Friday 30 March 2012

Characteristics of Denervated Muscle


The denervated muscle is very different to that of an innervated muscle. When innervation is lost the muscle undergoes a progressive decay, where many morphological and physiological changes occur. These are principally (Robinson & Snyder-Mackler, 2008):
 
o Loss of voluntary and reflex activity
o Muscle Atrophy
§ Decrease in muscle weight, and muscle sarcoplasm
§ Decrease in myofibril (muscle contractile protein)
§ Decrease in the number of muscle fibres
o Replacement of muscle by fibrous and adipose tissue
o Changes in muscle excitability
§ Fibrillation: spontaneous contraction of muscle fibres
§ Oscillations in resting membrane potential
Figure 2. Comparison of (A) healthy muscle biopsy and a biopsy of a (E) denervated muscle as a result of a LMN lession (Kern et al., 2010)
These progressive internal changes to the muscle make denervated muscle tissue less excitable than healthy normal muscle, requiring a greater electric charge to cause a contraction. Electrical stimulation to these muscles produces a slow worm-like contraction (Low & Reed, 2000). The electrical charge slowly spreads through the muscle with a diminished rate of contraction compared with innervated muscle (Low & Reed, 2000). Studies have shown that using electrical stimulation to produce isometric contractions of denervated muscle can retard the atrophy process. As such, electrical stimulation treatment of denervated muscle should commence as soon as possible after the event of denervation (but not before axonal sprouting) to decrease the amount of atrophy that will ensue (Kern et al., 2010).  The best results are seen with vigorous isometric stimulation to the point of fatigue (three sessions per day for at least 10 minutes in duration) (Low & Reed, 2000). However, this treatment has shown that it cannot completely prevent the degenerative process (Low & Reed, 2000). Further studies have used large surface electrodes with high intensity, long-duration impulses to directly elicit contraction with the aim to reverse and treat denervated muscle that have the longstanding severe atrophy (Kern et al., 2010).


Robinson, A. J.  & Synder-Mackler, L. , 2008. Electrotherapy and electrophysiological testing. Clinical Electrophysiology 3rd Edition.

Kern, H., Carraro, U., Adami N., Biral D., Hofer C., Frostner C., Modlin M., Vogelauer M., Pond A., Boncompagni S., Paolini C., Mayr W., Protasi F., & Zampieri S., (2010), Home-based functional electrical stimulation rescues permanently denervated muscles in paraplegic patients with complete lower motor neuron lesion. Neurorebilitation and Neural Repair, 24(8), 709 – 721.

Low, J., & Reed, A. (2000). Electrotherapy explained: principles and practice. Oxford: Butterworth-Heinemann



Friday 16 March 2012

Electrical Stimulation for Denervated Muscle



Muscle denervation occurs when the peripheral motor nerve innervation of a muscle is lost. Loss of innervation can occur at the lower motor neuron (LMN) due to trauma, which can lead to irreversible damage or at the upper motor neuron that can result from progressive conditions such as multiple sclerosis or non- progressive conditions such as stroke (Stein, Everaert, Thompson, Chong, Whittaker, Robertson & Kuether, 2010). This blog is going to focus on traumatic injuries to LMN that occur near the spinal level or anywhere along its path to the site of muscle innervation (Kern et al., 2010).  

Without a functional nerve supply, muscle can only be stimulated to contract by direct stimulation of the muscle fibre (Kern et al., 2010). Therefore, there are differences between stimulation of muscle via its nerve and direct stimulation of denervated muscle (Low & Reed, 2000). The name of the electrical stimulation used for denervated muscles is called Functional Electrical Stimulation (FES). FES is similar to neuromuscular electrical stimulation (NMES), but has the specific purpose to produce functional movements for those who are limited by denervation (Low & Reed, 2000)

The most common functional deficit experienced in the population of people with muscle denervation is foot drop (Everaert et al., 2010). Foot drop occurs due to damage of the LMN that innervates the dorsiflexor muscles of the ankle, causing a reduction in walking speed, increase in physiological costs of gait and increased risk of falls (Everaert, et al., 2010). Furthermore, a loss of innervation to the flexors of the forearm can be treated with FES to perform grasping actions. There are many components to the application of such a device, which has been shown in empirical research to offer many functional and physiological benefits. However, the application of FES is not widely known due to the niche market it is used to treat. The main aim of this blog is to bring an understanding of its application in relation to the internal physiological changes of denervated muscle and highlight contraindications and precautions when using FES.  


Everaert, D. G., Thompson, A. K., Chong, S. L., & Stein, B. R., (2010). Does functional electrical stimulation for foot drop strengthen corticospinal connections. Neurorebilitation and Neural Repair, 24(2), 168 -177. 


Stein, R.B., Everaert, D.G., Thompson, A.K., Chong, S.L., Whittaker, M., Robertson, J. & Kuether, G. (2010). Long-Term Therapeutic and Orthotic Effects of a Foot Drop Stimulator on Walking Performance in Progressive and Nonprogressive Neurological Disorders. Neurorehabilitation and Neural Repair 24(2) 152– 167.

Kern, H., Carraro, U., Adami, N., Biral, D., Hofer, C., Forstner, C., Modlin, M., Vogelauer, M., Pond, A., Boncompagni, S., Paolini, C., Mayr, W., Protasi, F. & Zampieri, S. (2010). Home-Based Functional Electrical Stimulation Rescues Permanently Denervated Muscles in Paraplegic Patients With Complete Lower Motor Neuron Lesion. Neurorehabilitation and Neural Repair, 24(8): 709-721
Low, J., & Reed, A. (2000). Electrotherapy explained: principles and practice. Oxford: Butterworth-Heinemann