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Purpose The aim of this study was to evaluate laxity in knees with pre-operative (preop) valgus alignment compared to knees with pre-operative varus alignment after total knee arthroplasty (TKA). Methods This was a retrospective study including 81 patients, with six years follow-up, for pre-operative valgus-or varus alignment of the leg. All patients had been supplied with the same cruciate retaining (CR) TKA with rotating platform. Clinical findings were assessed by KSS, OKS and IKDC 2000 score. Rotational knee laxity was evaluated by a validated instrument (Laxitester®) with 2 Nm torque in 30°flex-ion. Collateral ligament laxity was tested manually in 30°f lexion with a bending moment of approximately5 Nm. Biomechanical results were compared to the contralateral side. Results Thirty-one patients had a preop valgus alignment of 8.96°and 50 patients a varus leg axis of 4.99°in the mean. In the preop valgus knees rotational analysis showed an increased laxity of 10.7°compared to preop varus knees (p=0.001). There was no significant difference in medial (valgus 2.6 mm, varus 2.5 mm) and lateral (valgus 2.8 mm, varus 2.7 mm) laxity. KSS and OKS showed no significant differences in the follow-up results. In the IKDC 2000 objective score 50 % of the preop varus knees and 25.8 % of the preop valgus knees were classified as nearly normal. The difference in the IKDC objective was highly significant (p<0.001). Conclusion Preop valgus knees show a significantly increased rotational laxity but no increased collateral ligament laxity compared to pre-operative varus knees six years after TKA with rotating platform. There is a significant difference in IKDC objective.

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