1. NON-INVASIVE LUMBAR SPINE MOVEMENT: VALIDATION OF THE MOTIONSTARTM 3-D ELECTROMAGNETIC TRACKING SYSTEM & PRELIMINARY EVIDENCE Aubrey MONIE1,2, Roger PRICE1,3, Kevin SINGER1 School of Surgery1, The University of Western Australia; Precision Physiotherapy2 & Department of Medical Physics & Technology3, QEII Medical Centre, Nedlands WA 6009
APPENXIX XI
Introduction:
Disturbed movements of the lumbar spine can provide ‘signatures’ to underlying pathology and will usually differ from normal patterns in terms of quality and range [Fig 1]. Non-invasive spine movement assessment using 3-D motion tracking systems discriminates normal from symptomatic subjects1, and may help to triage pathology subgroups. System validation is a necessary prerequisite to ensure reliable data acquisition in clinical studies.
Figure 5. Example of inter-session repeatability of the combined movement examination in a 38yo male. Five trials per session are depicted.
Normal reference ranges for asymptomatic subjects are depicted in Figure 6 and show a gender difference for extension. Other range values are not significantly different.
Figure 1. Physiological spine motion requires an intact lumbar segment with normal hydration of the IVD [left]. This enables lumbar sagittal and coronal plane motion, with side-flexion inducing axial rotation [so called - coupled motion].
Method:
The MotionStarTM 3-D tracking device [Ascension Technology, VT, USA] records displacement coordinates at 50Hz in the three cardinal planes. A custom triaxial protractor with a known accuracy of 0.5° was designed for replicate trials to simulate the normal range of human lumbar movement [Fig 2]. Data from 10 trials for displacements: 0–10°, 0–30° and 0–60°, in each axis [X,Y&Z], were acquired in real-time using Labview software with post-processing in Excel.
Asymptomatic volunteers were assessed to map the coupled movement patterns for: flexion (F), side-flexion (SF) and extension (E) [Fig 3], to establish reliability from repeated trials and define a preliminary normal reference range.
A subset of cases were used for inter-session reliability assessment on five occasions. Normal asymptomatic volunteers involved 14 males [mean age 26, range 20-33yo] & 17 females [mean age 26, range 20-34yo].
Figure 6. Radial plot of 360° lumbar motion assessment presenting mean data for males [blue] and females [red], contrasting the asymptomatic movement signatures for each gender.
Figure 3. Physiological spine motion depicting the test sequences of lumbar flexion, extension, side flexion plus the coupled positions of flexion + side flexion and extension + side flexion.
Discussion & Conclusion
The MotionStarTM 3-D motion tracking system demonstrated low system error across all planes and ranges using a triaxial protractor standard with CV <0.15%, or an error <0.5degrees. Preliminary assessment of variability within normal subject data was acceptable and normal reference ranges were consistent with published data for lumbar movement relative to age.
Future investigations of composite lumbar spine movements, involving: flexion, side flexion and extension, which invoke coupled movements, may assist pattern recognition of mechanical spine pathologies.
Acknowledgement: Ray Smith for technical and data management advice.
References:
1. Barrett CJ, Singer KP, Day R. Assessment of combined movements of the lumbar spine in asymptomatic and low back pain subjects using a three-dimensional electromagnetic tracking system. Manual Therapy (2):94-9.
Results:
The Coefficients of Variation [CV%] for each triaxial protractor trial series, across all end-points and axes, ranged between – 0.14%, representing <0.5° error. Preliminary data for asymptomatic volunteers showed F>SF>E with ranges equivalent to published data for non-invasive lumbar range of motion. Intra-session repeatability trials involving the same subjects produced CVs <5% [Fig 4]. Inter-session reliability trials showed similar repeatability [Fig 5]. Data are depicted in 360° radial plots recording each adopted position shown in Figure 3 above.
Figure 2. Triaxial protractor [left] was custom designed to allow a 3-D assessment of the MotionStar system error. The protractor device had an intrinsic accuracy to ~0.5 degrees, although smaller gradations could be discerned. The MotionStar comprised an electromagnetic source with tracking sensors in the field calibrated to detect 3-D motion displacements.
Figure 4. Example of intra-session repeatability of the combined movement examination in a 52yo female. Replicate trials are depicted highlighting unique movement signatures.