Session VII - Spine

*The Stabilizing Effects of Different Orthoses in the Intact and Unstable Upper Cervical Spine: A Cadaver Study

Dirk Richter, MD; Loren L. Latta, PhD; Edward L. Milne; George M. Varkarakis, MD; Lutz Biedermann; Axel Ekkernkamp, MD, PhD; Reinhold A. Laun, MD; Peter A.W. Ostermann, MD, PhD, Ernst-Moritz-Arndt-University of Greifswald, Greifswald, Germany (all authors ­ a-Biedermann-Motech, Germany)

Purpose: Cervical orthoses are frequently used for temporary pre- or postoperative immobilization or nonoperative treatment of injuries of the cervical spine. However, there are hardly any reliable data regarding the stabilizing effect of these orthoses in individual segments of the intact and injured cervical spine, the basis for rational treatment. The halo device is still considered the standard treatment for the upper cervical spine. On the basis of the results of a pre-study the authors have created the prototype of a new orthosis meant to provide stability similar to that of the halo.

Methods: In an experimental study with 10 fresh cadavers with intact soft tissues, the vertebral bodies C1 to C3 were marked with screws of 1 cm in length in two planes. The intact cervical spine was moved under fluoroscopic and video control in anterior-posterior (AP) and mediolateral views. Radiographs in both planes were taken at the maximum of extension/flexion, right/left lateral bend, and right/left torque. The measurements were repeated after application of a soft collar, a Miami-J collar, a prefabricated Minerva brace, a prototype of a new orthosis, and the halo fixator. An unstable Anderson type-II fracture of the odontoid was created by an osteotomy through the open mouth. All measurements in all planes without and with all five devices were repeated with the unstable cervical spine. The relative movments in the vertebral segments C1 to C2 and C2 to C3 were assessed on the radiographs from the changes of the angles between the screws in the sagittal and frontal planes. Rotation was calculated by the projected changes of the lengths of the screws in the radiographs.

Results: The median relative motion in the sagittal plane was 10.2° in the segment C1 to C2 and 4.8° in the segment C2 to C3 of the intact spine. A significant restriction was gained after application of all five orthoses. Rotation of the upper cervical spine, which was median 59.1°, was also significantly reduced by all five orthoses. Mean unrestricted lateral bending in the intact spine was 7.5° in C 1 to C2 and 11.9° in C2 to C3, on average. The prototype Miami-J halo fixator achieved statistically significant reduction of lateral bending in C1 to C2. Only the prototype halo gained statistically significant reduction of lateral bending in C2 to C3. Relative movement of the segment C1 to C2 increased up to a median of 20.7° in the sagittal, 11.4° in the frontal, and 66.4° in the coronal plane with the fracture of the odontoid. All devices except the soft collar showed a significant stabilizing effect for the unstable segment C1 to C2. In the sagittal plane, the reduction of motion was 19.3° for the halo, 18.1° for the prototype, 16.7° for the Minerva, and 13.8° for the Miami-J. Rotation was restricted by the halo, the prototype, the Minerva, and the Miami-J. A statistically significant control of lateral bending of the injured segment was only given by the prototype and by the halo fixator.

Discussion and Conclusions: A new technique enabled us for the first time to measure relative motion in individual segments of the intact and unstable upper cervical spine in the sagittal, frontal, and coronal plane with the help of markers. All five orthoses showed a certain kind of restriction of the relative movement in the intact upper cervical spine, but to a very different degree. Our model of an unstable odontoid fracture revealed larger differences in the control provided by the different designs. The halo fixator provided the best control for the upper cervical spine segments in almost all conditions. The Miami-J and the Minerva both gave significant control to the injured segment, but still not enough to recommend their use for the nonoperative treatment of unstable lesions such as our experimental fracture. The prototype showed a better control for the injured segment than the other semi-rigid orthoses in almost all conditions. However, the restriction of motion was less than in the halo, although the differences were mostly not statistically significant. One reason for this may have been the bad fitting of the device in some cadavers that may be improved in future. Our data suggest that the new device is an improvement over the now existing semi-rigid devices. Further clinical and experimental studies will have to show whether the inconvenient halo can be replaced by an improved model of the prototype orthosis. On the basis of our data, the soft collar cannot be recommended for any unstable lesion of the (upper) cervical spine, not even for emergency immobilization.