Effect of lower limb alignment on outcome after lateral unicompartmental knee arthroplasty: a retrospective study

Purpose The objective of this study was to investigate the correlation between lower limb alignment and patient outcomes after lateral unicompartmental knee arthroplasty (LUKA). Methods In this retrospective study, the information of 51 patients who underwent lateral UKA was collected after an average of 27months of follow-up (13 to 60 months). Evaluation indicators include the AKS and WOMAC score. The Kellgren-Lawrence grade is used to evaluate the severity of osteoarthritis, while the hip-knee-ankle (HKA) angle is utilized to measure the valgus angle of lower limb alignment. Result Patients with postoperative valgus (>= 3 degrees) alignment had the best outcomes, while those with varus (<=-3 degrees) alignment had the worst outcomes (p < 0.001). Furthermore, it was noted that patients with preoperative mild valgus (<= 4 degrees) alignment had worse postoperative outcomes than those with severe valgus (>= 7 degrees) alignment (p < 0.05). The study also revealed a positive correlation between postoperative valgus and WOMAC scores (p < 0.001), whereas a negative correlation was observed between the change in valgus angle and WOMAC scores (p = 0.005). Conclusion During follow-ups, we found that lower limb alignment seems to be an independent predictor of postoperative outcomes. It is recommended that more than 3 degrees of valgus alignment should be maintained after LUKA. Surgeons performing lateral UKA should be cautious of overcorrecting alignment, particularly in patients with preoperative mild valgus alignment.