A 7 year old male, with a history of a right distal forearm fracture conservatively treated was re-evaluated 10 weeks after trauma. The clinical and laboratory data were unremarkable.
A 7 year old male, with a history of a right distal forearm fracture conservatively treated was re-evaluated on the 10th week after trauma. The clinical and laboratory data were unremarkable.
The initial radiographs demonstrated right forearm trauma with a complete transverse fracture of the distal radius metadiaphysis (Fig 1). Overriding of the bony fragments, foreshortening, and dorsal displacement of the distal fragment are seen. Moderate superimposed soft tissue thickening is also observed.
On follow-up radiographs, 6 weeks after the trauma, early callus formation on the right distal radial fracture is shown (Fig 2). Persistence of slight dorsal angulation of the distal fragment, and juxtaposition with overlap of nearly three quarters of the bony fragments shafts is demonstrated.
On the following control radiographs, on the 10th week after the trauma, progressive consolidation of the right distal radial metadiaphyseal fracture without significant displacement of bony fragments is appreciated (Fig 3). Slight dorsal angulation of the fracture is shown. Additionally, juxtacortical lucency is visible, projected on the dorsal aspect of the radial metadiaphysis measuring approximately 10 mm and located proximal to the previously described fracture. In this clinical setting, it is consistent with post-traumatic cortical defect.
Post-traumatic cortical defect (PTCD) is a rare and self-limited phenomenon observed in healing children’s’ fractures. These cyst-like defects correspond to a subperiosteal (juxtacortical) blood and/or fat filled cavity secondary to traumatic and/or surgical bone disruption with intact overlying periosteum.
Figure 4 summarizes the sequence of events that lead to it. Compression forces cause greenstick or torus fractures with release of blood and fat from the medullary canal, which collects under the intact periosteum. Fracture healing results in the appearance of periosteal callus separated from the original cortex. The resultant gap gives rise to the cyst-like defect which is slowly filled by periosteal new bone formation and eventually becomes bone marrow.
A similar mechanism has been proposed for displaced fractures in children, as in the present case. In displaced fractures, fat may also leak into the fracture haematoma contained by the intact periosteum. When callus is formed the fat would be entrapped by it, thus making apparent the cortical defect.
PTCD characteristically involve the distal radial metaphysis, owing to the same biomechanical properties that predispose this region to greenstick or torus fractures. More rarely they have been reported after fracture of the distal tibia or femur.
Radiographically, PTCD typically are solitary, subperiosteal, non-expansile cyst-like lucencies, located 10 mm proximal to the compression fracture, and measure less than 10 mm in diameter. The defects can occasionally be multiple or large, although this is the exception rather than the rule. When multiple, they can be seen up to 48 mm proximal to the fracture site. Sequential radiographs most frequently show these lesions “migrating” away from the growth plate and disappearing with time although PTCD can be visible until skeletal maturity is reached.
High-resolution CT with thin 2-mm sections is diagnostic when imaged on both soft tissue and bone settings and typically demonstrates a circumferential juxtacortical cavity with density identical to the medullar marrow and invariably associated with smaller defects not visible on plain film.
MRI is equally diagnostic. It demonstrates the characteristic morphological features described, with the advantage of using non-ionizing radiation. A typical mature lesion exhibits a fatty content similar to bone marrow (high signal on T1- and T2- weighted images and low signal in fat-suppressed sequences). PTCD usually displays a characteristic homogeneous signal in all sequences except in T2 gradient-echo sequences in which is not uncommonly heterogeneous, likely reflecting low-signal areas due to the ‘blooming’ artefact of haemosiderin or to bone strands.
The differential diagnosis includes Brodie’s abscess, non-ossifying fibroma, simple bone cyst, and eosinophilic granuloma. Features supporting the diagnosis are the previous history of a characteristic fracture, the timing of appearance after fracture, and the location.
Typical lesions require no follow-up and no further action other than reassurance and the warning that they may cause discomfort under stress prior to resolution. Atypical lesions may require CT or preferably MR complementary evaluations, which are diagnostic. Therefore, although detection of PTCD may cause concern due to their rarity, they are an innocuous self-limited phenomenon with fairly specific imaging features, thus precluding further invasive tests or interventions.
Paediatric Post-traumatic Cortical Defect
Based on the follow-up imaging of a child 10 weeks after a distal right forearm fracture (primarily X-ray images of the distal radius), the following features are observed:
Taking into account the patient’s past medical history (distal right forearm fracture treated conservatively) and current imaging findings of a subcortical cystic lucency at the distal radius, the potential diagnoses include:
Considering the child’s age (7 years), a clear trauma history and conservative treatment, together with the current radiographic findings (a cortically adjacent cystic lucency at the distal radius, small in size, with well-defined margins, corresponding to the fracture site), plus the absence of clinical or laboratory abnormalities, the most likely diagnosis is:
Post-traumatic Cortical Defect (PTCD).
This lesion is usually self-limiting, causes no significant functional impairment or further invasion, and may gradually be replaced by normal bone tissue over time.
For a typical Post-traumatic Cortical Defect (PTCD), no special intervention is usually required. Main recommendations include:
Disclaimer: This report is a reference analysis and cannot replace in-person consultation or the professional diagnosis and treatment advice of a physician. If you have any questions or changes in your condition, please seek medical attention promptly.
Paediatric Post-traumatic Cortical Defect
