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June/July 2002

By Arthur J. Nitz, PT, PhD, ECS, OCS

Diagnostic electro physiologic assessment (nerve conduction studies [NCS]) and electromyography (EMG) are excellent tools for acquiring accurate information about a patient's neuromusculoskeletal system. The shorthand designation for this form of testing is EMG/NCS. EMG/NCS testing provides a great deal of information about the neuromuscular system and, in particular, the motor unit. Since a primary goal of rehabilitation is to optimize motor control and the functional unit of the neuromuscular system is the motor unit, EMG/NCS testing is an ideal procedure for establishing muscle recruitment characteristics and, ultimately, rehab potential. It should be noted that EMG is also used in rehabilitation settings for biofeedback training and has become a common research tool for kinesiologic studies, but these forms of EMG are not the focus of this overview.

Needle EMG-electrode placement in tibialis anterior muscle for athlete following severe ankle sprain.

PROCEDURAL BASICS

Briefly, NCS are obtained by stimulating the peripheral nerve with a small electrical pulse and recording the response at a distal muscle using surface electrodes. Information derived from this aspect of the procedure provides details about the distal conductive characteristics of the muscle-nerve complex (distal motor or sensory latency) or about the speed with which messages are being conducted along the course of the nerve-nerve conduction velocity (NCV). EMG signals are recorded from the motor unit using concentric, bipolar, or Teflon-coated mono polar needle electrodes. Results from electro physiologic testing provide information about the extent of muscle-nerve abnormality present (severity), the probable site and nature of the nerve-muscle lesion, and any ongoing attempt at recovery (reinnervation potentials). Abnormal electrical potentials are graded from one to four, providing additional accuracy when establish- ing the extent of neu- romuscular involvement following injury. EMG/NCS data provide useful guidance for the clinician about what rehabilitation efforts will be most helpful, what procedures might be harmful for the patient, the level of aggressiveness appropriate for the patient's condition, and when to most advantageously institute more demanding aspects of the regimen so that athletes may safely return to practice or competition.

Arthur J. Nitz, PT, PhD, ECS, OCS, uses discrete motor unit recruitment during diagnostic EMG to examine postinjury nerve-muscle status.

BASIS FOR TESTING

Therapists are required to conduct a competent neurologic screening examination that includes sensory, muscle, reflex, and neurotension testing for the lower motor neuron. One complicating factor that makes interpretation of the neurologic examination difficult is the presence of redundancy in the neuromusculoskeletal system. It has been shown that a 50% loss of motor units is necessary before a clear voluntary muscle testing weakness is noted during standard manual examination.² This observation indicates that clarification by means of tests more sensitive than standard manual muscle testing is necessary if therapists are to obtain information of sufficient accuracy regarding the true status of the motor system. Such clarification can be accomplished by simple EMG testing in which an electrode is inserted into the key muscle(s) in question and the presence of denervation potentials or loss of motor units during recruitment can be identified. As such, EMG/NCS testing serves as an extension of the therapist's neuromusculoskeletal examination of the patient.

Further rationale for conducting electrophysiologic testing for those with sports-related injuries is its ability to provide a more accurate picture of a patient's true condition following injury or surgery. For example, most therapists have experience measuring circumferential limb girth during initial examination procedures and noting what appears to be a moderate amount of muscle atrophy as compared to the opposite limb. However, recent evidence indicates that circumferential girth measurement does not correlate well with the actual amount of muscle atrophy definitively established by computed tomography or diagnostic ultrasonography.³ In a similar way, girth measurements might indicate a 20% loss of thigh girth, for instance, but EMG testing often identifies a 50% or greater loss of motor units. In such cases, EMG/NCS testing provides a far clearer snapshot of the real state of affairs and allows the clinician to avoid useless treatments, and, more important, prevents harmful, overly aggressive rehab efforts. What EMG/NCS testing has established in many clinical cases is that following musculoskeletal injury or after limb surgery, patient's weakness and severe atrophy are not simply the result of disuse or inhibition, but are actually caused by muscle denervation.^4-6 This information should have an influence on clinical decisions regarding the nature of rehabilitation efforts and expectation for meeting goals, and reminds clinicians to be alert for possible complications in patients who have sustained such neuromuscular involvement following injury.

CASE STUDY

RB, a 21-year-old throwing athlete for a Division I baseball team, had undergone rotator cuff surgical repair by arthrotomy 3 weeks prior to referral for rehabilitation. Initial evaluation findings included the expected residual discomfort, loss of motion, and substantial muscle atrophy noted in the deltoid, supraspinatus, and infraspinatus muscles. Muscle weakness associated with the visually observed atrophy in the affected muscles was more than expected and was not particularly associated with a significant increase in discomfort. Consequently, the patient was examined electromyographically and found to have moderate amounts of abnormal potentials in the atrophied muscles suggestive of denervation. Since no other muscles demonstrated any evidence of denervation, it was concluded that the abnormality was not the result of a cervical radiculopathy or substantial brachial plexopathy. Rather, the patient was most likely experiencing the result of neurogenic inflammation, which has been observed to affect muscles in proximity to the site of trauma or surgery.⁷

Ordinarily, in the presence of muscle atrophy, we would treat the patient with intense, high-amplitude electrical stimulation to augment the muscle contraction characteristics. However, there is credible research indicating that electrical stimulation of denervated muscles actually delays the signal for reinnervation, which would prolong the recovery time if maintained for a protracted rehabilitation course.^8,9 Instead we applied muscle stimulation to scapular stabilizers that were weak, but not denervated. In addition, since partially denervated muscles are prone to fatigue, we developed an in-clinic and home exercise program characterized by multiple, short-duration bouts of fairly intense activity followed by periods of rest during which the muscles were allowed to recover.

During the rehabilitation regimen, we remained especially alert for evidence of joint reaction, eg, inflammation, or soft tissue failure, eg, impingement, and monitored movements carefully to note whether muscle fatigue or proprioceptive impairment was adversely affecting motion performance. Since several weeks to months are required before reinnervation fully occurs, we also delayed the most demanding muscle strength training until evidence of muscle recovery was established. In this way, modifying the timing of key aspects of the rehabilitation scheme was guided by knowledge provided by EMG assessment and we avoided injuring severely weakened muscles by inappropriately overworking them during the early postoperative stages.¹⁰ Although RB's rehabilitation course was somewhat protracted because of the delay associated with muscle denervation, the patient experienced a full recovery and returned to intercollegiate competition as a baseball player with no apparent sequelae or long-term impairment.

CONCLUSION

Systemic EMG/NCS assessment of patients who have sustained musculoskeletal trauma or limb surgery has established that a large proportion have muscle denervation, which affects rehabilitation in some manner.^4-6 This does not imply that all patients with such injuries or who have had surgery are necessarily candidates for electrophysiologic assessment. However, clinical practice indicates that patients who are experiencing delay in their rehabilitation are often suffering the effects of muscle denervation and should be more carefully re-evaluated, including EMG/NCS assessment where appropriate. Information from such testing can then be used to knowledgeably modify or adjust the nature of the rehab efforts to avoid useless or possibly deleterious treatment. Consequently, patients are the primary beneficiary of physical therapy treatment informed by the best possible information available, which includes electrophysiologic assessment in sports-related injuries.

References

Lorentzon R, Elmqvist LG, Sjostrom M, Fagerlund M, Fuglmeyer AR. Thigh musculature in relation to chronic anterior cruciate ligament tear: muscle size, morphology, and mechanical output before reconstruction. Am J Sports Med. 1989;17:423-429.
Beasley WC. Influence of method on estimates of normal knee extensor force among normal and postpolio children. Phys Ther Rev. 1956;36:21.
Arangio GA, Chen C, Kalady M, Reed JF. Thigh muscle size and strength after anterior cruciate ligament reconstruction and rehabilitation. J Orthop Sports Phy Ther. 1997;26:238-243.
Dobner JJ, Nitz AJ. Post-meniscectomy tourniquet palsy and functional sequelae. Am J Sports Med. 1982;10:211-214.
Nitz AJ. Limb denervation following anterior cruciate (ACL) without tourniquet application. Phys Ther. 1998;68:822.
de Laat EA, Visser CP, Coene LN, Pahlplatz PV, Tavy DL. Nerve lesions in primary shoulder dislocations and humeral neck fractures: a prospective clinical and EMG study. J Bone Joint Surg Br. 1994;76B:381-383.
Levine JD, Moskowitz MA, Basbaum AI. The contribution of neurogenic inflammation in experimental arthritis. J Immunol. 1985;135(2 Suppl):843s-847s.
Brown MC, Ironton R. Suppression of motor nerve terminal sprouting in partially denervated mouse muscles. J Physiol. 1977;272:70P-71.
Sanes J, Covault J. Axon guidance during reinnervation of skeletal muscle. Trends Neurosci. 1985;18:523-528.
Johnson EW, Braddom R. Over-work weakness in facioscapulohumeral muscular dystrophy. Arch Phys Med Rehabil. 1971;52:333-336.

Arthur J. Nitz, PT, PhD, ECS, OCS, is a full professor of physical therapy at the University of Kentucky, Lexington, and is coeditor of a textbook on orthopedic physical therapy. He also owns Frankfort Physical Therapy, Frankfort, Ky, where he conducts electrophysiologic evaluations on a daily basis.

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June/July 2002