title: The Natural History of Biointerference Screw Cyst and New Bone Formation in Anterior Cruciate Ligament Reconstruction: 16-Year Follow-up.
abstract: BACKGROUND
  A variety of fixation devices are available for anterior cruciate ligament reconstruction (ACLR). Bioabsorbable screws allow imaging postoperatively without image artefact, as with magnetic resonance imaging (MRI). There is also the perceived benefit of screw resorption and subsequent host tunnel bone ingrowth.
  
  
  OBJECTIVE
  The purpose of this study was to document the natural history of poly L-lactic acid (PLLA) bioabsorbable interference screws. Manufacturers claimed that screws would be resorbed and replaced by new bone within 2 years. The hypothesis was that these screws take considerably longer to achieve this claim.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  Ten consecutive patients undergoing routine ACLR with a PLLA bioabsorbable RCI screw (Arthrex) and a standard 4-strand hamstring graft technique were assessed via MRI and telephone questionnaire at 1, 2, 4, 7, 10, and 16 years postoperatively.
  
  
  RESULTS
  At 4-year follow-up, no resorption of the screw or bone formation had occurred. At 7-year follow-up, absorption of 7 screws was complete, cyst formation had occurred in 3 patients, and 5 patients had new bone formation. At 10-year follow-up, all screws were reabsorbed, cyst formation was evident in only 2 cases, and 7 patients had evidence of new bone formation. At 16-year follow-up, cyst formation was only present in 1 patient, and all patients had evidence of new bone formation. All patients had an intact anterior cruciate ligament and had returned to preinjury sporting activity.
  
  
  CONCLUSIONS
  PLLA bioabsorbable screws take longer to resorb than previously thought by the manufacturers (ie, 2 years). New bone formation is evident in 100% of patients by 16 years. Cyst formation does not occur in all patients with a bioabsorbable screw implant. In the 3 patients demonstrating the presence of a cyst, no associated adverse effects were found with regard to anterior cruciate ligament graft survival or instability.
authors.affiliation: North Sydney Orthopaedic and Sports Medicine Centre, Sydney, Australia s.m.thompson@ic.ac.uk.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Thompson
authors.affiliation: Mater Imaging, Sydney, Australia.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Fung
authors.affiliation: North Sydney Orthopaedic and Sports Medicine Centre, Sydney, Australia.
authors.forename: David G
authors.initials: DG
authors.lastname: Wood
mesh_terms: D020341:Absorbable Implants / Q000009:adverse effects*; D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000295:instrumentation*; D001863:Bone Screws; D003560:Cysts / Q000209:etiology* / Q000473:pathology; D005500:Follow-Up Studies; D006801:Humans; D019344:Lactic Acid; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D010012:Osteogenesis / Q000502:physiology*; D011091:Polyesters; D011108:Polymers; D055815:Young Adult
chemical_list: D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide)
keywords: MRI; bioabsorbable screw; ganglion cyst; hamstring; poly L-lactic acid; reconstruction