Rajiv Midha

Analysis of upper and lower extremity peripheral nerve injuries in a population of Patients with multiple injuries

BACKGROUND The purpose of this study was to determine the prevalence, cause, severity, and patterns of associated injuries of limb peripheral nerve injuries sustained by patients with multiple injuries seen at a regional Level 1 trauma center. METHODS Patients sustaining injuries to the radial, median, ulnar, sciatic, femoral, peroneal, or tibial nerves were identified using a prospectively collected computerized database, maintained by Sunnybrook Health Science Centre, and a detailed chart review was undertaken. RESULTS From a trauma population of 5,777 patients treated between January 1, 1986, and November 30, 1996, 162 patients were identified as having an injury to at least one of the peripheral nerves of interest, yielding a prevalence of 2.8%. These 162 patients sustained a total of 200 peripheral nerve injuries, 121 of which were in the upper extremity. The mean patient age was 34.6 years (SEM +/- 1.1 year), and 83% of patients were male. The mean injury severity score was 23.1 (+/-0.90), and the mean length of hospital stay was 28 days (+/-1.8). CONCLUSIONS Motor vehicles crashes predominated (46%) as the cause of injury. The most frequently injured nerve was the radial nerve (58 injuries), and in the lower limb, the peroneal nerve was most commonly injured (39 injuries). Diagnosis of a peripheral nerve injury was made within 4 days of admission to Sunnybrook Health Science Centre in 78% of the cases. Surgery was required to treat 54% of patients. Head injuries were the most common associated injury, occurring in 60% of patients. Other common associated injuries included fractures and dislocations. The present report aims to aid in identification and treatment of peripheral nerve injuries.

Peripheral nerve regeneration through guidance tubes

Abstract Biological nerve grafts have been extensively utilized in the past to repair peripheral nerve injuries. More recently,the use of synthetic guidance tubes in repairing these injuries has gained in popularity.This review focuses on artificial conduits, nerve regeneration through them, and an account of various synthetic materials that comprise these tubes in experimental animal and clinical trials. It also lists and describes several biomaterial considerations one should regard when designing, developing, and manufacturing potential guidance channel candidates. In the future, it it likely that the most successful synthetic nerve conduit will be one that has been fabricated with some of these strategies in mind.

Is multicomponent T2 a good measure of myelin content in peripheral nerve

Multicomponent T2 relaxation of normal and injured rat sciatic nerve was measured. The T2 relaxation was multiexponential, indicating the multicompartmental nature of T2 decay in nerve tissue. The size of the short, observed T2 component correlated very well with quantitative assessment of myelin using computer‐assisted histopathological image analysis of myelin. Specifically, the size of the short T2 component reflected the processes of myelin loss and remyelination accompanying Wallerian degeneration and regeneration following trauma. However, it represented all myelin present in the sample and did not distinguish between intact myelin and myelin debris. Other changes in T2 spectra were also observed and could be correlated with axonal loss and inflammation. The study also questions the validity of previously offered interpretations of T2 spectra of nerve. Magn Reson Med 49:638–645, 2003.

MR properties of excised neural tissue following experimentally induced inflammation

Changes in the MR parameters of inflamed neural tissue were measured in vitro. Tumor necrosis factor‐alpha (TNF‐α) was injected into rat sciatic nerves to induce inflammation with negligible axonal loss and demyelination. The MR parameters, such as T1/T2 relaxation and magnetization transfer (MT), were measured 2 days after TNF‐α injection and were found to be substantially different from those of normal nerves. The average T1/T2 relaxation times increased, whereas the MT ratio (MTR) and the quantitative MT parameter M0B (which describes the semisolid pool of protons) decreased. The MR parameters correlated very well with the extracellular volume fraction (EM) of neural tissue evaluated by quantitative histopathology. The multicomponent T2 relaxation was shown to provide the best quantitative assessment of changes in neural tissue microstructure, and allowed us to distinguish between the processes of inflammation and demyelination. In comparison, the MT measurements were less successful due to competing contributions of demyelination and pH‐sensitive changes in the MT effect. Magn Reson Med 51:473–479, 2004.

COLD PRESERVED NERVE ALLOGRAFTS: CHANGES IN BASEMENT MEMBRANE, VIABILITY, IMMUNOGENICITY, AND REGENERATION

Rat sciatic nerve graft segments were harvested and pretreated by either placement in the University of Wisconsin Cold Storage Solution at 5°C and storage from 1 to 26 weeks, or repeatedly freezing (−40°C) and thawing (20°C). Following pretreatment, grafts were transplanted as either syngeneic or allogeneic nerve grafts. Storage and freeze–thawing did not affect the Schwann cell basal lamina or laminin distribution of the peripheral nerve. Graft cell viability decreased with increasing time of storage, with some viable cells detectable even after 3 weeks of storage. Freeze–thawed grafts were not viable. Increasing time of storage led to decreasing immune response and graft rejection, but improved regeneration. Freeze–thawed and 26‐week stored allografts were nonimmunogenic and rejection was not seen, but regeneration was delayed compared to autografts. Graft storage may become a useful adjunct to clinical nerve allografting to permit elective scheduling of surgery, provide greater time for preoperative tissue testing, and possibly blunt the immune response.

Practical considerations concerning the use of stem cells for peripheral nerve repair

In this review the authors intend to demonstrate the need for supplementing conventional repair of the injured nerve with alternative therapies, namely transplantation of stem or progenitor cells. Although peripheral nerves do exhibit the potential to regenerate axons and reinnervate the end organ, outcome following severe nerve injury, even after repair, remains relatively poor. This is likely because of the extensive injury zone that prevents axon outgrowth. Even if outgrowth does occur, a relatively slow growth rate of regeneration results in prolonged denervation of the distal nerve. Whereas denervated Schwann cells (SCs) are key players in the early regenerative success of peripheral nerves, protracted loss of axonal contact renders Schwann cells unreceptive for axonal regeneration. Given that denervated Schwann cells appear to become effete, one logical approach is to support the distal denervated nerve environment by replacing host cells with those derived exogenously. A number of different sources of stem/precursor cells are being explored for their potential application in the scenario of peripheral nerve injury. The most promising candidate, transplant cells are derived from easily accessible sources such as the skin, bone marrow, or adipose tissue, all of which have demonstrated the capacity to differentiate into Schwann cell-like cells. Although recent studies have shown that stem cells can act as promising and beneficial adjuncts to nerve repair, considerable optimization of these therapies will be required for their potential to be realized in a clinical setting. The authors investigate the relevance of the delivery method (both the number and differentiation state of cells) on experimental outcomes, and seek to clarify whether stem cells must survive and differentiate in the injured nerve to convey a therapeutic effect. As our laboratory uses skin-derived precursor cells (SKPCs) in various nerve injury paradigms, we relate our findings on cell fate to other published studies to demonstrate the need to quantify stem cell survival and differentiation for future studies.

MR properties of rat sciatic nerve following trauma

T1 and T2 relaxation times, magnetization transfer (MT), and diffusion anisotropy of rat sciatic nerve were measured at different time intervals following trauma. The nerve injury was induced by either cutting (irreversible nerve degeneration) or crushing (degeneration followed by regeneration). The MR properties were measured for proximal and distal portions of the injured nerve. The portions of the nerve proximal to the induced injury exhibited MR characteristics similar to those of normal nerves, whereas the distal portions showed significant differences in all MR parameters. These differences diminished in the regenerating nerves within approximately 4 weeks post injury. In the case of irreversible nerve damage, the differences in the distal nerves were slightly larger and did not resolve even 6 weeks after induced trauma. The MR measurements were correlated with histopathology exams. Observed changes in tissue microstructure, such as demyelination, inflammation, and axonal loss, can result in a significant increase in the average T1 and T2 relaxation times, reduction in the MT effect, and decrease in diffusion anisotropy. MR parameters, therefore, are very good indicators of nerve damage and may be useful in monitoring therapies that assist nerve regeneration. Magn Reson Med 45:415–420, 2001.

The Fate of Schwann Cells in Peripheral Nerve Allografts

The phenotype of Schwann cells, whether of host or donor origin, in nerve allografts has been a source of debate. The origin of Schwann cells in peripheral nerve allografts under conditions of no, temporary or continuous immunosuppression was assessed by immunohistochemistry. We hypothesized that host-derived Schwann cells would replace rejected foreign donor Schwann cells after withdrawal of immunosuppression. A murine model of nerve transplantation to normal (wild-type) hosts from donor Shiverer mice, a mutant whose Schwann cells are deficient in myelin basic protein, was used and antibody reactivity against myelin basic protein was employed to ascertain the identity of Schwann cells in the nerve allograft. Without immunosuppression, donor Shiverer Schwann cells were rejected and the nerve graft morphology was restored by host-derived Schwann cells. With continuous immunosuppression, donor Shiverer Schwann cells persisted in the graft segment, associated with a chronic rejection phenomenon. The latter allowed migration of host-derived Schwann cells, over time, into the graft segment in approximately half the cases. After withdrawal of finite (6 weeks) immunosuppression, a rejection response eliminated donor Schwann cells. Replacement by host Schwann cells ensued as was hypothesized.

Walking Track Analysis: Utilization of Individual Footprint Parameters

Functional assessment of rat sciatic, tibial, and peroneal nerve injuries was performed using walking track analysis. Individual walking print length (PL), toe spread (TS), and intermediate toe spread (ITS) values were measured up to 24 weeks after specific nerve transection, with or without repair. Sciatic and tibial nerve manipulation initially affected all footprint measurements, consistent with loss of intrinsic and extrinsic motor function. After sciatic repair, TS demonstrated partial recovery without any substantial recovery in PL or ITS, compared with sciatic transection values. By contrast, after tibial repair, PL values recovered dramatically, between 16 and 24 weeks, to levels not significantly different from control subjects. This was not observed after tibial transection without repair. TS recovered partially, whereas ITS recovered to control levels by 20 weeks after tibial repair. Peroneal transection resulted in multiple contractures, rendering this group unmeasurable at 4 weeks. After peroneal repair, only the PL reflected significant loss of function at 2 weeks, recovering to control values by 8 weeks. Manual TS measurements in nonwalking rats did not reflect functional nerve regeneration. Thus, individual PL measurements alone can be used to characterize functional recovery after tibial and peroneal nerve injury, whereas TS reflected recovery after sciatic nerve injury.

Locally synthesized calcitonin gene-related Peptide has a critical role in peripheral nerve regeneration.

Abstract Regeneration of peripheral nerves involves complex and intimate interactions between axons and Schwann cells. Here, we show that local axon synthesis and action of the neuropeptide calcitonin gene-related peptide (CGRP) is critical for this collaboration. After peripheral sural sensory axon injury in rats, we observed an unexpectedly large proportion of axons that newly expressed CGRP during regeneration. Intense peptide expression accompanied local rises in &agr;CGRP mRNA in the nerve trunk, and there was evidence of transport of &agr;CGRP mRNA into regenerating axons, indicating intra-axonal peptide synthesis. Calcitonin gene-related peptide receptor and its receptor activity modifying protein were expressed onadjacent Schwann cells, where they were available for signaling. Moreover, exogenous CGRP induced proliferation in isolated adult Schwann cells. New axon outgrowth and CGRP expression depended on local peptide synthesis and were inhibited by exposure tolocal translation inhibitors. Local delivery of siRNAs to either &agr;CGRP or receptor activity modifying protein 1 to sites of nerve transection was associated with severe disruption of axon outgrowth.These findings indicate that robust localized intra-axonal translation of the CGRP neuropeptide during regeneration signals Schwann cell proliferation, behavior that is critical for partnering during adult peripheral nerve regrowth.