Does femoral strain distribution coincide with the occurrence of cervical versus trochanteric hip fractures? An experimental finite element study.

The objective of this experimental finite element (FE) study is to test the hypothesis that strain distributions coincide with the occurrence of cervical versus trochanteric hip fractures during loading conditions simulating a sideways fall, and that the cervical versus trochanteric principal strain ratio predicts different fracture patterns. Cadaver femora (female, 83 +/- 9 years) were CT scanned and mechanically tested simulating a fall. Thirteen cervical and 13 trochanteric fracture cases were selected for FE analysis. Principal strain distributions were analysed, and strain ratio epsilon(C)/epsilon(T) for strain patterns over the cervical and trochanteric regions was computed. The ratio epsilon(C)/epsilon(T) in the femora with cervical fractures (mean +/- SD 1.103 +/- 0.127) differed from that in trochanteric fractures (0.925 +/- 0.137) (p = 0.001). The significant difference in the strain ratio between fracture types remained after accounting for femoral neck and trochanteric BMD (p = 0.014), showing that it is independent of BMD. Area under the ROC curve was 0.858 in the discrimination of fracture types. The model predicted the experimental fracture type correctly in 22 of 26 cases. The cervical versus trochanteric region principal strain ratio differed significantly between femora with experimental cervical versus trochanteric fractures, and 85% agreement was achieved for the occurrence of hip fracture types using a simple FE model.