We investigated the effect of the location and the number of distal screws in the efficiency of an intramedullary nail implementing the finite element method (FEM). The left proximal femur of a 93-year old man was scanned and two series of full 3D models were developed. The first series, consisting of five models, concerned the use of a single distal screw inserted in five different distal locations. The second series, consisting of four models, concerned the use of four different pairs of distal screws. Each model was analyzed with the (FEM) twice, first considering that the femur is fractured and then considering that the femur is healed. For nails with a single distal screw, stresses around the nail hole were reduced with proximal placement of the distal screw but the area around the nail hole where the lag screw is inserted is stressed more. Furthermore, for nails with a pair of distal screws, placing the pair of distal screws at a specific location is most beneficial for the mechanical behavior of the femur/nail assembly. The distal area of the nail generally gets less stressed when a pair of distal screws is introduced, while the presence of two distal screws far away from each other results in lower proximal femoral head displacements. The stress field at the area of fracture is not influenced significantly by the presence of a single distal screw or a pair of distal screws.
Total hip arthroplasty is nowadays a common treatment for a large number of pathological cases regarding the hip joint and is considered as the most successful orthopedic operation. With the mean age of patients constantly decreasing and the more intense way of life, the need for versatile implant designs has arisen. Currently modular hip implant systems are used extensively in order to compensate for difficult occasions, where offset and version correction are required. In addition to this femoral heads of bigger diameter have been introduced to deal with issues such as dislocation and impingement, although their influence on the mechanical behavior on the bone – implant assembly is not widely documented. Towards this direction a finite element model was generated. Computed tomographies of a cadaveric femur were used as raw data and processed, a Profemur-E system with variable heads was digitized, thus leading to a complete assembly consisting of the femur, the stem, the necks and the femoral heads in the commercial CAD software Solidworks. For typical loading scenarios – the stance phase of the gait cycle – the finite element analysis was performed in ANSYS Workbench. The results showed that the implementation of BFH and the neck version produced an increase in strains and stresses with respect to a normal head of 28mm and a straight neck in areas of clinical interest such as the calcar, the greater trochanter area and the stem tip region, considered responsible for thigh pain.
Total Hip Arthroplasty (THA) is one of the most important procedures in the fields of Reconstructive Orthopaedics. This study aims to present the preliminary results of the clinical and radiological evaluation of patients who have undergone THA with metal bearings, modular necks and big femoral heads and to correlate them with the results of the Finite Element Analysis. In the period from 1/1/2006 until today 90 patients (33 men and 57 women) with mean age 62,4 years have undergone primary THA. The patients were clinically and radiographically evaluated preoperatively, as well as postoperatively, in regular time intervals (1st, 3rd, 6th, 12th month and every year afterwards). The clinical assessment was based on two scales, Harris Hip Score (HHS) and Merle d’ Aubigne (MDA) score, whereas the radiographic on Engh criteria. The mean follow up was 16 months. The mean preoperative HHS and MDA score were 45 and 10,3 respectively, whereas 89 and 16,74 at the last evaluation. The mean Engh score was 16,12. No incidence of dislocation, infection and cup or stem adverse effect occurred. We demonstrate extensively, with respect to the used combination of neck and femoral head, the radiographic findings in the zones of Grün and Charnley, in the areas of the tip of the stem and the calcar, as well as the resulting clinical manifestations. The early clinical and radiological data are in line with the increase in the stresses and strains on the upper part of the femur, which are revealed through the Finite Element Analysis.
