Development and Validation of a Method to Measure Lumbosacral Motion Using Ultrasound Imaging

Assessment of thoracic spinal curvatures in static postures using spatially tracked 3D ultrasound volumes: a proof-of-concept study

The assessment of spinal posture is a difficult endeavour given the lack of identifiable bony landmarks for placement of skin markers. Moreover, potentially significant soft tissue artefacts along the spine further affect the accuracy of marker-based approaches. The objective of this proof-of-concept study was to develop an experimental framework to assess spinal postures by using three-dimensional (3D) ultrasound (US) imaging. A phantom spine model immersed in water was scanned using 3D US in a neutral and two curved postures mimicking a forward flexion in the sagittal plane while the US probe was localised by three electromagnetic tracking sensors attached to the probe head. The obtained anatomical 'coarse' registrations were further refined using an automatic registration algorithm and validated by an experienced sonographer. Spinal landmarks were selected in the US images and validated against magnetic resonance imaging data of the same phantom through image registration. Their position was then related to the location of the tracking sensors identified in the acquired US volumes, enabling the localisation of landmarks in the global coordinate system of the tracking device. Results of this study show that localised 3D US enables US-based anatomical reconstructions comparable to clinical standards and the identification of spinal landmarks in different postures of the spine. The accuracy in sensor identification was 0.49 mm on average while the intra- and inter-observer reliability in sensor identification was strongly correlated with a maximum deviation of 0.8 mm. Mapping of landmarks had a small relative distance error of 0.21 mm (SD = ± 0.16) on average. This study implies that localised 3D US holds the potential for the assessment of full spinal posture by accurately and non-invasively localising vertebrae in space.

Musculoskeletal ultrasound for 3D bone modeling: A preliminary study applied to lumbar vertebra

BACKGROUND

There is no non-invasive in vivo method to assess intervertebral kinematics. Current kinematics models are based on in vitro bone reconstructions from computed tomography (CT)-scan imaging, fluoroscopy and MRIs, which are either expensive or deleterious for human tissues. Musculoskeletal ultrasound is an accessible, easy to use and cost-effective device that allows high-resolution, real-time imaging of bone structure.

OBJECTIVE

The aim of this preliminary study was to compare the concordance of 3D bone modeling of lumbar vertebrae between CT-scan and ultrasound imaging and to study the intra and inter-reliability of distances measured on 3D ultrasound bone models.

METHODS

CT-scan, ultrasound, and in situ data of five lumbar vertebrae from the same human specimen were used. All vertebrae were scanned by tomography and a new musculoskeletal ultrasound procedure. Then, 3D bone modeling was created from both CT-scan and ultrasound image data set. Distances between anatomical bones landmarks were measured on the 3D models and compared to in situ measurements.

The relationship between external thoracopelvic angle and lumbar segmental axial twist angle using an ultrasound imaging technique

The relationship between externally measured and internal spine axial twist motion (rotation about a vertical axis) is not well understood. Ultrasound is a validated technique for measurement of vertebral axial twist motion and has the potential for measuring segmental vertebral axial twist in vivo. The objective of this study was to evaluate lumbar segmental axial twist in relation to external thoracopelvic twist from optical motion capture using an ultrasound imaging technique. Sixteen participants were tested in a custom-built axial twist jig, which isolated motion to the lumbar spine. Participants were moved from neutral to 75% of maximum axial twist range of motion in an upright kneeling posture. Thoracopelvic motion was recorded with a motion capture system and L1 to S1 vertebral axial twist was recorded using ultrasound. From motion capture, maximum thoracopelvic axial twist motion was 41.1 degrees. From ultrasound, the majority of axial twist motion occurred at the L2-L3 (46.8% of lumbar axial twist motion) and L5-S1 (33.5%) intervertebral joints. Linear regression linking axial twist at each vertebral level to thoracopelvic axial twist ranged from 0.43 to 0.79. These findings demonstrate a mathematical relationship between internal and external axial twist motion and the distribution of motion across the lumbar spine suggests that classic use of L4-L5 to represent lumbar spine motion may not be appropriate for axial twist modelling approaches.

Current advances and research in ultrasound imaging to the assessment and management of musculoskeletal disorders

Currently evidence-based practice has given scientific weight to the physical therapist profession; it is essential that all medical professional and physical therapists know the usefulness of new tools that optimize the effectiveness of their interventions and allow the growing of the scientific knowledge base. The use of ultrasound imaging (USI) by physiotherapists has evolved in recent years, consolidating as an increasingly standardized technique, low cost compared to other imaging techniques, quickly of execution, feasible and reliable tool. USI offers a wide range of opportunities in clinical practice as well as in different research areas. Therefore, ultrasound has been currently used as a diagnostic tool by physicians and in recent years there has been an expansion of the use of ultrasound equipment by non-physicians professionals such as physical therapist or physical trainers, who incorporates USI as a means of assessing musculoskeletal system architecture and composition, musculoskeletal changes in dysfunction, pain or injury conditions, as an interventional technique assisting echo-guided procedures or using the visual real-time information as a biofeedback in control motor approaches, as guiding tool in clinical decisions as well as to improve the understanding of tissue adaptations to exercise or movement. The purpose of this article is to review and provide an overview about the currently research of the USI applications and their benefits for the diagnosis and management in individuals with musculoskeletal conditions.

Long-Duration Tracking of Cervical-Spine Kinematics With Ultrasound

Cervical-spine (C-spine) pathoanatomy is commonly evaluated by plane radiographs, computed tomography (CT), or magnetic resonance imaging (MRI); however, these modalities are unable to directly measure the dynamic mechanical properties of the functional spinal units (FSU) comprising the C-spine that account for its functional performance. We have developed an ultrasound-based technique that provides a non-invasive, real-time, quantitative, in vivo assessment of C-spine kinematics and FSU viscoelastic properties. The fidelity of the derived measurements is predicated on accurate tracking of vertebral motion over a prolonged time duration. The purpose of this work was to present a bundle adjustment method that enables accurate tracking of the relative motion of contiguous cervical vertebrae from ultrasound radio-frequency data. The tracking method was validated using both a plastic anatomical model of a cervical vertebra undergoing prescribed displacements and also human cadaveric C-spine specimens subjected to physiologically relevant loading configurations. While the velocity of motion and thickness of the surrounding soft tissue envelope affected accuracy, using the bundle adjustment method, B-mode ultrasound was capable of accurately tracking vertebral motion under clinically relevant physiologic conditions. Therefore, B-mode ultrasound can be used to evaluate in vivo real-time C-spine kinematics and FSU mechanical properties in environments where radiographs, CT, or MRI cannot be used.

Are Stability and Instability Relevant Concepts for Back Pain?

Individuals with back pain are often diagnosed with spine instability, even though it is unclear whether the spine is susceptible to unstable behavior. The spine is a complex system with many elements that cannot be directly observed, which makes the study of spine function and direct assessment of spine instability difficult. What is known is that trunk muscle activation is adjusted to meet stability demands, which highlights that the central nervous system closely monitors threats to spine stability. The spine appears to be protected by neural coupling and mechanical coupling that prevent erroneous motor control from producing segmental instability; however, this neural and mechanical coupling could be problematic in an injured spine. Finally, instability traditionally contemplated from a mechanical and control perspective could potentially be applied to study processes involved in pain sensitization, and possibly back pain that is iatrogenic in nature. This commentary argues for a more contemporary and broadened view of stability that integrates interdisciplinary knowledge in order to capture the complexity of back pain. J Orthop Sports Phys Ther 2019;49(6):415-424. Epub 25 Apr 2019. doi:10.2519/jospt.2019.8144.

Validation of an Ultrasound Protocol to Measure Intervertebral Axial Twist during Functional Twisting Movements in Isolated Functional Spinal Units

Ultrasound has potential for use in evaluation of bone and joint movement during axial twist of the lumbar spine both in vivo and in vitro. Such segmental rotations could then be measured under controlled external thoracic axial twist conditions and in response to mechanical loading. The purpose of this study was to measure vertebral segmental rotations in a porcine model of the human lumbar spine using an ultrasound imaging protocol and to validate use of this imaging technique with an optical motion capture system. In part 1, ultrasound transducer angle was confirmed to have no effect on sonogram point digitization. In part 2, 12 porcine functional spinal units were fixed to a mechanical testing system, and compression (15% of compressive tolerance), flexion-extension and axial twist (0°, 2°, 4° or 6°) were applied. Axial twist motion was tracked using an optical motion capture system and posterior surface ultrasound. Correlation between the two measurement systems was >0.903, and absolute system error was 0.01° across all flexion-extension postures. These findings indicate that ultrasound can be used to track axial twist motion in an in vitro spine motion segment and has the potential for use in vivo to evaluate absolute intervertebral axial twist motion.