A hip labral tear is a mechanically induced pathology thought to result from excessive forces at the hip joint. The symptoms are often manifested as groin pain, anterior thigh pain, lateral hip pain and in few cases as buttock pain. Labral tears are very common in patients undergoing hip arthroscopy and it usually occurs as a result of a traumatic injury, bony abnormality or degenerative changes. Hip labrum enhances joint stability and also plays the primary role in shock absorption, pressure distribution, and joint lubrication. Recognizing its functional importance, an injury to the labrum should be evaluated and managed carefully to restore the congruency and normal function of the joint.
The hip joint is a synovial articulation between the head of the femur and the acetabulum of the pelvis bone making it a muti-axial ball and socket joint. The hip labrum Is a dense connective tissue and fibrocartilaginous structure surrounding the bony acetabular rim. The labrum is continuous circumferentially and inferiorly, it bridges across the acetabular notch by the transverse acetabular ligament connecting the anterior and posterior horns of the labrum. Composed primarily of Type 1 collagen fibers, the labrum is attached both directly and indirectly to the acetabulum. Direct attachment is present at the nonarticular side of the thin bony rim of the acetabulum. Labrum is indirectly attached to the acetabulum through a calcified cartilage zone and the labrum blends into the articular hyaline cartilage anteriorly often creating a transition zone of 1 to 2 mm. The labrum is wider and thinner anteriorly and thicker in the posterior region of the acetabulum. The cross section of the labrum is triangular in most of the population but variations can be seen including round, irregular and flattened shapes.
Blood Vessels and Nerves
The vascularity of the labrum is not fully understood but the majority of it is thought to be avascular. The outer third of the labrum gets vascularized from the anastomotic ring surrounding the capsule and the synovium. The blood supply originates from the obturator, superior gluteal, and inferior gluteal arteries, and enters the labrum peripherally via the capsular side.
The labrum is innervated by a branch of the nerve to the quadratus femoris and by the obturator nerve. The anterior and superior part of the labrum is the mostly innervated portions consisting of free nerve endings and sensory nerve end organs. These structures are the receptors of pain, pressure, deep sensation, and temperature sensation from the labrum directing the source of hip pain to a labral tear.
The labrum provides stability to the hip joint by deepening the socket, and resists any lateral and vertical movements of the femoral head within the acetabulum. By increasing the surface area and distributing the weight load throughout the acetabular cartilage, labrum plays a vital role in decreasing the contact stress on the articular surfaces of the joint. Another important function of the acetabular labrum is to maintain the synovial fluid and the fluid pressure by sealing the joint and acting as a lubricator between the femoral head and acetabular cartilage. Thus, a tear in the labrum could result in an increase in the joint forces which could potentially put the joint in high risk of deterioration.
Labral tears are classified based on their location and morphology. With respect to the location, labral tears are divided as anterior, posterior, and superior/lateral. Anterior tears are most common in the United States and European countries where as posterior tears are commonly found in Asian population. The difference might be because people in Asian cultures tend to sit on the ground or do squatting more often exposing hip to more posterior stresses. The prevalence of anterior tears can be attributed to poor vascular supply, mechanically weaker tissue, and higher stress than the other regions of the labrum.
Labral tears are classified morphologically as radial flap, radial fibrillated, longitudinal peripheral, and unstable. Studies have shown the radial flap to be the most common type where the free margin of the labrum is disrupted. Fraying in the free margin of the labrum is noted in radial fibrillated and is associated with degenerative joint disease. The longitudinal peripheral is the least common type occurring at various lengths along the acetabulum-labrum junction. A detached labrum can make the tears abnormally mobile and unstable, and result in mechanical symptoms.
The etiology of labral tears can be classified as degenerative, dysplastic, traumatic, FAI, capsular laxity, and idiopathic. Since hip joint is a weight bearing joint, arthritic changes can be noted with the increase in age and such changes would lead to labral fraying and degenerative joint disease. The presence of dysplasia can be a predisposing factor towards labral tears. Legg-Calve-Perthes disease and Congenital Hip Dysplasia (CHD) are the two common conditions that fall under this criterion. Traumatic labral tears occur as a result of motor vehicle accidents and falls. Isolated traumatic tears can also be seen in contact sports involving repetitive twisting motions such as soccer, hockey, golf, ballet etc since they require frequent external rotation. Alterations in the morphological characteristics of the femur or acetabulum can lead to femoral acetabular impingement (FAI). As a result there will be decreased joint clearance between the femoral head and the acetabulum leading to the impingement of the osseous articular surfaces. This in turn limits hip ROM and cause articular cartilage damage. Capsular laxity or hip hypermobility is another cause for a labral tear. Connective tissue disorders (ie, Down’s, Marfan’s, and Ehlers-Danlos syndromes) and excessive forceful external rotation can put the underlying capsular tissue and ligaments into extreme laxity which can potentially lead to hip instability, dislocation, and/or a labral tear. Tears of idiopathic etiology are attributed to any unknown or intractable onset of hip pain with no evidence of trauma but could possibly due to repetitive micro trauma.
Labral injuries are often preceded by a traumatic event. The most common injury pattern for the labral tears is hyperextension with femoral external rotation. Repetitive pivoting and twisting can cause microtrauma which can also gradually progress into a labral tear. Athletes participating in sports involving repetitive end range movements into hyperflexion, hyperextension, and abduction are at greater risk for developing labral tears.
The prevalence of labral tears in patients with hip or groin pain has been reported to be 22–55%. The age range for labral tears are reported between 8 and 75 years. The incidence of the tears increases with age which can be attributed to the normal aging process causing deterioration of the joint surfaces. Females are more often reported of having labral tears than males which may be due to the increased prevalence of hip dysplasia in females.
Primary symptoms present in patients with a labral tear are hip and groin pain. Less commonly, pain may be reported at the lateral hip or posterior regions. Other symptoms associated with a tear include locking, catching, instability, giving way, and stiffness. Pain is usually of insidious onset followed by a low energy acute injury. The pain gets worsened often with activities like sitting, arising from the seated position, or descending stairs.
Differential diagnosis 9
Since hip and groin pain are a common symptom associated with several disorders besides labral tears, a differential diagnosis is required to accuradely identify the cause of the pain. Leibold et.al, describes a list of disorders that has hip and groin pain as their primary symptoms in the table below.
Magnetic resonance imaging (MRI), magnetic resonance arthrography (MRA), and computerized tomography (CT) are the diagnostic tests currently used to identify the presence of a labral tear. Fluoroscopic injections are found to distinguish intra- articular and extra -articular conditions because not all labral tears are symptomatic or the source of the pain.
A detailed physical examination should be done to observe the bilateral lower extremities. Gait and postural examination should follow with ROM and associated muscle strength tests. Tredenlenburg sign and leg length discrepancy should also be assessed. A wide range of physical tests has been established to assess the symptoms of a labral tear during a clinical examination. Pictures and videos of most routinely used ones are included below. Most of them are not validated to aid in the accurate diagnosis of acetabular labral tear since they cannot exclusively diagnose labral tears. Therefore, knowledge of other potential pathologies that could mimic the same symptoms is important to accurately diagnose the condition.
Following table is extracted from the article by Burgess et.al, which lists out some of the physical tests for diagnosing hip labral tear:
Videos of the widely used tests are shown below:
Fitzgerald test - Anterior labrum
Fitzgerald test - Posterior labrum
Conservative measures are recommended initially including relative rest, anti-inflammatory medications, pain medications, all combined with physical therapy intervention for 10-12 weeks. Weight bearing must be cautious or restricted in patients with acute or traumatic onset of symptoms and pivoting and twisting movements should be limited. Corticosteroid injections can also be used to ease the discomfort when indicated. The goal of conservative management is to optimize the hip joint alignment and provide quality and precision to the joint motions by distributing the joint forces and addressing proper recruitment, stabilization, and strengthening of the supporting musculature.
A surgical referral is appropriate when the conservative treatment does not manage the patient symptoms or when the functional limitations remain unsatisfactory. An arthroscopic debridement of labral tears and surgical repair of associated structural problems constitutes the current surgical procedure for a labral tear. This procedure is preferred over open surgery since it is less invasive. The goal of arthroscopic treatment of a torn labrum is to relieve pain by removing the loose or unstable flap tear that causes hip discomfort.
The video below gives an overview of a hip labral tear and describes the arthroscopic procedure: