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Acetabular labrum

Acetabular labrum tears

For one in five athletes, this hip pathology will be the source of the problem. Elizabeth Ashby and Fares Haddad explain

Acetabular labrum tears are a common cause of time away from sport in athletes. First described in 1957, it is only in the last 15 years, with advances in imaging and hip arthroscopy, that such lesions have been recognised as a common cause of groin pain in athletes. Other causes of groin pain include adductor strains, inguinal and femoral hernias, nerve entrapment, stress fractures of the femoral neck, avulsion fractures of the pelvis, osteitis pubis, intraabdominal disorders and referred back pain.

Acetabular labrum lesions that may have gone unrecognised in the past can now be seen using magnetic resonance arthrography and inspected directly using hip arthroscopy, followed by either arthroscopic resection (cutting back) or repair.

Function of the acetabular labrum

The acetabular labrum is a ring of fibrocartilage that attaches to the circular outer edge of the acetabulum (hip socket). It is made of alternating layers of Type I collagen fibres and hyaline cartilage matrix orientated in the direction of functional stress. A spur of bone extends from the acetabulum into the labrum to increase stability. The labrum has a highly variable shape and three surfaces:

* a basal surface which connects the labrum to the acetabular bony rim

* an internal articular surface which is in continuation with the articular surface of the acetabulum

* an external surface where the hip joint capsule attaches.

A network of blood vessels enter the outer third of the labrum on the external surface only. The lack of blood supply to the inner two-thirds is thought to impede healing after injury. Free nerve endings are found throughout the acetabular labrum but are most densely packed in the anterior and superior quadrants.

The main function of the acetabular labrum is to improve hip joint stability in two ways. Firstly it deepens the hip socket, providing it with extra structural support. Secondly it partially seals the joint to create a negative intra-articular pressure which counteracts any distractive (pulling-apart) forces.

A second important function of the acetabular labrum is to increase joint congruity. After removal of the labrum the frictional force between the femoral and acetabular articular surfaces is increased by up to 92%, showing that the labrum plays an important role in the even distribution of forces across the articular surface.

How injuries occur

The five most common causes of acetabular labrum tears are:

* trauma

* hip dysplasia (congenital abnormality)

* degeneration

* capsular laxity

* femoro-acetabular impingement.

In athletes, the main cause of tears is trauma, usually from a twisting or pivoting motion whilst weight-bearing. Such movements are common in football and hence the acetabular labral tear is often referred to as ‘footballer’s hip’. Athletes with hip dysplasia are at greater risk of developing a labral tear compared with those with a normal hip joint. Dysplastic hips are more common in hyper-mobile individuals such as dancers and track and field athletes

Symptoms and diagnosis

The presentation of acetabular labral tears is very inconsistent but the most common complaint is a sharp groin pain after trauma. Other possible sites of pain are the anterior thigh, greater trochanter and buttock region. Other symptoms include clicking, locking and ‘giving way’ of the hip. The pain may be reproduced in sport by weight-bearing activities that require twisting, such as kicking a football.

Examination of the hip is often entirely normal with a full range of movement. There are specific tests for a labral tear. The impingement test (flexion, adduction and internal rotation of the hip joint) commonly produces pain or a clicking sensation when an antero-superior tear is present. The McCarthy test involves flexing both hips and then extending the affected hip patients with a labral tear will feel a catch. Passive hyperextension, abduction and external rotation elicit pain with a posterior tear.

Plain radiographs, computed tomography (CT), magnetic resonance imaging (MRI) and arthrograms are all poor at identifying intraarticular disease. However, magnetic resonance arthrography (MRa) is proving to be more promising. MRa involves the injection of dye into the hip capsule followed by MR imaging in several planes.

Since a single radiological technique does not exist at present that can accurately diagnose labrum tears, diagnosis is usually based on a combination of clinical judgement, MRa and hip arthroscopy.

Hip arthroscopy has become increasingly popular over the last 15 years with the development of minimally invasive instruments and techniques. It is usually performed as a day-case procedure under general anaesthetic and takes approximately 30 to 40 minutes.

Arthroscopy can be used both to diagnose and to treat acetabular labrum tears. Diagnostic arthroscopic evaluation is considered when joint symptoms, examination and radiographic studies have failed to provide a diagnosis. Arthroscopy is reported to facilitate a diagnosis in 40% of these cases.

Acetabular Labrum Tears Treatment

Treatment can be conservative or surgical. Conservative management involves rest followed by a graded increase in weightbearing. Traction can also be used. But as yet there is no evidence as to whether the inner two-thirds of the labrum, which lack any blood supply, are able to heal with rest alone. Surgical treatment is either arthroscopic debridement (tidying up) or repair.

Debridement involves removal of damaged tissue back to a stable base while preserving as much of the labrum as possible. Techniques are evolving for repair such as suture anchor. The aim of arthroscopic treatment is to eliminate any unstable flap of labral cartilage, which is thought to relieve groin pain. This in turn should maintain normal function of the hip joint. While it may hypothetically also decrease the development of premature arthrosis, there is no evidence as yet that a labral tear leads to further degenerative changes in the hip.

Post-operatively there is usually four to five days of relative rest prior to starting a rehabilitation programme with gentle mobilisation of the hip joint. Exercises in a hydrotherapy pool are particularly effective, as they allow mobilisation without compression through the joint. Progressive muscle strengthening is undertaken and once the hip has a normal range of motion and strength, functional exercises can be started.

A return to sport is usually possible two to three months after the operation. Arthroscopic debridement is reported to improve symptoms in 67% to 90% of patients. Overall, younger patients and those with no arthritis have a better outcome.

Conclusion

Up to 20% of groin pain in athletes is now thought to be the result of acetabular labrum tears. All health care professionals who work with athletes should have a high index of suspicion for such lesions. Diagnostic tools include MRa and arthroscopy. Treatment is hip arthroscopy with debridement or repair and preliminary studies suggest a positive outcome.

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Acetabular labrum