Abstract
BackgroundSurgical treatment of neuromas involves excision of neuromas proximally to the level of grossly "normal" fascicles; however, proximal changes at the axonal level may have both functional and therapeutic implications with regard to amputated nerves. In order to better understand the retrograde "zone of injury" that occurs after nerve transection, we investigated the gross and histologic changes in transected nerves using a rabbit forelimb amputation model.MethodsFour New Zealand White rabbits underwent a forelimb amputation with transection and preservation of the median, radial, and ulnar nerves. After 8 weeks, serial sections of the amputated nerves were then obtained in a distal-to-proximal direction toward the brachial plexus. Quantitative histomorphometric analysis was performed on all nerve specimens.ResultsAll nerves demonstrated statistically significant increases in nerve cross-sectional area between treatment and control limbs at the distal nerve end, but these differences were not observed 10 mm more proximal to the neuroma bulb. At the axonal level, an increased number of myelinated fibers were seen at the distal end of all amputated nerves. The number of myelinated fibers progressively decreased in proximal sections, normalizing at 15 mm proximally, or the level of the brachial plexus. The cross-sectional area of myelinated fibers was significantly decreased in all sections of the treatment nerves, indicating that atrophic axonal changes proceed proximally at least to the level of the brachial plexus.ConclusionsMorphologic changes at the axonal level extend beyond the region of gross neuroma formation in a distal-to-proximal fashion after nerve transection. This discrepancy between gross and histologic neuromas signifies the need for improved standardization among neuroma models, while also providing a fresh perspective on how we should view neuromas during peripheral nerve surgery.
Highlights
Surgical treatment of neuromas involves excision of neuromas proximally to the level of grossly “normal” fascicles; proximal changes at the axonal level may have both functional and therapeutic implications with regard to amputated nerves
Gross examination of the amputated nerve stumps revealed traumatic neuroma tissue that was enlarged with nodular fusiform formation at the distal end of each of the transected nerves
In the amputated nerve stumps, axonal regeneration, axonal bundle disorganization and disorientation, and interstitial fibrosis progressively normalized in a distal-to-proximal fashion but are still present even at a distance of 15 mm proximal to the distal neuroma end when compared to control nerve specimens
Summary
Surgical treatment of neuromas involves excision of neuromas proximally to the level of grossly “normal” fascicles; proximal changes at the axonal level may have both functional and therapeutic implications with regard to amputated nerves. Numerous surgical techniques have been proposed for the prevention and treatment of neuromas, including simple ligation [10,11]; capping the nerve stump with various materials [12,13,14,15]; translocation into nerve tissue through end-to-side or centro-central coaptation [16,17,18]; and transposition of the nerve ending into bone [8,19], fat [20,21], muscle [6,22,23,24], and, more recently, vein [25,26,27,28]. Regardless of technique, the fundamental principle of neuroma surgery involves excising the injured nerve segment proximally to the level of grossly normal fascicles. The zone of injury of a peripheral nerve ending in a classic neuroma is not defined, and understanding the microanatomy of these situations is important both in clinical peripheral nerve surgery, as well as for the standardization of all animal nerve models that attempt to investigate neuroma treatments
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