Reconstruction of flexor tendon pulley with expanded polytetrafluoroethylene (E-PTFE). An experimental study in rabbits

Gore-Tex (expanded Polytetrafluoroethylene, E-PTFE) was used to replace the distal pulleys on the proximal phalanges of 20 rabbits. Morphology and function of the reconstructed pulleys were evaluated at 12-20 weeks. The breaking strength of the E-PTFE pulley equalled that of a normal pulley. Range of motion, tendon excursion, and force of flexion were no different from those of normal pulleys. No adhesions between flexor tendons and synovial tendon sheaths or the E-PTFE pulleys could be detected. No adverse tissue reactions were seen. Fibroblast-like cells from the surrounding tissues had grown into the membrane. In other experiments, where the pulleys had been either removed or detached, local fibrosis and adhesions were seen, and the deep flexor tendons had ruptured. The results of the present study indicate that E-PTFE can be used as a biosynthetic replacement for damaged pulleys.

Effects of sympathetic stimulation on C-fibre response after peripheral nerve compression: an experimental study in the rabbit common peroneal nerve

Non-myelinated C-fibre responses during sympathetic trunk stimulation were studied in rabbit common peroneal nerve 2 weeks after the nerve had been subjected to compression at 400 mmHg for 30 min. Our previous studies have demonstrated that during sympathetic trunk stimulation the compound action potential of uninjured somatic C-fibres is characterized by a reduced amplitude and an increased latency. In the present study, nerve compression changed the C-fibre response to sympathetic stimulation. Three out of eight nerves reacted to nerve compression by increased C-fibre compound action potential amplitude in response to sympathetic stimulation. In three other rabbits with compressed nerves the C-fibre action potential amplitude was unchanged, and in the remaining two rabbits the action potential amplitude was decreased during sympathetic stimulation. The action potential latency increased in all tested compressed C-fibres. The phenomenon of increased C-fibre amplitude during sympathetic activation has not been observed in uninjured nerves. As in uninjured nerves, noradrenaline infusion produced an increased C-fibre action potential amplitude and latency in six animals. Sympathetic stimulation did not affect the A-fibre response. These results indicate that sympathetic activity influences the conduction properties in C-fibres of somatic origin and that the response can be changed after a nerve injury. The findings may be of importance for the understanding of pain aggravation in different types of nerve injuries during increased sympathetic activity.

Vibration exposure and peripheral nerve fiber damage

The hind leg of adult rats was exposed to vibrations (82 Hz; amplitude peak-to-peak 0.21 mm) for 4 hours during 5 consecutive days. Light and electron microscopic examination of the plantar and sciatic nerves were done immediately after the exposure period or after a 2- or 4-week recovery period. Light microscopic examination did not reveal any distinct signs of injury. However, ultrastructurally unmyelinated fibers in the plantar nerves showed distinct changes, with deranged axoplasmic structure and/or accumulation of smooth endoplasmatic reticulum. These changes were to a large extent reversible in 2 weeks and appeared normalized after a 4-week recovery period. No ultrastructural changes could be observed in the sciatic nerve. However, when the sciatic nerve was crushed after 5 days of vibration exposure, axonal outgrowth was increased 23% as compared with controls. These findings confirm that vibration induces nerve fiber damage, in this experimental model expressed as a "conditioning effect" contributing to increased regeneration potential of the corresponding neurones.

The neurone and its response to peripheral nerve compression

In all types of peripheral nerve injury, it is important to realize that the lesion affects one extended cell, the neurone, which extends from the central nervous system down to the target tissue in the extremity. Compression of a peripheral nerve can disturb the intraneural transport (axonal transport) of a large variety of substances. This may be followed by morphological and biochemical changes in the nerve cell body. These central changes may effect the axon as a whole and confer on the nerve an increased susceptibility to trauma. Studies concerning the reaction of neurones to compression, relevant when discussing the double crush syndrome, are reviewed.

Effects of nerve compression or ischaemia on conduction properties of myelinated and non-myelinated nerve fibres. An experimental study in the rabbit common peroneal nerve

Compound action potentials of both myelinated (A) and non-myelinated (C) fibres in the common peroneal nerve of rabbits were studied during and after acute, graded compression of the nerve at 200 or 400 mmHg applied for 2 h or during ischaemia created by nitrogen inhalation or aortic occlusion. Compression of the nerve at 200 mmHg blocked the AI component (large myelinated fibres) after about 23 min, while compression at 400 mmHg shortened this time to 11 min. The A2 component (thinner myelinated fibres) had a lower conduction velocity and a higher resistance to compression. There was just a slight decrease in conduction velocity of the non-myelinated fibres when the nerves were compressed at 200 mmHg for 2 h. However, compression at 400 mmHg for 2 h induced a marked deterioration of amplitude and conduction velocity of the C-fibres. There was an incomplete restitution of function of A- and C-fibres during 2 h of recovery. The thinner myelinated fibres were more susceptible to deprivation of oxygen than the thicker ones, while non-myelinated fibres differed in response according to method of ischaemia induction. It is concluded that non-myelinated fibres are very resistant to compression and a very high pressure (greater than 400 mmHg) is needed to affect these fibres.

Axonal growth in mesothelial chambers: effects of a proximal preconditioning lesion and/or predegeneration of the distal nerve stump

Preformed, autologous mesothelial chambers were utilized to study axonal growth following selective predegeneration of the distal nerve stump and/or preconditioning of the proximal nerve stump. The left and/or right sciatic nerve of rats was exposed and transected in the thigh. Two weeks after transection, the left proximal nerve stump was cross-anastomosed with the right distal nerve stump by using a mesothelial chamber leaving a 15-mm gap between the two nerve stumps. Previous studies have shown that axonal overgrowth normally does not occur over this gap distance to the distal stump. Three months after cross-anastomosing, regeneration across the 15-mm gap was evaluated by muscle action potential recordings and light microscopical examination. In experiments in which a distal nerve stump was selectively degenerated and the proximal segment was freshly cut, axons had bridged the 15-mm gap in six of seven rats. When a proximal preconditioned nerve stump was matched with a freshly cut distal stump, axonal overgrowth occurred in only 4 of 10 experiments. In experiments including a proximal preconditioned nerve stump and a distal predegenerated stump, axons bridged the gap in 6 of 8 experiments. We concluded that a priming lesion, including manipulation with proximal and/or distal stump, enhances axonal growth in mesothelial chambers.

Peripheral nerve regeneration in Gore-tex chambers

Gore-tex chambers were used to bridge a 6 mm gap between the proximal and distal nerve stumps of a rat sciatic nerve. The wall structure of these chambers is characterized by "nodes" interconnected by smaller fibrils. Chambers with internodal distances of 5, 10 and 30 microns were used. Some 30 microns chambers were coated from the outside with Gore-tex (0.2 micron internodal distance) and others were coated from the inside. Regeneration after 12 weeks, as evidenced by muscle action potential recordings and light microscopy, was successful regardless of what type of chamber had been used. The organization of the nerve structure varied among different chamber types. A well organized coaxial nerve structure with myelinated axons was observed if inner-coated chambers were used. In chambers that were not coated or in outer-coated chambers tissue completely filled the chambers, and myelinated axons were arranged in mini-fascicles surrounded by loose connective tissue.

Transient increase in insulin-like growth factor I immunoreactivity in rat peripheral nerves exposed to vibrations

Hind legs of adult rats were exposed to vibrations (81 Hz; amplitude 0.50 mm peak to peak) for 4 h during two consecutive days. The sciatic, tibial and plantar nerves were isolated and processed for immunohistochemical demonstration of IGF-I (insulin-like growth factor I; somatomedin C) immunoreactivity at different time intervals after the vibration exposure. In sham-exposed rats the axons in peripheral nerves showed no or faint IGF-I immunoreactivity while most Schwann cells were negative. Exposure of the hind legs to vibrations induced increased IGF-I immunoreactivity in the Schwann cells, demonstrable at the end of the exposure period and reaching maximal intensity 2-3 days after vibration exposure. Several distended axons similarly showed increased staining. The IGF-I immunoreactivity decreased after 7-10 days to almost the level in the control nerves. The most extensive changes were observed in the plantar nerves. The tibial nerves similarly expressed strongly increased IGF-I immunoreactivity in their Schwann cells. The sciatic nerve showed, however, only slightly to moderately increased staining. Cells in the epineurium of the plantar and, to a limited extent, of the tibial nerves expressed concomitantly increased IGF-I immunoreactivity. We conclude that the transiently increased IGF-I immunoreactivity in peripheral nerves reflects reactive changes caused by vibrations and most prominently expressed by the Schwann cells.

Transiently increased insulin-like growth factor I immunoreactivity in tendons after vibration trauma. An immunohistochemical study on rats

The hind limbs of anaesthetized rats were exposed to vibration trauma (81 Hz; amplitude peak to peak 0.50 mm) for 4 hours during 2 consecutive days. The animals were examined in groups of 4 immediately after the last exposure, and after 1, 2, 3, 5, 7, 10, 14 and 28 days. The Achilles tendons and the tendons of the anterior tibialis muscles were sampled and processed to demonstrate IGF-I immunoreactivity. In the normal Achilles tendon and in the tendon of the anterior tibial muscle, slight IGF-I immunoreactivity was seen in many of the long slender fibroblasts between the collagen bundles. A strong increase in the IGF-I immunoreactivity appeared in the anterior tibialis muscle tendon 3 days after the last vibration exposure. In addition, the tendon fibroblasts became hypertrophic. A similar but less striking increase in IGF-I immunoreactivity appeared in the Achilles tendon. The peak intensity and frequency of stained cells were achieved after 7 days for both tendons. The intensity then levelled off, and was normalized after 28 days. It is concluded that acute exposure to vibrations induces reactive changes in fibroblasts in tendons, which may reflect a change to a more active synthesising state, as a response to the vibration trauma. The transiently altered expression of IGF-I immunoreactivity forms a link in a chain of events regulating the functional activity level of fibroblasts in response to a trauma.

Intraneural edema following exposure to vibration

Peripheral neuropathy represents a well-known complication from long-term exposure to vibration. In the present study an experimental model is presented with the purpose of analyzing the formation of intraneural edema following vibration exposure. Vibration (82 Hz, peak-to-peak amplitude 0.21 mm) was induced in the hind limb of rats by the use of vibrating electric motors during 4 h/d for 5 d. Tracer techniques (with albumin Evans blue and horseradish peroxidase) were used to study the permeability of intraneural microvessels after the vibration exposure on day 5. It was found that the vibration trauma in this model induced epineurial edema in the sciatic nerve. It is hypothesized that the formation of intraneural edema may be an important pathophysiological factor in the occurrence of vibration-induced neuropathy.

Effects of epidural and intrathecal application of collagenase in the lumbar spine: an experimental study in rabbits

An experimental model is described in which collagenase in different concentrations and volumes were applied epidurally or intrathecally in the rabbit lumbar spine. This made it possible to study the tissue effects in a situation similar to that of collagenase leaking from a disc or accidental epidural or intrathecal injection at chemonucleolysis. Epidurally applied collagenase, in higher concentration, caused a local thinning of the dura. This effect was reduced at lower concentrations and volumes. Intrathecally injected collagenase, even in small amounts, caused intrathecal hemorrhage and acute paraplegia in the hind limbs. Therefore, in the clinical situation, intrathecal injection of collagenase must be avoided.

Treatment with an aldose reductase inhibitor can reduce the susceptibility of fast axonal transport following nerve compression in the streptozotocin-diabetic rat

The effect of treatment with an aldose reductase inhibitor on the susceptibility of peripheral nerves to compression was studied in rats made diabetic by the injection of streptozotocin (50 mg.kg-1). The response to nerve compression was determined in untreated diabetic rats after 22 days of diabetes and compared with the response in two similar groups of diabetic rats which had been treated with the aldose reductase inhibitor 'Statil' (ICI 128436; 25 mg.kg-1.day-1 orally) either from the induction of diabetes or for 7 days prior to nerve compression. Two groups of non-diabetic rats were treated with 'Statil' for either 22 days or 7 days to act as controls. Inhibition of fast axonally transported proteins was induced by local compression of the sciatic nerves 4 h after application of 3H-leucine to the motor neurone cell bodies in the spinal cord. The inhibition of fast axonal transport was quantified by calculation of a transport block ratio. Compression at 30 mmHg for 3 h induced a significantly greater (p less than 0.05) inhibition of axonal transport at the site of compression in nerves of untreated diabetic rats (transport block ratio 0.96 +/- 0.24, n = 8) than in nerves of control rats treated with the aldose reductase inhibitor for either the shorter time of 7 days (0.71 +/- 0.17, n = 10) or the longer time of 22 days (0.69 +/- 0.08, n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Morphologic changes in nerve cell bodies induced by experimental graded nerve compression

The effects of experimental nerve fiber compression on the morphology of nerve cell bodies were studied. Rabbit cervical vagus nerves were crushed or subjected to compression at 0 (sham compression), 30, 200, or 400 mm Hg for 2 h. Morphometric measurements and light microscopical evaluation of the nerve cell bodies in the nodose ganglion were carried out 7 days after the injury on the injured and control sides. Crush and compression at 30, 200, or 400 mm Hg induced a slight decrease in total cell profile area compared with the control side, but it was not related to degree of injury. There was a marked decrease in the ratio between nuclear and total cell profile area (nuclear volume density) after compression at 200 and 400 mm Hg, as well as after crush, and to a lesser extent after compression at 30 mm Hg. Compression at 30, 200, or 400 mm Hg as well as crush of the vagus nerve induced migration of the nucleus to the periphery and dispersion of Nissl substance in the cytoplasm of the nerve cell bodies. Sham compression induced no obvious changes in total cell profile area, nuclear volume density, or migration of nucleus. There was a somewhat increased percentage of cells showing dispersion of Nissl substance in sham-compressed animals than in controls. The results show that nerve fiber compression induced pronounced reactive changes in nerve cell bodies, even at low pressures, corresponding to those found in human carpal tunnel syndrome. Such pressures are known to induce reversible inhibition of fast axonal transport as well as inhibition of retrograde axonal transport. The nerve cell body changes in the nodose ganglion may thus be a reaction to disturbances in axonal transport.

Graded inhibition of retrograde axonal transport by compression of rabbit vagus nerve

Effects of experimental compression at different pressures on retrograde axonal transport were studied in rabbit vagus nerve. Proteins in the sensory neurones were radiolabelled by injection of [3H]leucine into the nodose ganglion. Sixteen hours after labelling, a small compression chamber and/or ligatures were applied around the cervical part of the vagus nerve for 8 h. Compression of the vagus nerve at 20, 30 and 200 mm Hg pressure induced a graded inhibition of both retrograde and anterograde transport of the radiolabelled proteins. Neither retrograde nor anterograde transport was affected by the presence of the non-inflated chamber. The results indicate that compression at pressures similar to those found in human carpal tunnel syndrome can block retrograde axonal transport. The consequences of inhibition of retrograde and anterograde axonal transport for the metabolism in the nerve cell bodies are discussed.

Experimental hyperthyroidism stimulates axonal growth in mesothelial chambers

An experimental model is presented for studying axonal growth after experimental hyperthyroidism and hypothyroidism. The left sciatic nerve of the rat was transected and transposed to the back. The proximal nerve stump was inserted into a 50-mm-long mesothelial chamber leaving the distal end of the chamber open. Different groups of young adult rats were given daily injections of thyroxine (10 micrograms/100 g body weight) or the goitrogen, thiamazol, in the drinking water (0.125 g/liter) for 12 weeks. Thyroxine treatment increased significantly the extent of axonal outgrowth from the proximal nerve stump compared with untreated rats. Experimental hypothyroidism (thiamazol treatment), evidenced by a retarded body growth, did not affect the extent of axonal outgrowth. In other experiments the left proximal nerve stump was cross-anastomosed with the right distal nerve stump. The two nerve stumps were bridged with a mesothelial chamber leaving a 15-mm gap. This gap distance is known from our previous studies to inhibit axonal overgrowth to the distal nerve stump. As evidenced by histological evaluation, in three of six thyroxine-treated rats, axons had bridged the 15-mm gap. We conclude that experimentally induced hyperthyroidism enhances axonal growth in mesothelial chambers.

Absence of ongoing activity in fibres arising from proximal nerve ends regenerating into mesothelial chambers

Morphological studies have indicated that proximal nerve ends of transected rat sciatic nerves regenerating into preformed mesothelial chambers show a different organization as compared to neuromas developed in contact with a muscle fascia. We have studied the physiological properties of nerve fibres arising from these types of preparations with reference to ongoing activity, response to mechanical stimulation and noradrenaline sensitivity. The study included also fibres arising from ligated and encapsulated neuromas. Fibres with ongoing activity arising from the neuroma could be found from neuromas in contact with a muscle fascia and also from ligated and encapsulated neuromas. This ongoing activity was enhanced by mechanical stimulation and i.v. infusion of noradrenaline. In contrast, fibres arising from proximal nerve ends in mesothelial chambers did not show ongoing activity. These silent fibres responded dynamically to light mechanical stimulation. Noradrenaline did not induce ongoing activity in these fibres.

Mechanical effects of compression of peripheral nerves

Effects of graded compression on nerve function were analyzed in order to evaluate the relative importance of pressure level and duration of compression for functional deterioration. The pressure was applied by means of a small inflatable cuff. The effects of two pressure levels, i.e., 80 mm Hg applied for 2 hr or 400 mm Hg applied for 15 min, were studied in rabbit tibial nerves. The lower pressure tested, which is known to induce ischemia of the compressed nerve segment, also causes some degree of mechanical deformation of the nerve trunk, which leads to incomplete recovery following pressure release. The duration of compression is of importance for the degree of nerve injury even at the higher pressure level tested.

Evidence indicating trophic importance of IGF-I in regenerating peripheral nerves

The mechanisms influencing regeneration of peripheral nerves are incompletely known, but growth factors are supposed to play a key role. In the present study, we demonstrate, with the aid of immunohistochemical methods, that somatomedin C (Sm-C/insulin-like growth factor I/IGF-I) rapidly increased from low to high concentrations, reaching peak values in 2 weeks, in regenerating sciatic nerves of adult rats. In addition, IGF-I was demonstrated extracellularly, never observed in the control nerves. Reactive Schwann cells appeared to be the major source for IGF-synthesis. Higher concentrations were seen in tubulated nerves as compared to sutured ones. It is proposed that IGF-I exerts important growth supporting effects on regenerating peripheral nerves.

Effects of nerve compression on fast axonal transport in streptozotocin-induced diabetes mellitus. An experimental study in the sciatic nerve of rats

The hypothesis that nerves in diabetes mellitus exhibit an increased susceptibility to compression was experimentally tested. Inhibition of fast axonal transport was induced by local compression in sciatic nerves of rats with streptozotocin-induced diabetes mellitus. Fast anterograde axonal transport was measured after application of 3H-leucine to the motor neurone cell bodies in the spinal cord. The sciatic nerve was subjected to local, graded compression in vivo by a small compression chamber. The amount of accumulation of proteins was quantified by calculation of a transport block ratio. Compression at 30 mm Hg for 3 h induced a significantly greater (p less than 0.05) accumulation of axonally transported proteins at the site of compression in nerves of diabetic animals (transport block ratio: 1.01 +/- 0.35; n = 7) than in nerves of controls (0.67 +/- 0.16; n = 7). Accumulation was significantly higher in ligature experiments of both control (1.34 +/- 0.44; n = 8; p less than 0.01) and diabetic animals (1.45 +/- 0.30; n = 8; p less than 0.05), indicating that the block of transport in compressed nerves was incomplete. Neither sham compressed diabetic (0.50 +/- 0.09; n = 6) nor control (0.49 +/- 0.11; n = 6) nerves showed any block of axonal transport. The possible causes of the increased inhibition of fast axonal transport in diabetic rats are discussed. The results indicate that diabetes may lead to an increased susceptibility of peripheral nerves to compression.

Tissue specificity in nerve regeneration

In 1944 Weiss & Taylor presented experimental evidence against "neurotropism" in nerve regeneration. We used a silicone Y-chamber system to repeat some of those experiments. The proximal stump of transected rat sciatic nerve was introduced into the proximal inlet of the Y. One of the distal outlets was left empty, plugged or occupied by a tendon graft, the other outlet being occupied by a nerve graft. Analysis after 4 and 12 weeks showed in all cases a preferential or exclusive axonal growth towards the nerve piece. The results, indicating the existence of "tissue specificity", are contradictory to the results reported by Weiss & Taylor (30). The findings are discussed with respect to possible influence of humoral, cellular and molecular factors associated with the distal nerve stump as well as the matrix, formed between both nerve segments.

Effects of graded experimental compression on slow and fast axonal transport in rabbit vagus nerve

Effects of compression at low pressures on slow and fast axonal transport was investigated in rabbit vagus nerve. Proteins in the sensory fibres were radiolabelled by injection of [3H]leucine or [35S]methionine into the nodose ganglion. A small compression chamber and/or ligatures were applied around the cervical part of the vagus nerve for 8 h, at an appropriate time for the subsequent analysis of the effects of compression on both slow and fast transport of radiolabelled proteins. In normal nerves there were two waves of slowly transported proteins with rates of about 12-15 and 25-30 mm/day, respectively. SDS-polyacrylamide gel electrophoresis was used and confirmed that the main proteins which accumulated proximal to the ligatures had a molecular weight of 54 000-56 000. Neither compression of the nerve at 20 mm Hg nor sham-compression induced any statistically significant accumulation of slowly transported proteins at the site of compression. A higher pressure, i.e. 30 mm Hg, induced a marked but incomplete accumulation of slowly transported proteins. Fast transport was partially inhibited in some, but not all, nerves, when 20 mm Hg was applied for 8 h, in contrast to the lack of effect found previously with the same pressure applied for only 2 h. Despite these slight differences, the results indicate that both slow and fast transport are impaired by low pressure levels of around 20-30 mm Hg, which are comparable with those found in human compression neuropathies. The impaired provision of cytoskeletal elements to the distal axon may be of significance in the pathophysiology of nerve entrapment syndromes.

Changes in fast axonal transport during experimental nerve compression at low pressures

The minimal pressure for impairment of fast anterograde axonal transport was determined in rabbit vagus nerve. Proteins, transported by fast anterograde axonal transport, were labeled by a microinjection of [3H]leucine into the nodose ganglion, and a small compression chamber was applied around the cervical vagus nerve. In this way the nerve was subjected to acute, graded compression. Compression at 20 mm Hg for 2 h as well as sham compression did not induce accumulation of axonally transported proteins at the level of compression. However, a pressure of 30 mm Hg for 2 h induced a block of axonal transport at the site of compression. The causes of the axonal transport block are discussed as well as the minimal pressure level in relation to pressures found in clinical nerve compression lesions.

Axonal growth in mesothelial chambers. The role of the distal nerve segment

An experimental model is presented for studying nerve regeneration over gaps of various lengths between the both ends of a severed nerve. After transferring left and right sciatic nerves of rat to the back, the gap between the two nerve ends could be bridged by a preformed, tube-shaped mesothelial chamber of a desired length. When the gap length was 10 mm or less, a well developed nerve structure was generated in the chamber between the nerve ends, and axons from the left sciatic nerve reinnervated muscles in the right limb via the right sciatic nerve. When the gap length was extended to 15 mm or more no such regeneration occurred. When no distal nerve end was introduced into the chamber, there was a limited growth into this chamber over only 5-6 mm. This "limited growth phenomenon" is discussed with respect to a lack of "trophic" or cellular support from a distal nerve segment. It is also proposed that the termination of growth, seen under these circumstances, may suggest a new principle for avoiding the development of neuromas after nerve transections.