Knee function after anterior cruciate ligament injury. With special reference to muscle power, hop performance and kinematics during high-intensity running

Abstract

Background: The high incidence of ACL injuries, long time to recovery and the risk of developing knee osteoarthritis at an early stage are areas of major concern for athletes, clinicians and researchers. Furthermore, the decision when to return back to strenuous physical activity after an ACL injury or reconstruction is challenging.Aim: The overall aim of this thesis has been to develop reliable and sensitive methods for evaluation of knee function in patients having sustained an ACL injury during competitive or recreational sports. One of the goals has been to describe lower extremity knee function, in more detail than has been possible before. This would then improve the possibilities to evaluate and guide the patients through rehabilitation and to aid in the decision-making process on when to return to sports.Material, methods and results: Study I - 23 patients were studied 6 months after an ACL injury and 44 patients were studied 6 months after an ACL reconstruction, using a strength test battery. Three strength tests were selected to reflect quadriceps and hamstring muscular power in a knee-extension and a knee-flexion test (open kinetic chain) and lower-extremity muscular power in a leg-press test (closed kinetic chain). Study II - 30 patients with an ACL injury were studied 11 months after an ACL injury and 35 patients were studied 6 months after an ACL reconstruction. All subjects were tested using a hop test battery comprised of the vertical jump, the hop for distance and the side hop. Results from study I and II showed high test-retest reliability (ICC values ranged from 0.85 to 0.98) for the two test batteries. By using an LSI of 90%, i.e. the performance on the injured side should be ¡Ý90% compared with the uninjured side to be classified as normal, a higher sensitivity was found for the test batteries to discriminate abnormal leg power or hop performance compared with any of the individual tests in the test batteries. For the strength test battery, 60% of the patients after an ACL injury and 95% of the patients after an ACL reconstruction had an abnormal LSI. The corresponding results for the hop test battery were 87% and 91%, respectively. Study III - The test batteries from Study I and Study II were used prospectively on 123 patients (75 males and 48 females) with an ACL injury or having undergone ACL reconstruction. The patients were tested at 4, 6, 12 and 24 months after the ACL injury and pre-operatively, 6, 12 and 24 months after ACL reconstruction. Overall, both men and women increased their muscle function over time, but only a minority exhibited normal values for the muscle power test and the hop test batteries at the 24-months follow-ups. Study IV - High-intensity treadmill running kinematics of the lower extremity were analysed during ongoing fatigue in 12 patients, 10 months after ACL reconstruction, and in five healthy subjects. No significant changes were found in terms of lower-extremity kinematics between the first and last measurements of high-intensity running as a result of increasing fatigue, reaching a median value of 17.5 on the Borg scale of perceived exertion. Already at the beginning of the high-intensity running session, the patients had a significantly less internally rotated foot, more internally rotated hip and more extended knee on the involved leg compared with the non-injured leg and controls. The controls¡¯ kinematics remained unaltered during testing.Conclusions: The test batteries showed high ability to determine deficits in leg power and hop performance after ACL injury and reconstruction. Only a minority of the patients had restored leg muscle power and hop performance at the one and two year follow-ups. High-intensity treadmill running, while developing fatigue, did not change the lower-extremity kinematic pattern 10 months after an ACL reconstruction.