ROBOTIC QUANTIFICATION AND CLINICAL VALIDATION OF SURGICAL STRATEGIES FOR INTRAOPERATIVE EXTENSION DEFICIENCY IN TOTAL KNEE ARTHROPLASTY: DEVELOPMENT OF A PREDICTIVE ALGORITHM

Purpose Intraoperative extension deficiency (IED) following trial implantation in total knee arthroplasty (TKA) must be distinguished from preoperative fixed flexion contracture (FFC). Its optimal management remains poorly quantified and likely depends on patient-specific biomechanical and geometric factors. This study aimed to quantify the mechanical contribution of posterior capsule release (PCR), posterior cruciate ligament (PCL) excision, and incremental distal femoral resection using robotic-assisted measurement, and to develop a predictive model incorporating deformity and femoral geometry. Materials and Methods A two-phase study was performed. A cadaveric robotic-assisted TKA model (29 knees) assessed sequential effects of PCR, PCL excision, and distal femoral resection on extension and laxity. A prospective clinical cohort of 195 robotic-assisted TKAs with IED was then analyzed to validate biomechanical relationships in vivo. A multivariable regression model was constructed to estimate the effect of distal femoral resection on extension correction, incorporating flexion contracture coronal alignment, implant positioning, and femoral size as a geometric scaling factor. Results In the cadaveric model, PCR corrected IED in 36.8% of cases (1.68° ± 1.11°). Distal femoral resection produced 4.3°/mm with an intact PCL and 2.8°/mm after PCL excision. PCL excision alone provided minimal correction (1.1° ± 1.3°). Larger femoral morphology reduced angular gain per millimeter of resection, consistent with geometric scaling effects. In the clinical cohort, distal femoral resection showed a mean effect of 5.8°/mm but demonstrated marked inter-patient variability. Correction sensitivity increased with native flexion contracture (+0.72°/mm per degree) and varus alignment (+0.1°/mm per degree), while femoral size reduced angular response. PCL status was not significant. Conclusions Distal femoral resection is the dominant factor in correcting IED, but its effect is not fixed. It is modulated by deformity severity and femoral geometry, particularly size-dependent scaling of the femorotibial radius. These findings support a nonlinear, patient-specific mechanical model of extension correction and provide a basis for predictive intraoperative decision-making in TKA.