Robotic quantification of the mechanical effect of corrective manoeuvres for intraoperative extension deficiency in total knee arthroplasty: A cadaveric study.

Purpose: Intraoperative extension deficiency (IED) may arise after trial component implantation during total knee arthroplasty (TKA), a condition conceptually distinct from preoperative fixed flexion contracture (FFC). This study utilised a robotic system to quantify the incremental mechanical effect of sequential surgical actions-posterior capsule release (PCR), posterior cruciate ligament (PCL) excision and incremental distal femoral resections-to correct IED. A secondary objective was to evaluate their impact on manually assessed mediolateral laxity. Methods: Twenty-nine robotic TKAs were performed on 15 fresh-frozen cadaveric specimens. Nineteen knees presented with IED. All knees underwent PCR as the initial corrective manoeuvre. Subsequently, a quasi-experimental design based on laterality was employed to evaluate two sequences: right knees underwent PCL excision followed by up to four 1-mm distal femoral recuts; left knees followed the reverse order. Extension gains and manually assessed mediolateral laxities were recorded after each step. Results: Baseline IED averaged 6.6° ± 4.9°. Posterior capsule release corrected IED in 36.8% of the knees, yielding a mean extension gain of 1.68° ± 1.11°. The mechanical impact of distal femoral resections varied depending on PCL status: when the PCL remained intact, distal femoral recuts produced a substantial mean gain of 4.3° ± 0.6° per millimetre; however, following PCL excision, the gain per millimetre decreased to 2.8° ± 0.8°. PCL excision alone improved extension by a mean of 1.1° ± 1.3°. No significant changes in manually assessed mediolateral laxity at 0° and 90° of flexion were observed across manoeuvres. Conclusions: Robotic quantification demonstrates that the mechanical effectiveness of distal femoral resection is significantly enhanced by an intact PCL. While PCR is an impactful initial step for mild IED, distal femoral recuts provide greater extension gains. These objective data provide the foundation for a structured strategy to guide the intraoperative management of IED in both robotic and conventional TKA. Level of Evidence: N/A (cadaveric).