Biomechanics of healing of posterior cervical spinal injuries in a canine model.

The authors performed an in vivo experiment in a canine model to study the natural history of spinal stability as a function of healing time post-injury. Three injuries, in addition to sham, were investigated: 1) transection of supra- and interspinous ligaments at C4-C5; 2) laminectomy at C4; and 3) bilateral facetectomy at C4-C5. Standardized functional flexion/extension stereo-radiographs of the cervical spine were obtained before injury and at 1, 3, 6, 9, 12, and 24 weeks postinjury. The authors found decreased ranges of motion (ROM) at the C4-C5 level for all injuries, including the sham. The decreases, in general, seemed to be in direct proportion to the severity of the injury. When the ROM were normalized to that of the sham at each time point, the relative ROM at C4-C5 increased for Injury 1, remained the same for Injury 2, and decreased for Injury 3. The relative ROM remained the same or increased at C3-C4, and increased at C5-6 for all injuries. It should be emphasized that care should be taken in extrapolating any data from this animal study to the human cervical spine.