Preoperative measurement of the thickness of the center of the humeral head predicts screw cutout after locked plating of proximal humeral fractures

Abstract

Hypothesis and background: Preoperative computed tomography (CT) scans can be used to measure the thickness of the center of the humeral head to identify patients at a higher risk of screw cutout after open reduction-internal fixation.

Methods: At an academic medical center, we performed a retrospective review of all patients aged ≥ 18 years who had sustained a proximal humeral fracture that was treated with open reduction-internal fixation between January 1, 2005, and December 31, 2014, and who underwent preoperative shoulder CT. Ninety-four patients were included. Patient charts were reviewed to obtain demographic data, and radiographs were reviewed to assess screw cutout. A standardized method was devised to measure the thickness of the center of the humeral head.

Results: Screw cutout developed in 17 patients (17.7%). The mean humeral head thickness was significantly smaller on the axial (18 mm vs. 21 mm, P = .0031), coronal (18 mm vs. 21 mm, P = .0084), and sagittal (18 mm vs. 21 mm, P = .0033) sections in the patients who experienced screw cutout. When the smallest of the 3 measurements for each patient was analyzed, the risk of cutout was markedly greater when the humeral head thickness was <20 mm (25% vs. 6%). In addition, when the humeral head thickness was >25 mm, the risk of cutout was reduced to 0%. A low-energy injury was associated with a lower risk of cutout whereas age, sex, and fracture classification were not independent predictors of cutout on multivariate logistic regression.

Conclusions: In a patient with a proximal humeral fracture in whom a preoperative CT scan is available, calculating the thickness of the center of the humeral head may provide valuable information to both the surgeon and the patient for preoperative planning and counseling. A smaller thickness of the center of the humeral head on preoperative CT is predictive of screw cutout following locked plating of proximal humeral fractures. A measurement of >25 mm in any one plane is highly protective against cutout; however, extreme caution and consideration of supplemental fixation methods should be taken when the measurements in all planes are <15 mm. This information may be helpful in counseling patients regarding the possibility of postoperative screw cutout.

Keywords: Proximal humerus; complications; cutout; humeral head; internal fixation; shoulder.