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Subsidence after anterior cervical inter-body fusion. A randomized prospective clinical trial

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In ventral fusion after anterior cervical discectomy there is still a remarkable number of cage subsidence and segmental kyphosis seen. The aim of the present study is to assess whether the cage design influences the extent of correction loss during follow-up. Sixty patients with single-level cervical disc herniation were randomly treated with two different cervical inter-body cages (group1: Solis™ cage, Stryker Company and group2: Shell™ cage, AMT Company). Clinical and radiological follow-up was done before and after surgery, 3 and 6 months post-surgery. Clinical follow-up was done with the help of Odom’s criteria. Both groups were similar in the baseline parameters (age, sex, treated level). Statistically, the subsidence was significantly higher at 3 and 6-month follow-ups in group1 than in group2, however, clinical results showed no significant differences. In 67%, subsidence was seen in the anterior lower aspect of the treated segment. Segmental kyphosis was seen in seven patients of group1 and two patients of group2. A significant correlation is found between Odom’s criteria and subsidence. Although there was no significant difference in a short-term clinical result between the two treatment groups, we recommend the use of cages which preserve the determined segmental height and lordosis.

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Correspondence to Erich Kast.

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Peter Ulrich, Offenbach, Germany

The authors deal in their prospective study with a typical complication of anterior cervical discectomy, the loss of disc height and increasing kyphosis. Despite recent advances in spacer technology, the problem is far from being solved. Furthermore, the variety of solutions extolled by the industry makes it more difficult to make the right choice. The purpose of the study was to evaluate, in a randomized controlled protocol, whether the cage design influences the extent of correction loss and the clinical results. At 6 months after mono-segmental discectomy, the cage with the greater contact surface area increased at the anterior lower aspect (Shell™ cage, AMT Company, Nonnweiler, Germany) yielded significantly better results in the radiologic outcome than its counterpart (Solis™ cage, Stryker Company, Kalamazoo, USA). The correlation between radiologic criteria and clinic was less compelling. The authors present an innovative method of measuring segmental height, which seems quite valuable. The conclusion that a careful choice of the proper cage is crucial for obtaining good radiological and clinical results confirms a widespread experience. Despite a limited number of patients enrolled in the study and a relatively short follow-up, the paper presents a remarkable contribution to the ongoing discussion about the best technique in ventral fusion after anterior cervical discectomy.

Hiroshi Nakagawa, Nagoya, Japan

This is a randomized prospective clinical study on subsidence following anterior cervical inter-body fusion using two different cages made of PEEK.

It demonstrated a well-analyzed data which recommended usage of cages with a large-enough contact surface area to preserve the segmental height and lordosis, although this study is of limited value because of a relatively small number of cases, rather short follow-ups, and no CT follow-ups.

For the last decade, we have had some experience of more than 400 cases with cervical myelopathy and radiculopathy which were treated by anterior inter-body cage fixation using cyrindrical titanium cages. In cervical discs and spondylosis, two cages were inserted side by side in a locked fashion and with the anterior cage surface placed along the anterior cortex of the vertebrae in order to minimize the subsidence of the cages.

One thing I can not understand is that the authors used anterior plating in addition to inter-body cages in cases with cervical myelopathy. Is there any rationale for this? In our series, about 70% of the cases have myelopathy and have been treated mostly by cages only without much problem.

With more experience and cases, I hope they will come up with a lesser invasive method in the future.


None of the authors has received any financial support from any company cited in this study, and none of the authors has any financial or other interest in a company involved in this study.

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Kast, E., Derakhshani, S., Bothmann, M. et al. Subsidence after anterior cervical inter-body fusion. A randomized prospective clinical trial. Neurosurg Rev 32, 207–214 (2009).

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