Characteristics of the locomotor-like muscle activity during orthotic gait in paraplegic persons

We previously found that orthotic gait training can induce 'locomotor-like' coordinated muscle activity of the paralyzed lower limb in persons with spinal cord injury (SCI). The purpose of the present study was to characterize the locomotor-like muscle activity based on data obtained from electromyographic recordings and motion analysis during orthotic gait in nine motor complete SCI subjects. Seven of nine subjects showed a common EMG activation pattern mainly in the ankle (soleus: Sol) and hip extensor (biceps femoris: BF) muscles. The locomotor-like muscle activity was well synchronized with the gait cycle, namely, the EMG amplitude of both Sol and BF muscle had common temporal relationships with the ground reaction force, and hip and ankle joint motions. While the presence or absence of the EMG activity during orthotic gait was consistent with those of mechanically-induced stretch reflex, the duration and amount area of the locomotor-like muscle activity were significantly longer than those of the stretch reflex in the Sol muscle. Moreover, the Sol EMG magnitude had strong relevance to hip as well as ankle angular velocities. These results indicate that the locomotor-like muscle activity during orthotic gait is not a mere reflex response, but includes an activity of the central pattern generator (CPG) and its interaction with afferent inputs. Orthotic gait training for complete SCI persons might have a potential to activate the spinal locomotor center.

Neurocutaneous sural flap in paraplegic patients

Neurocutaneous flaps have been demonstrated to be a reliable option in different groups of patients but it remains unclear if distally-based sural flaps can be safely used in paraplegic patients because they suffer from significant nervous system alterations. The aim of this proof-of-concept study is to demonstrate that these flaps are reliable in paraplegic patients. We prospectively analysed a group (n=6) of paraplegic patients who underwent reversed sural flap surgery for ulcers on the lateral malleolus. Measurement of area and photographic documentation techniques have been employed to quantify the defect area. Sural nerve biopsies have been analysed histologically with several different staining techniques to assess the neurovascular network and the myelinisation of the nerve. The patients showed uneventful wound healing, except one case that suffered a partial flap necrosis that healed by secondary intention. Histologic analysis revealed an intact neurovascular network and myelinated nerve fibres. In this small series of paraplegic patients that underwent a distally-based sural flap, the complication rate was low, with only one case of superficial partial necrosis demonstrating the reliability and safety of the flap in this subset of patients. Histologic evaluation of sural nerve biopsies revealed an almost normal morphology. A possible explanation of this phenomenon is that the dorsal root ganglia remain intact in paraplegic patients and can preserve neural characteristics in the peripheral sensory nerve system.

Diagnostic role of deep tendon reflex latency measurement in small-fiber neuropathy

Small-fiber neuropathy (SFN) is diagnosed on the basis of clinical features and specialized tests of small-fiber function because standard nerve conduction studies are normal. Thus, the objective of this study was to determine the value of deep tendon reflex (DTR) latency measurement in the diagnosis of SFN in patients with preserved DTR on clinical examination. We prospectively examined electromyographic reflexes from the biceps brachii [biceps brachii reflex (BR)], patellar [patellar reflex (PR)], and ankle [ankle reflex (AR)] using a manually operated electronic reflex hammer attached to electromyography machine and recorded by means of surface electrodes in 18 patients with SFN and 38 controls. Intra- and inter-evaluator reliability was good (intraclass correlation coefficient: 0.80-0.91, p < 0.01). In controls, the latencies at all sites were correlated to the height (R= 0.6, p < 0.01). Compared with controls, in patients with SFN, the mean latency in milliseconds was prolonged at all sites (BR: 12.8 +/- 1.6 vs. 8.9 +/- 1.9, p < 0.01; PR: 23.0 +/- 5.8 vs. 17.4 +/- 2.4, p < 0.01; and AR: 34.5 +/- 4.8 vs. 30.0 +/- 2.4, p < 0.01). The sensitivity [61.1% (95% CI: 51-94.9)] and specificity [92% (95% CI: 73-97.3)] of BR latency were roughly equal to those of PR and AR. We conclude that DTR latencies were significantly abnormal in the majority of the patients with SFN, suggestive of subclinical involvement of large myelinated fibers. DTR latency measurement is a reproducible, valuable, sensitive tool in the evaluation of mild subclinical involvement of large fibers.

Improving functional magnetic resonance imaging motor studies through simultaneous electromyography recordings

Specially designed optoelectronic and data postprocessing methods are described that permit electromyography (EMG) of muscle activity simultaneous with functional MRI (fMRI). Hardware characterization and validation included simultaneous EMG and event-related fMRI in 17 healthy participants during either ankle (n = 12), index finger (n = 3), or wrist (n = 2) contractions cued by visual stimuli. Principal component analysis (PCA) and independent component analysis (ICA) were evaluated for their ability to remove residual fMRI gradient-induced signal contamination in EMG data. Contractions of ankle tibialis anterior and index finger abductor were clearly distinguishable, although observing contractions from the wrist flexors proved more challenging. To demonstrate the potential utility of simultaneous EMG and fMRI, data from the ankle experiments were analyzed using two approaches: 1) assuming contractions coincided precisely with visual cues, and 2) using EMG to time the onset and offset of muscle contraction precisely for each participant. Both methods produced complementary activation maps, although the EMG-guided approach recovered more active brain voxels and revealed activity better in the basal ganglia and cerebellum. Furthermore, numerical simulations confirmed that precise knowledge of behavioral responses, such as those provided by EMG, are much more important for event-related experimental designs compared to block designs. This simultaneous EMG and fMRI methodology has important applications where the amplitude or timing of motor output is impaired, such as after stroke.

Proactive and Reactive Mechanisms Play a Role in Stepping on Inverting Surfaces During Gait

Ankle inversions have been studied extensively during standing conditions. However, inversion traumas occur during more dynamic conditions, like walking. Therefore in this study sudden ankle inversions were elicited in 12 healthy subjects who stepped on a trap door while walking on a treadmill. First, 10 control trials (0° of rotation) were presented. Then, 20 stimulus (25° of rotation) and control trials were presented randomly. EMG recordings were made of six lower leg muscles. All muscles showed a short-latency response (SLR) of about 40 ms and a late-latency response (LLR) of about 90 ms. The peroneal muscles showed the largest amplitudes in both responses. The functionally more important, larger, and more consistent LLR response was too late to resist the induced stretch during the inversion. The functional relevance of this response must lie after the inversion. During the first trial a widespread “startle-like” coactivation of the LLR was observed. The last trials showed only a recruitment of the peroneal muscles and, to a lesser extent, the gastrocnemius lateralis, which is seen as a switch from reactive control to more proactive adaptive strategies. These proactive strategies were investigated separately by comparing trials in which inversion was expected (but did not occur) with those in which subjects knew that no inversion would occur. Anticipation of a possible inversion was expressed in decreased tibialis anterior activity before initial contact, consistent with a more cautious and stable foot placement. Furthermore, immediately after landing, the peroneal muscles were activated to counteract the upcoming stretch.

Muscle afferent contributions to tibial nerve somatosensory evoked potentials investigated using knee stimulations

OBJECTIVE

To investigate the contribution of muscle afferents to tibial nerve somatosensory evoked potentials (SEPs).

METHODS

The left tibial nerve was stimulated at the knee and ankle in eight normal subjects. We tried to selectively stimulate Ia fibers from the calf muscles at the popliteal fossa by subtly changing the stimulation site while monitoring the H-waves of the calf muscles and sensory events.

RESULTS

Selective or predominant Ia stimulation at the knee was achieved in seven subjects, and evoked a significantly smaller first cortical component (labeled as P38 for both ankle and knee stimulations) than that evoked by ankle stimulation or by mixed stimulation of the foot branch and muscle afferents at the knee. The P38 following mixed stimulation at the knee was smaller than that following ankle stimulation in six out of eight subjects, which must be due to a partial gating mechanism and also indicates that calf Ia afferent SEPs are not extremely large.

CONCLUSIONS

Physiologically important muscle afferents from the large calf muscles evoked rather small cortical components.

SIGNIFICANCE

It seems reasonable to infer that the contribution of muscle afferents from the small intrinsic foot muscles to routine tibial nerve SEPs following ankle stimulation is even smaller.

Re-weighting of somatosensory inputs from the foot and the ankle for controlling posture during quiet standing following trunk extensor muscles fatigue

The present study focused on the effects of trunk extensor muscles fatigue on postural control during quiet standing under different somatosensory conditions from the foot and the ankle. With this aim, 20 young healthy adults were asked to stand as immobile as possible in two conditions of No fatigue and Fatigue of trunk extensor muscles. In Experiment 1 (n = 10), somatosensation from the foot and the ankle was degraded by standing on a foam surface. In Experiment 2 (n = 10), somatosensation from the foot and ankle was facilitated through the increased cutaneous feedback at the foot and ankle provided by strips of athletic tape applied across both ankle joints. The centre of foot pressure displacements (CoP) were recorded using a force platform. The results showed that (1) trunk extensor muscles fatigue increased CoP displacements under normal somatosensatory conditions (Experiment 1 and Experiment 2), (2) this destabilizing effect was exacerbated when somatosensation from the foot and the ankle was degraded (Experiment 1), and (3) this destabilizing effect was mitigated when somatosensation from the foot and the ankle was facilitated (Experiment 2). Altogether, the present findings evidenced re-weighting of sensory cues for controlling posture during quiet standing following trunk extensor muscles fatigue by increasing the reliance on the somatosensory inputs from the foot and the ankle. This could have implications in clinical and rehabilitative areas.

Effects of fatigue and gender on peroneal reflexes elicited by sudden ankle inversion

The purpose of this study was to investigate the effects of neuromuscular fatigue and gender on peroneus brevis muscle (PB) and peroneus longus muscle (PL) reflexes elicited by sudden ankle inversion. Sixteen males and fifteen females stood on a "trap-door" platform that suddenly inverted the ankle 20 degrees when released. The resulting movement elicited peroneal reflexes. Reflex measurements were collected both before and after fatiguing the ankle evertors. Reflex delay in the PB and PL was not affected by fatigue, gender, or their interaction. Reflex amplitude in the PL exhibited no main effect of fatigue or gender, but their interaction was significant. Pairwise comparisons revealed PL reflex amplitude decreased by 11.3% in males (p=0.008) and increased 22.1% in females (p=0.003) with fatigue. A similar trend was found in the PB, but was not statistically significant. This opposite effect in females and males may be due to differences in how males and females compensate for fatigue, and may be related to the gender difference in ankle injury rate.

Positive force feedback in human walking

The objective of this study was to determine if load receptors contribute to the afferent-mediated enhancement of ankle extensor muscle activity during the late stance phase of the step cycle. Plantar flexion perturbations were presented in late stance while able-bodied human subjects walked on a treadmill that was declined by 4%, inclined by 4% or held level. The plantar flexion perturbation produced a transient, but marked, presumably spinally mediated decrease in soleus EMG that varied directly with the treadmill inclination. Similarly, the magnitude of the control step soleus EMG and Achilles' tendon force also varied directly with the treadmill inclination. In contrast, the ankle angular displacement and velocity were inversely related to the treadmill inclination. These results suggest that Golgi tendon organ feedback, via the group Ib pathway, is reduced when the muscle-tendon complex is unloaded by a rapid plantar flexion perturbation in late stance phase. The changes in the unload response with treadmill inclination suggest that the late stance phase soleus activity may be enhanced by force feedback.

Control of upright stance over inclined surfaces

The present work investigated the control of upright posture on inclined surfaces (14 degrees). Such conditions could, for example, change the contributions of muscle spindles resulting in alterations in postural sway. Subjects stood in quiet stance over a force platform positioned in one of three different fixed positions: horizontal (H), toes-up (ankle dorsi-flexion, D) and toes-down (ankle plantar-flexion, P). The experiments were done in the presence and also in the absence of vision. The analysis of the resulting sway was based on the power spectrum of the center of pressure displacement in the anterior-posterior direction (CP_ap). Analysis of the electromyogram (EMG) of the leg muscles and evaluation of the level of presynaptic inhibition (PSI) of the soleus (SO) Ia afferents complemented the study. The results showed that the spectrum of the CP_ap changed with the inclination of the surface of support. In condition D a higher instability was found as reflected by the higher spectral amplitudes at lower frequencies (below 0.3 Hz). On the other hand, the CP_ap of subjects in condition P contained increased amplitudes at high frequencies (above 0.3 Hz) and smaller amplitudes at low frequencies. The modifications found in the CP_ap power spectra when standing over an inclined surface may indicate changes in both short-term and long-term systems of postural control. These results do not seem to be associated with changes in group Ia feedback gain since no changes in the level of PSI were found among the three standing conditions. The SO EMG increased in condition P but did not change in condition D. On the other hand, the tibialis anterior had a tendency towards increased bursting activity in condition D. Eye closure caused an increase in the power of the oscillations at all spectral frequencies in the three standing conditions (H, P or D) and also a change in the profile of the CP_ap power spectrum. This may suggest a nonlinearity in the postural control system. The control of the slow component of the postural sway was more dependent on vision when the subject was in condition D, probably in association with the biomechanical constraints of standing on a toes-up ramp. A conclusion of this work was that, depending on the postural demand (direction of the ramp of support), the ensuing proprioceptive and biomechanical changes affect differentially the fast and slow mechanisms of balance control.

Are there any relationships among ankle proprioception acuity, pre-landing ankle muscle responses, and landing impact in man?

Proprioceptive input has been suggested to contribute to the pre-landing muscle responses associated with drop-landing, but its precise role has yet to be delineated. This study set out to examine the relationships among ankle proprioception, pre-landing muscle responses, and landing impact on drop-landing in healthy man. Fifteen healthy male basketball players aged 18 to 26 participated in this study. Passive ankle joint repositioning errors were used to examine ankle joint proprioception. Pre-landing EMG responses in the ankle muscles and the impact force on landing were recorded while the players performed self-initiated drops from a height of 30 cm. Results demonstrated that averaged ankle repositioning errors were significantly correlated with the co-contraction indexes between left tibialis anterior and medial gastrocnemius muscles (TA/MG CoI) (r=0.67, p=0.006), and showed a trend towards a relationship with the right TA/MG CoI (r=0.47, p=0.079). TA/MG CoI from both ankles were further related to the magnitude of the total impact force on landing (r=0.54 and 0.53, respectively; p<0.05). We concluded that male basketball players with less accurate ankle joint sense adopted greater co-contraction of ankle dorsiflexors and platarflexors, which was in turn associated with greater impact force at the moment of landing.

Postural coordination modes and transition: dynamical explanations

While research to date has been successful in quantifying postural behaviour, this paper examines the causes of transition between postural coordination mode using dynamical variables and, by inference, efficient control strategies underlying postural behaviour. To this end, six subjects in bipedal stance were instructed to maintain a constant distance between their head and a visual target that oscillated along the line of sight. Within sessions, participants were exposed to gradual changes in increasing target motion frequency. Kinematic results showed a sudden transition between in-phase and anti-phase postural coordination modes in visual target tracking. The dynamical analysis pointed out that (1) the center of pressure (CoP) position parameter is a crucial parameter in the determination of the adopted coordination mode, (2) the change occurred in response to limits bordered by the system: the interaction between equilibrium constraints (A/P displacements of CoP), physiological limits (net joint moments) support the emergence of different postural behaviours and, (3) finally, the anti-phase mode presents a better distribution of muscular moment between hip and ankle joints and is more effective to achieve high frequency oscillations with limited CoP displacements.

Intraepidermal nerve fiber density as a marker of early diabetic neuropathy

The purpose of the study was to reliably identify an early stage of diabetic polyneuropathy (DPN) by measuring injury to epidermal nerve fibers. We compared intraepidermal nerve fiber density (IENFD) at the ankle and thigh of 29 diabetic subjects who had no clinical or electrophysiological evidence of small- or large-fiber neuropathy to that of 84 healthy controls. The mean ankle IENFD of diabetic subjects was 9.1+/-5.0 mm and that of controls, 13.0+/-4.8 mm (P<0.001). The thigh IENFD did not differ significantly. The IENFD ratio (thigh IENFD divided by ankle IENFD) was 2.39+/-1.30 in diabetic subjects and 1.77+/-0.58 in controls (P<0.001), indicating a length-dependent reduction of IENFD in diabetics. Ankle IENFD remained significantly lower and the IENFD ratio higher in diabetic subjects after adjusting for age. Two subjects had parasympathetic dysfunction, two had retinopathy, and two early nephropathy. Age, height, weight, duration of diabetes, and average HbA1c did not influence IENFD among diabetic subjects. We used receiver operating characteristic (ROC) curves to describe and compare the utility of various threshold values of ankle IENFD and IENFD ratio for the diagnosis of early DPN. The sensitivity and specificity of diagnosing DPN using ankle IENFD of less than 10 mm were 72.4% and 76.2%, respectively. Thus, asymptomatic diabetics have a measurable, length-dependent reduction of distal epidermal nerves. Analogous to microalbuminuria in diabetic nephropathy, reliable identification and quantitation of nascent diabetic neuropathy may have potential therapeutic implications.

Three-dimensional reconstruction of the ankle by means of ultrathin slice plastination

Computerized reconstruction of anatomical structures is becoming very useful for developing anatomical teaching modules and animations. Although databases exist consisting of serial sections derived from frozen cadaver material, plastination represents an alternate method for developing anatomical data useful for computerized reconstruction. Plastination is used as an excellent tool for studying different anatomical and clinical questions. The sheet plastination technique is unique because it offers the possibility to produce transparent slices series, which can easily be processed morphometrically. The purpose of this study was to describe a method for developing a computerized model of the human ankle using plastinated slices. This method could be applied to reconstruct any desired region of the human body.A human ankle was obtained, plastinated, sectioned, and subjected to 3D computerized reconstruction using WinSURF modeling system (SURFdriver Software). Qualitative observations revealed that the morphological features of the model were consistent with those displayed by typical cadaveric specimens. Morphometric analysis indicated that the model did not significantly differ from a sample of cadaveric specimens. These data support the use of plastinates for generating tissues sections useful for 3D computerized modeling.

Modulation of soleus H-reflex by presynaptic spinal mechanisms during varying surface and ankle brace conditions

AIMS

Reflex excitability is modulated in part by presynaptic spinal mechanisms. Presynaptic inhibition may prevent an over-response of the motoneuron pool to afferent information. A paired-reflex depression (PRD) conditioning protocol can be used to monitor reflex plasticity. Manipulation of stance, surface, and external bracing are common methods of rehabilitating and treating lower extremity musculoskeletal injuries. The intent of this study was to evaluate changes in PRD of the soleus H-reflex during single-leg stance under varying stability conditions.

METHODS

Seven trials were completed for each condition in ten healthy volunteers (age=23+/-1.8 yr, weight 65.0+/-11.3 kg, height=168.7+/-28.0 cm). The conditioning stimuli were composed of soleus H-reflex pairs evoked 80 ms apart at an equal intensity. The mean percent decrease of the second H-reflex relative to the first represented PRD.

RESULTS

A 2 x 2 repeated measures ANOVA (P<0.05) was used to evaluate influence of surface (foam, no foam) and support (semi-rigid ankle brace, no ankle brace) on PRD. Main effects testing revealed a significantly greater soleus PRD (P=.034) for the foam surface (62.5%) compared the flat surface (57.5%). Ankle brace application did not influence soleus PRD (P=0.63).

CONCLUSION

The increase in soleus PRD during the foam condition suggests depression of the motoneuron pool. This may lessen postural over-corrections while maintaining upright stance during less stable conditions. No change in PRD during the ankle brace condition suggests that mechanical reinforcement provided an increase in ankle stability, decreasing the demand on the motoneuron pool.

[Diagnostic imaging of nerve compression syndrome]

Compression-induced neuropathy of peripheral nerves can cause severe pain of the foot and ankle. Early diagnosis is important to institute prompt treatment and to minimize potential injury. Although clinical examination combined with electrophysiological studies remain the cornerstone of the diagnostic work-up, in certain cases, imaging may provide key information with regard to the exact anatomic location of the lesion or aid in narrowing the differential diagnosis. In other patients with peripheral neuropathies of the foot and ankle, imaging may establish the etiology of the condition and provide information crucial for management and/or surgical planning. MR imaging and ultrasound provide direct visualization of the nerve and surrounding abnormalities. Bony abnormalities contributing to nerve compression are best assessed by radiographs and CT. Knowledge of the anatomy, the etiology, typical clinical findings, and imaging features of peripheral neuropathies affecting the peripheral nerves of the foot and ankle will allow for a more confident diagnosis.

Spastic Reflexes Triggered by Ankle Load Release in Human Spinal Cord Injury

The rapid decrease in firing of load-sensitive group Ib muscle afferents during unloading may be particularly important in triggering the swing phase of gait. However, it still remains unclear whether load-sensitive muscle afferents modulate reflex activity in human spinal cord injury (SCI), as suggested by studies in the cat. The right hip of 12 individuals with chronic SCI was subjected to ramp (60°/s) and hold (10 s) movements over a range from 40° flexion to 0–10°extension using a custom servomotor system. An ankle dorsiflexion load was imposed and released after the hip reached a targeted position using a custom-designed pneumatic motor system. Isometric joint torques of the hip and knee, reaction torque of the ankle, and surface electromyograms (EMGs) from eight muscles of the leg were recorded following the imposed hip movement and ankle load release. Reflexes, characterized by hip flexion torque, knee extension, and coactivation of ankle flexors and extensors, were triggered by ankle load release when the hip was in an extended position. The ankle load release was observed to enhance the reflexes triggered by hip extension itself, suggesting that ankle load afferents play an important role in spastic reflexes in human SCI and that the reflex pathways associated with ankle load afferents have important implications in the spinal reflex regulation of human movement. Such muscle behaviors emphasize the role of ankle load afferents and hip proprioceptors on locomotion. This knowledge may be especially helpful in the treatment of spasms and in identifying rehabilitation strategies for producing functional movements in human SCI.

Neuroselective transcutaneous electric stimulation reveals body area–specific differences in itch perception

BACKGROUND

Electrically evoked itch has been reported, although the electrodes, the frequency, and the pulse duration used were not standardized.

OBJECTIVE

To examine whether a neuroselective transcutaneous electrical stimulator (NTES; Neurometer; Neurotron, Inc, Baltimore, Md) can evoke itch and whether it can provoke itch on any body area.

METHODS

Twelve healthy subjects were stimulated on 30 body sites by 5 Hz alternating current produced by the NTES. We classified the evoked perceptions into two sensations (with and without itch) and divided the examined sites into 7 groups: G1, head and neck; G2, arm; G3, palm; G4, the dorsal surface of the hand; G5, knee and leg; G6, dorsal foot; and G7, ankle. The data were then statistically analyzed.

RESULTS

The NTES preferentially evoked itch at the G4 and G7 sites, and a sensation without itch at the G1 site.

LIMITATION

Tests were performed on limited body areas.

CONCLUSION

The NTES can provoke itch, it was discovered that there are body area-specific differences in itch sensation.

ANATOMICAL STUDY OF THE ANKLE WITH VIEW TO THE ANTERIOR ARTHROSCOPIC PORTALS

This article evaluates the risk of interference with the neurovascular structures in the four anterior ankle arthroscopic portals, described on each side of the extensor tendons: anteromedial, medial midline, anterocentral and anterolateral. Complications after ankle arthroscopies have been described in up to 17%, most being neurovascular. To quantify the neurovascular risks we dissected 68 cadaveric feet and evaluated the correlations between tendons, vessels and nerves. The mean distance between tibialis anterior and extensor hallucis longus and between extensor hallucis longus and extensor digitorum longus is 4 mm, but in 10-20% these tendons are in apposition or are overlapped. The tibialis anterior vascular bundle was absent in 11.8%, was located between the tibialis anterior and the extensor hallucis longus in 3% and between the extensor hallucis longus and the extensor digitorum longus in 64.7%. A peroneal vascular bundle or branches of the tibialis anterior vascular bundle were located lateral to the extensor digitorum longus/peroneus tertius tendon in 88.2%. Transverse vascular branches were identified in 41.2% over the medial side of the joint line and in 52.9% over the lateral side. The deep peroneal nerve was located between the extensor hallucis longus and the extensor digitorum longus tendons in 58.8%. The superficial peroneal nerve had branches located between the tibialis anterior and the extensor hallucis longus tendons in 2.9%, between the extensor hallucis longus and the extensor digitorum longus tendons in 23.5% and lateral to the extensor digitorum longus/peroneus tertius tendon in 32.4%. These results show that the anteromedial and medial midline portals are the safest. The anterolateral portal should be noted not only for the risks to the superficial peroneal nerve, but also to the peroneal vessels.

Wide-pulse-width, high-frequency neuromuscular stimulation: implications for functional electrical stimulation

Electrical stimulation (1-ms pulses, 100 Hz) produces more torque than expected from motor axon activation (extra contractions). This experiment investigates the most effective method of delivering this stimulation for neuromuscular electrical stimulation. Surface stimulation (1-ms pulses; 20 Hz for 2 s, 100 Hz for 2 s, 20 Hz for 3 s) was delivered to triceps surae and wrist flexors (muscle stimulation) and to median and tibial nerves (nerve stimulation) at two intensities. Contractions were evaluated for amplitude, consistency, and stability. Surface electromyograph was collected to assess how H-reflexes and M-waves contribute. In the triceps surae, muscle stimulation produced the largest absolute contractions (23% maximal voluntary contraction), evoked the largest extra contractions as torque increased by 412% after the 100-Hz stimulation, and was more consistent and stable compared with tibial nerve stimulation. Absolute and extra contraction amplitude, consistency, and stability of evoked wrist flexor torques were similar between stimulation types: torques reached 11% maximal voluntary contraction, and extra contractions increased torque by 161%. Extra contractions were 10 times larger in plantar flexors compared with wrist flexors with muscle stimulation but were similar with nerve stimulation. For triceps surae, H reflexes were 3.4 times larger than M waves during nerve stimulation, yet M waves were 15 times larger than H reflexes during muscle stimulation. M waves in the wrist flexors were larger than H reflexes during nerve (8.5 times) and muscle (18.5 times) stimulation. This is an initial step toward utilizing extra contractions for neuromuscular electrical stimulation and the first to demonstrate their presence in the wrist flexors.

Surgical anatomy and accuracy of percutaneous achilles tendon lengthening

BACKGROUND

Percutaneous Achilles tendon lengthening is frequently done to treat gastrocsoleus equinus contracture. To our knowledge, no study has documented the proximity of tendinous or neurovascular structures to the nearest edges of each hemisection in a percutaneous Achilles tendon lengthening, the complication rates related to injury of such structures, or the Achilles tendon rupture rates from inaccurate cuts. Thus, our goal was to document these distances and determine the accuracy of this procedure.

METHODS

We performed triple-hemisection percutaneous Achilles tendon lengthening (Hoke technique) in 15 cadaver specimens and documented the distance from each cut edge to various relevant anatomical structures. We also documented the accuracy of each cut (diameter of hemisection divided by total tendon diameter), with a reference goal of 50% transection at each level.

RESULTS

We found that percutaneous Achilles tendon lengthening is a relatively accurate procedure with hemisections averaging 50% for the middle cut and 60% at the most proximal cut, and 55% at the distal cut. Some tendinous and neurovascular structures are, on average, less than 1 cm from the nearest margin of a given hemisection and are, therefore, at risk. These included the flexor hallucis longus at the middle and proximal cuts (9.1 mm and 5.7 mm, respectively), the tibial nerve at the proximal cut (8.3 mm), and the sural nerve at the middle-lateral cut (7.9 mm).

CONCLUSION

In cadavers, reasonably accurate cuts can be made, with some vital structures less than 1 cm from the cut tendon.

[Peripheral neuropathy in the elderly]

Peripheral neurologic deficits are commonly found during physical examination of older patients. Losses of vibratory sensation in the lower extremities and ankle reflexes are so common that they are often listed in geriatric textbooks as normal physical findings in very old people. In this population, the detection of peripheral neuropathy, which may lead to a serious disability, is an important contribution to the health care but there is very little information in the literature about its actual prevalence and etiology. The epidemiological, clinical, morphological, electrophysiological data on the peripheral nervous system abnormalities in elderly are reviewed. A strategy of investigations is proposed to improve the identification of the etiology of their peripheral neuropathy.

Functional response to active and passive ankle movements with clinical correlations in patients with primary progressive multiple sclerosis

Patients with multiple sclerosis (MS) activate a more diffuse cortical network than do healthy subjects when they perform motor tasks. This brain functional reorganisation might contribute to the limiting of disability, but it is unclear whether there is a loss of regional activation in more advanced disease. The aim of this study was to assess whether functional reorganisation diminishes in more disabled patients with primary progressive (PP) MS. The differences in the fMRI response to active and passive movements of the dominant ankle of 13 patients and 16 controls were assessed. The relationships between functional activation and disability and brain lesion load and atrophy were investigated.Patients showed greater fMRI activation than controls with passive movements in the superior temporal gyrus, rolandic operculum, and putamen. The fMRI response to active and passive movements in the ipsilateral inferior frontal gyrus was lower in patients with greater disability and greater brain T2 lesion load, respectively. Furthermore, the fMRI activation with active movements in the contralateral cerebellum was lower in patients with worse mobility. The increased activity with passive movements in regions that participate in sensori-motor integration, such as the putamen, reflects true functional reorganisation, since passive movements induce brain activation through sensory afferents only. The inverse correlation between the fMRI response in regions that are associated with motor control, and clinical or MRI measures of disease progression, suggests that there is a loss of distributed activation in more disabled patients. This may inform future treatment strategies.

Treatment of posttraumatic injuries to the nerves in the foot and ankle

Nerve injuries of the foot and ankle can result in pain, numbness, or loss of motor function. A thorough history and physical examination are required to diagnose the injury correctly and guide treatment. Treatment may involve conservative measures, primary nerve repair or nerve grafting, or resection and relocation of painful neuroma. Potential complications include the development of chronic pain syndromes.

Tonic, Phasic, and Integrator Components of Psychophysical Responses to Topical Capsaicin Account for Differences of Location and Sex

We reanalyze data of Frot et al on sex and location differences in the pain response to topical capsaicin using a dynamic model developed from responses to oral capsaicin. This model considers the pain response as the sum of 3 underlying component processes: a phasic component, a tonic component, and an integrator component. Sex differences in response to stimulation of both the cheek and ankle could be accounted for by a greater gain in the tonic mechanism. Responses to ankle stimulation showed a greater integrator component than responses to cheek stimulation, a negligible phasic component, and required a time delay. This analysis demonstrates that the model is applicable to responses to stimuli outside the oral cavity and that it can explain differences due to location and sex, in addition to explaining sensitization, desensitization, and individual differences in earlier studies. Application of this model in future genetic studies, for instance, would be more appropriate than the use of the peak response or the response at an arbitrarily determined time.

PERSPECTIVE

This dynamic model provides insight into individual differences in sensitivity to vallinoid receptor-activating compounds including capsaicin, and it may be useful for the identification of subgroups of patients with differential responsiveness to therapeutic topical capsaicin. A similarly derived model might prove useful for the analysis of development of chronic pain.