Quantitative Study of Elbow Ligaments in Modern Humans (Homo sapiens) and Common Chimpanzees (Pan troglodytes)

We have analyzed the elbow ligaments in humans and chimpanzees in order to identify differences that may be related to the use of the upper limbs in these two species. Specifically, we expected to find adaptations to arboreal locomotion and knuckle-walking in chimpanzees and adaptations to non-weight-bearing manual activities in humans.

We dissected seven upper limbs from extant humans and seven from common chimpanzees and performed anatomical and qualitative analyses of the elbow ligaments. Subsequently, we calculated the absolute and relative size of the mass of these ligaments in the two species.

The anatomical description of the elbow ligaments was very similar in the two species. The quantitative analysis found a relatively larger anterior fascicle of the ulnar collateral ligament (UCL) in humans and a relatively larger lateral ulnar collateral ligament (LUCL) in chimpanzees.

The different ways humans and chimpanzees use their upper limbs could explain the quantitative differences we observed in the elbow ligaments. We can thus hypothesize that the more developed anterior fascicle of the UCL in humans may be related to a more pronounced carrying angle in the upper limb and to the valgus forces acting on the elbow during manual tasks. In contrast, the larger LUCL in chimpanzees may help stabilize the elbow during arboreal locomotion and during the support phase of knuckle-walking.