Clinical and finite element analysis of a modular femoral prosthesis consisting of a head and stem component in the treatment of pertrochanteric fractures

Objective: To determine the biomechanical characteristics and potential cli nical efficacy of a cementless modular femoral Prosthesis consisting of a v ariable head (50 to 80 millimeters) and stem (length 120 to 280 millimeters , diameter 10 to 20 millimeters) component in patients with pertrochanteric femoral fracture. Design: Finite element analysis (FEA) of different lengths and diameters of prosthesis components and first clinical prospective study in pertrochante ric femoral fracture. Method: Usings a 3D-CAD program, a model of femoral cortical bone with a pe rtrochanteric fracture was created and combined with a model of the prosthe sis. This model was transferred into an FEA program. After applying a torsi on-bending load of 2,000 N (25 degrees, 45 degrees) on the prosthesis, stre ss distribution in the cortical bone was determined for different lengths ( 160 to 240 millimeters) and diameters (10 and 12 millimeters) of stem. Patients: Twenty-eight patients with pertrochanteric fractures (very unstab le or osteoarthritis) were treated with a modular hip arthroplasty. Complic ations, fracture healing, and results at first follow-up (average 13 months ) were determined. Results: FEA analysis indicated that reduction in stress was less when a pr osthesis with a short stem was used. Shear stress in the interface bone/pro sthesis was not affected by stem length. Prostheses with thin stems produce d higher sheer stresses than those with thick stems. Results of FEA were us ed as the basis for clinical application of the device. None of the patient s died, and all patients were able to walk, although some needed a cane or walker after surgery. There was no increase in thigh pain compared with rep orted pretrauma levels. Radiographs showed subsidence of up to 5 millimeter s in 20 percent of patients. However, all but one prosthesis was stable at follow-up. Fracture healing was achieved in all patients. Conclusions: If proximal fixation of a femoral uncemented stem cannot be ac hieved, stem diameter should provide maximum cortical contact to reduce she er stress. Longer stems do not necessarily provide additional stability. By using this prosthesis and selection method, a good outcome at first follow -up was observed.