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Strain Shielding Effects of a Novel Microhook-based Nerve Repair Device
Brandon Smetana, MD
1; Ben Loflin, MS
2; Jonathan Isaacs, MD
3; Jason Koerner, MD
1; Isaac Clements, PhD
4; Stephen Schlecht, PhD
21Indiana Hand to Shoulder Center, Indianapolis, IN; 2Indiana University, Indianapolis, IN; 3Department of Orthopaedics, Virginia Commonwealth University, Richmond, VA; 4Biocircuit Technologies, Atlanta, GA
Hypotheses:
- Application of Nerve TapeŽ (BioCircuit Technologies) will limit focal strain concentration at the neurorrhaphy site through an even strain distribution when an axial load is applied as compared to a suture only based neurorrhaphy.
- Secondarily, multiple rows of fixation within the Nerve Tape device will permit re-engagement of the nerve without catastrophic failure after experiencing maximal loads during axial loading.
Methods: A cadaveric strain mapping model was designed. Median and ulnar nerves were sectioned into twenty 9cm segments and speckled (Figure 2) to permit focal strain mapping. Each nerve segment was transected at the midpoint then repaired using Nerve Tape according to the manufacturer's recommended technique. Nerves were then loaded until failure while video recording for strain mapping analyses using a high-definition camera. Focal strain mapping within the nerve tape was then completed using Digital Imaging Correlation at three different regions: the laceration site, and at two locations proximal and distal to the laceration site. Average strain was taken from each of the three regions. Data was then compared to previously collected data where a direct suture only coaptation technique was performed with otherwise identical methodology. Statistical analyses were completed using a two tailed unpaired T test.
| Assessed Parameter | Nerve Tape Repair (N=20) | Suture Only Repair (N=20) | P Value |
| Proximal Focal Strain Average | 0.36 | 0.14 | 0.35 |
| Laceration Site Focal Strain Average | 0.06 | 0.71 | <0.05 |
| Distal Focal Strain Average | 0.8 | 0.12 | <0.05 |
| Global Strain at Failure | 5.36 | 0.15 | <0.05 |
| Maximal Load (N) | 5.12 | 2.77 | <0.05 |
Summary Points:
- Repairs completed with Nerve Tape were able to withstand a higher maximum load.
- The suture only repair cohort's load curves had a dramatic drop in load after the maximum force, consistent with catastrophic failure.
- The load curves for the Nerve Tape cohort demonstrated integrity of the construct after maximal loads were recorded, consistent with either settling of nerve and further engagement of the Nitinol microhooks or slippage of the nerve within the Nerve Tape device and re-engagement to adjacent microhooks. These observations are reflected in the difference of global strain at failure, where repairs performed using Nerve Tape were able to elongate without catastrophic failure.
- Strain was focally concentrated at the laceration site in the suture only repair cohort, whereas this was seen away from the laceration site in the Nerve Tape cohort.
- The Nerve Tape device provided a strain shielding effect to the neurorrhaphy site during axial load application in our model.
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