Unicompartmental knee prostheses:in vitrowear assessment of the menisci tibial insert after two different fixation methods

Abstract

Knee osteoarthritis is a complex clinical scenario where many biological and mechanical factors influence the severity of articular degenerative changes. Minimally invasive knee prosthetic surgery, with only a compartment replacement (unicompartmental knee replacement), might be a good compromise between osteotomy and total knee prosthesis. The focus of this study was to develop and validate a protocol to assess the fixation method of the femoral components in mechanical simulation, for pre-clinical validation; the wear behaviour of two different fixation frames was quantified and compared. In particular, two different wear tests were conducted using the same knee simulator, the same load profiles and the same kinematics; two different fixation methods were applied to the femoral sleds (synthetic femur and metal block). Surface characterization on both articulating bearings was performed by a roughness measuring machine and coordinate measuring machine. The wear produced by the tibial inserts using the synthetic femur was considerably higher than the wear registered by the metal-block holder. Roughness measurements on femoral sleds showed a limited number of scratches with high R(t) values for the metal-block set-up; the damaged surface broadened in the case of femoral condyles and tibial inserts mounted on composite bone, but lower R(t) and linear penetration values were measured. The two holding frames showed different wear activities as a consequence of dissimilar dynamic performance. Further observations should be made in vivo to prove the actual importance of synthetic bone simulations and specific material behaviour.

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

“…This wear test was performed on the same aforementioned specimens, using the same simulator, same kinematics and same lubricating conditions used in [30] as recommended by ISO 14243. In the previous study, a simplified gait cycle was reproduced, according to ISO 14243-3 and on the basis of a consolidated internal protocol [32][33][34]. Instead, a new approach has been introduced in this study with regards to the applied load.…”

“…It is well known that UHMWPE is characterised by three phases [33,34]: an amorphous phase, an orthorhombic crystalline one and a disordered third phase. As reported in our previous study [21], the fraction of each phase (α a , α o and α b , respectively) in UHMWPE inserts was evaluated according to the equations developed by Strobl and Hagedorn [35]:…”

Does knee implant size affect wear variability?

“…A simplified gait cycle was reproduced, according to ISO 14243-3 and following an internal protocol of our laboratory [21,[24][25][26]. Load was applied vertically (normal to the tibial tray), ranging from 168 to 2600 N to reproduce a physiological profile.…”

Quantification of in vitro wear of a synthetic meniscus implant using gravimetric and micro-CT measurements

“…Wear testing of total knee replacements (TKR) typically employs simulators, which induce flexion-extension, tibial rotation, anteriorposterior translation, and vertical load, according to ISO-14243. Commonly used simulators include: Shore Western knee simulator (Spinelli et al, 2009;Affatato et al, 2008), Bionix s Knee wear simulator (Haider and Walker, 2005), AMTI-Boston six-station knee simulator (Bourne et al, 2003), The Durham six-station knee simulator (Scholes et al, 2007), and EndoLab four-station servo-hydraulic knee wear simulator (Grupp et al, 2010). Testing of unicompartmental prostheses is more closely related to the current meniscus implant.…”

“…Testing of unicompartmental prostheses is more closely related to the current meniscus implant. It is usually preformed on the same simulators mentioned above, in pairs (medial/lateral), since the simulators cannot allow for the correct motion to be applied if only one condyle is tested (Affatato et al, 2008;Scholes et al, 2007;Spinelli et al, 2009). For this reason, and since only a medial meniscus implant exists, we developed a simulator that can apply the loads and motions of the medial knee compartment without having to test both compartments.…”