The relationship between isokinetic quadriceps strength test and hop tests for distance and one-legged vertical jump test following anterior cruciate ligament reconstruction

Isokinetic measurements and functional tests are often used to assess function following knee ligament reconstruction using the opposite limb as a control. However, the question of whether the uninvolved leg may serve as a reference on functional tests has not been adequately answered. In particular, the one-legged rebound vertical jump has not been used to assess functional levels following surgery of the cruciate ligament. The purposes of this study were: 1) to determine whether the uninvolved leg is within normal range of an age- and weight-matched group, 2) to determine differences between the involved and uninvolved leg in patients after anterior cruciate ligament reconstruction, 3) to examine the relationship between knee extensor strength and four functional performance tests, and 4) to determine if the one-legged rebound vertical jump yields more information in the assessment of knee function than the other functional tests with respect to two time-frames. Fifty healthy subjects (group A, mean age = 28.1 years) and 55 anterior cruciate ligament patients (groups B and C) participated in dynamometric measurement, one-legged and two-legged vertical jump, and the single- and the triple-hop test. Mean time for testing was 13 weeks following surgery for group B (N = 30, mean age = 27.8 years) and 54 weeks following surgery for group C (N = 25, mean age = 29.9 years). Pearson product moment correlation coefficients between peak torque and single and triple hop were r = .45, r = .48, r = .51, and r = .55 for groups B and C, respectively. Pearson product moment correlation coefficients between peak torque and the height of the vertical jump was r = .51 for group C. Results for group A revealed limb symmetry indices of 95% or more on all functional performance and isokinetic tests. In group B, all patients showed a limb symmetry index of less than 85% on all tests. In group C, the index for the vertical jump was the only functional test that fell below the level of 85%. Regardless of whether the dominant or nondominant leg is involved, the uninvolved leg can be used adequately as a reference guide for outcome from rehabilitation using these measurements. The one-legged vertical jump test is capable of detecting functional limitations of the lower limb following knee ligament reconstruction up to 54 weeks postoperatively.