Article Figures & Data
Figures
- Fig. 1
TPDR is calculated as the sagittal plane translation, between flexion and extension, of the posterior inferior corner of the superior vertebra in a direction defined by the superior endplate of the inferior vertebra. The left half of an L5 vertebra is shown, reconstructed from CT. The left half of the L4 vertebra is shown in the flexed and extended position relative to L5. In this example, L4 rotated 13° between flexion and extension. The posterior corner of L4 translated 26% of the L5 endplate width, so the TPDR is 26/ 13 = 2% endplate width/degree. Average TPDR in the asymptomatic population was 0.53±0.14, so QSI = (2.0 – 0.53)/0.14 = 10.5. This would be considered very abnormal.
- Fig. 2
An out-of-plane (OOP) index was calculated for each level based on the distance between the apparent widest separation between the left-most and right-most edges of the vertebral endplate (white line with arrows on either end) divided by the anterior height of the vertebral body (black dashed line). Ideally, the OOP index would be zero. The most OOP endplate at the level where QSI was measured was used for this calculation. The calculation was made for the worst OOP in the flexion or extension radiographs.
- Fig. 3
The average QSI at the L4-5 level at preoperation for patients with no evidence of fluid in the facet joint, possible fluid in the joint, and with a definite fluid sign. The error bars show the standard error.
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