The measurement of muscle stiffness in anterior cruciate injuries—an experiment revisited

To investigate the reported changes in angular stiffness of the knee due to the hamstrings muscles in the anterior cruciate ligament (ACL) deficient knee. The flexors of the knee were modelled as springs and the model tested on patients and controls. A previous study had used a similar model but showed no difference between an ACl deficient and an uninjured knee. A modification of a recently described method for measuring the stiffness of the hamstrings was used. ACL deficient patients were investigated and also normal controls. We found that stiffness not only varied between patients, but also between legs, with the injured leg having significantly stiffer flexor muscles ( P