Computed tomography measurement of the bone matrix of vertebral pedicle and its clinical significance.

BACKGROUND: To provide the anatomic basis for the clinical application of the transpedicular screw fixation.

MATERIALS AND METHODS: 30 spine (C₂～L₅)specimens were used.The width of the pedicle cortex and medullary cavity(WPC and WPMC),and the height of the pedicle cortex and medullary cavity(HPC and HPMC)were measured at the isthmus of the pedical using CT scanning.

RESULTS: WPMC changed in a three-dovetailed-saddle shape with four peaks and three velleys, namely C₂(high),C4`5(low),T₂(high),T₄(the lowest),T₁₂(high),L₁(low)and L₅(the highest). HPMC of the cervical pedicle changed in a saddle shape, gradually increasing from C₅～L₅.WPC,WPMC,HPC and HPMC showed a regular change respectively. In each segment, the superior border of the pedicle cortex had a nearly consistent thickness to the interior border within an identical pedicle, while the pedicle cortex thickness radio of the medial and lateral border was nearly 3:1 among the cervical pedicles,2:1 among thoracic pedicles, and 1:1 among lumbar pedicles.

CONCLUSIONS: Both HPMC and WPMC are the dominant factors for the choice of screw diameter, but HPMC should also be considered in C₂～ T1 pedicles, especially C6 and C₇.Additionally,the screw for C3~6 or T4~6 pedicles should be about 3.0mm in diameter.