Upper limb neurodynamic testing with radial and ulnar nerve biases: an analysis of cervical spinal nerve mechanics

Key points

1. 01Radial nerve bias produced intraforaminal displacement of 2.44-3.04 mm and strain of 7.99-11.98% across C5-C8
2. 02Ulnar nerve bias produced intraforaminal displacement of 2.16-4.41 mm and strain of 7.12-12.95% across C5-C8
3. 03Significant strain occurred at all spinal levels (C5-C8) during ulnar bias, but only at C6-C8 during radial bias
4. 04Extraforaminal displacement was greater than intraforaminal displacement, likely due to restraining intraforaminal ligaments
5. 05Results support using all three ULNT strategies (median, radial, ulnar) in combination to reduce false-negative diagnoses

How it was conducted

Design

Cross-sectional cadaveric biomechanical study

Participants

9 unembalmed cadavers (6 male, 3 female), mean age 80.1 +/- 13.2 years, BMI 22.1 +/- 4.2

Spinal levels

C5-C8 cervical spinal nerves instrumented with radiolucent helical markers proximal and distal to the intervertebral foramen

Interventions

Standardized ULNT with radial nerve bias followed by ulnar nerve bias; 20-30 min rest between tests

Imaging

Posterior-anterior fluoroscopic images at rest and maximal tension; digitized via custom MATLAB program

Primary outcome

Spinal nerve displacement (mm) and strain (% length change) from rest to maximal tension position

What they found

• Radial bias: intraforaminal (x-axis) displacement ranged 2.44-3.04 mm, all P < 0.05 for C5-C8
• Radial bias: extraforaminal (x-axis) displacement ranged 3.47-4.62 mm, all P < 0.05 for C5-C8
• Radial bias: strain ranged 7.99-11.98%; significant at C6 (11.98 +/- 5.50%, P = 0.001), C7 (10.78 +/- 2.44%, P = 0.001), C8 (9.12 +/- 4.14%, P = 0.014); not significant at C5 (7.99 +/- 7.21%, P = 0.062)
• Ulnar bias: intraforaminal (x-axis) displacement ranged 2.16-2.71 mm, all P < 0.05 for C5-C8
• Ulnar bias: extraforaminal (x-axis) displacement ranged 3.29-4.41 mm, all P < 0.05 for C5-C8; significant differences between C5 and C6 (t = 2.691, p = 0.045), C5 and C7 (t = 3.048, p = 0.028), C5 and C8 (t = 2.820, p = 0.041)
• Ulnar bias: strain ranged 7.12-12.95%; significant at all levels: C5 (7.12 +/- 4.06%, P = 0.029), C6 (11.24 +/- 3.17%, P = 0.002), C7 (12.28 +/- 3.38%, P = 0.004), C8 (12.95 +/- 2.61%, P = 0.001); significant differences in strain by level, F(3,31) = 6.573, p = 0.001
• Inter-rater reliability of digitization: ICC 0.97 (95% CI 0.97-0.98)
• Perpendicular (y-axis) displacement was small and mostly non-significant; significant only at extraforaminal C7 for radial bias (P = 0.004) and extraforaminal C6 (P = 0.012) and C7 (P = 0.002) for ulnar bias

Limitations

• Testing order was not randomized (ulnar always followed radial), so larger ulnar strains may partly reflect creep from prior radial testing
• Small sample size (n = 9) with older cadavers limits generalizability to living patients
• Planar fluoroscopic imaging cannot fully capture three-dimensional spinal nerve movement
• Marker implantation required minimal dissection that may have altered tissue mechanics compared to intact in vivo conditions

Why it matters

For patients

Patients with neck pain or arm symptoms can be reassured that the arm positioning tests clinicians use during examination genuinely stress the relevant cervical nerves, making the tests mechanically meaningful.

For clinicians

All three ULNT biases (median, radial, and ulnar) load cervical spinal nerves C5-C8, supporting the practice of combining them to reduce false-negative results and justifying their use in neurodynamic mobilization treatment.

For readers

This cadaveric study fills a gap by confirming the biomechanical basis of radial and ulnar ULNT strategies, complementing prior work on the median nerve bias and strengthening the rationale for multi-strategy neurodynamic assessment.