Summary
Despite excellent long-term survivorship of conventional Total Knee Replacements (TKRs), a significant number of patients remain dissatisfied by the limitations of pain and function post-operatively. We describe excellent early outcomes and kinematic data in patients undergoing a novel kinematic retaining TKR in an effort to reduce this problem.
Abstract
Total Knee Replacement (TKR) has proved a successful and enduring treatment for severe degenerative knee disease. Despite advances, there remains a cohort of high-demand patients who are unable to return to full activities post-operatively due to pain or poor function. We describe promising early outcomes and in vivo kinematic data from a multicentre study of patients undergoing TKR using a novel ‘kinematic retaining’ design.
Methods
Following local and regional ethical approval 128 patients (70 men and 58 women, mean age 68 years) underwent TKR with a cruciate retaining (CR) ‘kinematic retaining’ knee implant. 82% were ‘high-demand’ patients with moderate or intense pre-operative activity levels. Patients were reviewed preoperatively (T0), and postoperatively at 6 weeks (T1) and 6 months (T2) using clinical and functional performance evaluations (Knee Society Score [KSS], Knee injury and Osteoarthritis Outcome Score [KOOS], Oxford Knee Score [OKS], Visual Analogue Scale [VAS] satisfaction) and radiographic assessment. A subgroup underwent three-dimensional fluoroscopic kinematic analysis at 6-12 weeks and 6 months postoperatively to track early post-operative knee kinematic patterns whilst performing three prescribed weight-bearing activities. Data were analysed using paired t-tests.
Results
The KSS improved in all patients with 24% and 22% reporting good or excellent pre-operative Clinical and Functional Scores respectively, improving to 57% and 68% at T1 and 80% and 85% at T2. Pain improved from 65% experiencing severe constant pain pre-operatively to 6% at T1 and 2% at T2. A walking capability of more than 10 blocks was reported preoperatively in 26% of patients, improving to 59% of patients at T1 and 90% at T2. All KOOS sub-scores improved significantly (p<0.005). OKS and VAS satisfaction indices confirmed these promising patient-reported outcomes. The adverse event rate was 14.1%. No cases of revision, loosening or implant migration were reported.
Early postoperative kinematic studies showed average knee flexion of 104°-110° and tibial internal rotation of 2°-6°. At 6-12 weeks, the medial/lateral condyles were at -3mm/-8mm and -1mm/-6mm during maximum flexion lunge and kneeling, respectively. During the stair activity from 0° to 70° flexion, there were small tibial internal rotations (1°/5°) and anterior medial (2mm/5mm) and lateral (3mm/3mm) condylar translations. The average centers of rotation (CoRs) for the stair activity were medial +18% and +5% for the 6-12 week and 6-month exams, respectively.
Discussion
Early clinical and radiographic outcomes of this kinematic retaining knee prosthesis are promising. Limitations of this study include a small kinematic study subgroup and no direct control comparison. Despite this, the prosthesis appears to offer prompt functional recovery with substantial pain relief even in active patients. Furthermore, the average CoRs were medial for the stair activity, which is normal for healthy knees but uncommon for CR TKA, indicating closer-to-physiologic motion than commonly is observed in cruciate retaining TKR.