Radiographic assessment of structural defects in Björk-Shiley convexo-concave prostheses

Following the implantation of Björk Shiley 60 degrees convexo-concave (BS-CC) prostheses, outlet strut fracture rates up to 2.5% per year have been reported. According to experimental results and clinical observations, single leg separations are regarded as the primary mechanisms leading to complete outlet strut fracture after a certain interval. In an experimental study the question was addressed, whether single leg separation can be identified by especially developed radiographic means, before outlet strut fracture occurs. Five BS-CC mitral prostheses (29-31 mm) with intentionally made single leg separations of defined gas sizes (0-75 microns) and one intact mitral prostheses were implanted in sheep in a double-blind study design. Repeat non-invasive investigations were then performed applying a recently developed fluoroscopy imaging technique with direct radiographic magnification (DIMA COR C22). Single leg separations with gap sizes of more than 25 microns were properly detected using DIMA COR C22. Separations 25 microns or less could not be detected with certainty but were evaluated as probable or possible as a result of multiple investigations. The intact prosthesis was correctly identified, but was investigated on only one occasion. Non-invasive control of Björk-Shiley CC mitral prostheses applying especially developed direct radiographic magnification may allow for a reliable assessment of single leg separation with gap sizes of more than 25 microns in sheep. Using this technique of non-invasive serial investigations on particular patients with high probability of outlet strut fracture appears feasible, anticipating single leg separation detectability in humans. This has to be assessed in a second step.(ABSTRACT TRUNCATED AT 250 WORDS)