The human knee is a deceptively simple hinge joint that flexes and extends the leg. But look closer, and you might call the knee a crazy and improbable Rube Goldberg mechanism, where the femur (thigh bone) balances the weight of the upper body atop the tibia (the larger of the two shin bones). The kneecap or patella, smaller than a mango seed, slides up and down the front of the …
