Anatomic considerations for plate-screw fixation of the cervical spine.

A cadaveric study was done to investigate the variability of interfacet distances from C3 to C7, to learn pedicle morphology at C7-T2, and to determine potential dangers of plate-screw osteosynthesis technique of the cervical spine. Twenty-two cadavers were dissected from C2 to C7 to expose the lateral masses and nerve roots. The interfacet distances from the center of the lateral mass to the next lateral mass from C3 to C7 vary widely among different individuals, ranging from 9 mm to 16 (average, 13 mm). A new plate design is necessary to better accommodate the differences in interfacet distances among different patients and different levels. The second part of the study involved 11 dissected cadaveric specimens of the cervicothoracic junction. The pedicle entry point was 1 mm inferior to the midportion of the facet joint for C7, T1, and T2. The medial angulation averaged 34 degrees at C7, 31.8 degrees at T1, and 26.5 degrees at T2. The mediolateral and superoinferior outer pedicle diameters were 6.9 mm and 7.5 mm at C7, 8.5 mm and 9.5 mm at T1, and 7.5 mm and 10.7 mm at T2, respectively. The mediolateral inner diameter averaged 5.18 mm, 6.4 mm, 5.5 mm for C7, T1 and T2, respectively. The pedicle distances (from the entry point to the posterior vertebral body line) measured 9.1 mm, 9.9 mm, and 10.4 mm for respective levels. The margins for error are small when using pedicle screws at these levels. If a pedicle screw must be used at C7, T1, and T2, one must have precise knowledge of the entrance point, diameters, and 25-30 degrees medial direction.(ABSTRACT TRUNCATED AT 250 WORDS)