Femoral External Rotation Adjustment Improves Patellar Tracking but Does Not Affect Short-Term Clinical Outcomes in Robotic-Assisted Functional-Alignment TKA

<title>Abstract</title> <p>Background Femoral rotational adjustment is a key intraoperative variable in robotic-assisted total knee arthroplasty (TKA) and may influence patellofemoral mechanics, soft tissue balancing, and anterior compartment morphology. However, the clinical and radiographic implications of individualized rotational adjustment remain incompletely understood. This study aimed to evaluate the effects of femoral external rotational adjustment on patellofemoral alignment, soft tissue release, anterior compartment morphology, and short-term clinical outcomes following robotic-assisted TKA. Methods A retrospective analysis was performed on 84 varus knees undergoing robotic-assisted TKA. Patients were stratified according to the magnitude of femoral external rotational adjustment into three groups: no adjustment (0°, n = 26), ≤ 2° adjustment (n = 33), and &gt; 2° adjustment (n = 25). Radiographic assessments included postoperative posterior condylar angle (PCA), patellar tilt, lateral patellar displacement, and changes in anterior femoral morphology (ΔAPD, ΔAFO, and ΔPFJD). Associations between rotational adjustment, deformity severity, and soft tissue release were evaluated. Multivariable linear and logistic regression analyses were performed to identify independent predictors of patellofemoral alignment, soft tissue release, and postoperative understuffing. Clinical outcomes were assessed using WOMAC scores. Result Rotational adjustment independently improved lateral patellar tracking but not patellar tilt. Multivariable linear regression demonstrated that rotational adjustment was independently associated with reduced lateral patellar displacement (β=-0.150, P = 0.043), whereas patellar tilt was primarily determined by its preoperative value (β=-0.596, P &lt; 0.001). Patients requiring greater rotational adjustment exhibited more severe preoperative varus deformity, reflected by lower HKA values (P = 0.034). Soft tissue release rates increased progressively across groups (23.1%, 33.3%, and 56.0%, respectively; P = 0.044). However, multivariable logistic regression identified preoperative HKA, rather than rotational adjustment, as the only independent predictor of soft tissue release (OR = 0.402, P &lt; 0.001). No significant predictors of postoperative understuffing were identified. WOMAC scores improved substantially in all groups, with no significant between-group differences at baseline, 3 months, or 6 months postoperatively (all P &gt; 0.05). Conclusions Femoral rotational adjustment in robotic-assisted TKA significantly influences patellofemoral alignment, particularly lateral patellar displacement, through both rotational and anterior femoral structural changes. However, it does not affect anterior compartment stuffing or the occurrence of stuffing. An external rotation adjustment greater than approximately 2° may be required to achieve meaningful improvement in patellar tracking Clinical trial registration Clinical trial number: not applicable.</p>