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An Update on the Anatomy, Biomechanics, and Repairs of Hip Labrum

Posted on: 06/22/2010
There isn't one part of the body (no matter how small) that doesn't have a specific function -- and often more than one job to do. That's also the case with the labrum, a horseshoe-shaped bit of fibrous cartilage lining the hip and shoulder sockets.

In this review article on the hip labrum, orthopedic surgeon Marc R. Safran, MD from Stanford University provides a detailed description of the labrum anatomy. Advanced technology including light microscopy has made it possible to take pictures and study the many layers of dense connective tissue that make up the labrum.

Blood supply, type of nerve endings, and biomechanics are explained. The symptoms and effects of a labral tear are discussed. Surgery is often needed to repair or remove the damaged tissue because it can't heal itself and can cause severe, disabling hip pain.

The labrum is small but mighty in effect. As recently as 1998, it was believed that the labrum had no apparent role in bearing weight through the hip. Since that time, scientists have discovered multiple functions of the labrum.

For example, the labrum increases the size of the joint surface and the joint socket. Another term for the hip socket is acetabulum. This increase allows for a more even distribution of load across the whole joint.

Another task the labrum carries out is to act like a suction cup creating negative pressure in the joint. The seal that forms holds the lubricating synovial fluid inside the joint. The net effect is that the labrum reduces joint friction, a protective feature against degeneration leading to arthritis.

Tiny receptors in the labrum signal the location and movement of the joint. The receptors are called mechanoreceptors. Awareness of tiny changes in joint position is called proprioception. The role of the labrum in proprioception is clear but not fully understood yet.

When combined together, the various functions of the labrum help maintain joint stability. With all these wonderful functions of the labrum, you can imagine that any damage to the labrum can create some serious problems.

Hip pain is the first indication that something's wrong. Sometimes there is a clicking sensation and the hip can even get locked up if the torn labrum gets caught between two structures of the hip. Loss of hip motion is the outcome of either of these symptoms.

Surgery is usually the recommended course of action for a symptomatic labral tear. Patients often ask if the problem can correct itself with time and rest. The answer to that question is maybe. The labrum doesn't have its own internal blood supply. Without a good blood supply, healing isn't possible.

The labrum depends on the blood vessels in the acetabulum (hip socket) and surrounding soft tissues. Someof the tiny blood vessels from these others areas reach the labrum to supply oxygen and healing nutrients. Some areas of the acetabulum have more blood than others. So depending on the location of the labral tear, self-healing might be possible. In other words, healing may occur when the tear is closest to the best blood supply.

But most of the time, surgery to remove the ragged edges of the torn labrum is required. This procedure is called debridement. Without an intact, functioning labrum, it is believed that the risk for joint degeneration and arthritic changes increases. Studies to support this idea have been done on cadavers. Cadaver studies involve using human hips preserved after death and used for study of problems like this one. Similar studies in live subjects have not been reported.

What researchers have been able to measure are the before and after results in live humans with labral tears following labral surgery. As mentioned, the main procedure used is debridement. The surgeon shaves off the ragged edge of the torn labrum and smoothes the remaining edges.

A more extensive surgery called a partial labrectomy may be needed. This involves removing part of the labrum. Studies show that partial labrectomies have better outcomes when there isn't damage to the underlying layer of cartilage attached to bone. The success rate drops from 90 per cent without chondral lesions down to 21 per cent for those patients with chondral defects.

One of the real difficulties in measuring results of partial labrectomy is the fact that researchers don't really have a specific tool to use. Outcome ratings are possible for patients who have had a hip replacement but those questionnaires assess pain and function in older, less active, arthritic patients.

Right now, the pressing need is for a similar tool to be developed and tested for use with labral tears in younger, more active patients who don't have arthritis. Then it would be possible to compare the results between a partial labrectomy and the newer procedure in use: labral repair. During a labral repair, the surgeon uses stitches and surgical anchors to reattach the torn labrum.

Results of labral repairs have not been published yet in English-language medical journals. Most of the research that has been done has been published in European or Spanish-language journals. When valid and reliable tools are available, the results of debridement, partial labrectomy, and labral repair can be compared.

There's no sense in doing surgery if the results are going to end up being the same as if the patient didn't have the procedure. Likewise, if there is one operation that works better than another, surgeons can make better informed treatment decisions for individual patients. With a better appreciation of labral anatomy and function, choosing the best plan of care for complete recovery will be the goal.

Marc R. Safran, MD. The Acetabular labrum: Anatomic and Functional Characteristics and Rationale for surgical Intervention. In Journal of the American Academy of Orthopaedic Surgeons. June 2010. Vol. 18. No. 6. Pp. 338-345.

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