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Biomechanical Assessment of Ultrasound-Guided Hydrodissection on Median Nerve Mobility in a Cadaveric Model.
Stefanie Evers, MD; Andrew Thoreson, MS, Jay Smith, MD; Chunfeng Zhao, MD; Peter C. Amadio, MD
Mayo Clinic, Rochester, MN
Introduction: Hydrodissection is a new technique to treat carpal tunnel syndrome (CTS), based on the theory that symptoms are exacerbated by nerve fixation to the flexor retinaculum. The goal is to use an ultrasound-guided injection of a volume of saline to create a perineural fluid plane and consequently free the nerve. While several reports have noted anecdotally the use of hydrodissection to treat CTS, the degree to which the nerve is mobilized by this technique has not been determined. The aim of this study was to assess alterations in median nerve biomechanics resulting from hydrodissection in a cadaveric model. We hypothesized that the gliding resistance of the median nerve would be decreased after hydrodissection.
Materials & Methods: Ten unembalmed human cadaver hands from donors unaffected by CTS were used. Hands were amputated 10 cm proximal to the wrist joint and the wrist fixed in a neutral position using a customized external fixator with the proximal radius and ulna immobilized. The median nerve was exposed and transected distal to the carpal tunnel, and then connected to a 50-gram weight and suspended over a pulley to maintain tension. The proximal median nerve was transected proximal to the carpal tunnel and connected to a mechanical actuator. The carpal tunnel region was kept intact. Median nerve gliding resistance was assessed pre- (first cycle) and post-hydrodissection (second cycle) by pulling the nerve proximally at a rate of 1 mm/s for a distance of 6 mm, which is within the physiological range of median nerve excursion with full finger motion, and then returning to the origin. Five specimens were treated with ultrasound-guided hydrodissection using the ulnar approach, and 5 were used as controls, measuring gliding resistance without hydrodissection. Paired t-test and independent t-test were used to compare means.
Results: Within the 5 hydrodissection specimens, we found a decrease in mean gliding resistance of 100.1 +/- 34.3 mN between baseline and post-hydrodissection (p=.003). The mean percentage difference between baseline and post-hydrodissection was 19 +/- 9 %. The mean percentage difference between baseline and second cycle in the control group was 1+/- 7 %; a statistically significant difference compared to the hydrodissection group (p=.01).
Conclusion: Based on this cadaver study we can conclude that hydrodissection can decrease the gliding resistance of the median nerve within the carpal tunnel, at least in wrists unaffected by CTS. A clinical trial of hydrodissection seems justified.
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