The objectives of this study are to determine the prevalence, risk factors, and time to onset of delayed hemothorax and pneumothorax in adults who experienced a minor blunt thoracic trauma.

A prospective cohort of 450 consecutive patients was recruited. Eligible patients had to be over 16 years of age, consulted within 72 hours for a trauma, and available for outpatient follow-up at 2, 7, and 14 days posttrauma. The clinical outcome investigated was the presence of delayed pneumothorax or hemothorax on the follow-up chest x-ray.

Delayed hemothorax occurred in 11.8% (95% CI 8.8–14.8), and delayed pneumothorax occurred in 0.9% (95% CI 0.2–2.3) of participants. During the 14-day follow-up period, 87.0% of these delayed complications developed in the first week. In the multivariate analysis, the only statistically significant risk factor for delayed complications was the location of fractures on the x-ray of the hemithorax. The adjusted odds ratio was 1.52 (95% CI 0.62–3.73) for the lower ribs (tenth to twelfth rib), 3.11 (95% CI 1.60–6.08) for the midline ribs (sixth to ninth rib), and 5.05 (95% CI 1.80–14.19) for the upper ribs (third to fifth rib) versus patients with no fractures.

The presence of at least one rib fracture between the third and ninth rib on the x-ray of the hemithorax is a significant risk factor for delayed hemothorax and pneumothorax.