Changes in the Standing Lumbar Spine at Above Bodyweight Loading

Dougill, GM, Reeves, N, LeMaitre, C and Cooper, G (2015) Changes in the Standing Lumbar Spine at Above Bodyweight Loading. In: XXV Congress of the International Society of Biomechanics.

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Abstract

Introduction and Objectives: Understanding the mechanical response of the spine and intervertebral disc to various loading situations is vital to predicting its behaviour, to verify computer models of the spine and to gaining insight in to how loading and spinal posture may cause or exacerbate injury. Studies of the lumbar spine and intervertebral disc under compression have typically been carried out in vitro; those which have used in vivo methods have mostly been conducted in the supine position at loading equal to or below static bodyweight. This study measures the lumbar spine response to above bodyweight loading in the standing position at loads equivalent to walking. Methods: Sagittal plane magnetic resonance imaging scans of the spine were taken of nine asymptomatic male subjects (22-32 years of age, 167-195 cm, 66.3-93.2 kg) in the supine and standing positions with a third scan taken in the standing position with additional loading. Additional load was applied by having subjects hold two 6 kg kettlebells, one in each hand, enough to increase loading on the IVD to levels experienced during walking. Disc heights were measured as the average of anterior and posterior distance between adjacent vertebrae in the midsagittal plane. Change in lordosis was measured in two ways; the relative angle between the lumbar spine and pelvis was measured as the posterior angle between L5 and S1 vertebrae whilst change in the upper lumbar spine was measured by the angle between the superior facet of L3 with the vertical plane. Results: Increased axial loading resulted in reduced disc height and lumbar lordosis. Initial disc heights in the supine position for L3/L4, L4/L5 and L5/S1 were found to be 10.7(1.6), 12.0(2.8) and 11.4(1.9) mm respectively (Fig. 1a). These heights were reduced to 10.4(1.9), 11.4(2.1) and 10.8(1.6) mm in the standing position and 10.3(1.4), 11.4(2.0) and 10.4(1.8) mm with additional loading but these changes were not statistically significant (P>0.05). Lumbar angle in supine, standing and with additional loading was found to be 140(9), 145(11) and 145(12) degrees respectively (Fig. 1b) with L3 angled 0.7 (3.5), 4.4 (4.4) and 4.8 (4.2) degrees posteriorly from the horizontal in the three loading positions (Fig. 1c). In all cases disc height change was greater posteriorly as loading increased lumbar lordosis.