What is the cause of shoulder pain in an adult when putting their arm behind their back?

Shoulder Pain with Arm Behind Back: Diagnosis and Management

Primary Diagnosis

Shoulder pain when putting the arm behind the back most commonly indicates rotator cuff tendinopathy or tear, particularly affecting the subscapularis and infraspinatus tendons, which are specifically stressed during internal rotation and extension movements required for this motion. 1, 2

Key Differential Diagnoses

Rotator Cuff Pathology (Most Likely)

• Pain with internal rotation and extension (arm behind back) specifically implicates the subscapularis tendon and posterior rotator cuff structures, which control and stabilize these movements 3, 1
• In patients over 35-40 years, rotator cuff disease and degenerative changes are the predominant causes of chronic shoulder pain 4, 5
• Rotator cuff injuries occur from repetitive eccentric stress on the supraspinatus, external rotators, and scapular stabilizers, leading to undersurface tears from overuse 3
• Physical examination findings include focal weakness with decreased range of motion during abduction with external or internal rotation, positive empty can test, and positive external rotation weakness 1

Adhesive Capsulitis (Frozen Shoulder)

• The key distinguishing feature is progressive loss of passive range of motion, particularly external rotation and abduction, not just pain with active movement 1, 5
• Adhesive capsulitis presents with diffuse shoulder pain and restricted passive range of motion on examination 5
• This condition can be associated with diabetes and thyroid disorders 5

Cervical Radiculopathy (Critical to Rule Out)

• If pain radiates down the arm with numbness, tingling, or weakness, cervical spine pathology with nerve root compression is strongly suggested 4
• Radiating pain accompanied by motor or sensory change, particularly below the elbow, strongly suggests a neurologic etiology 6
• Document the exact radiation pattern to determine if it follows a specific cervical nerve root distribution (C5, C6, C7, or C8) 4

Glenohumeral Instability

• In patients younger than 40 years, glenohumeral instability generally presents with a history of dislocation or subluxation events 5
• Document any sensation of shoulder "giving way" or feeling unstable during activities 1

Essential Clinical Assessment

History Components

• Document pain location precisely: anterior shoulder suggests rotator cuff or biceps pathology; superior shoulder indicates acromioclavicular joint disease; scapular region may indicate referred pain from cervical spine 1
• Record aggravating factors specifically: overhead activities, cross-body adduction, reaching behind back, and throwing motions 1
• Ask about history of previous similar injuries, including prior shoulder dislocations, fractures, or rotator cuff repairs 1
• Screen for neurological symptoms: numbness, tingling, weakness, or radiation of pain down the arm 4, 1

Physical Examination Maneuvers

• Perform Hawkins' test (92% sensitive) and Neer's test (88% sensitive) for rotator cuff impingement 1
• Test for focal weakness during abduction with external or internal rotation (empty can test) 1
• Assess passive range of motion: limited and painful passive motion indicates adhesive capsulitis, while preserved passive motion with painful/weak active motion suggests rotator cuff pathology 1
• Test for regional sensory changes, allodynia, or hyperpathia suggesting neuropathic pain component 4

Diagnostic Imaging Approach

Initial Imaging

• Plain radiographs are the mainstay for initial imaging, including AP, Grashey, axillary, and/or scapular Y projections 3
• Plain radiographs may help diagnose massive rotator cuff tears, shoulder instability, and shoulder arthritis 5

Advanced Imaging When Indicated

• MRI without contrast is the preferred imaging for rotator cuff disorders in patients over 35 years with suspected tendinopathy or tears 3, 5
• If cervical radiculopathy is suspected based on radiation pattern and neurological symptoms, MRI of the cervical spine without contrast is the preferred initial advanced imaging 4
• Ultrasound with appropriate local expertise is excellent for depicting rotator cuff and long head of biceps pathology 3

Management Algorithm

For Confirmed Rotator Cuff Pathology

• Complete rest from aggravating activities until the patient is asymptomatic 3
• Improve range of motion through stretching and mobilization techniques, focusing especially on external rotation and abduction to prevent frozen shoulder 3, 1
• Rotator cuff and scapular stabilizer strengthening once pain-free motion is achieved 3, 1
• Consider modalities: ice, heat, and soft tissue massage 3, 1
• NSAIDs for acute pain management 1
• Intra-articular corticosteroid injections (Triamcinolone) for more severe cases have been found to have significant effects on pain 3
• Return to activities may be allowed after completing a functional, progressive, and individualized program over 1 to 3 months without evidence of symptoms 3

For Confirmed Adhesive Capsulitis

• Aggressive stretching and mobilization focusing on external rotation and abduction 3
• Serial casting for contractures that interfere with function 3
• Consider intra-articular corticosteroid injections 3

For Confirmed Cervical Radiculopathy

• Continue or initiate pregabalin (300-600 mg daily in divided doses) as it may provide therapeutic benefit for neuropathic pain 4
• Consider other nerve-stabilizing agents such as gabapentin or duloxetine 4
• Refer to spine specialist if imaging confirms significant nerve root compression requiring intervention 4

Critical Pitfalls to Avoid

• Do not assume absence of trauma means absence of fracture, especially in elderly patients where osteoporotic fractures can occur with minimal or unrecognized trauma 1
• Avoid overhead pulley exercises, which encourage uncontrolled abduction and can worsen rotator cuff pathology 3
• Do not assume pain is simply "muscle tension" or "muscle spasm" without ruling out structural pathology, particularly cervical spine disease if radiation is present 4
• Most rotator cuff pathology can initially be managed conservatively without surgical intervention, so avoid premature surgical referral 4, 1