Study Design. A cadaveric cervical spine specimen fixed between a fibe
rglass torso and a plastic skull was used as a model to determine the
effect of halo structural parameters on motion at a lesion simulated a
t C5-C6. In a second part, nine commercially available halo devices we
re compared. of the halo apparatus to reducing motion in an injured ce
rvical spine and to compare the stability offered by a sample of comme
rcially available halo devices. Controversy exists concerning the abil
ity of the halo apparatus to stabilize the injured cervical spine. Sum
mary of Background Data. The halo apparatus has been shown to be the m
ost effective nonsurgical method for stabilizing the fractured spine.
Nonetheless, several clinical studies have demonstrated that unaccepta
bly large motions can occur at the injured spinal segment stabilized w
ith a halo apparatus. Methods. Each cadaveric cervical spine was mount
ed onto a fiberglass torso and a rigid plastic skull was attached to t
he base of the occiput. A posterior ligamentous lesion was created bet
ween C5 and C6. The halo ring was fitted to the skull and a vest to th
e torso. Loads were applied to the skull in flexion, extension, and la
teral bending, and relative angulation between C5 and C6 was measured
with electroinclinometers. In the first part, the effect of parameters
such as vest tightness, vest-thorax friction, vest deformation, and c
onnecting bar rigidity on spinal angulation were measured using one ve
st. In the second part, the stability offered by each of nine commerci
ally available halo devices was compared. Results. Increasing chest st
rap tightness and decreasing vest deformation reduced angulation at th
e spinal lesion. Once connecting bar joints were tightened to 25% of t
heir recommended torque, increased tightening or adding additional bar
s had no effect on rigidity. Although specific vests permitted signifi
cantly greater motion in specific directions, no vest allowed greater
angulation consistently in all loading planes. Conclusions. Increasing
vest tightness, decreasing the deformability of the vest, and ensurin
g a good fit can reduce motion in the fractured spine. Most commercial
ly available halo vests provide similar mechanical stability to the in
jured cervical spine.