In vivo monitoring of the degradation process of bioresorbable polymeric implants using magnetic resonance imaging

The degradation of a bioresorbable poly(image-lactide) osteosynthesis plug after fixation of a transferred coracoid bone block using the Bristow-Latarjet procedure was examined by means of magnetic resonance (MR) imaging. There were 15 patients with a mean follow-up time of 38 months (range 34–42 months). The gross geometry of the biomaterial plug remained unaltered on the MR images. The bone marrow signal reached the implant surfaces in all cases, and no signs of liquid phase around the implant could be discerned. The implants themselves were visible as homogeneous low signal intensity (SI) black linear structures when compared to the surrounding bone, which had a much higher SI. The mean implant SI was 18.2 (s.d. ± 6.6), that of the scapular bone 48.9 (s.d. ± 14.3) and that of the background 4.3 (s.d. + 1.5). The SI of a newly manufactured intact implant was 5.7. Serial plain radiographs showed no decreased bone density or focal osteolytic lesions around the poly(image-lactide) expansion plug. The implant channel was discernible on most of the radiographs and a sclerotic rim was detected to outline the implant profile in some of the projections of plain radiographs at each follow-up examination. Computer tomography scans on five patients 3 years postoperatively also revealed a discernible implant channel outlined with a sclerotic rim. The radiographic appearance of the radiolucent implant channel did not change over the follow-up period. Summarizing the present findings, MR imaging seems to be able to visualize poly(image-lactide) implants within the bone. Actually, at present it is the only method available to study the degradation process of implants made of this polymer in humans. No signs of degradation of or of an osteolytic foreign-body reaction to poly(image-lactide) at the host tissue-implant interface could be observed within the follow-up times of this study.