CAM – Impingement
A joint (articulatio) always consists of a joint head and a socket. In the hip joint (Articulatio coxae) the components involved are the femoral head (caput femoris) and the acetabulum. If these two anatomical structures do not harmonize exactly, an impingement (collision) may occur.
In hip impingement (femoroacatabular impingement), a distinction is made between CAM impingement (camshaft impingement) and pincer impingement. In both cases there is a deviation from the normal structural relationship between the acetabulum and the head. Such an anatomical constellation can cause the femoral head to strike the acetabular roof during certain movements.
The constriction caused by this causes injuries to the joint lip of the acetabulum (labrum) and the joint cartilage. If left untreated, this can result in hip joint arthrosis (coxarthrosis). With CAM or camshaft impingement, the femoral head is enlarged so that it merges directly into the neck of the femur without sufficient waist.
As a result, the originally usual spherical shape is lost and the head strikes the acetabulum during powerful movement. In the long term, this allows the cartilage to be worn away inwards from the edge of the acetabulum and the so-called joint lip at the front upper edge of the acetabulum can also be damaged (labrum lesion). Due to the high force applied, the cartilage is usually damaged more quickly with CAM implanted acetabular cup implants than with pincer implants.CAM impingement most frequently affects athletic young men who engage in intensive sports.
CAM impingement is particularly suitable for arthroscopic treatment. It allows the surgeon to reattach a loosened cup lip or restore the neck of the femur to its original waisted shape, thus restoring pain-free joint function. Red shows the typical CAM impingement change at the femoral neck.
Pincer
With pincer or biting forceps impingement, the acetabulum is usually significantly deepened, whereas the shape of the femoral head is normal. The cross-sectional view shows the image of a pair of pincers, with the acetabulum holding the thigh bone like the lever arms of the tool. As a result, the neck of the femur strikes the edge of the acetabulum during movement, thus displacing the joint lip.
The transition from femoral head to femoral neck is also subject to considerable stress and strain. Pincer impingement frequently occurs in women between 30 and 40 years of age. Disturbances of the acetabular region occur while the pelvis is being formed, i.e. as early as infancy or childhood.
Most patients, however, do not suffer from isolated CAM or isolated pincer impingement, but from a variety of variable intermediate forms. Hip impingement is diagnosed by means of an x-ray and magnetic resonance imaging (MRI). This imaging enables the physician to distinguish between CAM and pincer impingement.
