Bony defects: Glenoid and humeral side-on-track/off-track concept

Bone loss is one of the most relevant factors affecting shoulder stability. Effective assessment of the bone loss pattern might be the key to understand the behavior of a large number of shoulder instabilities, to plan the most effective treatment, and to establish the prognosis. Coexisting lesions on the glenoid side and the humeral head side interacting together are a highly relevant bone loss pattern affecting shoulder biomechanics. These are named “bipolar lesions.” Great effort was made to develop a method to quantify the negative influence of this relationship and to define a data-related therapeutic pathway, thus the “on-/off-track method” was refined. At 5 years from its publication, the advantages and limitations of this method are better defined.