Lower limb stability with ACL impairment

Study Design: Repeated measures (3 separate day sessions) to determine test reliability; single-session repeated measures to compare stability between limbs. Objectives: To develop a functional test measuring dynamic stability that i s capable of differentiating between the injured and uninjured lower limb i n 2 populations: (1) people with anterior cruciate ligament deficiency (ACL d) and (2) people with anterior cruciate ligament reconstruction (ACLr), an d to establish the reliability of this test. Background: Many functional tests of the lower limb used by clinicians, suc h as the 1-legged hop for distance, the 1-legged hop for time, the vertical jump, the triple hop for distance, shuttle run, and single-limb standing, do not allow the clinician to discern differences between function in the i njured and uninjured limbs. Methods and Measures: Twenty-five nonimpaired subjects (14 men, 11 women, a ged 31.2 +/- 9.1 years), 11 subjects with ACLr (9 men, 2 women, aged 26.3 /- 10.4 years), and 13 subjects with ACLd (5 men, 8 women, aged 40.4 +/- 12 .6 years) were tested. Twelve nonimpaired subjects participated in 3 testin g sessions to determine the reliability of the force plate measures. Ground reaction forces (vertical, medial-lateral, and anterior-posterior) were me asured while the subjects performed 1-legged hop and step-down tests onto a force plate. Stability was defined as the ability to transfer the vertical projection of the center of gravity to the supporting base and keep the kn ee still. A repeated-measures analysis of variance (2-factor; limbs by tria ls) was used to compare the stability between limbs. Results: The majority of the measures used to calculate dynamic stability w ere reliable. Moreover, the data provide normal standards of functional kne e stability for step-down and hop tests. In the step-down test, changes in vertical force did identify dysfunction in the injured limb (stabilization time = 1527 +/- 216 ms) compared to the uninjured limb (stabilization time = 892 +/- 498 ms) for subjects with ACLr. Conclusions: The normal standards may serve as a reference for comparing fu nctional differences in ACLr or ACLd populations. The vertical force parame ter during a step-down may be useful as an outcome measure to monitor progr ess during rehabilitation.