Pain and outcome prediction in muscle strength rehabilitation after knee injury in recreational athletes.

Effects of rehabilitation on knee function, activity and health-related quality of life after soft-tissue knee injury have been widely studied in clinical trials, but there is still a lack of data on the relation between knee muscle strength and athlete's perceived performance to identify sports-risk modifiers. We performed a prospective observational clinical study of knee muscle strength and self-reported health during rehabilitation after unilateral knee soft-tissue injury in recreational sports. Forty-three patients performed isokinetic dynamometry and filled in the Short form Health Survey (SF-36) and the Oxford Knee Score questionnaires before and after 4 months of instructed home strengthening program. We observed significant improvement in peak torque deficit between two limbs during concentric extension (PTDE) and flexion, dynamic control ratio of the involved knee, most of the SF-36 subscales and the Oxford Knee Score values (P ≤ 0.001). Dynamic control ratio of the uninvolved knee values remained below referential values and unchanged. Improvement of PTDE correlated positively with improvement of the bodily pain subscale of SF-36 score (r = 0.51, P < 0.001). Receiver operating characteristic analysis indicated that reduction of pain by at least nine points predicts at least 10% reduction in PTDE, whereby the bodily pain change achieved poor (56%) sensitivity and good (86%) specificity as a rehabilitation success measure for recreational athletes after knee injury. Primary inferior eccentric strength of noninjured knee hamstrings might indicate increased risk of knee injury. Diminished perceived pain predicts strength improvement of the injured knee extensors with poor sensitivity and good specificity.