Preservation of the Constitutional Coronal Plane Alignment of the Knee Phenotype in Varus and Neutral Knees Is Associated With Improved Early Functional Recovery: A Prospective In-Office Gait-Analysis.

INTRODUCTION: The coronal plane alignment of the knee (CPAK) classification provides an objective framework to describe alignment changes after total knee arthroplasty (TKA). Although preserving the native phenotype improves intraoperative soft-tissue balance in varus and neutral knees, its functional benefits remain uncertain. We therefore evaluated whether preserving the preoperative CPAK phenotype in varus and neutral knees is associated with superior early postoperative gait patterns following TKA. METHODS: We prospectively enrolled 44 patients who had varus and neutral coronal alignment who underwent robotic-assisted TKA performed by five fellowship-trained surgeons. Spatiotemporal gait parameters were evaluated preoperatively and at six weeks postoperatively using a pressure mat that captured velocity, cadence, step length, and support time. Patients were grouped according to whether their postoperative alignment preserved or altered their native CPAK phenotype, as measured in long-leg biplane radiographs. Between-group differences were assessed using analysis of covariance (ANCOVA) adjusted for confounding and baseline gait values. RESULTS: Of the 44 patients, 21 (47.7%) had their native CPAK phenotype preserved, and 23 (52.3%) experienced a phenotype change. Preserving CPAK was associated with significantly faster postoperative walking velocity (+11.7 cm/second, P = 0.01), higher cadence (+7.0 steps/minute, P = 0.02), longer single-limb support (+1.5%, P = 0.003), and shorter step time (P = 0.02) compared with patients whose CPAK phenotype changed. Pre-to-postoperative gait changes analysis further confirmed this pattern: the Changed group demonstrated significant reductions in walking velocity (P = 0.04) and cadence (P = 0.01), along with increased step time (P = 0.02), whereas the Unchanged group showed significant improvements in step length (P = 0.02), greater single-limb support (P < 0.01), and reduced double-limb support (P < 0.01). CONCLUSION: Preserving the native CPAK phenotype after TKA is associated with improved early gait metrics, suggesting a potential biomechanical advantage of restoring constitutional alignment. These findings should be confirmed in larger cohorts with longer-term follow-up.