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Hip Preservation

It has been firmly established that osteoarthritis of the hip is most commonly due to an underlying abnormality in hip anatomy.  Much like tires on a car that are malaligned will have their treads worn prematurely, the articular cartilage of the hip is worn my abnormal mechanics of movement.  Hip preservation surgery seeks to improve the anatomy of the hip joint with the goal of relieving early degenerative symptoms, and delaying or possibly preventing the eventual onset of end stage arthritis in the hip.

The two most common abnormalities of the hip are Femoro-Acetabular Impingement and Hip Dysplasia.  The hip is a ball and socket joint.

(Fig 1) 

The ball is represented by the femoral head and neck, and the socket by the acetabulum, and the cartilaginous labrum at its periphery.

(Fig 2) 

The degree of containment of the ball within the socket will affect the amount of unrestricted motion that is achievable.

(Fig 3)

Similarly, the sphericity or roundness of the ball and socket, and how well those two surfaces match each other also affect how they interact during the range of motion.

Femoro-Acetabular Impingement
There are two basic abnormalities in impingement, Pincer lesions, and Cam lesions.  The Pincer lesion involves a socket that is rotated less forward than normal (Fig 4), or otherwise extends too far over the femoral head. (Fig 5)  As a result, when the hip reaches the extremes of motion, the femoral neck impinges on the acetabulum, directly impacting the labrum.  (Fig 6)  Over the course of many years this can lead to tears in the labrum.  The labrum is directly adjacent to the articular cartilage, which is the tissue on the surface of the joints which cushions the bony surface of the joint.  The impact of the femoral neck on the labrum also leads to detachment of the articular cartilage from the underlying bone.  Finally, as the femoral neck makes contac t with the labrum, further force in that direction will result in the femoral head being pushed slightly outside of the socket on the opposite site of the socket, and the abnormal shear forces worsen the wear and tear of the articular cartilage and labrum.

Cam lesions are abnormalities of the roundness of the femoral head, and abnormalities at the junction of the femoral head and neck.  (Fig 7, 8) The larger the difference is between the diameters of the femoral head and neck, the greater the range of motion that is achievable between them. A cam lesion is a prominence of the head-neck junction anteriorly, which scrapes, or delaminates the articular cartilage off the acetabulum, displacing or sometimes tearing the labrum. (Fig 9)

Studies have shown that most cases of Femoro-Acetabular Impingment are a combination of both Cam and Pincer deformities, with one type being dominant.  The pain is likely due to the cartilage tears, the abnormal loading on the uncushioned bone.  The goal of treatment is to remove the torn cartilage fragments, and to attempt to correct or optimize the anatomic geometry of the hip.  This is classically done in an open procedure, involving an anterior surgical dislocation to reshape the femoral cam lesion, resect any acetabular pincer lesion, debride the torn articular cartilage, and repair the labrum.  (Fig 10)  Studies have shown that this type of treatment have improve the symptoms and with labral repair, slow the progression of arthiritis. (ref espinoza)  In cases with exposed bone at the joint surface, a treatment called Microfracture is used to make small holes in the bone which allow for new fibrocartilage to grow where the articular cartilage once had been.

More recently, the surgery for impingement has been done arthroscopically, or arthroscope assisted, with a small anterior opening. (Fig 11 11a 12 13)  The goal is to accomplish what can be done in an open procedure, with less tissue disruption, and therefore a more rapid recovery.  Recent studies have shown that approximately 75% of patients can achieve sustained pain relief and improved function at one year using arthroscopic techniques.  The remaining 25% likely represent a group of patients in whom the arthritic process has progress too far to be improved with hip preservation procedures, and therefore would benefit from hip resurfacing or hip replacement.

Hip Dysplasia
Hip Dysplasia is a developmental abnormality of the hip wherein the socket does not develop properly, and fails to provide adequate coverage of the femoral head. (Fig 14) The socket can be globally smaller, and shaped diagonally rather than horizontally at its edge.  As a result, the forces which should be distributed through a broad surface as simple compression, are focused on a small area, and manifest as shear forces which are less well tolerated by the articular cartilage.  In cases of Hip Dysplasia, the labrum is larger than normal, and because of the acetabular bony deficiency, it becomes a weight-bearing structure.  For this reason, the labrum is subject to fatigue failure, with tearing and detachment.  Labral tears in dysplasia are less amenable to arthroscopic management, because the underlying bony deficiency which caused detachment, persist, and make successful repair less likely.  Small peripheral tears in the labrum that cause mechanical symptoms of catching may be treated arthroscopically with an expectation of success, but a labral detachment in dysplasia is often the herald of a rapid arthritic deterioration.

In early stages, Hip Dysplasia can be treated with an operation to re-orient the bones to optimize their function, making a diagonal weight-bearing surface more horizontal.  This is accomplished with an open procedure called a Peri-Acetabular Osteotomy , where the socket bone is cut from the remainder of the pelvis and reoriented, and held with screws.  This can improve the mechanics of loading the joint, and has been shown to have a durable effect in delaying arthritic progression.  In this setting, the labrum can be successfully repaired because the changes in the loading conditions of the hip allow it to heal. Fig 16