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Non-Invasive Ultrasound as a Longitudinal Tool for Analysis of Nerve Regeneration
Caroline A. Hundepool, MSc; Tim H.J. Nijhuis, MD, PhD; Nadia Rbia, MD; Liselotte F. Bulstra; Ruud W. Selles, PhD; Steven E.R. Hovius, MD, PhD
Department of Plastic, Reconstructive and Handsurgery, Erasmus MC, University Medical Center, Rotterdam, Netherlands
Introduction: Functional recovery after nerve trauma can be measured using various techniques. Today’s golden standard in experimental studies is the muscle mass ratio, which is invasive and requires a sacrificial procedure. We propose a new, innovative, non-invasive method to obtain the muscle atrophy with the use of ultrasound. The reliability and validity of obtaining the muscle atrophy by ultrasound was already established for the gastrocnemic muscle. This study takes the next step in creating this new method: developing the ultrasound evaluation techniques for smaller muscles in the leg. Secondly, the ultrasonographic findings will be correlated and compared with the actual force. Lastly, the innervation of the muscle was studied with histology.
Methods: For this experiment fifty rats underwent a 10 mm autograft sciatic nerve reconstruction. With a two-week interval, 5 animals where tested with a total follow up period of 20 weeks. The functional recovery of the muscles of the hind limb measured with the new innovative and non-invasive ultrasound was compared with the muscle mass ratio, today’s most widely accepted assessment technique in this field, and the isometric tetanic force. In addition, neuromuscular junctions were histologically analyzed to study the innervation on the muscle level. The different evaluation techniques were compared using correlation analysis and the inter-rater reliability of the ultrasound assessment was determined.
Results: Four weeks after denervation the muscle showed extensive atrophy resulting in a decrease of muscle mass up to 30%. In the following weeks the muscle mass recovered, but it reached not higher than 75% of the original values. The ultrasound showed good correlations with the muscle mass ratio for both the tibial (r=0.85) and gastrocnemic muscles (r=0.89). The interrater reliability of the ultrasound of the tibial muscle showed a good correlation of r=0.88. The correlation of ultrasound with the isometric tetanic force was found to be 0.62.
Discussion &Conclusion: This study shows a new non-invasive method to analyze the functional recovery of the rat after nerve reconstruction. Ultrasound proves to be a valid and alternative method to obtain the muscle atrophy for both the gastrocnemic and tibial muscle. Compared to the golden standard, muscle mass ratio, ultrasound shows high correlations. Analyzing isometric tetanic force, ultrasound shows a lower, but still significant correlation, as compared to weight. We propose that ultrasound can be used as an alternative of muscle mass ratio to obtain study muscle atrophy after nerve injury in a less invasive, animal friendly manner.
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