title: MR imaging of biodegradable polylevolactide osteosynthesis devices in the ankle.
abstract: OBJECTIVE
  To assess the feasibility of magnetic resonance (MR) imaging in the postoperative follow-up after internal fracture fixation using biodegradable polylevolactide (PLLA) plugs and to investigate the MR characteristics of these devices.
  
  
  METHODS
  MR findings in ten patients with displaced malleolar fractures treated by internal fixation using absorbable PLLA plugs were evaluated after three different postoperative periods. The average postoperative follow-up time was thirty months for four patients, forty-two months for another four patients, and fifty-one months for the remaining two patients.
  
  
  RESULTS
  On T1-weighted coronal images, the geometry of the PLLA plug was clearly visible in all cases, without signs of fatigue failure or absorption. The host-to-tissue area between the deployed two fins of the plug showed higher signal intensity than the surrounding cancellous bone on fat-saturated proton density (PD) and turbo inversion recovery (tIR) images. This area had signal intensity similar to articular cartilage on T1-weighted coronal images. In none of the cases could any fluid accumulation be seen around the plug. In all ten cases, a thin rim with signal intensity similar to the area between the deployed fins was detected around the PLLA plug on fat-saturated axial PD images. On fat-saturated T2 and tIR sequences, this rim was less clearly detectable in all cases. No differences in the signal intensity or geometry of the PLLA plug on the MR images emerged between the three patient groups with mean follow-ups of thirty, forty-two, and fifty-one months. No artifacts produced by the implants were seen on any of the MR images. A biopsy specimen obtained at a reoperation necessary seventeen months postoperatively showed no signs of degradation of the PLLA plug.
  
  
  CONCLUSIONS
  MR imaging can visualize PLLA implants within bone. It also shows, without artifacts, the tissue interaction between the artificial biodegradable material and bone tissue in humans.
authors.affiliation: Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, Finland.
authors.forename: H K
authors.initials: HK
authors.lastname: Pihlajamäki
authors.forename: P T
authors.initials: PT
authors.lastname: Karjalainen
authors.forename: H J
authors.initials: HJ
authors.lastname: Aronen
authors.forename: O M
authors.initials: OM
authors.lastname: Böstman
mesh_terms: D000042:Absorption; D000293:Adolescent; D000328:Adult; D000368:Aged; D016512:Ankle Injuries / Q000473:pathology / Q000601:surgery*; D016477:Artifacts; D001672:Biocompatible Materials; D001673:Biodegradation, Environmental; D001858:Bone Nails; D002358:Cartilage, Articular / Q000473:pathology; D004867:Equipment Design; D004868:Equipment Failure; D005069:Evaluation Studies as Topic; D005240:Feasibility Studies; D005260:Female; D005500:Follow-Up Studies; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017102:Fracture Healing; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011091:Polyesters; D013499:Surface Properties; D013978:Tibial Fractures / Q000473:pathology / Q000601:surgery*
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C033616:poly(lactide)