The Biomechanical Effect of Notch Size, Notch Location, and Femur Orientation on Hip Resurfacing Failure.

IEEE transactions on bio-medical engineering

PubMedID: 23481682

Morison Z, Olsen M, Higgins GA, Zdero R, Schemitsch EH. The Biomechanical Effect of Notch Size, Notch Location, and Femur Orientation on Hip Resurfacing Failure. IEEE Trans Biomed Eng. 2013;.
For hip resurfacing, this is the first biomechanical study to assess anterior and posterior femoral neck notching and femur flexion and extension. Forty-seven artificial femurs were implanted with the Birmingham Hip Resurfacing (BHR) using a range of notch sizes (0, 2, 5 mm), notch locations (superior, anterior, posterior), and femur orientations (neutral stance, flexion, extension). Implant preparation was done using imageless computer navigation, and mechanical tests measured stiffness and strength. For notch size and location, in neutral stance the unnotched group had 1.9 times greater strength than the 5-mm superior notch group (4539 vs. 2423 N, p=0.047), and the 5-mm anterior notch group had 1.6 times greater strength than the 5-mm superior notch group, yielding a borderline statistical difference (3988 vs. 2423 N, p=0.056). For femur orientation, in the presence of a 5-mm anterior notch, femurs in neutral stance had 2.2 times greater stiffness than femurs in 25-deg flexion (1542 vs. 696 N/mm, p=0.000). Similarly, in the presence of a 5-mm posterior notch, femurs in neutral stance had 2.8 times greater stiffness than femurs in 25-deg extension (1637 vs. 575 N/mm, p=0.000). No other statistical differences were noted. All femurs failed through the neck. The results have implications for BHR surgical techniques and recommended patient activities.