Kinematic Comparison of Normal, Fused and Disc Replacement Cervical Spines in the Chimpanzee

Vincent E. Bryan, Robert Conta (Mercer Island, WA)
Richard Kornistek (Denver, CO)
John Heller (Decatur, GA)
Jeffrey Rouleau (Mercer Island WA)

Introduction:

This in vivo study compares the kinematic performance of the adult male chimpanzee cervical spine after implantation of a cervical disc prosthesis with that of normal and fused chimpanzees.

Methods:

Fluoroscopic video images of six disc replacement chimpanzees (six months post–implant at C3–4 & C5–6), one normal, and two fused chimpanzees were taken during manipulation of the head from full flexion to full extension, and recorded on videotape. Each cervical vertebra was digitized and four discrete points were located on each vertebra. The relative translation and angulation of adjacent vertebrae through the full range of motion (ROM) was plotted.

Results:

The normal subject maximum absolute rotation relative to a fixed reference ranged from 50 to 75 degrees. Rotation between vertebrae was progressive and similar throughout the ROM. Fused subjects' relative rotation of each vertebra compared to the fixed reference frame was not similar for each cervical joint and maximum rotation was less. Disc replacement subjects experienced rotational patterns and maximum vertebral rotation between each vertebra similar to the normal cervical spine. The maximum cervical vertebrae translation for the normal subject was less than 2.5mm. Fused subjects had no translation of the fused joints, but experienced larger amounts of translation of their other cervical joints as compared to the normal. The average translation for subjects having a C3–4 and C5–6 disc replacement was less than 1 mm. (Digitization error is 0.5–1.Omm in translation and less than II in rotation.)