- Fibrocartilagenous structure which outlines the acetebular rim
- Covers 170° of femoral head
- Functions: shock absorption, joint lubrication, pressure distribution, stability
- Horse-shoe shaped
- Continuous with the transverse acetabular ligament
- Articular side composed of fibrocartilage, capsular side composed of dense connective tissue
- Usually triangular in cross-section anteriorly
- More bulbous with square dimensions and a rounded distal edge posteriorly.
- Lecouvet et al: labrum was triangular in cross section in 66% of 200 asymptomatic volunteers
- Other studies, rounded, flattened, and irregular variants have been identified, particularly in older age groups
- The labrum has three surfaces and an apex
- Articular surface is located internally,
- External surface is in contact with the joint capsule
- Basal surface attaches to the transverse acetabular ligament as well as the bone and hyaline cartilage of the rim of the acetabulum
- The apex of the labrum is a free edge that embraces the head of the femur and forms a seal that enhances lubrication of the joint with synovial fluid.
- Thus the labrum deepens the cupshaped acetabulum to provide extra coverage for the femoral head
- The dimensions of the labrum are not uniform.
- Seldes et al reported that the widest portion is located anteriorly and the thickest superiorly
- Lecouvet et al found an absence of the labrum in 14% of asymptomatic volunteers
- Acts to increase stability at the hip joint by deepening the acetabulum and resisting lateral and vertical translation of the femoral head.
- Although the labrum deepens the acetabulum by 21%, this stabilizing effect is thought to be less important than the similar function provided by the glenoid labrum because the osseous acetabulum is considerably deeper than the glenoid fossa.
- Provides a seal for the joint, enhancing fluid lubrication, maintaining synovial fluid pressure, and preventing direct contact of the joint surfaces.
- This allows some of the load is borne by fluid pressure and applied forces are distributed more evenly across the articular surfaces.
- Preventing Osteoarthritis
- The role of the labrum in preventing early osteoarthritis is controversial.
- A labrum-free hip model showed that contact stress increased by 92%
- whereas a biomechanical study measuring contact and pressure distribution in cadaveric joints before and after labral removal showed no significant changes
- Capsule and synovium at acetabular margin
- Branch of nerve to the quadratus femoris
- Obturator Nerve
- Lecouvet FE, Vande Berg BC, Malghem J, et al. MR imaging of the acetabular labrum: variations in 200 asymptomatic hips. AJR Am J Roentgenol 1996;167(4):1025–1028
- Abe I, Harada Y, Oinuma K, et al. Acetabular labrum: abnormal findings atMR imaging in asymptomatic hips. Radiology 2000;216 (2):576–581
- Thomas, James D., et al. "Imaging of the acetabular labrum." Seminars in musculoskeletal radiology. Vol. 17. No. 03. Thieme Medical Publishers, 2013.
- Bharam S. Labral tears, extra-articular injuries, and hip arthroscopy in the athlete. Clin Sports Med 2006;25(2):279–292, ix
- Ferguson SJ, Bryant JT, Ganz R, Ito K. The influence of the acetabular labrum on hip joint cartilage consolidation: a poroelastic finite element model. J Biomech 2000;33(8):953–960