Musculoskeletal
Torticollis
Dystonic reaction
Cervical spondylosis
Cervical stenosis
Cancer
Cervical spine fracture and/or dislocation
Epidural abscess
Vertebral osteomyelitis
Transverse myelitis
Temporal arteritis
Epidural hematoma (anticoagulation, hemophilia)
Cervical disk herniation
Blunt neck trauma
Anterior horn disease
C1 and C2 fractures<unk> 
Traumatic/Acute:
Shoulder Dislocation
Anterior shoulder dislocation
Posterior shoulder dislocation
Inferior shoulder dislocation
Clavicle fracture
Humerus fracture
Scapula fracture
Acromioclavicular joint injury
Glenohumeral instability
Rotator cuff tear
Biceps tendon rupture
Triceps tendon rupture
Septic joint
Anterior shoulder dislocation
Posterior shoulder dislocation
Inferior shoulder dislocation
Nontraumatic/Chronic:
Rotator cuff tear
Impingement syndrome
Calcific tendinitis
Adhesive capsulitis
Biceps tendinitis
Subacromial bursitis<unk> 
Refered pain & non-orthopedic causes:
Referred pain from
Neck
Diaphragm (e.g. gallbladder disease)
Brachial plexus injury
Rucksack paralysis
Axillary artery thrombosis
Thoracic outlet syndrome
Subclavian steal syndrome
Pancoast tumor
Myocardial infarction
Pneumonia
Pulmonary embolism
Neck
Diaphragm (e.g. gallbladder disease)
Rucksack paralysis
Cervical radiculopathy
Musculoskeletal
Long thoracic neuropathy
Torticollis
Epidural compression syndromes
Dystonic reaction
Cervical disk herniation
Cervical spondylosis