An MRI study on the relations between muscle atrophy, shoulder function and glenohumeral deformity in shoulders of children with obstetric brachial plexus injury

Subscapularis impairment on magnetic resonance imaging is correlated with functional limitations in neonatal brachial plexus palsy

PURPOSE

The relationship between functional shoulder deficits in children with neonatal brachial plexus palsy (NBPP) and magnetic resonance imaging (MRI) shoulder abnormalities was evaluated.

METHODS

Shoulder function was assessed in 16 children (mean age: 5.8 years; range: 3-12 years) with NBPP based on shoulder rotator muscle strength, as measured using an isokinetic dynamometer and the modified Mallet score. The thickness and fatty infiltration of the subscapularis and infraspinatus muscles, and the morphology of the glenoid on MRI, were also determined.

RESULTS

The highest subscapularis fatty infiltration subgroup of NBPP patients promoted the highest alteration muscle thickness and modified Mallet score.

CONCLUSIONS

In NBPP children, subscapularis impairments play a major role in the functional limitations. This study of pediatric NBPP patients highlighted the value of adding an examination of the muscles to routine MRI assessment of bone parameters in the shoulders of NBPP children.

TRIAL REGISTRATION

NCT03440658.

Ultrasound assessment of glenohumeral dysplasia in infants

Brachial plexus birth injury can lead to irreversible neuromuscular dysfunction and skeletal deformity of the upper extremity and shoulder girdle, ultimately resulting in glenohumeral dysplasia. Diagnosis and treatment of affected infants requires a multi-disciplinary approach in which imaging plays a vital role. While MRI is excellent for assessing both the shoulder and spine of these children, it is costly and requires sedation and is thus typically reserved for preoperative planning. US, however, is inexpensive, dynamic and readily available and provides excellent visualization of the largely cartilaginous glenohumeral joint. As such, it has become a highly useful modality during early diagnosis and follow-up of children with brachial plexus birth injuries. In this review, we describe the relevant anatomy of the glenohumeral joint, outlining the normal sonographic appearance as well as providing tips and tricks for identifying and characterizing pathology.

Interobserver and intraobserver comparison of imaging glenoid morphology, glenoid version and humeral head subluxation

BACKGROUND

Glenoid morphology, glenoid version and humeral head subluxation represent important parameters for the treating physician. The most common method of assessing glenoid morphology is the Walch classification which has only been validated with computed tomography (CT).

METHODS

CT images and magnetic resonance imaging (MRI) images of 25 patients were de-identified and randomized. Three reviewers assessed the images for each parameter twice. The Walch classification was assessed with a weighted kappa value. Glenoid version and humeral head subluxation were comparted with a reproducibility coefficient.

RESULTS

The Walch classification demonstrated almost perfect intraobserver agreement for MRI and CT images (k = 0.87). Weighted interobserver agreement values for the Walch classification were fair for CT and MRI (k = 0.34). The weighted reproducibility coefficient for glenoid version measured 9.13 (CI 7.16-12.60) degrees for CT and 13.44 (CI 10.54-18.55) degrees for MRI images. The weighted reproducibility coefficient for percentage of humeral head subluxation was 17.43% (CI 13.67-24.06) for CT and 18.49% (CI 14.5-25.52) for MRI images.

DISCUSSION

CT and MRI images demonstrated similar efficacy in classifying glenoid morphology, measuring glenoid version and measuring posterior humeral head subluxation. MRI can be used as an alternative to CT for measuring these parameters.

Shoulder muscle atrophy and its relation to strength loss in obstetrical brachial plexus palsy

BACKGROUND

Treatment/prevention of shoulder muscle strength imbalances are major therapeutic goals for children with obstetrical brachial plexus palsy. The study aims were to characterize muscle atrophy in children/adolescents with unilateral obstetrical brachial plexus palsy, to quantify the agonist-antagonist muscle volume balance and the association between muscle volume and strength.

METHODS

Eight boys and four girls (age=12.1, standard deviation=3.3) participated in this case-control study. Three-dimensional magnetic resonance images of both shoulders were acquired. The unimpaired shoulder served as a reference. Volumes of deltoid, pectoralis major, supraspinatus, infraspinatus, teres major, subscapularis were calculated based on 3D models, derived through image segmentation. Maximal isometric torques were collected in six directions.

FINDINGS

All the major muscles studied were significantly atrophied. The teres major demonstrated the biggest difference in atrophy between groups (51 percentage points), the pectoralis major was the least atrophied (23 percentage points). The muscle volume distribution was significantly different between shoulders. Muscle volume could predict maximal voluntary isometric torques, but the regression coefficients were weaker on the impaired side (72% to 91% of the strength could be predicted in the uninvolved side and 24% to 90% in the involved side and external rotation strength could not be predicted).

INTERPRETATION

This study demonstrates muscle atrophy varied across all the main shoulder muscles of the glenohumeral joint, leading to significant muscle volume imbalances. The weaker coefficients of determination on the impaired side suggest that other variables may contribute to the loss of strength in addition to atrophy.

Brachial plexus injury: treatment options and outcomes

The brachial plexus is a series of nerves formed by roots of cervical segments 5 to 8 (C5-C8) as well as the first thoracic nerve (T1). It functions to provide sensation and motor innervation to the skin and muscles of the chest and upper limb. It does so through different segments: roots, trunks, divisions, and cords. Injuries to the brachial plexus occur relatively frequently and are due mainly to traumatic accidents that lead to traction or compression of the nerve roots. When considering the etiology and treatment of such injuries, it is important to make a distinction between adult versus obstetric brachial plexus injury. Although several surgical treatment options are described and used for patients with brachial plexus injury, no perfect remedy currently exists. Prevention and safety should be the focus. At the same time, high-quality studies and new technology and techniques are needed to determine more effective treatments for this group.

Contributions of muscle imbalance and impaired growth to postural and osseous shoulder deformity following brachial plexus birth palsy: a computational simulation analysis

PURPOSE

Two potential mechanisms leading to postural and osseous shoulder deformity after brachial plexus birth palsy are muscle imbalance between functioning internal rotators and paralyzed external rotators and impaired longitudinal growth of paralyzed muscles. Our goal was to evaluate the combined and isolated effects of these 2 mechanisms on transverse plane shoulder forces using a computational model of C5-6 brachial plexus injury.

METHODS

We modeled a C5-6 injury using a computational musculoskeletal upper limb model. Muscles expected to be denervated by C5-6 injury were classified as affected, with the remaining shoulder muscles classified as unaffected. To model muscle imbalance, affected muscles were given no resting tone whereas unaffected muscles were given resting tone at 30% of maximal activation. To model impaired growth, affected muscles were reduced in length by 30% compared with normal whereas unaffected muscles remained normal in length. Four scenarios were simulated: normal, muscle imbalance only, impaired growth only, and both muscle imbalance and impaired growth. Passive shoulder rotation range of motion and glenohumeral joint reaction forces were evaluated to assess postural and osseous deformity.

RESULTS

All impaired scenarios exhibited restricted range of motion and increased and posteriorly directed compressive glenohumeral joint forces. Individually, impaired muscle growth caused worse restriction in range of motion and higher and more posteriorly directed glenohumeral forces than did muscle imbalance. Combined muscle imbalance and impaired growth caused the most restricted joint range of motion and the highest joint reaction force of all scenarios.

CONCLUSIONS

Both muscle imbalance and impaired longitudinal growth contributed to range of motion and force changes consistent with clinically observed deformity, although the most substantial effects resulted from impaired muscle growth.

CLINICAL RELEVANCE

Simulations suggest that treatment strategies emphasizing treatment of impaired longitudinal growth are warranted for reducing deformity after brachial plexus birth palsy.

Elbow Flexion Contractures in Childhood in Obstetric Brachial Plexus Lesions: A Longitudinal Study of 20 Neurosurgically Reconstructed Infants with 8-Year Follow-up

OBJECTIVE

 Little knowledge exists on the development of elbow flexion contractures in children with obstetrical brachial plexus lesion (OBPL). This study aims to evaluate the prognostic significance of several neuromuscular parameters in infants with OBPL regarding the later development of elbow flexion contractures.

METHODS

 Twenty infants with OBPL with insufficient signs of recovery in the first months of life who were neurosurgically reconstructed were included. At a mean age of 4.6 months, the following neuromuscular parameters were assessed: existence of flexion contractures, cross-sectional area (CSA) of upper arm muscles on MRI, Narakas classification, EMG results, and elbow muscle function using the Gilbert score. In childhood at follow-up at mean age of 7.7 years, we measured the amount of flexion contractures and the upper arm peak force (Newton). Statistical analysis is used to assess relations between these parameters.

RESULTS

 Flexion contractures of greater than 10 degrees occurred in 55% of our patient group. The relation between the parameters in infancy and the flexion contractures in childhood is almost nonexistent. Only the Narakas classification was related to the development of flexion contractures in childhood (p = 0.006). Infant muscle CSA is related to childhood peak muscle force.

CONCLUSION

 The role of infancy upper arm muscle hypotrophy/hypertrophy, reinnervation, and early elbow muscle function in the development of childhood elbow contractures remains unclear. In this cohort prediction of childhood flexion, contractures were not possible using infancy neuromuscular parameters. We suggest that contractures might be an adaptive process to optimize residual muscle function.

The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model

We assessed the role of subscapularis muscle denervation in the development of shoulder internal rotation contracture in neonatal brachial plexus injury. Seventeen newborn rats underwent selective denervation of the subscapular muscle. The rats were evaluated at weekly intervals to measure passive shoulder external rotation. After 4 weeks, the animals were euthanized. The subscapularis thickness was measured using 7.2T MRI axial images. The subscapularis muscle was then studied grossly, and its mass was registered. The fiber area and the area of fibrosis were measured using collagen-I inmunostained muscle sections. Significant progressive decrease in passive shoulder external rotation was noted with a mean loss of 58° at four weeks. A significant decrease in thickness and mass of the subscapularis muscles in the involved shoulders was also found with a mean loss of 69%. Subscapularis muscle fiber size decreased significantly, while the area of fibrosis remained unchanged. Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation.

The role of muscle imbalance in the pathogenesis of shoulder contracture after neonatal brachial plexus palsy: a study in a rat model

BACKGROUND

An internal rotation contracture of the shoulder is common after neonatal brachial plexus injuries due to subscapularis shortening and atrophy. It has been explained by 2 theories: muscle denervation and muscle imbalance between the internal and external rotators of the shoulder. The goal of this study was to test the hypothesis that muscle imbalance alone could cause subscapularis changes and shoulder contracture.

MATERIALS AND METHODS

We performed selective neurectomy of the suprascapular nerve in 15 newborn rats to denervate only the supraspinatus and the infraspinatus muscles, leaving the subscapularis muscle intact. After 4 weeks, passive shoulder external rotation was measured and a 7.2-T magnetic resonance imaging scan of the shoulders was used to determine changes in the infraspinatus and subscapularis muscles. The subscapularis muscle was weighed to determine the degree of mass loss. An additional group of 10 newborn rats was evaluated to determine the sectional muscle fiber size and muscle area of fibrosis by use of images from type I collagen immunostaining.

RESULTS

There was a significant decrease in passive shoulder external rotation, with a mean loss of 66°; in the thickness of the denervated infraspinatus, with a mean loss of 40%; and in the thickness and weight of the non-denervated subscapularis, with mean losses of 28% and 25%, respectively. No differences were found in subscapularis muscle fiber size and area of fibrosis between shoulders after suprascapular nerve injury.

CONCLUSIONS

Our study supports the theory that shoulder muscle imbalance is a cause of shoulder contracture in patients with neonatal brachial plexus palsy.

Evaluation of the muscle volumes of the transverse rotator cuff force couple in nonpathologic shoulders

BACKGROUND

The balance between the subscapularis muscle and the infraspinatus/teres minor muscles, often referred to as the rotator cuff transverse force couple (TFC), has been proposed to be a critical component for normal shoulder function. The relationship between the muscle volume and the power means that TFC can be evaluated with the measurement of the muscle volume of the subscapularis muscle and the infraspinatus/teres minor. The aim of this study is to evaluate an innovative computed tomography (CT)-based technique to measure the muscle volume and to evaluate if there is a significant difference between muscle volumes of both the subscapularis muscle and the infraspinatus/teres minor in nonpathologic shoulders.

MATERIALS AND METHODS

CT images of 27 shoulders (21 patients) with a full scapula and a proximal humeral head were evaluated. Two volume masks (subscapularis and infraspinatus/teres minor) were calculated on the basis of the assigned muscle contours on the transverse slices. The intraobserver and interobserver correlation coefficient was calculated.

RESULTS

The intraobserver and interobserver correlation coefficient was excellent. The correlation between the anterior and posterior part of the TFC was strong. There was no significant difference between the volume masks.

CONCLUSIONS

Muscle volume of the TCF can be quantified using CT images. In nonpathologic shoulders, there is no significant difference between the muscle volume of the anterior (subscapularis) and posterior part (teres minor/infraspinatus) of the TFC.

Glenoid morphology rather than version predicts humeral subluxation: a different perspective on the glenoid in total shoulder arthroplasty

BACKGROUND

Glenoid retroversion is thought be important in shoulder stability before and after shoulder arthroplasty; thus, many authors recommend glenoid reaming to correct retroversion and improve stability. Genetic analysis has revealed that glenoid vault and scapular development are controlled by different genes and environmental factors, resulting in diverse glenoid morphologies. We therefore analyzed the relative contribution of glenoid morphology and version to humeral head position.

MATERIALS AND METHODS

We obtained 121 shoulder computed tomography scans preoperatively for shoulder arthroplasty. Humeral subluxation and glenoid version were measured on the axial image at the middle of each glenoid. Glenoid morphology was characterized as biconcave, worn, displaced, dysplastic, angled, or neutral. The strength of the correlation between humeral subluxation, glenoid version, and glenoid morphology was analyzed.

RESULTS

Glenoid version did not correlate with humeral subluxation. The highest frequency of posterior subluxation was noted in biconcave glenoids. Shoulders with other glenoid morphologies were more likely to have anterior or central positioning of the humerus. The mean subluxation ratio for biconcave glenoids was 0.56 and was significantly different from all other morphologies (P < .02).

DISCUSSION/CONCLUSION

Even in the arthritic shoulder, glenoid orientation does not appear to explain the complex biomechanics of shoulder stability. The causes of humeral head subluxation before and after total shoulder arthroplasty are likely multifactorial and may include static and dynamic soft-tissue forces. The biconcave glenoid deserves more attention at surgery because of the high association with posterior subluxation.

Hypoplasia of the trapezius and history of ipsilateral transient neonatal brachial plexus palsy

We present two children with hypoplasia of the left trapezius muscle and a history of ipsilateral transient neonatal brachial plexus palsy without documented trapezius weakness. Magnetic resonance imaging in these patients with unilateral left hypoplasia of the trapezius revealed decreased muscles in the left side of the neck and left supraclavicular region on coronal views, decreased muscle mass between the left splenius capitis muscle and the subcutaneous tissue at the level of the neck on axial views, and decreased size of the left paraspinal region on sagittal views. Three possibilities can explain the association of hypoplasia of the trapezius and obstetric brachial plexus palsy: increased vulnerability of the brachial plexus to stretch injury during delivery because of intrauterine trapezius weakness, a casual association of these two conditions, or an erroneous diagnosis of brachial plexus palsy in patients with trapezial weakness. Careful documentation of neck and shoulder movements can distinguish among shoulder weakness because of trapezius hypoplasia, brachial plexus palsy, or brachial plexus palsy with trapezius hypoplasia. Hence, we recommend precise documentation of neck movements in the initial description of patients with suspected neonatal brachial plexus palsy.