The structure of avian cartilage: a combined X-ray and biochemical analysis.

The antitrochanter is a cartilaginous extension of the avian hip joint that is susceptible to degenerative changes. This study consisted of X-ray diffraction and complementary biochemical examination of collagen in the turkey antitrochanter from the articulating surface through to the bone. X-ray diffraction was performed by means of synchrotron radiation with a 200 microns collimated beam to examine the antitrochanter from three 24-week-old, large, male turkeys. The arced distribution of intensity from equatorial reflections was used to determine the parameter g(psi), the probability distribution of fibril angular orientation. Analysis of five distinct regions showed a variety of fibril orientation profiles. The surface of the cartilage exhibited a near isotropic profile. The superficial fibrous region contained well-aligned fibrils parallel to the surface. The middle hyaline region was less well organized, but fibrils were orientated in a direction similar to that of fibrils in the superficial fibrous region. The deep hyaline region exhibited a bimodal distribution of fibril orientation. The ossified front (decalcified) showed an alignment similar to that seen in the middle hyaline region. Biochemically, two main regions were found. The first, 1.2 mm from the surface, consisted of type I collagen and the deeper region (1.26-3.0 mm) consisted of type II collagen. The change from type I to type II was abrupt (less than 80 microns).