Scanning electron microscopy examination of collagen network morphology at the cartilage, labrum, and bone interfaces in the acetabulum

Sheep acetabula of approximately 1cm3 in dimension consisting of cartilage, labrum, and bone were prepared for scanning electron microscopy. Examination of collagen architecture at the tissue interfaces fixed by conventional chemical, microwave enhanced chemical and cryo-fixation followed by freeze substitution were compared. Successful cryo-fracturing of dehydrated samples in liquid nitrogen cooled solvent was not possible. However, the specimens became sufficiently brittle when frozen in liquid nitrogen after critical point drying, and fracturing produced more consistent planes allowing imaging of the three interfaces. The labrum/ cartilage interface was best preserved with cryofixation whereas the cartilage/bone interface was better visualized after chemical fixation due to an unidentified substance covering the collagen fibers after cryo-fixation. Finally, the labrum/bone interface was preserved similarly by both chemical and cryo-fixation. For a specimen containing three different tissues types of both hard and soft variety with mixed collagen fiber orientation, it is very demanding to find one fixation method which will enable detailed examination of the collagen fibers