Characterizing Clinical and Biomechanical Contributions to Function Following ACL Reconstruction

University of Nebraska, National Institutes of Health (NIH), National Institute of General Medical Sciences (NIGMS)

Quantify differences in quadriceps function and gait biomechanics in individuals within 2 years of ACL reconstruction compared to a healthy comparison group and establish the feasibility of conducting a progressive strengthening program to improve clinical and patient-oriented outcomes in individuals who are within 2 years of ACL reconstruction

A maximal isometric muscle contraction of the quadriceps will be used to examine neural and peripheral contributions to quadriceps strength. Neural influences will be quantified using the interpolated twitch technique (voluntary activation) and early RTD. Peripheral influences will be quantified by examining the stimulus-evoked torque with the quadriceps relaxed (resting twitch) and late RTD. Knee joint biomechanics during treadmill walking and running will include sagittal plane (flexion, extension) movement variability (Lyapunov Exponent and approximate entropy), peak knee flexion angle, and peak external knee flexion and adduction moments. Additionally, the clinical relevance of impairments in the ACL reconstruction group will be determined by examining the relationship with performance on jumping tasks and patient function (secondary outcomes). The progressive strengthening program will be performed for 6 weeks and emphasize development of strength and power. Feasibility will be established if the researchers can recruit up to 8 participants and retain at least 80% over the 3 week intervention program. The researchers will determine effect sizes for changes outcome measures.

Subjects identified as having a clinically relevant strength deficit will be asked to participate in physical therapy sessions 3 times per week for 3 weeks. The strengthening program will consist of an individualized, progressive exercise program with an emphasis on increasing lower extremity strength, power, and biomechanics.

The progressive strengthening program will be performed for 3 weeks and emphasize development of strength and power. Feasibility will be established if we can recruit up to 8 participants and retain at least 80% over the 3 week intervention program. We will determine effect sizes for changes outcome measures.

Sagittal plane (knee flexion) movement variability (calculated using Lyapunov Exponent and approximate entropy)

Supramaximal electrical stimulus (interpolated twitch technique) used to augment a voluntary muscle contraction

Inclusion Criteria: Physically active History of primary unilateral ACL reconstruction within the past 3-24 months (ACL group only) Exclusion Criteria: History of lumbar spine or lower extremity injury or surgery (except ACL) within the past 1 year that required physician care Concomitant knee injury (ACL group only): ligament injury that requires surgical repair (medial collateral ligament [MCL], posterior cruciate ligament[PCL]), chondral defects >2cm, fracture, bilateral knee injury Medial conditions that are contraindications to electrical stimulation: Cardiac Pacemaker and Pregnancy Participants who are unable to understand procedures of experiment or provide consent (assent/parental permission)