As a result of that the analysis, the median time to the endpoint of the study (disappearance of high signal change in the pedicle adjacent to the pars interarticularis judged by T2-weighted MRI) was 61 days (95% CI, 58-69 days) for the LIPUS group and 167 days (95% CI, 135-263 days) for the control group (P < 0.01). At 90 days after the start of treatment, 65.7% of the patients with spondylolysis in the LIPUS group had recovered compared with only 12.8% of the patients in the control group; at 120 days, 82.9% of the patients with spondylolysis in the LIPUS group had recovered compared with only 25.5% of the patients in the control group (Figure 2).
The complete clinical follow-up rate was 91.4% for the LIPUS group and 57.4% for the control group (Table 3). A significant (P < 0.01) difference was found between the LIPUS and control groups.
During treatment, of the 7 patients [2 (5.7%) who had LIPUS treatment and 5 (10.6%) who had control treatment] who showed disease progression (P = 0.43), 2 patients who had LIPUS treatment returned to sports at 105 days and 214 days, respectively; 2 patients who had control treatment returned to sports at 203 days and 263 days, respectively; and 3 patients did not complete follow-up.
After analyzing compliance with the patients' follow-up protocol, the scheduled first MRI retesting examination rates were 97.1% in the LIPUS group and 97.9% in the control group. The LIPUS group was retested 58.3 ± 7.7 days after the first visit, and the control group was tested 58.5 ± 15 days after the first visit. Even with the subsequent treatment period, the MRI imaging interval of the LIPUS group averaged 59.6 ± 9.1 days (total number of imaging times, 79) and of the control group was 55.6 ± 19.0 days (total number of imaging times, 211). The median number of LIPUS irradiations was 27 (interquartile range, 18-35).
The most common nonoperative management of spondylolysis includes cessation of sports, thoracolumbosacral braces, and physiotherapy.13,14 These treatments are generally recommended for 3 to 6 months.9,15–17 Panteliadis et al14 analyzed the pooled outcomes of conservative management for an athletic population with spondylolysis and reported that the weighted mean duration of treatment was 3.7 months. However, this treatment period is very long for many young athletes, and it is not rare for some to drop out of treatment without complete recovery. In this study, the median time to return to achieve vigorous sports activities was 61 days in the LIPUS group, which was significantly shorter than that of the control group (167 days), and the treatment period was shortened by 63.5%. In addition, the lost during follow-up rate for the patients in the LIPUS group was lower than that for the patients in the control group. Debnath et al39 reported that motivation was also important for recovery from this injury. A short treatment period was useful for maintaining motivation and may have been effective for better treatment outcome.
There were several limitations in our study. First, owing to its retrospective nature, selection bias may have occurred in this study. In addition, there are problems of study design such as nonblinding of assessors, lack of a placebo control, and diagnosis not being quantified. These factors also had the potential to affect the results. In future, a large, randomized, prospective study is needed confirm the benefits of LIPUS on spondylolysis. Second, there was a lack of strict criteria for the follow-up imaging and treatment protocol. Regarding MRI re-examination, the examination rates were high in both groups. After MRI, the dropout rate of the control group was high (42.6%), but we believe that bias was suppressed by the survival time analysis that included those who dropped out. In this study, because the investigation was conducted within the scope of the Japanese public health insurance system, the MRI assessments interval was set to 2 months. This includes the possibility of setting the difference in treatment period of several days as a difference of about 60 days. During this treatment period, lack of data on clinical evaluation such as pain is limitation of this study. Regarding the treatment protocol, the LIPUS group included patients who were able to continue treatment more than 3 times a week. Daily LIPUS exposure could not be performed because of environmental factors during treatment. In this study, we could not determine the validity of this exposure frequency. However, this study had the advantage of enabling investigation of the effect of LIPUS on patients with early-stage lumbar spondylolysis relative to the effect on the control group.
In conclusion, the study findings indicate that LIPUS exposure may be useful not only for fracture treatment but also for treatment of bone stress injuries, such as early-stage lumbar spondylolysis,8,13 in young athletes.
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