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Low-Intensity Pulsed Ultrasound for Early-Stage Lumbar Spondylolysis in Young Athletes

Tsukada, Masahiro PT*; Takiuchi, Toshiro MD; Watanabe, Kota MD, PhD

Clinical Journal of Sport Medicine: July 2019 - Volume 29 - Issue 4 - p 262–266
doi: 10.1097/JSM.0000000000000531
Original Research
Free

Objective: To examine the effect of low-intensity pulsed ultrasound (LIPUS) on early-stage spondylolysis in young athletes.

Design: Case–control study.

Setting: A single outpatient orthopedic and sports clinic.

Patients: A total of 82 young athletes (80 boys and 2 girls; mean age, 14.8 years; range, 10-18 years) with early-stage lumbar spondylolysis were enrolled in this study. All patients were examined by plain radiography and magnetic resonance imaging.

Interventions: Patients received either standard conservative treatment combined with LIPUS (n = 35) or without LIPUS (n = 47), according to the sequence of admission. The standard conservative treatment included thoracolumbosacral brace, sports modification, and therapeutic exercise.

Main Outcome Measures: The time required to return to previous sports activities was analyzed by using Kaplan–Meier methods with the log-rank test.

Results: The baseline parameters of both groups were not significantly different. The median time to return to previous sports activities was 61 days [95% confidence interval (CI): 58-69 days] in the group treated with LIPUS, which was significantly shorter than that of the group treated without LIPUS (167 days, 95% CI: 135-263 days; P < 0.01).

Conclusions: These results suggest that LIPUS combined with conservative treatment for early-stage lumbar spondylolysis in young athletes could be a useful therapy for quick return to playing sports.

Departments of *Rehabilitation; and

Orthopedic Surgery, Takiuchi Orthopedic and Sports Clinic, Sapporo, Japan; and

Department of Physical Therapy, Sapporo Medical University School of Health Sciences, Sapporo, Japan.

Corresponding Author: Masahiro Tsukada, PT, Department of Rehabilitation, Takiuchi Orthopedic and Sports Clinic, Sapporo Hokushin Building 2F, 11 South-1, West-6, Chuo-ku, Sapporo 060-0061, Japan (nygsr331@gmail.com).

The authors report no conflicts of interest.

Research Ethics Committee of the Society of Physical Therapy Science: SPTS2016008.

Received April 12, 2017

Accepted August 24, 2017

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INTRODUCTION

Lumbar spondylolysis is a defect of the pars interarticularis and is a common cause of low back pain in young athletes.1–4 Although multiple factors may be involved in its genesis, when lumbar spondylolysis occurs among sports players, it is generally manifested as a stress fracture of the pars caused by repetitive extension and/or rotation activities.5–7 The treatment of spondylolysis is initially conservative and aims to reduce pain and facilitate healing. As previous studies have reported, early diagnosis and treatment of spondylolysis are clearly important for conservatively treating patients successfully.2,4,8–13 Conservative treatment typically requires use of a thoracolumbosacral brace and refraining from sporting activities for 3 to 6 months.9,13–17 However, the treatment period is very long in many athletes who require structural repair of their defects for rapid return to previous activities with minimal recovery time.14

Low-intensity pulsed ultrasound (LIPUS) has been extensively used in medicine as a diagnostic and therapeutic modality. Low-intensity pulsed ultrasound is a form of mechanical energy that can be transmitted into biological tissue as acoustic pressure waves.18,19 The micromechanical strain produced by these acoustic waves in biological tissue can result in biomechanical events at the cellular level.20 It has been reported to be effective in promoting fracture healing in animal models and clinical trials.20–23 Several studies have shown the benefits of LIPUS exposure for enhancing bone healing after fresh fractures and in patients with delayed and nonunion of various bones.24–30 More recently, various reports have suggested that LIPUS promotes healing in stress fracture injuries too.31–34 However, its potential role in stress fracture healing is still under investigation, with other studies unable to identify a benefit of LIPUS on recovery after bone stress injury.35 To our knowledge, the effect of LIPUS on bone stress injury of the pars interarticularis has not yet been published. The present study, using retrospective comparative protocol, has reported the effect of LIPUS for young athletes with early-stage spondylolysis. “Early-stage spondylolysis” consisted of a bone stress injury within the pars interarticularis identified by a signal change on magnetic resonance imaging (MRI) without a corresponding bone defect observable on plain radiography.

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MATERIALS AND METHODS

Patients

We retrospectively reviewed the clinical records of 294 patients with lumbar spondylolysis who had undergone conservative treatment at our outpatient clinic between April 2009 and September 2015. All patients were examined by plain radiography and MRI when first seen. Among them, 82 patients who (1) had low back pain without neurological abnormalities in the lower limbs, (2) had early-stage spondylolysis diagnosed by plain radiography (no findings of spondylolysis) and T1- and T2-weighted MRI (T1; low signal, T2; high signal change in the pedicle adjacent to the pars interarticularis, Figure 1A), (3) were 18 years or younger, and (4) were actively participating in sports were enrolled. Patients with clear spondylolysis or spondylolisthesis detectable by plain radiography were excluded from the study.

There were 80 boys and 2 girls, with a mean age of 14.8 years (range, 10-18 years). The patients were then allocated to standard conservative treatment with LIPUS (LIPUS group, n = 35) or standard conservative treatment only (control group, n = 47), according to the sequence of admission. Patients who visited our clinic before July 2010, when the LIPUS device was introduced in our clinic, were assigned to the control group, and patients after introduction were assigned to the LIPUS group. Written consent was obtained from all patients and their parents before start of treatment. The investigation was approved by the ethics committee of Society of Physical Therapy Science.

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Interventions

Patients with early-stage lumbar spondylolysis received either LIPUS combination or noncombination treatment. All patients received standard conservative treatment, including thoracolumbosacral brace, sports modification, and therapeutic exercise. The brace was a Damen-type soft corset, and patients were asked to use it during all active periods of the day. In principle, sports activities were prohibited. Therapeutic exercises included stretching of the muscles surrounding the hip and strengthening of the trunk muscles. Patients were also instructed in self-conditioning by a physical therapist.

In addition to these conservative therapies, the patients in the LIPUS group were treated by using an ultrasonic therapeutic device (Accellus; Nippon Sigmax Co, Ltd, Tokyo, Japan). The device has 2 treatment heads that could be exposed at the same time even if it is the case of bilateral pars defect. Low-intensity pulsed ultrasound exposure was performed once to the affected area more than 3 times a week during the treatment period. Low-intensity pulsed ultrasound exposure was provided by a physical therapist. The treatment head module was coupled with the skin over the site of bone stress injury using a standard ultrasound transmission gel (Aquasonic 100; Parker Laboratories Inc, Fairfield, NJ) and fixed with a Velcro strap. The ultrasound pressure wave signal was applied by using the following parameters: 1.5-MHz oscillation frequency, 1-kHz pulsed frequency, 30-mW/cm2 spatial intensity, and a duration of 20 minutes.

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Evaluation of Recovery

All patients were scheduled to return for follow-up radiography every month and for MRI every 2 months after the start of treatment. Clinical follow-up evaluations were performed by the same orthopedic surgeon. The endpoint of this study was healed spondylolysis, as judged by T2-weighted MRI (disappearance of high signal change in the pedicle adjacent to the pars interarticularis, Figure 1C) and by radiography (without separation). At this point, the patients were allowed to resume their previous sports activities.

Figure 1

Figure 1

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Statistical Analysis

The continuous variables were presented as the mean ± SD for normally distributed data and as the median [95% confidence interval (CI)] for non-normally distributed data. The Mann–Whitney U test was used to compare the continuous variables between groups, and the Fisher exact test or χ2 test was used to compare the categorical data between groups. In addition, log-rank life-table analysis was used to compare the time to return to sports activities between the 2 groups. Survival curves were determined by using Kaplan–Meier methods, and differences in survival between groups were compared by using the log-rank test. Survival analysis was performed because it properly analyzes censored observations by using days to the latest follow-up examination as the time-to-event value. All statistical analyses were performed by using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), and significance was defined as P ≤ 0.05.

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RESULTS

Eighty-two young athletes with early-stage lumbar spondylolysis (80 boys and 2 girls), mean age of 14.8 years (range, 10-18 years), were included. Table 1 gives more detailed information of the patients. All patients were active in sports (Table 2). There was no significant difference in any of the patient- or spondylolysis-related parameters between the 2 treatment groups.

TABLE 1

TABLE 1

TABLE 2

TABLE 2

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).

Figure 2

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.

TABLE 3

TABLE 3

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).

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DISCUSSION

This study investigated the effect of LIPUS on young athletes with early-stage spondylolysis. The patients treated with a combination of LIPUS and standard conservative treatment took a significantly shorter time to return to sports activities than that of the patients treated with standard conservative treatment only. The patients and spondylolysis characteristics in the 2 treatment groups were very similar before treatment, as shown by a comparative analysis. The clinical follow-up evaluation was performed by the same orthopedic surgeon, and a diagnosis was made on the basis of MRI and x-ray findings. Our results indicated that LIPUS was an effective treatment for promotion of healing early-stage spondylolysis and shortening of the treatment period. Furthermore, the lost during follow-up rate in the LIPUS group was significantly lower than that in the control group, which was probably because the treatment period was shortened. These results suggest that LIPUS combined with conservative treatment could be a useful therapy for quick return to sports.

Low-intensity pulsed ultrasound is a special type of acoustic pulsed energy that provides an optimal biological and biophysical environment promoting skeletal maintenance and repair as a safe and noninvasive method.18–22 To date, several investigators have demonstrated that mechanical force modulates bone formation both in vivo and in vitro.23–30,36 Regarding the effect of LIPUS on bone stress injuries, several studies focusing mainly on lower limb injuries have been reported.31–35,37 Yadav et al32 performed a double-blind, randomized, controlled trial of 67 military personnel with tibial stress fractures and also demonstrated that patients in the LIPUS treatment group were able to return to duty faster than those in the placebo group. Similar positive effects were observed by Uchiyama et al33 in delayed and nonunion tibial stress fractures. However, in a controlled clinical study by Rue et al,35 daily exposure of LIPUS did not significantly reduce the healing time for tibial stress fractures. The effect of LIPUS on bone stress injuries is still under discussion. To our knowledge, this is the first report on the effect of LIPUS on early-stage lumbar spondylolysis (ie, bone stress injury of the pars interarticularis) healing. The endpoint of this study was defined as the point in time when a high signal change in the pedicle adjacent to the pars interarticularis T2-weighted MRI disappeared without an observed change in the x-ray findings and the patients were allowed to return to sports. Sairyo et al8 reported that a high signal change in the pedicle was useful for diagnosis of early-stage spondylolysis and its change due to bone marrow edema. In this study, the high signal change exhibited by patients in the LIPUS group disappeared within approximately 2 months, and the patients were able to return to sports activities. Our results suggest that LIPUS promoted reduction of bone marrow edema. Uchiyama et al33 reported that bone marrow edema of the tibia completely disappeared within 4 months after treatment of LIPUS. Gan et al37 also reported that the bone marrow edema of lower limb decreased significantly faster in the LIPUS group than in the control group (P < 0.001). Regarding the action of LIPUS, several investigators have postulated a multifaceted biological mechanism. Previous studies suggested that the mechanical energy transferred by LIPUS acts on various processes, such as inflammatory reaction, angiogenesis, chondrogenesis, intramembranous ossification, endochondral ossification, and bone remodeling.36,38 Through these actions, LIPUS is believed to provide an optimal biological and biophysical environment to promote skeletal maintenance and repair.20–23 It is thought that the same mechanism acted on the results obtained in this study, but unfortunately, we did not collect evidence to confirm this in our study.

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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Keywords:

low-intensity pulsed ultrasound; early-stage lumbar spondylolysis; bone stress injury; conservative treatment; young athletes; return to sports activity

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