Large multiplanar changes to native alignment have no apparent impact on clinical outcomes following total knee arthroplasty.

PURPOSE: This study sought to examine if achieved postoperative alignment when compared to the native anatomy would lead to a difference in Patient Reported Outcome Measures (PROMs), and whether the achieved alignment could be broadly categorised by an accepted alignment strategy.

METHODS: A retrospective cohort study of prospectively collected data on patients undergoing single primary or bilateral simultaneous total knee arthroplasty (TKA) was carried out. CT scans were used to determine the mean change ("delta values") between the pre and postoperative; hip-knee-ankle angle, lateral distal femoral angle, medial proximal tibial angle and femoral implant rotation. Femoral implant flexion and tibial implant slope were measured postoperatively. The primary outcome was the relationship of the variables to the change in KOOS pain subscale after one year. The secondary outcome was the number of knees which could be categorised postoperatively to an alignment strategy, and the mean PROMs in each cohort.

RESULTS: A total of 296 knees in 261 patients were available for analysis. With regards to the primary outcome, the delta values for each variable did not demonstrate any association with the change in knee injury and osteoarthritis outcome score (KOOS) pain score. Approximately 46% of knees could not be categorised to an alignment strategy based on postoperatively measured alignment, with no significant difference between each cohort with regards to the change in KOOS Pain score.

CONCLUSION: Achieved alignment does not consistently match accepted alignment strategies, and appears to confer no benefit to clinical outcomes when the native anatomy is most closely approximated, nor results in poorer outcomes in outliers. This study highlights the importance of routine three dimensional pre and postoperative imaging in clinical practice and for the valid analysis of outcomes in studies on alignment.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.