ANATOMY
The acetabular labrum is a fundamental structural element of the hip joint. Although it is a delicate structure, it contributes greatly to the smooth functioning and to the longevity of the joint. A tear of the acetabular labrum is a very common finding during hip arthroscopy. It may be primary or secondary. The importance of a tear lies in the fact that it causes significant symptoms for the patient, and also that it is potentially the trigger for further deterioration of the hip, that is, osteoarthritis.
If one studies the acetabular labrum under magnification, one observes that it is essentially the anatomical continuation of the articular cartilage (figure). The articular cartilage – labrum complex thus works as a single surface for correct congruity between the femoral head and the acetabulum. For this reason, any damage to the labrum also has an impact on the structure of the articular cartilage and, secondarily, on the overall function of the joint.
In vertical cross-section the labrum appears to have a triangular shape, with its base attaching to the bony rim of the acetabulum and to the articular cartilage, while its apex lies free. In many cases part of the bony attachment extends deep into the body of the labrum. It has two surfaces: the articular surface, which is in continuous contact with the femoral head, and the capsular surface, which forms the peri-acetabular sulcus together with one side of the capsule. The composition of the labrum is fibrocartilaginous. Studies have shown that it consists of dense bundles of collagen fibres, resembling a ligament histologically. Chondrocytes have been observed on the articular surface, and fibrocytes within its body. The boundary between the labrum and the articular cartilage, the so-called transitional zone, is the most vulnerable point of the inner surface of the acetabulum, and for that reason it sustains injury, perhaps more than any other area.
Its arthroscopic appearance varies from person to person, both in dimensions and in shape. The anterior labrum, however, always has fundamental morphological differences from the posterior labrum, being broader and thicker, while it is also more vulnerable to tears. A good knowledge of the anatomy of the acetabular labrum is essential for the arthroscopic treatment of its lesions, whether by partial resection and smoothing or, preferably and wherever this is feasible, by repair and stabilisation, so as to secure improvement of the patient’s symptoms and to avoid further degeneration of the joint.
References
1. Tzaveas A, Villar R: The Open Sports Medicine Journal January 2010;4(1):64-74.
2. Grant AD, Sala DA, Davidovitch RI. The labrum: structure, function, and injury with femoro-acetabular impingement. J Child Orthop. 2012 Oct;6(5):357-72.
3. Harris JD. Hip labral repair: options and outcomes. Curr Rev Musculoskelet Med. 2016 Dec;9(4):361-367.
Read more about tears of the acetabular labrum and their treatment.