Optimal intraoperative medial joint gap in extension to prevent flexion contracture following total knee arthroplasty using modified gap balancing technique.

Background: Primary aim to identify the ideal medial joint gap in extension needed to prevent post-operative flexion contracture following total knee arthroplasty (TKA) in varus osteoarthritic knees by the modified gap balancing technique. A secondary aim was to analyze multiple factors that influence knee extension in TKA by modified gap balancing.
Methods: This is a prospective cohort study of 150 patients diagnosed with osteoarthritic varus knee who underwent TKA using the modified gap balancing technique. Operative and clinical records were assessed to determine factors including age, BMI (Body mass index), pre-operative extension angle and the medial extension laxity. Patients were followed for 6-months post-operatively and reviewed for knee extension angle.
Results: Six months final follow-up information was available for 148 patients with an average age of 75.5 years. Pre-operative knee extension and BMI were significantly associated with post-operative knee extension. Post-operative flexion contracture of ≧ 100 was not seen in any of 34 patients with a medial extension laxity ≧ 0 mm who had no pre-existing flexion contracture, and in 1/9 (11.1%) patients with a medial extension laxity ≧ 1 mm who had pre-existing flexion contracture. Conclusions: Pre-operative extension angle and BMI significantly influence the post-operative knee extension angle in TKA using the modified gap balancing technique. A medial extension laxity of at least 1 mm is ideally needed to prevent post-operative flexion contracture in patients with a pre-existing contracture ≧ 100. Level of evidence: Level II; Prospective cohort study.