Changes in Spinal Height Following Sustained Lumbar Flexion and Extension Postures: A Clinical Measure of Intervertebral Disc Hydration Using Stadiometry
From: J Manipulative Physiol Ther. 2009 Jun;32(5):352-7
Throughout the course of the day, the spinal intervertebral discs display viscoelastic creep properties that determine an individual’s overall stature. These properties were demonstrated by Tyrrell et al who used in vivo stadiometry measurements to detect 19.3 mm (1.1% of stature) variation in height between first arising and the end of the day.
Contributions to the total diurnal stature loss from structures other than the intervertebral disc are minimal. Kanlayanaphotporn et al used stadiometer measurements to assess the contribution of soft tissue structures below the sacrum and concluded that these structures accounted for 19% of the height change during the first 5 minutes of sitting. Based on these findings, stadiometry is considered to provide an accurate measure of spinal height changes after various loading conditions.
The 2 primary methods of measuring spine height changes are magnetic resonance imaging (MRI) and stadiometry. Stadiometry has been shown to be a valid and reliable tool to assess spinal height when compared to objectifiable measures made from MRI. Stadiometry assessment has advantages over MRI in terms of costs, use in clinical setting, as well as the ability to measure subjects that simultaneously sustain compressive loads of the trunk.
Several authors have assessed the effects of postures and different compressive loads on spinal height using stadiometry. Kourtis et al used stadiometry to identify increased height associated with prolonged hyperextension in lying, where a gain in intervertebral disc height after this activity was confirmed using MRI. The mean disk height gain from intervertebral discs T11 to L5 measured by MRI after extension lying was 2.1 mm, whereas the average total spine height gain measured by stadiometry was 5.2 mm. The results consistently demonstrated an increase in participant height when measured using MRI and stadiometry after a position of extension lying that followed a seated loaded position. Similar findings were reported by Magnusson et al who indicated sustained extension lying of 20° for 20 minutes provided the optimal impact on the increase of spine height.
Although previous studies have assessed the effects of extension postures on spine height, no previous investigation has assessed the effects of flexion postures. Therefore, the purposes of this study were 3-fold: (1) to determine if the authors test protocol using a commercially available stadiometer demonstrated findings consistent with prior laboratory-based protocols; (2) to determine if hyperextension in the prone position and trunk flexion in the supine position caused increased spine height after sustained loading; and (3) to compare the effects of hyperextension in the prone position and trunk flexion in the supine position on spine height changes after a period of sustained loading.
The authors clinically applicable protocol using a commercially available stadiometer confirmed the findings of previous research by Kourtis et al that reported loss of trunk height associated with loaded and unloaded sitting. Kourtis et al used MRI to measure changes of intervertebral disc height associated with loading and unloading of the spine. The research methods of the current study matched the methodology and population of Kourtis et al who reported mean changes (−5.03 mm) in spinal height similar to the changes recorded in this study (−3.24 mm). These findings are consistent with previous investigations including 4.28 mm height loss, 3.07 and 3.55 mm height loss, and 3.85 mm height loss recorded after 5 minutes of sitting in young adults.
This is the first reported investigation to assess the effect of trunk flexion in the supine position on spine height using a stadiometer measurement protocol. Magnusson et al suggested that increased lumbar intervertebral disc hydration occurred as a result of load transfer from the lumbar intervertebral disc to the zygapophyseal joints during lumbar extension postures. The authors findings suggest that trunk flexion in the supine position provides similar increase in spine height as those obtained through extension postures. Therefore, controlling the effects of gravity on the intervertebral diskc through unloading the spine seems to bear greater influence on increased spine height and hydration of the discs than the directionality (flexion or extension) of the position of the spine.
No significant differences were found between sexes for any of the experimental conditions, suggesting that sex and body frame were not associated with variability in spine height changes. These results are in agreement with previous findings, which indicated no effect on spine height changes associated with sex, suggesting that trunk height changes associated with various recovery positions can be generalized for both sexes in asymptomatic young adults.
Spine height measurements, using stadiometer protocols, are largely dependent on lumbar intervertebral disc hydration. Kourtis et al using both stadiometer and MRI to assess the effects of various positions on trunk height, reported similar results for extension recovery positions under both techniques. This reflects the intervertebral discs’ ability to imbibe fluid during periods of unloading and lose water with loading, translating into trunk height changes detected using stadiometer measurements. Under normal conditions, the lumbar intervertebral disc is able to imbibe large quantities of water. With intervertebral disc degeneration, the ability to bind water and maintain hydration is diminished. Positions that temporarily aid in the recovery of spine height may help offset these consequences and provide ergonomic applications.
Therapeutic interventions for the management of low back pain can be assessed in terms of intervertebral disc hydration level reflected through spine height changes. This includes the evaluation of various positions and exercises to prevent or treat back pain, the use of traction and manual therapy techniques as well as exercises in the aquatic setting. Future studies should include patients with various conditions such as nonspecific low back pain, lumbar radiculopathy, and lumbar intervertebral stenosis. Determining if a correlation exists between intervertebral disc hydration levels reflected in spine height measures using stadiometer protocols and patient symptoms may provide additional management strategies for the management of low back pain.
