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Introduction: Cervical spine pedicle morphology has been assessed by direct measurement and by CT in cadavers. We have assessed reproducibility and produced data for normal ranges in live subjects from the UK.

Method: 54 axial CT scans were examined. All subjects were scanned for the exclusion of fracture between December 2003 and December 2004. The digitised images were analysed on the Philips PACS system using SECTRA software. 168 individual vertebrae were assessed between C3 and C7. The following were measured; the angle of the pedicle relative to the sagittal plane, the smallest internal and external diameter, the angle of the lamina and the distance from the lateral mass to the anterior vertebral body (LMAVB) in the line of the pedicle. Reproducibility was assessed in a subset of 10 individuals with paired measures using the FDA approved formula for CV%.

Results: Angular measures had a CV% of 3.9%. The re-measurement error for distance was 0.5mm. 338 pedicles were assessed in 25 females and 29 males. Average age was 48.2 years (range 17–85). Our data from live subjects was comparable to previous cadaveric data. Mean pedicle external diameter was 4.9mm at C3 and 6.6mm at C7. Females were marginally smaller than males. Left and right did not significantly differ. Mean LMAVB was 34mm (min 21mm). In no case was the pedicle narrower than 3.2mm. Mean pedicle angle was 130 deg at C3 and 140 deg at C7.

Conclusions: CT measurement has acceptable reproducibility. Previous cadaveric measurements have been validated in live subjects in the UK. Although there is some variation in morphology, instrumentation no wider than 3.0mm and no longer than 20mm is unlikely to prove too large for an adult pedicle.

Correspondence should be addressed to: Sue Woodward, Secreteriat, Britspine, Vale Clinic, Hensol Park, Vale of Glamorgan, CF72 8JY Wales.