Comparing Cervical Spine Motion With Different Halo Devices In A Cadaveric Cervical Instability Model


Andrew Sawers
University of Rochester Medical Center
Rochester, New York

INTRODUCTION:

The conventional halo (CH) is considered the standard orthosis for obtaining the strictest immobility in the unstable cervical spine. Many successful outcomes have been reported with its use however, CHfs still fail to immobilize some fractures (1) and 11- 15% nonunion rates have been reported (2,3). Complications of CH treatment including pin and ring loosening, pin tract infection, poor fit, dysphagia and pressure ulcers (4-7) may limit their use. The non-invasive halo (NIH) was designed to combat the common CH complications and failure of immobilization of the cervical spine (8,9). Biomechanical studies have been performed on many cervical orthoses including conventional halos in an attempt to understand their effectiveness in cervical immobilization (10-16). The CH fails to completely immobilize the cervical spine, having documented range of motion from 31-70% of normal (13,14). Previous studies often use X-ray to assess instability and have employed subjects ranging from healthy volunteers to patients with spinal instability to cadaveric samples (10-14,16). To date no investigation has compared the biomechanical efficacy of the NIH to that of the CH or standard two-piece cervical collar, in restricting cervical spine motion, by using electromagnetic motion analysis. The goal of this study was to record the ability of these three devices to restrict motion in both a C1-2 and C5-6 global instability model.

METHODS:

A global instability was created at the C1-C2 level in two lightly embalmed cadavers and at C5-C6 in two other cadavers. Sensors for the electromagnetic motion analysis device (Liberty, Polhemus Inc. ., Colchester, VT) were then fixed above and below the level of injury, using custom made mounts. Relative motion between the superior and inferior vertebrae, in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) was recorded for intact and destabilized spines. Data was collected during the donning process, maximal ROM testing, log rolling and transferring from a supine to sitting position. This testing sequence was followed for both the conventional halo, noninvasive halo and a standard two piece cervical collar. Differences between groups were evaluated using a multi-variate Analysis of Variance (ANOVA), with the range of motion in each plane as the dependent variable. When there were more than two conditions, a Tukey HSD post-hoc test was used to determine which groups were significantly different from each other. The level of significance was set a priori at 0.05.

RESULTS:

The only statistically significant difference that was found during the application of the orthoses was during the donning of the conventional halo in relation to the 2-piece collar at the C5-6 level, p..033 (figure 1). While the NIH created greater motion then the 2-piece collar and less then the CH no statistically significant difference was found at either the C5-6 or C1-2 level.

Figure 1: Motion While Putting on Various Cervical Orthoses with a C5-C6 Instability (n=2)


No statistically significant differences were seen between any of the orthoses at C1-2 or C5-6 for the sitting up maneuver, log rolling maneuver or during the ROM assessment. When the log rolling maneuver was performed on cadavers with a C5-C6 injury, the twopiece collar allowed more motion than either the CH or the NIH. However when the same maneuver was performed on cadavers with C1-C2 injury, the two-piece collar was as effective as either the CH or NIH in limiting motion.

NIH ROM restriction for C1-2 and C5-6 compared favorably to the CH and overall performed better than the collar or no collar during ROM assessment (Figure 2&3).

Figure 2: Range of motion for various cervical orthoses (C12 instability)


Figure 3: Range of motion for various cervical orthoses (C56 instability)


CONCLUSIONS:

Both the NIH and CH perform much better compared to cervical collars or no collar when tested to the maximum range of motion allowed. The NIH appears to restrict motion to a similar degree as compared to the CH, expect for extension motions. This could be due to the floating occiput pad design on the NIH rather then the posterior shell and associated posts on the CH. The act of donning a CH was also found to create more motion than the application of a collar or a NIH. The aforementioned design feature may also explain these differences seen during donning of the NIH and CH as the patient does not need to be rolled to don the NIH.

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