An investigation of degenerative joint disease (DJD) studied data from chimpanzees, lowland gorillas, bonobos, and human samples to ascertain the relative rate of osteoarthritis and peripheral joint osteoarthritis in each species and found that all types of apes were significantly less prone to DJD than humans.
Museum skeletal samples of adult chimpanzees, lowland gorillas, and bonobos were examined and analyzed for vertebral osteoarthritis (VOP) and osteoarthritis (OE). The resulting data was compared to data sets from a series of adult human skeleton sets wherein comparable analytic methods had been used to determine the rate of VOP and OE. All samples were evaluated for DJD and the presence of VOP. The relative severity of the conditions was scored using ordinal scaling criteria, categorizing the groups into: none, slight, moderate, or severe DJD. The researchers discarded the “slight” sample data and focused instead on the “moderate” to “severe” data sets for the study.
There was a low prevalence of VOP in the ape samples (0-3.8 %) across all vertebral segments, while the human prevalence was between 11 and 85 times that of the apes, with more uniform involvement throughout the vertebral column.
OA of the spinal joints was also rare in African apes, with chimpanzees being least affected, followed by gorillas, and bonobos. Though OA is less prevalent than VOP in humans, it is still three to four times more common in humans than in apes. Broken down into spinal segments, gorillas were more susceptible to cervical and thoracic segments than chimpanzees. Where chimps showed no lumar involvement, gorillas were variably affected at the level. Humans were uniformly more prone to OA at all levels than any of the apes sampled.
Ape samples were much less likely to show signs of spinal degeneration at all levels than comparable human samples. Although it makes sense to assume that the divergence is due to the greater compressive stress on the bipedal human form, the patterning of VOP data in apes and humans suggests that other forces—such as torsional loads related to axial spinal rotation— are likely contributing to the higher incidence of DJD in humans.