In contrast, the labrum has a generous pattern of nerve endings such that labral tears tend to be quite painful. With cam impingement, symptoms may only begin to occur when the labrum starts to fail, long after the articular damage has advanced. With pincer impingement, the labrum tends to fail earlier where it is crushed by the rim of bone. In young people, the labrum is a hardy structure and can sometimes withstand crushing from the pincer lesion for years before it actually tears. This results in circumstances where painful disabling symptoms may be present for a longtime before an MRI shows evidence that the labrum is actually torn. The labrum may be crying wolf long before it tears.
FAI is not as simple as just pincer or cam or combinations of both. Numerous other factors come into play, contributing to FAI problems. Rotational features of the lower extremity (femoral version) and features of the lumbar spine, including reduced normal lordosis (flat back) or hyper lordosis (sway backed), just to mention a few, can both negatively and positively influence the FAI problem. It is not just a static feature of the bony architecture of the hip. There is a significant dynamic component to how the joint edges collide, and these can be influenced by other body parts.
Isolated FAI problems, without other secondary features going on, are actually uncommon. There are reasons for this observation. First, the body is compensating for the FAI condition long before joint damage and pain occurs. Second, symptoms associated with the joint damage are not always obvious, and may be present for a long time before being detected. In fact, it is common that patients may have made trips to several different physicians before an accurate diagnosis is reached. This delay in diagnosis results in more opportunity for secondary problems to set in. For the physician, it is important to maintain a sense of awareness and suspicion for potential underlying FAI problems, as the secondary compensatory problems may be more obvious on examination, and may obscure the presence of an underlying FAI disorder.
Most specifically, a frequent feature of FAI is reduced rotational motion of the hip, especially inward rotation. This is attributed to the shape of the joint where bony collision occurs between the bump on the femoral head and/or the protuberance of the rim of the acetabulum. These restrictions may result in compensatory problems long before joint damage occurs and the hip starts to become painful. Most commonly, these compensatory problems manifest as groin, low back, or gluteal muscle symptoms.