Prospective CT Scan Evaluation of Hindfoot Nonunions Treated with Revision Surgery and Low-Intensity Ultrasound Stimulation

Abstract

Background: The reported fusion rates of revision arthrodesis for hindfoot nonunions are relatively low compared to primary procedures. Exogenous ultrasound has been shown to accelerate the healing process of acute fractures and fracture nonunions but has not been previously evaluated for the treatment of hindfoot pseudarthroses. The purpose of this study was to evaluate the clinical and radiographic outcomes of revision hindfoot arthrodeses treated with postoperative low-intensity ultrasound. Methods: Thirteen patients (13 feet) with established hindfoot nonunions were treated with revision arthrodesis and adjunctive postoperative low-intensity ultrasound. The patients were prospectively evaluated with hindfoot American Orthopaedic Foot Ankle Society (AOFAS) and pain visual analog scores, subjective satisfaction surveys, and serial radiographs. All patients underwent postoperative CT to evaluate the fusion mass, which was quantitated using a novel system. The mean follow-up from revision surgery was 16.3 (range 12 to 25) months. The 10 subtalar and three triple revision arthrodeses comprised a total of 19 joints. Results: Based on the CT scans and the grading system devised, there was one nonunion (isolated subtalar revision), five partial unions, and 13 complete unions. The 10 isolated subtalar revision arthrodeses demonstrated a mean fusion ratio of 65.1% (range 14% to 100%). Excluding the one nonunion, the average fusion ratio for the subtalar revisions was 77.3%. The mean hindfoot AOFAS score improved significantly ( p < 0.005) from 45.3 (range 18 to 65) preoperatively to 72.3 (range 47 to 92) postoperatively out of 94 possible points. There was a significant ( p < 0.005) decrease in the pain visual analog scale (VAS) from a preoperative value of 7.7 (range 4 to 10) to a postoperative value of 2.5 (range 0 to 6). There was a weak inverse correlation between the fusion percentages and the pain VAS scores ( r = −0.26) and a weak correlation ( r = 0.29) between the fusion percentages and the final AOFAS scores. Conclusions: When used to evaluate hindfoot arthrodeses, plain radiographs may be misleading. CT provides a more accurate assessment of the healing, and we have devised a new system to quantitate the fusion mass. Postoperative low-intensity ultrasound is easy to apply and administer, with no identifiable risks or contraindications. Although this modality may facilitate the fusion process, we cannot definitely conclude the specific relative value of low-intensity ultrasound because this was not a controlled series.