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In this series, Dr. Deb Bennett examines the equine hind limb. In this installment, Bennett explores the stifle.
At first glance, the stifle joint appears to be a huge mistake — the worst-designed part of the musculoskeletal system.
Unlike the shoulder joint, hip socket, hock, elbow, intervertebral joints or the coffin joint, the articular surfaces of the femur and tibia, which face each other to form the stifle joint, do not closely correspond in shape. There is no neat ball-and-socket fit, no tight tongue and groove geometry and because of that the joint appears to have been “post-engineered” with a whole slew of auxiliary rims, pads, and straps that work to stabilize it and hold it together (Figures 1 and 2).
In terms of embryology and evolutionary history, the stifle joint’s design is indeed something of an “afterthought.” Lungfishes (Figure 3), have several modes of survival under conditions of drought, all of which have been…