Botulinum toxin and the pathophysiology of obstetric brachial plexus lesions

Predictors of Co-activation in Erb's Palsy: A Retrospective Study

Context

Three per thousand births have Erb's palsy. Spontaneous recovery is 50%. Co-activation yields poor outcomes. There are no objective indicators of its emergence.

Aims

Analyze if 1 month Axon Viability Index (AVI) of the axillary nerve and which active movement score (AMS) measures can predict co-activation.

Settings and Design

Tertiary level rehabilitation center, retrospective design.

Methods and Material

The electronic medical record (EMR) was reviewed for patients with Erb's palsy with Narakas grade 2 lesions, as having co-activation or not. The one-month Axillary AVI was used with monthly AMS scores. The inclusion criteria were an AVI greater than ten percent. Exclusion criteria were bi-brachial palsy, congenital anomalies, concomitant or subsequent neurological injuries, and orthopedic injuries.

Statistical Analysis Used

Descriptive statistics were used to calculate the median and interquartile values for AMS scores at each respective time point. Statistical significance for each time point was determined using a student's t-test.

Results

Regarding the t-test on the AVI data, a significant P value of 0.001 was found favoring the co-activation group. AVI of the Axillary nerve between 0.1 and 0.5 at 1 month is a reliable indicator of future development of co-activation. The following were strong indicators of the emergence of co-activation respectively: month three Wrist Extension in sitting, Shoulder Abduction in supine, Shoulder Abduction in sitting, Elbow Flexion in sitting, month six Elbow Flexion in sitting, month seven Elbow Flexion in sitting.

Conclusions

The axillary AVI at one month is a good predictor of future development of co-activation. The mentioned AMS items are the earliest indicators of co-activation.

Cocontraction measured with short-range stiffness was higher in obstetric brachial plexus lesions patients compared to healthy subjects

We suggest short range stiffness (SRS) at the elbow joint as an alternative diagnostic for EMG to assess cocontraction. Elbow SRS is compared between obstetric brachial plexus lesion (OBPL) patients and healthy subjects (cross-sectional study design). Seven controls (median 28years) and five patients (median 31years) isometrically flexed and extended the elbow at rest and three additional torques [2.1,4.3,6.4Nm] while a fast stretch stimulus was applied. SRS was estimated in silico using a neuromechanical elbow model simulating the torque response from the imposed elbow angle. SRS was higher in patients (250±36Nm/rad) than in controls (150±21Nm/rad, p=0.014), except for the rest condition. Higher elbow SRS suggested greater cocontraction in patients compared to controls. SRS is a promising mechanical alternative to assess cocontraction, which is a frequently encountered clinical problem in OBPL due to axonal misrouting.

Utility of ultrasound-guided injection of botulinum toxin type A for muscle imbalance in children with obstetric brachial plexus palsy: Description of the procedure and action protocol

INTRODUCTION

Obstetric brachial plexus palsy (OBPP) usually has a favourable prognosis. However, nearly one third of all severe cases have permanent sequelae causing a high level of disability. In this study, we explore the effectiveness of ultrasound-guided injection of botulinum toxin A (BoNT-A) and describe the procedure.

PATIENTS AND METHODS

We designed a prospective, descriptive study including patients with moderate to severe OBPP who were treated between January 2010 and December 2014. We gathered demographic data, type of OBPP, and progression. Treatment effectiveness was assessed with the Active Movement Scale (AMS), the Mallet classification, and video recordings.

RESULTS

We gathered a total of 14 133 newborns, 15 of whom had OBPP (1.6 per 1000 live births). Forty percent of the cases had severe OBPP (0.4/1000), a dystocic delivery, and APGAR scores < 5; mean weight was 4038g. Mean age at treatment onset was 11.5 months. The muscles most frequently receiving BoNT-A injections were the pronator teres, subscapularis, teres major, latissimus dorsi, and pectoralis major. All the patients who completed the follow-up period (83%) experienced progressive improvements: up to 3 points on the AMS and a mean score of 19.5 points out of 25 on the Mallet classification at 2 years. Treatment improved muscle function and abnormal posture in all cases. Surgery was avoided in 3 patients and delayed in one. Adverse events were mild and self-limited.

CONCLUSIONS

Due to its safety and effectiveness, BoNT-A may be used off-label as an adjuvant to physical therapy and/or surgery in moderate to severe OBPP. Ultrasound may increase effectiveness and reduce adverse effects.

Effects of Botulinum Toxin on Reducing the Co-contraction of Antagonists in Birth Brachial Plexus Palsy

Birth brachial plexus palsy (BBPP) is usually caused by plexus traction during difficult delivery. Although the possibility of complete recovery is relatively high, 5% to 25% of BBPP cases result in prolonged and persistent disability. In particular, muscle imbalance and co-contraction around the shoulder and elbow cause abnormal motor performance, osseous deformities, and joint contracture. Physical and occupational therapies have most commonly been used, but these conventional therapeutic strategies have often been inadequate, in managing the residual muscle imbalance and muscle co-contraction. Therefore, we attempted to improve the functional movements, by using botulinum toxin type A, to reduce the abnormal co-contraction of the antagonist muscles.

Needle electromyography at 1 month predicts paralysis of elbow flexion at 3 months in obstetric brachial plexus lesions

AIM

Treatment decisions in obstetric brachial plexus lesions are often based on clinical paralysis of elbow flexion at 3 months of age, when electromyography (EMG) is misleading because motor unit potentials (MUPs) occur in clinically paralytic muscles. We investigated whether EMG at 1 week or 1 month identifies infants with flexion paralysis at 3 months, allowing early referral.

METHOD

Forty-eight infants (27 females, 21 males) were prospectively studied. The presence or absence of flexion paralysis at around 1 week (median 9 d; range 5-17d), 1 month (median 31 d; range 24-53 d), and 3 months of age (median 87 d; range 77-106 d) was noted for clinical (shoulder external rotation, elbow flexion, extension, and supination) and EMG parameters (denervation activity, MUPs and polyphasic MUPs in the deltoid, biceps, and triceps muscles).

RESULTS

At 1 month, the absence of biceps MUPs had a sensitivity of 95% for later flexion paralysis, and absence of deltoid MUPs had a sensitivity of 100% for flexion paralysis; the false-positive rates for the same findings were 21% and 33% respectively. EMG at 3 months was highly misleading as MUPs were seen in 19 of 20 clinically paralytic biceps muscles.

INTERPRETATION

EMG at 1 month can identify severe cases of flexion paralysis for early referral EMG of the biceps at 3 months is highly misleading; the discrepancy between the EMG and clinical testing may be due to abnormal axonal branching and aberrant central motor control.

Indications and effects of botulinum toxin A for obstetric brachial plexus injury: a systematic literature review

AIM

To give an overview of indications for the use of botulinum toxin A (BoNT-A) treatment for children with obstetric brachial plexus injury (OBPI), and to present the best available evidence of the effectiveness of this treatment.

METHOD

Searches were performed in Cinahl, Cochrane Library, Embase, PubMed, and Web of Science, using the keywords 'botulinum' and 'plexus', to identify articles reporting on the use of BoNT-A as a treatment for children with OBPI. Studies found through the references of related articles were also selected.

RESULTS

Ten full-text papers and six congress abstracts were included, involving 343 children. Four groups of indications could be identified: internal rotation/adduction contracture of the shoulder, limited active elbow flexion, limited active elbow extension, and pronation contracture of the lower arm. Overall, positive results were reported for all except the indication for limited active elbow extension. However, only one study was comparative in nature; all others were classified as having a low level of evidence. There was a large variation in outcome measures.

INTERPRETATION

To provide better evidence for the already partly promising results of BoNT-A treatment for children with OBPI, multicentre randomized controlled trials are needed.

Electromyography, nerve action potential, and compound motor action potentials in obstetric brachial plexus lesions: validation in the absence of a "gold standard"

OBJECTIVE

Obstetric brachial plexus lesions (OBPLs) are caused by traction to the brachial plexus during labor. Typically, in these lesions, the nerves are usually not completely ruptured but form a "neuroma-in-continuity." Even in the most severe OBPL lesions, at least some axons will pass through this neuroma-in-continuity and reach the tubes distal to the lesion site. These axons may be particularly prone to abnormal branching and misrouting, which may explain the typical feature of co-contraction. An additional factor that may reduce functional regeneration is that improper central motor programming may occur. Surgery should be restricted to severe cases in which spontaneous restoration of function will not occur, i.e., in neurotmesis or root avulsions. A major problem is how to predict whether function will be best after spontaneous nerve outgrowth or after nerve reconstructive surgery. When a decision has been made to perform an early surgical exploration, what to do with the neuroma-in-continuity can be a problem. The intraoperative appraisal is difficult and depends on experience, but even in experienced hands, misjudgment can be made.

METHODS

We performed an observational study to assess whether early electromyography (at the age of 1 month) is able to predict severe lesions. Additionally, the value of intraoperative nerve action potential and compound motor action potentials was investigated.

RESULTS

Severe cases of OBPL can be identified at 1 month of age on the basis of clinical findings and needle electromyography of the biceps. This outcome needs independent validation, which is currently in progress. Nerve action potential and compound motor action potential recordings show statistically significant differences on the group level between avulsion, neurotmesis, axonotmesis, and normal. For the individual patient, a clinically useful cutoff point could not be found. Intraoperative nerve action potential and compound motor action potential recordings do not add to the decision making during surgery.

CONCLUSION

The absence of a "gold standard" for the assessment of the severity of the OBPL lesion makes prognostic studies of OBPL complex. The currently available assessment strategies used to obtain the best possible solutions are discussed.