Transfemoral Approach in Revision Hip Arthroplasty: A Prospective Analysis of 36 Cases: Radiological and Functional Results at a Minimum 2 Years Follow-up.

Background and Objectives: One of the most difficult aspects of hip revision is to remove the stem from the femoral canal with or without cement while maintaining the maximal amount of bone stock to obtain the best possible press-fit of the revision prosthesis. The transfemoral approach ensures direct access to the medullary canal so that the content removal is completed under direct control, while protecting the bone. This type of approach is particularly efficient for special conditions, such as deformation of the proximal femoral region, broken stems, or the presence of cement over a long distance distal to the prosthesis. The aim of this study was to evaluate the main advantages of transtrochanteric approach in hip revisions. Materials and Methods: Our series included 36 revisions performed using the transfemoral approach. We have analyzed the following postoperative radiological aspects: the length of the fixation zone distal to the osteotomized bone fragment (OBF), the gap between the OBF and the diaphysis, stem subsidence over time, and OBF consolidation. Results: The results were very good, both in terms of the rate of intraoperative complications and postoperative evolution. The fixation zone length was 4.2 cm on average (range: 2 to 5.8 cm). The distal gap between the OBF and the diaphysis was 1.2 cm on average (range: 0 to 2.3 cm). Stem subsidence was noted in four cases (11.1%). In all cases, stem subsidence occurred between three and six months and was 6 to 8 mm without affecting hip stability. OBF consolidation was radiologically confirmed for all cases at one year follow-up. Clinical assessment based on the Harris Hip Score showed an overall improvement from 43.2 preoperatively to 79.7 at 12 months and 83 at two years, respectively. The most important rate of progress was between 6 months and 12 months. Conclusions: The transtrochanteric approach has been shown to be very efficient for hip revisions. Understanding the hip biomechanics, applying a less aggressive surgical technique, and using efficient fixation methods such as cables significantly improved the results.

Periprosthetic bone remodelling in total knee arthroplasty.

INTRODUCTION: The clinical studies have shown that the displacement of the prosthesis components, especially of the tibial one is higher during the first year, after which it reaches an equilibrum position compatible with a good long term functioning. This displacement takes place due to bone remodelling close to the implant secondary to different loading concentrations over different areas of bone. MATERIAL AND METHOD: Our study implies a simulation on a computational model using the finite element analysis. The simulation started taking into account arbitrary points because of non-linear conditions of bone-prosthesis interface and it was iterative.. A hundred consecutive situations corresponding to intermediate bone remodelling phases have been calculated according to given loadings. Bone remodelling was appreciated as a function of time and bone density for each constitutive element of the computational model created by finite element method. For each constitutive element a medium value of stress during the walking cycle was applied. RESULTS: Analyse of proximal epiphysis-prosthesis complex slices showed that bone density increase is maintained all over the stem in the immediately post-operative period. At 10 months, the moment considered to be the end of bone remodelling, areas with increased bone density are fewer and smaller. Meanwhile, their distribution with a concentration toward the internal compartment in the distal metaphysis is preserved. CONCLUSIONS: After the total knee arthroplasty the tibial bone suffered a process of remodelling adapted to the new stress conditions. This bone remodelling can influence, sometimes negatively, especially in the cases with tibial component varus malposition, the fixation, respectively the survival of the prosthesis. This process has been demonstrated both by clinical trials and by simulation, using the finite elements method of periprosthetic bone remodelling.