Knowles pinning of experimental femoral neck fractures: biomechanical study.

This experimental study demonstrates the rigidity and durability of Knowles pin fixation of femoral neck fractures. Embalmed proximal femora were utilized. A "fracture' was created by osteotomy, then reduced and fixed with Knowles pins. Four groups of reduction and pin configurations were created ("optimal reduction and pinning,' "poor reduction,' "inadequate pinning,' and "comminution') to simulate the clinical situation. With the Materials Testing Systems(MTS) machine, 3 months of walking by a patient with a femoral neck fracture were simulated. Results suggest that Knowles pinning of a femoral neck fracture can provide adequate support for immediate full weight-bearing ambulation until fracture healing. Stability and durability of fixation are compromised by loss of cortical bone support by "comminution,' short nonparallel pins not engaging the subchondral bone, and osteoporosis evidenced by a low Singh index.