The influence of extension-flexion gap imbalance on the joint function in primary total knee arthroplasty

Introduction A poorly balanced, unstable, or stiff joint is a major cause of residual pain, dissatisfaction, and revision after total knee replacement (TKA), but the definition of a well-balanced joint remains debatable. The aim of the study was to explore the influence of the knee space and the extensionflexion gap being accurately restored in primary TKA on the knee function and the quality of life of the patient. Material and methods A prospective, single-center, randomized, controlled study was performed for 41 patients with grade 3-4 knee osteoarthritis. (K-L): the first group (n = 21) underwent primary TKA with the method proposed for precise realignment of the extension-flexion gap, the second group (n = 20) underwent standard arthroplasty. The patients had CT scans of the knee performed preoperatively and postoperatively, and VAS scale pain, knee joint scales: OKS, FJS‑12, KSS (pain and function), SF-36 (parameters: PF, RP, BP, GH, VI, SF, RE, MH) were used at 3, 6 and 12 months. Results Comparison of the standing height of the joint space preoperatively and postoperatively showed a high statistical significance measuring about 20.7 % in frontal plane (group 1: 2.06 ± 2.368, group 2: 2.629 ± 2.455, р < 0.001), 28.2 % in the sagittal projection (group 1: 2.657 ± 2.143, group 2: 3.7 ± 1.717, р < 0.001), i.e., the method proposed allowed for more accurate positioning of the extension gap by 20.7 %, the flexion gap by 28.2 % and more accurate positioning of the knee space level. Preoperative and postoperative VAS, OKS, FJS-12 and SF-36 scores showed significant positive dynamics in both groups with no statistically significant difference between the groups. A statistically significant difference was seen in the functional KSS score in the groups measuring 90.6 ± 3.5 in group 1 - 12 months after surgery - and 85.6 ± 4.2 (p < 0.001) in group 2 - 12 months after surgery. Conclusion The study demonstrated the simple and effective technique proposed for positioning the flexion and extension gap of the knee joint in primary TKA and facilitated more accurate positioning of the implant and improved knee function at standard testing 12 months after surgery.