Evidensia Small Animal Referral Clinic Strömsholm, Vastmanlands Lan, Sweden
We investigated the incidence of stifle OCD in the extinct saber-toothed cat Smilodon fatalis. Given the rarity of published cases in modern felids, we predicted that subchondral defects resembling OC/OCD would be rare in extinct felids. Methods: We inspected 300 distal femoral epiphyses of juvenile and 380 distal femora of adult Smilodon from the Rancho La Brea fossil locality in Los Angeles, CA. Subchondral defects were documented as 1 (<7mm), 2 (7-12mm), and 3 (>12mm). Osteoarthritic changes were documented in adult specimens as mild, moderate, and severe. 214 tibiae were included in the control group.
Results: 33 subchondral defects were documented in the adults and 20 in the juveniles. In 25 cases the defect size was 1 (47%), in 22 cases size 2 (41.5%), and in 6 cases size 3 (11.3%). In 9 adult stifle joints, osteoarthritis was also documented. Discussion and limitations: Only 9 of the 33 subchondral defects in adult Smilodon showed mild to moderate osteoarthritic pathologies. It is possible that a substantial number of Smilodon stifles were affected by OC latens that did not progress to OCD. Only the bones, without soft tissue, could be examined and not the patients themselves for stifle function. Scientific relevance: Our prediction that OC/OCD was a rare pathology in Smilodon was not supported; however, our findings suggest that OC/OCD has existed since prehistoric times. Careful monitoring of breeding is recommended because the disease is dormant in the genome and can surge unexpectedly under conditions like inbreeding.
