Abstract
BACKGROUND CONTEXT
Previous clinical studies of interbody fusion cages have generally failed to report sagittal plane alignment. In some cases, parallel-sided cages have contributed to loss of lumbar lordosis. A wedged-shaped carbon-fiber-reinforced polymer (CFRP) cage implant filled with autologous bone was designed to allow surgeons to more easily achieve normal sagittal plane alignment in posterior lumbar interbody fusion (PLIF).
PURPOSE
This study was conducted to test the safety and efficacy of the wedged CFRP cage and the ability of surgeons to achieve normal anatomic alignment using an implant of this shape.
STUDY DESIGN/SETTING
The wedged CFRP cage with pedicle screw fixation was evaluated in the treatment of patients with spondylolisthesis in a 2-year prospective study performed at 12 centers under a Food and Drug Administration (FDA)-approved protocol
PATIENT SAMPLE
Inclusion criteria included patients with isthmic or degenerative spondylolisthesis at a single level below L4 with a translational malalignment of 3 mm or greater. Exclusion criteria included patients with more than 90% translation, previous surgery or abnormalities at more than two levels.
OUTCOME MEASURES
Traditional outcome measures have included clinical success (improvement in pain and function) and fusion success (proof of living bone bridging the fusion area). This study adds a more complete analysis of anatomic success (restoration or maintenance of normal disc space height and sagittal plane alignment).
METHODS
A clinical study of PLIF with pedicle screw fixation included a prospective group of 46 patients treated for spondylolisthesis. This article presents the data from the FDA-approval protocol.
RESULTS
Fusion success was achieved in 35 of 36 patients (97.2%) reaching the 2-year follow-up interval. Clinical success was achieved in 35 of 37 (94.6%), and overall success was achieved in 33 of 36 (91.2%). Disc space height averaged 8.3 mm preoperatively, was increased to 10.2 mm at surgery and was maintained at 9.8 mm at 2 years. L4-S1 sagittal plane alignment was maintained within normal range, averaging 30.6 degrees after surgery. Clinical and fusion success rates trended higher than previous results with the rectangular cage but were not statistically different. Fusion success was significantly better than prior literature for treatment of spondylolisthesis (p=.0160). Complications of the surgery trended lower but were not statistically different from the study of the rectangular cage.
CONCLUSIONS
The wedged CFRP cage with pedicle screw fixation allows surgeons to maintain normal sagittal plane alignment. These devices are safe and effective for treatment of spondylolisthesis and are FDA approved in the United States.
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