- Discussion: 
- involves vertical loading of calcaneus by talus at crucial angle of Gissane;
- usually occurs from a fall from ht landing on heels; 
- primary fracture line may take one of three paths: 
- lateral to posterior facet (from impact on pronated foot) 
- thru posterior facet (neutral foot position) 
- secondary frx line will appear beneath facet, exiting posteriorly and resulting in a tounge type fracture; 
- anteromedial to the posterior facet: 
- from impact on supinated foot; 
- primary saggital frx line enters calcaneal sulcus, anteriomedial to posterior facets, & entire posterior facet remains intact; 
- secondary frx line: 
- results from axial force; 
- posterolateral aspect of talus impacts on posterior facet resulting in explosion of lateral wall that may extend as far laterally as the calcaneocuboid joint; 
- if load is more horizontal, secondary frx line will exit just behind posteior facet which results in joint depression type of injury; 
- resultant free lateral fragment of posterior facet separates from tuberosity fragment; 
- this superolateral fragment is also known as semilunar fragment