Clinical and radiological evaluation of the Codman semiconstrained load-sharing anterior cervical plate: prospective multicenter trial and independent blinded evaluation of outcome

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Object. Semiconstrained load-sharing implants for spinal fixation accommodate change in the screw—plate interface as bone grafts shrink. The authors evaluated the clinical and radiological outcome in patients after placement of the Codman anterior cervical plate (ACP) system, which allows change in the screw—plate angle.

Methods. The authors undertook a 10-center prospective study with independent blinded evaluation. All patients underwent cervical fusion and placement of ACPs. Clinical and radiological evaluations were performed at 1, 3, 6, 12, and 24 months. Radiographs were examined for screw angles, construct height, fusion, and screw fracture or displacement.

One hundred ninety-five patients were enrolled. The mean follow-up period was 17 months. At 24 months neurological improvement was demonstrated in 68.7% and pain improvement in 76.6% of the patients. Fusion was successful in 93.8%. Varying degrees (most minor) of hardware-related failure occurred in 10.4% of cases; however, reoperation was required in only four (2.1%). A significant change in screw angles occurred over time (mean 6.4° in caudal screw angle [p < 0.001] and 2.4° in the rostral screw angle [p = 0.003]). These changes plateaued by 6 months. A change in construct height (mean 3.48 mm) occurred by 6 months (p < 0.05).

Conclusions. Based on an independent blinded evaluation, the Codman ACP provides effective fixation with load sharing and is effective in achieving fusion with a 94% success rate. Direct comparison with rigidly locked devices is required to establish definitively the optimal method for anterior cervical fixation.

Article Information

Address reprint requests to: Michael G. Fehlings, M.D., Division of Neurosurgery, Toronto Western Hospital, University Health Network, University of Toronto, 399 Bathurst Street, Toronto, ON M5T 2S8, Canada. email: Michael.fehlings@uhn.on.ca.

© AANS, except where prohibited by US copyright law.

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Figures

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    A: The screw plate angle measured relative to the plate perpendicular on lateral radiographs. B: Construct height (Line A), plate height (Line B), distance of construct above and below the plate (Lines C and D) as measured on lateral radiographs. Measurements in Fig. 1B were adjusted between radiographs by using plate height as a constant.

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    Illustrative case of a multilevel decompression and fusion. A 67-year-old noninsulin-dependent diabetic woman presented with progressive myelopathy. Left: Sagittal MR images revealing multilevel degenerative disc disease with cord compression. Right: Lateral cervical radiograph obtained 2 years following her three-level discectomy and ACP-assisted fusion procedure demonstrating fusion. Clinically she denied any pain and experienced complete resolution of myelopathy.

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    Graph showing change in screw—plate angle observed over time, illustrating a caudal change of the superior screw angle and a rostral change of the inferior screw angle. Most of the change occurred within the first 6 months remaining relatively unchanged through 24 months. Change was more pronounced at the inferior screws.

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    Lateral radiographs obtained at initial postoperative period (left) and at 3 months (right), demonstrating graft settling and dramatic change in both rostral and caudal screw—plate angles. Semiconstrained load-sharing cervical plates

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    Lateral radiograph demonstrating fracture of both rostral screws and partial plate backout at 6 months.

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