| Opportunities to evaluate spinal loading in vivo are limited and a large majority of studies on the
mechanical functions of the spine have been in vitro cadaveric studies and/or models based on many
assumptions that are difficult to validate. The purpose of this study was to investigate the feasibility of
magnetic resonance imaging (MRI) in obtaining nucleus pulposus (NP) water content measurements with
changing postures. MRI studies were conducted on 25 healthy males with no history of low back pain (age
20–38). The L1 to S1 intradiscal levels were imaged in supine, sitting and standing postures using an upright
0.6 Tesla magnet, where a set of H2O: D2O7 phantoms were mounted on the back of the subjects. A
calibration curve, provided from these phantoms, was applied to the absolute proton density image,
yielding a pixel-by-pixel map of the water content of the NP. The NP at all levels showed a highly significant
water loss (p b 0.001) in sitting and standing postures compared with the supine posture. A trend towards
higher levels of water was observed at all levels in the standing posture relative to sitting postures,
however statistically significant differences were found only at L4-L5 and L5-S1 levels. This study
demonstrates that variations in water content of the NP in different postures are in agreement with those
determined from published invasive disc pressure measurements. The result of study demonstrates the
feasibility of using MRI to determine the water content of the NP with changing postures and to use these
data to evaluate spinal loading in these postures. This measurement method of water content by
quantitative MR imaging could become a powerful tool for both clinical and ergonomic applications. The
proposed methodology does not require invasive pressure measurement techniques. |