Nerve Biomechanics Research Articles

Cisternal, Falciform, and Optic Canal Decompression Influencing Optic Nerve Biomechanics: A Microsurgical Anatomic Study.

Questions remain regarding optic nerve (ON) physiology, mechanical compliance, and microvasculature, particularly surgical outcomes and atypical visual field defects associated with sellar/parasellar pathology (eg, tumors and aneurysms). To study the microsurgical/histological anatomy of each ON segment and corresponding microvasculature, calculate area of optic-carotid space at each decompression stage, and measure ON tension before/after compression. Five cadaveric heads (10 sides) underwent sequential dissection: (1) intradural (arachnoidal) ON dissection; (2) falciform ligament opening; (3) anterior clinoidectomy, optic canal decompression, and ON sheath release. At each step, we pulled the nerve superiorly/laterally with a force meter and measured maximal mobility/mechanical tension in each position. Cisternal ON microvasculature was more superficial and less dense vs the orbital segment. ON tension was significantly lower with higher mobility when manipulated superiorly vs lateromedially. Optic-carotid space significantly increased in size at each decompression stage and with ON mobilization both superiorly and laterally, but the increase was statistically significant in favor of upward mobilization. At decompression step, upward pull provided more space with less tension vs side pull. For upward pull, each step of decompression provided added space as did side pull. Opening the optic canal, falciform ligament, and arachnoid membrane decompresses the ON for safer manipulation and provided a wider optic-carotid surgical corridor to access sellar/parasellar pathology. When tailoring decompression, the ON should be manipulated superiorly rather than lateromedially, which may guide surgical technique, help prevent intraoperative visual deterioration, facilitate postoperative visual improvement, and help understand preoperative visual field deficits based on mechanical factors.

Sciatic nerve excursion during neural mobilization with ankle movement using dynamic ultrasound imaging: a cross-sectional study.

Ankle movement is used as a sensitizing maneuver for sciatica during neurodynamic techniques. In vivo studies on the sciatic nerve biomechanics associated with ankle movement during different positions of neighboring joints are scarce. The aim of this study was to investigate sciatic nerve excursion during ankle dorsiflexion in different positions in a healthy population. This is a cross-sectional study. High-resolution dynamic ultrasound imaging was used to measure longitudinal excursion of the sciatic nerve in the posterior thigh of 27 healthy participants during ankle dorsiflexion in six positions of the neck, hip, and knee. Both the long and short distance of the nerve excursion were measured. Wilcoxon signed-rank tests were used for data analysis, and Eta squared (r) was used to quantify the effect size. Ankle dorsiflexion resulted in distal sciatic nerve excursion that was significantly higher in positions in which the knee was extended (median 0.7-1.6mm) than in positions in which the knee was flexed (median 0.5-1.4mm) (P ≤ 0.049, r ≥ 0.379). There were no significant differences in nerve excursion between positions where the neck was neutral compared with positions where the neck was flexed (P ≥ 0.710, r ≤ 0.072) or between positions where the hip was neutral compared with positions where the hip was flexed (P ≥ 0.456, r ≤ 0.143). The positions of adjacent joints, particularly the knee, had an impact on the excursion of the sciatic nerve in the thigh during ankle movement.

Patient expectations about a clinical diagnostic test may influence the clinician's test interpretation

BackgroundWith medical information widely available, patients often have preconceived ideas regarding diagnostic procedures and management strategies. ObjectivesTo investigate whether expectations, such as beliefs about the source of symptoms and knowledge about diagnostic tests, influence pain perception during a clinical diagnostic test. DesignCross-sectional study. MethodsPain was induced by intramuscular hypertonic saline infusion in the thenar muscles. In line with sample size calculations, fifteen participants were included. All participants received identical background information regarding basic median nerve biomechanics and basic concepts of differential diagnosis via mechanical loading of painful structures. Based on different explanations about the origin of their induced pain, half of the participants believed (correctly) they had ‘muscle pain’ and half believed (incorrectly) they had ‘nerve pain’. Pain intensity and size of the painful area were evaluated in five different positions of the median nerve neurodynamic test (ULNT1 MEDIAN). Data were analysed with two-way analyses of variance. Results/findings: Changes in pain in the ULNT1 MEDIAN positions were different between the ‘muscle pain’ and ‘nerve pain’ group (p < 0.001). In line with their expectations, the ‘muscle pain’ group demonstrated no changes in pain throughout the test (p > 0.38). In contrast, pain intensity (p ≤ 0.003) and size of the painful area (p ≤ 0.03) increased and decreased in the ‘nerve pain’ group consistent with their expectations and the level of mechanical nerve loading. ConclusionPain perception during a clinical diagnostic test may be substantially influenced by pain anticipation. Moreover, pain was more aligned with beliefs and expectations than with the actual pathobiological process.

Mechanical changes of peripheral nerve tissue microenvironment and their structural basis during development.

Peripheral nerves are constantly exposed to mechanical stresses associated with body growth and limb movements. Although some aspects of these nerves' biomechanical properties are known, the link between nerve biomechanics and tissue microstructures during development is poorly understood. Here, we used atomic force microscopy to comprehensively investigate the elastic modulus of living peripheral nerve tissue cross sections ex vivo at distinct stages of development and correlated these elastic moduli with various cellular and extracellular aspects of the underlying histological microstructure. We found that local nerve tissue stiffness is spatially heterogeneous and evolves biphasically during maturation. Furthermore, we found the intracellular microtubule network and the extracellular matrix collagens type I and type IV as major contributors to the nerves' biomechanical properties, but surprisingly not cellular density and myelin content as previously shown for the central nervous system. Overall, these findings characterize the mechanical microenvironment that surrounds Schwann cells and neurons and will further our understanding of their mechanosensing mechanisms during nerve development. These data also provide the design of artificial nerve scaffolds to promote biomedical nerve regeneration therapies by considering mechanical properties that better reflect the nerve microenvironment.

The 45th Annual Meeting of the North American Neuro-Ophthalmology Society in Las Vegas, Nevada

The North American Neuro-Ophthalmology Society (NANOS) held its 45th annual meeting at the Red Rock Casino, Resort and Spa, Las Vegas, Nevada, March 16–21, 2019. The Frank B. Walsh Society meeting was hosted by the University of Pennsylvania group along with special experts in neuroradiology, Dr. Laurie Loevner, and neuropathologist, Dr. Zissimos Mourelatos. The award for best Walsh paper was presented to Dr. Paul R. Freund, and was entitled “Go with your Gut Feeling” (Fig. 1).FIG. 1.: Dr. Paul R. Freund (left) won the award for best Frank B. Walsh session paper presentation by a fellow. The award was presented by Drs. Peter Quiros (middle) and Andrew Lee (right).Once again, the educational symposia were exceptional. “New Information I Should Know” highlighted neuro-immunological therapies from encephalitis to migraine. “Hot Topics” covered treatment of commonly encountered neuro-ophthalmic disorders. An educational session, “Retinal Microvascular Changes and Neurologic Disorders,” provided insight into retinal microvascular changes in relation to acute and chronic neurologic diseases. Dr. Tien Yin Wong reported on the advancement in artificial intelligence in retinal imaging. Drs. David Newman-Toker and Dan Gold thoroughly highlighted the approach to dizziness and vertigo. On the final day, pediatric neuro-ophthalmology topics were highlighted, including the evaluation of children vs. adults and a case-based approach to eye movement disorders in children. The Jacobson Lecture featured Dr. Nancy Newman's talk, “Leber Hereditary Optic Neuropathy: From Bedside to Bench to Bedside.” This presentation traced the history of Leber hereditary optic neuropathy from clinical recognition, to discovery of the first point mutation in mitochondrial DNA, to ground-breaking attempts at gene therapy (Fig. 2).FIG. 2.: Dr. Nancy Newman, our 2019 Jacobson Lecturer.This year's optional symposia were very popular and included a dynamic skills transfer session on extraocular muscle and vestibular testing, along with a session providing updates in headache medicine important for neuro-ophthalmologists. Two additional symposia included “Reading an OCT Like We Read an MRI” and “Worldwide Wonders: Cases Defining the International Language of Neuro-Ophthalmology.” This year's meeting offered two poster sessions, featuring 248 posters divided between 125 Clinical Highlights in Neuro-Ophthalmology on Sunday afternoon during the Walsh Session and 123 posters on Scientific Advancement in Neuro-Ophthalmology on Tuesday afternoon. There were three insightful scientific platform sessions. This year's awardees were as follows: James A. Sharpe Award by a Fellow: Melanie N. Truong-Le, DO, OD—“Reflex Upper and Lower Eyelid Movement in Response to Light Stimuli.” Best Abstract by a Resident: Michael J. Gilhooley, MA, MB, BChir, FRCOphth—“Melanopsin: targeted ectopic expression for optogenetic visual restoration.” Best Abstract by a Student: Perry J. Thompson, BA—“Near Infrared Videography versus Direct Ophthalmoscopy for the Detection of Spontaneous Venous Pulsations.” 2019 Pilot Grant Award: Heather Moss, MD, PhD, for her project “Optic Nerve Biomechanics in High Intracranial Pressure States.” The Thomas and Susan Carlow Young Investigator Award: Ghislaine L. Traber, MD, for her project “The Untuned Visuo-Temporal Cortex in Patients with Visual Snow.” Hoyt Lecture Award (given at the AAO in 2018): Joseph F. Rizzo III, MD, for his presentation of the William F. Hoyt Lecture “Unraveling the Enigma of Non-Arteritic Anterior Ischemic Optic Neuropathy.” NANOS Merit Awards (for extraordinary contributions of time, energy, and resources to NANOS): Sachin Kedar, MD; Lanning Kline, MD; Christian J. Lueck, PhD, FRACP, FRCP (UK), FAAN. J. Lawton Smith Award (given a top original contribution published in the JNO): Hong Jiang, MD, for her paper “Altered Macular Microvasculature in Mild Cognitive Impairment and Alzheimer Disease.” Thomas Carlow Distinguished Service Award: Nancy J. Newman, MD, for her lifetime contributions to NANOS and the field of Neuro-Ophthalmology (Fig. 3).FIG. 3.: Dr. Nancy Newman (middle) received the Thomas Carlow Distinguished Service Award. She was introduced by Dr. Paul Phillips (left).Pilot Grant Leadership Development Award: Barbara Yates, MD. AAO Leadership Development Program Nominee: John Chen, MD, PhD. The 2019 meeting had an all-time high attendance with 738 registrants from 39 countries! Our international members made up 29% of the attendees! The annual banquet was held in the hotel with an amazing NON-STOP dancing frenzy until the end! Janel Fick, Trish Shomion, Toma Ossian, and Tara Thebeau hosted another very well-organized meeting. The 46th NANOS annual meeting will be Amelia Island, Florida, March 7–12, 2020. Thanks to all for their hard work and support of the annual meeting!

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.

Decoupled epineurial and axonal deformation in mouse median and ulnar nerves.

Peripheral nerves accommodate mechanical loads during joint movement. Hypothesized protective features include increased nerve compliance near joints and axonal undulation. How axons perceive nerve deformation is poorly understood. We tested whether nerves increase local axonal undulation in regions of high epineurial strain to protect nerve fibers from strain-induced damage. Regional epineurial strain was measured near the elbow in median and ulnar nerves of mice expressing axonal fluorescence before and after decompression. Regional axonal tortuosity was quantified under confocal microscopy. Nerves showed higher epineurial strain just distal to the medial epicondyle; these differences were eliminated after decompression. Axonal tortuosity also varied regionally; however, unlike in the epineurium, it was greater in proximal regions. In this study we have proposed a neuromechanical model whereby axons can unravel along their entire length due to looser mechanical coupling to the peri/epineurium. Our findings have major implications for understanding nerve biomechanics and dysfunction. Muscle Nerve 59:619-619, 2019.

Femoral nerve excursion with knee and neck movements in supine, sitting and side-lying slump: An in vivo study using ultrasound imaging

BackgroundNeurodynamic assessment and management are advocated for femoral nerve pathology. Contrary to neurodynamic techniques for other nerves, there is limited research that quantifies femoral nerve biomechanics. ObjectivesTo quantify longitudinal and transverse excursion of the femoral nerve during knee and neck movements. DesignSingle-group, experimental study, with within-participant comparisons. MethodsHigh-resolution ultrasound recordings of the femoral nerve were made in the proximal thigh/groin region in 30 asymptomatic participants. Scans were made during knee flexion in supine and a semi-seated position, and during neck flexion in side-lying slump (Slump FEMORAL). Healthy participants were assessed to reveal normal nerve biomechanics, not influenced by pathology. Data were analysed with one-sample and paired t-tests. Reliability was assessed with intraclass correlation coefficients (ICC). ResultsLongitudinal and transverse excursion measurements were reliable (ICC≥0.87). With knee flexion, longitudinal femoral nerve excursion was significant and larger in supine than in sitting (supine (mean (SD)): 3.6 (2.0) mm; p < 0.001; sitting: 1.1 (1.6) mm; p = 0.001; comparison: p = 0.001). There was also excursion in a medial direction (supine: 1.4 (0.3) mm; p < 0.001; sitting: 0.7 (0.6) mm; p < 0.001) and anterior direction (supine: 0.2 (0.2) mm; p < 0.001; sitting: 0.1 (0.2) mm; p = 0.06). Neck flexion in Slump FEMORAL did not result in longitudinal (0.0 (0.3) mm; p = 0.55) or anteroposterior (0.0 (0.1) mm; p = 0.10) excursion, but resulted in medial excursion (1.1 (0.5) mm; p < 0.001). ConclusionAlthough the femoral nerve terminates proximal to the knee, femoral nerve excursion in the proximal thigh occurred with knee flexion; Neck flexion in Slump FEMORAL resulted in medial excursion.

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

The mechanical behavior of the peripheral nervous system under elongation and tension has not been adequately established in vivo. The purpose of this review is to investigate the mechanical behavior of the peripheral nervous system in vivo. 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. 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. 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.

Ultrasound-guided hydrodissection decreases gliding resistance of the median nerve within the carpal tunnel.

The aim of this study was to assess alterations in median nerve (MN) biomechanics within the carpal tunnel resulting from ultrasound-guided hydrodissection in a cadaveric model. Twelve fresh frozen human cadaver hands were used. MN gliding resistance was measured at baseline and posthydrodissection, by pulling the nerve proximally and then returning it to the origin. Six specimens were treated with hydrodissection, and 6 were used as controls. In the hydrodissection group there was a significant reduction in mean peak gliding resistance of 92.9 ± 34.8 mN between baseline and immediately posthydrodissection (21.4% ± 10.5%; P = 0.001). No significant reduction between baseline and the second cycle occurred in the control group: 9.6 ± 29.8 mN (0.4% ± 5.3%; P = 0.467). Hydrodissection can decrease the gliding resistance of the MN within the carpal tunnel, at least in wrists unaffected by carpal tunnel syndrome. A clinical trial of hydrodissection seems justified. Muscle Nerve 57: 25-32, 2018.

The effects of hip abduction on sciatic nerve biomechanics during terminal hip flexion.

Terminal hip flexion contributes to increased strain in peripheral nerves at the level of the hip joint. The effects of hip abduction and femoral version on sciatic nerve biomechanics are not well understood. A decrease in sciatic nerve strain will be observed during terminal hip flexion and hip abduction, independent of femoral version. Six un-embalmed human cadavers were utilized. Three Differential Variable Reluctance Transducers (DVRTs) sensors were placed on the sciatic nerve while the leg was flexed to 70° with a combination of − 10°, 0°, 20° and 40° adduction/abduction. DVRT placement included: (i) under piriformis, (ii) immediately distal to the gemelli/obturator, (iii) four centimeters distal to sensor two. A de-rotational osteotomy to decrease femoral version 10° was performed, and sciatic nerve strain was measured by the same procedure. Data were analyzed with three-way analysis of variance and Bonferroni post-hoc analysis to identify differences in the mean values of sciatic nerve strain between native and decreased version state, hip abduction angle and DVRT sensor location. Significant main effects were observed for femoral version (P = 0.04) and DVRT sensor location (P = 0.01). Sciatic nerve strain decreased during terminal hip flexion and abduction in the decreased version state. An 84.23% decrease in sciatic nerve strain was observed during hip abduction from neutral to 40° in the presence of decreased version at terminal hip flexion. The results obtained from this study confirm the role of decreased femoral version and hip abduction at terminal hip flexion to decrease the strain in the sciatic nerve.

Posture-induced changes in peripheral nerve stiffness measured by ultrasound shear-wave elastography.

Peripheral nerves slide and stretch during limb movements. Changes in nerve stiffness associated with such movements have not been examined in detail but may be important in understanding movement-evoked pain in patients with a variety of different musculoskeletal conditions. Shear-wave elastography was used to examine stiffness in the median and tibial nerves of healthy individuals during postures used clinically to stretch these nerves. Shear-wave velocity increased when limbs were moved into postures that are thought to increase nerve stiffness (mean increase: median nerve = 208% in arm, 236% in forearm; tibial nerve = 136%). There was a trend toward a negative correlation between age and shear-wave velocity (r = 0.58 for tibial nerve). Shear-wave elastography provides a tool for examining nerve biomechanics in healthy individuals and patients. However, limb position, age, and effects of nerve tension on neural architecture should be taken into consideration. Muscle Nerve 55: 213-222, 2017.

Excursion of the Sciatic Nerve During Nerve Mobilization Exercises: An In Vivo Cross-sectional Study Using Dynamic Ultrasound Imaging.

Controlled laboratory cross-sectional study using single-group, within-subject comparisons. To determine whether different types of neurodynamic techniques result in differences in longitudinal sciatic nerve excursion. Large differences in nerve biomechanics have been demonstrated for different neurodynamic techniques for the upper limb (median nerve), but recent findings for the sciatic nerve have only revealed small differences in nerve excursion that may not be clinically meaningful. High-resolution ultrasound imaging was used to quantify longitudinal sciatic nerve movement in the thigh of 15 asymptomatic participants during 6 different mobilization techniques for the sciatic nerve involving the hip and knee. Healthy volunteers were selected to demonstrate normal nerve biomechanics and to eliminate potentially confounding variables associated with dysfunction. Repeated-measures analyses of variance were used to analyze the data. The techniques resulted in markedly different amounts of nerve movement (P<.001). The tensioning technique was associated with the smallest excursion (mean ± SD, 3.2 ± 2.1 mm; P < or = .004). The sliding technique resulted in the largest excursion (mean ± SD, 17.0 ± 5.2 mm; P<.001), which was approximately 5 times larger than that resulting from the tensioning technique and, on average, twice as large as that resulting from individual hip or knee movements. Consistent with current theories and findings for the median nerve, different neurodynamic exercises for the lower limb resulted in markedly different sciatic nerve excursions. Considering the continuity of the nervous system, the movement and position of adjacent joints have a large impact on nerve biomechanics.

Unravelling crucial biomechanical resilience of myelinated peripheral nerve fibres provided by the Schwann cell basal lamina and PMP22.

There is an urgent need for the research of the close and enigmatic relationship between nerve biomechanics and the development of neuropathies. Here we present a research strategy based on the application atomic force and confocal microscopy for simultaneous nerve biomechanics and integrity investigations. Using wild-type and hereditary neuropathy mouse models, we reveal surprising mechanical protection of peripheral nerves. Myelinated peripheral wild-type fibres promptly and fully recover from acute enormous local mechanical compression while maintaining functional and structural integrity. The basal lamina which enwraps each myelinated fibre separately is identified as the major contributor to the striking fibre's resilience and integrity. In contrast, neuropathic fibres lacking the peripheral myelin protein 22 (PMP22), which is closely connected with several hereditary human neuropathies, fail to recover from light compression. Interestingly, the structural arrangement of the basal lamina of Pmp22−/− fibres is significantly altered compared to wild-type fibres. In conclusion, the basal lamina and PMP22 act in concert to contribute to a resilience and integrity of peripheral nerves at the single fibre level. Our findings and the presented technology set the stage for a comprehensive research of the links between nerve biomechanics and neuropathies.

Effect of glenohumeral forward flexion on upper limb myoelectric activity during simulated mills manipulation; relations to peripheral nerve biomechanics.

BackgroundIt is generally accepted that muscles may activate via the common nociceptive flexion reflex (NFR) in response to painful stimuli associated with tensile or compressive forces on peripheral nerves. Following the basic assumption that the radial nerve may be stressed around the elbow during the execution of the Mills manipulation, t wo positions considered to have different mechanical effects on the radial nerve and the brachial plexus were tested in order to i) explore whether muscles are activated in certain patterns with concomitant changes in nerve tension, ii) establish whether muscle responses can be modified with mechanical unloading of the brachial plexus.MethodsMuscle responses were quantified bilaterally in eight subjects (N = 16) during Mills Manipulation (MM) pre-manipulative positioning and a Varied position that putatively produces less mechanical tension in the brachial plexus. End range pre-manipulative stretch was used in order to simulate the effects of Mills manipulation. Electromyographic signals were recorded with a 16 channel portable EMG unit and correlated with kinematic data from three charge-coupled device adjustable cameras which allowed for precise movement tracking.ResultsCompared with the Standard Mills manipulation position, the Varied position produced significantly reduced myoelectric activity (P ≤ .001) in all test muscles. Additional subjective data support the notion that certain muscle activity patterns were protective.ConclusionIt seems that protective muscles are selectively activated in a specific pattern in order to protect the radial nerve from mechanical tension by shortening its pathway, suggesting integration of muscle and neural mechanisms. Furthermore, the significantly decreased myoelectric activity with reduced mechanical tension in the brachial plexus may help controlling collateral effects of the Mills manipulation itself, making it potentially safer and more specific.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-288) contains supplementary material, which is available to authorized users.

Altered tibial nerve biomechanics in patients with diabetes mellitus

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. 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. 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. 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.

Impact of Movement Sequencing on Sciatic and Tibial Nerve Strain and Excursion During the Straight Leg Raise Test in Embalmed Cadavers

Laboratory study, repeated-measures design. To quantify differences in sciatic and tibial nerve biomechanics (strain and excursion) during common variations of the straight leg raise (SLR) test. Hip flexion and ankle dorsiflexion are the primary movement components of the SLR. It has been suggested that the nervous system is loaded differently when ankle dorsiflexion is added before or after hip flexion. There are, however, no data to either support or refute this suggestion. Strain and excursion in the sciatic and tibial nerve were measured in the hip, knee, and ankle regions during 2 movement sequences for the SLR test in 10 embalmed cadavers. The proximal-to-distal sequence consisted of hip flexion followed by ankle dorsiflexion; the distal-to-proximal sequence consisted of ankle dorsiflexion followed by hip flexion. In the SLR end position, strain and excursion were comparable for both sequences for the sciatic and tibial nerve at the knee (P>.24). Strain in the tibial nerve at the ankle was greater with the proximal-to-distal sequence (P = .008), but the actual difference was small (0.8%). The pattern of strain increase and nerve excursion varied between sequences (P≤.009), with nerve strain increasing earlier and being maintained longer in regions closest to the joint that was moved first in the movement sequence. Varying the movement sequence does not substantially impact excursion and strain in the end position of the SLR. Therefore, if neurodynamic test sequencing is useful in the differential diagnosis of neuropathies, it is not likely due to differences in strain in the end position of testing.

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

BackgroundThe 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. MethodsUltrasound 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. FindingsIn healthy individuals, ankle dorsiflexion created mean tibial nerve movement of 2.18mm distally, 1.36mm medially and 3.98mm 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. InterpretationWe 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.

Effect of cervical spine position on upper limb myoelectric activity during pre-manipulative stretch for Mills manipulation: A new model, relations to peripheral nerve biomechanics and specificity of Mills manipulation

Objectives(A) Describe a new method of investigation of the possible muscular effects of the commonly practiced Mills manipulation for lateral elbow pain (epicondylalgia), (B) ascertain if myoelectric activity is influenced during the pre-manipulative stretch for Mills manipulation, (C) establish whether muscle responses are influenced by ipsilateral lateral flexion of the cervical spine which reduces mechanical tension in the peripheral nerves of the upper limb. SampleEight asymptomatic subjects were tested bilaterally (N=16). MethodsMyoelectric measurements – EMG signals were recorded with a 16 channel pocket EMG patient unit and processed off-line. Measurement of joint positions-three CCD adjustable cameras sensitive to 10mm reflective passive markers applied at specific locations on the subjects’ bodies were used to reconstruct and verify accuracy of body movements and were correlated with EMG recordings. ResultsCompared with the standard (anatomical) position of the cervical spine in which Mills manipulation is typically performed, cervical spine ipsilateral lateral flexion produced significantly reduced activity in muscles that restrain the manipulation movement (elbow extension), namely biceps brachii (P=0.018) and brachioradialis (P=0.000). The affected muscles may therefore produce protective effects during the manipulation. ConclusionsChanges in myoelectric activity were in a pattern that suggests that muscle and neural mechanisms may be an integral part of the Mills manipulation. Cervical spine ipsilateral lateral flexion may be used to reduce mechanical stresses in the peripheral nerves and extraneous muscle activity, making Mills’ manipulation potentially safer and more specific.

Strain in the Tibial and Plantar Nerves with Foot and Ankle Movements and the Influence of Adjacent Joint Positions

We studied the influence of different positions in neighboring joints on strain in the tibial and plantar nerves during ankle and toe movements. Tibial nerve strain at the ankle was measured during ankle dorsiflexion in ten cadavers; plantar nerve strain was measured during toe extension. Tibial nerve strain increased with ankle dorsiflexion (mean increase: 3.9%) and strain was higher when the nervous system was pretensioned by either knee extension or hip flexion (p < or = .011). Strain was even higher when the nerve bed was elongated at both the hip and knee (p < or = .006) before performing dorsiflexion. A similar trend was observed for the plantar nerves with ankle positioning. In conclusion, the change in nerve strain is strongly influenced by positions in neighboring joints. This insight into nerve biomechanics provides a foundation for progressive mobilization exercises for disorders such as tarsal tunnel syndrome.