Tension of the ulnar, median, and radial nerves during ulnar nerve neurodynamic testing: observational cadaveric study

Assessment of ulnar nerve tension directed towards understanding cubital tunnel syndrome

Background

Ulnar nerve compression at the elbow is the second most common compressive neuropathy of the upper extremity. We hypothesize that tension on the ulnar nerve produced by elbow flexion and distraction contributes to this condition. We measured ulnar nerve tension generated during elbow flexion and proportional distraction to evaluate locations of soft tissue constraints to nerve translation.

Methods

Eight fresh-frozen upper limb specimens were tested. Each specimen included the proximal humeral shaft to the wrist. The ulnar nerve was dissected proximally and clamped to the humerus 8 ​cm proximal to the medial epicondyle. At 8 ​cm distal to the medial epicondyle, the ulnar nerve was dissected and clamped distally to a load cell that was mounted on a laboratory stand. A stage on the stand could be translated distally to apply load. Soft tissue was removed distal to the load cell clamp; all soft tissue from the load cell to the proximal humeral clamp was left intact.We measured the tension generated on the nerve throughout the full arc of elbow flexion with additional distal distractions of 0%, 2.5% and 5% of nerve length applied by distal translation of the stage on the lab stand. We then repeated these steps with the nerve unclamped proximally. We then excised 1 ​cm of soft tissue distally, clamped the nerve 7 ​cm distal to the medial epicondyle, and repeated the measurements. We continued this sequential dissection and testing until the nerve was clamped to the load cell 1 ​cm distal to the medial epicondyle.

Results

Flexion, distraction, and proximal clamping each increased nerve tension. Tension was greatest at 4, 5, and 6 ​cm distal to the medial epicondyle (p ​< ​0.01).

Conclusion

Flexion, distraction, and proximal clamping each increased ulnar nerve tension. The greatest ulnar nerve tension was recorded between 4 and 6 ​cm distal to the medial epicondyle.

Micro-nanofiber composite biomimetic conduits promote long-gap peripheral nerve regeneration in canine models

Peripheral nerve injuries may result in severe long-gap interruptions that are challenging to repair. Autografting is the gold standard surgical approach for repairing long-gap nerve injuries but can result in prominent donor-site complications. Instead, imitating the native neural microarchitecture using synthetic conduits is expected to offer an alternative strategy for improving nerve regeneration. Here, we designed nerve conduits composed of high-resolution anisotropic microfiber grid-cordes with randomly organized nanofiber sheaths to interrogate the positive effects of these biomimetic structures on peripheral nerve regeneration. Anisotropic microfiber-grids demonstrated the capacity to directionally guide Schwann cells and neurites. Nanofiber sheaths conveyed adequate elasticity and permeability, whilst exhibiting a barrier function against the infiltration of fibroblasts. We then used the composite nerve conduits bridge 30-mm long sciatic nerve defects in canine models. At 12 months post-implant, the morphometric and histological recovery, gait recovery, electrophysiological function, and degree of muscle atrophy were assessed. The newly regenerated nerve tissue that formed within the composite nerve conduits showed restored neurological functions that were superior compared to sheaths-only scaffolds and Neurolac nerve conduit controls. Our findings demonstrate the feasibility of using synthetic biophysical cues to effectively bridge long-gap peripheral nerve injuries and indicates the promising clinical application prospects of biomimetic composite nerve conduits.

The consequences of a thoracic outlet syndrome's entrapment model on the biomechanics of the ulnar nerve - Cadaveric study

STUDY DESIGN

A cross sectional cadaveric measurement study.

INTRODUCTION

The etiology of entrapment neuropathies, such as carpal tunnel syndromes or thoracic outlet syndromes (TOS), is usually not only linked with the compressive lesion of the nerve but can also be associated with fibrosis and traction neuropathy.

PURPOSE OF THE STUDY

This work studies the biomechanics of the ulnar nerve in a cadaveric model of thoracic outlet syndrome (TOS). We explored the biomechanical impact of a restriction of mobility of the ulnar nerve. We measured if it could significantly affect the deformation undergone by the nerve on the rest of its path.

METHODS

We studied 14 ulnar nerves from 7 embalmed cadavers. We opened three 6.5cm windows (at the wrist, forearm, and arm), and two optical markers 2cm apart were sutured to the ulnar nerve. We then studied the deformation of the ulnar nerve in three successive tensioning positions inspired by the ULNT3 manoeuvre (Upper Limb Neural Test 3). We then fixed the brachial plexus to the clavicle to mimic a nerve adhesion at the thoracic outlet.

RESULTS

Fixing the brachial plexus to the clavicle bone had significant effects on ulnar nerve mobility. In the position of intermediate tension, the nerve deformation increased by +0.68% / +1.43% compared to the control measure. In the position of maximum tension, it increased by +1.16% / +1.94%, pushing the nerve beyond the traumatic threshold of 8% of deformation causing reversible damage to axonal transport and vascularization.

CONCLUSIONS

Our nerve adhesion at the thoracic outlet showed significant effects on the mobility of the ulnar nerve compared to the control situation, by significantly increasing the deformation undergone throughout the rest of the nerve's course, and by taking it over the 8% of physiological traumatic deformation.

A cadaveric study of ulnar nerve strain at the elbow associated with cubitus valgus/varus deformity

Background

Cubital tunnel syndrome can be caused by overtraction and dynamic compression in elbow deformities. The extent to which elbow deformities contribute to ulnar nerve strain is unknown. Here, we investigated ulnar nerve strain caused by cubitus valgus/varus deformity using fresh-frozen cadavers.

Methods

We used six fresh-frozen cadaver upper extremities. A strain gauge was placed on the ulnar nerve 2 cm proximal to the medial epicondyle of the humerus. For the elbow deformity model, osteotomy was performed at the distal humerus, and plate fixation was performed to create cubitus valgus/varus deformities (10°, 20°, and 30°). Ulnar nerve strain caused by elbow flexion (0–125°) was measured in both the normal and deformity models. The strains at different elbow flexion angles within each model were compared, and the strains at elbow extension and at maximum elbow flexion were compared between the normal model and each elbow deformity model. However, in the cubitus varus model, the ulnar nerve deflected more than the measurable range of the strain gauge; elbow flexion of 60° or more were considered effective values. Statistical analysis of the strain values was performed with Friedman test, followed by the Williams’ test (the Shirley‒Williams’ test for non-parametric analysis).

Results

In all models, ulnar nerve strain increased significantly from elbow extension to maximal flexion (control: 13.2%; cubitus valgus 10°: 13.6%; cubitus valgus 20°: 13.5%; cubitus valgus 30°: 12.2%; cubitus varus 10°: 8.3%; cubitus varus 20°: 8.2%; cubitus varus 30°: 6.3%, P < 0.001). The control and cubitus valgus models had similar values, but the cubitus varus models revealed that this deformity caused ulnar nerve relaxation.

Conclusions

Ulnar nerve strain significantly increased during elbow flexion. No significant increase in strain 2 cm proximal to the medial epicondyle was observed in the cubitus valgus model. Major changes may have been observed in the measurement behind the medial epicondyle. In the cubitus varus model, the ulnar nerve was relaxed during elbow extension, but this effect was reduced by elbow flexion.

Cyclic Stretch of Either PNS or CNS Located Nerves Can Stimulate Neurite Outgrowth

The central nervous system (CNS) does not recover from traumatic axonal injury, but the peripheral nervous system (PNS) does. We hypothesize that this fundamental difference in regenerative capacity may be based upon the absence of stimulatory mechanical forces in the CNS due to the protective rigidity of the vertebral column and skull. We developed a bioreactor to apply low-strain cyclic axonal stretch to adult rat dorsal root ganglia (DRG) connected to either the peripheral or central nerves in an explant model for inducing axonal growth. In response, larger diameter DRG neurons, mechanoreceptors and proprioceptors showed enhanced neurite outgrowth as well as increased Activating Transcription Factor 3 (ATF3).

Nerve stretching: a history of tension

Stretch injuries are among the most devastating forms of peripheral nerve injury; unfortunately, the scientific understanding of nerve biomechanics is widely and impressively conflicting. Experimental models are unique and disparate, victim to different testing conditions, and thus yield gulfs between conclusions. The details of the divergent reports on nerve biomechanics are essential for critical appraisal as we try to understand clinical stretch injuries in light of research evidence. These conflicts preclude broad conclusion, but they highlight a duality in thought on nerve stretch and, within the details, some agreement exists. To synthesize trends in nerve stretch understanding, the author describes the literature since its introduction in the 19th century. Research has paralleled clinical inquiry, so nerve research can be divided into epochs based largely on clinical or scientific technique. The first epoch revolves around therapeutic nerve stretching-a procedure known as neurectasy-in the late 19th century. The second epoch involves studies of nerves repaired under tension in the early 20th century, often the result of war. The third epoch occurs later in the 20th century and is notable for increasing scientific refinement and disagreement. A fourth epoch of research from the 21st century is just dawning. More than 150 years of research has demonstrated a stable and inherent duality: the terribly destructive impact of stretch injuries, as well as the therapeutic benefits from nerve stretching. Yet, despite significant study, the precise border between safe and damaging stretch remains an enigma.

In vivo effects of limb movement on nerve stretch, strain, and tension: A systematic review

BACKROUND

The mechanical behavior of the peripheral nervous system under elongation and tension has not been adequately established in vivo.

OBJECTIVE

The purpose of this review is to investigate the mechanical behavior of the peripheral nervous system in vivo.

METHODS

In vivo studies which evaluated the effects of limb movement and neurodynamic tests on peripheral nerve biomechanics were systematically searched in PubMed (Medline), the Cochrane Database, CINAHL, PEDro, Embase and Web of Science. Studies fulfilling the search criteria were assessed for methodological quality with a modified version of the Down & Blacks scale by two reviewers.

RESULTS

This review includes the results of 22 studies, of which 15 examined limb movement influencing the median nerve, four the sciatic nerve, two the tibial nerve; and one each the ulnar and peroneal nerves respectively. Substantial nerve longitudinal and transverse excursion and changes in diameter were reported. Despite this, increased nerve strain was not a major finding.

CONCLUSION

The heterogeneity of included studies, including wide variety of nerves tested, measurement location and joint position prevented comparisons between studies and also amalgamation of data. Limb movement induces complex biomechanical effects of which nerve elongation plays only a minor role.

Impact of shoulder internal rotation on normal sensory response during ulnar nerve-biased neurodynamic testing of asymptomatic individuals

OBJECTIVE

To determine if substitution of shoulder internal rotation for external rotation during the upper limb neurodynamic test (ULNT₃) evokes comparable ulnar nerve sensory responses in asymptomatic individuals.

METHODS

Range of motion, quality, quantity, and distribution of sensory responses in 50 asymptomatic individuals during the traditional ULNT₃ were compared to identical measures during an experimental maneuver using shoulder internal rotation. Quality and quantity of sensory responses were recorded using a 10-cm visual analog scale.

RESULTS

Means of sensory responses for traditional and experimental maneuvers, respectively, were as follows: stretching, 3.84 ± 8.85 and 5.38 ± 2.85 cm; burning, 1.82 ± 2.82 and 2.50 ± 3.10 cm; tingling, 2.13 ± 3.12 and 2.18 ± 2.97 cm; and numbness, 1.04 ± 2.17 and 1.01 ± 2.03 cm. A moderate to strong correlation (ICC = 0.51-0.86) was shown to exist between maneuvers; this relationship was significant (p = .001).

DISCUSSION

Results of this study provide evidence that there was no appreciable difference in sensory responses with regard to burning and tingling when substituting shoulder internal rotation for external rotation during the ULNT₃. The results also suggest that there were only marginal differences in the sensory responses of stretching and numbness during the same substitution.

CONCLUSION

Patients who have limited glenohumeral external rotation due to pain, instability, and/or articular limitation may benefit from this substitution when presenting with signs of ulnar nerve pathodynamics. Further research will be needed to validate this maneuver in a symptomatic population.

LEVEL OF EVIDENCE

Level 2b.