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"Patients with camFAI are not good candidates for hip resurfacing."
Men with cam Femoral Acetabular Impingement (camFAI) are in fact classically the best candidates for hip resurfacing. Most (80%) of the young men that I perform hip resurfacing on have this mild femoral deformity which likely contributed to them getting severe arthritis at a young age (40-60).
This deformity is manifested as a femoral head that is not centered on the neck. The head is like a ball of ice cream sliding off the cone posteriorly and inferiorly. In addition, there is often an additional bump of bone at the anterior/superior head/neck junction. There is considerable variability in the degree of this malformation. Lack of an anterior offset between the head and neck leads to a cam effect when the hip is flexed and internally rotated.
Cam FAI probably develops as a growth plate slip in the late teenage years. The male growth plate closes at age 12-14 years. It is a painless condition until the repetitive cam effect damages the labrum and hyaline cartilage of the hip, usually in the anterior-superior corner of the joint. Patients who present early can be treated arthroscopically. But most patients don’t present until substantial cartilage is lost (severe osteoarthritis).
At this point, hip resurfacing is the best treatment. The lost cartilage surface is restored with metal surfaces; the deformity is corrected by differentially resecting the femoral head bone more from the inferior and posterior side and moving the head center more anterior and superior. The bump is also removed. The result is improved anterior offset as well as new artificial cartilage. This same condition is seen less commonly in women. 17-year implant survivorship is 99%.