What causes posterior right shoulder scratches and muscular pain feeling like a knot?

Posterior Right Shoulder Pain with Knot-Like Sensation

The posterior right shoulder pain with a muscular "knot" sensation is most likely myofascial pain syndrome with trigger points, though subacromial impingement syndrome and referred cervical spine pathology must be excluded based on specific clinical features.

Most Likely Diagnosis: Myofascial Trigger Points

The description of pain feeling "like a knot" is pathognomonic for myofascial pain syndrome (MPS), which is characterized by:

• Myofascial trigger points with palpable taut bands in the muscle that cause localized and referred pain 1
• Tenderness that can be quantified with algometry, with objective evidence detectable via EMG and diagnostic ultrasound 1
• Always secondary to some muscle stressor, such as repetitive activities, poor posture, or overuse 1

The posterior location suggests involvement of the posterior shoulder musculature, particularly the infraspinatus, teres minor, or posterior deltoid muscles.

Critical Differential Diagnoses to Exclude

Subacromial Impingement Syndrome

Rule this out if the patient has:

• Pain in the anterior or anterolateral shoulder (not posterior) that worsens with overhead activities 2
• Positive Neer's test (88% sensitive) or Hawkins' test (92% sensitive) 2
• Pain during specific phases of arm motion, particularly abduction with rotation 2
• Rotator cuff weakness (present in 75% of cases) 2

If these features are absent and pain is purely posterior with a palpable knot, impingement is less likely.

Cervical Spine Referred Pain

Consider cervical radiculopathy if:

• Cervical spine pathology and nerve compression syndromes can manifest as shoulder pain 3
• Pain radiates down the arm or is associated with neck movements
• Neurological symptoms (numbness, tingling, weakness) are present

Age-Related Considerations

• Patients under 35 years predominantly experience instability-related injuries, labral tears, and sports-related trauma 3
• Patients over 35-40 years predominantly experience rotator cuff disease and degenerative changes 3
• Degenerative acromioclavicular joint arthritis is common in patients over 35-40 years 3

Red Flags Requiring Immediate Evaluation

Ensure none of these are present:

• Fever, chills, or constitutional symptoms suggesting septic arthritis 3
• Signs of vascular compromise (rare but debilitating) 3
• Neurological deficits suggesting brachial plexus or peripheral nerve injury 3

Treatment Algorithm for Myofascial Pain

First-Line Conservative Management

• Trigger point inactivation is effective when combined with correction of underlying mechanical or medical perpetuating factors 1
• Physical therapy focusing on stretching the affected muscle and correcting postural abnormalities
• Identify and address muscle stressors (repetitive activities, poor ergonomics, overuse)

Pharmacological Options

• Topical analgesics offer analgesic relief with minimal systemic adverse effects 4
• Strong evidence supports topical diclofenac and topical ibuprofen for acute soft tissue injuries and chronic joint-related conditions 4
• Topical lidocaine has evidence for neuropathic pain conditions 4
• For shoulder impingement-type pain, heated lidocaine-tetracaine patches have shown success in case reports 5

Common Pitfalls to Avoid

• Do not assume fibromyalgia syndrome (FMS) for localized posterior shoulder pain with a discrete knot - FMS presents with diffuse muscle pain, fatigue, and sleep disturbances using the Widespread Pain Index and Symptom Severity Scale 6
• Delayed onset muscle soreness (24-48 hours post-exercise, especially after eccentric contractions) is self-limited and should not be confused with chronic myofascial pain 7
• Treatment of myofascial pain fails if perpetuating factors (mechanical stressors, poor posture, repetitive strain) are not corrected 1

When to Escalate Care

Consider advanced imaging (MRI or ultrasound) if:

• Conservative management fails after 4-6 weeks
• Progressive weakness develops (suggesting rotator cuff pathology) 2
• Clinical examination suggests structural pathology rather than pure myofascial pain
• MRI shows 90% sensitivity and 80% specificity for subacromial impingement, while ultrasound has 85% sensitivity and 90% specificity for rotator cuff abnormalities 2