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

PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.