Purpose or Case Report: Radiologic diagnosis of rib fractures in suspected infant abuse is often challenging, and costochondral junction (CCJ) rib fractures can be particularly problematic. In an effort to enhance diagnostic accuracy and dating, we studied the dynamic radiologic spectrum of CCJ rib fractures on serial skeletal surveys (SSs).
Methods & Materials: Reports of SSs performed for suspected infant abuse (7/2005-6/2019) and images of those cases with CCJ rib fractures were reviewed. Inclusion criteria were: 1) anteroposterior (AP), right posterior oblique (RPO), and left posterior oblique (LPO) radiographs of CCJ rib fractures from both initial and ~two-week follow-up (FU) SSs, 2) additional fractures documented radiographically, 3) child protection team consults, and 4) state report filing for suspected abuse. CCJ rib fractures were excluded if they were only suspected on the initial SS but not confirmed on the FU SS, or identified on CT and/or MRI but not adequately documented radiographically. We identified 84 CCJ rib fractures from 26 infants (mean age=2.7 months; SD=2.1). Six radiographs (AP, RPO, LPO of initial and FU SSs) of each fracture were retrospectively assessed on PACS by a pediatric radiologist aware of the diagnosis. This reader indicated: 1) likely presence/absence of primary injury pattern, i.e. visible fracture line with a crescentic (bucket-handle), triangular (corner), or other fracture fragment pattern; 2) likely presence/absence of a secondary (healing) injury pattern: subperiosteal new bone formation (SPNBF), sclerosis, or growth disturbance (nodular enlargement, excessive cupping, flaring, and cartilage invagination) of the rib end. Results from the AP, RPO, and LPO radiographs of each survey were combined for analysis.
Results: On initial SSs, 64 of 84 fractures showed a primary injury pattern, and of those 64, 48 (75%) demonstrated a secondary injury pattern. On FU SSs, only 7 of 84 fractures showed a primary injury pattern, and all of these showed a secondary injury pattern. On combined initial and FU SSs, the most common primary injury pattern was a crescentic fracture fragment; the most common secondary injury pattern was a bony growth disturbance; and SPNBF was only noted on 26 of 84 fractures.
Conclusions: Three quarters of CCJ rib fractures identified on initial SSs show healing. An actual fracture line with a crescentic or triangular fracture fragment is less often encountered, and is usually associated with signs of healing. SPNBF is uncommon, despite other features of healing.