Commentary on the Article of D. Kemmesies, U. Meier: Experience with Five Different Intervertebral Disc Spacers for Cervical Spondylodesis

More than 60 papers are listed in Medline under the search criteria “cervical spinal cage” and more than half of these compare different types of spacers. The present study evaluates 5 commercially available spacers of different makes, implanted by 5 surgeons in a total of 207 cases of degenerative cervical disease. Technical details, clinical and radiological results after a follow-up period of 3 and 12 months, fusion and complication rates are presented.

The main issues determining the quality of the procedure emerge to be the spacer contact area, vertebral realignment and physiological angulation. The authors conclude that the decision which spacer is best suited should be based on clinical and radiological findings and the experience level of the respective surgeon. Where biomechanical characteristics of the spacers compare, economical considerations can be allowed for.

It appears highly unlikely that the large number of variables: 5 spacers, 5 surgeons, degree of osteoporosis and varying clinical presentation with myelopathy or radiculopathy, will allow a statistically profound analysis. Unfortunately, however, there is no data concerning the time period of symptoms or the degree of neurological deficit prior to surgery. It is common knowledge that these factors will significantly influence the long-term outcome of cervical spondylodesis. It would also be desirable to see a longer follow-up period in cases of strictly monosegmental fusion. Furthermore, it would be of interest to see a correlation between the degree of subsidence and segmental kyphosis with clinical findings. Suboptimal radiological findings need not necessarily mean inferior clinical results, let alone require a corrective operation.

The different spacers should be termed using the name of the describing author. The use of trade names should be avoided.

The assumption that the ventral approach to the cervical spine is the technically less intricate procedure is simply not true albeit it may be the approach the authors are best acquainted with. Complication rates of the different options militate against their view.