EARLY IDENTIFICATION OF IMPAIRED FRACTURE HEALING USING BIOMARKERS: A PILOT STUDY

Femoral non-union occurs in up to 14% of patients and results in an immense patient and societal burden. Predicting which patients will exhibit impaired healing is difficult. Radiographs identify delayed healing based on a lack of interval callus formation; however, they offer limited early prognostic ability. Biomarker analysis may allow for early identification of patients who are progressing towards non-union, thereby facilitating early intervention. The aim of this pilot study was to determine the relationship between radiographic healing and collagen-10 (CXM), leptin, bone morphogenetic protein (BMP-2), insulin-like growth factor (IGF-1), and platelet-derived growth factor (PDGF-b). We hypothesized that biomarker levels would be correlated with radiographic healing and incidence of non-union. Ethics approval was granted for this analysis of patients aged 18–65 years undergoing intramedullary fixation of a closed unilateral diaphyseal femur fracture. Age, sex, fracture classification, and injury severity score (ISS) were collected. Blood samples were collected two and six weeks postoperatively. Leptin, BMP2, IGF-1, PDGF-b, and CXM were analysed using analyte-specific assays (MESO QuickPlex, Meso Scale Diagnostics) and enzyme-linked immunosorbent assay (SomaScan, SomaLogic Inc.). Radiographs were reviewed at six weeks, twelve weeks, and six months post-operatively, and until union. Radiographs were classified as healed (bridging of three or more cortices), partially healed, or not healed, and scored using the modified Radiographic Union Score for Tibial fractures (mRUST). Time to union was measured in months. Statistical analyses were performed using t-tests, Spearman and Pearson correlation, and analysis-of-variance. Sixteen patients were included, 68.8% of whom were male with a mean age of 34.9 years (SD=14.1) and mean ISS of 10.5 (SD=3.8). Three patients (19%) met the diagnostic criteria for non-union. By six months 79% of fractures had healed, with a mean time to union of 6.15 months (SD=3.4). Age, sex, and ISS were not associated with fracture healing. Patients who developed non-union had significantly lower CXM at two weeks (p = 0.006). Patients who demonstrated early callus formation at six weeks had lower BMP-2 and higher CXM at two and six weeks (p < 0.05). Similarly, two- and six-week BMP-2 levels were lower in patients who healed by six months (p < 0.05). Six-week mRUST was significantly correlated with two-week CXM (r = 0.6, p = 0.02) and negatively correlated with six-week BMP-2 (r = −0.7, p = 0.03). Similarly, six-month mRUST was negatively correlated with two-week BMP-2 (r = −0.9, p = 0.009). Shorter time to union was associated with lower BMP-2 at both timepoints (r = 0.83–0.85, p < 0.05) and higher six-week IGF-1 (r = −0.6, p = 0.02). This is one of the first studies to evaluate early identification of impending non-union using biomarkers in humans. Leptin, BMP-2, IGF-1, PDGF-b, and CXM were detectable two and six weeks postoperatively. We identified associations between BMP-2, IGF-1, and CXM and radiographic healing. Most notably, patients who developed non-union had significantly lower two-week CXM compared to patients who united. This study is limited by our small sample size and only two biomarker timepoints. However, our results provide promising data which have informed ongoing studies on early detection of impaired healing using biomarkers, with the goal of improving patient outcomes.