Reliability and validity of a new measurement of lumbar foraminal volume using a computed tomography

Measuring foraminal stenosis is generally determined by an area calculation. It is difficult to know exactly where it is most appropriate to measure. No precise data are available on a method for calculating the foraminal volume using a CT. To develop a new method for measuring lumbar foraminal volume, we analyzed repeatability and reliability for measuring methods for foraminal volume using CT.

The measurements were performed using a CT scan from ten healthy patients, with a mean age of 26.3 years. L3-L4, L4-L5 and L5-S1 foramen were studied, to obtain 60 foraminal measurements. Inter- and intra-observer reproducibility was calculated. Each series was analyzed using the VitreaCore® reconstruction software for volume calculation.

Average volume measurements of 60 foramina and 20 L4-L5 foramina were, respectively, 1.17 and 1.25 mm(3) for observer 1 and 1.21 and 1.29 for observer 2. The intra-observer correlation coefficients for observer 1 when measuring all foramina and L4-L5 foramina were 0.98 and 0.99, respectively. For observer 2, coefficients were 0.90 and 0.92, respectively. The inter-observer correlation coefficients for observer 1 when measuring all foramina and L4-L5 foramina were 0.78 and 0.83, respectively. For observer 2, coefficients were 0.77 and 0.8, respectively. The average differences in intra- and inter-observer measurements regardless of the evaluator group were less than 0.2 mm(3).

This is the first study measuring lumbar foraminal volume using CT. The excellent reproducibility of this simple measure can supplement a range of foramen measurement tools.