Back to 2017 Annual Meeting Program
Validation of Anatomy and Motor Functional Outcome in a C7 to Biceps Rabbit Model of Brachial Plexus Injury
Kathleen Kollitz, MD; Guilherme Giusti, MD; Patricia F. Friedrich, BA; Allen T. Bishop, MD; Alexander Y. Shin, MD
Mayo Clinic, Rochester, MN
Introduction: Proximal brachial plexus injuries pose a reconstructive challenge to surgeons. While the rabbit has been used to model brachial plexus injury previously, reports conflict in anatomic detail and do not validate a nerve-muscle pair to measure motor function recovery after injury. The purpose of the current study is to 1) describe the innervation pattern of the rabbit biceps and 2) validate a technique for measurement of isometric tetanic force in the rabbit biceps muscle in order to establish an animal model of brachial plexus injury.
Methods: Part 1: Anatomy. Eight rabbits underwent electrophysiologic investigation. A bipolar nerve stimulator was used to systematically stimulate the roots, trunks and divisions and nerve branches of the rabbit brachial plexus and compound muscle action potential (CMAP) was used to record muscle response to stimulation.
Part 2: Motor Recovery Validation. Eighteen rabbits were anesthetized. The trunk formed by C6, C7 was clamped in a bipolar electrode. Compound muscle action potential (CMAP) was obtained. The proximal tendinous portion of the biceps was clamped in a force transducer. Muscle preload and electrical stimulation variables were optimized to obtain the highest tetanic muscle contraction. Wet muscle weight and nerve histomorphometry were also analyzed.
Results: Part 1: The C7, C8, and TI nerves form the middle and lower portions of the brachial plexus to terminate in the axillary, radial, median, and ulnar nerves. The musculocutaneous nerve innervates the biceps and branches from the median nerve. The biceps was innervated primarily by C7.
Part 2: The rabbit biceps muscle force demonstrated side-to-side equivalence. The maximum force for the right side averaged 2247.71g ± 378.20g (95%CI 2038.27-2457.15g) and for the left side was 2302.16g ±401.29g (95%CI 2079.94-2524.39g). The right side expressed as a percentage of the left averaged 99.7% (95%CI 88.9-110.5%). The wet muscle weight of the right expressed as a percentage of the left was 98.9% (95%CI 95.8-101.9%).
Discussion: The trunk formed by C6, C7 and the biceps muscle are an ideal model for studying reconstruction techniques after brachial plexus injury. Isometric tetanic force is equivalent from side-to-side in the rabbit as demonstrated by the high degree of overlap in the 95% confidence intervals for each side. The width of the 95% confidence interval demonstrates that there is more variability in the rabbit upper extremity than there is for the lower extremity or for the rat, and researchers should take this into account when performing power analyses in pre-experimental planning.
Back to 2017 Annual Meeting Program