Benjamin S. Boyd

Mechanosensitivity of the lower extremity nervous system during straight-leg raise neurodynamic testing in healthy individuals.

STUDY DESIGN Cross-sectional, observational study. OBJECTIVES To explore how ankle position affects lower extremity neurodynamic testing. BACKGROUND Upper extremity limb movements that increase neural loading create a protective muscle action of the upper trapezius, resulting in shoulder girdle elevation during neurodynamic testing. A similar mechanism has been suggested in the lower extremities. METHODS Twenty healthy subjects without low back pain participated in this study. Hip flexion angle and surface electromyographic measures were taken and compared at the onset of symptoms (P1) and at the point of maximally tolerated symptoms (P2) during straight-leg raise tests performed with ankle dorsiflexion (DF-SLR) and plantar flexion (PF-SLR). RESULTS Hip flexion was reduced during DF-SLR by a mean +/- SD of 5.5 degrees +/- 6.6 degrees at P1 (P = .001) and 10.1 degrees +/- 9.7 degrees at P2 (P<.001), compared to PF-SLR. DF-SLR induced distal muscle activation and broader proximal muscle contractions at P1 compared to PF-SLR. CONCLUSION These findings support the hypothesis that addition of ankle dorsiflexion during straight-leg raise testing induces earlier distal muscle activation and reduces hip flexion motion. The straight-leg test, performed to the onset of symptoms (P1) and with sensitizing maneuvers, allows for identification of meaningful differences in test outcomes and is an appropriate end point for lower extremity neurodynamic testing.

Peripheral Nerve: From the Microscopic Functional Unit of the Axon to the Biomechanically Loaded Macroscopic Structure

Peripheral nerves are composed of motor and sensory axons, associated ensheathing Schwann cells, and organized layers of connective tissues that are in continuity with the tissues of the central nervous system. Nerve fiber anatomy facilitates conduction of electrical impulses to convey information over a distance, and the length of these polarized cells necessitates regulated axonal transport of organelles and structural proteins for normal cell function. Nerve connective tissues serve a protective function as the limb is subjected to the stresses of myriad limb positions and postures. Thus, the tissues are uniquely arranged to control the local nerve fiber environment and modulate physical stresses. In this brief review, we describe the microscopic anatomy and physiology of peripheral nerve and the biomechanical properties that enable nerve to withstand the physical stresses of everyday life.

Measurement properties of a hand-held inclinometer during straight leg raise neurodynamic testing.

OBJECTIVES The most common lower quarter neurodynamic test is the straight leg raise (SLR) test. Quantification of limb motion during SLR testing should utilize reliable and valid measurement tools that are highly sensitive to change. The purpose of this study was to determine the psychometric properties of a hand-held inclinometer commonly utilized during SLR testing. DESIGN Cross-sectional measurement, intra-rater reliability and validity study. SETTING Research laboratory. PARTICIPANTS Twenty individuals without pain in their low back or extremities and no history of nerve injury participated in the study. MAIN OUTCOME MEASURES Two repetitions of the SLR were performed in each limb in two ankle positions (plantar flexion and dorsiflexion). A digital inclinometer and digital goniometer were utilized as the comparisons for range of motion measurements. RESULTS Intra-rater reliability for the hand-held inclinometer during SLR testing was excellent (ICCs, 0.95 to 0.98). The standard error of measurement was between 0.54° and 1.22° and the minimal detectable change was between 1.50° and 3.41°. Construct validity revealed hand-held inclinometer measurements were highly correlated with both the digital inclinometer and digital goniometer measures. The mean difference scores between hand-held inclinometer and digital inclinometer (∼1.5°) and digital goniometer (∼10°) suggest that the hand-held inclinometer better matches the construct measured by the digital inclinometer (limb elevation angle) compared to the digital goniometer (hip flexion angle). CONCLUSIONS The hand-held inclinometer is a valid method for measuring limb elevation angle during the SLR neurodynamic test in a research setting. The hand-held inclinometer has high reliability and low minimal detectable change when used in healthy individuals.

The pattern of tibial nerve excursion with active ankle dorsiflexion is different in older people with diabetes mellitus

BACKGROUND The peripheral nervous system has an inherent capability to tolerate the gliding (excursion), stretching (increased strain), and compression associated with limb motions necessary for functional activities. The biomechanical properties during joint movements are well studied but the influence of other factors such as limb pre-positioning, age and the effects of diabetes mellitus are not well established for the lower extremity. The purposes of this pilot study were to compare the impact of two different hip positions on lower extremity nerve biomechanics during an active ankle dorsiflexion motion in healthy individuals and to determine whether nerve biomechanics are altered in older individuals with diabetes mellitus. METHODS Ultrasound imaging was used to quantify longitudinal motion of the tibial nerve and transverse plane motion of the tibial and common fibular nerves in the popliteal fossa during active ankle movements. FINDINGS In healthy individuals, ankle dorsiflexion created mean tibial nerve movement of 2.18 mm distally, 1.36 mm medially and 3.98 mm superficially. When the hip was in a flexed position there was a mean three-fold reduction in distal movement. In people with diabetes mellitus there was significantly less distal movement of the tibial nerve in the neutral hip position and less superficial movement of the nerve in both hip positions compared to healthy individuals. INTERPRETATION We have documented reductions in tibial nerve excursion due to limb pre-positioning thought to pre-load the nervous system using a non-invasive methodology. Thus, lower limb pre-positioning impacts nerve biomechanics during ankle motions common in functional activities. Additionally, our findings indicate that nerve biomechanics have the potential to be altered in older individuals with diabetes mellitus compared to younger healthy individuals.

Mechanosensitivity during lower extremity neurodynamic testing is diminished in individuals with Type 2 Diabetes Mellitus and peripheral neuropathy: a cross sectional study

BackgroundType 2 Diabetes Mellitus (T2DM) and diabetic symmetrical polyneuropathy (DSP) impact multiple modalities of sensation including light touch, temperature, position sense and vibration perception. No study to date has examined the mechanosensitivity of peripheral nerves during limb movement in this population. The objective was to determine the unique effects T2DM and DSP have on nerve mechanosensitivity in the lower extremity.MethodsThis cross-sectional study included 43 people with T2DM. Straight leg raise neurodynamic tests were performed with ankle plantar flexion (PF/SLR) and dorsiflexion (DF/SLR). Hip flexion range of motion (ROM), lower extremity muscle activity and symptom profile, intensity and location were measured at rest, first onset of symptoms (P1) and maximally tolerated symptoms (P2).ResultsThe addition of ankle dorsiflexion during SLR testing reduced the hip flexion ROM by 4.3° ± 6.5° at P1 and by 5.4° ± 4.9° at P2. Individuals in the T2DM group with signs of severe DSP (n = 9) had no difference in hip flexion ROM between PF/SLR and DF/SLR at P1 (1.4° ± 4.2°; paired t-test p = 0.34) or P2 (0.9° ± 2.5°; paired t-test p = 0.31). Movement induced muscle activity was absent during SLR with the exception of the tibialis anterior during DF/SLR testing. Increases in symptom intensity during SLR testing were similar for both PF/SLR and DF/SLR. The addition of ankle dorsiflexion induced more frequent posterior leg symptoms when taken to P2.ConclusionsConsistent with previous recommendations in the literature, P1 is an appropriate test end point for SLR neurodynamic testing in people with T2DM. However, our findings suggest that people with T2DM and severe DSP have limited responses to SLR neurodynamic testing, and thus may be at risk for harm from nerve overstretch and the information gathered will be of limited clinical value.

Deviations in gait pattern in experimental models of hindlimb paresis shown by a novel pressure mapping system.

Injuries to the central and peripheral nervous system result in varying degrees of paresis and as such alter gait. We developed novel quantitative measures to assess compensatory patterns of gait in experimental models of unilateral and bilateral hindlimb paresis. We hypothesized that hindlimb paresis results in unique alterations in the gait cycle that reflect the symmetry of the initial lesion. To test this hypothesis, adult, male Sprague‐Dawley rats were subjected to a unilateral sciatic nerve crush injury or a moderately severe spinal cord contusion injury at T8. Kinematic and timing parameters were captured simultaneously in all four limbs and alterations in gait were then compared to relevant sham controls. Gait analysis consisted of walking trials through a gait tunnel positioned over a Tekscan pressure sensor grid. After sciatic nerve injury, animals unweighted the injured limb by shifting their center of mass toward the contralateral forelimb and hindlimb. These changes in weight‐bearing occurred simultaneously with an increase in stance time on the contralateral limbs. As might be expected spinal cord injured animals unweighted their hindlimbs, as shown by reduced hindlimb contact force and contact pressure. These adjustments coincided with a shortening of forelimb stance time and stride length. These findings show both alterations and compensatory changes in gait that reflect the symmetry of the initial injury.

Normal inter-limb differences during the straight leg raise neurodynamic test: a cross sectional study

BackgroundThe straight leg raise (SLR) neurodynamic test is commonly used to examine the sensitivity of the lower quarter nervous system to movement. Range of motion during the SLR varies considerably, due to factors such as age, sex and activity level. Knowing intra-individual, inter-limb differences may provide a normative measure that is not influenced by such demographic characteristics. This study aimed to determine normal asymmetries between limbs in healthy, asymptomatic individuals during SLR testing and the relationship of various demographic characteristics.MethodsThe limb elevation angle was measured using an inclinometer during SLR neurodynamic testing that involved pre-positioning the ankle in plantar flexion (PF/SLR) and neutral dorsiflexion (DF/SLR). Phase 1 of the study included 20 participants where the ankle was positioned using an ankle brace replicating research testing conditions. Phase 2 included 20 additional participants where the ankle was manually positioned to replicate clinical testing conditions.ResultsThe group average range of motion during PF/SLR was 57.1 degrees (SD: 16.8 degrees) on the left and 56.7 degrees (SD: 17.2 degrees) on the right while during DF/SLR the group average was 48.5 degrees (SD: 16.1 degrees) on the left and 48.9 degrees (SD: 16.4 degrees) on the right. The range of motion during SLR was moderately correlated to weight (−0.40 to −0.52), body mass index (−0.41 to −0.52), sex (0.40 to 0.42) and self-reported activity level (0.50 to 0.57). Intra-individual differences between limbs for range of motion during PF/SLR averaged 5.0 degrees (SD: 3.5 degrees) (95% CI: 3.8 degrees, 6.1 degrees) and during DF/SLR averaged 4.1 degrees (SD: 3.2 degrees) (95% CI: 3.1 degrees, 5.1 degrees) but were not correlated with any demographic characteristic. There were no significant differences between Phase 1 and Phase 2.ConclusionsOverall range of motion during SLR was related to sex, weight, BMI and activity level, which is likely reflected in the high variability documented. We can be 95% confident that inter-limb differences during SLR neurodynamic testing fall below 11 degrees in 90% of the general population of healthy individuals. In addition, inter-limb differences were not affected by demographic factors and thus may be a more valuable comparison for test interpretation.

Altered tibial nerve biomechanics in patients with diabetes mellitus

Introduction: Hyperglycemia associated with diabetes mellitus (DM) has adverse impacts on peripheral nerve connective tissue structure, and there is preliminary evidence that nerve biomechanics may be altered. Methods: Ultrasound imaging was utilized to quantify the magnitude and timing of tibial nerve excursion during ankle dorsiflexion in patients with DM and matched healthy controls. Results: Tibial nerve longitudinal excursion at the ankle and knee was reduced, and timing was delayed at the ankle in the DM group. Severity of neuropathy was correlated with larger reductions in longitudinal excursion. Nerve cross‐sectional area was increased at the ankle in the DM group. Conclusions: Larger tibial nerve size within the tarsal tunnel in patients with DM may restrict longitudinal excursion, which was most evident with more severe neuropathy. It is hypothesized that these alterations may be related to painful symptoms during functional activities that utilize similar physiological motions through various biomechanical and physiological mechanisms. Muscle Nerve 50:216–223, 2014

The influence of scapular depression on upper limb neurodynamic test responses

Abstract Objectives Upper limb neurodynamic testing (ULNT) can be used clinically to assist in identifying neural tissue involvement in patients with upper quarter pain and dysfunction. Consideration for scapular positioning is a crucial component of ULNT standardization, as variations in positioning may dramatically impact sensory and motor responses. This study aimed to determine if there was a meaningful difference in test outcomes when the ULNT was performed in alternative scapular positions. Methods This cross-sectional study included 40 asymptomatic individuals. Repeated ULNT testing was performed on the dominant limb with the scapula blocked in neutral (ULNTb) and in scapular depression (ULNTd). Sensory responses, muscle activity, and range of motion outcomes were compared between the two test variations. Results Pre-positioning in scapular depression (ULNTd) led to reduced elbow extension range of motion, provoked greater upper trapezius muscle activity and an earlier onset and broader area of sensory responses compared to ULNTb. Discussion During ULNTb, the limbs were taken further into range and elicited reduced muscle activation and more localized sensory response providing a less vigorous version of the test. This study demonstrates that scapular positioning has a meaningful impact on ULNT test outcomes in healthy, asymptomatic individuals. The ULNTd can be considered a more vigorous version that may be appropriate when the cervical motions commonly utilized for structural differentiation are limited or contraindicated.

Common Interlimb Asymmetries and Neurogenic Responses during Upper Limb Neurodynamic Testing: Implications for Test Interpretation

STUDY DESIGN Clinical measurement pilot study. INTRODUCTION Upper limb neurodynamic testing (ULNT1) uses interlimb comparisons to investigate nerve sensitivity to movement. PURPOSE OF THE STUDY To establish the magnitude of range of motion asymmetries between limbs and the frequency of neurogenic sensory responses during ULNT1. METHODS Elbow extension range of motion (EE-ROM) and sensory responses were measured during ULNT1 in dominant and nondominant limbs for 40 asymptomatic participants. Structural differentiation was performed to examine if sensory responses were associated with neurogenic sources. RESULTS The average intraindividual EE-ROM asymmetry was 7.28 deg (6.68 standard deviation) (95% confidence interval: 5.18, 9.28). Sensory responses in the limbs during ULNT1 were altered by structural differentiation in 95% of participants. An intraindividual, interlimb difference of ≥10 deg exceeds the range of common asymmetry during ULNT1. CONCLUSIONS Neurogenic sensory responses are common findings in healthy individuals and should be acknowledged when interpreting ULNT1 findings. LEVEL OF EVIDENCE 3a.