Abstract
Introduction
An important factor in the functional results after total knee arthroplasty (TKA) is the achieved maximal flexion. To date, a TKA still provides dissimilar flexion capabilities compared to the healthy knee, which could be due to the mismatch between the normal knee geometry and the implant geometry. The implant design of the Journey (Smith&Nephew) aims to replicate the normal knee function. According to the manufacturer of the Journey system, it intends to replicate PCL and ACL function, accommodates deep flexion, induces normal tibiofemoral axial rotation and provides proper patellar tracking throughout the entire range of flexion (‘guided motion’). The objective of this study is to investigate the maximal knee flexion one year after surgery of the Journey and its predecessor the Genesis II (Smith&Nephew). In addition, clinical and functional outcomes will be evaluated.
Methods
A total of 124 patients presenting with noninflammatory osteoarthritis received the Journey or the Genesis II prosthesis, by randomization. The primary outcome was defined as the maximum flexion angle on a lateral X-ray performed with the patient lying on a bench and using manual force on bending the knee. Secondary outcomes were: active flexion (lying and standing), Knee Society System score (KSS), Patella Scoring System (PSS), number of adverse events (AE) and satisfaction. The changes in KSS and PSS between the pre-operative situation and 1 year after surgery were calculated as: δKSS = KSS1 year – KSSpre-op, and δPSS = PSS1 year – PSSpre-op. Two-sided t-tests and non-parametric alternatives were performed in order to test for differences between the Journey and the Genesis II group.
Results
The demographic and flexion characteristics were comparable between the two groups at baseline. No significant differences could be observed in maximal flexion on X-ray as well as the active flexion between both groups at 1 year (Figure). Median maximal flexion on X-ray was 127° (range 83°-150°) in the Journey group and 125° (range 81°-145°) in the Genesis II group. The active flexion was lower (p<0.001) than the flexion on X-ray (both lying and standing, median 120°). The δKSS and δPSS scores improved significantly more for the Genesis II (p=0.018 and p=0.005, respectively). In the Journey group 40 AEs in 27 patients were reported, including 14 manipulations under anaesthesia (MUA), 10 patients with persistent pain, 3 insert exchanges, and 2 total system revisions. In the Genesis group, 13 AEs were observed in 12 patients, including 6 MUAs, 3 patients with persistent pain, and 1 insert exchange. Patients were equally satisfied in both groups.
Discussion
An increased maximal flexion of the Journey prosthesis could not be shown. In both groups patients did not use the maximum of their flexion ability. Less improvement in clinical and functional outcomes and a higher number of adverse events were observed in the Journey group. The achieved kinematics of this current Journey implant design show an increased lateral roll-back as compared to the native knee which probably causes the functional problems. In conclusion, this new design does not result in the desired increased flexion and better clinical and functional outcome.
