The temporomandibular joint of California sea lions (Zalophus californianus): Part 2-osteoarthritic changes

•We study the TMJ of California sea lions in a museum collection of skull specimens.•California sea lions have high occurrence (63.5%) of osteoarthritis of the TMJ.•There is no association between age and sex with the presence or severity of TMJ-OA.•TMJ-OA is present at the mandibular head and affects the entire articular surface.•The high incidence of TMJ-OA is likely to affect morbidity and mortality.

ObjectivesFollowing comprehensive characterization of the temporomandibular joint (TMJ) of the California sea lion, as well demonstrating that TMJ-osteoarthritis (OA) occurs in this species, the objective of this part of the investigation was to describe the macroscopic osteologic findings associated with TMJ-OA in a large museum collection of skull specimens.DesignMuseum skull specimens (n = 497) of California sea lions were examined macroscopically according to defined criteria for the presence, severity, location and characteristics of TMJ-OA. The specimens, acquired from strandings, varied in age from young adults to mature adults.ResultsOverall 63.5% of the specimens had findings consistent with TMJ-OA. Of these, 56.2% were from females 43.8% were from males. Moreover, 71.2% specimens were from mature adults and 28.8% from young adults. However, there was no significant association between age and sex with the presence or severity of TMJ-OA. The most prominent TMJ-OA changes were the presence of subchondral bone defects and abnormal porosity. The majority of the OA present at the mandibular head affected the entire articular surface. In contrast, the OA present on the mandibular fossa of the temporal bone was located primarily on the medial aspect (P < 0.001).ConclusionThe incidence of TMJ-OA in California sea lions is high and varies in severity. Although the significance of the high incidence of this disease in the California sea lion remains elusive, the occurrence and severity of TMJ-OA detected in this study may play an important role in the species’ morbidity and mortality.