American Society for Peripheral Nerve

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Revitalizing the Common Peroneal Index for Assessing Functional Recovery Following Nerve Injury
Calder Fontaine,MD1; Eric A Yeager, MS1; Michael Sledziona, B.S.1; Hyun Woo Joo, MD1; Amanda K Jones, PhD2; Tim P Moore, B.S.1; Jonathan Cheetham, VetMB, PhD, DACVS1;
1Cornell University, Ithaca, NY, 2University of Colorado Denver, Denver, CO

Sciatic Function Index (SFI) is a widely used metric for serial assessment of functional recovery following nerve injury. Nerve transection models have consistently shown a moderate degree of observable functional recovery when estimated using SFI. This is in part the result of the mixed grouping of fascicles that contribute to the tibial (TIB) and common peroneal (CP) branches of the sciatic nerve, supplying flexors and extensors combined with axonal misdirection during the regenerative process, leading to non-selective reinnervation of the distal stump fascicles and altered activation patterns of opposing muscle groups during locomotion. Alternative models for CP and TIB branches rarely appear in the literature.

23 rats were randomly divided into three groups: CP nerve crush (1.35N for 2 minutes), transection and coaptation, transection and ligation. Animals were trained to use a corridor apparatus for three weeks before obtaining baseline data. For each animal, at least three observations were obtained prior to injury then 2,4,6,8 and 16 weeks after injury. Three observations were obtained at each time point. Gait analysis and video tracking software (SIMI) were used to determine toe spread (TS), intermediate TS (ITS), print length (PL) and hock height at toe off (HH).

All injury modalities produced a significant reduction in TS, ITS and PL in the ipsilateral limb (all p<0.05). We also observed significant increases in all three parameters in the contralateral (uninjured) limb in all three groups (p<0.05). As a result variables were subsequently standardized to baseline measurements rather than contralateral limb measurements. Standardized PL, TS and ITS measures returned to baseline values within 4 weeks in the crush group and 8 weeks in the transection group. Full recovery was not observed in the transection and ligation group. No significant differences in HH were observed after injury. Cranial tibial muscle weight data confirmed full recovery after crush, partial recovery after repair and no recovery after transection (p<0.0001). Use of the previous published index did not reflect an injury and recovery phase. Using multiple linear regression, we generated a new common peroneal index (CPI) using a 100 (full function) to 0 (no function) scale. CPI demonstrated accelerated recovery following crush vs repair and fitted the data well (Adjusted R2 =0.76).

A revised CPI provides a reliable metric for tracking recovery after nerve injury in a relatively short experimental period. This will allow effective testing of new therapies.

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