Intramedullary nailing versus external ring fixation for tibial shaft fractures: an explorative analysis of muscle strength from the IMVEX trial.

Background: To explore the effect of intramedullary nailing versus external ring fixation for patients with tibial shaft fractures on 12-month maximal isometric muscle strength for knee extension and knee flexion. We hypothesise that patients treated with external ring fixation will show significantly better maximal isometric muscle strength for knee extension and knee flexion 12 months after surgery compared to treatment with intramedullary nailing. Moreover, we aim to explore the association between muscle strength and the Knee Injury and Osteoarthritis Outcome Score (KOOS) at 12 months following surgery.

Methods: A pragmatic multicentre randomised, non-blinded trial with a two-group parallel design. This study is an explorative analysis of the IntraMedullary nailing Versus EXternal ring fixation Trial (IMVEX). 67 patients with a tibial shaft fracture were randomized to external ring fixation or intramedullary nailing. The primary outcome: maximal isometric muscle strength for knee extension and knee flexion. Secondary outcome was KOOS.

Results: No statistically significant difference in muscle strength between treatment with intramedullary nailing and external ring fixation was observed (P < 0.31). Examination of maximal isometric muscle strength showed significant difference between the injured and the non-injured leg (knee extension: mean difference of 53N, (95%CI 33.9-72.4), knee flexion: mean difference of 35N, (95%CI 21.2-47.9)) The association between KOOS subscale scores and the relative difference in muscle strength for knee extension showed significant and moderate to high correlation (0.4-0.8) for all subscales.

Conclusion: Muscle strength of knee flexion and extension was markedly decreased one year after fracture. We observed no statistically significant difference in recovery of muscle strength between treatment with intramedullary nailing and external ring fixation. Results indicate that a decrease in muscle strength is associated with worse patient-reported outcomes for all five KOOS subscales.

Trial registration: NCT03945669.

Level of evidence: II.