Elbow fat pad and the Salter-Harris paediatric elbow

(a) The ABCCS read. Adequacy and alignment — two orthogonal views (AP and lateral), confirm the patient and the side, trace the arcs of Gartland (the anterior humeral line should intersect the middle third of the capitellum on the lateral) and the radio-capitellar line (the radial head should point to the capitellum on every view, ruling out a radial head dislocation). Bones — the cortex is intact with no visible fracture line, but a supracondylar fracture may be occult; trace the olecranon and the radial neck. Cartilage and joints — the joint space is preserved; in a 9-year-old the physis is open and the capitellum, radial head and internal epicondyle are visible ossification centres (capitellum appears first, around 1 year, then radial head, internal epicondyle, trochlea, olecranon, lateral epicondyle — CRITOE). Soft tissue — the positive posterior fat pad and the prominent anterior fat pad (the sail sign) indicate an elbow effusion and an intra-articular injury. Summary — occult supracondylar or lateral condyle injury until proven otherwise. (b) The fat-pad signs and Salter-Harris. The anterior and posterior fat pads lie in the coronoid and olecranon fossae; in flexion they are hidden within the bony fossae and not seen on the lateral. An effusion displaces them out of the fossae — the anterior fat pad becomes the sail sign and the posterior fat pad becomes visible. The anterior fat pad alone can be a normal variant, but a visible posterior fat pad is always abnormal. In a child with a positive posterior fat pad and no visible fracture line, a meta-analysis of 10 studies found a pooled occult-fracture rate of 44.6 per cent (95 per cent CI 30.4 to 59.7 per cent), commonest in the supracondylar humerus.^[1] An occult supracondylar fracture in a 9-year-old crosses the distal humeral metaphysis — a Salter-Harris II (through the metaphysis and the physis) if it extends to the plate, or a transcondylar pattern if purely metaphyseal. A Salter-Harris IV crosses the epiphysis, physis and metaphysis; intra-articular physeal injuries carry real growth-arrest risk — in a Salter-Harris III/IV medial-malleolus series, physeal bars formed in 30.4 per cent with nearly half needing secondary surgery.^[2] (c) Analgesia and disposition. Immobilise in an above-elbow backslab in flexion, give weight-based oral or intranasal analgesia (paracetamol or intranasal fentanyl per local paediatric dosing), and refer to orthopaedics; a displaced extension supracondylar fracture (Gartland II or III) is reduced under general anaesthesia or weight-based ketamine procedural sedation by a credentialed sedationist, with assessment of the radial and median nerves before and after reduction (anterior interosseous nerve palsy is the commonest neurovascular injury). Admit for neurovascular observation.