Intraoperative joint line assessment in Oxford UKA: quantitative analysis and influencing factors.

Abstract

In Oxford unicompartmental knee arthroplasty (UKA), the joint line (JL) may shift distally because of flexion gap balancing and distal femoral resection. However, no study has directly quantified this. A total of 217 knees from 151 patients who underwent Oxford medial UKA were included in this study. The intraoperative joint line difference (JLD) was measured before and after implantation using a custom device. Radiographic measurements included the LDFA, HKA, and posterior slope. The correlation between JLD and radiographic parameters and the last spigot size (LSS), which represents femoral resection depth, was evaluated. The mean JLD was 2.7 mm. JLD was moderately negatively correlated with LSS (r = -0.431, p < 0.001), whereas correlations with LDFA and posterior slope were not significant. JLD was primarily influenced by the amount of distal femoral resection, whereas its associations with alignment-related parameters were generally weak. Despite the gap-balancing approach in Oxford UKA, the joint line was largely preserved. JLD was primarily influenced by the amount of distal femoral resection, whereas its associations with alignment-related parameters were generally weak, suggesting an independent adjustment of resection depth without altering the distal femoral alignment.