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The Journal of Bone and Joint Surgery (American). 2009;91:701-710. doi:10.2106/JBJS.H.00802 © 2009 The Journal of Bone and Joint Surgery, Inc.
Acetabular Labral Tears1 The Ottawa Hospital, University of Ottawa. 501 Smyth Road CCW 1646, Ottawa, ON K1H 8L6, Canada. E-mail address for P.E. Beaulé: pbeaule{at}ottawahospital.on.ca
Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. Also, commercial entities (Zimmer, Stryker, and Wright Medical Technology) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.
Acetabular labral tears rarely occur in the absence of a structural osseous abnormality. Labral tears are frequently associated with lesions of acetabular cartilage such as delamination. Hip arthroscopy is the preferred operative approach in the treatment of labral injuries in the absence of substantial structural osseous abnormalities.
The knowledge base and understanding of acetabular labral tears has greatly evolved in the last decade. Initial reports on labral pathology were limited to descriptions of alterations associated with well-established hip deformities such as hip dysplasia, Legg-Calvé-Perthes disease1-4, and traumatic events5. Until recently, the diagnosis and imaging of these lesions were difficult, and operative intervention (i.e., hip arthroscopy) was often required to confirm the diagnosis6-10. Because surgeons initially had to rely on hip arthroscopy for the diagnosis of labral tears in a large proportion of patients, this operative technique was commonly applied for the treatment of these conditions7,10,11 without a complete comprehension of the exact etiology. With the advent of more advanced imaging techniques such as magnetic resonance arthrography12,13 combined with a better understanding of the importance of a labral tear as it relates to degenerative hip arthritis14,15, the treatment of labral injuries has generated a substantial amount of interest in recent years9,16,17. Despite the recent advancements in imaging as well as operative techniques, patients are often misdiagnosed. In one report, it was documented that patients visited, on the average, 3.3 health-care providers before being correctly diagnosed with a labral tear and waited an average of twenty-one months for the diagnosis18. More importantly, 33% (twenty-two) of sixty-six patients received an alternate diagnosis prior to being diagnosed with a labral tear. In addition, the lack of a complete understanding of the function of the acetabular labrum as well as its anatomy has made treatment recommendations difficult to establish. The goals of this review are to provide an overview of the anatomy and function of the acetabular labrum and review the current understanding of the diagnosis and treatment of lesions involving the labrum.
The acetabular labrum is triangular in cross section, with the base attached to the acetabular rim and the apex being the free margin19. The joint capsule attaches to its external edge, creating a potential recess between the capsule and the labrum. The labrum can be divided into two distinct zones, with the extra-articular side, consisting of dense connective tissue, being well-vascularized at its junction with the joint capsule and the intra-articular portion being largely avascular (Fig. 1). In addition, recent embryological studies of the hip joint have shown that the anterior and posterior chondrolabral junctions have different morphological appearances20,21. In a study of eleven human embryos, it was found that the anterior aspect of the labrum has a rather marginal attachment to the acetabular cartilage, with an intra-articular projection, whereas the posterior aspect of the labrum is attached to and continuous with the acetabular cartilage20. In addition, anteriorly the chondrolabral transition zone is sharp and abrupt while posteriorly it is gradual and interdigitated. These most recent findings are in contrast to initial descriptions of the acetabular labrum as being continuous with the articular cartilage throughout the acetabulum19,22. This abrupt anterior transition zone would make the labrum more susceptible to tearing in this zone and corresponds to some extent to the so-called watershed lesion23. On the basis of observations during a large number of hip arthroscopies for labral tears as well as cadaver dissections, McCarthy et al.23 described the anterior aspect of the labrum as an at-risk zone due to potential inferior mechanical properties, higher mechanical demands, and relative hypovascularity and proposed that a labral tear alters the biomechanical environment of the hip, leading to degeneration of the articular cartilage and eventually to osteoarthritis14.
Another important consideration in the treatment of labral tears is the vascularity of the labrum and how this may relate to its capacity to heal after injury and/or operative repair. Only the external one-third of the labrum at the junction with the capsule is well vascularized19,22. In a recent cadaver study, it was found that the labrum had a relatively poor vascular supply but that there were regional differences, with the capsular side having more vascularity than the articular side24. In terms of its predilection for failure, Dorrell and Catterall2 correlated the occurrence of a labral tear with abnormal shear stresses transmitted by the uncovered femoral head as may occur in acetabular dysplasia. From this clinical situation, they postulated that the hypertrophied labrum contributes to the stability of the femoral head within the acetabulum in adulthood. This aspect of load-sharing was later supported by a study that demonstrated that the labrum contributes to the growth and development of the acetabular roof3. Although the labrum may have a load-sharing role, similar to that of the meniscus in the knee, in cases of dysplasia, more recent work has demonstrated that it does not have an important load-sharing role in the normal hip25. Instead, a finite-element analysis and cadaver investigation showed that the labrum acts as a seal, ensuring more constant fluid-film lubrication within the hip joint and limiting the rate of fluid expression from the articular cartilage layers of the joint, as indicated by a greater hydrostatic fluid pressurization within the intra-articular space when the labrum is intact26. In addition, because the labrum adds resistance to the flow path for interstitial fluid expression, cartilage consolidation was significantly quicker without the labrum26,27. Consequently, disruption of the labral seal could be detrimental to the overall nutrition of the cartilage, leading to its premature degeneration28. Takechi et al.29 also showed the labrum contributing to the stability of the hip joint by its valve effect and structure. Both of these mechanisms are dependent on the fit of the labrum against the femoral head27. In a similar study, the loss of the labral seal was found to be the critical event leading to destabilization of the hip, shifting the hip center of rotation and making the hip susceptible to increased impact loading and repetitive trauma through loss of the protective function provided by the intact labrum and its seal30. This finding is supported by the fact that the labrum is known to contain nerve endings31, making it a source of pain as well.
Historically, the reported leading cause of acetabular labral tears has been traumatic events of varying intensity5,32,33, with the proportion caused by traumatic events ranging from 19% to 55%4,7,34,35, with most tears being minor injuries from running, twisting, or slipping. More importantly, 48% to 95%23,34-37 of labral tears are associated with substantial damage to the acetabular cartilage (Table I). These findings have important implications, not only in terms of the long-term survival of the native joint and the pathogenesis of arthritis, but also for our understanding of the mechanism by which acetabular cartilage damage and labral tears occur38,39 and how they should be managed.
Lage et al.7 described four categories of labral tears based on etiology. 1. Traumatic, based on a clear history of hip injury and the subsequent onset of symptoms. More recently, a traction injury of the labrum by the iliopsoas tendon has been reported in some cases40, with the intra-articular portion of the iliopsoas tendon noted to be attached to the labrum in those cases. 2. Congenital, based on the presence of acetabular dysplasia, defined as a center-edge angle of <25° and/or a Tönnis angle of >10°41-43. 3. Degenerative, based on radiographic evidence of arthritic changes, such as joint space narrowing or osteophytes, or the identification of severe chondral damage at the time of operative intervention. 4. Idiopathic, based on the absence of any other findings. However, three recent studies in which the presence of osseous abnormalities was retrospectively examined in patients with a labral tear demonstrated that the majority (49% of seventy-eight, 79% of ninety-nine, and 87% of thirty-one17,44,45) had an osseous dysmorphism consistent with femoroacetabular impingement. It would thus be more appropriate to rename the so-called idiopathic group femoroacetabular impingement. Ganz et al. described two mechanisms of femoroacetabular impingement15: pincer type secondary to acetabular overcoverage and cam type secondary to a lack of femoral head-neck offset (Fig. 2). In pincer-type impingement, repeated contact between the femoral neck and the prominent anterior aspect of the acetabular rim leads to initial damage of the labrum36,46 and often a contre-coup lesion leading to premature wear of the posterior articular surface. In cam-type impingement, abnormal jamming of the head-neck junction causes an outside-in intrasubstance avulsion of the labrum from the adjoining acetabular cartilage15,36. Labral tears secondary to impingement can also be differentiated histologically19. Tears caused by the pincer-type mechanism extend perpendicular to the surface of the labrum and, in more severe cases, to the subchondral bone, in which case the labrum will become calcified and can be seen as a duplication of the tidemark. Endochondral ossification within the labrum is also typically seen. Tears caused by the cam-type mechanism occur at the transition zone between the fibrocartilaginous labrum and the articular hyaline cartilage and are perpendicular to the articular surface.
Interestingly, the morphological appearance of the labrum can also differ between hips with dysplasia and those with femoroacetabular impingement47,48. Both Klaue et al.49 and Leunig et al.47 demonstrated that, in patients with hip dysplasia, the labrum is distinctly hypertrophic with myxoid degeneration and/or detachment from the osseous rim whereas, in those with femoroacetabular impingement, the labrum is characterized by an undersurface tear with no hypertrophy47. These findings can be helpful in establishing the dominating underlying osseous abnormality.
Clinical Evaluation In the majority of patients, the chief symptom is anterior groin pain made worse by long periods of standing, sitting, or walking. The pain can also be referred to the gluteal area or the trochanteric region. The onset of pain is usually insidious4, with the patient often unable to recall a specific traumatic event9. In one study, only 9% (six) of sixty-six patients with a labral tear had a major traumatic episode as a causative factor18. The pain is often sharp in nature and aggravated by activity such as walking and pivoting on the affected side. The presence of mechanical symptoms such as clicking and catching is highly variable and not necessarily indicative of intra-articular hip pathology9. When obtaining a history, it is critical to inquire about childhood hip diseases such as dysplasia3, Legg-Calvé-Perthes disease1, and slipped capital femoral epiphysis50, which are known causes of labral tears as well as hip arthritis51,52. On physical examination, the most reliable sign of labral pathology is pain reproduced with flexion beyond 90° combined with internal rotation and adduction4. This is referred to as the impingement sign49. Forced external rotation with hip extension can also irritate the torn labrum53. It is not possible to consistently differentiate between anterior and posterior labral tears on the basis of a physical examination34. Other less common findings are a mild limp and a positive Trendelenburg sign. Rarely, the patient requires assistive devices to walk. Although labral pathology is now recognized as a common cause of hip pain, it is important to include in the differential diagnosis other causes of hip pain such as osteonecrosis, stress fractures, and snapping psoas tendon. In cases of abnormal physical findings and normal or equivocal radiographic findings, an anesthetic block of the symptomatic hip may provide important diagnostic information in terms of delineating intra-articular from extra-articular hip pathology. Temporary pain relief represents a positive finding for intra-articular hip pathology54.
Radiographic Evaluation
Magnetic resonance imaging is the preferred modality for the investigation of intra-articular hip pathology, as it provides exquisite resolution of the labrum, cartilage, and joint space as well as depicting the regional soft tissues. In addition, magnetic resonance imaging permits multiplanar image acquisition such as radial imaging. Magnetic resonance arthrography is the combination of magnetic resonance imaging with intra-articular injection of gadolinium-based contrast agents and is the test of choice for evaluation of the acetabular labrum12,13,62-64. The arthrogram component distends the joint, causing separation of the labrum from the capsule and osteochondral structures and thus increased spatial resolution. The injected contrast solution outlines both normal anatomical structures and abnormalities, further improving contrast resolution and increasing the conspicuity of the labral pathology65,66. Labral tears are demonstrated by contrast solution extending into the substance of the labrum and are most commonly seen in the anterosuperior quadrant62,63,67-69 (Fig. 6). With labral detachments, the contrast medium undermines the base of the labrum at the chondrolabral and acetabular-labral junctions. As compared with hip arthroscopy, which is the gold standard for diagnosing labral pathology, magnetic resonance arthrography has a sensitivity and accuracy ranging from 92% to 100% and 93% to 96%, respectively63,64,68. Pitfalls that may lead to a false diagnosis of a labral tear include a sublabral sulcus, an anteroinferior cleft at the junction between the labrum and the transverse ligament, cartilage undercutting of the labrum, and increased signal intensity at the chondrolabral junction64,67,70-72. Given its high sensitivity and accuracy, magnetic resonance arthrography is an effective preoperative tool for defining the location and extent of a labral tear12. Perhaps more importantly, magnetic resonance imaging with radial reformatting can permit the proper identification of associated osseous abnormalities of the femoral head-neck junction, which can be critical to the ability to offer a patient proper counseling17,42.
In patients for whom magnetic resonance imaging is contraindicated (because of claustrophobia, metallic prostheses, electronic implanted devices, cardiac pacing wires, or orbital metal bodies), computed tomographic arthrography is an acceptable alternative with equally high sensitivity, specificity, and accuracy, although it results in gonadal radiation exposure73,74.
Most published data on the treatment of labral tears have been derived from larger clinical series of patients treated with hip arthroscopy for a wide spectrum of intra-articular pathology53,75,76. This may be partially due to the use of hip arthroscopy as an investigative tool for idiopathic hip pain77. Recent publications37,39,78,79 on labral pathology have focused on the treatment of osseous dysmorphisms such as femoroacetabular impingement, and they have also provided critical insight into the importance of preserving labral integrity79. When Espinosa et al.79 compared the clinical outcomes of open treatment of femoroacetabular impingement, they found that patients who had been managed with refixation of the labrum after trimming of the acetabular rim did significantly better than those who had undergone labral resection. In that study, labral refixation was performed through the same operative exposure as was used for resection of the acetabular rim, which was required in order to correct the acetabular overcoverage. Other methods for treatment of labral tears are partial débridement37,80 and/or repair81. The most common technique used for labral repair is the simple stitch technique, in which the suture is passed between the labrum and the acetabular rim and the looped monofilament is sutured as a lasso on the extra-articular aspect of the labrum40. This technique was derived from shoulder surgery to repair the avulsed glenoid labrum82. However, techniques of labral repair are still evolving in order to minimize interference with fluid lubrication as well as the blood supply to the labrum. In a systematic review of outcomes following labral débridement with hip arthroscopy, Robertson et al.83 reported that 67% of fifty-eight patients and 91% of twenty-two patients were satisfied with their outcome at 3.5 years, with 45% of the twenty-two patients having complete resolution of mechanical symptoms and up to 90% of the twenty-two patients reporting some reduction in the frequency of symptoms. Table III summarizes the outcomes of isolated treatment of labral tears with débridement and/or excision, which for the most part were performed with hip arthroscopy.
Currently, hip arthroscopy requires an orthopaedic traction table and can be performed with the patient in either the lateral or the supine position40,84,85. Portal placement can vary depending on patient position, but in general two portals are required: one anterolateral and one anterior, with a posterolateral portal being optional. Special instrumentation sets for performing hip arthroscopy are now widely available with 70° and 30° angled cameras. The labral débridement can be performed with a variety of tools, similar to those used in shoulder arthroscopy, such as radiofrequency ablators, motorized shavers, and basic graspers. As stated above, it is not uncommon for a labral tear to be associated with damage to the acetabular cartilage in the form of either a cartilage flap or subchondral erosion14,36. How one should manage the cartilage lesions is still being debated, and methods can range from débridement and microfracture to labral refixation with resection of the cartilage flap to a stable edge after trimming of the acetabular rim37,78,79. Another consideration with regard to the technique of labral refixation is that it permits correction of overcoverage by the acetabular anterior wall (i.e., acetabular retroversion)79. When correction of acetabular retroversion is being considered, the absence of a posterior wall sign (i.e., full coverage of the femoral head posteriorly) would currently favor trimming of the acetabular rim as the treatment of choice since a reverse periacetabular osteotomy could predispose to impingement posteriorly46. If a posterior wall sign is present, it is unclear whether trimming of the acetabular rim or a reverse periacetabular osteotomy is preferable to correct the retroversion. It is important to differentiate the indications for, and rationale of labral refixation for, the treatment of acetabular retroversion79, as discussed above, as opposed to isolated labral tears40. If the labrum is detached from its extra-articular osseous insertion, refixation with use of suture anchors can be done with a high potential for healing since the labrum is very well vascularized in its outer third24. However, the majority of labral tears occur on the articular side adjacent to the chondrolabral junction with the presence of fibrillation and/or radial tearing. As stated above, this area is avascular and, more importantly, a cleft is normally present at the chondrolabral junction in the anterosuperior area. Thus, in the presence of labral damage on the articular side, the indications for labral repair and/or refixation are not clear since the labrum is still attached to the acetabular rim. Alternatively, localized débridement of the torn intra-articular portion of the labrum addresses the main pathology and has also been shown to provide good-to-excellent outcomes in several clinical series, both when used as isolated labral treatment53,75 and when performed in conjunction with the treatment of femoroacetabular impingement37,78. For example, in one study of thirty-eight patients treated with isolated labral débridement with hip arthroscopy, sixteen had an excellent Harris hip score (range, 90 to 100 points)75. Similarly, using validated functional outcome measures including general health-related quality-of-life questionnaires, in a series of patients with femoroacetabular impingement, one of us (P.E.B.) and colleagues reported significant improvements on the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index), UCLA (University of California at Los Angeles) activity scale, and both the physical and the mental health component of the Short Form-12 (SF-12)37 (Table III). At this point in time, there is no clear evidence as to whether labral repair/refixation or limited labral débridement is the preferred approach in the treatment of isolated labral tears since long-term follow-up data still are not available. In addition to the heterogeneity in the treatment methods, the authors of most clinical studies have also used nonvalidated outcome measurement tools and/or ones commonly used to study the outcome of total hip replacements, making it difficult to draw broad conclusions regarding the treatment methods86,87. Nonetheless, there is a sufficient body of evidence to recommend the treatment of isolated labral tears with hip arthroscopy (Figs. 7-A and 7-B). However, because the majority of labral tears are associated with osseous abnormalities such as dysplasia and femoroacetabular impingement, it is critical to carefully rule out these osseous dysmorphisms to ensure an optimal outcome88. There have been reports of reoperations after failed arthroscopic labral débridement that, by correcting the underlying osseous abnormality, led to significant improvements in hip function89,90. In their case series, May et al.89 reported on five patients presenting with persistent hip pain after having undergone treatment with hip arthroscopy. All five patients had an osseous abnormality consistent with femoroacetabular impingement, and the correction of that abnormality led to significant improvement in function as well as pain relief. Similarly, Peters and Erickson90 reported an improved outcome after correction of the underlying structural abnormality in eleven hips that had been referred because of persistent symptoms after isolated arthroscopic treatment of the labrum. Finally, because these osseous dysmorphisms are known causes of degenerative hip arthritis48,91, it is not uncommon for patients to present with some degree of arthritic changes on radiographs. Currently, there are no clear guidelines regarding what degree of arthritis is a contraindication to hip arthroscopy, although patients presenting with >2 mm of joint space narrowing are certainly not appropriate candidates92.
Currently there is no definitive evidence that the clinical outcome achieved with combined treatment of the osseous abnormality93,94 and the labral tear will be more favorable than that provided by isolated treatment of the labral tear95. Other factors such as patient age, the severity of the osseous deformity, and damage to the articular cartilage may be more important than the simple presence of an osseous abnormality; however, it is still unclear how all of these factors interact or affect the natural history of the native hip joint93,96. Better methods for cartilage imaging97 and a better understanding of human hip kinematics are needed to determine how the treatment of labral pathology may affect the longevity of the native hip joint23,26,27. 
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