Fixation of trochanteric hip fractures. A cadaver study of static and dynamic loading

Human cadaveric femora were subjected to static and uniaxial dynamic load applied on the femoral head by a simulator. By two transducer-mounted aluminium rings attached to the bone, the static and the dynamic load causing an elastic deformation of 1 mm in the trochanteric region was assessed. A trochanteric fracture was then produced and stabilized by one of three fixation devices, after which the test was repeated. The unfractured femora had the most rigid appearance (static load, 25.9 KN/mm; dynamic load, 33.1 KN/mm). Of the fractured and stabilized specimens, the Jewett nail-plate gave the most rigid fixation (static load, 5.4 KN/mm; dynamic load, 11.5 KN/mm). The least rigid femora were those stabilized by the dynamic Nolok (static, 4.7 KN/mm; dynamic, 9.2 KN/mm) and Hansson (static, 3.2 KN/mm; dynamic 6.1 KN/mm) telescoping devices. Because of the viscoelastic properties of bone, the load applied in a hip simulator should be dynamic; otherwise, the ability of the device to withstand in vivo loading might be underestimated.