Osteoarthritis is a degenerative bone disease that affects over 27 million Americans (Neogi, 2013). It is characterized by the loss of functional cartilage that normally bears mechanical stresses, which is then transferred onto bone and leads to untreatable pain. The objective of this study was to histologically characterize the nature of subchondral bone cysts found in different anatomical sites of the femoral heads from patients who had undergone arthroplastic surgical replacement.
Femoral heads were collected from sixteen patients (5 males and 11 females) aged 43-77 years who had all underwent a total hip arthroplasty. Heads were fixed for two weeks and computerized tomography (micro CT) was then carried out to identify subchondral bone cysts (regions within the head devoid of bone tissue). The head was segmented into three regions: The large cyst region, where the largest micro CT identified cyst was found, the primary compressive region, in accordance with the orientation of the trabeculae, and the anterior cartilage region which was where the healthiest articular cartilage is typically found. These regions were then dissected and slices were decalcified and embedded in paraffin for histological processing. The embedded tissues where stained with either Safranin-O and Fast green or hematoxylin and eosin to visualize the histological properties of each region. The subchondral bone cysts were then identified histologically within the sections and matched to the micro CT findings as an area of subchondral bone devoid of normal trabeculation.
Three separate types of cysts were identified from the above criteria: fibrous cysts composed of dense fibrous tissues; cartilage intrusion cysts, containing cartilage tissues that had moved deep to the subchondral bone plate; and fatty cysts containing high amounts of unilocular adipocytes. Throughout the course of this study it was noted that the fibrous cysts tended to be more numerous and larger than the other two types. This finding is in accord with the bony contusion theory that subchondral cysts are created from excessive mechanical loading and can grow larger as the bone becomes increasingly ill equipped to handle stress. The cartilage intrusion cysts most likely arose from the process outlined in the synovial intrusion theory, where a small amount of synovial fluid breaks through the subchondral bone plate and creates a cyst. This would account for why the cartilaginous cysts were found so close to the plate and were much smaller in size than their fibrous counterparts. The fatty cysts ranged in size and location with the larger ones deep to the articulating surface while the smaller ones were superficial, suggesting a mixed mechanism of formation. The varying locations and identities of the cysts may provide evidence to both of the conflicting theories of subchondral bone cyst formation. Further research is indicated to help elucidate the pathogenesis of subchondral bone cysts.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/30871 |
| Date | 03 July 2018 |
| Creators | Babbin, Joshua |
| Contributors | Gerstenfeld, Louis |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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