Why do we have kneecaps on our legs but no “armcaps” on our arms?

Question

Why do we have kneecaps on our legs but no “armcaps” on our arms?

In: 3724

Answer 1

Human limbs are modified (evolved) from their quadrupedal terrestrial antecedents, most of which also have patellas but no equivalent sesamoid on the elbow.
These quadrupeds bear most of their body weight on their forelimbs, while rear limbs are more for propulsion.
Pronation/ supination in thoracic limbs becomes more important in primates, but power remains critical in pelvic limbs for bipedal primates (humans)
Without a patella, the ligaments of the quadriceps group would not tolerate the tension across the knee joint required to propel us and other species in ordinary locomotion.