Isokinetic knee extensor strength deficit following matrix-induced autologous chondrocyte implantation

Background: Autologous chondrocyte implantation has become an established technique for addressing knee cartilage defects. Despite reported improvement in pain and regeneration of hyaline-like repair tissue, little has been reported on the recovery of knee strength. Methods: Knee strength assessment was undertaken in 60 patients at 5 years following autologous chondrocyte implantation. Using an isokinetic dynamometer, and during isokinetic knee extension and flexion angular velocities of 60 degrees, 90 degrees and 120 degrees/s, the peak torque, torque at 45 degrees of knee flexion and hamstrings/quadriceps ratio was obtained, in both the operated and non-operated limbs. Pain at the time of assessment was obtained. Independent sample t-tests were used to assess differences in the operated and non-operated sides. Findings: There were no significant differences (p>0.05) between the operated and non-operated legs in the peak knee flexor torque or knee flexor torque at a knee flexion angle of 45, at all angular velocities (60, 90 and 120 degrees/s). While the peak knee extensor torque was less in the operated leg at all angular velocities, these differences were not significant (p>0.05). However, a significantly reduced (p<0.05) knee extensor torque at a knee flexion angle of 45, was observed at all speeds. Interpretation: While patients had recovered their knee flexor strength, they still demonstrated a reduced knee extensor strength profile at 5 years. This demonstrates that the early supervised rehabilitation phase following autologous chondrocyte implantation is not sufficient to restore long-term knee strength, and ongoing patient advice and rehabilitation is required extending beyond this early period. It is unknown how this prolonged reduction in strength may affect long-term graft outcome. (C) 2012 Elsevier Ltd. All rights reserved.