As you probably know by now, femoroacetabular impingement (FAI) refers to some portion of the soft tissue around the hip socket getting pinched or compressed. Femoroacetabular tells us the impingement is occurring where the femur (thigh bone) meets the acetabulum (hip socket).
There are several different types of impingement. They differ slightly depending on what gets pinched and where the impingement occurs. Anatomic abnormalities of the femur and/or the acetabulum predispose the person to damage of the soft tissue structures inside the joint. Vigorous, repetitive hip motion creates abnormal contact and collision that result in hip pain.
It looks like one particular impingement type (called cam-type impingement) is more likely to lead to tears of the labrum (fibrous rim of cartilage around the hip socket). The cam-type of impingement occurs when the round head of the femur isn’t as round as it should be. It’s more of a pistol grip shape. It’s even referred to as a pistol grip deformity. The femoral head isn’t round enough on one side (and it’s too round on the other side) to move properly inside the socket.
There is some new evidence that the cam-type impingement is the result of participation in high-impact sports. Adolescents (teens) develop this condition as the bones mature. In other words, they aren’t born this way. It appears as though the repetitive motion of the sports activity reshapes the hip resulting in a femoroacetabular impingement (FAI).
Several studies have shown that cam-type deformities are linked with osteoarthritis. But people with cam-type deformities and osteoarthritis are not more likely to end up with a total hip replacement than people without this type of femoroacetabular impingement.
Future studies will focus on finding out who is at risk for developing femoroacetabular impingement that will lead to osteoarthritis and hip replacement. Finding ways to prevent femoroacetabular impingement (and osteoarthritis) would be a natural outcome of these findings. It is possible that risk factors for those who develop osteoarthritis early in life are different than risk factors for adults who develop osteoarthritis in mid- to late-life. This must be investigated as well.