Biomechanical Basis of Shoulder Osseous Deformity and Contracture in a Rat Model of Brachial Plexus Birth Palsy

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.

Nerve Tracing in Juvenile Rats: A Feasible Model for the Study of Brachial Plexus Birth Palsy and Cocontractions?

Brachial plexus birth injuries cause diminished motor function in the upper extremity. The most common sequel is internal rotation contracture. A number of these patients also suffer from cocontractions, preventing the use of an otherwise good passive range of motion in the shoulder. One theory behind the co-contracture problem is that injured nerve fibers grow into distal support tissue not corresponding to the proximal support tissue, resulting in reinnervation of the wrong muscle groups. To further elucidate this hypothesis, we used rat neonates to investigate a possible model for the study of cocontractions in brachial plexus birth injuries. Five-day-old rats were subjected to a crush injury to the C5-C6 roots. After a healing period of 4 weeks, the infraspinatus muscle was injected with Fluoro-Gold. A week later, the animals were perfused and spinal cords harvested and sectioned. Differences in the uptake of Fluoro-Gold and NeuN positive cells of between sides of the spinal cord were recorded. We found a larger amount of Fluoro-Gold positive cells on the uninjured side, while the injured side had positive cells dispersed over a longer area in the craniocaudal direction. Our findings indicate that the method can be used to trace Fluoro-Gold from muscle through a neuroma. Our results also indicate that a neuroma in continuity somewhat prevents the correct connection from being established between the motor neuron pool in the spinal cord and target muscle and that some neurons succumb to a crushing injury. We also present future research ideas.

The role of sympathetic innervation in neonatal muscle growth and neuromuscular contractures

Neonatal brachial plexus injury (NBPI), a leading cause of pediatric upper limb paralysis, results in disabling and incurable muscle contractures that are driven by impaired longitudinal growth of denervated muscles. A rare form of NBPI, which maintains both afferent and sympathetic muscle innervation despite motor denervation, protects against contractures. We have previously ruled out a role for NRG/ErbB signaling, the predominant pathway governing antegrade afferent neuromuscular transmission, in modulating the formation of contractures. Our current study therefore investigated the contributions of sympathetic innervation of skeletal muscle in modulating NBPI-induced contractures. Through chemical sympathectomy and pharmacologic modification with a β2 -adrenergic agonist, we discovered that sympathetic innervation alone is neither required nor sufficient to modulate contracture formation in neonatal mice. Despite this, sympathetic innervation plays an intriguing sex-specific role in mediating neonatal muscle growth, as the cross-sectional area (CSA) and volume of normally innervated male muscles were diminished by ablation of sympathetic neurons and increased by β-adrenergic stimulation. Intriguingly, the robust alterations in CSA occurred with minimal changes to normal longitudinal muscle growth as determined by sarcomere length. Instead, β-adrenergic stimulation exacerbated sarcomere overstretch in denervated male muscles, indicating potentially discrete regulation of muscle width and length. Future investigations into the mechanistic underpinnings of these distinct aspects of muscle growth are thus essential for improving clinical outcomes in patients affected by muscle disorders in which both length and width are affected.

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.

Clinical and psychosocial outcomes following correction of supination deformity in obstetrical brachial plexus palsy patients: A retrospective study

Background

Forearm supination contracture is the mostAQ common deformity of the forearm following obstetric brachial plexus palsy (OBPP). Supination deformities in OBPP may be corrected by performing forearm osteotomy; however, the high recurrence rate limits patient satisfaction. Apart from the cosmetic impairment of this deformity, there are no previous reports on the clinical and psychosocial outcomes of forearm osteotomy in patients with supination deformities secondary to OBPP. Therefore, our study aimed to assess the clinical, functional, and psychosocial outcomes following forearm pronation osteotomy in OBPP patients with supination deformity.

Methods

This retrospective study was conducted after a chart review of all OBPP sequelae with supination forearm deformity in patients who underwent forearm pronating osteotomy from 2006 to 2018. Data relating to OBPP were gathered, and functional and psychosocial outcomes were assessed using the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire through interviews

Results

This study included 60 patients with a mean age of 8.7 years at the time of surgery. A total of 46 patients had lesions involving C5-T1 (76.7%). The mean preoperative supination deformity position was 68.5°, the mean amount of correction was 98.9°, and the mean forearm position was 30.5°, postoperatively. In the DASH assessment scale used postoperatively, 24 patients (42.9%) reported no restrictions on their daily activities, 25 patients (44.6%) believed that their social activities were unaffected, and 20 patients (35.7%) strongly disagreed with feeling less capable or less confident due to arm, shoulder, or hand problems. The factors significantly affecting position at the final follow-up were the amount of correction (p = 0.011), postoperative position (p = 0.005), and degree of pronation achieved (p = 0.02). The amount of correction significantly affected both self-confidence (p = 0.049) and activities of daily living (p = 0.033).

Conclusion

In conclusion, our study showed that the position at the final follow-up, the degree of pronation achieved intraoperatively, and the postoperative position significantly affected the position at follow-up and the outcome assessment. The amount of intraoperative correction was significantly associated with higher self-confidence and normal activities of daily living.

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.

Effect of arthroscopic shoulder release on shoulder mobility and bone deformity following brachial plexus birth injury: a systematic review and meta-analysis

BACKGROUND

Specific information to guide clinical practice is lacking for the effects of arthroscopic release on bone and joint deformities, as well as the additional benefits of tendon transfer, in children with brachial plexus birth injury. The aims of this study were (1) to evaluate changes in shoulder mobility and bone and joint deformity, (2) to evaluate the effect of release with and without tendon transfer on the same outcomes, and (3) to evaluate the perioperative and long-term complications.

METHODS

We conducted a systematic review and meta-analysis. Four databases were searched using relevant inclusion and exclusion criteria from inception until May 2020. The quality of articles was evaluated using the Methodological Index for Non-randomized Studies (MINORS) scale. Data regarding patients, interventions, and clinical and radiologic outcomes were reported.

RESULTS

Thirteen articles were included: 6 of low quality and 7 of moderate quality separated into 17 studies (266 children). The mean follow-up duration was 32.4 months (standard deviation, 15.2 months). Arthroscopic release significantly improved the Mallet score (standardized mean difference [SMD], 3.1 [95% confidence interval (CI), 1.5-4.7]; P < .001) and passive external rotation (SMD, 3.6 [95% CI, 2.3-4.9]; P = .02). The percentage of humeral head anterior (SMD, 1.3 [95% CI, 0.7-1.9]; P = .003) and glenoid retroversion (SMD, 1.4 [95% CI, 0.9-2]; P = .01) also improved. Descriptive analysis of the data suggested that concomitant tendon transfer further improved mobility. Recurrence of internal-rotation contracture was reported in 8 of 157 children.

DISCUSSION

This systematic review showed that arthroscopic release effectively improves both shoulder mobility and bone deformity, with few complications in young children with brachial plexus birth injury. As such, it seems reasonable to propose a stepwise approach starting with a release without transfer.

The outcome of soft-tissue release and tendon transfer in shoulders with brachial plexus birth palsy

Background

Shoulder involvement in brachial plexus birth palsy is common, and the adduction, internal rotation contracture deformity often requires some form of surgical treatment. There are very few long-term reports on release of contracted muscles and tendon transfers, especially in older children. We are reporting the single-center results of such a surgery with detailed outcome analysis.

Methods

The prospectively collected data from brachial plexus birth palsy cases who had undergone contracture release and tendon transfer were retrospectively studied and examined. The new Mallet and functional scores were compared with the original data forms and then analyzed. The radiographic evidence of glenoid dysplasia and its correlation with age and functional outcome was assessed.

Results

A total of 82 cases with surgery at mean age of 9.5 ± 5.09 years and a follow-up of 8 ± 3.8 (3-20) years entered the study. Of these, 56% of cases had 7 to 20 years of age at surgery. Fifty-four (66%) patients had only shoulder surgery, and 28 (34%) required additional reconstructive surgeries for hand and wrist. Moderate to severe glenohumeral dysplasia was present in 38%. The preoperative Mallet score of 10.6 ± 2.97 improved to 19.3 ± 3.39 (P < .001). Eighty-one percent of patients showed improvement in “reaching face” functions, 71% in “above head” functions, and 74% in “midline functions.” The cases with lack of improvement in midline function mostly belonged to pan-plexus injuries. Noticeable subjective and objective improvement was also observed in cases with glenohumeral dysplasia in their Mallet and functional scores (P < .001). The improvement in function and subjective satisfaction of 92% was observed irrespective of age at surgery.

Conclusion

Soft-tissue release and tendon transfer for brachial plexus birth palsy shoulder can improve function and limb appearance even in older children and young adults and even in the presence of glenohumeral dysplasia.

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.

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

PURPOSE

Brachial plexus birth injury can differ in presentation, depending on whether the nerve ruptures distal to, or avulses proximal to, the dorsal root ganglion. More substantial contracture and bone deformity at the shoulder is typical in postganglionic injuries. However, changes to the underlying muscle structure that drive these differences in presentation are unclear.

METHODS

Seventeen Sprague-Dawley rats received preganglionic or postganglionic neurectomy on a single limb on postnatal days 3 and 4. Muscles crossing the shoulder were retrieved once the rats were sacrificed at 8 weeks after birth. External rotation range of motion, muscle mass, muscle length, muscle sarcomere length, and calculated optimal muscle length were measured bilaterally.

RESULTS

Average shoulder range of motion in the postganglionic group was 61.8% and 56.2% more restricted at 4 and 8 weeks, respectively, compared with that in the preganglionic group, but affected muscles after preganglionic injury were altered more severely (compared with the unaffected limb) than after postganglionic injury. Optimal muscle length in preganglionic injury was shorter in the affected limb (compared with the unaffected limb: -18.2% ± 9.2%) and to a greater extent than in postganglionic injury (-5.1% ± 6.2%). Muscle mass in preganglionic injury was lower in the affected limb (relative to the unaffected limb: -57.2% ± 24.1%) and to a greater extent than in postganglionic injury (-28.1% ± 17.7%).

CONCLUSIONS

The findings suggest that the presence of contracture does not derive from restricted longitudinal muscle growth alone, but also depends on the extent of muscle mass loss occurring simultaneously after the injury.

CLINICAL RELEVANCE

This study expands our understanding of differences in muscle architecture and the role of muscle structure in contracture formation for preganglionic and postganglionic brachial plexus birth injury.

Timing of proteasome inhibition as a pharmacologic strategy for prevention of muscle contractures in neonatal brachial plexus injury

Neonatal brachial plexus injury (NBPI) causes disabling and incurable contractures, or limb stiffness, which result from proteasome‐mediated protein degradation impairing the longitudinal growth of neonatally denervated muscles. We recently showed in a mouse model that the 20S proteasome inhibitor, bortezomib, prevents contractures after NBPI. Given that contractures uniquely follow neonatal denervation, the current study tests the hypothesis that proteasome inhibition during a finite window of neonatal development can prevent long‐term contracture development. Following neonatal forelimb denervation in P5 mice, we first outlined the minimum period for proteasome inhibition to prevent contractures 4 weeks post‐NBPI by treating mice with saline or bortezomib for varying durations between P8 and P32. We then compared the ability of varying durations of longer‐term proteasome inhibition to prevent contractures at 8 and 12 weeks post‐NBPI. Our findings revealed that proteasome inhibition can be delayed 3‐4 days after denervation but is required throughout skeletal growth to prevent contractures long term. Furthermore, proteasome inhibition becomes less effective in preventing contractures beyond the neonatal period. These therapeutic effects are primarily associated with bortezomib‐induced attenuation of 20S proteasome β1 subunit activity. Our collective results, therefore, demonstrate that temporary neonatal proteasome inhibition is not a viable strategy for preventing contractures long term. Instead, neonatal denervation causes a permanent longitudinal growth deficiency that must be continuously ameliorated during skeletal growth. Additional mechanisms must be explored to minimize the necessary period of proteasome inhibition and reduce the risk of toxicity from long‐term treatment.

Follow-up Study on the Effects of Tendon Transfers and Open Reduction on Moderate Glenohumeral Joint Deformity in Brachial Plexus Birth Injury

BACKGROUND

Soft-tissue contractures about the shoulder in patients with brachial plexus birth injury are common and can lead to progressive shoulder displacement and glenohumeral dysplasia. Open or arthroscopic reduction with musculotendinous lengthening and tendon transfers have become the standard of care. The clinical function and radiographic joint remodeling beyond the first 2 years after surgery are not well understood.

METHODS

We performed a follow-up study of 20 patients with preexisting mild to moderate glenohumeral joint deformity who had undergone open glenohumeral joint reduction with latissimus dorsi and teres major tendon transfers and concomitant musculotendinous lengthening of the pectoralis major and/or subscapularis. Prospective collection of Modified Mallet and Active Movement Scale (AMS) scores and radiographic analysis of cross-sectional imaging for glenoid version, humeral head subluxation, and glenohumeral joint deformity classification were analyzed for changes over time.

RESULTS

The average duration of radiographic follow-up was 4.2 years (range, 2 to 6 years). The mean glenoid version improved from -31.8° to -15.4° (p < 0.0001). The mean percentage of the humeral head anterior to the middle of the glenoid (PHHA) improved from 9.6% to 30.4% (p < 0.0001). The mean glenohumeral joint deformity score improved from 3.7 to 2.1 (p < 0.0001).

CONCLUSIONS

All parameters showed the greatest magnitude of improvement between preoperative measurements and 1 year of follow-up. There were no significant changes beyond the 1-year time point in the Mallet scores, AMS scores, or radiographic outcome measures, possibly because of insufficient power, although trends of improvement were noted for some outcomes. No decline in outcome measures was found during the study period.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Integrated iterative musculoskeletal modeling predicts bone morphology following brachial plexus birth injury (BPBI)

Brachial plexus birth injury (BPBI) is the most common nerve injury among children. The glenohumeral joint of affected children can undergo severe osseous deformation and altered muscle properties, depending on location of the injury relative to the dorsal root ganglion (preganglionic or postganglionic). Preganglionic injury results in lower muscle mass and shorter optimal muscle length compared to postganglionic injury. We investigated whether these changes to muscle properties over time following BPBI provide a mechanically-driven explanation for observed differences in bone deformity between preganglionic and postganglionic BPBI. We developed a computational framework integrating musculoskeletal modeling to represent muscle changes over time and finite element modeling to simulate bone growth in response to mechanical and biological stimuli. The simulations predicted that the net glenohumeral joint loads in the postganglionic injury case were nearly 10.5% greater than in preganglionic. Predicted bone deformations were more severe in the postganglionic case, with the glenoid more declined (pre: -43.8°, post: -51.0°), flatter with higher radius of curvature (pre: 3.0 mm, post: 3.7 mm), and anteverted (pre: 2.53°, post: 4.93°) than in the preganglionic case. These simulated glenoid deformations were consistent with previous experimental studies. Thus, we concluded that the differences in muscle mass and length between the preganglionic and postganglionic injuries are critical mechanical drivers of the altered glenohumeral joint shape.

Proteasome inhibition preserves longitudinal growth of denervated muscle and prevents neonatal neuromuscular contractures

Muscle contractures are a prominent and disabling feature of many neuromuscular disorders, including the 2 most common forms of childhood neurologic dysfunction: neonatal brachial plexus injury (NBPI) and cerebral palsy. There are currently no treatment strategies to directly alter the contracture pathology, as the pathogenesis of these contractures is unknown. We previously showed in a mouse model of NBPI that contractures result from impaired longitudinal muscle growth. Current presumed explanations for growth impairment in contractures focus on the dysregulation of muscle stem cells, which differentiate and fuse to existing myofibers during growth, as this process has classically been thought to control muscle growth during the neonatal period. Here, we demonstrate in a mouse model of NBPI that denervation does not prevent myonuclear accretion and that reduction in myonuclear number has no effect on functional muscle length or contracture development, providing definitive evidence that altered myonuclear accretion is not a driver of neuromuscular contractures. In contrast, we observed elevated levels of protein degradation in NBPI muscle, and we demonstrate that contractures can be pharmacologically prevented with the proteasome inhibitor bortezomib. These studies provide what we believe is the first strategy to prevent neuromuscular contractures by correcting the underlying deficit in longitudinal muscle growth.

The Pathogenesis of Glenohumeral Deformity and Contracture Formation in Obstetric Brachial Plexus Palsy-A Review

Contractures of the shoulder joint and glenohumeral joint dysplasia are well known complications to obstetrical brachial plexus palsy. Despite extensive description of these sequelae, the exact pathogenesis remains unknown. The prevailing theory to explain the contractures and glenohumeral joint dysplasia states that upper trunk injury leads to nonuniform muscle recovery and thus imbalance between internal and external rotators of the shoulder. More recently, another explanation has been proposed, hypothesizing that denervation leads to reduced growth of developing muscles and that reinnervation might suppress contracture formation. An understanding of the pathogenesis is desirable for development of effective prophylactic treatment. This article aims to describe the current state of knowledge regarding these important complications.

Computational analysis of glenohumeral joint growth and morphology following a brachial plexus birth injury

Children affected with brachial plexus birth injury (BPBI) undergo muscle paralysis. About 33% of affected children experience permanent osseous deformities of the glenohumeral joint. Recent evidence suggests that some cases experience restricted muscle longitudinal growth in addition to paralysis and reduced range of motion at the shoulder and elbow. It is unknown whether altered loading due to paralysis, muscle growth restriction and contracture, or static loading due to disuse is the primary driver of joint deformity after BPBI. This study uses a computational framework integrating finite element analysis and musculoskeletal modeling to examine the mechanical factors contributing to changes in bone growth and morphometry following BPBI. Simulations of 8 weeks of glenohumeral growth in a rat model of BPBI predicted that static loading of the joint is primarily responsible for joint deformation consistent with experimental measures of bone morphology, whereas dynamic loads resulted in normal bone growth. Under dynamic loading, glenoid version angle (GVA), glenoid inclination angle (GIA), and glenoid radius of curvature (GRC) (-1.3°, 38.2°, 2.5 mm respectively) were similar to the baseline values (-1.8°, -38°, 2.1 mm respectively). In the static case with unrestricted muscle growth, these measures increased in magnitude (5.2°, -48°, 3.5 mm respectively). More severe joint deformations were observed in GIA and GRC when muscle growth was restricted (GVA: 3.6°, GIA: -55°, GRC: 4.0 mm). Predicted morphology was consistent with literature reports of in vivo glenoid morphology following postganglionic BPBI. This growth model provides a framework for understanding the most influential mechanical factors driving glenohumeral deformity following BPBI.

Humeral retroversion and shoulder muscle changes in infants with internal rotation contractures following brachial plexus birth palsy

AIM

To examine humeral retroversion in infants who sustained brachial plexus birth palsy (BPBI) and suffered from an internal rotation contracture. Additionally, the role of the infraspinatus (IS) and subscapularis (SSc) muscles in the genesis of this bony deformation is explored.

METHODS

Bilateral magnetic resonance imaging (MRI) scans of 35 infants (age range: 2-7 mo old) with BPBI were retrospectively analyzed. Retroversion was measured according to two proximal axes and one distal axis (transepicondylar axis). The proximal axes were: (1) the perpendicular line to the borders of the articular surface (humeral centerline); and (2) the longest diameter through the humeral head. Muscle cross-sectional areas of the IS and SSc muscles were measured on the MRI-slides representing the largest muscle belly. The difference in retroversion was correlated with the ratio of muscle-sizes and passive external rotation measurements.

RESULTS

Retroversion on the involved side was significantly decreased, 1.0° vs 27.6° (1) and 8.5° vs 27.2° (2), (P < 0.01), as compared to the uninvolved side. The size of the SSc and IS muscles on the involved side was significantly decreased, 2.26 cm² vs 2.79 cm² and 1.53 cm² vs 2.19 cm², respectively (P < 0.05). Furthermore, the muscle ratio (SSc/IS) at the involved side was significantly smaller compared to the uninvolved side (P = 0.007).

CONCLUSION

Even in our youngest patient population, humeral retroversion has a high likelihood of being decreased. Altered humeral retroversion warrants attention as a structural change in any child being evaluated for the treatment of an internal rotation contracture.

Relationship between glenoid deformity and gait characteristics in a rat model of neonatal brachial plexus injury

Neonatal brachial plexus injury (NBPI) results in substantial postural and functional impairments associated with underlying muscular and osseous deformities. We examined the relationship between glenoid deformity severity and gait in a rat model of NBPI, an established model for studying the in vivo pathomechanics of NBPI. At 8 weeks post-operatively, we monitored the gait of 24 rat pups who exhibited varying degrees of glenoid deformity following unilateral brachial plexus neurectomy and chemodenervation interventions administered 5 days postnatal. Five basic stride and stance metrics were calculated for the impaired forelimbs over four consecutive gait cycles. Bilateral differences in glenoid version (ΔGA_v ) and inclination (ΔGA_i ) angles were computed from data for the same rats as reported in a previous study. A linear regression model was generated for each deformity-gait pair to identify significant relationships between the two. ΔGA_v was not significantly correlated with any gait measurements, while ΔGA_i significantly correlated with all five gait measurements. Specifically, ΔGA_i was significantly positively correlated with stride length (R²  = 0.38, p = 0.001) and stance factor (R²  = 0.45, p < 0.001), and significantly negatively correlated with stance width (R²  = 0.24, p = 0.016), swing/stance ratio (R²  = 0.17, p = 0.046), and stride frequency (R²  = 0.33, p = 0.003). Rats with declined glenoids exhibited the most altered gait.

CLINICAL SIGNIFICANCE

Our findings link musculoskeletal changes and functional outcomes in an NBPI rat model. Thus, gait analysis is a potentially useful, non-invasive, quantitative way to investigate the effects of injury and deformity on limb function in the NBPI rat model. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1991-1997, 2018.

Triplanar Humeral Osteotomy for Restoration of Midline Function in Patients With Brachial Plexus Birth Palsy

Brachial plexus birth palsy resolves spontaneously in a majority of patients, however, others may have serious permanent dysfunction. Although nerve transfers or grafts are early options for treatment, many children have residual deficits or present too late for such procedures. In these patients, rotational osteotomy of the humerus may restore improved function and motion. Unfortunately, traditional humeral osteotomies only provide correction in a single plane, therefore appropriate correction of the typical residual deformity is incomplete. Here, we describe a novel technique for obtaining a calculated correction in 3 planes using a single osteotomy of the humerus on the basis of a mathematical equation. Nine patients are described here with an average of 35.4 months follow-up. Corrections were obtained in adduction, extension, and either internal or external rotation depending on the initial deformity and Modified Mallet scores were collected for each patient. There was 1 case of transient radial nerve palsy with no long-term complications overall.

Humeral Retroversion in Children with Shoulder Internal Rotation Contractures Secondary to Upper-Trunk Neonatal Brachial Plexus Palsy

BACKGROUND

The most common sequela of neonatal brachial plexus palsy is an internal rotation contracture of the shoulder that impairs function and leads to skeletal deformation of the glenohumeral joint. Treatment options include release, transfers, and humeral osteotomy, all ultimately striving for better function through increased external rotation. Prior studies have shown that neonatal brachial plexus palsy alters humeral retroversion but with conflicting findings. We studied retroversion in children with internal rotation contractures from neonatal brachial plexus palsy to clarify its effect on version and surgical planning.

METHODS

Bilateral shoulder and elbow magnetic resonance imaging scans of 21 children with neonatal brachial plexus palsy were retrospectively analyzed. Retroversion referenced to the transepicondylar line at the elbow was measured with respect to 2 different proximal reference axes, the longest diameter of an axial cut of the proximal part of the humerus (the skew axis) and the line perpendicular to the articular surface (the humeral center line). Glenoid version and glenohumeral morphology type (concentric glenoid, posterior-concentric glenoid, biconcave, or pseudoglenoid) were also determined. All geometric variables were assessed for correlation with patient age and the severity of the internal rotation contracture.

RESULTS

Retroversion on the involved side was decreased at 6° compared with 19° (p = 0.003), as measured between the skew axis and transepicondylar line. Retroversion referenced to the humeral center line was also decreased at -2° (anteversion) compared with 20° (p < 0.001). Patient age was inversely correlated with retroversion, but was only significant for the skew axis (r = -0.497, p = 0.022), decreasing in linear regression by 2.4° per year (p = 0.038). Humeral retroversion did not correlate with the severity of the internal rotation contracture, glenoid version, or glenoid morphology type.

CONCLUSIONS

Humeral retroversion is likely to be less on the affected side in children with internal rotation contractures from upper trunk neonatal brachial plexus palsy and merits consideration in surgical planning.

LEVEL OF EVIDENCE

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

The natural history and management of brachial plexus birth palsy

Brachial plexus birth palsy (BPBP) is an upper extremity paralysis that occurs due to traction injury of the brachial plexus during childbirth. Approximately 20 % of children with brachial plexus birth palsy will have residual neurologic deficits. These permanent and significant impacts on upper limb function continue to spur interest in optimizing the management of a problem with a highly variable natural history. BPBP is generally diagnosed on clinical examination and does not typically require cross-sectional imaging. Physical examination is also the best modality to determine candidates for microsurgical reconstruction of the brachial plexus. The key finding on physical examination that determines need for microsurgery is recovery of antigravity elbow flexion by 3-6 months of age. When indicated, both microsurgery and secondary shoulder and elbow procedures are effective and can substantially improve functional outcomes. These procedures include nerve transfers and nerve grafting in infants and secondary procedures in children, such as botulinum toxin injection, shoulder tendon transfers, and humeral derotational osteotomy.

Boston Children's Hospital approach to brachial plexus birth palsy

The treatment of infants with brachial plexus birth palsy (BPBP) continues to be a focus at Boston Children's Hospital. Over the last 15 years, there have been many developments in the treatment of infants with BPBP. Some of the greatest changes have emerged through technical advances such as the advent of distal nerve transfers to allow targeted reinnervation as well as through research to understand the pathoanatomical changes that lead to glenohumeral dysplasia and how this dysplasia can be remodeled. This review will discuss our current practice of evaluation of the infant with BPBP, techniques for microsurgical reconstruction, and prevention and treatment of secondary glenohumeral dysplasia.