The Radiographic Union Score for Hip (RUSH) Identifies Radiographic Nonunion of Femoral Neck Fractures

BACKGROUND: The Radiographic Union Score for Hip (RUSH) is a previously validated outcome instrument designed to improve intra- and interobserver reliability when describing the radiographic healing of femoral neck fractures. The ability to identify fractures that have not healed is important for defining nonunion in clinical trials and predicting patients who will likely require additional surgery to promote fracture healing. We sought to investigate the utility of the RUSH score to define femoral neck fracture nonunion. QUESTIONS/PURPOSES: (1) What RUSH score threshold yields at least 98% specificity to diagnose nonunion at 6 months postinjury? (2) Using the threshold identified, are patients below this threshold at greater risk of reoperation for nonunion and for other indications? METHODS: A representative sample of 250 out of a cohort of 725 patients with adequate 6-month hip radiographs was analyzed from a multinational elderly hip fracture trial (FAITH). All patients had a femoral neck fracture and were treated with either multiple cancellous screws or a sliding hip screw. Two reviewers independently determined the RUSH score based on the 6-month postinjury radiographs and interrater reliability was assessed with the interclass correlation coefficient (ICC). There was substantial reliability between the reviewers assigning the RUSH scores (ICC, 0.81; 95% confidence interval [CI], 0.76-0.85). The RUSH score is a checklist-based system that quantifies four measures of healing: cortical bridging, cortical fracture disappearance, trabecular consolidation, and trabecular fracture disappearance.. Fracture healing was determined by two independent methods: (1) concurrently by the treating surgeon using both clinical and radiographic assessments as per routine clinical care; and (2) retrospectively by a Central Adjudication Committee using complete obliteration of the fracture line on radiographs alone. Receiver operating characteristic tables were used to define a RUSH threshold score that was > 98% specific for fracture nonunion. RESULTS: A threshold score of < 18 was associated with a 100% specificity (95% CI, 97%-100%) and a positive predictive value of 100% (95% CI, 73%-100%) for radiographic nonunion. In contrast, using the fracture healing assessments of the treating surgeons failed to identify a useful discriminatory nonunion threshold and the highest positive predictive value was 43%. With respect to complications, patients with RUSH scores below 18 had greater risk of undergoing reoperation for nonunion (reoperation when < 18: six of 13 [46%]; reoperation when ≥ 18: 11 of 237 [54%]; relative risk [RR], 9.9 [95% CI, 4.4-22.7]; p < 0.001) and for all indications (reoperation when < 18: eight of 13 [62%]; reoperation when ≥ 18: 54 of 237 [38%]; RR, 2.7 [95% CI, 1.7-4.4]; p = 0.004). CONCLUSIONS: The 6-month RUSH score is a reliable method for assessing radiographic healing. Our results highlight the discordance between radiographic determinations and clinician assessments of fracture healing and stress the need for clinical data to be incorporated in research studies evaluating fracture healing. LEVEL OF EVIDENCE: Level III, diagnostic study.