There is considerable evidence that patellofemeral pain dosorder, chrondromalacia patellae, "runner's knee" and patella subluxation were rare in humans until all classes of humans commenced wearing shoes with the European Renaissance. Footwear use is associated with increase in stride length which results in greater extension of the knee prior to the weight-bearing phase of locomotion. This results in poor tracking of the patella in the trochlea of the femur. This causes micro-fissures and fractures of the articular cartilage of the patella and femur when patellae tracking is poor, and catastrophic events when subluxation is complete.
These disorders are treated in shod individuals be conscious shortening of stride length. A more certain solution is barefoot locomotion since plantar sensory feedback when barefoot induces locomotion with a shorter stride length and greater knee flexion.