Clinical advantages of gradually reducing radius versus multi-radius total knee arthroplasty: a noninferiority randomized trial

BACKGROUND: The rationale for gradually reducing radius (GR) femoral component aims to prevent flexion instability by gradually change the center of femoral rotation, unlike a discrete change by the multi-radius (MR) which is more common for most of total knee arthroplasties (TKA). However, no strong evidence has been reported the clinical significance of the GR design. METHODS: This patient-blinded, parallel, non-inferiority trial conducted in September 2020. Patients with knee osteoarthritis consented for cruciate retaining TKA were randomly allocated to a GR or MR group. Primary outcome measures were knee functions at postoperative 6 and 12 months using the Knee injury and Osteoarthritis Outcome Score (KOOS). Secondary outcome measures were performance-based tests (30-s chair stand test, 40-m fast paced walk test, and 3-m timed up and go test), and knee motions. RESULTS: Sixty patients were enrolled and randomized; GR (n = 30) and MR (n = 30) group. The changes of KOOS at 6 and 12 months from baseline showed clinical meaningful for both GR and MR group. At 6 and 12 months postoperatively, there was no significant difference between both groups in all KOOS subscales. The length of stay was not different between GR and MR group (5.93 ± 1.44 vs 6.17 ± 1.86 days, p = 0.59). Patients on both groups presented similar performance-based tests. However, the improvement in degrees of knee motion for the GR group was significantly greater than the MR group (34.67 ± 12.52 vs 23.67 ± 12.59, p = 0.001). CONCLUSION: GR was noninferiority to MR for the functional outcomes and performances after TKA. The GR femoral component gave more knee motions than did the MR prostheses. LEVEL OF EVIDENCE: Level I, therapeutic study.