Relationship of cortical thickness of the proximal humerus and pullout strength of a locked plate and screw construct.
BACKGROUND
No study to date has evaluated cortical thickness as it relates to locking plate failure or screw pullout in the proximal humerus. The purpose of this study is to determine the relationship between proximal humerus cortical thickness and locked plate hardware failure in a cadaveric proximal humerus fracture model.


METHODS
Twelve humerus specimens were placed into two groups based on the proximal humerus cortical thickness on an anteroposterior radiograph: less than 4 mm and greater than 4 mm. The specimens were plated with a six-hole proximal humerus locking plate and a 15-mm resection osteotomy at the surgical neck was performed. The specimens were tested in a materials testing machine at a displacement of 5 mm/min to failure.


RESULTS
Load at failure, stiffness, maximum load, failure, and fracture gap closure were all statistically similar (P > 0.05) between the groups.


CONCLUSIONS
Our biomechanical study used modern locked plate-screw construct fixation of a simulated two-part proximal humerus fracture. The mechanical strength was unaffected based on a threshold combined proximal humerus cortical thickness of 4 mm.
Department of Orthopaedic Surgery, St Louis University, St Louis, MO 63110, USA.
Maegen J
MJ
Wallace
Gary
G
Bledsoe
Berton R
BR
Moed
Heidi A
HA
Israel
Scott G
SG
Kaar
D000369:Aged, 80 and over; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D055119:Elastic Modulus; D019544:Equipment Failure Analysis; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017276:Friction; D006801:Humans; D006811:Humerus / Q000503:physiopathology* / Q000601:surgery*; D008297:Male; D011474:Prosthesis Design; D012784:Shoulder Fractures / Q000503:physiopathology* / Q000601:surgery*; D013718:Tensile Strength