Polydioxanone biodegradable pins in the knee: MR imaging.
OBJECTIVE
Biodegradable solid implants have been developed as an alternative to metallic orthopedic fixation. In animal models, implants degrade within and are replaced by bone. This study documents the resorption of these devices in human patients with MR imaging.


METHODS
One hundred seventy-five 1.3-mm biodegradable pins made of polydioxanone were used to secure a total of 59 osteochondral allografts 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-saturated 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 months after surgery. By 24 months, only 20% of the pin channels were visible, with the remainder having been replaced by bone. At 3 months, nearly 40% of the pins were associated with adjacent marrow edema. Edema generally diminished, 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 thereafter.


CONCLUSIONS
Biodegradable polydioxanone pins usually resorb completely by 24 months. Marrow edema, presumably representing inflammation related to pin resorption, is infrequent and tends to resolve. Cartilage defects related to pin placement heal spontaneously.
Sirlin
C B
CB
Department of Radiology, UCSD Medical Center, 200 W. Arbor Dr., San Diego, CA 92103, USA.
Boutin
R D
RD
Brossmann
J
J
Pathria
M N
MN
Convery
F R
FR
Bugbee
W
W
Resnick
D
D
D020341:Absorbable Implants; D000293:Adolescent; D000328:Adult; D001858:Bone Nails / Q000009:adverse effects; D016025:Bone Transplantation; D002358:Cartilage, Articular / Q000637:transplantation; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016687:Polydioxanone
D016687:Polydioxanone