Abstract
Background
Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) introduce significant anatomic modifications and secondary ligament imbalances. A restricted kinematic alignment (rKA) protocol was proposed to minimize these issues and improve TKA clinical results.
Method
rKA tibial and femoral bone resections were simulated on 1000 knee CT-Scans from a database of patients undergoing TKA. rKA is defined by the following criteria: Independent tibial and femoral cuts within ± 5° of the bone neutral mechanical axis and; a resulting HKA within ±3° of neutral. Medial-lateral (ΔML) and flexion-extension (ΔFE) gap differences were calculated and compared with measured resection MA results.
Results
Extension space ML imbalances ≥3mm occurred in 33% of TKA with MA technique versus 8% with rKA, and ≥5mm were present in up to 11% of MA knees versus 1% rKA (p<0.001). Using the MA technique, for the flexion space, higher ML imbalance rates were created by both MA techniques (using TEA or 3°PC) versus rKA (p<0.001). When all the differences between ΔML and ΔFE are considered together: using MA with TEA there were 41% of the knees with <3mm imbalances throughout; using PC this was 55% and using rKA it was 92% (p<0.001).
Conclusion
Significantly less ML or FE gap imbalances are created using rKA versus MA for TKA. Using rKA may help the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range.
