This retrospective study examined the relationship between the mechanical axis throughout a functional arc of motion and functional outcome scores in patients undergoing computer-assisted navigation-based total knee arthroplasty (CAN-TKA) at 6-year follow-up.
The Stryker eNact Precision Knee Navigation System was utilized to obtain pre- and postoperative alignment measurements throughout the functional arc of motion. Patients were contacted via telephone and asked to complete the Short Form-12 and Western Ontario and McMaster Universities, which have been demonstrated to be reliable, valid, and sensitive assessment tools in this patient population. Statistical analysis was performed to determine the correlation between arc alignment and patient-reported functional outcome measures.
A total of 47 patients at a mean of 76.1 (±6.3)-month follow-up and mean age of 65.9 (±7.9) years were surveyed. No correlation was found between the postoperative alignment or degree of intraoperative correction and the functional outcome scores. In a planned subgroup analysis of patients with a mean functional arc alignment greater than 3° from neutral, mean intraoperative degree of correction correlated with decreasing physical function (Spearman's ρ = 0.772, p = 0.04) and mean postoperative arc alignment positively correlated with increasing stiffness (ρ = 0.798, p = 0.03).
This study suggests that patients undergoing CAN-TKA with mean functional arc range of motion greater than 3° may be at increased risk for suboptimal patient-reported functional outcomes. This study also illustrates the ability of CAN-TKA to measure the varus or valgus alignment of the knee throughout the entire range of motion.