Table 1.

Comparison of knee OA in Old World Monkey species and humans.

	Humans	Baboons (based on this study)	Rhesus macaques	Cynomolgus macaques
Prevalence of knee OA with increasing age	Prevalence increases with age – humans over the age of 65 have higher prevalence48	Disease severity differs significantly between younger and older (21.67 years +) baboons	OA prevalence increases with age9,17,18	Knee OA prevalence increases with age11
Effects of weight on knee OA	Heavy weight is risk factor for knee OA in multiple populations worldwide36	OA severity correlated with increased weight in females, but not in males	Relationship between weight and OA severity is inconclusive17,18,49	Increased weight correlated with subchondral bone thickness, but not articular cartilage lesions in the tibial plateau11
Sex differences in prevalence of knee OA	Significantly higher occurrence of knee OA in older women (> 55 years) than older men36,37	Males develop knee OA earlier, but females progress more rapidly to advanced disease	Knee OA is more frequent in female than male rhesus macaques (10.9% vs. 23.5%, respectively)9	No significant sex difference in knee OA prevalence in cynomolgus monkeys11
Prevalence of knee OA in females relative to reproductive status	Postmenopausal women show higher prevalence of OA than premenopausal women36,37	Post- and peri-menopausal females show higher prevalence of knee OA than pre- menopausal baboons	Lumbar vertebrate OA is more common in postmenopausal monkeys than premenopausal ones49	Ovariectomized monkeys were examined with respect to knee OA, but not compared to intact females50
Osteophytes	More prevalent in older individuals than younger ones44	Higher prevalence in older baboons than younger ones	Associated with joints with limited passive excursion capabilities and with radiographic OA8,21	Osteophytes present in monkeys with knee OA11
Gross pathology/ Macroscopic assessment of OA	Five OA stages in modified Outerbridge classification based on cartilage33	Four OA stages (unaffected, mild moderate, advanced) based on cartilage degradation	Four OA stages (normal, mild, moderate, severe) applied to knees of rhesus macaques21	Gross anatomy examined on specimens but the grading system is unclear11
Histology	OARSI grading system47	OARSI grading system appears to work for baboons	Modified Mankin grading scheme applied to histology from knee joint21	Semiquantitative histological grading scheme applied to cynomolgus monkeys11
Radiographic or MRI evidence of OA	Assessment typically based on Kellgren and Lawrence34	Radiographic diagnosis based primarily on osteophytes	OA diagnosed from MRI using osteophytes, articular cartilage thickness, joint space21	Radiographic evidence of knee OA in cynomolgus monkeys50
Symptomatic evidence of OA	Inflammation, pain, stiffness, and loss of joint mobility2	Based on weight loss, reduced range of motion, & crepitation in knee joint; also limited observational data on baboons dragging their legs	Obvious disability and gait abnormalities with advanced OA; also studies on passive joint excursions reveal OA in knee joint9,18	Some older animals were observed to have a stiff gait and/or a limp50