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 is capable of differentiating between the injured and uninjured lower limb in 2 populations: (1) people with anterior cruciate ligament deficiency (ACLd) and (2) people with anterior cruciate ligament reconstruction (ACLr), and to establish the reliability of this test. Background: Many functional tests of the lower limb used by clinicians, such 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 injured and uninjured limbs. Methods and Measures: Twenty-five nonimpaired subjects (14 men, 11 women, aged 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 testing sessions to determine the reliability of the force plate measures. Ground reaction forces (vertical, medial-lateral, and anterior-posterior) were measured while the subjects performed 1-legged hop and stepdown 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 knee still. A repeated-measures analysis of variance (2-factor; limbs by trials) was used to compare the stability between limbs. Results: The majority of the measures used to calculate dynamic stability were reliable. Moreover, the data provide normal standards of functional knee 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 functional differences in ACLr or ACLd populations. The vertical force parameter during a step-down may be useful as an outcome measure to monitor progress during rehabilitation.

J Orthop Sports Phys Ther. 1999;29(8):444-454.

Key Words: dynamic stabilization, force plate, knee, rehabilitation

Elastic resistance exercises are frequently used for knee rehabilitation following injury and/or surgery. The evidence supporting this mode of rehabilitation is primarily anecdotal, and no biomechanical assessment of elastic resistance exercises has been previously published. The purpose of this project was to quantify muscle activation levels, knee joint angles, and applied force during 5 rehabilitation exercises utilizing an elastic resistance device. Twelve subjects with no previous knee injury performed double knee dip, hamstring pull, leg press, single knee dip, and side-to-side jump exercises while sagittal plane kinematics, applied force from the elastic resistance device, and electromyographic activity of 8 lower extremity muscles were collected. The muscle activation patterns suggest a progressive continuum of rehabilitation exercises that can be applied to nonoperative injuries as well as anterior cruciate ligament reconstructions.

J Orthop Sports Phys Ther. 1998;28(1):40-50.

Key Words: rehabilitation, knee, biomechanics

Muscle activity, joint angles, and heart rate during uphill walking were compared for application in knee rehabilitation. The objectives of this study were to quantify muscle activation levels at different treadmill grades and to determine the grade(s) at which knee range of motion would not further compromise the joint. Average and peak electromyographic activity of the quadriceps (vastus medialis oblique and vastus lateralis) and hamstrings [biceps femoris and medial hamstrings (semimembranosus/semitendinosus)] were recorded during walking at 0%, 12%, and 24% grade. Six subjects (age = 28.5 ± 3.7 years, stature = 1.79 ± .05 m, and mass = 74.7 ± 7.9 kg) walked at self-selected speeds at each grade while ankle, knee, and hip angles, heart rate, and electromyographic activity (surface electrodes) were recorded. Maximum voluntary contractions provided a relative reference for the electromyographic activity during walking. Average and peak electromyographic activity increased significantly across grades for the vastus medialis oblique (125 and 154%), vastus lateralis (109 and 139%), and biceps femoris (53 and 46%), but remained similar for the medial hamstrings. Maximum knee flexion at heel strike increased significantly with grade. Despite decreased self-selected speeds with increasing grade, there were significant increases in heart rate across grades. The results of this study provide a basic understanding of the quadriceps and hamstrings activity levels, lower extremity joint range of motion, and cardiovascular requirements of graded treadmill walking in normal subjects. The results also suggest that a grade just greater than 12% may be most beneficial for knee rehabilitation to minimize patellofemoral discomfort or potential strain on the anterior cruciate ligament. The benefits achieved through this functional activity encourage its implementation in rehabilitation and provide a basis for comparison with injured patients.

J Orthop Sports Phys Ther. 1996;23(5):294-301.

Key Words: knee, rehabilitation, electromyography, gait