Semiquantifying of fascicles of the C7 spinal nerve in the upper and lower subscapular nerves innervating the subscapularis and its clinical inference in Erb's palsy

Techniques for Managing the Subscapularis and Addressing Failures of the Tendon in Anatomic Total Shoulder Arthroplasty

Anatomic total shoulder arthroplasty (aTSA) is an accepted treatment for a variety of degenerative conditions of the glenohumeral joint. The manner in which the subscapularis tendon is handled during the approach in aTSA is not universally agreed on. Failure of the repair after aTSA has been shown to be associated with poorer outcomes in some cases. There is no consensus on how to treat failures, as all techniques described in the literature demonstrate shortcomings. The purpose of this review is to evaluate the methods of handling the tendon in aTSA and to review options for treating failure following surgery. [Orthopedics. 2023;46(5):e264-e272.].

Comparison of the Goutallier Classification of Fatty Infiltration for the Subscapularis With a Novel Modified Classification

Background

Fatty infiltration in the subscapularis muscle extends to the upper portion of the muscle first and then to the lower portion only after some degree of fatty change has taken place in the upper region. Although the Goutallier classification is the most widely used method to categorize fatty infiltration, how to accurately and reliably determine the extent of infiltration is controversial.

Purpose

To examine a modified classification that is more reliable in (1) assessing fatty infiltration of the subscapularis muscle and (2) predicting the structural integrity of the repaired tendon by identifying cutoff points for retear.

Study Design

Cohort study (diagnosis); Level of evidence, 3.

Methods

This study retrospectively examined the records of 545 patients who underwent arthroscopic repair for a subscapularis tear. Two shoulder surgeons reviewed the preoperative magnetic resonance imaging scans of all enrolled patients and evaluated the fatty infiltration of the subscapularis muscle based on the original Goutallier classification, as well as a novel modified Goutallier classification designed to measure the proportion of fat and muscle in the upper and lower portions of the muscle separately. Intra- and interobserver agreement of the reviewers was calculated using κ statistics. Using receiver operating characteristic curve analysis, we determined the cutoff point for the particular fatty infiltration grade related to the occurrence of retear for each classification scheme.

Results

The κ values for interobserver reliability were 0.743 and 0.856 for the original and modified Goutallier classifications, respectively, with the modified classification having significantly higher reliability (Z = 4.064; P < .001). Cutoff points for the fatty infiltration grade associated with retear were 2.5 for the original Goutallier classification (sensitivity, 65.3%; specificity, 95.6%; accuracy, 87.8%) and 3.5 for the modified classification (sensitivity, 52.5%; specificity, 97.8%; accuracy, 89.7%).

Conclusion

In assessing fatty infiltration of the subscapularis muscle, the modified Goutallier classification showed higher reliability than the original Goutallier classification. The cutoff point for potential retear (grade 3.5) was at a point where the fatty infiltration extended to the lower portion of the subscapularis muscle.

Anatomical feasibility study of the infraspinatus muscle neurotization by lower subscapular nerve

OBJECTIVES

To investigate the anatomical feasibility of the infraspinatus branch of the suprascapular nerve (IB-SSN) reconstruction by lower subscapular nerve (LSN) transfer.

METHODS

The morphological study was performed on 18 adult human cadavers. The length of the distal stump of the IB-SSN, the length of the LSN available for reconstruction and diameter of both stumps were measured. The feasibility study of the LSN to IB-SSN transfer was performed.

RESULTS

The mean length of the IB-SSN to the end of its first branch was 40.9 mm (±4.6). Its mean diameter was 2.3 mm (±0.3). The mean length of the LSN stump, which was mobilized from its original course and transferred to reach the distal stump of the IB-SSN was 66.5 mm (±11.8). Its mean diameter was 2.1 mm (±0.3). The mean ratio between LSN and IB-SSN diameters was 0.9 (±0.1). The nerve transfer was feasible in 17 out of 18 cases (94.4%).

CONCLUSION

This study demonstrates that direct LSN to IB-SSN transfer is anatomically feasible in most cases in the adult population. It may be used in cases of complex scapular fractures resulting in severe suprascapular nerve injury.

A meta-analysis on the anatomical variability of the brachial plexus: Part III - Branching of the infraclavicular part

INTRODUCTION

The anatomy of the brachial plexus has been a subject of interest to many researchers over time resulting in an inconsistent amount of data. Previously, our team had published two evidence-based studies on the anatomical variations involving the brachial plexus, therefore the aim of this study was to analyze the findings regarding the infraclavicular part of the brachial plexus with the use of meta-analytic techniques to complete the comprehensive series.

MATERIAL AND METHODS

Major scientific databases were extensively searched to compile anatomical studies investigating the morphology of the infraclavicular part of the brachial plexus. Extracted data were classified based on our proposed classification system and subsequently analyzed with the use of random effects meta-analysis to state the pooled prevalence estimates of the distinct variation patterns.

RESULTS

A total of 75 studies (4772 upper limbs) were selected for the meta-analysis. The branches of the lateral cord, including the lateral pectoral nerve and musculocutaneous nerve, resembled their usual origin in 76.8% (95% CI 50-96%) and 98.8% (95% CI 98-100%), respectively. The medial pectoral nerve, medial brachial cutaneous nerves, medial antebrachial cutaneous nerve and ulnar nerve emerging from the medial cord were observed originating from their usual origins in 90.9% (95% CI 68-100%), 90.7% (95% CI 73-100%), 87.9% (95% CI 67-99%) and 97.7% (95% CI 94-100%), respectively. Lastly, nerves branching from the posterior cord, including the superior and inferior subscapular nerves, thoracodorsal nerve, axillary nerve and radial nerve, originated as per textbook description in 90.7% (95% CI 80-98%), 76.1% (95% CI 61-89%), 90.1% (95% CI 84-95%), 79.8% (95% CI 68-90%) and 99.0% (95% CI 96-100%), respectively. Moreover, the usual origin of the median nerve from the lateral and medial cord via the corresponding roots was encountered in 89.7% (95% CI 84-95%) of cases.

CONCLUSIONS

The nerves originating from the infraclavicular part of the brachial plexus exhibit a wide spectrum of possible origins. However, the usual patterns were significantly the most common types present in more than three quarters of cases. Especially clinicians might profit from the enhanced understanding of the brachial plexus anatomy presented herein, since we offer a strong guide for handling the anatomically challenging pathologies in this specific area.

Lower subscapular nerve transfer for axillary nerve repair in upper brachial plexus palsy

BACKGROUND

The potential to utilize the lower subscapular nerve for brachial plexus surgery has been suggested in many anatomical studies. However, we know of no studies in the literature describing the use of the lower subscapular nerve for axillary nerve reconstruction to date. This study aimed to examine the effectiveness of this nerve transfer in patients with upper brachial plexus palsy.

METHODS

Of 1340 nerve reconstructions in 568 patients with brachial plexus injury performed by the senior author (P.H.), a subset of 18 patients underwent axillary nerve reconstruction using the lower subscapular nerve and constitutes the patient group for this study. The median age was 48 years, and the median time between trauma and surgery was 6 months. A concomitant radial nerve injury was found in 8 patients.

RESULTS

Thirteen patients completed a minimum follow-up period of 24 months. Successful deltoid recovery was defined as (1) muscle strength MRC grade ≥ 3, (2) electromyographic signs of reinnervation, and (3) increase in deltoid muscle mass. Axillary nerve reconstruction was successful in 9 of 13 patients, which represents a success rate of 69.2%. No significant postoperative weakness of shoulder internal rotation or adduction was observed after transecting the lower subscapular nerve.

CONCLUSIONS

The lower subscapular nerve can be used as a safe and effective neurotization tool for upper brachial plexus injury, having a success rate of 69.2% for axillary nerve repair. Our technique presents a suitable alternative for patients with concomitant radial nerve injury.

Anatomy of the Subscapularis: A Review

The subscapularis is the largest and most powerful muscle of the rotator cuff. Occupying the vast majority of the subscapular fossa, it is the only internal rotator of the rotator cuff. The subscapularis innervation is classically taught as a dual innervation of 1 upper subscapular and 1 lower subscapular nerve arising from the posterior cord of the brachial plexus. However, there is a large amount of research that suggests there is significant variance in the innervation of the muscle from multiple upper subscapular nerves to multiple lower subscapular nerves arising from various portions of the plexus. Although one of the main functions of the subscapularis is to internally rotate the humerus, there is substantial evidence that displays its importance in glenohumeral stability as well. The insertion of the subscapularis is both tendinous as well as muscular. The more superior tendinous portion inserts on the lesser tuberosity while the more muscular portion inserts inferior to the less tuberosity. The medial to lateral spread of the insertion is quite variable ranging from only on the lesser tuberosity to merging with fibers from the supraspinatus. Understanding the anatomy of the subscapularis improves subscapularis management during shoulder arthroplasty including techniques for takedown, release, and repair.

Magnetic resonance imaging patterns of mononeuropathic denervation in muscles with dual innervation

Magnetic resonance imaging (MRI) of mononeuropathy in muscles with dual innervation depicts geographic denervation corresponding to the affected nerve. Knowledge of the normal distribution of a muscle's neural supply is clinically relevant as partial muscle denervation represents a potential imaging pitfall that can be confused with other pathology, such as muscle strain. This article reviews the normal innervation pattern of extremity muscles with dual supply, providing illustrative examples of mononeuropathy affecting such muscles.

Nerve supply of the subscapularis during anterior shoulder surgery: definition of a potential risk area

PURPOSE

The purpose of the study was to evaluate the position of the subscapular nerves relative to surgical landmarks during exposure and to analyze the pattern of innervation of the subscapularis to avoid injury during anterior shoulder surgery.

METHODS

20 embalmed human cadaveric shoulder specimens were used in the study. The muscular insertions of the subscapular nerves were marked and their closest branches to the musculotendinous junction and the coracoid process were measured in horizontal and vertical distances. In addition, the innervation pattern of each specimen was documented.

RESULTS

14/20 specimens showed an innervation of the subscapularis with an upper, middle and lower subscapular nerve branch. Even though the nerve branches were in average more than 2 cm medial to the musculotendinous junction, minimal distances of 1.1-1.3 cm were found. The mean vertical distance as measured from the medial base of the coracoid to the nerve innervation point into the muscle was 0.7 cm for the upper nerve branch, 2.2 cm for the middle nerve branch and 4.4 cm for the lower nerve branch.

CONCLUSIONS

The subscapularis has a variable nerve supply, which increases the risk of muscle denervation during open shoulder surgery. Dissection or release should be avoided at the anterior aspect of the subscapularis muscle more than 1 cm medial to the musculotendinous junction. In approaches with a horizontal incision of the subscapularis, splitting should be performed at a vertical distance of 3.2-3.6 cm to the coracoid base to avoid iatrogenic subscapular nerve injuries.