Three-year follow-up of changes of cortical bone thickness after implantation of Endo-Exo-Prosthesis (EEP) for transfemoral amputees

INTRODUCTION: Transcutaneous Osseointegrated Prosthetic Systems (TOPS) offer a good alternative for patients who cannot be satisfactorily rehabilitated by conventional suspension sockets. The Endo-Exo-Prothesis (EEP, ESKA Orthopaedic Handels GmbH®, Deutschland) is the most implanted TOPS in Germany. Previous studies have shown that cortical thickness increases after implantation of TOPS. The aim of this study is to determine changes of cortical thickness in relation to the time after implantation of the Endo-Fix-Stem. PATIENTS AND METHODS: All transfemoral amputees treated by EEP from 2007 to 2013 were operated by the last author of this study. X-ray images of 4 follow-up intervals (postoperative, 3 months, 12 months, 3 years) were analyzed retrospectively. The femoral residuum was divided into 3 sections (proximal, middle, distal) with 2 measuring points in each section: medial and lateral. Cortical thickness was measured at these 6 points and compared at regular intervals using the Friedman test for non-parametric dependent variables. RESULTS: Thirty-seven patients with 40 implants were included. The average age was 52.2 years (30–79 years). 83.7% of the patients were male. No statistical significance could be shown for any of the measuring points of the femoral residual (proximal medial, proximal lateral, middle medial, middle lateral, distal medial, distal lateral) among the mean values of the cortical thickness at the different follow-up times (p > 0.05 for all measuring points). Cortical remodeling processes (> 1 millimeter (mm)) occurred in all implants despite a missing statistical significance. Hypertrophy could be confirmed for 42.5% and atrophy for 37.5%. Twenty percent of the cases showed a parallel occurrence of both entities. Cortical changes greater than 5 mm were only observed at the distal end of the femur. CONCLUSION: Even if our results did not show any significant difference, it can be deduced that the osseointegration process leads to a remodeling of the bone structure, both in terms of increased bone formation and bone resorption. However, it has not yet been conclusively clarified which processes lead to hyper- or atrophy. The force transmission between prosthesis and bone and the facultative bacterial colonization of the stoma are still the main factors which may be responsible for the bone remodeling processes.