The evaluation of unstable lumbar-sacral junction with function X-rays films

Abstract

Background: Dynamic radiographs are commonly used to demonstrate segmental instability by demonstrating a varying range of motion and sometimes paradoxical movement of its articulating elements. The disparity is observable and measurable at the opposite extremes of motion; maximum extension and flexion. The level of dissociation within a segment that is responsible for the instability may be partial or complete. Partial dissociations are of two types, anterior or posterior and are referred to as anterior or posterior resistant failure. Complete dissociation is also referred to as circumferential failure. Theoretically, measurement values should reflect and differentiate these pathological processes. This study will
look at any discernible patterns that would be useful indicators of instability. These findings are correlated with MRI scans which show the level of disease.

Objectives: To determine the reliability of dynamic X-ray views in the diagnosis of lumbosacral junction instability in individuals with chronic low back pain.

Design: Case control study.

Methods: Two hundred and one patients with chronic low back pain were subjected to dynamic lumbarsacral plain films as part of clinical evaluation. The views taken are anteroposterior and two lateral views done in maximum tolerable extension and flexion with patient standing with hips and knees extended. A total of 88 patients with lumbosacral junction degeneration were selected for the study. This degeneration consisted of reduction of disc space height, facet arthropathy, fractures through the isthmus, formation of syndesmophytes etc. Measurements to determine extension and flexion angles were done on these films using the Cobb method. The difference between the extension and flexion angle was taken as the flexion arc (range of maximum motion). 

The MRI scans of all the 88 patients were then carefully analysed for tell-tale signs of instability such as disc degeneration (annular fissures), vacuum sign, traction spurs, Modic changes, facet joints osteoarthritis or oedema of the isthmus etc. Thirty seven with signs of segmental instability became the study group1 and the remaining 51without any signs of instability made the control group 2.

Results: A total of 88 patients with monosegmental degenerative disc disease at the lumbosacral junction were analysed. There were 57 women and 31 men. There were no statistical differences between the gender distributions (P > 0.10098) within the groups. There were no statistical differences in the age distribution (P > 0.82337) within the groups. In the study group the mean extension angle was 31.1˚ compared to 19.6˚ in the control group (P = 0.50367). The range of motion was minimal in the study group (ROM = 3.3˚) compared to control group (ROM = 10.2˚), P = 0.00036. Seventeen segments showed paradoxical movement under stress; mean ROM -5˚ compared to 10.2˚ in the control group (P = 00001).

Conclusions: In patients with chronic low back pain, apart from the well-known paradoxical movement dynamic films in an abnormal segment will show a large extension angle (> 30˚) with a reduced range of motion (< 5˚). MRI as a stand-alone modality does not unequivocally confirm or reject segmental instability.

Keywords: Lumbosacral spine, Dynamic radiography, Instability, Range of motion