The cause is not currently known, and the condition appears to be multifactorial. Several candidate genes (such as FBN1, which has been associated with Marfan) have been proposed and excluded.

There are many causes of TOS. The most frequent cause is trauma, either sudden (as in a clavicle fracture caused by a car accident), or repetitive (as in a legal secretary who works with his/her hands, wrists, and arms at a fast paced desk station with non-ergonomic posture for many years). TOS is also found in certain occupations involving lots of lifting of the arms and repetitive use of the wrists and arms.

One cause of arterial compression is trauma, and a recent case involving fracture of the clavicle has been reported.

The two groups of people most likely to develop TOS are those suffering from neck injuries due to traffic accidents and those who use computers in non-ergonomic postures for extended periods of time. TOS is frequently a repetitive stress injury (RSI) caused by certain types of work environments. Other groups which may develop TOS are athletes who frequently raise their arms above the head (such as swimmers, volleyball players, dancers, badminton players, baseball pitchers, and weightlifters), rock climbers, electricians who work long hours with their hands above their heads, and some musicians.

The risk of serious complications from spinal fusion surgery for kyphosis is estimated to be 5%, similar to the risks of surgery for scoliosis. Possible complications include inflammation of the soft tissue or deep inflammatory processes, breathing impairments, bleeding, and nerve injuries. According to the latest evidence, the actual rate of complications may be substantially higher. Even among those who do not suffer from serious complications, 5% of patients require reoperation within five years of the procedure, and in general it is not yet clear what one would expect from spine surgery during the long-term. Taking into account that signs and symptoms of spinal deformity cannot be changed by surgical intervention, surgery remains to be a cosmetic indication. Unfortunately, the cosmetic effects of surgery are not necessarily stable.

Many with Scheuermann's disease often have an excessive lordotic curve in the lumbar spine; this is the body's natural way to compensate for the kyphotic curve above. Interestingly, many with Scheuermann's disease have very large lung capacities and males often have broad, barrel chests. Most people have forced vital capacity (FVC) scores above average. It has been proposed that this is the body's natural way to compensate for a loss of breathing depth.

Often patients have tight hamstrings, which, again, is related to the body compensating for excessive spinal curvature, though this is also debated (for example, some suggest the tightness of ligament is the initial cause of the growth abnormality). In addition to the common lordosis, it has been suggested that between 20–30% of patients with Scheuermann's Disease also have scoliosis, though most cases are negligible. In more serious cases, however, the combination is classified as a separate condition known as kyphoscoliosis.

Many vertebrates, especially reptiles, have cervical ribs as a normal part of their anatomy rather than a pathological condition. Some sauropods had exceptionally long cervical ribs; those of "Mamenchisaurus hochuanensis" were nearly 4 meters long.

In birds, the cervical ribs are small and completely fused to the vertebrae.

In mammals the ventral parts of the transverse processes of the cervical vertebrae are the fused-on cervical ribs.

Recent studies have also found a high percent of cervical ribs in woolly mammoths. It is believed that the decline in mammoth numbers may have forced inbreeding within the species which in turn has increased the number of mammoths being born with cervical ribs. Cervical ribs have been connected with leukaemia in human children, so it has given scientists new evidence to believe that the mammoth's extinction was attributed to the condition.

TOS can be attributed to one or more of the following factors:

- Congenital abnormalities are frequently found in persons with TOS. These include cervical rib, prolonged transverse process, and muscular abnormalities (e.g., in the scalenus anterior muscle, a sickle-shaped scalenus medius) or fibrous connective tissue anomalies.

- Trauma (e.g., whiplash injuries) or repetitive strain is frequently implicated.

- Rarer acquired causes include tumors, hyperostosis, and osteomyelitis

The most common causes of upper back pain are unknown but theorized to originate from muscular irritation, intervertebral discs, spinal facet joints, ribs or soft tissue (e.g. ligament/fascia) problems. Commonly intra-scapular pain is referred from the lower cervical spine. Contributing factors to injury include; lack of strength, poor posture, overuse injuries (such as repetitive motion), or a trauma (such as a car accident or sports injury). Often thoracic pain can be aggravated twisting, side bending and with prolonged bent spinal postures.

A compression fracture of the vertebra can also cause acute and/or chronic pain in the upper back. Trauma may cause a fracture, but in women over age 50 without significant trauma or someone known to have osteoporosis, a spontaneous vertebral compression fracture is possible.

Other, less common causes of thoracic back pain include a spinal disc herniation which often may have radicular pain (wrapping around the ribs associated with numbness and burning pain), spinal tumors and rib fractures may mimic thoracic pain/radicular pain. Other possible sources of referral pain into the thoracic region include visceral organs like: lungs, gallbladder, stomach, liver duodenum, pleura and cardiac.

Middle back pain has long been considered a "red flag" to alert healthcare professionals to the possibility of cancer (metastasis or spread to the spine). This is not a sensitive or specific phenomenon and can therefore not be relied upon in isolation.

Thoracic spinal pain was significantly associated with: concurrent musculoskeletal pain; growth and physical; lifestyle and social; backpack; postural; psychological; and environmental factors. Specific risk factors identified in adolescents included age (being older) and poorer mental health.

A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Sometimes known as "neck ribs", their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% (1 in 500 people) to 0.5% of the population. People may have a cervical rib on the right, left or both sides.

Most cases of cervical ribs are not clinically relevant and do not have symptoms; cervical ribs are generally discovered incidentally. However, they vary widely in size and shape, and in rare cases, they may cause problems such as contributing to thoracic outlet syndrome, because of pressure on the nerves that may be caused by the presence of the rib.

A cervical rib represents a persistent ossification of the C7 lateral costal element. During early development, this ossified costal element typically becomes re-absorbed. Failure of this process results in a variably elongated transverse process or complete rib that can be anteriorly fused with the T1 first rib below.

On imaging, cervical ribs can be distinguished because their transverse processes are directed inferolaterally, whereas those of the adjacent thoracic spine are directed anterolaterally.

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate, in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bones—vertebrae separated by intervertebral discs. The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

There are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples.

Spondylocostal dysostosis is a rare, heritable axial skeleton growth disorder. It is characterized by widespread and sometimes severe malformations of the vertebral column and ribs, shortened thorax, and moderate to severe scoliosis and kyphosis. Individuals with Jarcho-Levin typically appear to have a short trunk and neck, with arms appearing relatively long in comparison, and a slightly protuberant abdomen. Severely affected individuals may have life-threatening pulmonary complications due to deformities of the thorax. The syndrome was first described by Saul Jarcho and Paul M. Levin at Johns Hopkins University in 1938.

The exact cause is unknown. Mechanical factors, dietary and long term use of some antidepressants may be of significance. There is a correlation between these factors but not a cause or effect. The distinctive radiological feature of DISH is the continuous linear calcification along the antero-medial aspect of the thoracic spine. The disease is usually found in people in their 60s and above, and is extremely rare in people in their 40s and 30s. The disease can spread to any joint of the body, affecting the neck, shoulders, ribs, hips, pelvis, knees, ankles, and hands. The disease is not fatal, however some associated complications can lead to death. Complications include paralysis, dysphagia (the inability to swallow), and pulmonary infections. Although DISH manifests in a similar manner to ankylosing spondylitis, these two are totally separate diseases. Ankylosing spondylitis is a genetic disease with identifiable marks, and affects organs. DISH has no indication of a genetic link, and does not affect organs other than the lungs, which is only indirect due to the fusion of the rib cage.

Long term treatment of acne with vitamin derived retinoids, such as etretinate and acitretin, have been associated with "extraspinal" hyperostosis.

In 1968, Dr. David Rimoin and colleagues in Baltimore first distinguished between the two major presentations of Jarcho-Levin. Both conditions were characterized as failures of proper vertebral segmentation. However, the condition within the family described in their article appeared to be inherited in an autosomal dominant fashion and had a less severe course than that reported by other investigators. They specified their condition as spondylocostal dysplasia, which has since become known as spondylocostal dysostosis. The subtype of Jarcho-Levin with which they contrasted their reported cases to is now known as spondylothoracic dysplasia.

Several studies have reported that life expectancy appears to be normal for people with CCD.

Workers in certain fields are at risk of repetitive strains. Most occupational injuries are musculoskeletal disorders, and many of these are caused by cumulative trauma rather than a single event. Miners and poultry workers, for example, must make repeated motions which can cause tendon, muscular, and skeletal injuries.

Vertebral fractures of the thoracic vertebrae, lumbar vertebrae or sacrum are usually associated with major trauma and can cause spinal cord injury that results in a neurological deficit.

There are several kinds of kyphosis (ICD-10 codes are provided):

- Postural kyphosis (M40.0), the most common type, normally attributed to slouching, can occur in both the old and the young. In the young, it can be called "slouching" and is reversible by correcting muscular imbalances. In the old, it may be a case of hyperkyphosis and called "dowager's hump". About one third of the most severe hyperkyphosis cases in older people have vertebral fractures. Otherwise, the aging body does tend towards a loss of musculoskeletal integrity, and hyperkyphosis can develop due to aging alone.

- Scheuermann's kyphosis (M42.0) is significantly worse cosmetically and can cause varying degrees of pain, and can also affect different areas of the spine (the most common being the midthoracic area). Scheuermann's kyphosis is considered a form of juvenile osteochondrosis of the spine, and is more commonly called Scheuermann's disease. It is found mostly in teenagers and presents a significantly worse deformity than postural kyphosis. A patient suffering from Scheuermann’s kyphosis cannot consciously correct posture. The apex of the curve, located in the thoracic vertebrae, is quite rigid. The patient may feel pain at this apex, which can be aggravated by physical activity and by long periods of standing or sitting. This can have a significantly detrimental effect on their lives, as their level of activity is curbed by their condition; they may feel isolated or uneasy amongst peers if they are children, depending on the level of deformity. Whereas in postural kyphosis, the vertebrae and discs appear normal, in Scheuermann’s kyphosis, they are irregular, often herniated, and wedge-shaped over at least three adjacent levels. Fatigue is a very common symptom, most likely because of the intense muscle work that has to be put into standing or sitting properly. The condition appears to run in families. Most patients who undergo surgery to correct their kyphosis have Scheuermann's disease.

- Congenital kyphosis (Q76.4) can result in infants whose spinal column has not developed correctly in the womb. Vertebrae may be malformed or fused together and can cause further progressive kyphosis as the child develops. Surgical treatment may be necessary at a very early stage and can help maintain a normal curve in coordination with consistent follow-ups to monitor changes. However, the decision to carry out the procedure can be very difficult due to the potential risks to the child. A congenital kyphosis can also suddenly appear in teenage years, more commonly in children with cerebral palsy and other neurological disorders.

- Nutritional kyphosis can result from nutritional deficiencies, especially during childhood, such as vitamin D deficiency (producing rickets), which softens bones and results in curving of the spine and limbs under the child's body weight.

- Gibbus deformity is a form of structural kyphosis, often a "sequela" to tuberculosis.

- Post-traumatic kyphosis (M84.0) can arise from untreated or ineffectively treated vertebral fractures.

It is usually autosomal dominant, but in some cases the cause is not known. It occurs due to haploinsufficiency caused by mutations in the CBFA1 gene (also called Runx2), located on the short arm of chromosome 6, which encodes transcription factor required for osteoblast differentiation. It results in delayed ossification of midline structures of the body, particularly membranous bone.

A new article reports that the CCD cause is thought to be due to a CBFA1 (core binding factor activity 1) gene defect on the short arm of chromosome 6p21 . CBFA1 is vital for differentiation of stem cells into osteoblasts, so any defect in this gene will cause defects in membranous and endochondral bone formation.

Diffuse idiopathic skeletal hyperostosis (DISH) is a non-inflammatory spondyloarthropathy which predominantly affects the spine. It is characterized by ankylosis and enthesopathy (ossification of the ligaments and entheses). It most commonly affects the thoracic and thoraco-lumbar spine, but involvement is variable and can include the entire spine.

A spinal fracture, also called a vertebral fracture or a broken back, is a fracture affecting the vertebrae of the spinal column. Most types of spinal fracture confer a significant risk of spinal cord injury. After the immediate trauma, there is a risk of spinal cord injury (or worsening of an already injured spine) if the fracture is "unstable", that is, likely to change alignment without internal or external fixation.

One source of snapping scapula is when the muscles underneath the scapula (the subscapularis muscle) atrophies. This causes the scapula to become very close to the rib cage, eventually causing rubbing or bumping during arm/shoulder movement. Another cause is bursitis, which is when the tissues between the shoulder blade and thoracic wall inflame. Muscle and bone abnormalities in the shoulder area can also contribute to the pain.

Tarsal coalition is almost exclusively a product of an error during the dividing of embryonic cells in utero. Other causes of synostosis (bone fusion) could include a surgical 'screwing together' of two bones, a very advanced case of arthritis leading to self-fusion of a joint by an internal process within the body or some other very traumatic event. The birth defect responsible for tarsal coalition is thought to often be an autosomal dominant genetic condition. This means that if you have a parent with the disorder it is highly likely to be passed on to offspring.

The condition develops in the fetus at approximately 4 weeks gestational age, when some form of vascular problem such as blood clotting leads to insufficient blood supply to the face. This can be caused by physical trauma, though there is some evidence of it being hereditary . This restricts the developmental ability of that area of the face. Currently there are no definitive reasons for the development of the condition.

Snapping Scapula Syndrome, also known as scapulocostal syndrome or scapulothoracic syndrome, is described by a “grating, grinding, popping or snapping sensation of the scapula onto the back side of the ribs or thoracic area of the spine” (Hauser). Disruption of the normal scapulothoracic mechanics causes this problem. The most common cases are found in young, active patients who tend to excessively use the overhead or throwing motion.

Thoracic insufficiency syndrome is the inability of the thorax to support normal respiration. It is frequently associated with chest and/or spinal abnormalities. Treatment options are limited, but include supportive pulmonary care and surgical options (thoracoplasty and/or implantation of vertical expandable prosthetic titanium rib (VEPTR) devices).