Von Frey monofilament testing successfully discriminates between sensory function of mixed nerve and sensory nerve regenerative peripheral nerve interfaces

Regenerative peripheral nerve interfaces (RPNIs) transfer motor and sensory signals between amputee and prosthesis. Von Frey (VF) monofilaments are used clinically to evaluate sensory feedback but have not been validated at locations used in our rodent studies. Our purposes were to determine VF sensory test reliability at the ankle and thigh, and to evaluate sensory function of Mixed Nerve (MN) and Sensory Nerve (SN) RPNIs. For reliability testing, VF monofilaments were applied to Normal rats at the ankle and thigh in an up-down pattern. Paw Withdraw Thresholds were determined by alternately exceeding and reducing filament pressure. VF tests were then administered to experimental MN-RPNIs or SN-RPNIs. Reliability results at the ankle showed sensation did not vary over six weeks. At the thigh, reliability was similar during week 0 and 1, but with further testing sensation increased. Comparison between location found at weeks 0 and 1, the ankle was significantly more sensitive than the thigh (p<;0.05). VF administration to experimental animals revealed that the MN-PRNI group was significantly less sensitive than both the SN-RPNI and Normal groups (p<;0.05); while the SN-RPNI and Normal groups did not differ. VF monofilament testing was reliable and successful at distinguishing between sensations of normal skin with dense sensory endings (ankle) and disperse sensory endings (thigh). VF testing successfully discriminated between mixed and sensory nerve RPNI groups.