Normal, Fused, and Disc Replacement Cervical SpineCervical disc replacement is a rather new treatment option for persons needing fusion of their neck. It is estimated that 70 percent of spinal surgeries in the United States will involvine disc replacement by 2010. While anterior cervical decompression and fusion (ACDF) surgery seems to have successful outcomes long-term, some studies have shown that it is common for the development of wear and tear of the segments above and below the level that has been fused. It is felt that this is due to decreased range of motion at the segment that has been fused. This then causes the adjacent segments to have increased motion and forces on the discs, facet joints and soft tissues.
The authors of this study evaluated range of motion in live subjects rather than cadavers. Ten subjects had ACDF at C5-6. Ten subjects had cervical anterior disc replacement (CADR) at C5-6. Surgery was at minimum six months before the start of the study. The normal group consisted of 10 subjects who had not had neck surgery. Evaluation of forward bending or flexion, backward bending or extension of the neck was done by using special X-rays called fluoroscopy. Motions of each segment to include C3-4, C4-C5, C5-6, and C6-C7 were measured.
This study demonstrated that subjects with CADR had range of motion at all segments close to those in the normal group. However, the CADR subjects had larger range of motion than the normal subjects at the implanted level, C5-6. When compared to the normal and CADR groups, the ACDF group had two to three times more range of motion at both adjacent levels. The range of motion at C3-4 was similar among all groups.
Contact forces were extrapolated from measurements also. Transverse forces were increased in the ACDF group when compared with the normal group and the CADR group. Vertical forces were not significantly different among the three groups.
This study demonstrated that CADR may prevent adjacent segment wear and tear when compared with anterior cervical decompression and fusion. CADR preserves the motion and force patterns of the normal spine. However, the increase in motion at the implanted segment may be a cause for concern. Long-term follow-up studies are needed to determine if CADR can replace ACDF.
Fei Liu, et.al. In Vivo Evaluation of Dynamic Characteristics of the Normal, Fused, and Disc Replacement Cervical Spines. InSpine. November 2007. Volume 32. Number 23. Pp. 2578-2584.
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