Temporal Pattern of Radiographic Findings of Costochondral Junction Rib Fractures on Serial Skeletal Surveys in Suspected Infant Abuse.

BACKGROUND. Costochondral junction (CCJ) rib fractures pose a challenge in the radiographic detection and dating of infant abuse. OBJECTIVE. To assess the temporal pattern of radiographic findings of CCJ fractures on serial skeletal surveys (SSs). METHODS. Reports of SSs performed for suspected infant abuse were reviewed to identify those reporting a CCJ fracture. Study inclusion required undergoing initial and approximately 2-week follow-up SSs that included AP and bilateral oblique radiographs of the reported CCJ rib fracture. Two pediatric radiologists retrospectively classified fractures in terms of the primary injury pattern (bucket-handle: visible crescentic fracture line; corner: visible triangular fracture line; other) and secondary healing pattern (growth disturbance; sclerosis; subperiosteal new bone formation [SPNBF]). Discrepant readings were resolved by consensus. RESULTS. The final cohort included 26 infants with 81 CCJ fractures. On initial SS, 59% (48/81) of fractures showed a primary pattern, most commonly a bucket-handle pattern (46% [37/81]); 6% (5/81) showed a primary pattern on follow-up SS (p<0.001). On initial SS, the prevalence of a secondary pattern was 89% (72/81), most commonly a growth disturbance (85% [69/81]), followed by sclerosis (57% [46/81]); 80% (65/81) showed a secondary pattern on follow-up SS (p=0.12). Overall prevalence of SPNBF was 28% (23/81). Addition of bilateral oblique views on initial SS resulted in a significant increase relative to the AP views alone in the detection of primary and secondary patterns by 15% (p=0.04) and 31% (p<0.001), respectively. CONCLUSION. A bucket-handle appearance is the most common primary pattern. The significantly lower prevalence of a primary pattern on follow-up vs. initial SSs suggests that the CCJ fracture line is usually visible for only approximately 2 weeks. A growth disturbance of the rib end is the most common secondary pattern, followed by bony sclerosis, consistent with a healing injury. SPNBF is uncommon. Most CCJ fractures are in a healing phase at initial diagnosis. The signs of repair commonly remain visible on 2-week follow-up. The increased diagnostic yield of oblique views provides support to the inclusion of these projections in routine SS protocols. CLINICAL IMPACT. The findings will help radiologists improve the diagnosis and dating of CCJ rib fractures.