Effects of Mentholated Gel on Quadriceps Activation Following Knee Surgery

Abstract

Arthrogenic muscle inhibition can interfere with postsurgical restoration of quadriceps function, increasing the risk for reinjury and joint degeneration. Topical application of mentholated gel was assessed as a means to promote voluntary activation of inhibited quadriceps musculature. A total of 17 physically active individuals who had undergone knee surgery within the previous 10 to 17 days participated. Approximately 10 mL of mentholated gel was applied to the skin overlying the quadriceps of the involved extremity between measurements of Hoff mann’s refl ex amplitude and isometric quadriceps average torque output. Ratings of change in the level of exercise-related discomfort and exercise-performance capability were also obtained. No signifi cant change in Hoff mann’s refl ex amplitude was observed. Patient perception of increased exercise performance capability and decreased exercise-related discomfort were documented. The grouping of patients by type of surgical procedure suggests that a possible benefi cial eff ect on strength depends on the extent of surgically imposed tissue disruption. [Athletic Training & Sports Health Care. 2013;5(4):177-184.] Restoration of muscle strength and neuromuscular control following joint injury or surgery are often impeded by an inability to voluntarily achieve maximum activation of a muscle that usually contributes to dynamic stabilization of the affected joint.1-3 Arthrogenic muscle inhibition (AMI) refers to suppression of motor neuron excitability (MNE), which results from a combination of postsynaptic inhibition, generated by abnormal joint mechanoreceptor afference at the spinal cord level, and presynaptic inhibition, produced by descending neural signals from higher centers.4-8 Numerous studies have demonstrated that the quadriceps muscle group is highly susceptible to the AMI associated with a knee ligament injury,3,4,6,8,9 knee surgery,10-14 or an artifi cially induced knee joint effusion.15-20 A defi ciency in afferent input to the central nervous system (CNS) that results from knee ligament rupture may induce quadriceps AMI, but it can also be produced by an increase in afferent input to the CNS that results from fl uid distension of the knee joint capsule.2,21 Although substantial damage to knee joint structures elicits AMI, the phenomenon can also occur in the absence of pain or knee effusion,6,22,23 and it may be an important factor in the pathogenesis of joint degeneration.5,21,24-28 Failure to restore an optimal level of quadriceps activation will limit the dissipation of ground reaction forces provided by eccentric muscle tension, which has been reported to subject the articular surfaces and passive stabilizers of the knee to proportionately greater loads.29 A quadriceps avoidance gait pattern often develops in individuals who sustained an anterior cruciate ligament (ACL) injury, which is characterized by diminished knee fl exion excursion from heel strike to midstance and diminished knee extension excursion from midstance to push off during the gait cycle.3,8,9,14,30-33 Artifi cially induced Dr Wilkerson is from the Department of Health & Human Performance, University of Tennessee at Chattanooga, Chattanooga, Tennessee; and Dr Faltus is from Howard Head Sports Medicine, Avon, Colorado. Received: May 31, 2012 Accepted: May 8, 2013 Posted Online: July 1, 2013 This research was supported by Chattem Incorporated, Chattanooga, Tennessee. The authors have no fi nancial or proprietary interest in the materials presented herein. Address correspondence to Gary B. Wilkerson, EdD, ATC, Department of Health & Human Performance, University of Tennessee at Chattanooga, 615 McCallie Avenue, Dept. 6606, Chattanooga, TN 37403-2598; e-mail: Gary-Wilkerson@utc. edu. doi:10.3928/19425864-20130701-02