The aim of this study was to analyze the long-term outcomes of extensor tendon ruptures of the knee using exact measuring tools.
The results of patients treated for extensor tendon rupture with a minimum follow up of 10 years were reviewed. Electromyography (EMG) and three-dimensional (3D) gait analyses were performed and compared with the healthy side of each patient and with the gait patterns of 20 healthy controls. Functional outcome scores were assessed using the Lysholm score and Knee Injury and Osteoarthritis Outcome Score (KOOS).
After a mean of 13.4 ± 3 years, 23 patients were available for follow up. The mean Lysholm score was 86.6, and the KOOS averaged 78.1. Gait analysis showed no major kinematic differences between these patients compared with healthy controls. In the squat test, the mean peak amplitude of the rectus femoris muscle was significantly smaller on the injured side than on the healthy side (140.21 ± 66.13 μV vs. 168.25 ± 91.77 μV; P = 0.01). The mean peaks of the vastus lateralis and medialis EMG signals were also lower on the injured side (P = 0.63; P = 0.08). Correspondingly, the thigh girth at 20 cm and 10 cm above the knee was significantly lower on the injured side. One patient had re-rupture after patella tendon repair.
At long-term follow up the patients reached good clinical outcomes and exhibited mainly physiological gait patterns after rupture of knee extensor tendons. However, the thigh muscles showed hypotrophy and a significantly smaller EMG signal amplitude during a high-intensity task on the formerly injured side.

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