The additional tibial stem extension is not mandatory for the stability of 5 mm metal block augmented tibial prosthesis construct in primary total knee arthroplasty: 5-year minimum follow-up results.

Purpose: To determine whether additional stem extension for stability is necessary, we performed mid-term follow-up of patients who had been managed with 5-mm metal block augmentation for a tibial defect, where tibial prosthesis was fixed using bone cement without stem extension. Also, we evaluated clinical and radiologic results including survival rate of patients without stem extension.

Methods: We retrospectively analyzed patients with tibial bone defect, had undergone primary total knee arthroplasty, and had been treated with 5-mm metal block augmentation without stem extension between March 2003 and September 2013. Among 74 patients (80 cases), 47 patients (52 cases) were followed up for at least 5 years.

Results: Mean flexion contracture improved from 8.8° (0-40°) preoperatively to 0.4° (-5° to 15°) at final follow-up (P < 0.01), but there was no significant change in the mean angle of great flexion: 124.6° (75-150°) preoperatively and 126.2° (90-145°) at final follow-up (P = 0.488). Mean range of motion improved from 115.8° (35-150°) preoperatively to 125.5° (90-145°) at final follow-up (P < 0.01). Mean knee score improved from 38.7 points (0-66 points) preoperatively to 93.2 points (79-100 points) at final follow-up (P < 0.01), and mean functional score also improved from 50.4 points (10-70 points) preoperatively to 81.8 points (15-100 points) at final follow-up (P < 0.01). The mean postoperative Western Ontario and McMaster University osteoarthritis score was 19.5 points (0-66.0 points). The mean femorotibial angle was corrected from 9.0° varus (23.0° varus-6.3° valgus) preoperatively to 5.5° valgus (2.2° varus-11.1° valgus) at final follow-up (P < 0.01). There was no change in the mean β-angle, which was 90.7° (87.2-94.9°) immediately postoperative and 90.8° (87.2-94.9°) at final follow-up (P = 0.748) and in the mean δ-angle, which was 86.2° (81.3-90.0°) immediately postoperative and 87.2° (83.1-96.5°) at final follow-up (P = 0.272). Radiolucent lines (RLL) were observed in ten cases (26.3%), and the mean RLL scores at final follow-up were 0.34 points (0-3 points) in the anteroposterior view and 0.42 points (0-6 points) in the lateral view. Scores for the RLL were ≤ 4 points in 36 cases, 5-9 points in two cases. Revision surgery due to aseptic loosening (three cases) is rarely required, and the Kaplan-Meier survival rate at 10 postoperative years was 96.4% CONCLUSION: When performing 5-mm metal block augmentation for a proximal tibial defect, no additional tibial stem extension can be a good surgical option for the stability of tibial prosthetic construct and mid-term clinical and radiologic results.

Level of evidence: IV.