Imaging pitfalls of interbody spinal implants.

STUDY DESIGN A variety of interbody implants were imaged by computed tomography and plain radiography within cadaveric spines to evaluate their basic imaging characteristics. OBJECTIVES Sources of interpretation error by both computed tomography and plain radiography of interbody implants were investigated. SUMMARY OF BACKGROUND DATA Lucencies have been reported around bone dowel implants in the postoperative period, which have been shown to resolve. The diagnosis of fusion through metallic implants has been difficult with both false-positive and false-negative results. The literature of imaging these implants is very sparse. METHODS Four interbody constructs were placed in cadaveric spines under different conditions and imaged using both computed tomography and plain film radiography. RESULTS Plain radiographs could not predict the presence of intraimplant bone whereas computed tomography was accurate. Metallic implants had a 1-3-mm computed tomography artifact limiting peri-implant interpretation. Lucencies could be seen on computed tomography but not on plain radiographs. However, the opposite was also seen. Lucencies around nonmetallic implants were more visible by a 4:1 ratio. CONCLUSIONS Potential errors in interpretation were identified including assessment for bridging bone, assessment for lucency, and obscuration of peri-implant detail from metallic artifact. Lucencies were more visible with nonmetallic implants than with metallic constructs. Plain radiograph analysis of metallic implants tended to underestimate lucencies, whereas analysis of nonmetallic implants tended to overestimate lucencies.