Electrical Stimulation and Eccentric Exercise for Anterior Cruciate Ligament (ACL) Injury

Quadriceps muscle weakness is a common consequence of ACL injury. This muscle weakness is considered to result from neural inhibition preventing full muscle contraction and is referred to as arthrogenic muscle inhibition (AMI). AMI hinders rehabilitation by preventing gains in strength, increasing the risk of re-injury, and potentially placing patients at risk for chronic degenerative joint conditions. Quadriceps weakness that occurs following ACL injury is also thought to be caused by muscle atrophy which is thought to manifest due to alterations in muscle architecture, selective fiber atrophy or even neural deficits such as AMI. Importantly, interventions that are designed to counter this muscle weakness are required in order to promote long-term knee joint health. Hence, the purpose of the current study is to determine the efficacy of interventions that target quadriceps weakness to improve quadriceps muscle function and biomechanics in patients prior to and following ACL reconstruction. Specifically, the efficacy of neuromuscular electrical stimulation aimed at improving quadriceps neural activity and eccentric exercise intended to minimize quadriceps muscle atrophy will be investigated. The investigators expect that patients who receive the electrical stimulation therapy will demonstrate improvements in quadriceps strength and activation. Furthermore, it is expected that patients who receive both the electrical stimulation and eccentric intervention will demonstrate markedly greater gains in quadriceps strength and activation than patients who receive only the electrical stimulation therapy or standard of care post-surgery. The investigators also hypothesize that the patients who receive the electrical stimulation therapy and/or eccentrics will display knee motion similar to uninjured control subjects.

Neuromuscular electrical stimulation (NMES) has been shown to reduce quadriceps activation failure (QAF) and eccentric exercise has been shown to lessen muscle atrophy post-ACL reconstruction. Given thatthese are two critical components of quadriceps strength, intervention combining these therapies may be effective at reinstituting quadriceps function post-reconstruction. Therefore, the aim of this study is to evaluate the effectiveness of a combined NMES and eccentric exercise intervention to improve the recovery of quadriceps activation and strength post-reconstruction. Patients post ACL-injury will be placed into four treatment groups (NMES and eccentrics; eccentrics only; NMES only, and standard of care) Patients assigned to the NMES and eccentric and the NMES only groups will receive the NMES protocol 2× per week for the first 6 weeks post-reconstruction. MES and eccentric and the eccentrics only groups will receive the eccentric exercise protocol 2× perweek beginning 6 weeks post-reconstruction. Quadriceps activation was assessed via the superimposed burst technique and quantified via the central activation ratio.Quadriceps strength was assessed via maximal voluntary isomeric contractions (Nm/kg). Data will be gathered on three occasions: pre-operative, 12-weeks-post-surgery and at return-to-play.

Subjects placed into this group will undergo electrical stimulation following anterior cruciate ligament reconstruction (ACLr). Subjects will be required to report 2 times per week for 6 weeks following ACLr for electrical stimulation therapy. Electrical stimulation therapy post-reconstruction will commence immediately post-ACLr and end at week 6.

Subjects placed into this group will undergo eccentric exercise strength training following ACLr. Subjects will be required to report 2 times per week for 6 weeks following ACLr. Eccentric strengthening will begin at week 6 post-ACLr and will end at week 12 post-ACLr.

Subjects placed into this group will undergo a combined electrical stimulation and eccentric exercise intervention following ACLr. The electrical stimulation intervention will be delivered immediately following ACLr and will end at 6 weeks post-ACLr. Subjects will receive the electrical stimulation therapy 2 times per week for the first 6 weeks post-ACLr. At six weeks post-ACLr, subjects will begin the eccentric strengthening protocol. Subjects will eccentrically train 2 times per week for 6 weeks. The eccentric strengthening will end at 12 weeks post-ACLr.

CAR = maximal voluntary isometric contractions force / maximal voluntary isometric contractions force + stimulated force

Inclusion Criteria: Aged 14-35 years Willingness to participate in testing and follow-up as outlined in the protocol Scheduled to undergo ACL reconstruction Exclusion Criteria: Previous quadriceps injury Inability to provide informed consent Pregnant females ACL injury sustained more than 48 hours prior to reporting to physician ACL injury sustained when not engaged in sports participation (i.e. while engaged in activities of daily living) Previous partial ACL tear Previous surgery to injured knee Total or partial meniscectomy accompanying ACL reconstruction Other ligamentous injury accompanying ACL injury

Lepley LK, Palmieri-Smith RM. Quadriceps Strength, Muscle Activation Failure, and Patient-Reported Function at the Time of Return to Activity in Patients Following Anterior Cruciate Ligament Reconstruction: A Cross-sectional Study. J Orthop Sports Phys Ther. 2015 Dec;45(12):1017-25. doi: 10.2519/jospt.2015.5753. Epub 2015 Oct 15.