Key points

Introduction

Acetabular labral tears are recognized as an important cause of hip pain in young, athletic individuals. Acetabular labral tears were first described by Paterson in 1957 after traumatic posterior hip dislocations, with a resulting bucket-handle labral tear serving as a block to a concentric reduction. Until recently, labral tears were thought to be relatively uncommon. However, advances in imaging and surgical techniques, as well as an improved understanding of hip pain, have led to increased awareness regarding labral tears and other pathologic conditions around the hip joint. The prevalence of labral tears in painful hips has been reported to be 22% to 55%, and Register and colleagues recently identified labral tears present in 69% of asymptomatic hips. Historically, treatment of labral lesions consisted of nonoperative measures or a partial excision performed through an anterior arthrotomy. Although Harris and colleagues suggested that an “intra-acetabular labrum” with degenerative labral changes could lead to the development of hip osteoarthritis, it was not until much later that Ganz and colleagues described femoroacetabular impingement (FAI), and the relationship of bony abnormalities of the acetabular rim and femoral head-neck junction with labral tears and hip osteoarthritis. The investigators theorized that repetitive bony impingement causes damage to both the acetabular labrum and articular cartilage. McCarthy and colleagues described a possible sequence of events that leads to joint degeneration, including excessive loading of the labrum through traction or impingement, fraying of the anterior margin of the labrum, articular cartilage delamination adjacent to the labrum lesion, and more global degenerative changes that occur in both the labrum and articular cartilage. The purpose of this article is to review the anatomy of the acetabular labrum, discuss the pathogenesis of labral tears, and discuss the various treatment options available, including arthroscopic labral repair and reconstruction.

Introduction

Acetabular labral tears are recognized as an important cause of hip pain in young, athletic individuals. Acetabular labral tears were first described by Paterson in 1957 after traumatic posterior hip dislocations, with a resulting bucket-handle labral tear serving as a block to a concentric reduction. Until recently, labral tears were thought to be relatively uncommon. However, advances in imaging and surgical techniques, as well as an improved understanding of hip pain, have led to increased awareness regarding labral tears and other pathologic conditions around the hip joint. The prevalence of labral tears in painful hips has been reported to be 22% to 55%, and Register and colleagues recently identified labral tears present in 69% of asymptomatic hips. Historically, treatment of labral lesions consisted of nonoperative measures or a partial excision performed through an anterior arthrotomy. Although Harris and colleagues suggested that an “intra-acetabular labrum” with degenerative labral changes could lead to the development of hip osteoarthritis, it was not until much later that Ganz and colleagues described femoroacetabular impingement (FAI), and the relationship of bony abnormalities of the acetabular rim and femoral head-neck junction with labral tears and hip osteoarthritis. The investigators theorized that repetitive bony impingement causes damage to both the acetabular labrum and articular cartilage. McCarthy and colleagues described a possible sequence of events that leads to joint degeneration, including excessive loading of the labrum through traction or impingement, fraying of the anterior margin of the labrum, articular cartilage delamination adjacent to the labrum lesion, and more global degenerative changes that occur in both the labrum and articular cartilage. The purpose of this article is to review the anatomy of the acetabular labrum, discuss the pathogenesis of labral tears, and discuss the various treatment options available, including arthroscopic labral repair and reconstruction.

Anatomy and function of the acetabular labrum

The hip is a ball-and-socket joint that is inherently stable, owing to highly constrained osseous anatomy. The labrum is a fibrocartilage structure that runs circumferentially around the margin of the acetabular rim and is attached to the transverse acetabular ligament both anteriorly and posteriorly. It has numerous functions, including maintenance of joint lubrication and the “suction-seal” effect, enhancement of joint stability, and protection of articular cartilage through improved distribution of pressure across the articulation between the femoral head and acetabulum. The labrum increases the effective depth of the bony acetabulum and provides stability to the femoral head while increasing the effective amount of femoral-head coverage. It contributes, on average, up to 22% of the acetabular surface area that articulates with the femoral head, and increases the volume of the acetabulum by up to 33%. The labrum, however, has limited healing capabilities. Kelly and colleagues studied the vascular supply of the labrum in a cadaveric study, showing that it is a relatively avascular structure with most vessels originating from the capsular periphery, with few reaching the more central articular-sided region. Furthermore, the distribution of vessels is not homogeneous through the labrum. The presence of free nerve endings has also been reported by Kim and Azuma, suggesting proprioceptive and nociceptive properties.

The labrum contributes to the suction-seal effect to improve fluid-film lubrication and maintain negative intra-articular pressure within the central compartment. A recent cadaveric study by Cadet and colleagues demonstrated significant efflux of fluid from the hip joint in the presence of a labral tear, suggesting disruption of the fluid seal effect. Although labral repair decreased the outflow of fluid from the hip joint, a repaired labrum was not shown to be as effective as the labrum-intact condition. The hip labrum has also been identified as an important secondary stabilizer in cases of simulated disruption of iliofemoral ligament, and large tensile forces have been measured in the anterior acetabular labrum during hip external rotation and abduction movements. Smith and colleagues showed that even a damaged labrum continues to provide hip stability and resist femoral-head dislocation after the creation of circumferential tears less than 3 cm in length or after creation of a 1-cm labrectomy.

Labral pathology

Labral tears are most common in the presence of a structural hip abnormality such as FAI or hip dysplasia. Recent retrospective studies have shown that between 49% and 87% of all patients with a labral tear have osseous changes consistent with FAI. In addition, although labral abnormality most commonly affects the anterosuperior labrum, the pattern of injury is highly dependent on the unique morphologic “fingerprint” present in the acetabulum and proximal femur, including the external mechanical loads and the arc of motion applied to the hip. In cases of pincer-type FAI with acetabular overcoverage, there is repetitive contact between the femoral neck and the acetabular rim, with compression of the labrum that leads to degeneration early in the process. The articular cartilage is relatively uninvolved, with chondral injury limited to a narrow margin along the acetabular rim. Eventually there is ossification of the labrum and further appositional bone formation that can exacerbate the magnitude of impingement, in addition to contre-coup lesions of the posteroinferior acetabular articular cartilage and the posteromedial aspect of the femoral head.

In cam-type FAI with loss of femoral head-neck offset, there is early damage to the articular cartilage, in contrast to the pattern seen with pincer-type FAI. During hip motion, the cam deformity is rotated into the acetabular socket with a shearing-type injury pattern and delamination of the articular cartilage. The damage is localized to the corresponding location where the abnormal head-neck junction ( Fig. 1 ) and acetabular rim make contact. Eventually there is separation of the labrum from the underlying subchondral bone, occurring at the transitional zone between the labrum and hyaline cartilage ( Fig. 2 ). Johnston and colleagues reported an association between the lack of femoral head-neck sphericity and the size of the cam lesion with the extent of acetabular chondral damage and delamination. The investigators noted more intra-articular damage in patients with a higher α angle, including detachment of the labrum and full-thickness delamination of the articular cartilage.

View of the femoral head-neck junction showing a typical cam deformity with loss of offset.

Anterosuperior labral tear with delamination of the articular cartilage at the transition zone.

Acetabular dysplasia is also responsible for pathologic changes to the labrum. The dysplastic hip is characterized by a shallow acetabulum with anterior and lateral acetabular undercoverage. In these cases, there is a shift in the normal center of contact between the femoral head and acetabulum to a more posterosuperior location, leading to pressure overload of the labrum and articular cartilage. This shift has been associated with the premature development of osteoarthritis as well as pathologic changes to the labrum, including hypertrophy, myxoid degeneration, and detachment from the acetabular rim.

Lage and colleagues described an arthroscopic classification for labral tears. Tears were divided into 4 categories based on the etiology: traumatic, degenerative, idiopathic, and congenital. In addition, 4 morphologic categories were used to classify labral tears: radial flap, radial fibrillated, longitudinal peripheral, and unstable. Seldes and colleagues also described 2 different histologic types of labral tears, include Type 1 tears whereby there is detachment of the labrum from the articular surface at the transition zone between labrum and articular cartilage, and Type 2 tears whereby there are 1 or more cleavage planes within the substance of the labrum. Capsular laxity and psoas impingement can also lead to the development of labral tears. It is important to understand the cause of the labral tearing and ensure that all pathologic aspects are properly addressed, as poor clinical outcomes can result from a failure to adequately decompress all bony impingement at the time of surgery. A summary of the various types of labral tears and the associated conditions is summarized in Table 1 .

Patient history and clinical evaluation

A thorough history is important in making the correct diagnosis and determining the cause of the complaint. Most commonly, patients with labral tears will present with groin pain that is exacerbated by hip flexion. The exact location of the pain and any exacerbating or relieving factors is important in helping to narrow the differential diagnosis. A characteristic sign in patients with labral tears and hip impingement is the “C sign,” whereby the patient holds his or her hand in the shape of a C proximal to the greater trochanter with the thumb directed posteriorly and the fingers pointing anteriorly toward the groin. This sign often indicates pain deep within the hip joint. The clinician must determine if there is a history of trauma that may have caused labral injury, or if the symptoms are insidious in nature. Young athletes may also complain of mechanical symptoms such as locking, catching, or clicking. Certain sporting activities are highly associated with labral tearing, including football, hockey, skiing, bicycling, and dancing. Pain may also be present with activities of daily living, such as putting on shoes and socks or getting in and out of a car. Radicular symptoms can also be confused with groin pain from a labral tear, and disorders of the gastrointestinal, genitourinary, and vascular systems can all cause referred pain to the hip and groin. Pain over the lateral aspect of the hip suggests greater trochanteric bursitis and possible tightness of the iliotibial band. The clinician must also recognize that in patients with hip laxity there is greater reliance on the surrounding hip musculature to act as secondary stabilizers; therefore, these structures may become overused and tender or weakened on physical examination.

In young patients with a suspected labral tear, the clinical examination should focus on evaluation of gait and posture, active and passive range of motion of the lower extremities, and an assessment of the neurovascular structures. In the standing position, the presence of a Trendelenburg gait indicates weakness of the hip abductor muscles. A shortened stance phase indicates an antalgic gait caused by a painful extremity. Range of motion and strength testing should be performed in the bilateral extremities, and any differences noted. Mechanical symptoms including catching, clicking, or popping suggest intra-articular abnormality, such as damage to the articular cartilage, labral damage, or a loose body. In addition, a snapping iliotibial band over the greater trochanter or the iliopsoas tendon over the pelvic brim can cause a popping sensation with a circumduction motion of the hip. Several special tests have been described for evaluation of the hip in the supine position, including the FADDIR test, whereby the hip is moved into flexion, adduction, and internal rotation to recreate the patient’s pain and to measure the amount of flexion and internal rotation; the Thomas test for psoas tightness; and the Patrick or FABER test to differentiate sacroiliac/lumbar spine abnormality from hip problems. Capsular laxity is assessed with the hip dial test, performed in the supine position. All patients should also be examined for signs of systemic ligamentous laxity according to the criteria of Beighton and colleagues. A thorough physical examination with provocative testing to recreate the location and intensity of the patient’s pain is critical in understanding the underlying abnormality, including labral tears and any associated injuries to the surrounding structures.

A thorough and systematic radiographic examination is performed in all patients with hip pain and suspected labral disorder, including anteroposterior (AP) pelvis, cross-table lateral, and false-profile plain radiographic views of the involved hip. The AP pelvis is evaluated for the outline of the acetabular lines, and any pathologic features such as the presence of a crossover sign, whereby the outlines of the anterior and posterior acetabular wall cross to form a figure-of-8 pattern. This sign indicates relative anterior acetabular overcoverage. Global acetabular overcoverage, as seen in coxa profunda and coxa protrusio deformities, is suspected when the floor of the acetabular fossa touches or passes medially to the ilioischial line. On the cross-table lateral view, the α angle is measured to evaluate for cam-type FAI and any loss of femoral head-neck offset. Anterior acetabular overcoverage or undercoverage and joint-space narrowing in the posteroinferior acetabular are assessed on the false-profile view. Magnetic resonance imaging (MRI) or magnetic resonance arthrography is often used in young patients with a painful hip to evaluate the acetabular labrum, joint capsule, articular cartilage, and periarticular structures.

Nonoperative treatment

There is a paucity of evidence to support the nonoperative treatment of acetabular labral tears in young patients. Philippon and colleagues reported that early intervention for labral abnormality may lead to improved results, as shown in a cohort of professional hockey players where those who underwent intervention within 1 year from the time of injury returned to play earlier than those who waited. Simple measures such as activity modification and preventing provocative positions such as hip flexion and interior rotation can improve pain and prevent further episodes of impingement. Focused physical therapy and nonsteroidal anti-inflammatory drugs (NSAIDs) can be used initially, and can be combined with physical therapy for 10 to 12 weeks. Greater trochanteric bursitis and a snapping iliopsoas are managed with rest/activity modification, NSAIDs, and stretching. Corticosteroid injections into the bursa can be administered if needed. Intra-articular steroid injections may also be beneficial, especially in patients who have pain that is not responsive to nonoperative treatments.

Physical therapy can be used in patients with hip pain and labral tears to decrease pain and improve function. Casartelli and colleagues compared hip-muscle strength testing and hip-flexor electromyography in 22 patients with FAI and compared the results with those of healthy, age-matched controls during active hip flexion. Whereas there was significant weakness in the FAI group when compared with the healthy controls, in particular of the abductions, adductors, hip flexors, and external rotators, there was no significant difference in the strength of hip internal rotators and extensors. Although the weakness observed could be due to many factors (eg, atrophy, reduced muscle activation, pain), these results may aid in the development of specific rehabilitation and therapy protocols to improve strength in those with FAI. Yazbek described a nonsurgical therapy program used in 4 patients with clinical and MRI findings consistent with a labral tear. The rehabilitation protocol emphasized stabilization of the hip and lumbopelvic regions with correction of muscular imbalance, biomechanical control, and sport-specific functional progression. All patients showed an overall decrease in pain and an increase in function, correction of muscular imbalances, and improved muscle strength of the hip flexors, abductors, and extensors. Patients who fail to improve after a trial of nonoperative treatment are candidates for arthroscopic treatment.