Radiographic characteristics on conventional radiographs after posterior lumbar interbody fusion: Comparative study between radiotranslucent and radiopaque cages

The problem of determining solidity of a fused spinal segment still remains . Our purpose is to evaluate radiographic findings after posterior lumbar i nterbody fusion (PLIF) with cages and estimate their relative value in judg ing fusion status. Radiographic follow-up was per-formed in patients after PLIF with cages of either radiotranslucent or radiopaque material. Conventi onal radiographs were obtained 6 weeks. 3 and 6 months, and then yearly aft er surgery for spinal instability for 64 patients. We differentiated betwee n uncertain (increased density within the cage. increase of sclerotic endpl ates. and posterolateral fusion) and definite (trabecular continuous bone b ridging within the implant and periimplant new bone formation with bridging of the intervertebral space) fusion signs. A fusion rate of 51.5% after 12 months, 61.4% after 24 months, 66.7% after 36 months, and 77.8% after 48 m onths postoperatively was found. We found only a slight, nonsignificant cor relation between radiographic fusion and patient-assessed clinical outcome, There is evidence that radiographic fusion criteria occur in a specific ch ronologic order. The interpretation of fusion status is notably impaired by the use of radiopaque cages. Criteria to standardize the interpretation an d evaluation of radiographic findings after PLIF are discussed.