What causes limited range of motion in the left arm with small muscle knots?

Limited Left Arm Range of Motion with Muscle Knots

The most likely cause is rotator cuff tendinopathy with associated myofascial trigger points (muscle knots), which responds well to physical therapy including stretching, strengthening exercises, and manual techniques, combined with relative rest from aggravating activities. 1

Primary Differential Diagnosis

The presentation of limited ROM with palpable muscle knots ("small knts") that are relieved by capsaicin suggests a musculoskeletal soft tissue disorder rather than a structural joint problem. The key considerations include:

Rotator Cuff Tendinopathy (Most Likely)

• Rotator cuff tendinopathy affects one in 50 adults and commonly presents with pain, weakness, and decreased range of motion during abduction with external or internal rotation 1
• The muscle "knots" likely represent myofascial trigger points or areas of muscle spasm secondary to rotator cuff dysfunction 1
• Palpation typically elicits well-localized tenderness similar to the pain experienced during activity 1
• Atrophy is often present with chronic conditions and indicates duration of the tendinopathy 1

Secondary Shoulder Impingement

• Weakness in rotator cuff muscles combined with repetitive stress can lead to secondary impingement syndrome, particularly in the supraspinatus tendon 1
• Pain typically occurs with overhead activities and arm elevation 1
• The mechanism involves repetitive eccentric stress on the supraspinatus and external rotators, leading to fatigue and injury 1

Adhesive Capsulitis ("Frozen Shoulder")

• Can present with progressive stiffness and pain limiting ROM 1
• However, this typically presents with more global restriction rather than focal muscle knots 1

Clinical Evaluation Priorities

Physical examination should specifically assess:

• Focal weakness with decreased ROM during abduction with external or internal rotation 1
• Palpation for well-localized tenderness at the rotator cuff insertion sites 1
• Hawkins' test (92% sensitive) and Neer's test (88% sensitive) for supraspinatus impingement 1
• Scapular dyskinesis, which contributes to rotator cuff injury through poor coordination of upward rotation and posterior tilting 1
• Muscle atrophy suggesting chronicity 1

Range of motion testing should document:

• Active and passive shoulder flexion, extension, abduction, and internal/external rotation 2, 3
• Note that the contralateral side may not always be a reliable control, as the dominant arm typically has slightly reduced ROM 2

Evidence-Based Treatment Algorithm

Phase 1: Initial Management (First 2-4 Weeks)

Relative rest is the cornerstone of initial treatment 1

• Reduce activities that involve repetitive loading of the damaged tendon 1
• Avoid overhead activities and positions that reproduce pain 1
• Complete rest from aggravating movements until asymptomatic 1

Physical therapy should begin immediately and include: 1

• Rotator cuff strengthening exercises (particularly posterior shoulder musculature) 1
• Scapular stabilizer strengthening to address dyskinesis 1
• Stretching to restore range of motion, especially anterior shoulder girdle flexibility 1
• Deep transverse friction massage to reduce pain 1

Adjunctive modalities may provide temporary benefit: 1

• Capsaicin (as patient is already using) for topical pain relief
• Physical modalities such as NMES or vibration applied to spastic muscles as adjunct to therapy 1
• Therapeutic ultrasound may decrease pain and increase collagen synthesis, though evidence is weak 1

Phase 2: Progressive Rehabilitation (4-12 Weeks)

Once pain-free motion and strength are achieved: 1

• Initiate progressive strengthening program emphasizing proper mechanics 1
• Focus on neck, rotator cuff, and posterior shoulder girdle strengthening 1
• Re-establish proper mechanics of the shoulder and spine 1
• Duration typically 1-3 months depending on severity 1

For persistent symptoms despite 6-8 weeks of conservative therapy: 1

• Consider targeted botulinum toxin injection into localized muscles if spasticity is present 1
• Corticosteroid injection may be considered, though evidence shows benefit only in acute phase without changing long-term outcomes 1
• Extracorporeal shock wave therapy appears safe and effective but is expensive 1

Phase 3: Refractory Cases (After 3-6 Months)

If pain persists despite well-managed conservative treatment: 1

• Imaging with MRI is 95% sensitive and specific for detecting rotator cuff tears, degeneration, and partial tears 1
• Referral to orthopedic surgeon for surgical evaluation 1
• Surgery typically includes excision of abnormal tendon tissue and longitudinal tenotomies 1

Common Pitfalls to Avoid

Do not overlook scapular dysfunction - Scapular dyskinesis is a major contributor to rotator cuff injury and must be addressed in rehabilitation 1

Avoid being overly restrictive with activity - While caution is needed, complete immobilization can lead to adhesive capsulitis 1

Do not rely solely on passive treatments - Active strengthening and stretching exercises are essential for recovery 1

Recognize that splints are not recommended - Splinting for prevention of shoulder spasticity is not supported by evidence 1

Be aware that perceived disability may exceed measured functional loss - Patients often report greater impairment than objective testing reveals 4