Subclavius posticus muscle: supernumerary muscle as a potential cause for thoracic outlet syndrome

Surgical resolution of chronic thoracic pain stemming from a rare osteo-muscular conflict: A case report

INTRODUCTION

Chronic thoracic pain presents significant diagnostic and therapeutic challenges, particularly when arising from rare osteo-muscular conflicts. This report details a unique case of chronic pain due to an osteo-muscular conflict between the right tenth rib and the internal oblique muscle, highlighting the complexities involved in diagnosis and the potential for surgical resolution.

CASE PRESENTATION

A 33-year-old male with a decade-long history of chronic right hemithorax pain, unresponsive to conservative treatments, underwent diagnostic evaluation. Advanced imaging techniques, including a thoracic CT scan, revealed an ipodense area between the ninth and tenth ribs, suggesting an osteo-muscular conflict. Surgical intervention, specifically a partial costectomy of the right tenth rib, was pursued, resulting in significant symptom relief and improved quality of life.

CLINICAL DISCUSSION

This case underscores the importance of considering advanced diagnostic evaluations in persistent chronic pain cases and the effectiveness of targeted surgical interventions in resolving anatomical conflicts. It contributes to the body of knowledge on managing complex musculoskeletal conditions and underscores the need for personalized treatment approaches.

CONCLUSION

Surgical intervention in selected cases of chronic pain due to rare anatomical conflicts can offer significant relief and enhance patient outcomes. This case advocates for a nuanced approach to the diagnosis and treatment of chronic thoracic pain, emphasizing the role of advanced imaging and the potential benefits of surgical resolution.

Prevalence and anatomy of the anomalous subclavius posticus muscle and its clinical implications with emphasis in neurogenic thoracic outlet syndrome: Scoping review and meta-analysis

BACKGROUND

The subclavius muscle runs underneath the clavicle. However, there have been a few reports of a duplicated subclavius muscle which is commonly referred to as subclavius posticus muscle due to its orientation being posterior to the proper subclavius muscle. Its occurrence seems to potentially create a narrowing interval at the superior thoracic aperture as it crosses over the brachial plexus. It might also have functional influence on the shoulder girdle.

PURPOSE

To provide comprehensive gross anatomy description of the variant "subclavius posticus muscle" and to investigate its reported clinical implications with emphasis on its involvement in causing brachial plexus compression.

BASIC PROCEDURES

A scoping review with meta-analysis of the gross anatomy of the subclavius posticus muscle was conducted along with investigating its correlation to the thoracic outlet syndrome. Forty-seven articles were pooled through two rounds of the selection process. The relevant information was extracted and meta-analyzed.

MAIN FINDINGS

The scoping review and meta-analysis of the 47 articles revealed a total prevalence of 11/2069 (4.9%); 10/1369 (5.1%) in cadaveric studies, and 1/700 (5.0%) in MRI studies. The subclavius posticus muscle is a short triangular muscle with an average length of 12 cm and an average width of 1 cm. It originates from the sternal end of the first rib in most cases with reported variants of one case originating from the costoclavicular ligament and one case where it was fused with the proper subclavius muscle. Its insertion is more variable: on the superior border of the scapula with variable length in 71.35%, on the coracoid process of the scapula in 25.42%, and on the clavicle in 0.90%. The subclavian nerve seems to be the dominant nerve supply with a 57.6% prevalence, while 25.8% are innervated by the suprascapular nerve. Other reported nerves were the nerve to the myolohyoid (4.5%), accessory phrenic nerve (4.5%), and a direct branch from the brachial plexus (2.0%). The blood supply was reported (only once) to be from the suprascapular artery. However, the venous drainage was not established at all.

PRINCIPAL CONCLUSIONS

The subclavius posticus muscle is a variant muscle occurring with a reported overall prevalence of 4.9%. It can compress the brachial plexus as it runs across at the space of the superior thoracic aperture with exquisite contact, and this can lead to a neurogenic thoracic outlet syndrome. It also can be involved in the vascular thoracic outlet syndrome. Lastly, it is important not to omit its potential influence in shoulder joint instability to some extent.

Supraclavius muscle observed during anterior scalenectomy for thoracic outlet syndrome: A report of two cases and review of the literature

Background

Thoracic outlet syndrome (TOS) is a clinical diagnosis caused by compression of neurovascular structures in the thoracic outlet. There are a variety of structures that cause compression implicated in TOS. TOS patients frequently require surgical decompression. Various structural anomalies encountered during decompression have been reported in the literature.

Case Description

We present two females (ages 42 and 45) that each underwent anterior scalenectomy for thoracic outlet decompression through a supraclavicular approach. A supraclavius muscle anomaly was observed in both patients. Analogous to the two reports previously described in the literature, the muscle inserted, along the medial superior undersurface of the clavicle and originated dorsally along the trapezius muscle. This is not to be confused with the subclavius posticus muscle, which originates from the first rib and inserts on the upper border of the scapula.

Conclusion

These two cases represent just the third and fourth ever descriptions of a supraclavius muscle anomaly encountered during TOS surgery. Due to the wide variety of anatomical variations encountered during TOS surgery, it is not only crucial for continued reporting of such anatomical variations to be reported in the literature but equally important for clinicians that treat TOS to be aware of such variations.

Paralysis of the Upper Extremity Due to Acute Thoracic Outlet Syndrome Caused by the Subclavius Posticus Muscle: A Case Report With Literature Review

The subclavius posticus muscle is a rare aberrant muscle that traverses from the costal cartilage of the first rib posterolaterally to the superior border of the scapula. We report a patient having persistent paralysis of shoulder abduction with wrist and finger extension after a humeral neck fracture. Electromyography (EMG) examination revealed injuries to several upper extremity peripheral nerves, including the radial, axillary, and musculocutaneous nerves. Magnetic resonance imaging (MRI) performed at 10 months post-injury showed severe entrapment of the left brachial plexus by the subclavius posticus muscle at the thoracic outlet. The diagnosis of brachial plexus injury due to a rare abnormal subclavius posticus muscle was typically delayed until the MRI was performed for unexplained multiple peripheral nerve palsy. Resection of the aberrant muscle and brachial plexus decompression did not yield significant improvement in the patient’s radial nerve palsy until 6 months after surgery. Entrapment of the brachial plexus caused by the subclavius posticus muscle can cause symptoms of acute thoracic outlet syndrome following trauma to the upper extremity. In a case of inexplicable multiple peripheral nerve injuries in the upper extremity that are not proportional to the degree of trauma, MRI imaging along with EMG is required.

The prevalence and characteristics of the subclavius posticus muscle in the adult population on MRI

PURPOSE

The subclavius posticus muscle (SPM) is an aberrant muscle, and the presence of the SPM has a clinical significance, since the SPM might lead to thoracic outlet syndrome (TOS). To date, no radiological study has been evaluated the prevalence of the SPM in the adult population. In this study, we aimed to assess the prevalence of the SPM using magnetic resonance imaging (MRI).

METHODS

We retrospectively reviewed brachial plexus, neck, and thoracic MRI of the patients who underwent MRI for various pathologies. Only the patients whose MRI examinations did not have sufficient image quality and the patients who had any pathology that directly involved the thoracic outlet region were excluded from the study. The observers assessed images in the coronal plane to detect the presence of the SPM. The thickness of the muscle and the distance between the SPM and brachial plexus were also noted.

RESULTS

MRI examinations of 350 patients, 174 males and 176 females, were evaluated. SPM was detected in 29 patients (8.3%). In 6 patients (1.7%), we identified bilateral SPM. The mean thickness of the muscle was 6.10 ± 1.60 mm (range 2.5-10 mm). In 21 sides (60%), the brachial plexus and SPM were touching each other. In the remaining 14 sides (40%), the mean distances between the SPM and brachial plexus were 2.32 ± 0.62 mm (range from 1.7 to 3.6 mm).

CONCLUSIONS

We conducted the first radiological study that evaluated the prevalence of the SPM, and we also assessed the thickness of the SPM and the distance between the SPM and brachial plexus. We highlight that our study might be accounted as a first step for future studies to assess the role of the SPM in TOS.

An Aberrant Subclavius Posticus Muscle: A Case Report

OBJECTIVE

An aberrant subclavius posticus muscle was found during routine dissection of the left infraclavicular fossa of a 60-year-old male cadaver.

PRESENTATION

This aberrant muscle arises antero-medially, from the costoclavicular ligament, runs postero-laterally, over the trunks of the brachial plexus, and postero-lateral has a common insertion with the omohyoid muscle.

CONCLUSION

The presence of such an aberrant muscle may cause a dynamic compression of the subclavian artery and brachial plexus.

Absence of the subclavius muscle with contralateral subclavius posticus muscle: first imaging report

We present a case of a 56-year-old man with pain in in his right anterior shoulder, arm, and hand. MRI studies demonstrated absence of the subclavius muscle with contralateral subclavius posticus muscle. To our knowledge, imaging of the total absence of subclavius muscle has not been previously described. Understanding and recognition of subclavius posticus muscle are important for its potential role in thoracic outlet syndrome.

Thoracic Outlet Syndrome in the Overhead Athlete: A Report of 2 Cases of Subclavius Posticus Muscle

Subclavius posticus muscle is a supernumerary anatomical variation of the subclavius muscle. The aim of this study was to show the possible contribution of the posticus muscle in the development of unilateral thoracic outlet syndrome (TOS) in overhead athletes, presenting hypertrophy of the dominant arm due to their sport activity. Reported here are 2 young overhead athletes complaining pain, paresthesia, weakness in the dominant upper limb, although presenting none of the main shoulder and neurological disorders. After developing subclavian vein thrombosis, TOS was suspected and finally diagnosed by dynamic magnetic resonance angiography, which also showed bilateral subclavius posticus muscle in both patients. Despite bilateral subclavius posticus, TOS was only evident in the dominant limb in which the association of hypertrophy of lateral cervical muscles, resulting from the overhead sport activity, to the subclavius posticus likely led to a significant reduction of the upper thoracic outlet space.

Neurogenic thoracic outlet syndrome due to subclavius posticus muscle with dynamic brachial plexus compression: a case report

Background

Neurogenic thoracic outlet syndrome is an underestimated cause of brachial weakness and pain. The subclavius posticus muscle (SPM) is an aberrant muscle originating from the medial aspect of the first rib reaching to superior border of the scapula, which may cause, depending on its activation, dynamic compression of the brachial plexus.

Case presentation

In the present study, we report about a 32-year-old male caucasian patient with weakness in radial deviation of his left hand. An isolated macrodactyly of his left middle finger had been operated twice. Electroneurography showed a carpal-tunnel-syndrome (CTS) on the left side. MRI of the brachial plexus revealed an additional muscle in the costoclavicular space, identified as SPM. To our knowledge, this is the second case report of a neurogenic thoracic outlet syndrome due to SPM, and the first case described with isolated macrodactyly and CTS in the same patient.

Conclusion

If complaints about hand weakness are only reported in cases of distinct hand positions, a dynamic compression of the brachial plexus by SPM may be the cause. A neurogenic thoracic outlet syndrome may facilitate the development of CTS.

Subclavius posticus: an anomalous muscle in association with suprascapular nerve compression in an athlete

Subclavius posticus is a rare anomalous muscle that traverses from the costal cartilage of the first rib posterolaterally to the superior border of the scapula. We present an athlete who presented with incapacitating suprascapular nerve compression associated with a subclavius posticus diagnosed by MRI. Symptoms were relieved, and function was restored by decompression of the nerve and excision of the anomalous muscle. We present this case to bring awareness of the subclavius posticus as an anatomic variant and a potential additional source for compression in suprascapular neuropathy. We recommend high-resolution magnetic resonance imaging to evaluate cases of isolated suprascapular neuropathy.

LEVEL OF EVIDENCE

V.

The subclavius posticus muscle: an unusual cause of thoracic outlet syndrome

We present the case of a 30-year-old female, complaining of thoracic outlet compression symptoms caused by a supernumerary muscle, the subclavius posticus, accompanied by a caudally inserted middle scalenus muscle on the second rib. This rare anatomic variant was clearly shown on CT angiography and MRI images and surgical treatment was successful. As first described by Rosenmuller in 1800, subclavius posticus is a supernumerary muscle originating from the cranial surface of the sternal end of the first rib, running laterodorsally beneath the clavicle, and inserting into the superior border of the scapula. Its role in thoracic outlet syndrome has been seldom demonstrated in living patients nor described in imaging, although it is theoretically easily recognizable on modern imaging modalities. It should be taken into account during workout of patients with thoracic outlet syndrome, since it can be potentially treated.

A review of thoracic outlet syndrome and the possible role of botulinum toxin in the treatment of this syndrome

The objective of this paper is to discuss the classification, diagnosis, pathophysiology and management of Thoracic outlet syndrome (TOS). Thoracic outlet syndrome (TOS) is a complex entity that is characterized by different neurovascular signs and symptoms involving the upper limb. TOS is defined as upper extremity symptoms due to compression of the neurovascular bundle in the area of the neck just above the first rib. Compression is thought to occur at one or more of the three anatomical compartments: the interscalene triangle, the costoclavicular space and the retropectoralis minor spaces. The clinical presentation can include both neurogenic and vascular symptoms. TOS can be difficult to diagnose because there is no standardized objective test that can be used and the clinician must rely on history and several positive findings on physical exam. The medial antebrachial cutaneous nerve conduction may be a sensitive way to detect pathology in the lower trunks of the brachial plexus which is promising for future research. Treatment options continue to be conservative and surgical. However, for those who have failed physical therapy there is research to suggest that botulinum toxin may help with symptom relief. However, given that there has been conflicting evidence, further research is required using randomized controlled trials.

A sledgehammer on the brachial plexus: thoracic outlet syndrome, subclavius posticus muscle, and traction in aggregate

Reported here is a 30-year-old man who was seen because of pain and weakness in the upper extremities after a tractional injury. Physical examination revealed significant atrophy in the left deltoid and right intrinsic hand muscles, generalized hypoesthesia, decreased deep tendon reflexes bilaterally, and decreased strength in various muscle groups. Roos (right) and hyperabduction (bilateral) tests were positive. Electrodiagnostic studies were consistent with bilateral brachial plexopathy. Cervical radiographs showed long transverse process of C7 on the right side and a small rudimentary rib articulating with C7 on the left side. Brachial plexus magnetic resonance imaging demonstrated an aberrant muscle and compressive brachial plexus injury on the left side. Surgery via transaxillary approach was performed on the left side. The occurrence of traumatic brachial plexopathy in the presence of underlying thoracic outlet syndrome and subclavius posticus muscle is discussed for the first time in the literature.

Axillary arch: Potential cause of neurovascular compression syndrome

During routine bilateral dissection of 64 upper limbs in 32 adult human cadavers, four cases of an axillary arch, a muscular anomaly, were found. In one case, the axillary arch presented on both sides and in two cases it presented unilaterally on the right side. The innervation and relationships of the axillary arches are reported and the surgical significance of the anomaly is discussed.