Figure 7.

The mechanism by which this uncommonly occurring, at the posterior portion of the rib, first rib stress fracture is proposed. The first rib has a rigid attachment to both the sternum anteriorly and to the first thoracic verteblae posteriorly. Horizontal abduction in the shoulder, adduction of the scapula, and the rotation of the trunk to the back cause great stress to the posterior portion of the first rib at the top position during pitching. In this case, the repetition of over horizontal abduction in the shoulder at the top position of the patient’s sidearm pitching appears to have caused the stress fracture of the first rib at this uncommon location.