gms | German Medical Science

Objectives: UKA is a valid and less invasive alternative to TKA for well-selected patients presenting single-compartment knee degeneration.

Nowadays both Fixed Bearing (FB) and Mobile Bearing (MB) UKAs designs are available on the market, and different meta-analyses have demonstrated that both prostheses provided excellent clinical outcomes and survivorship in patients with UNI knee OA.

However, each design is based on the selection of different design parameters, and each factor has its own effect on the overall knee biomechanics. Therefore, the aims of this study were to identify the main design and surgical parameters for FB and MB UKA and to analyze their effects on knee performance.

Methods: The analysis of this study were based on a previously validated and published knee finite element model. This method is adopted as it allows to perform precise biomechanical analysis, providing the possibility to identify the effects of the different configurations on the same bone geometries (a comparison that cannot be investigated in vivo nor in cadaveric bones).

For both MB and FB UKA, five design parameters were considered: poly thickness, tibial component material, friction coefficient, Antero-posterior slope, and tibial bone cut thickness. Each parameter was analyzed in the study considering clinical relevant values.

Two control models were defined based on the conventional features for both implants.

A total of 216 configurations were analyzed, considering each possible different parameters combinations, both at 0° and 90° of flexion.

The results of the analysis were evaluated in terms of medial tibio-femoral contact area and Von Mises stress in the polyethylene and in the tibial bone stress. For each configurations, the results were compared with the one determined for the control configurations used as reference.

Results and conclusion: Among the five different analysed parameters, bearing thickness, tibial bone cut, and slope angle are the most sensitive parameters, for both implants, in terms of change in bone and implant stress. However, the different implants show a clear difference in the sensibility of the design parameter, as reported in Figure 1 [Fig. 1].

The FB UKA induces more relevant variation in the polyethylene insert, both in terms of polyethylene stress and contact area, the MB UKA influence more the bone stress especially proximally and laterally.

Any change in the design parameters induced a variation in terms of poly and bone stress in comparison with the control configuration.

For both MB & FB, the effect of the slope is the strongest one and therefore surgeons should be careful with too much slope, especially when it is combined with an error in the tibial cut.