Preoperative flexion contracture influences magnitude of planned resections in robotic-assisted total knee...

Varying degrees of flexion contracture appear commonly in total knee arthroplasty (TKA) patients and can be corrected using increasing distal femoral bone resection. Robotic-assisted (RA) technology aims to avoid ligament release through optimized bony resections. This study evaluated the influence of preoperative flexion contracture on the magnitude of resections surgeons perform to balance knees in RA-TKA.

We reviewed 789 primary RA-TKAs from 2023 to 2024 using cruciate-retaining (CR) implants. The cohort was divided by native flexion deformity into three groups: <0° flexion ("hyperextension", n = 157), 0-9.9° flexion ("minimal contracture", n = 457), and ≥ 10° flexion ("clinically important contracture", n = 175). Mean preoperative flexion contracture was - 3.8, 4.1, and 13.5° for the hyperextension, minimal contracture, and clinically important contracture cohorts, respectively. Demographics, implants, and intraoperative data were collected and analyzed. The arithmetic hip-knee-ankle (aHKA) angle was used to determine native deformity groups for additional subanalyses.

Significant differences were found between cohorts for mean distal femur and proximal tibia resections, with the clinically important contracture group having the largest resections. After accounting for implanted polyethylene thickness, differences in mean tibia resections were quite small, varying by 0.9 millimeters (mm) laterally and 0.7 mm medially. Similarly, the mean distal femoral resection varied by only 1.4 mm laterally and 0.7 mm medially between the hyperextension and clinically important contracture cohorts. Indeed, 85% of cases with clinically important contractures were managed with less than 2 mm of additional distal femoral resection compared to the minimal contracture cohort.

With robotic-assisted TKA, bone resections can be guided by collateral ligament tension in flexion and extension. Our data suggest that surgeons can follow this strategy and successfully address flexion contractures with very small increases in resection magnitudes, which may help to maintain the joint line.