Biomechanical assessment of balance and posture in subjects with ankylosing spondylitis

Abstract

Background: Ankylosing spondylitis is a major chronic rheumatic disease that predominantly affects axial joints, determining a rigid spine from the occiput to the sacrum. The dorsal hyperkyphosis may induce the patients to stand in a stooped position with consequent restriction in patients' daily living activities. The aim of this study was to develop a method for quantitatively and objectively assessing both balance and posture and their mutual relationship in ankylosing spondylitis subjects.

Methods: The data of 12 healthy and 12 ankylosing spondylitis subjects (treated with anti-TNF-α stabilized), with a mean age of 51.42 and 49.42 years; mean BMI of 23.08 and 25.44 kg/m(2) were collected. Subjects underwent a morphological examination of the spinal mobility by means of a pocket compass needle goniometer, together with an evaluation of both spinal and hip mobility (Bath Ankylosing Spondylitis Metrology Index), and disease activity (Bath Ankylosing Spondylitis Disease Activity Index). Quantitative evaluation of kinematics and balance were performed through a six cameras stereophotogrammetric system and a force plate. Kinematic models together with a test for evaluating balance in different eye level conditions were developed. Head protrusion, trunk flexion-extension, pelvic tilt, hip-knee-ankle flexion-extension were evaluated during Romberg Test, together with centre of pressure parameters.

Results: Each subject was able to accomplish the required task. Subjects' were comparable for demographic parameters. A significant increment was observed in ankylosing spondylitis subjects for knee joint angle with the target placed at each eye level on both sides (p < 0.042). When considering the pelvic tilt angle a statistically significant reduction was found with the target placed respectively at 10° (p = 0.034) and at 30° (p = 0.019) less than eye level. Furthermore in ankylosing spondylitis subjects both hip (p = 0.048) and ankle (p = 0.029) joints angles differs significantly. When considering the posturographic parameters significant differences were observed for ellipse, center of pressure path and mean velocity (p < 0.04). Goniometric evaluation revealed significant increment of thoracic kyphosis reduction of cervical and lumbar range of motion compared to healthy subjects.

Conclusions: Our findings confirm the need to investigate both balance and posture in ankylosing spondylitis subjects. This methodology could help clinicians to plan rehabilitation treatments.

Figures

Figure 1

Subjects while undergoing a morphological examination of the spine using a specific assessment tool. Both kyphosis and lumbar lordosis were measured and the range of motion of cervical and thoraco-lumbar spine through a pocket compass needle goniometer (IncliMed®). From the top to the bottom and from left to right: first the subject is standing barefoot while the goniometer is placed orthogonal to the spine in correspondence of vertebra T12 performs the maximum extension with his knee straighten, and with two goniometers placed in T12 and S2 performs the maximum flexion of thoraco-lumbar spine; the subject stands and the goniometer is positioned flat and parallel to the spine in correspondence of T12 and performs the lateral thoraco-lumbar inclination; the subject seats with the goniometer fixed in neutral position; in this position the subject performs one head flexion and extension; the subject seats with the goniometer fixed in neutral position; the subject performs one head lateral left and right inclination; the subject seats with the goniometer fixed in neutral position; the subject performs left and right thoraco-lumbar rotation.

Figure 2

Description of the joint angles in the sagittal plane. Head protrusion (a), trunk flexion-extension (b), pelvic tilt (c), hip flexion-extension (d), knee flexion-extension (e), ankle flexion-extension (f).

Figure 3

Boxplots of the kinematic parameters: Ankylosing spondylitis (AS) in red, Control Subjects (CS) in blue. Horizontal axis depicts the 7 eyes eights (eyes level = e.l.); from top to bottom vertical axes represent: the head protrusion (HP), the upper trunk flexion-extension (UTFE), the trunk flexion-extension (TFE), the pelvic tilt (PT) (Figure  3a), the right hip flexion-extension (rHFE), the right knee flexion-extension (rKFE), the right ankle flexion-extension (rAFE), the left hip flexion-extension (lHFE), the left knee flexion-extension (lKFE), and the left ankle flexion-extension (lAFE) (Figure  3b). * Statistical significance (P < 0.05).

Figure 4

Boxplots of the posturographic parameters: Ankylosing spondylitis (AS) in red Control Subjects (CS) in blue. Horizontal axis depicts the 7 eyes eights (eyes level = e.l., eyes closed = e.c.); from top to bottom vertical axes represent: the ellipse 95% (Ellipse95%), the sway area (Sway Area), the total path (Path), the path in medio-lateral direction (Path ML), the path in anterior-posterior direction (Path AP) (Figure  4a), the total mean velocity (Mean Velocity), the mean velocity in medio-lateral direction (Mean Velocity ML), and the mean velocity in anterior-posterior direction (Mean Velocity AP) (Figure  4b). * Statistical significance ( P < 0.05).