Combination of extracorporeal shock wave therapy and low intensity ultrasound for inducing healing of non-union in a rabbit model

Abstract

Introduction: Despite the advances in modern orthopedic fracture treatment, the rate of delayed union or non-union in all types of fractures remains about 10%. Most recently, two biophysical methods, extracorporeal shock waves (ESW) and low intensity pulsed ultrasound (LIPU), have been shown to be effective in healing fracture non-union. It is suggested that, single ESW treatment could be a trigger that can "initiate" the ossification procedure in the non-union site. On the contrast, LIPU therapy requires daily application over a time period of months to enhance repair process. Objectives of this study were: (1) to compare the success rate, healing quality of a non-union among 3 treatment methods of isolated ESW, LIPU and combined therapy; (2) to investigate the pattern of healing to non-union by the 3 different methods. Methods: New Zealand White rabbit of 18 weeks (about 3kg) was used in the study. With 24 rabbits performed right tibia osteotomy, they were equally divided into four groups at post-operation week 12: the control group, ESW treatment group, LIPU treatment group and the ESW plus daily LIPU treatment group. Radiographs were taken for all groups postoperatively week 12,14 and then biweekly until week 22. Rabbits were sacrificed postoperatively at week 22 for evaluations of repair using peripheral quantitative computerized tomography (pQCT), microcomputerized tomography, fluorescence microscopy and light microscopy. Results: The union rate in isolated ESW and LIPU group were both 66.7%, as well as the combined treatment was 66.7%, while there was no single union case formed in the control group at week 22. The difference was of statistic significance (p<0.05). Fluorescence microscopic findings suggested that 3 treatment methods promoted bony bridging mainly by endochondral bone formation in the non-union gap, without obvious periosteal callus formation. The healing pattern of LIPU and combined treatment was similar with slower onset of new bone formation than ESW but the healing quality was better and bone cell density was higher than ESW group at week 22 in microscopic evaluations. Conclusion: ESW, LIPU and combined treatment were effective to the healing of non-union. The pattern and the process of ESW promoted bony bridging in fracture non-union were distinct from those found in typical primary or secondary fracture healing. Similar pattern was also revealed in the combined treatment and LIPU treatment groups.