1Department of Anatomical Sciences, Stony Brook University School of Medicine, 2Department of Kinesiology, University of Massachusetts Amherst
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Changes in lower limb joint morphology have played major roles in the evolution of hominin locomotion. Reduction in ankle range of motion and stabilization of the tarsal joints were necessary to transform the lower limb into an efficient lever for bipedalism. Ranges of joint motion in hominids are usually inferred from osteological landmarks on skeletal elements; however, such osteological correlates of joint motion need to be verified via in vivo studies of joint motion.
2D cineradiographs of the knee, ankle, and foot were taken during passive flexion/extension bouts in three chimpanzees (Pan troglodytes, ages 4-5). Osteological markers were digitally tracked in order to determine ranges of motion and instantaneous joint centers (IJCs).
Range of knee motion was near or within that of modern humans. However, extreme flexion in chimpanzees was accomplished by a posterior ‘rolling’ of the femoral condyles on the tibia, as evidenced by a posterior movement of the IJC. Ankle range of motion was double that seen in a human sample, and greater than the range predicted by some osteological metrics. In particular, maximum plantarflexion did not appear to be limited by the talar tubercles. Midtarsal motion exhibited greater complexity than previous studies have suggested. In light of these results, osteological features used to infer joint mobility in the hominid knee, ankle and foot may need to be reevaluated. These results will benefit musculoskeletal modeling studies of chimpanzees and extinct hominins by allowing more accurate reconstructions of ranges of motion and estimation of muscle moment arms.
This research was supported by the NSF, BCS 0935321.