Prayer's fracture: rare cases of knee insufficiency fracture in non-weight-bearing femoral condyle.

Insufficiency fractures are a relatively common sub-type of stress fractures and occur as a result of decreased bone resistance due to underlying conditions such as osteoporosis. Insufficiency fractures of the knee most commonly occur at the central weight-bearing zone of the medial femoral condyle. We present five unusual cases of insufficiency fractures occurring at the posterior non-weight-bearing zone of condyles. After investigating commonalities between these patients, we discovered that all of these patients performed the daily practice of prayer rituals that include high knee flexion. We have chosen to coin this type of fracture a "Prayer's fracture". Considering the mechanics of high knee flexion, transient changes in the weight-bearing zone of knee explain the unusual location of this fracture. We describe these cases, the characteristic imaging appearance, and the probable biomechanics that we believe predispose patients to this type of injury.