Sciatic nerve regeneration in the rat after frozen muscle grafting. A comparative study using somatosensory evoked potentials

Evaluation of Gastrocnemius Motor Evoked Potentials Induced by Trans-Spinal Magnetic Stimulation Following Tibial Nerve Crush in Rats

Peripheral nerve injuries induce long-lasting physiological and severe functional impairment due to motor, sensory, and autonomic denervation. Preclinical models allow us to study the process of nerve damage, evaluate the capacity of the peripheral nervous system for spontaneous recovery, and test diagnostic tools to assess the damage and subsequent recovery. Methods: In this study on Sprague-Dawley rats, we: (1) compared the use of two different anesthetics (isoflurane and urethane) for the evaluation of motor evoked potentials (MEPs) induced by trans-spinal magnetic stimulation (TSMS) in gastrocnemius and brachioradialis muscles; (2) monitored the evolution of gastrocnemius MEPs by applying paired-pulse stimulation to evaluate the neuromuscular junction activity; and (3) evaluated the MEP amplitude before and after left tibialis nerve crush (up to 7 days post-injury under isoflurane anesthesia). The results showed that muscle MEPs had higher amplitudes under isoflurane anesthesia, as compared with urethane anesthesia in the rats, demonstrating higher motoneuronal excitability under isoflurane anesthesia evaluated by TSMS. Following tibial nerve crush, a significant reduction in gastrocnemius MEP amplitude was observed on the injured side, mainly due to axonal damage from the initial crush. No spontaneous recovery of MEP amplitude in gastrocnemius muscles was observed up to 7 days post-crush; even a nerve section did not induce any variation in residual MEP amplitude, suggesting that the initial crush effectively severed the axonal fibers. These observations were confirmed histologically by a drastic reduction in the remaining myelinated fibers in the crushed tibial nerve. These data demonstrate that TSMS can be reliably used to noninvasively evaluate peripheral nerve function in rats. This method could therefore readily be applied to evaluate nerve conductance in the clinical environment.

Radial nerve repair using an autologous denatured muscle graft: comparison with outcomes of nerve graft repair

BACKGROUND

The efficiency of denatured muscle grafting in nerve repair has been confirmed in experimental models and animals. The first clinical trials to repair digital nerves and mixed sensory-motor nerves were encouraging regarding sensory recovery but motor recovery was poor, probably because of delayed repair. We present the functional outcome of repair of motor nerves using denatured muscle graft and compare the results with those using standard nerve graft techniques.

METHODS

This prospective study included 9 radial nerve defects repaired with denatured muscle grafts and 23 radial nerve defects repaired using nerve grafts. Missile induced nerve injury, mid-arm level of lesion, a nerve gap smaller than 6 cm, and a preoperative interval of less than 5 months were characteristics shared by all patients. None of the patients had concomitant vascular injury, severe scarring, or significant soft tissue damage in the region of nerve repair. Motor recovery was estimated with 0-5 points, at least 4.7 years after surgery, according to the BMRC scale.

RESULTS

A successful outcome (>or=M3) was achieved in 7 out of the 9 patients treated using a muscle graft and in 21 out of the 23 patients treated using nerve grafts (P > 0.05). Excellent recovery and the clinically significant re-establishment of thumb extension (M5 grade) were never achieved in the patients treated using muscle grafts. The average motor score was significantly better in patients treated with nerve grafts than in those who received muscle grafts (3.8 +/- 0.9 and 3.2 +/- 0.8; P = 0.035). With the patients who received muscle grafts, an inverse correlation existed between motor recovery and the length of the nerve gap (P = 0.017).

CONCLUSIONS

Denatured muscle grafts can be useful for bridging short radial nerve defects, but the quality of recovery is significantly worse than after nerve graft repair. Even if relatively short nerve defects are bridged with denatured muscle grafts, the outcomes correlate inversely with the length of the gap.

Use of Skeletal Muscle Tissue in Peripheral Nerve Repair: Review of the Literature

The management of peripheral nerve injury continues to be a major clinical challenge. The most widely used technique for bridging defects in peripheral nerves is the use of autologous nerve grafts. This technique, however, necessitates a donor nerve and corresponding deficit. Many alternative techniques have thus been developed. The use of skeletal muscle tissue as graft material for nerve repair is one example. The rationale regarding the use of the skeletal muscle tissue technique is the availability of a longitudinally oriented basal lamina and extracellular matrix components that direct and enhance regenerating nerve fibers. These factors provide superiority over other bridging methods as vein grafts or (non)degradable nerve conduits. The main disadvantages of this technique are the risk that nerve fibers can grow out of the muscle tissue during nerve regeneration, and that a donor site is necessary to harvest the muscle tissue. Despite publications on nerve conduits as an alternative for peripheral nerve repair, autologous nerve grafting is still the standard care for treatment of a nerve gap in the clinical situation; however, the use of the skeletal muscle tissue technique can be added to the surgeon's arsenal of peripheral nerve repair tools, especially for bridging short nerve defects or when traditional nerve autografts cannot be employed. This technique has been investigated both experimentally and clinically and, in this article, an overview of the literature on skeletal muscle grafts for bridging peripheral nerve defects is presented.

Functional assessment of sciatic nerve recovery: biodegradable poly (DLLA-epsilon-CL) nerve guide filled with fresh skeletal muscle

The aim of this study was to compare functional peripheral nerve recovery in the rat sciatic nerve model after reconstruction of a 10-mm gap with a biodegradable poly (DLLA-epsilon-CL) nerve guide, as filled with either fresh skeletal muscle or phosphate-buffered saline (PBS). During 24 weeks of recovery, motor and sensory functional evaluation was tested by extensor postural thrust (EPT) and withdrawal reflex latency (WRL), respectively. At the end of the experiment, anesthetized animals were prepared for motor nerve conduction velocity (MNCV) studies, followed by gastrocnemius and soleus muscle weight measurement. Motor functional recovery was greater in the muscle-grafted group, and reached a significant difference from weeks 8-12 (P < 0.05). The results of this investigation suggest that filling a nerve guide with fresh skeletal muscle induces faster maturation of regenerated nerve fibers in comparison with traditional tubular repair.

Assessment of muscle flap sensibility by evoked potentials in the rat

This study investigated whether the sensory-to-motor reinervation of the muscle flap provides a better sensory recovery of an overlying skin graft. Fifty-four animals were studied in three groups of 18 rats each: group I (control): 1 cm of the gastrocnemius muscle motor nerve was excised and no repair was performed; group II (motor-to-motor repair): the motor nerve of the gastrocnemius flap was transected and repaired; group III (sensory-to-motor repair): the motor nerve of the gastrocnemius muscle and sural nerve were transected and their distal and proximal ends, respectively, were repaired. At follow-up periods of 6, 12, and 24 weeks, evaluation of hair growth, muscle atrophy, and sensory evoked potentials was performed. Somatosensory evoked potentials (SSEP) at 6 weeks in the sensory-to-motor repair (group III) revealed a significant (P < 0. 05) increase (104.4% +/- 22.9) in the relative response of peak-to-peak potentials when compared with group I (46.6% +/- 19) and group II (51.8% +/- 14.0). Muscle flap stimulation was most prominent at 6 weeks in sensory-to-motor reinvervated flaps (group III 133.1% +/- 25.4; group I 84.9% +/- 20.2). In this study, sensory-to-motor nerve repair significantly improved the sensibility of skin flaps at 6 weeks. Denervated flaps presented with 3 months of sensory recovery delay.