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The Difference between Muscle Burying and RPNI in the Treatment of Neuromas
Elisabeth Maria Brakkee, MD, MSc1; Erick DeVinney, BS2; Niels Eijkelkamp, PhD3; J. Henk Coert, M.D. PhD4
1UMC Utrecht, Utrecht, Netherlands; 2AxoGen, Alachua, FL; 3Universiteit Utrecht, Utrecht, Netherlands; 4University Medical Center Utrecht, Utrecht, Netherlands

Objective Neuromas are bulbs of sprouting nerve fibers that develop after nerve injury, which can be very painful. The classical treatment entails surgical removal of the neuroma and burying the proximal nerve end into muscle. Recently, Regenerative Peripheral Nerve Interfaces (RPNI) are developed and are used to treat neuroma pain. However, it is not known whether RPNI is superior in treating neuroma pain compared to burying into muscle.
Methods A total of 75 Sprague Dawley rats were randomly divided over five experimental groups (n=15/group): Tibial Nerve was cut and Transposed to pretibial (TNT, positive control), anterior tibial Muscle Burying (MB) or a RPNI was made out of the anterior tibial muscle distally attached (vascularized/vRPNI) or cut loose (devascularized/dRPNI). In Sham surgery (negative control) the tibial nerve remained untouched. Von Frey testing was performed on the pretibial neuroma site and on the sural and tibial nerve distribution on the plantar side of the paw. The rats were measured at baseline and once a week for 12 weeks after surgery. After 12 weeks, rats were killed and new innervation was tested by cutting the nerve and scoring animation of the muscle. Neuroma specimen, dorsal root ganglia (DRG) and spinal cord were harvested. This study was approved by the Animal Welfare Committee (DEC).
Results Allodynia over the neuroma site (area under the curve (AUC)) was highest in TNT, absent in Sham and lower in vRPNI compared to TNT (p<0.05). MB and dRPNI did not differ from vRPNI (p>0.05). Hypersensitivity over the sural nerve and hyposensitivity over the tibial nerve developed after surgery and was similar between groups (TNT, vRPNI, dRPNI and MB) but not in Sham. Animation of the muscle was most prominent in vRPNI (87%) and MB (71%), and less prominent in dRPNI (50%) (p=0.1). A neuroma had formed in all groups except Sham. Results of DRG and spinal cord analysis will follow.
Conclusions Our study showed 1) only minor differences in allodynia over the neuroma site between vRPNI, dRPNI and MB, 2) no alterations in sural hypersensitivity when a neuroma is treated, and that 3) MB also leads to reinnervation of the muscle, which was previously only demonstrated in RPNI. Since RPNI or MB are neither superior in treating neuroma pain, we feel that RPNI treatment is an valuable addition, but not a substitute for MB in the treatment of neuroma pain.


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