Transphyseal Distal Humerus Fracture (Distal Humeral Physeal Separation)

The distal humeral epiphysis ossifies from several centres in the CRITOE order at roughly 1, 3, 5, 7, 9 and 11 years. In the under-3 age group of this injury, often only the capitellum (and sometimes the radial head) has begun to ossify, so most of the epiphysis - and the physis itself - is radiolucent cartilage. That single fact explains the whole diagnostic difficulty: the separation occurs through tissue the X-ray cannot show, and you must read it indirectly from bony alignment and from the position of the ossified capitellum relative to the metaphysis.

The physis is the mechanically weakest link in the immature elbow, so a shear/rotatory force (birth canal forces, a twist, or a fall) separates the epiphysis rather than dislocating the joint. Displacement is typically posteromedial, producing an apparent varus tilt that, if it heals malreduced, becomes cubitus varus. The medial crista of the trochlea / medial condylar ossification centre has a relatively tenuous blood supply, which is why osteonecrosis of the medial condyle is a recognised complication; and because the injury crosses the physis, partial growth arrest and progressive angular deformity are possible.

Treatment is guided by displacement, age and the soft tissues, and mirrors supracondylar fracture principles. The aims are an anatomic reduction to restore the carrying angle and to protect the physis and its blood supply.

With timely diagnosis and restoration of alignment, outcomes are generally good: small published series report union with full range of motion and few deformities requiring further surgery. The dominant determinant of a poor result is late or missed diagnosis (the cartilaginous epiphysis) and residual varus/valgus malalignment. The main long-term issues are cubitus varus (cosmetic/alignment, correctable by osteotomy) and, less often, medial-condyle osteonecrosis or growth arrest - which is why follow-up continues past union.

There is no dedicated registry for this rare injury, and management is extrapolated from paediatric supracondylar fracture principles, which national bodies address directly (e.g. BOA/BOAST standards in the UK, and AAOS/POSNA guidance in North America) - emphasising timely assessment, neurovascular documentation and appropriate-urgency surgery. The one point with strong global consensus specific to this injury is the safeguarding obligation: across health systems (e.g. NICE/RCPCH child-maltreatment guidance in the UK and equivalent mandatory-reporting frameworks elsewhere), an unexplained or inconsistent fracture in a child under 3 must trigger a non-accidental-injury assessment including a skeletal survey. Practice on fixation vs casting in neonates varies by centre and resource setting, united by the principle that restoring alignment and protecting the physis matters more than the specific construct.

The original description - posteromedial displacement as the cardinal sign, the abuse association (6 of 16) and cubitus varus from inadequate reduction - is the DeLee et al. series, which also underpins the DeLee classification (J Bone Joint Surg Am 1980;62(1):46-51, PMID 7351415). The age group, mechanisms (including non-accidental trauma), the forearm-humerus malalignment clue, arthrogram-assisted CRPP and the complication profile come from the Abzug et al. review (DOI); the neonatal diagnostic-and-outcome data from the Galeotti et al. case series (DOI); the quantitative imaging/misdiagnosis and complication figures from the Nguyen et al. systematic review (DOI); and the reduction-quality/outcome comparison from the Chen et al. series (DOI). The CRITOE ossification sequence and the Salter-Harris and DeLee classifications are standard, long-established paediatric concepts. (See also our Supracondylar Humerus Fracture, Lateral Condyle Fractures and Physis topics.)