Thoracic Outlet Syndrome (TOS) is a group of disorders that results in compression of the brachial plexus and subclavian axillary vessels in the area of the thoracic outlet [1]. The structures involved in TOS include the clavicle, first rib, and scalene muscles. TOS occurs in three spaces: the intercostal-scalene triangle, costoclavicular space, and coracopectoral space [2]. Peer et al. first proposed the term TOS in 1956 to summarize symptoms caused by compression of the neurovascular bundle [3], and the disease was termed “TOS” by Rob and Standeven in 1958 [4]. TOS occurs more frequently in women than in men and develops in patients in their third or fifth decades of life [5]. TOS is usually classified into neurogenic, arterial, and venous TOS [6]. Common causes of TOS are congenital, acquired, or traumatic. It can be further divided into arterial vascular, venous vascular, true neurologic, traumatic neurovascular, and disputed types [7].

The brachial plexus, subclavian artery, and vein are the main structures passing through the thoracic outlet. Initially, the subclavian artery and brachial plexus pass through the scalene triangle, which is bordered by the anterior and middle scalene muscles and the first rib. Then then brachial plexus, subclavian artery, and vein run medially to the anterior scalene muscle in the costoclavicular space, which is formed by the first rib and clavicle. Finally, the coracopectroal space is bordered by the ribs and pectoralis minor muscles. The brachial plexus and axillary arteries pass through this space. It is important to consider the anatomical structures of the thoracic outlet while determining the treatment options for patients with TOS.

The symptoms of TOS vary between studies. The common symptoms of neurogenic TOS are characterized by neuropathic pain, paresthesia, numbness, and weakness [8]. The lower trunk (C8-T1) is the most common site of isolated distribution, and most patients with TOS exhibit lower trunk symptoms with or without upper trunk symptoms [9]. Pain can occur on palpation above the entrapped site and worsen with exertion. In venous TOS, upper-limb edema is common and sometimes shows cyanotic coloration and dilated superficial veins in the upper limb [10]. In arterial TOS, non-radicular pain, discomfort, numbness, coldness, and paleness of the upper limb can be present [11]. TOS can be misdiagnosed as other disorders that show similar symptoms, such as radicular, muscle-, or tendon-origin pain. The physical examination should include a detailed history of symptoms and provocative tests such as the Adson, Wright, or Roos tests, which are commonly used for the diagnosis of neurogenic TOS [12]. The Adson and Wright maneuvers were performed to check if the TOS symptoms were aggravated by a certain posture. The physician palpated the radial pulse on the affected upper limb and evaluated the decrease or absence of an ipsilateral radial pulse in specific postures. In the Roos test, the patient abducts and externally rotates his shoulders to 90° with the elbows flexed and opens and closes the hands for 3 min. If the pain or weakness was aggravated with this maneuver, the test was considered positive. Radiographs of the cervical spine, neck, and chest should be included to visualize the presence of cervical ribs, prominent C7 transverse processes, and other bony abnormalities. Magnetic resonance imaging, electromyography, and nerve conduction studies can also be used to identify neurogenic TOS [9]. An MRI was performed to identify edema, fibrotic bands, or high signal intensity in the brachial plexus. In electromyography, muscle fibers innervated by C8 and T1 roots can accompany denervation potentials. In a nerve conduction study, the motor part of the median nerve and the medial cutaneous nerve of the forearm showed slow conduction velocities.

The mobility of the shoulder should be thoroughly assessed in patients with TOS. Patients with TOS often show depressed and anteriorly shifted shoulders, a protracted scapula, and a flexed head posture [13,14]. When this abnormal position of the shoulder is combined with movements such as 90° of flexion or abduction, symptoms can be aggravated due to a decrease in the costoclavicular space, increased friction in the neurovascular bundle in the subpectoral bundle, and shortening of the sternocleidomastoid. This can also lead to the shortening of the scalene and pectoralis muscles, resulting in head and neck misalignment and postural abnormalities [15].

There is no definite consensus on the appropriate treatment method for TOS, and the treatment usually varies depending on the type of TOS. Patients with venous or arterial TOS usually undergo surgery, considering the severity of the injury [1]. Thrombolysis with a continuous infusion of a plasminogen activator is most commonly used for venous TOS [16]. Thrombolysis or embolectomy is the most effective treatment for arterial TOS [17]. When they do not respond to these less invasive treatments for 4-6 months, surgical treatments, such as first rib or cervical rib resection, are indicated [18]. In contrast, patients with neurogenic TOS are typically treated conservatively. The conservative treatment includes oral medication, injections, and rehabilitation programs. Oral medications are commonly administered to manage neuropathic pain [19]. Nonsteroidal anti-inflammatory drugs (NSAIDs) can help decrease excessive anti-inflammatory responses initially, but long-term use of NSAIDs is not recommended owing to potential health risks [20]. Injections using corticosteroids and botulinum toxin are also used in muscles such as the scalene and pectoralis to relieve the symptoms of neurogenic TOS patients [2]. Rehabilitation programs are effective in relieving symptoms in neurogenic TOS patients [12]. Rehabilitation programs usually include exercise, activity modification, and patient education [12,21]. Frequently, stretching and strengthening exercises targeting the back and shoulder muscles are recommended [2,22]. Daily modification and postural education have additive effects on augmenting the benefits of rehabilitation therapy [18,23]. The effect of manipulation therapy on the thoracic outlet is still controversial; it may be effective for widening the thoracic outlet but can worsen the symptoms by provocating the neurovascular bundle [24,25].

Exercise programs

Exercise programs focusing on proper scapular function during upper-body movements, head and pelvis alignment, and breathing techniques have been reported to be useful for the symptoms of TOS [1,26,27]. Stretching of the scalene and pectoralis muscles is commonly recommended, considering that shortening of these muscles, which border the thoracic outlet, can aggravate the symptoms of TOS [15]. Strengthening exercises of the rhomboids, lower trapezius, and cervical erector muscles using dumbbells or resistance bands can improve muscle endurance, although they cannot change the overall pathophysiology of TOS [15]. A combination of strengthening, stretching, and postural correction is usually recommended [14,26]. An overview of the exercise programs recommended for the treatment of TOS is presented in Table 1.

Table 1 . A brief summary of exercise programs that are recommended for the treatment of TOS.

Exercise programs	Goal
Stretching exercises (scalenes and pectoralis)	Lengthening of the shortened muscles that can lead to entrapment of the neurovascular structures of the thoracic outlet
Strengthening exercises (rhobmoids, lower trapezius, cervical erectors)	Improve muscle endurance
Shoulder girdle exercises	Correct shoulder girdle depression and depress the first rib
Nerve gliding exercise	Decrease extrinsic and intraneural pressure, mitigate scarring, and minimize irritation of the surrounding neurovascular structures
Head and pelvis alignment	Correct abnormal muscle mechanics that are affect posture, gait, and alignment of the axial skeleton
Proper breathing exercises	Encourage rib depression and discourage over-activation of paraspinal muscles

The exercise protocol for NTOS was first designed by Peet et al. in 1956 [28]. He focused on the morphodynamic problems related to the shoulder girdle, which may aggravate TOS. Peet’s protocol consisted of moist heat, massage, postural correction, strengthening of the levator scapulae muscle, and stretching of the pectoralis minor muscle [28]. Peet’s protocol aimed to strengthen muscles that open the thoracic outlet by raising the shoulder girdle (e.g., trapezius and sternocleidomastoid muscles) and stretch muscles that close the thoracic outlet (e.g., lower trapezius and scalene muscles) to achieve postural correction. Later, more complex rehabilitation programs were designed to restore muscle balance, and several modifications to Peet’s protocol have been suggested. These included isometric exercises for the serratus anterior and pectoralis minor muscles and exercises for depressing the first rib and strengthening the posterior spinal muscles [15]. For example, Britt’s method adds shoulder girdle exercises using a strapping device to elevate the shoulders. It also included the following exercises: cervical retraction exercises, stretching exercises for shoulder girdle elevators, and strengthening of the lower scapular stabilizers and shoulder girdle elevators [15].

Exercise programs focusing on the range of motion were also designed. Levin et al. recommended specific exercise programs that include shoulder flexion ranging from 0° to 30° with a horizontal abduction of 40° [27]. Shoulder flexion progressed from 45° to 90°, and functional overhead tasks were performed to target the scapular muscles, such as the middle and lower trapezius and rhomboids. Strengthening of the serratus anterior muscle was also included; however, horizontal adduction was limited to avoid injury [26]. The authors also recommended programs involving stretching of the scalene and pectoralis muscles, along with strengthening of the cervical spinal and lower trapezius muscles, as effective treatments for TOS.

The importance of correcting abnormal scapular kinematics has been addressed. In 2010, Watson et al. proposed exercises aimed at correcting shoulder girdle depression (“dropping shoulder”) in patients with neurogenic TOS. Shoulder girdle depression can lead to abnormal scapular kinematics and induce traction stress on the neurovascular bundle of the thoracic outlet. The program progressed from lower to broader ranges of shoulder abduction and flexion and focused on training the scapular muscles in more functional movement patterns. Exercises were developed to decompress the thoracic outlet by elevating the shoulder girdle and restoring normal scapular control [26].

The nerve gliding exercises for TOS were also found to be beneficial for the treatment of TOS. In 2004, Crosby et al. suggested that tendon and nerve gliding exercises decreased extrinsic and intraneural pressure, mitigated scarring, and minimized irritation of the surrounding neurovascular structures [29]. The rehabilitation program included stretching (upper trapezius, scalene, and pectoralis) and strengthening (cervical extensors, scapular adductors, and scapular retractors) exercises, cervical range of motion exercises, and shoulder pendulum exercises [29]. Another study also reported that exercises including nerve gliding, postural, and shoulder girdle exercises are effective in improving neural mobility and relieving neural tension in the brachial plexus [30]. It was also found that adding cervical traction to nerve-gliding exercise programs effectively decompressed the brachial plexus [31,32].

Aerobic exercises, such as walking or diaphragmatic breathing exercises, may also have an additive effect on the symptoms of TOS when combined with stretching and strengthening exercises [31]. Breathing exercises may encourage rib depression and discourage over-activation of the paraspinal muscles [32]. Restoring and retraining overdeveloped faulty respiratory muscles seem to be effective for the treatment of TOS [32].

It remains controversial whether it would be beneficial to strengthen or stretch the muscles responsible for shoulder elevation [1]. In addition, the appropriate amount of exercise dosage, including frequency, number of sets, and repetitions, is still controversial [31]. Some studies recommended exercising five times a day for 3 weeks [28], while others recommended five to 10 times a day [33] or 20 repetitions three times a day [26].

Treatment depends on the type of TOS used. For patients with venous or arterial TOS, thrombolysis or embolectomy is usually considered first; however, when they do not respond to these treatments, surgical treatments are indicated. Rehabilitation programs for neurogenic TOS include stretching and strengthening exercises for the neck and shoulders. Various types of exercise appear to be beneficial for the treatment of neurogenic TOS. More studies on the appropriate exercise dosage, including frequency, number of sets, and repetitions, are warranted in the future.

None.

No potential conflict of interest relevant to this article was reported.