207 REVIEW Br J Sports Med: first published as 10.1136/bjsm.37.3.207 on 1 June 2003. Downloaded from Acetabular labrum and its tears A A Narvani, E Tsiridis, C C Tai, P Thomas ............................................................................................................................. Br J Sports Med 2003;37:207–211 Groin pain is a major cause of morbidity in athletes. merges with the articular hyaline cartilage of the Only in the last decade have acetabular labrum tears joint surface of the acetabulum through a transi- tion zone of 1–2 mm. A consistent thin tongue of been recognised as a possible diagnosis. Awareness of bone extends from the edge of the bony acetabu- this condition is important for appropriate management. lum into the substance of the labrum. They also The basic science and pathological and clinical features showed that the labrum is attached firmly to the articular side of this bony extension by a zone of of acetabular labrum tears are reviewed, and calcified cartilage with a well defined tidemark, diagnostic and treatment options are presented. and a narrow synovial lined recess separates the .......................................................................... labrum from the capsule. The lining of the cleft consists of highly vascularised, loose connective tissue and fat.8 roin pain is a significant cause of morbid- ity in athletes. There have been numerous NERVE SUPPLY Gstudies on causes of groin pain in athletes In a study using immunohistochemical tech- such as adductor strains, hernias, iliopsoas niques in acetabular labra from 24 fresh human related pathology, referred back pain, and osteitis 1–3 4 cadavers, free nerve endings were seen in all parts pubis. Although first reported in 1957, it is only of the acetabular labrum; however, they seemed in the last decade that acetabular labrum tears to be more numerous in the superior and anterior have become recognised as a cause of groin pain. quarters.9 The authors suggested that these nerve In a recent study, they were found to be the cause endings may well be involved in nociceptive and of groin pain in more than 20% of athletes 5 proprioceptive mechanisms. Therefore, in the presenting with groin pain. Awareness of this same way that lesions of the meniscus in the knee condition among sport clinicians is of great can stimulate pain fibres, nerve endings also exist importance, as clinical suspicion of the condition for the acetabular labrum lesions to cause pain. would lead to appropriate management, espe- cially in athletes who have not responded to FUNCTION treatment designed for the more familiar causes As one form of treatment for labrum tears is sur- of groin pain. The purpose of this paper is to http://bjsm.bmj.com/ gical removal, the function of the labrum needs to review the basic science and pathological and be fully evaluated to avoid similar chronic clinical features of acetabular labrum tears. The problems to those faced by patients who have had diagnostic and therapeutic options for this condi- knee menisectomies. The acetabular labrum tion are also presented. deepens the hip socket in a fashion that is similar to the way the glenoid labrum deepens the socket. ANATOMY However, in contrast with the glenoid in the The labrum is a fibrocartilaginous rim which glenohumeral joint, the osseous acetabulum in encompasses the circumference of the acetabu- the hip is much deeper and provides substantial on October 1, 2021 by guest. Protected copyright. 6 lum, effectively deepening the socket. It varies stability to the hip joint. The deepening of the greatly in form and thickness. It has three acetabulum that is provided by the labrum is surfaces: an internal articular surface, an external therefore thought to be less important. The surface contacting the joint capsule, and a basal labrum, however, may enhance stability by surface attached to the acetabular bone and providing negative intra-articular pressures in the 7 transverse ligaments. Its distal edge is free, form- hip joint upon joint distraction (by partially seal- ing the lateral limit of the acetabulum. Anteriorly ing the joint).10 Besides improving the stability of the labrum is equilaterally triangular in radial the joint, the sealing function of the labrum section. Posteriorly it is more bulbous and lip like, enhances a fluid film lubrication mechanism, dimensionally square but with a rounded distal prevents direct contact of the joint surfaces, and surface. distributes the applied force more evenly across the cartilage surface.11 HISTOLOGY See end of article for The role of the acetabular labrum in load trans- authors’ affiliations Most of the labrum is composed of thick, type I mission was further examined in a biomechanical ....................... collagen fibre bundles principally arranged paral- study by Konrath’s team in 1998.12 The distribu- lel to the acetabular rim, with some fibres tion of contact area and pressure between the Correspondence to: Dr Narvani, 69a Frognal, scattered throughout this layer running obliquely acetabulum and the femoral head was measured 8 London NW3 6YA, UK; to the predominant fibre orientation. Seldes et al [email protected] investigated the histological features of the acetabular labrum by studying 55 embalmed and ................................................. Accepted 20 October 2002 12 fresh frozen adult hips with a mean age of 78 Abbreviations: MRI, magnetic resonance imaging; MRa, ....................... years. They reported that the acetabular labrum magnetic resonance arthrography www.bjsportmed.com 208 Narvani, Tsiridis, Tai, et al Table 1 Classification of labral tears Br J Sports Med: first published as 10.1136/bjsm.37.3.207 on 1 June 2003. Downloaded from Radial flap Disruption of the free margin of the labrum with subsequent formation of discrete (most common) flap Radial fibrillated Appearance of a shaving brush; generally of a hairy appearance at the free margins of the labrum. More common with degenerative tears Longitudinal peripheral Of variable length along the acetabular insertion of the labrum Unstable Subluxing labra, a reflection of abnormal function rather than shape. in cadaver hips before and after removal of the acetabular Clinical features labrum. No appreciable changes with regard to contact area, Clinical features of acetabular labrum tears have been studied load, and mean pressure were noted after removal of the extensively over the last 15 years.15–25 These studies suggest labrum. From these findings they concluded that removal of that labral tears may have a variety of clinical presentations the acetabular labrum does not predispose to premature hip associated with a wide degree of clinical findings. There may osteoarthritis. or may not be a history of trauma. In the presence of a recalled incident, the trauma can vary from severe to very mild such as twisting or falling. The injury is usually caused by the hip joint being stressed in rotation. The pain is mainly in the groin, but ACETABULAR LABRUM TEARS could be in the trochanteric and buttock region. It could have Causes an acute onset or be gradual. It is common for it to be sharp Whereas the torn meniscus is a common cause of mechanical with a clicking and catching sensation. It could also be associ- symptoms in the knee, the torn acetabular labrum, until ated with a sensation of locking in the hip joint. Activities that recently, had received little attention as a cause of mechanical involve force adduction of the hip joint in association with hip pain. Previous studies indicate that the acetabular labrum rotation in either direction tend to aggravate the pain. tear is a common finding in the aging adult hip and may occur On examination, range of motion may not be limited but 81314 as part of the degeneration process. Acetabular labrum there may be pain at the extremes. There are a number of tears have also been associated with posterior dislocation of clinical tests, but generally speaking the combined movement 415 the hip and acetabular dysplasia. There have also been sev- of flexion and rotation causes pain in the groin. More 16–18 eral studies linking acetabular labrum tears to trauma. In precisely, the specific manoeuvres that may cause pain in the these studies, although traumatic injuries ranged from a groin include: poorly defined incident occurring in a road traffic accident to • flexion, adduction, and internal rotation of the hip joint a simple twisting injury, most were relatively minor injuries (with anterior superior tears)17 20 from running, twisting, slipping, and falling. • passive hyperextension, abduction, and external rotation (with posterior tears)17 20 Epidemiology Epidemiological studies have shown that labral tears occur in • acute flexion of the hip with external rotation and full both sexes with the same frequency. They are also seen in all abduction, followed by extension, abduction, and internal http://bjsm.bmj.com/ 19 age groups.16 17 19 20 rotation (anterior tears) • extension, abduction, and external rotation brought to a Pathology flexed, adducted, and internally rotated position (posterior 19 In the last 15 years, there have been numerous studies on the tears) location and anatomical features of acetabular labrum tears, The above manoeuvres may also produce clicking and locking including cadaver, arthroscopic, and magnetic resonance sensations. imaging (MRI) studies.15–24 Most suggest that the tear occurs most commonly in the anterior part of the labrum, especially Investigations on October 1, 2021 by guest. Protected copyright. the anterosuperior quadrant, but the posterior part may also As acetabular labrum tears have become recognised as a cause be affected. Seldes et al8 have classified the tears into type 1 and of hip and groin pain, there has been a growing interest in the type 2 on the basis of their anatomical and histological search for a suitable diagnostic tool. The investigations that features. Type 1 tears consist of detachment of the labrum have been assessed as diagnostic tools include plain radio- from the articular cartilage surface.