Abstract
Introduction
In Total Knee Arthroplasty (TKA) a proper choice of the implant size is mandatory in order to guarantee the success of the prosthesis, although the tribological behavior TKA is strongly influenced by the implant design.
Retrieval analysis of failed total knee prosthesis is essential to investigate the wear mechanism leading to osteolysis and loosening of the implant. Assessments from retrieval studies constitute crucial information in the effort to improve prosthesis functionality and reduce the risk of revision. The aim of the present study was to investigate the correlation among different implant sizes of retrieved TKA and patients' variables such as Body Mass Index (BMI) in terms of surface modifications and morphology change, in order to examine prosthesis properties and performances. In particular, this study can improve the understanding of the tribological behavior of total knee prosthesis and it can help the surgeon to select the best implant size of TKA considering patient's variables.
Methods
Twelve retrieved total knee prostheses of the same design but with different sizes were investigated. These prostheses were all cemented, fixed and posterior stabilized. These prostheses were explanted from 12 patients after a mean of 3.2 years (from 1.1 to 7.4 years). These patients had undergone a primary TKA at our hospital between 2005 and 2010; there were 10 women and 2 men with a mean age of 68 years (ranging from 48 to 77 years) at implantation. A qualitative assessment of wear patterns and surface damages was performed on femoral components and polyethylene inserts. Roughness analyses were obtained on femoral components to assess surface modifications. Surface roughness of the metallic femoral components was performed with a contact rugosimeter. Following an internal protocol, thirty measurements were acquired from each condyle. Two roughness parameters were take into account: Ra (the Mean Roughness, i.e. the arithmetical mean value of the deviations of the roughness profile about the centre line) and Rsk. (i.e. the skewness, indicates the prevalence of peaks or valleys and quantifies the asymmetry of the profile variation from the mean line). Prostheses time in-vivo and patient details were known.
Results
Results from roughness studies were compared among the specimens and then matched. In Figures 1 and 2 there are showed the Ra and Rsk values measured on the retrieved femoral prosthesis. The correlation between implant size, surface roughness and morphological alterations were found and showed that prosthesis size is a significant factor on the TKA overall performance. Moreover, differences were highlighted through the specimens characterized by different time in-vivo.
Discussion
No previous study, to the best of authors' knowledge, was addressed to examine the implant size of retrieved total knee prosthesis in terms of surface and morphological modifications. The present study, however, has some limitations due to the small number of retrieved TKAs and the lack of information on the level of activity of the considered patients. This study can give a novel insight into tribological mechanisms leading to knee prosthesis failure and it can also offer indications for improving its functionality.
