Etiology
- Congenital abnormalities (anomalies of the transverse process of seven cervical vertebra, cervical rib, first rib, enlarged scalene tubercle, scalene muscles, costoclavicular ligaments, subclavius or pectoralis minor)
- Traumatic injuries (motor vehicle accident or sporting incident)
- Traumatic bony lesions (remodeling after fractures of the clavicle or first rib or posterior subluxation of the acromioclavicular joint)
- Anterior scalene muscle hypertrophy
- Postural or occupational stressors with repetitive overuse and associated soft tissue adaptation such as hypertrophy in some muscles and atrophy in others
- Poor posture 5