Research Review By Dr. Demetry Assimakopoulos©

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Date Posted:

December 2015

Studies Reviewed:

  1. Lohman CM, Gilbert KK, Sobczak S et al. Cervical Nerve Root Displacement and Strain During Upper Limb Tension Testing. Part 1: A Minimally Invasive Assessment in Unembalmed Cadavers. Spine 2015; 40(11): 793-800.
  2. Lohman CM, Gilbert KK, Sobczak S et al. Cervical Nerve Root Displacement and Strain During Upper Limb Tension Testing. Part 2: Role of Foraminal Ligaments in the Cervical Spine. Spine 2015; 40(11): 801-808.

Author's Affiliations:

Department of Interdisciplinary Health Sciences, Arizona School of Health Sciences, Still University, Arizona; Center for Rehabilitation Research and Department of Rehabilitation Sciences, School of Allied Health Sciences, Texas Tech University Health Sciences Center, Lubbock Texas; Laboratory of Anatomy, Biomechanics and Organogenesis (LABO), Universite Libre de Bruxelles, Bruxelles, Belgium; Department of Medical Education, Albany Medical College, Albany NY; Research Unit in Osteopathy, Universite Libre de Bruzelles, Bruxelles, Belgium.

Background Information:

Upper limb nerve (or neural) tension testing (ULNTT) procedures are theorized to evaluate pathology of the brachial plexus and upper extremity peripheral nerves (1). To date, much of the research into the mechanics of ULNTT utilized laminectomy procedures to visualize proximal and distal displacement of nerve roots. Laminectomies disrupt the foraminal ligaments and alter the mechanical behaviour of nerve roots, therefore potentially limiting applicability to the general population.

The authors of this study endeavoured to measure the amount of cervical nerve root displacement and strain during ULNTT using fluoroscopy, to only minimally disrupt the surrounding tissues. The authors then cut the surrounding transforaminal and extra-foraminal ligaments, to determine if the dissection altered the biomechanics of adjacent nerve roots.

Pertinent Results:

During the ULNTT, the intra-foraminal nerve roots were significantly displaced inferolaterally, in line with the nerve root, travelling a distance of approximately 2.16-2.29 mm. There was no significant difference in displacement between the nerve root levels. The intra-foraminal nerve roots were also displaced inferomedially (i.e. perpendicular to the nerve root) during ULNTT, but not significantly.

The extra-foraminal nerve roots were also significantly displaced inferolaterally during the ULNTT, travelling a distance of 3.15-4.32 mm. The C5-C7 extra-foraminal roots were also displaced inferomedially (perpendicular to the plane of the nerve root) travelling a distance of -0.61 to -0.72 mm. No significant difference was observed among nerve root levels.

After selectively cutting the surrounding foraminal ligaments (part 2 of the study), inferolateral displacement of the intra-foraminal nerve roots increased to 2.60-3.11 mm. This change in intra-foraminal nerve root displacement was NOT statistically significant.

Cutting the foraminal ligaments increased inferolateral displacement of the extra-foraminal nerve roots to 4.77-6.09 mm. The change in extra-foraminal nerve root displacement after cutting WAS statistically significant. Cutting the foraminal ligaments did not significantly improve inferomedial nerve root displacement.

ULNTT caused significant cervical nerve root strain (defined as a percent change in nerve root length) at all levels, ranging from 6.80-11.87%. There was a significant difference in strain between the C5 and C6 extra-foraminal nerve roots. Selective cutting of the foraminal ligaments increased strain on all nerve roots, ranging from 12.15-19.60%; a 74.79% increase! There was initially a significant difference in strain between nerve root levels after cutting the foraminal ligaments, but these results did not retain significance post-hoc.

Clinical Application & Conclusions:

The median nerve ULNTT displaced both the intra-foraminal and extra-foraminal cervical nerve roots. The majority of the nerve root movement occurred in the infero-lateral direction (in line with the cervical nerve roots). The C5-C7 extra-foraminal nerve roots were also displaced inferomedially.

ULNTT also produced a significant amount of strain upon the cervical nerve roots, with the greatest strain exhibited at C6. The change in length was extrapolated to 1.00 N, 1.74 N, 1.5 N and 1.48 N for roots C5-C8, respectively. Strain above 6% can have a number of ramifications, including impaired nerve amplitude, revascularization, venular flow, intraneural circulation and mechanical failure. The strain theoretically occurred because the extra-foraminal nerve roots were displaced farther than the intra-foraminal roots, due to the fact that the intra-foraminal roots are anatomically tethered by transforaminal ligaments.

The abovementioned findings suggest a mechanical foundation for the use of ULNTT in the evaluation of cervical spine injury, such as radiculopathy, nerve entrapment or thoracic outlet syndrome (TOS).

Cutting the intra-foraminal ligaments increased the strain placed upon the cervical nerve roots. One can logically conclude that the intra-foraminal ligaments protect from traction injury by decreasing potential imparted strain upon cervical nerve roots. These findings might be valuable in patients who have undergone invasive procedures which cut the intra-foraminal ligaments, such as laminectomy, foraminotomy and epidural lysis of adhesions (Racz Procedure). Post-surgical rehabilitation should include gentle ULNTT to prevent further adhesions or scar tissue (in this case, the test can also be a treatment, utilized in a ‘nerve-flossing’ manner).

It has been speculated that the foraminal ligaments are capable of becoming fibrotic as a result of inflammatory processes, leading to irritation of surrounding soft tissues. However, it is still uncertain how much these ligaments participate in the creation of cervical spinal pathology. Future studies should endeavour to determine if the foraminal ligaments have nociceptive properties.

Study Methods:

Eleven un-embalmed cadavers were obtained for the study. The authors excluded cadavers which underwent previous cervical spinal surgery or upper extremity amputation. Similarly, those that suffered from cervical spinal cancer, low bone mineral density or current upper extremity fracture were also excluded. Cervical nerve roots C5-C8 were exposed using an anterior approach. Fluoroscopic images of the cervical spine were taken at rest, and during the ULNTT procedure. Strain of the nerve root along with displacement and strain (defined as a percent change in length) were calculated.

The authors chose the ULNTT with median nerve bias, because it has been empirically shown to place the greatest strain on the brachial plexus (2). The procedure was performed in the following manner:
  1. Shoulder depression
  2. Shoulder abduction to 110°
  3. Maximal shoulder external rotation
  4. Maximal wrist and finger extension
  5. Maximal elbow extension
Side bending of the neck was not included, but will be described in a future study.

Fluoroscopic images were digitized and computerized coordinates were used to assess cervical nerve root displacement and strain relative to the cervical vertebrae. Intra- and extra-foraminal neural markers were placed on each cervical nerve root and analyzed for positional movement. Strain was then calculated, as a percentage of change in length between two markers.

After neurodynamic testing, the C5-C8 transforaminal and extraforaminal ligaments were cut, after which the ULNTT procedure was repeated.

One-sample t-tests were used to determine whether ULNTT caused cervical nerve root displacement and strain. The authors then performed 5 one-way repeated measures ANOVA to assess for differences between nerve root levels (C5-C8). Post-hoc testing was done with a Bonferroni post hoc analysis.

Study Strengths / Weaknesses:

Strengths:
  • Use of intraneural markers that were monitored by fluoroscopy, so as to not disturb the internal environment of the nerve.
Weaknesses:
  • The intraneural markers can potentially disrupt nerve movement within the neuroforamen. The authors speculate that this occurred at the C5 level, as it was displaced less than the other roots. Similar discrepancies have been cited in analogous studies in the lumbar spine (3).
  • The authors utilized elderly, unembalmed cadavers, which cannot necessarily be extrapolated to live or younger populations.
  • Radial and ulnar nerve tension tests were not studied.
  • Small sample size.

Additional References:

  1. Shacklock M. Neurodynamics. Physiotherapy 1995; 81: 9–16.
  2. Kleinrensink GJ, Stoeckart R, Mulder PG, et al. Upper limb tension tests as tools in the diagnosis of nerve and plexus lesions. Anatomical and biomechanical aspects. Clin Biomech 2000; 15: 9–14.
  3. Gilbert KK, Brismée J-M, Collins DL, et al. 2006 Young Investigator Award Winner: Lumbosacral nerve root displacement and strain: Part 1. A novel measurement technique during straight leg raise in unembalmed cadavers. Spine 2007; 32: 1513–1520.