Clinical Efficacy of Ultrasound-Assisted Scoliosis-Specific Exercise in Mild-Grade Adolescent Idiopathic Scoliosis

Summary

Here, we present a protocol to evaluate ultrasound-assisted scoliosis-specific exercise in adolescents with mild idiopathic scoliosis, with participants randomly assigned to a training program conducted three times per week for three months, followed by a three-month observation period, providing real-time feedback on intercostal muscle activation and breathing control.

Abstract

The present protocol describes a randomized clinical trial evaluating ultrasound-assisted scoliosis-specific exercise (USSE) for adolescents with mild idiopathic scoliosis. Participants were randomly assigned using a random number method to either the control group or the treatment group (n = 10 per group). The intervention, performed three times per week for three months, aims to prevent curve progression and enhance pulmonary function by providing real-time ultrasound feedback to optimize thoracic muscle activation and breathing control during targeted therapeutic exercises. The control group received conventional functional training, whereas the treatment group additionally underwent USSE alongside home-based functional training. Outcome measures included primary structural indicators, defined as the change in main curve angle before and after treatment and the difference between groups; secondary structural indicators included respiratory function measures such as tidal volume (TV), inspiratory capacity (IC), vital capacity (VC), and maximal voluntary ventilation (MVV); and ultrasound-based measures, including changes in intercostal space width. The results demonstrated that USSE effectively controls and reduces progression of mild scoliosis, improves the structure of the concave-side intercostal space, enhances diaphragmatic mobility.

Introduction

AIS is a three-dimensional (3D) structural spinal deformity of unknown etiology, characterized by axial rotation, lateral curvature in the coronal plane, and abnormal sagittal alignment, including thoracic hypokyphosis or lumbar hyperlordosis¹. AIS affects the growth and development of healthy children and adolescents (hereafter referred to as adolescents) and, in severe cases, may lead to significant physiological complications, such as chronic back pain, cardiopulmonary dysfunction, and psychological distress.

Currently, the diagnosis of scoliosis is primarily based on standing X-ray imaging, with the Cobb angle -- measured between the upper and lower end vertebrae of the curve -- used as the standard diagnostic criterion. A Cobb angle of ≥10° is defined as scoliosis, and according to international classification guidelines, a curve measuring between 10°and 25° is classified as mild AIS ². In China, the prevalence of scoliosis among adolescents aged 10-18 is approximately 1.2%, with a rising trend observed in recent years³. Although the majority of AIS cases are classified as mild, the risk of curve progression in untreated patients underscores the need for timely intervention³.

AIS patients exhibit significantly lower pulmonary function - including forced vital capacity (FVC), forced expiratory volume in 1s (FEV₁), and peak expiratory flow (PEF) - and reduced respiratory muscle strength - including maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) -- compared with age-matched healthy controls (P < 0.01). ⁴These impairments are negatively correlated with both Cobb angle and trunk rotation angle. Structural deformities of the thoracic cage may place the intercostal muscles and diaphragm in a mechanically disadvantaged position, reducing contractile efficiency. Evidence indicates that respiratory training can enhance diaphragmatic and intercostal muscle contractility, improve thoracic compliance, optimize ventilation-perfusion matching, and modulate respiratory center sensitivity, leading to significant improvements in respiratory muscle strength and pulmonary function (P < 0.001)^5,6,7.

The International Society on Scoliosis Orthopaedic and Rehabilitation Treatment (SOSORT) regards physiotherapeutic scoliosis-specific exercises (PSSE) as a core intervention for preventing or delaying the progression of mild AIS⁸. The primary objective of PSSE is to achieve three-dimensional correction tailored to the individual curve type during daily activities, with corrective breathing exercises considered a key component. This training emphasizes maintaining thoracic and spinal coordination in the corrective posture to enhance postural control and improve respiratory function. However, in clinical practice, the absence of effective real-time feedback mechanisms often prevents patients from accurately targeting the training load to the intended spinal segments, resulting in insufficient correction and limited efficacy⁹. Moreover, instability in motor control may induce excessive compensation by non-target muscle groups, causing muscle fatigue or localized pain, which further diminishes the corrective effect¹⁰.

Ultrasound is a widely used medical technology for imaging internal body structures, such as tendons, muscles, joints, blood vessels, and organs, as well as for certain therapeutic applications. Several studies have reported the use of ultrasound to evaluate diaphragmatic motion in patients with COPD or respiratory failure, and to guide respiratory training interventions aimed at improving diaphragmatic function^11,12.

Based on this concept, the present study innovatively applies ultrasound technology to respiratory training in AIS patients. By providing visual feedback, patients can directly observe changes in bilateral intercostal space width, intercostal muscle thickness, and diaphragmatic excursion during respiratory exercises, thereby enhancing training effectiveness and facilitating more precise scoliosis correction¹³.

Protocol

Ethics Statement:
This study protocol has been approved by the Human Research Ethics Committee of the Ninth People's Hospital of Wuxi, affiliated with Soochow University (Approval No. KS2025036). Before the trail, Written informed consent was obtained from all participants prior to the initiation of the trial .This protocol outlines a trial using USSE to prevent progression of the scoliotic curve, as quantified by the Cobb angle, and to improve respiratory function in adolescents with scoliosis.

A total of 20 patients with adolescent idiopathic scoliosis (AIS) who met the inclusion criteria were recruited from the Department of Rehabilitation at the Ninth People's Hospital of Wuxi between May 2024 and May 2025. Participants were randomly assigned to either the control group or the treatment group, with 10 patients in each group. All interventionists were required to be familiar with spinal anatomy and the specific scoliosis-specific exercise techniques employed in the study.

1. Recruitment of patients

1. The inclusion criteria were as follows: Patients were required to have immature skeletal development (Risser sign < 5) and be aged 9-19 years^14,15. A confirmed diagnosis of idiopathic or structural thoracic scoliosis with the apical vertebra located between T3 and T10 (to ensure the feasibility of assessing intercostal symmetry); a Cobb angle between 15° and 25°⁸; no use of orthopedic braces; normal cognitive function; and the ability to cooperate with breathing training
2. Use the following exclusion criteria included: the presence of severe cardiopulmonary diseases, rib deformities, or a history of thoracic surgery; neuromuscular scoliosis; or other forms of secondary scoliosis.

2. Exercises regime for control group

1. Encourage AIS patients to engage in at least 60 min of daily physical activity as per the WHO recommendations; in this study, the target was 30 min per day. The USSE group was encouraged to meet the same activity quota^16,17.
2. Subject patients in the control group to a treatment course of functional exercises as described below¹⁸.
3. Have the physical therapist demonstrate the full Bird-Dog sequence from the start position through contralateral arm-leg extension and return. Model the intended breathing pattern and movement tempo.
   NOTE: Train the patient's parents to supervise home-based exercises. Have the patient use a mirror or ultrasound screen to observe waist, back, and pelvic symmetry for immediate posture feedback.
4. Adopt the starting position (Figure 1A) by positioning the patient on all fours with hands under the shoulders and knees under the hips, maintaining a neutral spine with relaxed neck and forward gaze, while gently engaging the core by drawing the navel inward.
   NOTE: Place an empty paper cup at the center of the patient's waist and the center of the chest. If the spine deviates or collapses, the cup will fall, providing immediate feedback on posture.
5. Ask the patient to perform 1-2 deep breaths. Inhale without shrugging the shoulders, allowing the lower thorax to expand fully; exhale while gently engaging the abdomen to stabilize the trunk.
6. Exhale and extend the right arm forward and the left leg backward in line with the shoulder and hip joints (Figure 1B). Keep both limbs parallel to the floor, maintain steady breathing, engage the core, and avoid lumbar sagging.
   NOTE: Place a light book at the lumbosacral junction. If the book falls during the exercise, it indicates instability in the pelvis or spine.
7. Inhale and slowly return the arm and leg to the starting position, maintaining a neutral spine and avoiding any rotation or deviation.
8. Repeat the movement on the opposite side by extending the left arm and right leg, alternating sides for 8 repetitions per set, and perform 3-5 sets daily.
9. Have the physician or physical therapist demonstrate the complete side-lying lateral plank, explain the movement principles, key muscle activation points, and common errors, and ask the patient to perform one supervised repetition to confirm understanding of the objectives and mechanics.
10. Lie on a yoga mat with the lower arm bent and the elbow positioned directly under the shoulder. Align the ear with the shoulder and maintain the spine in a neutral position without sagging or rotation (Figure 1C).
11. Flex the lower knee slightly to provide additional support and extend the upper leg with the toes lightly touching the floor to maintain balance. Keep the pelvis and shoulders in the same plane.
12. Direct the gaze forward to relax the cervical spine. Place the upper arm naturally on the hip or extend it toward the ceiling according to the training objective, maintaining spinal neutrality and pelvic alignment throughout the posture.
13. Lift the hips from the starting position to form a straight line from the shoulders through the hips to the knees and feet. Engage the core and stabilize the pelvis and scapulae to maintain alignment, holding the position for 10-15 seconds while maintaining steady breathing and trunk stability (Figure 1D).
14. Return slowly to the starting position, and then perform the same exercise on the opposite side.
    NOTE: In the control group, participants were instructed to perform the bird-dog exercise and the side-lying lateral plank, repeating each side 8 times per set for 3-5 sets daily. The intervention was continued each day from enrollment until the end of the observation period.
    NOTE: During functional training, follow the principles of gradually progressing from light to heavy loads and from small to large ranges of motion in a stepwise and continuous manner. Instruct patients to avoid prolonged unilateral weight-bearing, refrain from maintaining the same posture for extended periods, and maintain an appropriate level of activity.

3. Exercise regime for treatment group

1. Materials Preparation: Ultrasound device (Figure 2A), coupling gel (Figure 2B), disposable mat (Figure 2C), and disposable gloves (Figure 2D).
2. Explain the procedure by informing the patient and their parents about the examination and training process. Clarify that the treatment area will be exposed and that coupling gel needs to be applied between the ribs. Instruct the patient to observe the real-time imaging on the screen, and emphasize that the procedure is radiation-free and painless.
3. Position the patient either in a seated posture or in lateral decubitus with the concave side facing up. If using the lateral position, place a 5–10 cm pillow under the ribs at the level of the apical vertebra. Keep both feet flat or stacked, maintain spinal neutrality, and expose the target intercostal area.
   NOTE:In the seated position, gravity acts vertically on the thorax, enhancing activation of the erector spinae and accessory inspiratory muscles to promote thoracic expansion and coordinated breathing. In contrast, when lying laterally, gravity acts sideways, decreasing balance and core demands, making this position preferable for patients with limited core stability who struggle to maintain spinal neutrality during breathing training.
4. Wear disposable gloves and apply a small amount of medical ultrasound coupling gel evenly over the skin of the target intercostal space. At the end of the treatment, wipe off the gel with a disposable tissue and assist the patient in adjusting their clothing.
5. Power on and set up the device: Press the Power button on the right side of the main unit and wait approximately 30s for the system to complete the self-check and enter the main interface. Enter the patient's name, sex, age, ID, and examination date.
   NOTE:For intercostal muscle imaging, select MSK Superficial (linear probe L10-5); for diaphragm imaging, select Abdomen General (convex probe C5-2).
6. Locate the concave intercostal space: perform preliminary palpation based on anatomical landmarks, place the probe over the concave intercostal space corresponding to the apical vertebra along the mid-axillary line (Figure 3A), orient the ultrasound plane perpendicular to the long axis of the rib, and visualize the intercostal muscles and rib dynamics.
   NOTE: Anatomical landmarks for rib localization include the acromion, approximately aligned with the second rib; the spine of the scapula, corresponding to the third rib; and the inferior angle of the scapula, approximately aligned with the seventh rib.
7. Adjust the Depth knob to 2–4 cm, set the 2D Gain knob to clearly display the rib interface and fascial line, fine-tune brightness at different depths using the TGC sliders, and set the Focus Position on the touchscreen at the level of the intercostal muscle layer.
8. Perform baseline measurement: at end-expiration, press Freeze → Measure → Distance on the touchscreen to measure intercostal space width (mm) and intercostal muscle thickness (mm); at end-inspiration, repeat the measurement, save two static images (Save Image), and label them "Exp End" and "Insp End."
9. Instruct the patient to perform slow, deep breaths while observing the expansion of the concave intercostal space on the ultrasound screen (Figure 3B).
10. Encourage active control of breathing to increase concave mobility by elevating the ribs to their maximal position (Figure 3C), holding for 5s, and then exhaling slowly through the mouth. Complete 10 breaths per set, performing 3-5 sets with 30-60s of rest between sets.
11. Ensure that patients in both the treatment and control groups perform the same functional training.

4. Post-intervention outcome assessments

1. Evaluation index
   1. Evaluation index: Define the primary structural outcome as the change difference in the main-curve Cobb angle (ΔCobb) from baseline to post-treatment, measured on standardized standing posteroanterior (PA) radiographs. Define ΔCobb as baseline Cobb minus post-treatment Cobb, so that positive values indicate greater correction. Use the same upper and lower end vertebrae identified at baseline for post-treatment measurements, and obtain them from two blinded readers, recording the average.
   2. Pulmonary function outcomes: Include assessments of tidal volume (TV), inspiratory capacity (IC), vital capacity (VC), and maximum voluntary ventilation (MVV) before and after treatment.
   3. Ultrasound outcomes: Include parameters assessing changes in intercostal space width and intercostal muscle thickness before and after treatment.
      NOTE: The baseline measurements were performed before and 1 week after the treatment.
2. Assessment
   ​Measure the Cobb angle from standing PA radiographs using a digital X-ray system (PACS software). Assess pulmonary function parameters (TV, IC, VC, MVV) with a spirometer. Evaluate intercostal space width and muscle thickness using high-frequency ultrasound (7-12 MHz linear probe).
   1. Radiographic Assessment of Spinal Curvature
      1. Instruct the subject to stand barefoot in an upright position on the X-ray platform, feet shoulder-width apart, arms relaxed at the sides. Ensure the subject maintains a natural standing posture without intentional correction.
      2. Acquire a standing posteroanterior (PA) radiograph of the entire spine. Import radiographs into PACS software.
      3. Locate the apical vertebra (AV), defined as the vertebra that is most laterally deviated from the central vertical line of the spine and has pedicles most symmetrically distant from the midline; this vertebra represents the apex of the curvature.
      4. Determine the upper end vertebra (UEV), identified as the most tilted vertebra above the apical vertebra whose superior endplate is maximally inclined toward the curve's concavity; this is the uppermost vertebra with a visibly inclined endplate.
      5. Determine the lower end vertebra (LEV), identified as the most tilted vertebra below the apical vertebra whose inferior endplate is maximally inclined toward the curve's concavity and transitions toward horizontal alignment below it.
      6. Draw the first reference line by positioning the cursor at one end of the superior endplate of the UEV, then clicking and dragging along the visible cortical margin to the opposite end of the same endplate to establish the line.
      7. Draw the second reference line by clicking and dragging along the inferior endplate of the LEV, following the cortical margin from one end to the other to generate the line. Once both lines are drawn, the software automatically calculates the Cobb angle as the angle between the two lines
         NOTE: Confirm selection by ensuring that the UEV and LEV together encompass the full extent of the curve, and that vertebrae above and below them show progressively reduced tilt.
      8. Repeat measurements by two independent raters. Use the average value.
   2. Pulmonary Function Assessment
      1. Calibrate the spirometer before each measurement according to the manufacturer's instructions. Seat the subject comfortably with feet flat on the floor, and apply a nose clip to prevent nasal air leakage. Instruct the subject to place the disposable mouthpiece firmly between the lips, ensuring an airtight seal.
      2. Measure the tidal volume (TV) by instructing the subject to breathe calmly and normally for one minute, then record the average volume of air inhaled and exhaled per breath.
      3. Measure the inspiratory capacity (IC) by instructing the subject, after completing a normal expiration, to inhale as deeply as possible, and record the maximal volume of air inspired.
      4. Measure the vital capacity (VC) by instructing the subject to perform a maximal inhalation followed by a maximal exhalation down to the residual volume, and record the difference between the two volumes.
      5. Measure the maximal voluntary ventilation (MVV) by instructing the subject to breathe as rapidly and deeply as possible for 12 seconds, then extrapolate the measured volume to one minute to calculate the MVV.
         NOTE: Repeat each test at least three times, ensuring reproducibility within 5%, and record the best trial for analysis.
   3. Ultrasound Assessment of Intercostal Space and Muscle Thickness
      1. Seat the subject upright on a stable examination chair or treatment bed with feet flat on the floor and arms relaxed alongside the body. Instruct the subject to maintain a natural sitting posture without leaning forward or backward.
      2. Apply sufficient ultrasound coupling gel to the target intercostal space to ensure optimal acoustic contact. Use a linear probe (7-12 MHz) set to musculoskeletal or high-resolution mode.
      3. Place the probe longitudinally along the intercostal space on the concave side of the thorax, typically at the mid-axillary line. Adjust the probe angle until the adjacent ribs and intercostal muscle layer are clearly visualized. Instruct the subject to perform quiet breathing for orientation, and acquire images at end-expiration and end-inspiration, holding each phase for 2-3s.
      4. Measure the intercostal space width using the ultrasound caliper tool by determining the distance between the inner margins of two adjacent ribs. Record the values at both end-inspiration and end-expiration to assess dynamic changes.
      5. Identify the intercostal muscle layer between two adjacent ribs. Place calipers perpendicular to the muscle belly and measure the vertical distance between the inner and outer fascia. Record the values at both end-inspiration and end-expiration.
      6. Perform three repeated measurements for each parameter at the same anatomical site. Calculate and record the mean value. Ensure the operator is blinded to patient group allocation to minimize bias.

5. Statistical analysis

1. Present the continuous variables as mean ± standard deviation (SD). Use the independent sample t-test to compare the differences between the two groups. All statistical tests were two-sided, and P<0.05 was considered statistically significant. All analyses were performed using statistical software.

Results

All 10 patients in the control group and all 10 patients in the treatment group were included in the final statistical analysis.

Baseline characteristics
The two groups were comparable in terms of gender, age, weight, height, Cobb angle of the major curve, and respiratory parameters, including tidal volume (TV), inspiratory capacity (IC), vital capacity (VC), and maximum voluntary ventilation (MVV) (P > 0.05). The control group included 3 males and 7 females, w...

Discussion

Successful implementation of this protocol relies on several key technical steps. Accurate localization of the concave intercostal space using ultrasound imaging is essential for identifying the optimal training site and ensuring consistent visualization of rib and thoracic movement during breathing. Maintaining spinal neutrality and proper patient positioning are critical to avoid compensatory trunk or pelvic motion that may offset the corrective effect. Furthermore, therapists must provide real-time verbal feedback to ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
ACUSON Juniper Ultrasound System	SIEMENS MEDICAL SOLUTIONS USA, INC	553867	multi-probe system with multimodal imaging for broad clinical use.
Ultrasound Gel (250 mL)	Tianjin Grand Paper Industry Co., Ltd.	20190019	Medical, water-soluble, hypoallergenic gel for ultrasound coupling.
Examination gloves	Zhende Medical Co., Ltd.	20170091	Examination gloves
Medical Pads	Hengtong Medical & Health Products Co., Ltd.	20150036