Sagittal range of motion of the thoracic spine using inertial tracking device and effect of measurement errors on model predictions
Introduction
Though less frequent than low back and neck pain, thoracic spine pain has been identified as a significant work-related disease (Briggs et al., 2009, Fouquet et al., 2014). A large population study indicates that 20% of women and 10% of men workers suffer from thoracic pain (Fouquet et al., 2015). Frequent trunk bending has been suggested to be a strong occupational risk factor for thoracic spine pain (Roquelaure et al., 2014). Consequently, surgeries on the thoracic spine have increased according to a nationwide cohort study in Japan (Nohara et al., 2004). As musculoskeletal disorders limit joint movements and thus its range of motion (ROM), motion analysis of the thoracic spine can serve as a potential tool for patient discrimination and subsequent diagnostic purposes. It has been also suggested that assessment of the thoracic spine ROM can help in the diagnosis and therapy of patients with shoulder outlet impingement syndrome (Theisen et al., 2010).
Evaluation of sagittal ROM of the thoracic spine (i.e., maximal relative flexion of T1 to T12) is also valuable in the biomechanical modeling for prediction of muscle forces and spinal loads (Arjmand and Shirazi-Adl, 2006, Arjmand et al., 2011, Arjmand et al., 2012). Based on the general assumption of the relatively smaller sagittal ROM of the thoracic spine compared with the lumbar spine, thoracolumbar musculoskeletal models (e.g., Arjmand and Shirazi-Adl, 2006; Cholewicki and McGill, 1996; Granata and Wilson, 2001; Stokes and Gardner-Morse, 1995) as well as commercial software such as the AnyBody(R) Modeling System (Damsgaard et al., 2006) assume the whole T1–T12 thoracic spine to move rigidly as a single body. Ligamentous passive contribution of the thoracic spine in balancing external moments is hence neglected in these models.
Generally three techniques have been used to measure sagittal ROM of the thoracic spine, including skin-surface devices such as optical marker-video camera (Tully and Stillman, 1997), electronic inclinometer (Mannion et al., 2004), or electromagnetic tracking (Hsu et al., 2008, Troke et al., 1998, Willems et al., 1996), computed tomography (CT) imaging (Morita et al., 2014), and in vitro cadaveric investigations (White and Panjabi, 1990). These studies have reported quite different sagittal thoracic (T1–T12) ROMs varying from ~18° to 32° for forward flexion alone (Hsu et al., 2008, Mannion et al., 2004, Tully and Stillman, 1997, Willems et al., 1996) and from ~32° to 70° (Morita et al., 2014, O׳Gorman and Jull, 1987, Troke et al., 1998, Willems et al., 1996, White and Panjabi, 1990) for total flexion–extension. The video camera, medical imaging, and in vitro techniques require equipped laboratories and thus are impractical for easy and comprehensive use in workplaces for ergonomics and in hospitals for clinical applications. The electromagnetic tracking devices are accurate, but usually confined to a limited space to allow the “sensors” to detect the magnetic field generated by a fixed “source” (Saber-Sheikh et al., 2010). Moreover, their accuracy and calibration process are adversely affected by the presence of metallic objects in the experiment environment or of implants in patients (Ng et al., 2009).
We have recently used an inertial tracking device (Xsens MTx, Xsens Technologies, Enschede, Netherlands) for measurement of lumbopelvic rhythm during trunk flexion–extension (Tafazzol et al., 2014). Compared to other skin-surface methods, inertial tracking devices are source-less (no cameras), low-cost, light, portable and, hence, indispensable easy-to-use tools for the quick recording of the spinal ROMs. This study, hence, has two aims:
- (1)
Measure total (T1–T12), lower (T5–T12) and upper (T1–T5) thoracic, lumbar (T12–S1), pelvis (P), and total trunk (T1) ROMs and their movement rhythms in the sagittal plane as asymptomatic subjects flex forward from their neutral upright posture to full forward flexion in unconstrained upright standing using an inertial tracking device. Correlations between body height and the foregoing ROMs were also conducted.
- (2)
Quantify the effect of inherent errors (uncertainties) in the in vivo measurements of upper trunk flexion angle (T1) on the responses (i.e., predicted spinal loads) of a previously developed musculoskeletal finite element model of the thoracolumbar spine Arjmand and Shirazi-Adl, 2005, Arjmand and Shirazi-Adl, 2006; Arjmand et al., 2009, Arjmand et al., 2010, Arjmand et al., 2011, Arjmand et al., 2012). In other words, this modeling study aims to investigate the sensitivity of biomechanical models to the measured trunk flexion angle that is required as input into these models. As magnitude of trunk flexion angle affects the trunk posture, position of its center of mass, and thus trunk external moments, it is hypothesized that errors in the measurements of trunk flexion angles will have an impact on the model predictions for spinal loads.
Section snippets
Inertial tracking device
Four small (38 mm×53 mm×21 mm) and light (~30 g) inertial and magnetic sensors (Xsens MTx, Xsens Technologies, Enschede, Netherlands) are used to capture the 3D rotations of the pelvis, lumbar and thoracic spine. Each sensor has triaxial accelerometers, gyroscopes, and magnetometers whose signals are fused using a Kalman filter to estimate drift-free 3D orientations of the sensor coordinate system with respect to the reference earth-fixed coordinate system which, in turn, is created using
In vivo study
Mean of peak voluntary total flexion of trunk (T1) was 118.4° (SD 13.9°), of which 20.5° (SD 6.5°) was provided by the relative angular movement of the T1 to T12 (i.e., T1–T12 ROM), and the remaining by relative rotation of the T12 to S1 (i.e., lumbar spine ROM) (50.2°, SD 7.0°) as well as pelvis (P) (47.8°, SD 6.9°). Lower thoracic spine (T5–T12) contributed more to the total thoracic (T1–T12) ROM as compared with the upper thoracic spine (T1–T5) (14.8°, SD 5.4° versus 5.8°, SD 3.1°) (p
Discussion
This study primarily aimed to measure normal sagittal thoracic (T1–T12) spine ROM, whose magnitude has been somewhat controversial, in healthy population using, for the first time, inertial tracking sensors. Mean ROM of the thoracic spine in full forward flexion was found 20.5° (SD 6.5°) most of which was generated by the relative flexion of the T5 to T12 (lower thoracic). Contribution of the thoracic spine to generate the total forward trunk rotation remained almost constant (~16% to 20%)
Conflict of interest statement
We have no conflict of interest to declare.
Acknowledgment
This work was supported by grants from the Iran National Science Foundation (INSF) (93028571) and Sharif University of Technology (Tehran, Iran).
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2019, Journal of Clinical NeuroscienceCitation Excerpt :Several studies have reported that the thoracic spine shows some dynamic changes with positional changes [9–11]. The study of Hajibozorgi et al. showed that while mean thoracic flexion (T1-12) was 20.5° ± 6.5°, most of the flexion occurred between T5 and T12 [12]. Furthermore, Morita et al. studied thoracic angular motion by using multi detector-row computed tomography scanning and found that the angular motion increased gradually from T4-5 to T12-L1 [9].