplasia) may still be the single most common cause of osteoarthritis25,26. Because osteoarthritis is familial and culturally selective, these deformities can be assumed to be genetic in origin. Rotation of the hips occurs in the first two years of life with increasing anteversion, particularly after children begin standing, and then it gradually decreases to the values found in adults27-29. Watanabe29 examined 144 stillborn fetuses and embryos, after twenty to twenty-four weeks of gestation or more, and found femoral rotation ranging from 10° of retroversion to 35° of anteversion. External rotation was more common in males, and internal rotation was more common in females. Pitkow27 observed that, of 500 children with gait deformities, forty-five (9%) had an external rotation contracture presumed to be caused by an intrauterine position of flexion and external rotation of the hips. A persistent external rotation posture most likely led to the development of retroversion of the acetabulum27. Pitkow observed that about 5% of the children had a persistent external rotation contracture of the limb, a finding that correlates with the observation by Giori and Trousdale30 that 5% of the general adult population (five of ninety-nine people) have radiographic evidence of acetabular retroversion. Measurement of the McKibbin instability index28,31 in the hips of children confirms the variability of hip rotation. McKibbin31 observed that the combined anteversion of the acetabulum and femur in newborns ranged from <20° to >40°. Combined anteversion of 30° to 40° is considered normal in adults, and Tönnis and Heinecke28 observed that 181 (62%) of 290 hips had <30° of combined anteversion and 110 (38%) had <20°. The prevalence of acetabular retroversion causing impingement in patients with osteoarthritis is high30,32. Retroversion of the acetabulum alone is termed pincer impingement because of overcoverage of the femoral head by the prominent anterior aspect of the acetabular rim. The amount of retroversion of the acetabulum measured in four different radiographic studies ranged from 5% to 20%30,32-34. We found that, of 178 arthritic hips undergoing total hip replacement with use of computer navigation, eighty-nine (50%) showed acetabular anteversion of <10°, a rate that is more than twice that measured on radiographs (unpublished data). The difference in the rates may be due to the fact that we focused on arthritic hips and were measuring the structure of the acetabulum, or the fact that we adjusted for the tilt of the pelvis, which cannot easily be done with standard radiographs. An abnormal femoral head-neck ratio (offset) is the most common impingement deformity. Stulberg et al.24 termed this a pistol-grip deformity. It causes cam impingement of the femoral neck against the anterior aspect of the acetabular rim during flexion, adduction, and internal rotation. Stulberg et al. observed this deformity in thirty (40%) of seventy-five hips with osteoarthritis (66% of the hips in males and 10% of those in females). Retroversion of the femur can occur without an obvious pistol-grip deformity. Some retroversion of the acetabulum combined with some retroversion of the femur can result in a McKibbin index of <20°, which is considered to be severe retroversion28. With use of computer navigation, we observed that 102 (57%) of 178 hips had combined anteversion of <20° (unpublished data). Again, this percentage may be high because we performed the measurements only in arthritic hips.
On the basis of the pattern and stages of chondral and labral injuries, two distinct types of femoroacetabular impingement have been identified (Fig. 1)7. The first type, cam impingement, is more common in young athletic men. It is caused by the jamming of an abnormal femoral head, or head-neck junction (resulting in a reduced head-neck ratio or offset), against the acetabulum, especially with flexion and internal rotation. The prevalence of cam impingement in men is consistent with the finding of external rotation deformities being more common in male children29.
The second type, pincer impingement, is most common in middle-aged athletic women. It is the result of linear contact between a prominent anterior aspect of the acetabular rim and the femoral head or femoral head-neck junction such as occurs with coxa profunda, acetabular protrusion, or retroversion of the acetabulum7. The femoral head may have normal morphologic features or may have an indentation caused by the abutment against the prominent anterior aspect of the acetabular rim. The repeated microtrauma may result in an ossified labrum, which compounds the impingement. Cam and pincer impingement rarely occur in isolation, and the combination has been termed mixed cam-pincer impingement1. With this disorder, an abnormal femoral head or head-neck junction articulates with an abnormal acetabulum. In one epidemiological study of 149 hips with impingement, twenty-six (17.4%) had isolated cam impingement, sixteen (10.7%) had isolated pincer impingement, and 107 (71.8%) had combined cam-pincer impingement1. In the cam type of impingement, the resulting shear forces produce an outside-in abrasion of the acetabular cartilage and/or its avulsion from the labrum and the subchondral bone in the anterosuperior rim area7. Chondral avulsion in turn can lead to a tear or detachment of the initially uninvolved labrum. In contrast, the first structure to fail when there is pincer-type impingement is the acetabular labrum. The continued impact of the abutment results in the degeneration of the labrum with intrasubstance ganglion formation, or ossification that deepens the socket and increases anterior impingement. The persistent abutment, which often is anterior, with chronic leverage of the head in the acetabulum can result in injury to the cartilage directly opposite—i.e., in the posteroinferior aspect of the acetabulum (termed the contre-coup region)7. Chondral lesions in hips with pincer impingement often are limited to a small area of the rim and usually include only a narrow strip of acetabular cartilage and therefore are more benign. This is in contrast to what occurs with cam impingement, which can cause deep chondral lesions and/or extensive labral tears7,11. Arthritis develops when damage at the labral-cartilage junction extends to the articular cartilage and subchondral bone. This damage extends by shearing of the adjacent articular cartilage from the underlying subchondral bone18,35. In the aberrant, nonspherical area of the femoral head in young patients with femoroacetabular impingement, the hyaline cartilage showed clear degeneration similar to that in hips affected by osteoarthritis22. Wagner et al.22 described damage to the acetabular cartilage as a result of impingement in young patients, and Leunig et al.14 observed damage to the acetabular cartilage and labrum resulting from impingement in elderly patients without arthritis.
History A young or middle-aged patient who, at the time of presentation, describes the gradual onset of unilateral hip pain that is predominantly in the groin must be considered to have femoroacetabular impingement7,36. Occasionally, the pain is bilateral35. If the patient presents with knee pain, it is critical that the surgeon think about the hip as the possible cause. The patient may report mechanical symptoms (locking, catching, and giving-way) indicative of a labral tear or a delamination injury of the articular cartilage35. The pain is often intermittent and exacerbated by an excessive demand on hip flexion, such as occurs with athletic activities and in very flexible hips. Patients with impingement can have pain with these activities and even while sitting with the hip extremely flexed. In a recent study by Burnett et al.37, sixty (91%) of sixty-six patients had activity-related pain and forty-seven (71%) had night pain. Thus, a diagnosis of impingement must be considered when a patient presents with this history. Jäger et al.38 reported a mean delay of 5.4 years between the onset of symptoms and the diagnosis, and Burnett et al.37 reported a mean delay of twenty-one months, with an average of 3.3 previous doctor visits. Patients have even had laparoscopy, spine surgery, or an inguinal hernia repair as the result of a missed diagnosis caused by confusing symptoms7.
Physical Examination
Posteroinferior impingement can also be discovered by extending the patient's leg over the side of the examining table and rotating it externally; this maneuver should produce pain7. Alternatively, posterior impingement may be tested with the patient lying prone and the examiner extending and externally rotating the hip until pain is produced by impingement of the femoral head-neck junction against the posteroinferior aspect of the acetabular rim36. Posterior impingement becomes more common as the disease progresses and posteroinferior traction osteophytes develop36.
Plain radiographs are the most important imaging studies for the diagnosis of impingement. The recommended radiographs are an anteroposterior view of the pelvis and a cross-table lateral view of the hip in 15° of internal rotation17. Tilting of the pelvis on the anteroposterior view may obscure overcoverage or undercoverage of the femoral head as well as affect the measurement of acetabular anteversion. An optimal anteroposterior pelvic radiograph is one on which the coccyx points toward the symphysis pubis with a distance of no more than 2 cm between them and with symmetrical teardrops, obturator foramina, and iliac wings (Figs. 2-A, 2-B, and 2-C)7,20. Siebenrock et al.20 suggested that the optimal distance between the symphysis pubis and the middle of the sacrococcygeal joint is 25 to 40 mm in females and 40 to 55 mm in males. A reconstructed computed tomography scan to correct for tilt can be used in place of a tilted anteroposterior pelvic radiograph13,28,39.
The morphologic features on the radiograph that favor a diagnosis of anterior impingement are a congruent but nonspherical femoral head, a short femoral neck, and/or a small head-to-neck ratio with a reduced head-neck offset. The most prevalent finding on the anteroposterior radiograph is a flattened head-neck junction or a pistol-grip deformity24 (Fig. 2-B). A pistol-grip deformity is characterized by flattening of the usually concave surface of the femoral head, a bump on the anterolateral surface of the femoral neck, a so-called medial hook at the medial head-neck junction, and failure of the femoral head to be centered over the femoral neck4,24,26,40. With milder forms of anterior impingement, the findings may be seen on only lateral radiographs, which show displacement of the head over the neck and the medial hook4,24,26,40. Specific acetabular changes include an os acetabuli or ossification of the acetabular rim. Pincer impingement is commonly associated with acetabular protrusion, coxa profunda, or a retroverted acetabulum1. An additional observation on plain radiographs may be juxta-articular fibrocystic changes (herniation pits) at the anterosuperior aspect of the femoral neck13,35,41. Fluoroscopy of the hip can be used in equivocal cases to observe whether impingement occurs with dynamic motion of the hip36.
Radiographic Measurements
Computed Tomography and Magnetic Resonance Imaging The common use for computed tomography scans in the evaluation of impingement is to allow three-dimensional reconstruction of the hip joint for detailed definition of femoral head-neck asphericities and reduced offset, which cause osseous impingement, as well as determination of the version of the femoral neck and the acetabulum43. A computed tomography scan also provides the opportunity to produce software that can simulate impingement. A gadolinium-enhanced magnetic resonance arthrogram is needed to assess labral injury and the articular cartilage as well as to demonstrate the contour of the femoral head-neck junction7,9,15,16,35,44-46. In one study, the sensitivity of magnetic resonance arthrography in detecting labral hypertrophy, degeneration, and/or tears was between 63% and 90%, while specificity was >70% when only labral tears were present16. (The specificity is poor for detecting chondral separations that remain undetached7,44.) Measurements made on computed tomography or magnetic resonance imaging scans can suggest impingement9,15-17,35,43-46. Kassarjian et al.45, using magnetic resonance arthrography, defined a triad of anomalies in 88% of patients with cam impingement: an abnormal head-neck morphology, anterosuperior cartilage abnormality, and anterosuperior labral abnormality. In addition, dynamic magnetic resonance imaging with an open or large-bore unit can provide real-time imaging of the impingement35.
Nonoperative Treatment The goal of treatment is relief of the impingement. An initial trial of nonoperative treatment has been recommended by some authors7,11,38,44,47. This may include modification of activity; restriction of athletic pursuits; and reduction of excessive motion of, and demand on, the hip. Nonsteroidal anti-inflammatory medication may relieve pain, but it may also mask symptoms. Physical therapy should emphasize muscle-strengthening and avoidance of extremes of range of motion. The young age of these patients means that they have a high activity level and athletic ambitions, which usually jeopardize compliance with nonoperative treatment.
Hip impingement is a mechanical problem, and nonoperative measures will not eliminate the pathomechanics of structural deformities1,47. Jäger et al.38 recommended an operation in patients with symptoms that persist beyond six months, provided that the articular damage is not severe. In their study, all nine patients who underwent nonoperative treatment had continued pain and hip dysfunction whereas six patients treated with an open osteoplasty all rated the hip as excellent or good and had resolution of the clinical symptoms. There seems to be little place for nonoperative treatment except when the cause is overuse without structural deformity.
Operative Treatment
Arthroscopy The most common use for this minimally invasive treatment option is assessment and reconstruction of a nonspherical femoral head with a decreased head-neck offset44,47-49. Associated labral and chondral lesions are treated in the hope of restoring nearly normal mechanics of the hip joint during the extremes of motion47. The technique separates the hip into two compartments, central and peripheral. The central compartment includes the weight-bearing part of the head, the articular cartilage of the head, the acetabular fossa, and the ligamentum teres. The peripheral compartment contains the non-weight-bearing portions of the femoral head, the femoral neck, the hip capsule, synovial folds, and the orbicular ligaments. Access to the anterolateral aspect of the neck is through the peripheral compartment, and visualization of the labrum is through the central compartment47. Labral lesions and any areas of chondral damage can be addressed, and labral tears can be repaired. Labral resection should be conservative, and attempts should be made to leave a stable labral remnant. In areas of exposed subchondral bone, a microfracture technique, chondroplasty, or drilling may be performed to stimulate a fibrocartilaginous response47-49, although we are not aware of any reports of the clinical outcomes of these techniques in hips with impingement. Osteophytes on the femoral head or neck may be resected with a power burr or a radiothermal device to restore the concavity of the femoral head-neck junction. To avoid injury to the branches of the medial circumflex vessels, the distal and posterior extent of the procedure should be limited on the femoral neck to the area of impingement, typically about 10 mm from the articular margin47. A concomitant excision of the anterior part of the acetabular rim is indicated when that part of the rim contributes to the impingement.
Weight-bearing is restricted following reconstruction to decrease the risk of postoperative femoral neck fracture47,49. Patients are allowed to stop using crutches in two to four weeks, and for four to six weeks activities are limited to range-of-motion exercises with use of a stationary bicycle or swimming. The femoral neck should be protected from fracture after osteochondroplasty of the head-neck junction for three to six months. The results of arthroscopic surgery reported to date have been short-term, and we have no knowledge of the ability of this operative technique to alter the course toward total hip arthroplasty. Of 156 patients (age range, fourteen to seventy-three years) who had been treated with arthroscopy, 50% stated that the pain had resolved by three months; 75%, by five months; and 95%, by one year49. During that time, three patients required a total hip arthroplasty, and these failures correlated with the amount of articular cartilage damage noted at arthroscopy. Similarly, Guanche and Bare47 found that their results correlated with the presence of degenerative cartilage changes. The advocates for arthroscopic surgery have suggested that the results will be comparable with those reported following open operations, but the patients recover much earlier after arthroscopic surgery44,49; however, most arthroscopically treated patients have early-stage disease.
Hybrid Arthroscopy and Open Procedures
Open Procedures Open procedures have been performed with a posterior incision made from the posterior-superior edge of the greater trochanter distally to the posterior border of the vastus lateralis ridge6,52. After placement of drill holes for later reattachment, a trochanteric flip osteotomy (or a trigastric osteotomy with the gluteus medius, vastus lateralis, and gluteus minimus remaining attached to the trochanteric fragment) is performed6. The osteotomy consists of a horizontal cut with the leg internally rotated. It has a maximum thickness of 1.5 to 2.0 cm at its proximal limit6,52. The osteotomy (Figs. 4-A and 4-B) must be anterior to the most posterior insertion of the gluteus medius tendon and should exit superficial to the piriformis fossa superiorly. At the vastus ridge distally, the integrity of the external rotator muscles is respected, with preservation and protection of the profundus branch of the medial circumflex femoral artery, which becomes intracapsular at the level of the superior gemellus muscle53. It is also necessary to protect the epiphyseal branches of the medial circumflex femoral artery, which lie subperiosteally on the posterior-superior surface of the femoral neck. It must be remembered that the blood supply to the femoral head arises mainly from the medial circumflex femoral artery, and during dislocation of the hip this vessel is protected by the intact obturator externus muscle6,7,53. Some surgeons prefer to assess the sciatic nerve to determine if it bifurcates over the belly of the piriformis, and, if it does, the piriformis is released to prevent traction injury to the more superficial branch during hip dislocation. Capsular incision: The capsule is incised anterolaterally along the axis of the femoral neck. The capsulotomy must remain anterior to the lesser trochanter to avoid damage to the main branch of the medial circumflex femoral artery, which lies just superior and posterior to the lesser trochanter. Elevation of the anteroinferior capsular flap allows visualization of the acetabular labrum. The first capsular incision is then extended toward the acetabular rim, where it is sharply turned posteriorly, parallel to the labrum, reaching the retracted tendon of the piriformis (completing the z-shaped capsulotomy for the right hip6 [Fig. 5] and an inverse z-shaped capsulectomy for the left hip). Alternatively, a T-shaped capsulotomy may be done52.
Dislocation: Anterior dislocation of the femoral head provides up to an 11-cm gap between the femoral head and the acetabular surface and provides a 360° view of the joint, including the acetabular rim, labrum, articular cartilage, and femoral head-neck junction6. The ligamentum teres can be torn by further external rotation of the femoral head, or incised without loss of the important blood supply to the head6,54. Placement of a 2.0-mm-diameter drill hole into the dislocated femoral head can document the preservation of its blood supply, although this should not be used as an absolute test6,54. Bleeding of the surfaces of the cancellous bone after trimming of osteophytes on the periphery of the head is an additional sign of satisfactory vascularity. Laser Doppler flowmetry has shown that blood flow is consistently restored after relocation of the hip54. After operative treatment, the capsule of the hip may be repaired, but it should not be tightened since this may create tension on the retinacular vessels, causing a decrease in perfusion of the femoral head. The greater trochanter is reattached with use of two or three 3.5 or 4.5-mm cortical screws. Cerclage wires may endanger the blood supply to the head, and their use is not encouraged. Ganz et al.6 stated that they did not routinely use prophylaxis against heterotopic ossification but did use subcutaneous low-dose heparin for eight weeks postoperatively for prophylaxis against venous thrombosis.
Some authors have used other approaches for localized or less extensive lesions25,38. The direct lateral exposure can be chosen for hips in which less exposure of the posterior-inferior aspect of the acetabulum is required, and the iliofemoral exposure may be chosen for hips with pure anterior impingement. However, global visualization and comprehensive deformity correction on both sides of the joint are best obtained with the trochanteric flip operation6. All approaches that retain an intact greater trochanter are associated with greater difficulty in separating and mobilizing the gluteus minimus from its attachment to the capsule, since the tip of the greater trochanter overlies the most critical part of its insertion6.
Treatment Options for the Lesions Seen with Impingement This review has not focused on extra-articular impingement, but it should be noted that reorientation of the proximal part of the femur with a flexion-valgus intertrochanteric osteotomy can be done to reduce extra-articular impingement caused by decreased femoral anteversion or a varus position of the neck6,11. Relative neck lengthening through trochanteric advancement is another option for increasing clearance and alleviating the extra-articular impingement to optimize hip abduction7.
Acetabular Osteotomy Simple rim osteoplasty and labral repair can be done after dislocation of the hip. Identified labral and chondral lesions are tested, with use of a nerve hook, for partial or complete avulsions from the acetabular rim11. In cases of anterior overcoverage, a resection osteoplasty of the anterosuperior aspect of the rim is done after mobilization of the acetabular labrum. Resection of the labrum (limited to the injured area) is done when it is ossified or when excessive scarring, attrition, or degeneration of the labrum is seen. The amount of rim resection can be estimated after reduction of the head and evaluation of the impingement. The labrum is then reattached to the acetabular rim with anchored sutures. The hip is reduced, and the stability of labral fixation and the resolution of impingement are confirmed. In a retrospective study of matched cohorts, Espinosa et al.5 found that thirty-two patients treated with labral refixation recovered earlier and had superior clinical and radiographic results at one and two years when compared with twenty patients who had undergone resection of the torn labrum.
Postoperative Rehabilitation and Pattern of Recovery
Clinical Outcomes
Although long-term analyses of the outcomes of surgical intervention are
not available, the preliminary results indicate that surgical dislocation of
the hip to allow improvement in the head-neck offset, as well as rim
osteoplasty, is successful in alleviating the symptoms of impingement in most
patients. It is important that the treatment, particularly realignment
osteotomies of the acetabulum and proximal part of the femur, do not result in
secondary impingement. Although early correction of impingement has improved
hip function, it is not yet known how often the correction prevents the
progression of osteoarthritis.
NOTE: The authors appreciate the suggestions and advice of Reinholz Ganz, MD, in the preparation of this manuscript.
  CiteULike  Connotea  Del.icio.us  Technorati What's this?
Letters to the Editor:Read all Letters to the Editor
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Top
Introduction
Origin of Impingement
9 mm or a ratio of the head diameter of
