# The association between surgeon grade and radiographic implant alignment following oxford unicompartmental knee replacement

## TL;DR

This study compares implant alignment in knee surgeries performed by trainees and consultants, finding that trainees often position components in excessive flexion.

## Contribution

The study identifies specific alignment differences between trainees and consultants in unicompartmental knee replacement surgeries.

## Key findings

- Trainees and consultants showed no significant difference in varus/valgus angles for femoral and tibial components.
- Trainees had significantly greater posterior tibial slope and more outliers in femoral component flexion/extension angles.
- Direct supervision reduced the difference in implant positioning between trainees and consultants.

## Abstract

Unicompartmental knee replacement (UKR) is a technically challenging operation. Component alignment can influence implant longevity and knee function post-operatively. This study aimed to investigate implant alignment following UKR performed by consultants compared to trainees.

100 Oxford UKRs performed by trainees and consultants were analysed. Two blinded surgeons independently assessed post-operative knee radiographs on four parameters: flexion/extension of femoral component, posterior slope of tibial component, and varus/valgus of femoral and tibial components. Logistic regression was performed to predict the probability of implant malpositioning outside the optimal position range.

Median varus/valgus angles for femoral components did not differ significantly between trainees and consultants (p = 0.92), nor did the angles for tibial components (p = 0.43). Posterior tibial slope measurements showed a significant difference between trainees and consultants (7.08° [IQR 5.2–9.30], and 5.35° [IQR 2.65–7.05], respectively; p < 0.01). Median flexion/extension angles for femoral components also differed significantly between trainees and consultants (−14.45° [IQR −19.2 to −9.85] and −10.2°[IQR −13.55 to −6.95], respectively; p < 0.01). A greater proportion of implants positioned by trainees were classified as outliers for this parameter (46% versus 20%, p < 0.01; aOR 5.39, 95% CI 2.05–14.18, p < 0.01). However, no differences in the proportion of outliers was found when trainees were directly supervised by consultants (p = 0.73).

Trainees achieved adequate component alignment within optimal ranges for most parameters however were more prone to positioning the femoral component in excessive flexion. Greater emphasis on achieving optimal flexion/extension positioning of the femoral component during surgical training and direct supervision may improve the outcomes of patients undergoing an Oxford UKR by trainees.