The effect of 4-hour partial axial reloading via the Mk VI SkinSuit upon recumbent lumbar geometry and kinematics after 8-hour hyper-buoyancy flotation
Conference: 2nd Human Physiology Workshop
Dates: 9 December 2017Abstract:
Introduction: Prolonged spinal unloading in microgravity has been associated with elongation, back pain and increased risk of intervertebral disc (IVD) herniation, particularly in the lumbar spine. Novel countermeasures to reintroduce axial loading in space are therefore required. This study evaluated the impact of 8h of unloading followed by 4h reloading with a novel axial loading countermeasure, the Mk VI SkinSuit, on lumbar geometry (magnetic resonance imaging; MRI) and kinematics (quantitative fluoroscopy; QF) utilising a new microgravity analogue, hyper-buoyancy flotation (HBF).
Methods: Eight male participants (28±5y; 1.77±0.05m; 73±5.3kg) gave written informed consent to participate in this study. MRI-compatible Mk VI SkinSuits were tailored for each participant, providing on average 0.19±0.03Gz axial loading at the foot (ForceShoes, Xsens). A HBF bed (part filled with saline saturated water; ~1.7gcm3) was built within the imaging centre to allow supine transport from the HBF to the MRI scanner. Participants lay for 8h overnight on the HBF in loose attire on two separate occasions, followed by a further 4h on the HBF, once with and once without the SkinSuit. T2-weighted lumbar (L1-S1), sagittal and axial scans were analysed for lumbar length, curvature, IVD height, cross-sectional area and volume. Following MRI, participants were positioned recumbent on their side upon a motorised control table for QF. They were passively moved through two ranges of movement, 40o flexion and 40o extension, over a period of ~15 seconds at 6os-1. The c-arm fluoroscope took continuous images whilst positioned at L3/L4 with all vertebrae from L2-S1 in view. Vertebral body positions (L2-S1) were tracked throughout the motion sequences (Matlab), with each of the vertebra traced five times before a pooled average was calculated for laxity, intervertebral range of motion (IV-ROMMAX), motion sharing variability (MSV) and inequality (MSI). Results: Neither lumbar length (138.86.4 vs. 138.96.8mm) nor lordotic curvature (426.8 vs. 41.17.2o) were affected by axial reloading, post HBF. Mean IVD height tended (p<0.2) to be reduced at L3/L4 (0.40.7mm) and L4/5 (0.30.7mm). There was also a tendency for IVD cross sectional area to increase with reloading at L4/L5 and L5/S1 and for IVD volume at L2/L3 and again at L4/L5 to decrease.
During flexion, whilst all median QF parameters tended to be slightly higher with reloading, only IV-ROMMAX was statistically significant. During extension, there was a trend (P<0.2) for an increase in MSI with reloading. This study suggests that 4h of approximately 0.2Gz axial reloading acted to reduce disc height and decrease measures of intervertebral restraint, although this was only a minor effect with acute SkinSuit wear. Though reloading with the Mk VI SkinSuit did not significantly reduce lumbar length or lordotic curvature, at the IVD level cross-sectional area increased and volume decreased. Whether these effects are functionally significant warrants further study.