Can end-to-side neurorrhaphy bridge large defects? An experimental study in rats

Utilizing Lateral Sprouting Axons to Reinnervate a Transferred Free Muscle to Enhance Distal Muscle Recovery When Performing High-Level Nerve Repair: Experimental Rat Study

BACKGROUND

 High-level median or ulnar nerve injuries and repairs typically result in suboptimal reinnervation of distal muscles. Functioning free muscle transplantation (FFMT) is increasingly recognized as an effective method to restore function in chronic muscle denervation cases. This study investigates the efficacy of using an additional FFMT, neurotized by lateral sprouting axons from a repaired high-level mixed nerve in the upper limb, to enhance distal hand function.

METHODS

 Thirty-five Sprague-Dawley rats were divided into four groups to evaluate the proposed FFMT technique. The infraclavicular median nerve (MN) was transected and repaired in each animal. The nearby musculocutaneous nerve (MCN) was transected, and the terminal nerve after the biceps muscle was divided and embedded into the biceps muscle, creating an FFMT model. The distal stump of the MCN was anchored to the MN, 1.5 mm distal to the MN repair site. Assessments of nerve and muscle function were conducted 4 months postoperatively.

RESULTS

 Behavioral analysis, along with measurements of biceps muscle weight and tetanic contraction force, indicated significant recovery in the biceps muscle. Histological staining confirmed reinnervation of the MCN from the repaired MN. Additionally, functional examination of the flexor digitorum superficialis muscle revealed no deterioration associated with the repaired MN.

CONCLUSION

 The study demonstrates the potentiality of utilizing lateral sprouting axons from a repaired high-level MN to reinnervate an additional FFMT to enhance flexor digitorum superficialis function. The surgical strategy promises recovery of distal muscle function and implies for diverse clinical applications.

Alternative Nerve Coaptations: End-To-Side and Beyond

Modern end-to-side (ETS) nerve transfers have undergone several permutations since the early 1990's. Preclinical data have revealed important mechanisms and patterns of donor axon outgrowth into the recipient nerves and target reinnervation. The versatility of ETS nerve transfers can also potentially address several processes that limit functional recovery after nerve injury by babysitting motor end-plates and/or supporting the regenerative environment within the denervated nerve. Further clinical and basic science work is required to clarify the ideal clinical indications, contraindications, and mechanisms of action for these techniques in order to maximize their potential as reconstructive options.

Current concepts in peripheral nerve surgery

The injuries of the peripheral nerves are relatively frequent. Some of them may lead to defects which cannot be repaired with direct end-to-end repair without tension. These injuries may cause function loss to the patient, and they consist a challenge for the treating microsurgeon. Autologous nerve grafts remain the gold standard for bridging the peripheral nerve defects. Nevertheless, there are selected cases where alternative types of nerve reconstruction can be performed in order to cover the peripheral nerve defects. In all these types of reconstruction, the basic principles of microsurgery are necessary and the surgeon should be aware of them in order to achieve a successful reconstruction. The purpose of the present review was to present the most current data concerning the surgical options available for bridging such defects.

End-to-side versus end-to-end neurorrhaphy at the peroneal nerve in rats

PURPOSE

To evaluate three different kinds of neurorrhaphy of the peroneal nerve.

METHODS

Eigthy rats were divided into 5 groups. Control: nerve had no intervention. End-to-end (EE): nerve was cut and elongated with a nerve graft with two end-to-end neurorrhaphies. End-to-side (ES): nerve was cut and sutured to the graft with at the lateral side of the nerve. Side-to-end (SE): the nerve was cut and sutured to the graft with end-to-end neurorrhaphy. Denervated: nerve was cut and both endings were buried into the muscle. The evaluation was done by walking track analysis, electrophysiology, body mass, cranial tibial muscle mass, nerve and muscle fibers morphometry.

RESULTS

The EE, ES and SE have the same potential of reinnervation.

CONCLUSION

There is no functional or histological difference between these different types of neurorrhaphy.

Comparison of Peripheral Nerve Regeneration with Side-to-side, End-to-side, and End-to-end Repairs: An Experimental Study

Background:

The present study was conducted to find out a tool to enable improved functional recovery with proximal nerve injury. In this experimental study, nerve regeneration was compared between side-to-side (STS), end-to-side (ETS), and end-to-end repairs.

Methods:

The walk track analysis was used as an outcome of functional recovery. Nerve regeneration was studied with morphometry and histology 6 or 26 weeks postoperatively.

Results:

All 3 repair techniques showed regeneration of the nerve. From 12 weeks onward, the functional results of the 3 intervention groups were significantly better compared with the unrepaired control group. End-to-end repair was significantly better when compared with the STS and ETS groups. At 26 weeks, the functional and morphometric results and histologic findings did not differ between the STS and ETS groups. The functional results correlated with the morphometric findings in all groups.

Conclusions:

STS neurorrhaphy showed nerve regeneration, and the end results did not differ from clinically widely used ETS repair. Further studies are warranted to optimize the neurorrhaphy technique and examine possible applications of STS repair in peripheral nerve surgery.

Current concepts in end-to-side neurorrhaphy

In peripheral nerve injury, end-to-side neurorrhaphy involves coaptation of the distal stump of a transected nerve to the trunk of an adjacent donor nerve. It has been proposed as an alternative technique when the proximal stump of an injured nerve is unavailable or the nerve gap is too long to be bridged by a nerve graft. Experimental and clinical data suggests that end-to-side neurorrhaphy can provide satisfactory functional recovery for the recipient nerve, without any deterioration of the donor nerve function. The most accepted mechanism of nerve regeneration following end-to-side neurorrhaphy is collateral sprouting. The source of the regenerating axons traveling in the epineurium of the donor nerve is thought to be the proximal Ranvier’s nodes at the site of end-to-side neurorrhaphy, however, histologic evidence is still lacking. Partial neurotomy of the donor nerve may enhance regeneration of motor neurons through end-to-side neurorrhaphy and reinnervation of motor targets.

Role of chronic Schwann cell denervation in poor functional recovery after nerve injuries and experimental strategies to combat it

OBJECTIVE

To present our data about the role of chronic denervation (CD) of the distal nerve stumps as compared with muscle denervation atrophy and experimental strategies to promote better functional recovery.

METHODS

A rat model of nerve injury and repair was used. The common peroneal branch of the sciatic nerve was subjected to 0 to 24 weeks of CD before cross-suture with the tibial motoneurons. Our outcome measures included the numbers of motoneurons that regenerated their axons and the numbers that reinnervated muscle targets (motor units). To overcome the effects of CD, we used subcutaneous injection of FK506 and in vitro reactivation of Schwann cells that had been subjected to 24 weeks of CD with transforming growth factor beta.

RESULTS

Numbers of regenerated motoneurons and reinnervated motor units decreased as a function of duration of CD. However, axons that regenerated through the distal nerve stumps reinnervated the muscle targets and even formed enlarged motor unit size regardless of the duration of CD. FK506 doubled the numbers of tibial motoneurons that regenerated their axons into the common peroneal nerve even after delayed repair. Reactivation of chronically denervated Schwann cells with transforming growth factor beta significantly increased their capacity to support axonal regeneration.

CONCLUSION

CD of the distal nerve stumps is the primary factor that results in poor axonal regeneration and subsequently poor functional recovery. Acceleration of the rate of axonal regeneration and/or reactivation of Schwann cells of the distal nerve stumps are effective experimental strategies to promote axonal regeneration and functional recovery.