The effect of shoulder abduction and medial epicondylectomy on ulnar nerve strain: A preliminary study

Abstract

The primary aim was to determine whether a dynamic suture marker method of measuring ulnar nerve strain yields comparable results to strain gauges. The secondary aim was to assess the effect of elbow flexion, shoulder abduction and medial epicondylectomy on strain. Methods: In four embalmed elbows, ulnar nerve strain was measured using suture markers during elbow flexion and shoulder abduction before and after medial epicondylectomy. Linear regression analysis and Wilcoxon signed-rank test were used to analyse the results. Results: Ulnar nerve strain increased in direct proportion to elbow flexion angle before and after medial epicondylectomy, with one exception. At 90° shoulder abduction, strain was 0%-17%. Strain was greatest at 90° and least at 110° before and after medial epicondylectomy, P > 0.05. The effect of medial epicondylectomy varied. Strain was reduced at 90° by 5%, at 110° by 0% and at 120° by 1%; P > 0.05. Conclusions: The suture marker method yielded comparable results to strain gauges. Both shoulder abduction and medial epicondylectomy did not have statistically significant effects on ulnar nerve strain. However, only four embalmed elbows were studied in this preliminary study, so a large difference would be needed to produce a significant change. The finding that medial epicondylectomy fails to reduce strain raises questions about its role in treating cubital tunnel syndrome and highlights the need for further research. The authors believe that the technique described for dynamic strain assessment is applicable in an in vivo setting and therefore, should be used to compare strain properties of cadaveric and in vivo nerves.

Towards viscoelastic characterisation of the human ulnar nerve: An early assessment using embalmed cadavers

“…This variation may be due to differences in testing procedure (quasi-static versus dynamic) or may also be due to the linearity assumption of using the complex modulus for the estimated strain [20]. In relation to in situ strain of human cadavers, numerous studies have quantified a wide range of strains; 0-17% [15], 0-14% [7], 29% [8], 9-69% [33]. The values estimated in this present study are within these ranges; thus, the viscoelastic measurements provided are within a range which corresponds to existing measures of strain.…”

“…Three nerves were divided into 40 mm sections, (approximately 20 mm of a gauge and two mm shoulder sections used to grip the nerve for mechanical testing) and one nerve was divided into 50 mm sections, (approximately 30 mm of a gauge and two 10 mm shoulder sections). The difference in length was to maintain consistent suture positioning from a previous study [15]. Specimens were hydrated with the aforementioned damping down solution.…”

“…Therefore, for adequate nerve function, nerve strain must be minimised. It has previously been shown that during normal motion of the elbow and shoulder joints, strain is applied dynamically to the ulnar nerve to levels that could result in both impaired conduction and perfusion [8,14,15].…”

A Finite Element Model for Trigger Finger

“…There are limitations to using cadaver models; for instance, specimens might be embalmed or treated with chemicals to prevent degradation, embalming may increase stiffness of the tissue [29,30], and treatments such as dehydration [31] and cross-linking (e.g., using glutaraldehyde) alter the physical and mechanical properties of tissues. If samples undergo freeze-thaw cycles, this too may alter their mechanical properties [32,33].…”

Cubital tunnel syndrome

“… 11 Elbow flexion to 90 degrees with shoulder abduction to 90 degrees results in a 14% strain. 12 The UN structure is locally adapted to areas of high strain. Surgical techniques to address focal compression points may modify the strain distribution along the nerve, and postoperative scar may limit excursion, further contributing to areas of high strain.…”