Preganglionic and Postganglionic Brachial Plexus Birth Injury Effects on Shoulder Muscle Growth

Promotive effect of skin precursor-derived Schwann cells on brachial plexus neurotomy and motor neuron damage repair through milieu-regulating secretome

Brachial plexus injury (BPI) with motor neurons (MNs) damage still remain poor recovery in preclinical research and clinical therapy, while cell-based therapy approaches emerged as novel strategies. Previous work of rat skin precursor-derived Schwann cells (SKP-SCs) provided substantial foundation for repairing peripheral nerve injury (PNI). Given that, our present work focused on exploring the repair efficacy and possible mechanisms of SKP-SCs implantation on rat BPI combined with neurorrhaphy post-neurotomy. Results indicated the significant locomotive and sensory function recovery, with improved morphological remodeling of regenerated nerves and angiogenesis, as well as amelioration of target muscles atrophy and motor endplate degeneration. Besides, MNs could restore from oxygen-glucose-deprivation (OGD) injury upon SKP-SCs-sourced secretome treatment, implying the underlying paracrine mechanisms. Moreover, rat cytokine array assay detected 67 cytokines from SKP-SC-secretome, and bioinformatic analyses of screened 32 cytokines presented multiple functional clusters covering diverse cell types, including inflammatory cells, Schwann cells, vascular endothelial cells (VECs), neurons, and SKP-SCs themselves, relating distinct biological processes to nerve regeneration. Especially, a panel of hypoxia-responsive cytokines (HRCK), can participate into multicellular biological process regulation for permissive regeneration milieu, which underscored the benefits of SKP-SCs and sourced secretome, facilitating the chorus of nerve regenerative microenvironment. Furthermore, platelet-derived growth factor-AA (PDGF-AA) and vascular endothelial growth factor-A (VEGF-A) were outstanding cytokines involved with nerve regenerative microenvironment regulating, with significantly elevated mRNA expression level in hypoxia-responsive SKP-SCs. Altogether, through recapitulating the implanted SKP-SCs and derived secretome as niche sensor and paracrine transmitters respectively, HRCK would be further excavated as molecular underpinning of the neural recuperative mechanizations for efficient cell therapy; meanwhile, the analysis paradigm in this study validated and anticipated the actions and mechanisms of SKP-SCs on traumatic BPI repair, and was beneficial to identify promising bioactive molecule cocktail and signaling targets for cell-free therapy strategy on neural repair and regeneration.

The Relative Efficacy of Available Proteasome Inhibitors in Preventing Muscle Contractures Following Neonatal Brachial Plexus Injury

BACKGROUND

Contractures following neonatal brachial plexus injury (NBPI) are associated with growth deficits in denervated muscles. This impairment is mediated by an increase in muscle protein degradation, as contractures can be prevented in an NBPI mouse model with bortezomib (BTZ), a proteasome inhibitor (PI). However, BTZ treatment causes substantial toxicity (0% to 80% mortality). The current study tested the hypothesis that newer-generation PIs can prevent contractures with less severe toxicity than BTZ.

METHODS

Unilateral brachial plexus injuries were surgically created in postnatal (5-day-old) mice. Following NBPI, mice were treated with either saline solution or various doses of 1 of 3 different PIs: ixazomib (IXZ), carfilzomib (CFZ), or marizomib (MRZ). Four weeks post-NBPI, mice were assessed for bilateral passive range of motion at the shoulder and elbow joints, with blinding to the treatment group, through an established digital photography technique to determine contracture severity. Drug toxicity was assessed with survival curves.

RESULTS

All PIs prevented contractures at both the elbow and shoulder (p < 0.05 versus saline solution controls), with the exception of IXZ, which did not prevent shoulder contractures. However, their efficacies and toxicity profiles differed. At lower doses, CFZ was limited by toxicity (30% to 40% mortality), whereas MRZ was limited by efficacy. At higher doses, CFZ was limited by loss of efficacy, MRZ was limited by toxicity (50% to 60% mortality), and IXZ was limited by toxicity (80% to 100% mortality) and loss of efficacy. Comparisons of the data on these drugs as well as data on BTZ generated in prior studies revealed BTZ to be optimal for preventing contractures, although it, too, was limited by toxicity.

CONCLUSIONS

All of the tested second-generation PIs were able to reduce NBPI-induced contractures, offering further proof of concept for a regulatory role of the proteasome in contracture formation. However, the narrow dose ranges of efficacy for all PIs highlight the necessity of precise proteasome regulation for preventing contractures. Finally, the substantial toxicity stemming from proteasome inhibition underscores the importance of identifying muscle-targeted strategies to suppress protein degradation and prevent contractures safely.

CLINICAL RELEVANCE

Although PIs offer unique opportunities to establish critical mechanistic insights into contracture pathophysiology, their clinical use is contraindicated in patients with NPBI at this time.

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.

Promoting Recovery Following Birth Brachial Plexus Palsy

Neonatal brachial plexus palsies (NBPP) occur in 1.74 per 1000 live births with 20% to 30% having persistent deficits. Dysfunction can range from mild to severe and is correlated with the number of nerves involved and the degree of injury. In addition, there are several comorbidities and musculoskeletal sequelae that directly impact the overall functional development. This review addresses the nonsurgical and surgical management options and provides guidance for pediatricians on monitoring and when to refer for specialty care.

Shoulder Internal Rotation Contracture Formation in Surgically Managed C5, C6 Brachial Plexus Birth Injuries: Neurotmetic Lesions Fare Worse Than Avulsions

BACKGROUND

A typical feature in infants with severe C5-C6 brachial plexus birth injury (BPBI) requiring nerve repair is the formation of shoulder internal rotation contracture (IRC). The underlying pathophysiological mechanism is unknown, and the sequelae can be difficult to treat. The severity of the IRC differs among children. C5-C6 lesions are heterogeneous at the root level. Our null hypothesis was that the type of root-level lesion (axonotmesis or neurotmesis versus avulsion) was not associated with the extent of IRC formation over time in children with upper-trunk BPBI.

METHODS

We performed a retrospective analysis of all patients with upper-trunk BPBI who underwent primary surgery of the C5 and/or C6 spinal nerves between 1990 and 2020 and had follow-up of at least 2 years. The primary outcome was passive shoulder external rotation (ER) in adduction at 1, 3, 5, 7, and 15 years of age. The secondary outcome was whether additional shoulder surgery was performed. The relationship between the nature of the C5-C6 lesion and IRC formation was analyzed using linear mixed models. The Kaplan-Meier method was used to estimate the cumulative risk of secondary shoulder procedures.

RESULTS

In total, 322 patients were analyzed; mean follow-up was 7.2 ± 4.6 years. The C5-C6 root lesion type was significantly related to the passive range of ER (overall test in linear mixed model, p = 0.007). Children with avulsion of C5 and C6 (n = 21) had, on average, 18° (95% confidence interval [CI], 6.3° to 30°) less IRC formation than those with neurotmesis of C5 and C6 (n = 175) and 17° (2.9° to 31°) less than those with neurotmesis of C5 and avulsion of C6 (n = 34). IRC formation did not differ between the neurotmesis C5-C6 and neurotmesis C5-avulsion C6 groups. Secondary shoulder procedures were performed in 77 patients (10-year risk, 28% [95%CI, 23% to 34%]).

CONCLUSIONS

Shoulder IRC formation in infants with BPBI with surgically treated C5-C6 lesions occurs to a lesser degree if the C5 root is avulsed than when C5 is neurotmetic. This finding provides insight into the possible causative pathoanatomy and may ultimately lead to strategies to mitigate IRC.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Location of brachial plexus birth injury affects functional outcomes in a rat model

Brachial plexus birth injury (BPBI) results in shoulder and elbow paralysis with shoulder internal rotation and elbow flexion contracture as frequent sequelae. The purpose of this study was to develop a technique for measuring functional movement and examine the effect of brachial plexus injury location (preganglionic and postganglionic) on functional movement outcomes in a rat model of BPBI, which we achieved through integration of gait analysis with musculoskeletal modeling and simulation. Eight weeks following unilateral brachial plexus injury, sagittal plane shoulder and elbow angles were extracted from gait recordings of young rats (n = 18), after which rats were sacrificed for bilateral muscle architecture measurements. Musculoskeletal models reflecting animal-specific muscle architecture parameters were used to simulate gait and extract muscle fiber lengths. The preganglionic neurectomy group spent significantly less (p = 0.00116) time in stance and walked with significantly less (p < 0.05) elbow flexion and shoulder protraction in the affected limb than postganglionic neurectomy or control groups. Linear regression revealed no significant linear relationship between passive shoulder external rotation and functional shoulder protraction range of motion. Despite significant restriction in longitudinal muscle growth, normalized functional fiber excursions did not differ significantly between groups. In fact, when superimposed on a normalized force-length curve, neurectomy-impaired muscle fibers (except subscapularis) accessed regions of the curve that overlapped with the control group. Our results suggest the presence of compensatory motor control strategies during locomotion following BPBI. The clinical implications of our findings support emphasis on functional movement analysis in treatment of BPBI, as functional and passive outcomes may differ substantially.

Influence of Brachial Plexus Birth Injury Location on Glenohumeral Joint Morphology

PURPOSE

Patient presentation after brachial plexus birth injury (BPBI) is influenced by nerve injury location; more contracture and bone deformity occur at the shoulder in postganglionic injuries. Although bone deformity after postganglionic injury is well-characterized, the extent of glenohumeral deformity after preganglionic BPBI is unclear.

METHODS

Twenty Sprague-Dawley rat pups received preganglionic or postganglionic neurectomy on a single forelimb at postnatal days 3 to 4. Glenohumeral joints on affected and unaffected sides were analyzed using micro-computed tomography scans after death at 8 weeks after birth. Glenoid version, glenoid inclination, glenoid and humeral head radius of curvature, and humeral head thickness and width were measured bilaterally.

RESULTS

The glenoid was significantly more declined in affected compared with unaffected shoulders after postganglionic (-17.7° ± 16.9°) but not preganglionic injury. Compared with the preganglionic group, the affected shoulder in the postganglionic group exhibited significantly greater declination and increased glenoid radius of curvature. In contrast, the humeral head was only affected after preganglionic but not postganglionic injury, with a significantly smaller humeral head radius of curvature (-0.2 ± 0.2 mm), thickness (-0.2 ± 0.3 mm), and width (-0.3 ± 0.4 mm) on the affected side compared with the unaffected side; changes in these metrics were significantly associated with each other.

CONCLUSIONS

These findings suggest that glenoid deformities occur after postganglionic BPBI but not after preganglionic BPBI, whereas the humeral head is smaller after preganglionic injury, possibly suggesting an overall decreased biological growth rate in this group.

CLINICAL RELEVANCE

This study expands understanding of the altered glenoid and humeral head morphologies after preganglionic BPBI and its comparisons with morphologies after postganglionic BPBI.