Normalizing Stimulated Grip Strength Data with Total Body Weight in Rats
Erica B Lee, MS1, Thomas G.W. Harris, MBBS1, Alison L Wong, MD, MSE, FRCSC1, Matthew Generoso, BS1, Nicholas von Guionneau, MBBS1 and Sami Tuffaha, MD2, (1)Johns Hopkins University School of Medicine, Baltimore, MD, (2)Plastic and Reconstructive Surgery, Johns Hopkins University School of Medicine, Baltimore, MD
Background: Reliable and accurate measurement of functional recovery is critical in translational peripheral nerve regeneration research and is notoriously difficult to achieve in rodent models. Stimulated grip strength testing (sGST) involves percutaneous stimulation of the median nerve to elicit maximal tetanic contraction of digital flexors; it provides similar reliability to isometric tetanic force testing while also allowing for serial in vivo testing. However, a practical, reliable method for normalizing sGST data is needed. A single baseline measurement of pre-injury strength does not account for growth of the animal during the recovery period. Serial measurements of the contralateral naïve limb is time intensive and does not account for compensatory mechanisms and systemic treatments, both of which can favor the uninjured control limb and confound the data. We sought to characterize the relationship between total body weight and grip strength in a cohort of naïve rats with the aim of developing an efficient, reliable method for normalizing sGST data based on body weight.
Methods: Animal weight and sGST measurements were recorded weekly over a 10-week period in Lewis rats (n=10). Linear regression analysis of maximal grip strength and body weight was conducted.
Results: Maximal grip strength and body weight in rats demonstrated a significant positive correlation (R = 0.821, F = 298.2, p<0.0001,). We derived an equation that can be used to predict expected maximal flexion force in naïve rat forelimbs at a given weight.
Conclusion: We demonstrated that total body weight is predictive of maximal stimulated grip force in rats and can be used to normalize sGST measurements in the injured, experimental forelimb. We will continue to add animals to this cohort to strengthen the validity of this predictive model. Future studies will compare this data normalization method to the use of baseline grip strength in the experimental limb and serial measurements of contralateral naïve limb grip strength post-operation. We will also repeat these studies in different strains of rats to determine generalizability.
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