Validating the measurement of passive Musculo-articular wrist stiffness without intentional or reactive contraction using axillary plexus block

BACKGROUND

Passive stiffness describes how easily a joint may move passively. To accurately measure wrist stiffness, an electro-oscillation device was developed. The objectives were to 1) ensuring that the measurement are free from intentional or reflex contraction, 2) analyzing how forearm anatomy affects the passive stiffness of the wrist and 3) determining the clinical practical relevance of the device.

METHODS

In this prospective study, the device generated low amplitude sinusoidal motions in flexion and extension on the wrist to quantify elastic and viscous passive stiffness in voluntary orthopaedic patients. The first series of measurements was carried out in the state of voluntary relaxation, the second series of measurements was carried out after an axillary plexus anesthetic block. A matched group of healthy subjects were use for control.

FINDINGS

The Electromechanical Oscillation methods effectively enable the measurement of passive joint stiffness since the stiffness values obtained show no statistically significant difference pre-post the anesthesia. The stiffness values are comparable to those of healthy subjects. The effect of forearm passive structure, estimated by the perimeter of the forearm, influences the passive stiffness of the wrist, mainly the viscous component.

INTERPRETATION

The use of sinusoidal oscillation was well accepted by the participants, demonstrating its usefulness and applicability in a clinical setting. This work serves as a foundation for future investigations of orthopaedic and/or neurological pathological conditions characterized by abnormal passive joint stiffness of the wrist. It paves the way for its use as a diagnostic, prognostic, and monitoring tool in these pathologies.

Effect of lidocaine iontophoresis combined with exercise intervention on gait and spasticity in children with spastic hemiplegic cerebral palsy: A randomized controlled trial

BACKGROUND

Gait deviations and spasticity are common impairments seen in children with cerebral palsy (CP) and may interfere with functional performance and effective walking pattern. Lidocaine iontophoresis is effective for reducing muscle spasticity in adults.

PURPOSE

To investigate the effect of lidocaine epinephrine iontophoresis combined with exercises on gait and spasticity in children with spastic hemiplegic cerebral palsy (HCP).

METHODS

Thirty children with spastic HCP aged 4-6 (5.20±0.32) years were randomly assigned to the experimental group (n = 15) and control group (n = 15). Children in both groups received one hour of exercises, three times a week for three months. Children in the experimental group received 2% lidocaine iontophoresis immediately before the exercises. The lidocaine iontophoresis was delivered for 20 minutes (1mA/min). Spatio-temporal gait parameters were assessed within one week before and after the intervention using 3D motion analysis. Surface electromyography was used to assess muscle tone using H/M ratio of the soleus muscle. ANOVA was used to investigate the differences between experimental and control groups. Statistical significance was set at P value less than 0.05.

RESULTS

There was no difference between groups at baseline. Post-intervention, the experimental group showed significant improvements when compared to the control group for gait speed (p = 0.03), stride length (p = 0.04), cadence (p = 0.0001), cycle time (p = 0.0001), and H/M ratio (p = 0.02).

CONCLUSION

Lidocaine iontophoresis combined with exercises was effective in improving gait spatiotemporal parameters and reducing spasticity in children with CP.

Influence of low muscle activation levels on the ankle torque and muscle shear modulus during plantar flexor stretching

During stretching studies, surface electromyography (sEMG) is used to ensure the passive state of the muscle, for the characterization of passive muscle mechanical properties. Different thresholds (1%, 2% or 5% of maximal) are indifferently used to set "passive state". This study aimed to investigate the effects of a slight activity on the joint and muscle mechanical properties during stretching. The joint torque and muscle shear modulus of the triceps surae muscles were measured in fifteen healthy volunteers during ankle dorsiflexions: (i) in a "fully relaxed" state, (ii) during active conditions where participants were asked to produce an sEMG amplitude of 1%, 2% or 5% of their maximal sEMG amplitude of the triceps surae. The 1% condition was the only that did not result in significant differences in joint torque or shear modulus compared to the relaxed condition. In the 2% condition, increases in joint torque were found at 80% of the maximal angle in dorsiflexion, and in the shear modulus of gastrocnemius medialis and gastrocnemius lateralis at the maximal angle in dorsiflexion. During the 5% condition, joint torque and the shear modulus of gastrocnemius medialis were higher than during relaxed condition at angles larger than 40% of maximal angle in dorsiflexion. The results provide new insights on the thresholds that should be considered for the design of stretching studies. A threshold of 1% seems much more appropriate than a 2% or 5% threshold in healthy participants. Further studies are required to define similar thresholds for patients.

Does the sensorimotor system minimize prediction error or select the most likely prediction during object lifting?

The human sensorimotor system is routinely capable of making accurate predictions about an object's weight, which allows for energetically efficient lifts and prevents objects from being dropped. Often, however, poor predictions arise when the weight of an object can vary and sensory cues about object weight are sparse (e.g., picking up an opaque water bottle). The question arises, what strategies does the sensorimotor system use to make weight predictions when one is dealing with an object whose weight may vary? For example, does the sensorimotor system use a strategy that minimizes prediction error (minimal squared error) or one that selects the weight that is most likely to be correct (maximum a posteriori)? In this study we dissociated the predictions of these two strategies by having participants lift an object whose weight varied according to a skewed probability distribution. We found, using a small range of weight uncertainty, that four indexes of sensorimotor prediction (grip force rate, grip force, load force rate, and load force) were consistent with a feedforward strategy that minimizes the square of prediction errors. These findings match research in the visuomotor system, suggesting parallels in underlying processes. We interpret our findings within a Bayesian framework and discuss the potential benefits of using a minimal squared error strategy.

NEW & NOTEWORTHY

Using a novel experimental model of object lifting, we tested whether the sensorimotor system models the weight of objects by minimizing lifting errors or by selecting the statistically most likely weight. We found that the sensorimotor system minimizes the square of prediction errors for object lifting. This parallels the results of studies that investigated visually guided reaching, suggesting an overlap in the underlying mechanisms between tasks that involve different sensory systems.

Benefits of repetitive transcranial magnetic stimulation (rTMS) for spastic subjects: clinical, functional, and biomechanical parameters for lower limb and walking in five hemiparetic patients

Introduction. Spasticity is a disabling symptom resulting from reorganization of spinal reflexes no longer inhibited by supraspinal control. Several studies have demonstrated interest in repetitive transcranial magnetic stimulation in spastic patients. We conducted a prospective, randomized, double-blind crossover study on five spastic hemiparetic patients to determine whether this type of stimulation of the premotor cortex can provide a clinical benefit. Material and Methods. Two stimulation frequencies (1 Hz and 10 Hz) were tested versus placebo. Patients were assessed clinically, by quantitative analysis of walking and measurement of neuromechanical parameters (H and T reflexes, musculoarticular stiffness of the ankle). Results. No change was observed after placebo and 10 Hz protocols. Clinical parameters were not significantly modified after 1 Hz stimulation, apart from a tendency towards improved recruitment of antagonist muscles on the Fügl-Meyer scale. Only cadence and recurvatum were significantly modified on quantitative analysis of walking. Neuromechanical parameters were modified with significant decreases in H max⁡ /M max⁡ and T/M max⁡ ratios and stiffness indices 9 days or 31 days after initiation of TMS. Conclusion. This preliminary study supports the efficacy of low-frequency TMS to reduce reflex excitability and stiffness of ankle plantar flexors, while clinical signs of spasticity were not significantly modified.