Background: There is biomechanical evidence that bone density predicts the mechanical failure of implants. The aim of this prospective study was to evaluate the influence of local bone mineral density on the rate of mechanical failure after locking plate fixation of proximal humeral fractures.
Methods: We enrolled 150 patients who were from fifty to ninety years old with a closed, displaced proximal humeral fracture fixed with use of a locking plate from July 2007 to April 2010. There were 118 women and thirty-two men who had a mean age of sixty-nine years. Preoperative computed tomography (CT) scans were done to assess bone mineral density of the contralateral humerus, and dual x-ray absorptiometry of the distal end of the radius of the unaffected arm was conducted within the first six weeks postoperatively. At follow-up evaluations at six weeks, three months, and one year postoperatively, pain, shoulder mobility, strength, and multiple functional and quality-of-life outcome measures (Disabilities of the Arm, Shoulder and Hand [DASH] questionnaire; Shoulder Pain and Disability Index [SPADI]; Constant score; and EuroQuol-5D [EQ-5D]) were done and standard radiographs were made. We defined mechanical failure as all complications related to bone quality experienced within one year.
Results: After locking plate fixation, fifty-three (35%) of 150 patients had mechanical failure; loss of reduction and secondary screw loosening with perforation were common. CT assessments of local bone mineral density showed no difference between patients with and without mechanical failure (89.82 versus 91.51 mg/cm3, respectively; p = 0.670). One-year DASH, SPADI, and Constant scores were significantly better for patients without mechanical failure (p ≤ 0.05).
Conclusions: We did not find evidence of an association between bone mineral density and the rate of mechanical failures, which may suggest that patients with normal bone mineral density are less prone to sustain a proximal humeral fracture. Future studies should target other discriminating factors between patients with and without mechanical failure.
Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
1Department of Trauma Surgery and Sports Traumatology, Medical University Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria. E-mail address for F. Kralinger: email@example.com
2Institute for Biomechanics, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland
3Department of Trauma Surgery, Kantonsspital Winterthur, Brauerstr. 15, CH-8401 Winterthur, Switzerland
4Department of Trauma and Reconstructive Surgery, Friederikenstift, Humboldstr. 5, D-30169 Hannover, Germany
5Department of General, Hand, and Trauma Surgery, Stadtspital Triemli, Birmensdorferstr. 497, CH-8063 Zürich, Switzerland
6AO Clinical Investigation and Documentation, AO Foundation, Stettbachstrasse 6, CH-8600 Duebendorf, Switzerland