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Abstract
This study determined the accuracy of standard radiographs in observing radiolucency adjacent to the tibial component in total knee arthroplasty. A model of the proximal tibia was used. Plastic sleeves of different heights were glued under the tibial tray to imitate radiolucency. By tilting the x-ray tube 1° at a time, an investigation was performed to determine how many degrees it would take to cover the heights of the different plastic sleeves.
In a clinical study of patients at standard follow-up, 21 knees were examined using standard radiographs. Radiographs using image intensification were then taken of the same knees to obtain radiographs with views parallel to the plane of the tibial tray. The results of the study on the phantom showed that a 1 ° deviation of the x-ray beam from the optimal position would obscure a 0.5-mm "radiolucency." This was true for radiolucencies of 2, 3, 4, and 5 mm. This was confirmed in the clinical study where ≤4 mm of radiolucency was obscured on standard radiographs. Therefore, standard radiographs cannot be used to determine radiolucency. The 2-mm radiolucency normally associated with loosening is not clinically valid.
Clinical failure in arthroplasty surgery often is associated with radiolucency adjacent to the prosthetic components. However, the recognition of radiolucency depends on the quality of the radiographic examination.1 Unless strict anteroposterior (AP) and sagittal views are used, it may be impossible to detect radiolucent zones of up to 3-4 mm under a tibial tray.2,3 The present study was performed to define the degrees of tolerance for radiographic examination of the tibial component in total knee arthroplasty (TKA).
MATERIALS AND METHODS
Experimental Study
Saw bones of the lower leg were used. The proximal tibial plafond was cut off tangentially to the long axis of the tibia using the AGC 2000 (Biomet, United Kingdom). A plastic sleeve - imitating the radiolucent zone - of either 2-, 3-, 4-, or 5-mm thickness was placed and glued on the cut surface, and a 5-mm thick metal tray was glued on top (Figure I).
Radiographic examination was performed using...