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Method Article
Evaluation of motor recovery remains the benchmark outcome measure in experimental peripheral nerve studies. The isometric tetanic force measurement of the tibialis anterior muscle in the rat is an invaluable tool to assess functional outcomes after reconstruction of sciatic nerve defects. The methods and nuances are detailed in this article.
Traumatic nerve injuries result in substantial functional loss and segmental nerve defects often necessitate the use of autologous interposition nerve grafts. Due to their limited availability and associated donor side morbidity, many studies in the field of nerve regeneration focus on alternative techniques to bridge a segmental nerve gap. In order to investigate the outcomes of surgical or pharmacological experimental treatment options, the rat sciatic nerve model is often used as a bioassay. There are a variety of outcome measurements used in rat models to determine the extent of nerve regeneration. The maximum output force of the target muscle remains the most relevant outcome for clinical translation of experimental therapies. Isometric force measurement of tetanic muscle contraction has previously been described as a reproducible and valid technique for evaluating motor recovery after nerve injury or repair in both rat and rabbit models. In this video, we will provide a step-by-step instruction of this invaluable procedure for assessment of functional recovery of the tibialis anterior muscle in a rat sciatic nerve defect model using optimized parameters. We will describe the necessary pre-surgical preparations in addition to the surgical approach and dissection of the common peroneal nerve and tibialis anterior muscle tendon. The isometric tetanic force measurement technique will be detailed. Determining the optimal muscle length and stimulus pulse frequency is explained and measuring the maximum tetanic muscle contraction is demonstrated.
Loss of motor function following traumatic peripheral nerve injury has a significant impact on the quality of life and socioeconomic status of patients1,2,3. The prognosis of this patient population remains poor due to minimal improvements in surgical techniques over the years4. Direct end-to-end tension-free epineural repair forms the gold standard surgical reconstruction. However, in cases with extended nerve gaps interposition of an autologous nerve graft has proven to be superior5,6. The associated donor site morbidity and limited availability of autologous nerve grafts have imposed the need for alternative techniques7,8.
Experimental animal models have been used to elucidate the mechanism of peripheral nerve regeneration and to evaluate outcomes of a variety of reconstructive and pharmacological treatment options8,9. The rat sciatic nerve model is the most frequently used animal model10. Their small size makes them easy to handle and house. Due to their superlative neuroregenerative potential, the diminished time between intervention and evaluation of outcomes can result in relatively lower costs11,12. Other advantages of its use include morphological similarities to human nerve fibers and the high number of comparative/historic studies13. Although the latter should be approached cautiously, as a wide variety of different outcome measures between studies makes it difficult to compare results14,15,16,17,18.
Outcome measures to assess nerve regeneration range from electrophysiology to histomorphometry, but these methods imply a correlation but do not necessarily directly measure the return of motor function14,15. Regenerating nerve fibers might not make appropriate connections which can cause an overestimation of the number of functional connections14,15,19,20. The best and clinically most relevant measurement to demonstrate correct reinnervation of end organs remains assessment of muscle function21,22,23. Creating motor function assessment tools for animal models is, however, challenging. Medinaceli et al. first described the walking track analysis, which has since been the most frequently used method to evaluate functional recovery in experimental peripheral nerve studies21,24,25,26,27,28. The walking track analysis quantifies the sciatic functional index (SFI) based on measurements of pawprints from walking rats21,29. Major limitations of the walking track analysis, such as toe contractures, automutilation, smearing of the print and poor correlation with other measures of reinnervation, have necessitated the use of other parameters for quantification of functional recovery30,31.
In previous studies in Lewis rats32 and New Zealand rabbits33, we validated the isometric tetanic force (ITF) measurement for the tibialis anterior (TA) muscle and demonstrated its effectiveness in the evaluation of muscle recovery after different types of nerve repair34,35,36,37,38,39. The TA muscle is well suited because of its relatively large size, innervation by the peroneal branch of the sciatic nerve and well elucidated biochemical properties40,41,42,43. When muscle length (preload force) and electrical parameters are optimized the ITF provides a side-to-side variability of 4.4% and 7.5% in rats32 and rabbits33, respectively.
This article provides a detailed protocol of the ITF measurement in the rat sciatic nerve model, including a thorough description of the necessary pre-surgical planning, surgical approach and dissection of the common peroneal nerve and the distal TA muscle tendon. Using predetermined values for the stimulus intensity and duration, the optimal muscle length and stimulus pulse frequency will be defined. With these four parameters, the ITF can subsequently be consistently and accurately measured.
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All animal procedures were performed with approval of the Institutional Animal Care and Use Committee (IACUC A334818).
1. Calibration of the force transducer
2. Animal subjects
3. Surgical preparation
4. Surgical approach to the common peroneal nerve
5. Dissection of the distal tibialis anterior muscle tendon
6. Isometric tetanic force measurement
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Five parameters are used to measure the ITF measurement. These include muscle tension (preload force), stimulus intensity (voltage), stimulus pulse frequency, stimulus duration of 0.4 ms and a delay of 2 ms. Prior to measuring the ITF, the optimal muscle tension has to be determined using two single twitch muscle contractions at an intensity of 2 V during the parameter test. These stimuli cause dorsiflexion of the paw and produce an output signal on the graph in the VI (Figure 5). These sing...
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This protocol describes a previously validated method for acquiring accurate maximum ITF measurements of the TA muscle in the rat model32. The recovery of maximum strength after experimental nerve reconstruction treatments is of primary interest in the clinical setting as it proves that the nerve not only regenerated, but also made working connections with the target muscle. The ITF can be used in a small nerve gap model, such as the rat sciatic nerve model32, and with a fe...
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The authors have nothing to disclose.
Research reported in this publication was supported by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under Award Number RO1 NS 102360. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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Name | Company | Catalog Number | Comments |
0.9% Sodium Chloride | Baxter Healthcare Corporation, Deerfield, IL, USA | G130203 | |
1 mm Kirshner wires | Pfizer Howmedica, Rutherford, NJ | N/A | |
Adson Tissue Forceps | ASSI, Westbury, NY, USA | MTK-6801226 | |
Bipolar electrode cables | Grass Instrument, Quincy, MA | N/A | |
Bipolar stimulator device | Grass SD9, Grass Instrument, Quincy, MA | N/A | |
Cotton-tip Applicators | Cardinal Health, Waukegan, IL, USA | C15055-006 | |
Curved Mosquito forceps | ASSI, Westbury, NY, USA | MTK-1201112 | |
Force Transducer MDB-2.5 | Transducer Techniques, Temecula, CA | N/A | |
Gauze Sponges 4x4 | Covidien, Mansfield, MA, USA | 2733 | |
Ground cable | Grass Instrument, Quincy, MA | N/A | |
Isoflurane chamber | N/A | N/A | Custom-made |
Ketamine | Ketalar, Par Pharmaceutical, Chestnut, NJ | 42023-115-10 | |
LabView Software | National Instruments, Austin, TX | ||
Loop | N/A | N/A | Custom-made |
Microsurgical curved forceps | ASSI, Westbury, NY, USA | JFA-5B | |
Microsurgical scissors | ASSI, Westbury, NY, USA | SAS-15R-8-18 | |
Microsurgical straight forceps | ASSI, Westbury, NY, USA | JF-3 | |
Retractor | ASSI, Westbury, NY, USA | AG-124426 | |
Scalpel Blade No. 15 | Bard-Parker, Aspen Surgical, Caledonia, MI, USA | 371115 | |
Slim Body Skin Stapler | Covidien, Mansfield, MA, USA | 8886803512 | |
Subminiature electrode | Harvard Apparatus, Holliston, MA | N/A | |
Surgical Nerve Stimulator | Checkpoint Surgical LCC, Cleveland, OH, USA | 9094 | |
Terrell Isoflurane | Piramal Critical Care Inc., Bethlehem, PA, USA | H961J19A | |
Testing platform | N/A | N/A | Custom-made |
Tetontomy Scissors | ASSI, Westbury, NY, USA | ASIM-187 | |
Traceable Big-Digit Timer/Stopwatch | Fisher Scientific, Waltham, MA, USA | S407992 | |
USB-6009 multifunctional I/O data acquisition (DAQ) device | National Instruments, Austin, TX | 779026-01 | |
Vacuum Base Holder | Noga Engineering & Technology Ltd., Shlomi, Isreal | N/A | Attached clamp is custom-made |
Weight (10 g) | Denver Instruments, Denver, CO, USA | 820010.4 | |
Weight (20 g) | Denver Instruments, Denver, CO, USA | 820020.4 | |
Weight (50 g) | Denver Instruments, Denver, CO, USA | 820050.4 | |
Xylazine | Xylamed, Bimeda MTC Animal Health, Cambridge, Canada | 1XYL002 |
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