Extreme leg action and hip-joint dynamics in wild primates

We measure how leg actions of cadaver monkeys are transferred within the hip-joint, and we compare physical femoral mobility of wild and captive monkeys in Panama, Costa Rica, and in zoological parks of California. We acquire leg movement data of howler, capuchin and spider monkeys with random 1 second digital photography during 4 months in Central America, and weekly visits for 2 months in California zoos (n=47 wild primates, 1879 focal events; 24 captive primates, 959 focal events). We employ computer software to objectively assess leg angle in regards to flexion, neutral and extension postures of the femur, relative to the hip socket. We apply leg action data to cadaver pelvises in primate bone collections at University of California, Davis, University of Oregon Osteology Lab, and the Denver Museum. Our study reveals that extreme femoral action translates as high diversity of articular contacts within the primate hip joint, and that captive monkeys in artificial habitats have less femoral movements than wild monkeys, with statistical comparisons being: Full leg flexion P = 0.0012; Flexion P = 0.023; Ambulatory as in walking P = 0.075; Extension P = 0.002; and Full extension with leg in line with body P = 0.00011. We speculate that the primate body is built to move in extreme but non-traumatic, wide-ranging appendicular actions. Such movements may help to simulate peripheral articular cartilage, contributing to the longevity of joints, and perhaps extending the life of primates who move in this manner.