AAHS ASPN ASRM - 2013 Annual Meeting - American Association ...

Accuracy of Motor Axon Regeneration After Different Types of Nerve Injury and Repair in the Rat Sciatic Nerve Model
Institution where the work was prepared: Mayo Clinic, Rochester, MN, USA
Godard C.W. De Ruiter, MD1; M.J.A. Malessy2; Robert J. Spinner, MD1; A.O. Alaid1; J.K. Engelstad1; E.J. Sorenson, MD1; K.R. Kaufman, PhD1; P.J. Dyck, MD1;
A.J. Windebank, MD1; (1)Mayo Clinic, (2)Leiden University Medical Center
BACKGROUND:
Misrouting of regenerating axons is one of the factors that may explain the poor results often found after nerve injury and repair. Different techniques have
been used to investigate the accuracy of regeneration, but little is known about the degree of misrouting, especially in the repair of motor nerves that innervate
different target muscles.
MATERIALS:
We investigated the accuracy of motor axon regeneration in the rat sciatic nerve model after crush injury, direct coaptation, and autograft repair using two
recently introduced evaluation techniques: sequential retrograde tracing and digital video ankle motion analysis. Sequential tracing with retrograde labeling of
the peroneal motoneuron pool before and 8 weeks after nerve injury and repair was performed to quantify the accuracy of motor axon regeneration. Ankle
motion was analyzed to investigate the impact of misrouting on the recovery of ankle plantar and dorsiflexion. In addition, quantitative results of regeneration
were determined from compound muscle action potential recordings every other week, as well as nerve and muscle morphometry.
RESULTS:
After sequential tracing, only 71.4% (± 4.9%) of the peroneal motoneurons were found to be correctly routed 8 weeks after sciatic crush injury, 42.0% (± 4.2%)
after direct coaptation repair, and 25.1% (± 6.6%) after autograft repair. Functional recovery after all types of nerve injury and repair function was incomplete
partly as a result of a disturbed balance of ankle plantar and dorsiflexion. Quantitative results showed that reinnervation was faster after sciatic crush injury
than after direct coaptation and autograft repair. The mean muscle fiber size was also larger after crush injury. The number of regenerated motoneurons after
all types of nerve injury and repair was not significantly different from normal, but the number of myelinated axons was significantly increased distal to the
site of injury.
CONCLUSION:
Accuracy of regeneration after different types of nerve injury and repair in this study was found to be limited. These results can be used as basis for the development
of new nerve repair techniques that may improve the accuracy of regeneration.
Reconstruction of a 40 mm Nerve Gap in Rats Using Biodegradable Nerve Conduits Filled with Schwann Cells
Institution where the work was prepared: University of Tuebingen, Department of Handsurgery, Tuebingen/Germany, Germany
nektarios Sinis, MD1; Max Haerle, MD1; Stefan Becker, MD1; Burkhard Schlosshauer, PhD1; Michael Doser, PhD2; Harald Roesner, PhD3; Klaus Dietz, MD1; Hans-Werner
Mueller, PhD4; Hans-Eberhard Schaller, MD1; (1)University of Tuebingen, (2)ITV-Denkendorf, (3)University of Hohenheim, (4)University of Duesseldorf
In a former study we used a biodegradable nerve conduit consisting of a trimethylenecarbonate-co-epsilon-caprolactone (TMC/CL) polymer seeded with
Schwann cells to induce and promote regeneration across a 20 mm nerve gap in the rat median nerve. Regeneration was estimated to be equal to that of an
autologous graft, as judged by functional, histological, and electrophysiological parameters, as well as by muscle weight analysis of the flexor digitorum sublimis
muscle. In this study we increased the gap distance to 40 mm using a cross-chest procedure with interposition of the Schwann cell-filled nerve conduits
from the left median nerve to the right (group 3; n=16). For the autologous graft subjects, both ulnar nerves were harvested and interposed between the median
nerve stumps to create a 40 mm long autograft (group 2; n=16). A further control group was created using 16 non-operated animals (group 1). The functional
regeneration was assessed by means of the grasping test. Further examination was performed with histological analysis (S-100, PAM, Nissl), electrophysiological
recordings, and weighing of the flexor digitorum sublimis muscle. After 12 postoperative months, functional regeneration was seen only in three animals
of group 3 which reached about 10 % of that of the non-operated control animals (group I), however all autologous grafted animals demonstrated a partial
functional regeneration. Histological analysis of sections collected from these animals with the bioartificial nerve conduit confirmed strong morphological
changes with signs of Wallerian degeneration. In animals supplied with an autologous graft the histology demonstrated a more organized architecture of axons.
Electrophysiological recordings in the nerve tube supplied animals were displayed only in those three animals that demonstrated regeneration, while all animals
in the autologous graft group exhibited regenerative potentials. Furthermore, there was a significant decrease of muscle weight in the nerve conduit supplied
animals, which was more prominent than in the autologous grafted group. These results draw attention to the complexity of the mechanisms involved in nerve
regeneration since the bioartificial nerve conduit was successfully applied in a 20 mm gap however demonstrated only minor success in experiments 12 months
post surgery across the double gap length of 40 mm. Further consideration should be taken in optimizing the cellular and material components critical for
successful application.
Schwann cells, nerve conduit, nerve regeneration, cross-chest procedure
Biodegradability of Synthetic Nerve Grafts Is Beneficial to Peripheral Nerve Regeneration
Institution where the work was prepared: Leiden University Medical Centre, Department of Neurosurgery, Leiden, Netherlands
Carmen L.A.M. Vleggeert-Lankamp, Drs1; J.F.C. Wolfs1; Ana P. Pego, Drs2; R.J. van den Berg1; H.K.P. Feirabend1; Martijn J.A. Malessy1; E.A.J.F. Lakke1; (1)Leiden University
Medical Center, (2)University of Twente
In the present study we consider the influence of biodegradability of the synthetic nerve graft on regeneration. TriMethylene Carbonate (TMC) was copolymerized
with poly-Â-caprolactone (CL) to create a faster degrading copolymer. Nerve guides with an outer layer of TMC/CL and an inner layer of either TMC/CL
(fast degradable graft) or TMC (slowly degradable graft) were compared to each other, and to autografts and unoperated nerves. Twelve weeks after bridging
a 6 mm sciatic nerve lesion in the rat, the integrity of the nerve guides, the morphology of nerve at midgraft, morphometrical parameters of nerve and innervated
muscle, and electrophysiological parameters of the nerve were evaluated. The observed changes in nerve fibre morphology were used to calculate predicted
values of the electrophysiological parameters. We attribute differences between measured and predicted electrophysiological parameter values to compensatory
changes of the axonal ion channel composition. This study shows that the fast degradable graft disintegrated and that the slowly degradable graft
remained partially intact. The values of the morphometrical parameters of the peroneal nerves and the gastrocnemic and tibial muscles were similar if not equal
in the synthetic nerve grafted rats, while some of the electrophysiological parameters were different. The refractory period in the fast degradable nerve grafts
was equal to unoperated nerves, while it lenghtened in slowly degradable nerve grafts. In both slow and fast degradable nerve grafts the conducted charge
diminished, and in slowly degradable grafts the charge even fell below the expected value. Based on these data it can be concluded that fast degradable grafts
are better than slowly degradable grafts, though the observed differences are small.
123