SLR - April 2019 - Alisha Poonja

Bone Density Correlates with Clinical Outcomes After Ankle Fracture Fixation

Reference: Warner SJ, Garner MR, Fabricant PD, Lorich DG. Bone density correlates with clinical outcomes after ankle fracture fixation. Arch Orthop Trauma Surg. 2018 Dec; 138(12): 1653–1657. doi: 10.1007/s00402-018-3017-7.

Scientific Literature Review

Reviewed By: Alisha Poonja, DPM
Residency Program: Montefiore Medical Center, Bronx, NY

Podiatric Relevance: The increasing prevalence of osteoporosis provides numerous challenges in ankle fracture fixation. Decreased bone density is a known risk for fracture incidence and severity; however, the effects of bone quality on postoperative clinical outcomes is unknown. Dual-energy X-ray absorptiometry (DEXA) scans are often used to define osteoporosis; however, they are not routinely performed in preoperative evaluations and local bone quality may not correlate with systemic osteoporosis. Alternatively, osteoporosis can be evaluated using Hounsfield Units (HU), a quantitative measure of radiodensity on CT scan. Given that CT scans are often obtained prior to ankle ORIF, the objective of this study was to determine whether bone quality, as assessed by HU values on preoperative CT scan, correlates with postoperative clinical outcomes.

Methods: A prospective database of operatively treated ankle fractures by a single surgeon from 2003 to 2013 was used to identify eligible patients. Inclusion criteria consisted of a preoperative CT scan of the injured ankle, as well as a contralateral postoperative CT scan. The primary clinical outcome was the Foot and Ankle Outcome Score (FAOS), and the secondary outcome was ankle range of motion, which were both measured at 12 months postoperatively. 

HU values were measured by drawing the largest possible ellipse in the metaphyseal region on axial CT at the level of the plafond, excluding fracture fragments and cortical margins to prevent distortion of the value. The values for each tibia and fibula were averaged over three axial slices to determine the mean HU for each ankle.

Results: Sixty-four patients were included in the study. Sixty-four percent were women, with an average age of 54 years old. The injuries were classified as 39 SER, 8 PER, 3 SAD and 14 variant fracture patterns. 

HU values for the injured distal tibia and fibula were 253.8 and 255.0, while the scores for the contralateral tibia and fibula were 256.6 and 246.6, respectively. Interrater reliability was assessed using the intraclass correlation coefficient (ICC), which ranged between 0.989 and 0.996.  The nearly perfect ICC validated that HU scores obtained from the injured ankles were accurate, despite initial concerns that there may be discrepancies compared to the contralateral side due to artifact from the fracture fragments. Twenty patients also underwent DEXA analysis within three months of surgery. The HU values from the injured ankle correlated with the bone mineral density (BMD) obtained from the DEXA scans. Increased HU values were associated with improved outcomes in three out of five FAOS categories: activities of daily living, sports and quality of life. Once the confounding variables of age and smoking were considered, improved outcomes were also noted in patient symptoms. Ankle range of motion did not significantly correlate with HU values.

Conclusions: The results of this study suggest that there is a correlation between bone quality, as measured using HU values on preoperative CT, and short-term clinical outcomes. As the prevalence of osteoporosis continues to increase, the ability to quantitatively assess bone quality has implications for integrating bone quality into surgical treatment algorithms for ankle fracture fixation.

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