Goal of the Study?
In this study 1, the authors investigate degenerative joint disease in the spine and major peripheral joints (shoulder, elbow, hip and knee) in chimpanzees, lowland gorillas and bonobos.
Why are they doing this study?
Degenerative joint disease is one of the most common pathological musculoskeletal conditions in human populations. It has also been observed in a variety of nonhuman animals, including nonhuman primates. Existing research has illustrated degenerative disease in chimpanzees, gorillas, orangutans, gibbons, macaques, baboons and probosci’s monkeys. Overall, prevalence has been reported as quite low in wild monkeys (with some exceptions) compared to colony-reared Old-World monkeys.
The authors want better to understand the evolutionary basis of degenerative joint disease.
What was done?
This investigation’s skeletal materials are drawn from two samples of chimpanzees, a sample of lowland gorillas and a small sample of bonobos. The samples from the chimpanzees are from Gombe National Park, Tanzania, while the other materials are from museum materials originally collected in west/central Africa. In total, 5807 sample surfaces for vertebral osteophytosis (VOP), 12,479 surfaces for spinal osteoarthritis (OA) and 1211 joints for evaluation of peripheral joint OA.
The human osteological samples are from two areas, Central California and a group of Inuit from Alaska.
The presence of VOP was based on a determination of osteophyte development. OA presence was based on hypertrophic development and changes to joint spacing. The severity of VOP and OA was scored based on slight, moderate or severe.
What did they find?
All apes display significantly less spinal disease compared to humans. The authors suggest that this is most likely related to movement on two legs. Among the African apes, gorillas are slightly more involved in the spine than chimpanzees with almost no spinal degeneration. Both bonobos and gorillas have significantly more involvement than chimpanzees in the cervical and thoracic regions (but the sample size for bonobos is so small that it is hard to say there is any significance). As with previous research, the authors found that colony reared Old World monkeys, such as macaques, have higher OA levels than other free-ranging apes. The authors argue that the variation between humans and African apes in VOP and OA prevalence may be explained by human longevity.
Why do these findings matter?
This study can help understand basic processes in degenerative joint disease among humans and our closest relatives in a broader evolutionary context.