Predictive value of the deltoid tuberosity index for assessing the risk of screw cut-out

Abstract

Background Reconstruction of the proximal humerus with a locking plate is often the first surgical approach for proximal humerus fractures. Screw cut-out is a common complication and is relevant in osteoporotic bone of older adults. The Deltoid Tuberosity Index (DTI) is an indirect measure for assessing local bone quality and failure rate before surgery, providing important information for surgical planning. This was the first independent, large-sample retrospective analysis of the correlation between local bone density, indirectly measured through the DTI, and screw cut-out. Methods In total, 306 cases of proximal humerus fractures treated with the PHILOS plate (DePuy Synthes, Oberdorf, Switzerland) were retrospectively analyzed. The DTI was measured on anteroposterior x‑rays. The primary endpoint was screw cut-out defined as the intra-articular position of at least one screw associated with a reduction loss after surgery. Results The mean clinical follow-up was 935 days. The DTI varied from 1.10 to 2.28 (average: 1.45). Screw cut-out occurred on average in 8% of the cases and was positively correlated with a DTI of ≤ 1.44 (p = 0.003). However, the rate of cut-out and correlation with DTI varied widely according to age group: for ages 65–80 years, a DTI of ≤ 1.44 increased the cut-out rate from 0% to 17% (p = 0.02); in younger ages (< 65 years) the DTI did not correlate with cut-out and in the oldest group (> 80 years) cut-out rates were high (17–20%) independently of the DTI. Conclusion We confirm the correlation between a DTI of ≤ 1.44 and screw cut-out. High-risk groups for screw cut-out are patients over 65 years with a DTI of ≤ 1.44 or any patient older than 80 years. Applying the DTI in the age group of 65–80 years offers relevant information for surgical planning in the trauma setting via a fast, cheap, and easy-to-use tool. Level of Evidence: Level 3, Retrospective Cohort Study.