Pathophysiology And Mechanism of injury

Pathophysiology of NTOS

The primary cause of nTOS is the compression of the brachial plexus, in the spinal nerve roots of C5-T1 that innervate the upper limb. This compression occurs mostly in the interscalene triangle however is also depicted in the costoclavicular space and beneath the pectoralis minor muscle (Grunebach et al., 2015).

Pathophysiology of VTOS

vTOS is caused by compression of the subclavian vein, most often in the costoclavicular space between the clavicle and the first rib. The vein may be compressed or occluded causing a venous stasis, clot formation or thrombosis, commonly referred to as Paget-Schroetter syndrome (Jones et al., 2019).

Pathophysiology of ATOS

aTOS is caused by the compression of the subclavian artery between the anterior scalene and the first rib, restricting blood flow to the upper extremities (Schneider et al., 2004). Arterial compression occurs at the level of the pectoralis minor tendon and the humeral head (Duwayri et al., 2011). aTOS incites intimal damage in the endothelium and subendothelial layer of the connective tissue causing turbulent blood flow and vessel dilation away from the heart. Undiagnosed aTOS may eventuate to a distal embolism and arterial thrombosis, causing acute distal upper limb ischemia.

Congenital and traumatic mechanisms of TOS

The pathological characteristics of TOS are elicited by a variety of mechanisms, including anatomical anomalies and traumatic experiences. Firstly, a myriad of anatomical variations can incite TOS. The presence of a cervical rib is prevalent in roughly two percent of the general population. It accounts for 30% of nTOS cases, as it narrows the thoracic outlet and compresses the neurovascular bundle in the brachial plexus (Stewman et al., 2014). The existence of a cervical rib is also considered to be a predisposing factor in aTOS as it causes a compression of the subclavian artery leading to possible stenosis or aneurysm. Further congenital anomalies include variations in the shape or position of the first rib. The presence of a supernumerary scalene muscle can cause prolonged nerve compression, resulting in microvascular changes leading to fibrosis in the connective tissue of the cervical spine. These anatomical variants can create muscular tension and narrow the thoracic outlet, exacerbating the potential for compression, thus leading to TOS (Sanders et al., 2007).

Furthermore, traumatic incidents, including high-impact motor vehicle accidents cause whiplash injuries, straining or damaging the scalene muscles, leading to compression of the brachial plexus. Displaced fractures of the clavicle can also directly compress the neurovascular structures of the thoracic outlet due to haemorrhaging and haematoma (Ferrante & Ferrante, 2017).

Pancoast tumours located at the lung’s apex can compress the brachial plexus, mimicking the symptoms of nTOS (Davis & Knight, 2008).

Presence of a cervical rib indicated via the arrow (Jones et al., 2019).

(Waseem, 2020).

Lifestyle factors That cause TOS

nTOS is caused by occupations and recreational activities that require heavy lifting or repeated overhead arm use (e.g., throwing a baseball or grabbing a rebound in basketball). These activities can cause overuse injuries, straining the pectoralis minor and anterior and middle scalene muscles, leading to swelling, haemorrhaging, and fibrosis (Ohman & Thompson, 2020).

Poor postures including exasperated thoracic kyphosis, rounded shoulders and forward head posture can also narrow the thoracic outlet increasing the pressure on the neurovascular structures (Levine & Rigby, 2018).

(Spine info, 2023).

(South Melbourne Physio, 2022).