Elbow Effusion

Christopher G. Anton, MD

DIFFERENTIAL DIAGNOSIS

Common

Supracondylar Fracture
Lateral Condylar Fracture
Medial Epicondyle Avulsion
Trauma without Fracture
Radial Neck Fracture
Other Less Common Fractures

Less Common

Osteochondritis Dissecans
Juvenile Idiopathic Arthritis (JIA)
Septic Arthritis
Panner Disease

Rare but Important

Tumor
Hemophilia

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Anatomy
- Elbow ossification center appearance (CRITOE)
  - Capitellum, radial head, medial (internal) epicondyle, trochlea, olecranon, lateral (external) epicondyle
Trauma
- Anterior humeral line
  - Lateral view: Line should pass through middle 1/3 of capitellum
  - When anterior humeral line is abnormal, may indicate minimally displaced supracondylar fracture (fx)
- Coronoid line
  - Line along volar border of coronoid process should barely contact volar portion of lateral condyle on lateral view
- Radiocapitellar line
  - Line drawn from center of radial shaft that normally extends through capitellar ossification center
  - Not necessarily passing through middle 1/3 of capitellum
  - When abnormal, radial head dislocation is likely
- Teardrop
  - On lateral view, dense anterior line reflects posterior margin of coronoid fossa
  - Posterior dense line reflects anterior margin of olecranon fossa
- Fat pad signs
  - Anterior fat pad: Nondisplaced and visualized in normal elbows
  - If elevated (“sail” sign), consider joint effusion; if trauma history, must exclude occult fx
  - Supinator fat pad: Anterior aspect of supinator muscle along proximal radius; if displaced, consider radial neck fx
  - Posterior fat pad sign more sensitive to underlying occult elbow fx
  - Joint capsule must be intact to detect fat pad displacement

Helpful Clues for Common Diagnoses

Supracondylar Fracture
- ˜ 50-70% of elbow fxs in children
- Most commonly extension type injury
- Age: 3-10 years old
- Cubitus varus (calculated by Baumann angle) most common complication
- Vascular injury: Most serious complication
- Displaced fx: 10-15% injury rate for anterior interosseous branch of median nerve injury
Lateral Condylar Fracture
- ˜ 20% of elbow fxs in children
- Age: typically 4-10 years old
- Fx line parallels metaphyseal margin of lateral physis
- Oblique views are often helpful in detection and assessing amount of displacement
- ≥ 2 mm of displacement may require open surgical reduction and pinning
- Nondisplaced fxs: Posterior splint and lateral gutter
Medial Epicondyle Avulsion
- Displacement > 5 mm, surgical reduction
- Valgus stress with avulsion from flexor-pronator muscle group
- 50% associated with elbow dislocations
- Should see medial epicondyle on AP radiograph if trochlea is identified
- May become displaced and trapped into elbow joint; simulates trochlear ossification center
- Unreliable fat pad sign; tends to be extracapsular in location in children > 2 years old
Trauma without Fracture
- If elbow effusion initially found without detection of fx, > 80% likelihood of seeing fx on follow-up radiographs
Radial Neck Fracture
- Most cases are Salter-Harris type 2 fxs (90%); average age of 10 years
Other Less Common Fractures
- Transphyseal fracture
  - < 2 years old, > 50% result of nonaccidental trauma
  - May be mistaken for elbow dislocation; in true dislocation, radiocapitellar (RC) line is disrupted
  - Capitellum still aligns with radial head
- Olecranon (normal ossification center can be mistaken for fx), intercondylar, medial condylar, radial head dislocation

Helpful Clues for Less Common Diagnoses

Osteochondritis Dissecans
- a.k.a. osteochondral lesion
- Medial femoral condyle is most common site
- Elbow: Most commonly anterolateral aspect of capitellum
- Typically adolescent boys (> 13 years old)
- Related to repetitive valgus stress and impaction with radial head
Juvenile Idiopathic Arthritis (JIA)
- Begins < 16 years old, symptoms > 6 weeks
- Systemic, pauciarticular, polyarticular
- Pannus, synovial proliferation, joint effusion, erosions
Septic Arthritis
- Infection via bloodstream but may become infected due to injection, surgery, or injury
- Staphylococcus aureus most common pathogen
- Most common symptoms: Fever, arthralgia, and joint swelling
- < 1/2 have arthritis and osteomyelitis
Panner Disease
- Osteochondrosis of capitellum
- Capitellar ossification center irregular mineralization, similar changes to Legg-Calvé-Perthes disease
- Most commonly: Boys 5-12 years old, dominant arm
  - Distinguish from osteochondritis dissecans (patients > 13 years old)
- ± effusion

Helpful Clues for Rare Diagnoses

Tumor
- Chondroblastoma, giant cell tumor, Langerhans cell histiocytosis, etc.
Hemophilia
- Bleeding disorder; knee, elbow, ankle, hip, and shoulder most commonly involved joints
- Diagnosis usually known prior to imaging
- Joint effusion may appear radiodense on conventional radiographs
- MR: Subchondral erosion, synovial proliferation, joint effusion, hemosiderin deposition