Deltoid Fibrosis — A Comprehensive Clinical Review

1. Introduction & Definition

2. Anatomy Relevant to the Condition

• Anterior (clavicular) — flexion, medial rotation
• Middle (acromial) — pure abduction (the most prominent part, most frequently injected)
• Posterior (spinous) — extension, lateral rotation

Intramuscular injection into the deltoid — layers traversed and correct site (Harrison's Principles of Internal Medicine)

3. Etiology

Primary Cause: Repeated Intramuscular (IM) Injections

• Quinine — historically the most notorious offender; highly irritating to muscle tissue, causing intense local necrosis and subsequent fibrosis. As noted in Das' Manual on Clinical Surgery, "Irritating drugs such as quinine when injected intramuscularly in the deltoid may affect the axillary nerve."
• Penicillin (long-acting preparations) — benzathine penicillin, procaine penicillin
• Antimalarial agents (chloroquine, quinine)
• Vaccines administered too high (into the subdeltoid bursa rather than muscle)
• Oily/depot injections — iron dextran, vitamin preparations
• Antibiotics — streptomycin, tetracycline

Other Causes

4. Pathology

Macroscopic

• The deltoid muscle (particularly its middle head) is replaced by a dense white fibrous band
• The fibrotic band is firm to hard on palpation, running vertically from the acromion toward the deltoid tuberosity
• Overlying skin may show a characteristic skin dimple or furrow corresponding to the fibrous cord beneath (see clinical photo below)
• In chronic cases, the muscle belly is atrophied and pale

Microscopic

• Collagen deposition — dense type I and III collagen bundles replace muscle fibers
• Myofibroblasts — key cellular mediators of fibrosis; identical to those seen in Dupuytren's contracture (as noted in Miller's Review of Orthopaedics: "Frozen shoulder histologic evaluation demonstrates evidence of inflammation and fibrosis. There is a dense matrix of type III collagen–containing fibroblasts and myofibroblasts")
• Loss of muscle architecture — sarcomeres and cross-striations absent in fibrotic areas
• Chronic inflammatory infiltrate — lymphocytes, macrophages in early stages
• Fatty infiltration — in longstanding cases
• Calcification — dystrophic calcification may occur in old fibrotic bands

Pathogenesis Sequence

Repeated injection / chemical irritant
        ↓
Local myonecrosis (ischemic or direct toxic)
        ↓
Inflammatory response (macrophages, mast cells)
        ↓
Fibroblast/myofibroblast recruitment & activation
        ↓
Excessive ECM (collagen) deposition
        ↓
Fibrous band formation
        ↓
Progressive contracture & mechanical restriction

5. Clinical Features

Signs & Symptoms

Typical Presentation

• The arm is held in fixed partial abduction (typically 30–50°)
• The child cannot fully adduct the arm to the side of the body
• The shoulder appears "sprung out" from the body

• Skin dimple or vertical furrow over the lateral deltoid (pathognomonic) — corresponds to the fibrous band pulling skin inward
• Deltoid atrophy — particularly if the axillary nerve is also affected
• Shoulder asymmetry — on frontal view, the affected shoulder appears higher and projected laterally
• Winging of the scapula — secondary to altered shoulder mechanics

• Restricted passive adduction — cannot bring arm close to trunk
• Abduction is often preserved or even excessive — because the fibrotic band acts as a passive abductor
• "Reverse shoulder rhythm" — the scapula elevates early on attempted adduction

Pediatric patient with deltoid fibrosis. (a) Anterior view: arm held in fixed abduction. (b) Lateral view: vertical skin dimple over the fibrous band within the deltoid.

Secondary Complications

• Glenohumeral joint subluxation/dislocation — in long-standing neglected cases; the humeral head may sublux anteriorly
• Shoulder joint dysplasia — disrupted development in children
• Scoliosis — compensatory spinal curvature
• Thoracic cage asymmetry
• Axillary nerve damage — may coexist if the injection caused direct nerve injury

6. Radiological Investigations

Plain X-Ray (AP & Axial Shoulder)

• Usually normal in early cases
• In advanced/neglected cases:
  • Inferior subluxation or anterior dislocation of humeral head
  • Drooping/elongation of acromion
  • Tapering of distal clavicle
  • Joint space narrowing
  • Evidence of glenohumeral dysplasia

AP radiograph of left shoulder in chronic deltoid fibrosis: drooping acromion, anterior subluxation of humeral head, and distal clavicular tapering.

Ultrasound (USG)

• First-line imaging in children (no radiation, dynamic assessment)
• Demonstrates:
  • Hyperechoic fibrous band within deltoid
  • Muscle atrophy and echogenicity changes
  • Axillary nerve assessment
  • Dynamic assessment of band tightness during abduction/adduction

MRI

• Best for soft tissue characterization
• Shows:
  • Low T1 and T2 signal fibrous band within deltoid (collagen is hypointense on both sequences)
  • Muscle atrophy and fatty infiltration (high T1 signal)
  • Associated joint changes
  • Axillary nerve status

EMG/Nerve Conduction Studies

• Indicated when axillary nerve injury is suspected
• May show:
  • Reduced CMAP amplitude from deltoid
  • Denervation potentials (fibrillations, positive sharp waves) on EMG
  • Normal conduction velocity (axonotmesis pattern)

7. Differential Diagnosis

8. Treatment

Conservative Treatment

1. Physiotherapy
   • Passive stretching of the deltoid into adduction
   • Heat therapy (ultrasound/shortwave diathermy) to soften fibrotic tissue
   • Massage of the fibrous band
   • Active-assisted range of motion exercises
2. Corticosteroid injection
   • Into the fibrous band
   • May soften early fibrosis
   • Limited long-term benefit in established contracture
3. Extracorporeal shockwave therapy (ESWT)
   • Emerging modality for early fibrosis

Important: Conservative treatment alone is rarely curative for established deltoid fibrosis with significant contracture. Surgery is usually required.

Surgical Treatment

Principle

Approaches

• Most commonly performed
• Incision over the lateral deltoid
• Identification and excision of the fibrous band
• Preservation of normal muscle fibers
• If the band is extensive, deltoid muscle Z-plasty or stepcut lengthening is performed
• The axillary nerve is identified and protected throughout

• Emerging technique in specialized centers
• Endoscopic visualization and division of fibrotic tissue
• Lower morbidity, faster recovery

• Capsular release if secondary adhesive capsulitis
• Reduction of subluxed joint
• Rare cases may need shoulder arthroplasty in adults

Postoperative Care

• Immobilization in adduction for 2–3 weeks
• Early passive mobilization commenced
• Intensive physiotherapy for 3–6 months
• Progressive active strengthening of deltoid

Postoperative result: (a) Persistent mild abduction posture after surgical release. (b) Full bilateral shoulder abduction restored, demonstrating successful excision of the fibrotic band.

9. Complications of Untreated Deltoid Fibrosis

• Progressive worsening of the abduction contracture
• Glenohumeral joint subluxation → dislocation
• Joint dysplasia and irreversible cartilage damage
• Scoliosis and thoracic asymmetry
• Cosmetic deformity and social/psychological impact
• Functional disability (difficulty with activities of daily living requiring adduction)

10. Prevention (Critical)

1. Correct injection technique — inject into the middle third of the deltoid, not too superiorly (avoids bursa, axillary nerve, and periosteum)
2. Rotate injection sites — never repeatedly inject the same quadrant
3. Appropriate needle length and gauge — ensure delivery into muscle, not subcutaneous fat
4. Use the least irritating drug formulation available
5. Avoid irritating drugs (quinine, depot preparations) via the deltoid whenever possible — use gluteal or thigh muscles instead
6. Train healthcare workers in proper IM injection technique
7. Vaccination programs should follow standardized injection protocols

Summary Table

• S Das — A Manual on Clinical Surgery, 13th Edition (injection injury to deltoid and nerve)
• Miller's Review of Orthopaedics, 9th Edition (fibrosis histology, myofibroblasts)
• Gray's Anatomy for Students (deltoid and quadrangular space anatomy)
• Harrison's Principles of Internal Medicine, 21st Edition (IM injection technique)
• Clinical images from published PMC literature (deltoid contracture clinical series)