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Anatomic considerations for uncovertebral involvement in cervical spondylosis.

Morphometric analysis of 54 dry cervical spines from C3 to C7 (a total of 270 cervical vertebrae) and bilateral dissection of 10 anatomic specimen cervical spines were performed. The uncinate processes were significantly higher at C4 to C6 (5.8 +/- 1.1 mm to 6.1 +/- 1.3 mm) levels than at C3 or C7 levels. The anteroposterior diameter of the intervertebral foramina was smaller at the C4, C5, and C6 levels compared with that at the C3 or C7 levels. The length of nerve root between the lateral border of dural tube and medial border of vertebral artery gradually increased from C3 (3.3 +/- 1.1 mm) to C7 (8.1 +/- 2.1 mm). A combination of higher uncinate process, smaller anteroposterior diameter of intervertebral foramina, and longer course of nerve roots in close proximity of the uncovertebral joints at the C4 to C6 levels may explain the predilection of nerve root compression by uncovertebral osteophytes at these levels. The distance from apex of the uncinate process to medial border of the transverse foramen gradually increased from C3 (1.7 +/- 0.8 mm) to C7 (3.3 +/- 1.0 mm), which may predispose the midcervical level to compression of the vertebral artery by laterally projecting uncovertebral osteophytes.