Fat Pad Signs
| Sign | Normal | Pathologic |
|---|---|---|
| Anterior fat pad | Thin lucency anterior to distal humerus — normal | Elevated / sail-shaped = pathologic (effusion displaces it anteriorly) |
| Posterior fat pad | Hidden in olecranon fossa — not visible | Any visibility = pathologic — most specific sign of joint effusion |
Posterior fat pad sign = occult fracture until proven otherwise. If the posterior fat pad is visible after elbow trauma and no fracture line is seen, treat as an occult fracture — splint and follow up with repeat films at 7–10 days or MRI.
CRITOE — Ossification Sequence
Ossification centers appear in a predictable sequence. An ossification center should not appear before the preceding one in the sequence.
| Letter | Center | Approximate Age |
|---|---|---|
| C | Capitellum | ~1 year |
| R | Radial head | ~3 years |
| I | Internal (medial) epicondyle | ~5 years |
| T | Trochlea | ~7 years |
| O | Olecranon | ~9 years |
| E | External (lateral) epicondyle | ~11 years |
Critical CRITOE pitfall — entrapped medial epicondyle: The medial epicondyle (I) ossifies before the trochlea (T). If you see a bony fragment in the trochlear position but the medial epicondyle ossification center is absent from its normal medial position, that "trochlea" is actually the avulsed, entrapped medial epicondyle lying within the joint — a surgical emergency. Do not mistake it for normal trochlear ossification. Ages are approximate and earlier in girls.
Common Elbow Fractures
| Fracture | Key Features | Pitfalls / Pearls |
|---|---|---|
| Supracondylar | Most common pediatric elbow fracture; hyperextension mechanism (posterior displacement); anterior humeral line on lateral should intersect middle third of capitellum | Fracture line may be invisible — posterior fat pad is the key clue; rotation on lateral view makes anterior humeral line unreliable in toddlers; nondisplaced still requires immobilization |
| Lateral condyle | Salter-Harris IV; cartilaginous articular extension is nearly always invisible on plain film; measure displacement on internal oblique view | Displacement >2 mm = surgical; undertreated → non-union, cubitus valgus, tardy ulnar nerve palsy; do not underestimate extent based on plain film alone |
| Medial epicondyle | Avulsion fracture (valgus stress / elbow dislocation); fragment may be entrapped intra-articularly after reduction | Apply CRITOE — if trochlea appears without medial epicondyle in its normal position, suspect entrapment |
| Proximal radius | Radial neck most common; spectrum from buckle to SH II to SH IV; assess angulation on both views | Subtle angulation may be the only finding; coexists commonly with elbow dislocation |
| Proximal ulna / Monteggia | Ulnar shaft fracture + radial head dislocation; always trace the radiocapitellar line — long axis of radius should bisect the capitellum on every view | Satisfaction of search error is common — finding the ulnar fracture does not exclude radial head dislocation |
Key Alignment Lines
- Anterior humeral line (lateral view): drawn along the anterior cortex of the distal humerus — should intersect the middle third of the capitellum. If it intersects the anterior third or misses entirely → posterior displacement of the capitellum = supracondylar fracture.
- Radiocapitellar line (all views): long axis of the proximal radius should bisect the capitellum on every radiographic projection. Disruption on any view = radial head dislocation.