Computed tomography based distal femoral morphology and comparative multi-implant total knee replacement fit analysis...

Accurate medio-lateral sizing of the distal femur during total knee replacement (TKR) is essential to optimise implant fit and avoid over- or under-hang, which have been associated with suboptimal outcomes. National guidance supports implant standardisation within hospitals, however, the appropriateness of using one system for a given population remains uncertain.

Retrospective analysis of the most recent 90 male & 90 female CT knee scans performed on adult knees in a single UK hospital were analysed to obtain distal femoral mediolateral (ML) and anteroposterior (AP) measurements from simulated distal femoral resections. Optimal femoral component sizes were assessed utilising a Euclidian best-fit model for five common TKR systems. Mediolateral over- or under-hang was calculated for each knee. Institutional approval was obtained by the local clinical audit review panel.

In 180 knees, there was a statistically significant difference in mediolateral fit between implant systems (p < 0.001). The magnitude and direction of mismatch varied between implant designs, with absolute ML difference ranging from 1.78 mm to 2.08 mm. No significant difference was observed in absolute mismatch between sexes (p = 0.648), however, male knees demonstrated a tendency towards under-hang and female knees towards over-hang (p < 0.005). Presence of multiple implant systems significantly reduced mismatch for any given knee.

Choice of implant significantly influenced mediolateral femoral fit in our population. These findings raise questions regarding the universal suitability of a single femoral component system for all patients and support consideration for local population morphology when implementing implant standardisation policies. The findings suggest that having multiple implant systems on the shelf may be beneficial.