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Four-part fracture
2%
99/4585
Head-splitting fracture
5%
214/4585
Neck fracture with a long calcar segment
84%
3856/4585
Disrupted medial periosteal hinge
6%
258/4585
AO type C3 fracture
3%
138/4585
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A long calcar fracture segment, also known as the posteromedial metaphyseal head extension, is a good prognostic sign against the development of osteonecrosis in displaced proximal humerus fractures. The humeral head is directly supplied by the anterior and posterior humeral circumflex arteries. Disruption of these vessels can result in humeral head osteonecrosis. Fracture patterns with long medial metaphyseal segments (greater than 8 mm) have not shown to critically disrupt the vascular supply to the humeral head causing osteonecrosis. Other factors shown to be protective against osteonecrosis after trauma include an intact medial hinge and simple fracture patterns. Hertel et al. examined the factors predictive of osteonecrosis of the humeral head after fracture. These include four-part fragments, angular displacement >45 degrees of the head, displacement of the tuberosities greater than 10 mm, glenohumeral fracture-dislocation, and head-splitting fractures. In Hertel's second paper and follow up study they noted that the initial post-fracture humeral head ischemia does not predict development of necrosis. Illustration A shows an example of a long and short calcar fracture segment. Illustration B shows the AO classification of proximal humerus fractures. Incorrect Answers: Answers 1,2,4,5: All these factors are predictive of osteonecrosis.
4.8
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