What the Experts Are Saying About Femoroacetabular ImpingementEven with the best imaging equipment, sometimes the surgeon doesn't really find out what's causing the patient's hip pain until he or she is looking inside the joint during surgery. What looks like a labral tear might really be a separation of the layers of articular cartilage in the joint. More and more people (especially athletes and older adults) are showing up in surgeons' offices with complaints of hip pain that turn out to be femoroacetabular impingement (FAI) with labral tears.
The labrum is a dense fibrocartilage ring around the hip socket. It is firmly attached to the bone and serves to deepen the socket, giving depth and stability to the hip joint. Femoroacetabular impingement occurs when the head of the femur (thigh bone) butts up against the hip joint cartilage and pinches this cartilage. Impingement means pinching.
Normally, the femoral head moves smoothly inside the hip socket. The socket is just the right size to hold the head in place. If the acetabulum is too shallow or too small, the hip can dislocate. In the case of FAI, the socket may be too deep. The rim of the cartilage hangs too far over the head. When the femur flexes and rotates, the cartilage gets pinched. This causes deep groin pain with activities that stress hip motion. Prolonged walking is especially difficult.
The etiology (cause) of the problem is under considerable debate. The discussion in this article among four orthopedic surgeons from around the United States offers some insight into surgeons' opinions, experiences, and what the latest research has to say about the relationship between the labrum and impingement syndrome. The director of hip arthroscopic surgery at Kaiser-Permanente in California (Dr. Dean Matsuda, who is a hip patient himself) gathered these experts together to ask them some questions about the underlying cause(s) of femoroacetabular impingement (FAI).
Everyone agreed from doing thousands of hip arthroscopic surgeries that femoroacetabular impingement and labral tears go hand-in-hand. And labral tears don't just happen out of the blue. The majority of hip labral tears probably develop as a result of some structural problems.
But there are some interesting findings about femoroacetabular impingement and labral tears. Younger patients (usually athletes) can have labral lesions without bony impingement. But there are groups of patients like hockey goalies who load the hip in a flexed position over and over leading to chronic impingement and eventual labral tears.
And despite the correlation between these two problems (labral tears and impingement), it is possible to have labral-cartilage lesions without any symptoms of impingement. They know this from autopsies on older adults who never complained of hip pain but had significant labral damage.
Studies have also shown that labral injury can occur without impingement as the start of the problem. That means there is some other reason why the labrum was damaged, but what? Well, improved quality of MRIs is helping to answer that question. It's becoming clear now that over time slight changes in the normal hip anatomy result in plain old wear and tear (degeneration) of the junction between the labrum and the joint cartilage. That points to structural problems in the hip as the underlying cause of labral tears.
The word normal is highlighted because those same autopsies are also showing us that what we define as normal rarely exists. Most people do have alterations in anatomy that could lead to arthritis from uneven wear. Yet only a small percentage (five to seven per cent) of people with joint degeneration actually experience symptoms of hip pain from osteoarthritis. That's true even when there is damage to the labrum and decreased hip motion from impingement.
So, what's really happening here? Who develops labral tears, impingement, and eventual arthritis? And why do they present with hip pain when others who have the same changes in the form and structure of the hip and surrounding soft tissues have no symptoms at all? No one knows for sure but this group of experts agreed that it is likely a combination of several risk factors and mechanisms.
There is the anatomy to consider -- structural problems are probably the most important factor (even if it's not the only factor). Shape of the socket, angle of the femur as it connects with the socket, ligament laxity (looseness), and mechanical properties of the labrum and cartilage head up the list of possible structural causes of femoroacetabular impingement.
New research has also shown that when the labrum is damaged (no matter what the cause), a seal is broken that normally keeps synovial fluid inside the joint. When the labrum is healthy and well-sealed, friction inside the joint is kept to a minimum. Without this protection, fluid is pushed out or leaks out of the joint. This may be a big factor in why osteoarthritis develops.
But there's also the role of inflammation and the immune system to be considered and explored. Some people seem more susceptible to inflammatory chemicals in the body. And with enough load and postural changes over time, labral tears and/or impingement lead to hip joint osteoarthritis.
So, where does that leave us? Even without full knowledge and understanding of femoroacetabular impingement and labral tears, decisions must be made about treatment. At first, surgeons just removed the torn cartilage and shaved smooth any frayed edges. Now, this procedure is being reconsidered.
Some surgeons propose reattaching the labrum. Others point out that only part of the labrum has any blood supply. The success of the reattachment depends on blood from nearby sources getting to the healing labrum. The strength of the stitches, not healing tissue filling in the gap is another important factor.
Even so, patients do seem to get relief from their hip pain with labral preservation and reattachment. Surgeons are still scratching their heads trying to figure that out -- do they get such good results because the surgery helps stabilize the joint? Improve lubrication? Redistribute pressure? Can the protective seal be restored? Does it mean that these folks WON'T go on to develop osteoarthritis?
These are all questions yet to be answered. Based on what research is available so far, this group of experts favor labral repair. Trying to save the labrum and restore the fluid seal in the hip joint is the goal right now. When the tear is more than seven millimeters wide, then repair may not be possible. The group will continue their discussion of treatment options in the next issue of this journal.
FAI: An Emerging Problem in Orthopedics That Can Have a Major Clinical Impact. In Orthopedics Today. June 2009. Vol. 29. No. 6. Pp. 12, 24, 18.
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