[Fatigue fractures of the 1st rib and their combination with spontaneous pneumothorax].

The pathogenesis and the causal atraumatic mechanism of uni- and bilateral stress fractures of the first rib in 4 cases of young men will be discussed. In 3 cases the discovery of these fractures has been the result of mass x-ray survey alone without complaints by the patients. As a causal factor there must be supposed a permanent strain and (or) an overstrain of the mm. scaleni. At a 15-year-old schoolboy we found a combination of bilateral fracture of the first rib and bilateral spontaneous pneumothorax. In this case we suppose that an overstrain of the mm. scaleni medius and anterior is responsible for the fractures of the rib, and an abrupt distension of the pleural cupola by the m. scalenus minimus - occurring among 72% of all European children - for spontaneous pneumothorax. Minimal subpleural emphysematous bullae adherent to the pleural cupola might be ruptured by this distension. This mechanism is probably also responsible for other cases of spontaneous pneumothorax, in which no stronger physical strains of the patient were preceding.