Decreased eccentric muscle endurance in the conservatively treated anterior cruciate-deficient knee

Concentric (CON) and eccentric (ECC) isokinetic knee extensor endurance, during 100 repetitive isokinetic contractions, were analysed in 32 consecutive patients with conservatively treated unilateral anterior cruciate ligament ruptured knees. There were 20 men and 12 women (mean age 34 years). The test was performed 6.8 years after the injury (range 4–14). The uninjured leg in each patient served as control. Lysholm subjective score, Tegner activity score and IKDC grading were used to relate the subjective knee function to muscle performance. Knee extensor endurance for concentric as well as for eccentric contractions were significantly lower in the injured side than the uninjured side. The magnitude of decrease in muscle performance was 7.6% for concentric (range-12 to 27%) and 15.3% for eccentric (range -9 to 50%) endurance. The eccentric injured/uninjured endurance ratio correlated significantly to the Lysholm subjective score. We conclude that the knee extensor endurance is decreased in patients with conservatively treated anterior cruciate ligament-ruptured knees. The eccentric endurance test seems to reflect the patients' subjective knee functioning.