Polydioxanone biodegradable pins in the knee: MR imaging

OBJECTIVE. Biodegradable solid implants have been developed as an alternati ve to metallic orthopedic fixation. In animal models, implants degrade with in and are replaced by bone. This study documents the resorption of these d evices in human patients with MR imaging. SUBJECTS AND METHODS. One hundred seventy-five 1.3-mm biodegradable pins ma de of polydioxanone were used to secure a total of 59 osteochondral allogra fts of the knee. Patients with the pins underwent scanning on a 1.5-T unit with 3.3- to 4-mm contiguous T1-weighted spin-echo (TR/TE, 600/15), fat-sat urated proton density-weighted (3000/40), T2-weighted fast spin-echo (3000/ 63), and three-dimensional spoiled gradient-recalled (47/7; flip angle, 60 degrees) sequences at 3, 6, 12, 24, or 36 months after surgery. Eighty-nine pins were imaged on multiple occasions. Two osteoradiologists interpreted the MR examinations. RESULTS. More than 80% of the pin channels were visible at 3 and at 6 month s after surgery. By 24 months, only 20% of the pin channels were visible, w ith the remainder having been replaced by bone. At 3 months, nearly 40% of the pins were associated with adjacent marrow edema. Edema generally dimini shed, involving less than 20% of pins at later time points. Focal cartilage defects were evident at 32% of the pin insertion sites during the first 6 months, but these defects were present in only 4% of the insertion sites th ereafter. CONCLUSION. Biodegradable polydioxanone pins usually resorb completely by 2 4 months. Marrow edema, presumably representing inflammation related to pin resorption, is infrequent and tends to resolve. Cartilage defects related to pin placement heal spontaneously.