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The Effect of Conduit Length on Offloading Nerve Repairs Through Strain Shielding
Alexander Hahn, MD1; Benjamin Loflin, MS2; Stephen Schlecht, PhD2; Kent Rinehart, MD1; Sameer Puri, MD1; Jeffrey A. Greenberg, MD, MS1; Brandon S. Smetana, MD1
1Indiana Hand to Shoulder Center, Indianapolis, IN; 2Indiana University, Indianapolis, IN

Introduction Excess strain is adverse to nerve function and regeneration, and is a rationale for tension-free coaptation during nerve repair. Conduits are used as an adjunct in nerve repair with several proposed benefits, including redistributing strain from the coaptation site, effectively “de-tensioning” the repair. As a cost-saving measure, surgeons may divide one conduit into multiple units for different coaptation sites. The purpose of this study was to determine if there is a minimum conduit length needed to shield the coaptation site from undue strain during an applied load.
Materials & Methods A cadaveric nerve laceration model was employed (n=24 forearm nerve segments). Nerves were distributed among 3 groups of conduit assisted repairs (CARs) performed using varying conduit lengths: 2mm, 4mm, and 6mm. Direct end-to-end repairs were additionally performed for paired analysis comparing CAR to direct repair within each cohort. Nerves were speckled, lacerated, then repaired according to assigned group in either a direct or CAR fashion. 5x10mm porcine submucosal-based conduits were sectioned into 2, 4, and 6mm lengths for repairs. Samples were mounted onto an Instron and loaded at a constant rate until failure. Strain analysis using a digital image correlation protocol was performed using change in distance between speckles to map strain. ANOVA was used to compare percent strain at the repair site among CAR groups, and a paired t-test was used to compare CAR to direct repair within each cohort.
Results There was lower percent total strain at the repair site in the 6mm CAR group (35%) compared to 4mm CAR (61%) and 2mm CAR (56%) cohorts (p<0.05). Comparing direct repair to CAR, there was no difference in percent total strain at the repair site in the 2mm, nor 4mm groups. However, in the 6mm group, a significantly lower percent total strain at the repair site with CAR (35%) compared to direct repair (66%) was found (p<0.05)
Conclusion A 6mm conduit significantly decreased the percent total strain at the repair site compared to primary repair alone, an effect not observed at shorter conduit lengths. Based on our findings, a threshold exists between 4mm and 6mm below which conduits cannot effectively shield the coaptation site, and higher strain is experienced with load. If surgeons choose to divide a conduit into multiple sections, we recommend a minimum conduit length of 6mm (with suture anchor points 3mm on either side of the coaptation) to effectively de-tension the repair.


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