Reliability of Shear Wave Elastography and Ultrasound Measurement in Children with Unilateral Spastic Cerebral Palsy

In clinical practice, few data exist on the feasibility of performing reliable shear wave elastography (SWE) and ultrasonography (US) measurements in spastic muscles of children with cerebral palsy (CP). Ten children with unilateral CP took part in SWE and US assessment of the tibialis anterior and medialis gastrocnemius muscles during two sessions separated by a 1-wk interval. Intra- and inter-investigator reliability of shear modulus (µ) and muscle thickness (MT) measurements, at neutral and maximal dorsiflexion angles on both legs, was assessed by two investigators with different levels of experience. Reliability was assessed with the coefficient of variation (CV), standard error of measurement and intra-class correlation coefficient (ICC). Reliability of the µ measurement was insufficient, regardless of angle position (CV >10% and >20% for neutral and maximal dorsiflexion angles, respectively). The intra- and inter-investigator reliability of MT measurements was good (CV >10%, ICC >0.74) for both muscles in both legs. SWE measurements must be performed using a rigorous standardized protocol while MT should be considered an important parameter to monitor change in muscle morphology.

Reduced Active Muscle Stiffness after Intermittent Submaximal Isometric Contractions

PURPOSE

Whether muscle stiffness is influenced by fatigue remains unclear. Classical methods used to assess muscle stiffness provide a global measure at the joint level. As fatigue may selectively affect specific muscles, a joint-level approach may not be sensitive enough to detect potential changes in muscle stiffness. Taking advantage of ultrasound shear wave elastography, this study aimed to determine the influence of a fatiguing protocol involving intermittent submaximal isometric contractions on muscle shear modulus (an index of stiffness).

METHODS

Shear modulus was measured on either the vastus lateralis (n = 9) or the abductor digiti minimi (n = 10) before and after 15 min of intermittent submaximal isometric contractions at 60% of maximal voluntary contraction (MVC) (4 s ON, 4 s OFF). An index of active muscle stiffness was estimated PRE- and POST-fatigue as the slope of the linear regression established between shear modulus and absolute joint force up to 60% MVC.

RESULTS

After the fatiguing exercise, MVC was significantly decreased by 22% ± 7% and 32% ± 15% for knee extension and little finger abduction, respectively (P < 0.001). When compared to PRE-fatigue, the index of active muscle stiffness was 12% ± 15% lower for the vastus lateralis (P < 0.031) and 44% ± 19% lower for the abductor digiti minimi (P < 0.001) POST-fatigue.

CONCLUSIONS

Although the present results cannot clearly determine the involved mechanisms, they demonstrate a decreased active muscle stiffness after a fatiguing task involving intermittent submaximal isometric contractions. Further studies should now determine whether this change in stiffness affects performance and risk of injury.

Immunogenicity induced by botulinum toxin injections for limb spasticity: A systematic review

BACKGROUND

The imputability of neutralizing antibodies (NABs) in secondary non-response (SnR) to botulinum toxin (BoNT) injections for limb spasticity is still debated.

OBJECTIVE

This systematic literature review aimed to determine the prevalence of NABs after BoNT injections for limb spasticity and analyze their determinants and their causal role in SnR.

METHODS

We searched MEDLINE via PubMed, Cochrane and Embase databases for articles published during 1990-2018. Two independent reviewers extracted the data and assessed the quality of studies with a specific scale (according to PRISMA and STROBE guidelines). Because the techniques used to detect NABs did not influence the results, we calculated the global (all studies) sensitivity and specificity of NAB positivity to reveal SnR.

RESULTS

We included 14 articles published from 2002 to 2018 (including an epublication) describing 5 randomized controlled trials and 5 interventional and 4 observational studies. The quality was satisfactory (mean score 18/28 arbitrary units). NAB detection was the primary criterion in 5 studies and a secondary criterion in 9. In total, 1234 serum samples for 1234 participants (91% with stroke) were tested after injection. NAB prevalence was about 1%, with no significant difference among formulations. NAB positivity seemed favoured by long-duration therapy with high doses and a short interval between injections. The identification of non-response by NAB positivity had poor global sensitivity (56%) but very high specificity (99.6%). No consensual criteria were used to diagnose non-response to BoNT injection.

CONCLUSIONS

NAB prevalence is much lower after BoNT treatment for limb spasticity than cervical dystonia. Consensual criteria must be defined to diagnose non-response to BoNT injection. Because immunogenicity is not the most common cause of non-response to BoNT injection, NABs should be sought in individuals with SnR with no other cause explaining the treatment inefficacy. A test with 100% specificity is recommended. In cases for which immunogenicity is the most likely cause of non-response to BoNT injections, some biological arguments suggest trying another BoNT, but no clinical evidence supports this strategy.

The Acute Effect of Local Vibration As a Recovery Modality from Exercise-Induced Increased Muscle Stiffness

Exercise involving eccentric muscle contractions is known to decrease range of motion and increase passive muscle stiffness. This study aimed at using ultrasound shear wave elastography to investigate acute changes in biceps brachii passive stiffness following intense barbell curl exercise involving both concentric and eccentric contractions. The effect of local vibration (LV) as a recovery modality from exercise-induced increased stiffness was further investigated. Eleven subjects performed 4 bouts of 10 bilateral barbell curl movements at 70% of the one-rep maximal flexion force. An arm-to-arm comparison model was then used with one arm randomly assigned to the passive recovery condition and the other arm assigned to the LV recovery condition (10 min of 55-Hz vibration frequency and 0.9-mm amplitude). Biceps brachii shear elastic modulus measurements were performed prior to exercise (PRE), immediately after exercise (POST-EX) and 5 min after the recovery period (POST-REC). Biceps brachii shear elastic modulus was significantly increased at POST-EX (+53 ± 48%; p < 0.001) and POST-REC (+31 ± 46%; p = 0.025) when compared to PRE. No differences were found between passive and LV recovery (p = 0.210). LV as a recovery strategy from exercise-induced increased muscle stiffness was not beneficial, probably due to an insufficient mechanical action of vibrations. Key pointsBouts of barbell curl exercise induce an immediate increased passive stiffness of the biceps brachii muscle, as evidenced by greater shear elastic modulus measured by supersonic shear imaging.The administration of a vibratory massage did not reduce this acute exercise-induced increased stiffness.