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. 2008 Jan;17(1):30-5.
doi: 10.1007/s00586-007-0486-8. Epub 2007 Sep 11.

Consequences of patient position in the radiographic measurement of artificial disc replacement angles

Victor Kosmopoulos  1 , John McManus, Constantin Schizas
Affiliations

Consequences of patient position in the radiographic measurement of artificial disc replacement angles

Victor Kosmopoulos et al. Eur Spine J. 2008 Jan.

Abstract

Accurate clinical measurement of spinal range of motion (ROM) is essential in the evaluation of artificial disc performance. The effect of patient placement with respect to the X-ray beam source is yet to be reported and may be an influencing factor in radiographic artificial disc angle measurements. This study aims to evaluate how radiographic patient placement influences artificial disc angle measurements. An anatomically accurate synthetic L4-L5 motion segment was instrumented with an artificial disc and two pins. The instrumented motion segment was mounted onto a frame allowing for independent rotation and elevation while holding the artificial disc angle and anatomical position between L4 and L5 fixed. Analyses included descriptive statistics, evaluation of uncertainty, intra- and inter-observer, and a 2-way analysis of variance (ANOVA). The mean angle measurement range at the various positions was 1.26 degrees for the pin, and 2.74 degrees for the artificial disc endplates. The centered patient position had the highest inter- and intra-observer reliability. ANOVA results showed elevation effects to be statistically significant (P = 0.021), and rotational effects to be extremely statistically significant (P < 0.0001) for the pin angles. In terms of the mean artificial disc angle, however, the ANOVA showed a highly statistically significant interaction term (P = 0.002). A significant difference was found in the angle measurements of a fixed artificial disc prosthesis based on a sample of patient radiographic placement positions. Since it is important to assess the success of an artificial disc replacement by evaluating the relatively small ROM present, it is crucial to aim at minimizing the error by placing the patient parallel to the plate with the beam centered not at the mid lumbar spine, but at the level of the arthroplasty, for both flexion and extension views.

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Figures

Fig. 1
Fig. 1
Digital radiograph of the instrumented motion segment model at the centered (0 cm, 0°) position displaying the landmark points and respective coordinates chosen for calculation of the pin (P) angle and the artificial disc endplate (E) angle
Fig. 2
Fig. 2
Mean pin angles with uncertainty bars for the seven rotations and four elevations studied
Fig. 3
Fig. 3
Mean artificial disc endplate angles with uncertainty bars for the seven rotations and four elevations studied
See this image and copyright information in PMC

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