Lumbar sagittal contour after posterior interbody fusion - Threaded devices alone versus vertical cages plus posterior instrumentation

Study Design. An observational radiographic study examining lumbar sagittal contour of patients undergoing posterior interbody arthrodesis. Objectives. To compare operative alterations of lumbar sagittal contour aft er posterior interbody fusion using threaded interbody devices alone versus vertical cages combined with posterior compression instrumentation. Summary of Background Data. Technique-related alterations of lumbar sagitta l contour during interbody arthrodesis have received little attention in th e spinal literature. Methods. Standing lumbar radiographs were measured for preoperative and pos toperative segmental lordosis at levels undergoing posterior interbody arth rodesis using either stand-alone side-by-side threaded devices or vertical cages combined with posterior transpedicular compression instrumentation. S agittal plane segmental correction (or loss of correction) was calculated a nd statistically compared. Results. The radiographs of 30 patients (34 spinal segments) undergoing lum bar or lumbosacral arthrodesis were compared. Seventeen patients (18 segmen ts) had undergone interbody fusion using threaded cages, whereas 13 patient s (16 segments) underwent fusion using vertically oriented mesh cages combi ned with posterior compression instrumentation. Preoperative segmental lord osis averaged 8 degrees for both groups. For patients undergoing fusion wit h threaded cages, there was a mean lordotic loss of 3 degrees /segment. For patients undergoing fusion with vertically oriented mesh cages combined wi th posterior compression instrumentation, there was a mean lordotic gain of 5 degrees /segment. This difference in segmental sagittal plane contour wa s highly significant (P = 0.00). Conclusion. Threaded fusion devices placed under interbody distraction with the endplates parallel fail to preserve or reestablish segmental lordosis. Vertical cages, however, when combined with posterior compression instrume ntation, not only maintain segmental lordosis, but also can correct sagitta l plane deformity.