Longitudinal development of spinal osteoarthritis in Macaca mulatta

This study represents the first long-term longitudinal assessment of naturally-occurring spinal osteoarthritis (OA) in primates. Twelve years of radiographic spinal data for 68 Macaca mulatta (41 males, 27 females, aged 11-32 years) were evaluated for disc space narrowing (DSN) and osteophytosis (OST) at each vertebral level and average scores were computed for the thoracolumbar spine (T8-L7). Cross-sectional analyses of spinal (OA) in primates have shown that age, body mass, and sex are significant predictors, but whether or not these relationships hold true in longitudinal evaluations remained unclear. Because spinal OA manifests similarly in humans and monkeys, and macaque monkeys age ∼3.5 times the rate of humans, macaque models offer opportunities for longitudinal study that are difficult in humans. The initial longitudinal analyses confirmed the cross-sectional results in regard to age and body mass. Sex differences were analyzed further and were also compared to a secondary analysis of existing human spinal radiograph data. Male rhesus macaques had higher prevalence but similar vertebral distribution of spinal OA compared to females. No gender difference was apparent in the prevalence of spinal OA in humans, but the distribution along the spine was different. Overall, macaques had higher prevalence of spinal OA than humans. These longitudinal data also made it possible for the first time to characterize two case studies of the twelve-year progression of spinal OA in macaques. In a male rhesus macaque, a possible non-traumatic event may have resulted in rapid osteophytic growth at the L1/L2 joint within a one-year interval. In a female rhesus macaque, kyphosis at the thoracolumbar joint occurred in the absence of vertebral fractures. Each case study described an atypical illustration of spinal OA. The longitudinal assessment of spinal OA in macaques has added to our understanding of the progression of OA across the lifetime of an individual and the risk factors and biological and morphological changes with which it is associated. Ultimately, a better understanding of the condition in nonhuman primates presents opportunities for a better understanding of the condition in people and to aid in developing preventative and therapeutic interventions.