Do radiolucent lines in uncemented glenoid implants appear and disappear with x-ray beam tilting? A cadaveric radiographic study.

BACKGROUND: This cadaveric study investigated whether radiolucent lines (RLLs) in x-rays of uncemented polyethylene (PE) glenoid implants with a thin titanium layer at the back can appear or disappear due to tilting of the x-ray projection. METHODS: Eight RM Pressfit Vitamys glenoids (Mathys) were implanted in cadaveric scapulae. A computed tomography (CT) scan confirmed where the PE implant was flush with bone and where a gap was present. In addition to the 0° projection as a starting point, the glenoid was tilted in 10° and 20° retro- and anteversion and superior and inferior tilt directions. The glenoid was subdivided into five zones. Each zone was quantified with no RLLs or RLLs. RESULTS: In all zones, tilting from 0° to 10° inferior tilt (P=0.028), 10° retroversion (P<0.001), and 20° anteversion (P<0.001) caused RLLs to appear or disappear. Tilting from 0° to 20° inferior tilt (P=0.087), 10° (P=0.218) and 20° superior tilt (P=0.484), and 10° anteversion (P=0.126) did not cause any RLLs to appear or disappear. The RLLs always disappeared at 20° retroversion. CONCLUSIONS: True anteroposterior images should be obtained during x-ray assessment following uncemented glenoid component implantation. A CT scan is advised to confirm or exclude the presence of RLLs. Level of evidence: Laboratory cadaveric study.