Hip morphology influences the pattern of damage to the acetabular cartilage

Abstract

Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification. Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone.

Acetabular Morphology: Implications for Joint-preserving Surgery

“…Likewise, backward tilt of a horizontal line along the transverse acetabular ligament was described in another study [43]. Allocations of acetabular surface particularities or lesions were given either with reference to the acetabular incision [4,6,35,39,55,66] or in relation to the vertical axis of the patient as seen during surgery [30,38,58]. The individual acetabular tilt and variations in pelvic tilt [2,10,12,32,33,41,48,57] complicate comparison of these data.…”

“…Our approach was analogous to that of the earth's globe: distances along the meridian were given in degrees with reference to the acetabular (center) pole at 0°and defined as depth (latitudes). The extent along the acetabular rim was defined as width (longitudes), given in degrees [4]. The 90°latitude circle defined the equatorial line of a hemisphere.…”

“…Direct damage to the hip can be caused by variations in size, shape, and orientation of either the proximal femur [15,24,27,36,47,50], the acetabulum [11,22,54], or a combination of both [4]. The predilection for femoroacetabular abutment and subsequent lesions is the anterosuperior acetabular rim [3,4,26,35,37,38,58], with gender differences in the damage pattern for cam and pincer impingement [4,26].…”

Radiological Assessment of Femoroacetabular Impingement Morphology Using Computed Tomography in an Asymptomatic Young Population

“…The prevalence of FAI in adults is approximately 10-15% (3) and, depending on the clinical and radiographic findings, two types of impingement (which are often present in combination) can be distinguished: the cam type and the pincer type. Most patients (86%) have a combination of both forms of impingement (4). The main abnormality in the cam type of impingement is a reduced offset between the femoral head and neck, caused by an aspherical portion of the femoral head-neck junction.…”

“…If the underlying cause of femoroacetabular impingement is not addressed, it can progress, and result in degenerative diseases of the hip joint (4,5).…”