title: Degradation of poly-D-L-lactide (PDLLA) interference screws (Megafix ®).
abstract: BACKGROUND
  Interference screw fixation is a standard procedure in anterior cruciate ligament (ACL) replacement. Aim of this study was to evaluate the degradation process of Poly-D-L-lactide (PDLLA) interference screws used for tibial ACL graft fixation.
  
  
  METHODS
  We evaluated magnetic resonance imaging (MRI) scans of 18 patients who underwent ACL revision surgery at different time points after anatomic ACL reconstruction. At primary surgery, a tibial hybrid fixation was performed with a degradable interference (IF) screw made of PDLLA (Megafix(®)) and a button.
  
  
  RESULTS
  MRI revealed three different phases of degradation of the PDLLA screw. 6-8 months after surgery the IF screw was clearly visible as a well-defined structure on MRI and CT scan. After 12-16 months, the screws appeared less defined with central ingrowths' of connective tissue. In some cases only fragmented screw material was visible. At these time points, there was a slight edema surrounding the tunnel visible on MRI. After 22 months and later, the mean screw site densities were comparable with the surrounding bone density. There was no edema or signs of inflammation around the bone tunnels visible. Presence of cystic or osteolytic changes was not detected.
  
  
  CONCLUSIONS
  After 22 months, a PDLLA screw may not interfere with ACL revision surgery. Regarding the degradation process of PDLLA screws, we noted three different phases. Furthermore, the degradation process observed by MRI resembles to that described by animal studies. The PDLLA screws fully absorb and are partially replaced by bone. The degradation process in humans seems to be longer than that described in animals.
authors.affiliation: Klinik für Orthopädie und Unfallchirurgie, Martin Luther Krankenhaus, Caspar Theyß Strasse 27-31, Grunewald, 14193, Berlin, Germany, andreaellen@gmx.de.
authors.forename: Andrea
authors.initials: A
authors.lastname: Achtnich
authors.forename: Philipp
authors.initials: P
authors.lastname: Forkel
authors.forename: Sebastain
authors.initials: S
authors.lastname: Metzlaff
authors.forename: Thore
authors.initials: T
authors.lastname: Zantop
authors.forename: Wolf
authors.initials: W
authors.lastname: Petersen
mesh_terms: D020341:Absorbable Implants; D000293:Adolescent; D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D001863:Bone Screws; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008422:Materials Testing; D011091:Polyesters; D012086:Reoperation; D012421:Rupture; D013977:Tibia / Q000601:surgery; D055815:Young Adult
chemical_list: D011091:Polyesters; C033616:poly(lactide)