Rate of complications and short-term Functional Results of Revision Total Knee Arthroplasty for Tibio-femoral Instability: do stability and range of motion are restored in 62 revisions.

Background: Tibio-femoral instability (TFI) due to ligament imbalance is a growing cause of revision total knee arthroplasty (TKA). The results are heterogeneous in the event of revision and literature is scarce regarding this issue particularly when use of hinge prostheses is not exclusive to manage this complication. Therefore, a retrospective investigation was conducted aiming to (1) analyze the one-year functional results, (2) determine the rate of complications after revision for TFI using posterior-stabilized or condylar constrained knees (CCK), 3) identify the factors that could influence the function outcome.

Hypothesis: Patients undergoing revision TKA for TFI would show an improvement in Oxford Knee Score at one year postoperative.

Methods: Sixty-two patients were included (40 females, 22 males) mean age 62,9 years ± 8.2 (range, 45,7-78,4). Instability was classified as instability in extension (n = 28), midflexion (n = 12), flexion (n = 12) or global (n = 15). Revisions were done because of isolated instability. Revision consisted in implant revision using a CCK (n = 42), a hinge prosthesis (n = 12) or an isolated polyethylene insert exchange (n = 8). Patients were assessed at one year by the difference between the preoperative Oxford Knee Score (OKS) and the score at one year postoperatively. The results were deemed satisfactory if the variation between preoperative OKS and one-year follow-up was greater than or equal to 5 points (Minimal Clinically Important Difference (MCID) following TKA). Complication rate and risk factors influencing the outcome were also analyzed.

Results: Of the 62 patients, 59 could be assessed at one year using postoperative OKS (one death at 0.66 years from unrelated reason, and two had repeated revision within one year postoperative [1 aseptic loosening and 1 Co-Cr allergy]). Preoperative OKS was 15.5 points ± 7.1 (range, 2-37), rising to 28.9 points ± 8.7 (range, 11-45) at follow-up. The mean OKS improvement was 13.4 points ± 10.3 (range, -8 to 33) (p < 0.001) and 47 patients (79.6%) reached the MCID at follow-up. Female gender was associated with a worse evolution of OKS (-5.8, 95% CI: -11.26 to -0.34 (p = 0.038)). In contrast, there was no significant difference in the evolution of the OKS according to the type of TFI in extension or in flexion, in midflexion or global (p = 0.5). Likewise, there was no significant difference in the evolution of the OKS between RTKA using CCK, hinged prosthesis or isolated polyethylene insert exchange (p = 0.3). There was no recurrence of instability at final follow-up (3.04 years ± 1.5 (range, 0.66-6.25)). Revision for instability did not drive to stiffness since mean flexion prior to RTKA was 116 ° ± 13 ° (range, 90 ° to 130 °) versus 116.7 ° ± 12 ° (range, 90 ° to 130 °) at follow-up. Fourteen patients (22.6%) experienced postoperative complications, including 3 revisions (4.8%) at final follow-up.

Conclusion: RTKA for TFI leads to significant functional improvement at one-year postoperative. However, the risk of complications is almost high at 22.6%.

Level of evidence: IV; retrospective study.