Trunk motor control deficits in acute and subacute low back pain are not associated with pain or fear of movement

Abstract

Background context: A subgroup of patients with acute to subacute low back pain (LBP) presenting with trunk movement control deficits, pain provocation with segmental testing, and segmental hypermobility have been clinically identified as having movement coordination impairments (MCIs) of the trunk. It is hypothesized that these patients have proprioceptive, postural, and movement control impairments of the trunk associated with LBP. Although trunk control impairments have been identified in patients with chronic LBP, they have not been investigated in this subgroup or closer to symptom onset.

Purpose: The purpose of the study was to identify trunk motor control (postural control and movement precision) impairments in a subgroup of patients with acute to subacute LBP who have been clinically identified to have MCIs and determine association of these impairments with pain and fear of movement.

Study design/setting: The study design includes observational design, university biomechanics laboratory, and clinical practice.

Patient sample: Thirty-three patients with acute to subacute LBP presenting with trunk MCIs and 33 healthy controls matched with gender, age, and body mass index were identified.

Outcome measures: Self-report measures included Numeric Pain Rating Scale, Oswestry Disability Index Questionnaire, and Fear-Avoidance Beliefs Questionnaire and physiologic measures included postural control and movement precision.

Methods: Center-of-pressure movement was measured while subjects attempted to volitionally control trunk posture and movement while sitting on a platform with a hemisphere mounted underneath. This created an unstable surface that required coordinated trunk control to maintain an upright seated posture. Postural control was tested using eyes-open and -closed balance protocols. Movement precision was tested with a dynamic control test requiring movement of the center of pressure along a discrete path. Group trunk motor control performance was compared with analysis of variance and t test. Performance association with pain and fear of movement were assessed with Pearson correlations.

Results: Patients' postural control in the eyes-closed condition (p=.02) and movement precision (p=.04) were significantly impaired compared with healthy controls, with moderate-to-large group difference effect sizes. These trunk motor control impairments were not significantly associated with the patients self-reported pain characteristics and fear of movement.

Conclusions: Patients with clinical identification of trunk MCIs demonstrated decreased trunk motor control, suggesting that impairments in proprioception, motor output, or central processing occur early in the back pain episode. This information may help to guide interventions to address these specific limitations, improving delivery of care.

Trial registration: ClinicalTrials.gov NCT01085604.

Keywords: Low back pain; Motor control; Movement control; Movement coordination impairment; Postural control; Proprioception.

Copyright © 2015 Elsevier Inc. All rights reserved.

Figures

Figure 1

Custom designed apparatus to test isolated trunk motor control. Subject’s legs are constrained to prevent lower extremity compensation. Seat is balanced on a hemisphere designed to tip forward if lower extremities are involved in moving the trunk. Graphic demonstrates the trunk motions (dashed lines) performed while the patient is seated in the chair and making adjustments in the sagittal and frontal planes. The chair allows for movements in the sagittal, frontal, and transverse planes.

Figure 2

The order and the 8 directions in which the subjects were required to move their center of pressure during the directional control test. The directional control region was calculated summing the area of the 8 octants, with each octant defined by an angle (a) and two known sides (b and c). The precision of the COP trajectory in the 8 directions was determined by a standardized stability boundary. This boundary (lines to the left or right of the directional line) was calculated in real time, at 10% of the distance the subject moved their COP away from the center position. Thus, at a distance of 10 mm along the line, the boundaries would be set 1 mm. Between 10 and 20 mm from the center, the boundaries would gradually increase to 2 mm. Maximum distance for each of the direction was the maximum excursion the subject was able to move away from the center along the directional line without his or her COP crossing the stability boundary. This provided the length of sides b and c.

Figure 3

Flow diagram outlining the screening process, clinical examination and trunk postural and dynamic control testing of subjects with low back pain and the matching healthy control subjects.

Figure 4

This graph provides an example of a directional control region for a matched healthy control subject and patient with non-specific low back pain. The patient has a smaller area and less symmetry in their directional control region.