Simulated postoperative weight-bearing after fixation of a severe osteoporotic intertrochanteric fracture

Unstable intertrochanteric fractures in elderly patients are often associated with a high rate of postoperative complications. The operative procedure used has a great influence on patient outcome, even going so far as to influence mortality rates. Postoperative weight-bearing is also a controversial issue in terms of early rehabilitation and fracture healing. This study uses biomechanical tests and finite element analyses to evaluate the stability of severe osteoporotic intertrochanteric fractures fixed with an Asian proximal femur intramedullary nail antirotation system (PFNA-II). 17 synthetic femoral bones were used for simulating the fracture pattern (AO/OTA type 31-A2) and subsequent fixation. Acetabular loading was manually increased in 100 N increments from 200 N to 1800 N, or until the point of failure. The load applied and number of cycles to failure were recorded and used as inputs to the finite-element analysis. The femur-implant construct had a maximum load to failure of approximately 900 N. The results also revealed the head part had a relative varus displacement to the shaft part. The vertical displacement of the head part is 9.30±0.38 mm (range 9.96-8.91 mm) and transversal displacement is 5.21±0.26 mm (range 5.64-4.91 mm). For securing unstable intertrochanteric fractures, implants are typically designed to substitute as a major weight-bearing structure and to immobilize the fracture. This is particularly important in osteoporosis bone, where the bone is already weakened and susceptible to further damage. This study found that an early weightbearing load of 900 N (1.45 times body weight) can be recommended for postoperative rehabilitation.