Mid-term clinical outcomes of the unlinked type K-NOW total elbow arthroplasty

This study aimed to evaluate the mid-term clinical outcomes, complications, and survival rates of the unlinked K-NOW (Teijin Nakashima Medical, Japan) total elbow arthroplasty (TEA), focusing on the use of cementless fixation.

This retrospective study included 41 elbows in 37 patients who underwent primary TEA using unlinked K-NOW between April 2012 and March 2021, with a minimum follow-up of two years. Surgical approaches included the lateral paraolecranon (LPO) and triceps-off approaches. Clinical evaluations included range of motion (ROM) and Mayo Elbow Performance Score (MEPS). Complications were recorded, and Kaplan-Meier survival analysis was performed, with aseptic loosening and revision surgery as endpoints.

The mean patient age was 68.4 years (SD 11.6), and the mean follow-up period was 4.7 years (2.1 to 10.1). The LPO approach was used in 35 elbows (85.4%), and cementless fixation was applied to 41 humeral components (100%) and 35 ulnar components (85.4%). Among patients with ≥ five years of follow-up (n = 16), significant improvements were observed in ROM (extension, from -38° to -19°; flexion, from 107° to 130°; pronation, from 55° to 72°; supination, from 62° to 73°; p < 0.001), and MEPS (from 48 to 93 points; p < 0.001) at five years postoperatively. Complications occurred in six elbows (14.6%): three elbows (7.3%) with aseptic loosening and three elbows (7.3%) with periprosthetic fractures; no postoperative dislocation was observed. Revision surgeries were required in two elbows (4.9%). Kaplan-Meier survival rates were 92.7% (95% CI 84.7 to 100) at five years for loosening, and 97.1% (95% CI 91.4 to 100) at five years for revision. All aseptic loosening occurred within three months postoperatively.

The unlinked K-NOW with cementless fixation, mostly using the LPO approach, demonstrated favourable outcomes with improved ROM and MEPS, a low complication rate, and promising survival. In cases with severe osteoporosis or bone-implant instability, cemented fixation or a triceps-off approach may help reduce the risk of early complications.