Sex-specific trunk movement coordination in participants with low-back pain and asymptomatic controls

Abstract

Background: Trunk posture and lumbo-pelvic coordination can influence spinal loading and are commonly used as clinical measures in the diagnosis and management of low-back pain and injury risk. However, sex and pain specific characteristics have rarely been investigated in a large cohort of both healthy individuals and low-back pain patients. It has also been suggested that the motor control of trunk stability and trunk movement variability is altered in individuals with low-back pain, with possible implications for pain progression. Nonetheless, clear links to low-back pain are currently lacking.

Objective: To investigate trunk posture, lumbo-pelvic coordination, trunk dynamic stability and trunk movement variability in an adequately large cohort of individuals with low-back pain and asymptomatic controls and to explore specific effects of sex, pain intensity and pain chronicity.

Methods: We measured lumbo-pelvic kinematics during trunk flexion and trunk dynamic stability and movement variability during a cyclic pointing task in 306 adults (156 females) aged between 18 and 64 years, reporting either no low-back pain or pain in the lumbar area of the trunk. Participants were grouped based on their characteristic pain intensity as asymptomatic (ASY, N = 53), low to medium pain (LMP, N = 185) or medium to high pain (MHP, N = 68). Participants with low-back pain that persisted for 12 weeks or longer were categorized as chronic (N = 104). Data were analyzed using linear mixed models in the style of a two way anova.

Results: Female participants showed a higher range of motion in both the trunk and pelvis during trunk flexion, as well as an increased lumbar lordosis in standing attributed to a higher pelvic angle that persisted throughout the entire trunk flexion movement, resulting in a longer duration of lumbar lordosis. The intensity and chronicity of the pain had a negligible effect on trunk posture and the lumbo-pelvic coordination. Pain chronicity had an effect on trunk dynamic stability (i.e., increased trunk instability), while no effects of sex and pain intensity were detected in trunk dynamic stability and movement variability.

Conclusions: Low-back pain intensity and chronicity was not associated with lumbo-pelvic posture and kinematics, indicating that lumbo-pelvic posture and kinematics during a trunk flexion movement have limited practicality in the clinical diagnosis and management of low-back pain. On the other hand, the increased local instability of the trunk during the cyclic coordination task studied indicates control errors in the regulation of trunk movement in participants with chronic low-back pain and could be considered a useful diagnostic tool in chronic low-back pain.

Keywords: lordosis; lumbo-pelvic rhythm; spine alignment; trunk stability; trunk variability.

Figure 1

(A) Two 3-dimensional accelerometers positioned at sacral vertebrae 1 (S1) and thoracic vertebrae 12 (T12) were used to measure the pelvic (pelvic_angle) and trunk (trunk_angle) angles during three trunk flexion movements. (B) Positive values (+) indicate a forward-rotated orientation with respect to the vertical, while negative values (−) indicate a backward-rotated orientation of the pelvis or trunk. The lumbar angle (lumbar_angle) was calculated as the difference between trunk_angle and pelvic_angle. (C) Angles of trunk, pelvis and lumbar spine during the three trunk flexion movements. The range of motion of the pelvis (pelvic_RoM), the trunk (trunk_RoM) and the lumbar spine (lumbar_RoM) was calculated as the difference of the respective maximum angle during the movement and the respective angle in the upright standing position. Values of the lumbar angle less than zero indicate the phase of lumbar lordosis while values of the lumbar angle above zero indicate the phase of lumbar kyphosis.

Figure 2

Movement task and assessment of the local dynamic stability of the trunk. (A) Participants repeatedly executed a pointing task from position 1 over 2 with the right arm and 3–4 with the left arm with a frequency of 10 cycles per minute (0.17 Hz); (B) one-dimensional time-series x(t) derived from the norm of the 3-dimensional accelerations of the trunk (accelerometer at the level of the second thoracic vertebrae); (C) reconstructed state space of the trunk movement using dimension m = 3 and time delay τ = 75; (D) diverging Euclidean distances of a nearest neighbor pair in the reconstructed state space; (E) average logarithmic rate (ln) of divergence of all nearest neighbor pairs over time and the maximum Lyapunov exponent (λ_max) as slope of the linear fit to the resulting ln(divergence) curve for 0–40 samples.

Figure 3

Individual lumbar angle as a function of pelvic angle for participants with different low-back pain intensities during trunk flexion. Crosses represent means ± standard deviations at upright standing, end of lumbar lordosis and end of movement, respectively. The average slope of each segment represents the corresponding lumbo-pelvic ratio.