Toward the interpretation of the combined effect of size and body weight on the tribological performance of total knee prostheses

Abstract

Purpose The research questions of the present study were: (1) Is total knee prosthesis wear behaviour influenced by implant size, body weight and their combined effect? (2) Are these findings significant and helpful from a clinical point of view? Methods Two very different sizes of the same total knee prosthesis (TKP), previously tested with ISO 14243 parameters, were tested on a knee simulator for a further two million cycles using a modified ISO 14243 load waveform. Roughness examination was performed on the metallic components. Gravimetric and micro-Raman spectroscopic analyses were carried out on the polyethylene inserts. Results The average volumetric mass loss was 69 ± 3 mm 3 and 88 ± 4 mm 3 for smaller and bigger size, respectively. Bigger TKPs are little influenced by an increased load, while the wear trend of the smaller TKP showed a redoubled slope, and more significant morphology changes were observed. However, the two sizes seem to behave similarly when subjected to a load increase of 15 %; the slope of the volumetric mass loss trend was comparable for the two sets of inserts, which did not appear significantly different also at the molecular level. Roughness average parameters of the lateral femoral condyle support this evidence. Conclusions It can be asserted that the body weight and implant size are relevant to the understanding of TKP wear behaviour. A post-implantation body weight increase in a patient with smaller knee dimensions could results in more critical effects on prosthesis long-term performance.

Combined effect of the body mass index and implant size on the wear of retrieved total knee prostheses

“…The Raman analyses confirmed the results obtained in in vitro tests (Battaglia et al, 2014;Affatato et al, 2013;Tozzi et al, accepted for publication); in our previous studies we investigated the effect of the implant size and applied load on the morphology changes induced by wear on UHMWPE inserts. Raman spectroscopy showed a more significant polymer degradation in the smaller prostheses, suggesting that a lower contact area is responsible for a higher wear at the molecular level.…”

“…As already demonstrated in-vitro, the body weight and implant size are relevant factors to the understanding of TKA wear behaviour (Battaglia et al, 2014;Affatato et al, 2013). The main goal of this study was to evaluate the combined effect of BMI and implant size on wear in order to better understand the TKA performances.…”

“…In contrast, a recent study has found that post-operative complication rates were not significantly high for morbidly obese patients (Napier et al, 2014). Although the tribological behaviour of a TKA is strongly influenced by the implant design (McEwen et al, 2005;Battaglia et al, 2014;Affatato et al, 2013), a proper choice of the implant size is mandatory in order to guarantee the success of the implant and to respect the bone stock of tibial plateau and femoral condyles. The knee is characterized by a complex morphometric relation and, nowadays, there are no studies about the combined effect of patient weight and knee size on wear.…”

“…The knee is characterized by a complex morphometric relation and, nowadays, there are no studies about the combined effect of patient weight and knee size on wear. In fact, the patient weight does not simply reflect the knee size; it is not surprising to observe patients with the same weight but very different knee sizes (Battaglia et al, 2014;Glave et al, 2014;Cimmino et al, 2013).…”

“…Moreover, UHMWPE exhibits the so-called cross-shear effect and its wear cannot be simply predictable by Archard's equation (Battaglia et al, 2014;Archard and Hirst, 1956;Mazzucco and Spector, 2003).…”