The inclusion criteria included knees underwent consecutive primary TKA with substantial pain and loss of function due to knee osteoarthritis between May 2014 to April 2016. The exclusion criteria included knees with severe bony defect and deformity requiring constrained condylar knee. A total of 135 patients (157 knees) who underwent primary TKA with navigation and were to have intraoperative medio-lateral laxity measured were studied. Minimally invasive surgery was performed in all knees by one experienced surgeon using a mini-midvastus approach without patellar eversion. Our institutional review board approved the study. Written informed consent was provided by all patients.
The image-free navigation system (Orthopilot 4.2. B. Braun; Aesculap, Tuttlingen, Germany) was used to ensure the accuracy of implantations and measure the flexion angle of the knee during the joint component gap measurement using a tensor. The study included 17 men (21 knees) and 118 women (136 knees), with a mean age of 73 years (range, 48 to 88 years) and a mean body mass index of 26.1 kg/m2 (range, 17.2 to 44.1 kg/m2). The diagnosis was osteoarthritis in all patients. The mean preoperative flexion and extension angles were 117.2° ± 17.2° and − 11.6° ± 9.0°, respectively. Full-length standing anteroposterior radiograph of the knee was carried out, and the mean preoperative hip-knee-ankle (HKA) angle with the standing condition was 9.9° ± 7.2° varus.
A balanced gap technique was used. The tibial cut was first performed perpendicular to the tibial axis in the coronal and sagittal planes using navigation. The posterior cruciate ligament was sacrificed. After the tibial osteotomy, osteophyte removal and release of the deep medial collateral ligament (MCL) were performed in varus knee. Superficial MCL was released to obtain medial tightness < 3°. Rotation of the femoral component was determined according to the navigation system after soft tissue balancing; however, the surgeon checked to ensure that they were near parallel to the surgical epicondylar axis. The amounts of bony cut and varus/valgus alignment on the screen of the navigation system were determined based on the measurement of the extension and flexion gaps using the offset-type tensor. Posterior osteophytes in the femur were removed to avoid limitations associated with deep flexion. Following bony resections and soft tissue releases, a posterior stabilized (PS) design was used for all cases (Vega, Aesculap), and all components were fixed with cement. All patellae were resurfaced. After implantation of all components, the arthrotomy was temporarily repaired by applying stitches, and varus/valgus laxity of the knee was measured intraoperatively with the knee at 0°, 30°, 60°, 90°, and 120° guided by a navigation system. Intraoperative measurements were taken manually in the position of no stress, varus stress, and valgus stress up to palpable endpoints by one surgeon. Intraoperative medio-lateral laxity was defined as the difference between varus stress and valgus stress. Various changes in medio-lateral laxity were calculated, including from 0° to 30°, 30° to 60°, 60° to 90°, and 90° to 120°. Anatomic alignment was measured on the full leg-length standing radiograph postoperatively, and flexion and extension of the knee were measured at the time of last follow-up.
All patients were evaluated using the new Knee Society Knee Scoring System (KSS 2011) after a mean follow-up of 3 years (range, 2 years–4 years). The KSS 2011 has five components, including patient demographics, objective knee score, patient expectations, patient satisfaction score, and functional knee score. Patient expectations, patient satisfaction score, and functional knee score were completed by the patient. Higher scores were associated with better outcomes .
Factors that affected patient satisfaction and expectations were evaluated. Correlation analyses were performed using Spearman’s rank correlation test. Dependent variables included symptom score, functional activities score, age, body mass index, preoperative and postoperative HKA, postoperative flexion and extension, lateral laxity, medial laxity, medio-lateral laxity including midflexion laxity, which was defined as medio-lateral laxity at 30° and 60°, and changes in medio-lateral laxity from 0° to 30°,, 30° to 60°, 60° to 90°, and 90° to 120°. The Mann-Whitney U test was used for categorical data, including sex. The Wilcoxon signed-rank test was used to compare preoperative and postoperative flexion and extension. Lateral laxity, medial laxity, and medio-lateral laxity at various angles were compared using Friedman test with Bonferroni adjustment. Values are reported as means or correlation coefficients. P < 0.05 was considered significant. Data were statistically analyzed using IBM SPSS Statistics 24 (SPSS Inc., Chicago, IL, USA) and R version 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria; http://www.R-project.org/).