title: Long-term degradation of a poly-lactide co-glycolide/β-tricalcium phosphate biocomposite interference screw.
abstract: OBJECTIVE
  To evaluate the long-term in vivo degradation of biodegradable interference screws made of poly-L-lactide co-glycolide (poly-L-lactic acid [PLLA]/polyglycolic acid [PGA]) and β-tricalcium phosphate (β-TCP).
  
  
  METHODS
  To study in vivo the biological behavior of a PLLA/PGA/β-TCP biocomposite screw (Milagro; DePuy Mitek, Raynham, MA), an institutional review board-approved program using anterior cruciate ligament (ACL) interference fixation screws was initiated in 2005. Thirteen patients who had bone-patellar tendon-bone ACL reconstruction fixed at both the femur and tibia with PLLA/PGA/β-TCP screws at least 24 months earlier were evaluated by physical, radiographic, and computed tomography (CT) evaluations. Lysholm, Tegner, Cincinnati, and International Knee Documentation Committee scores were also obtained. Radiographs and CT scans of the operated knee were obtained. CT scan data measured in Hounsfield units (HU) evaluated the material density at the screw and bone plug sites. Soft-tissue and cancellous and cortical bone site readings were also taken. Osteoconductivity scores were determined at the screw sites by use of an ossification quality score (range, 1 to 4).
  
  
  RESULTS
  Eleven men and two women were evaluated at a mean of 38 months after surgery (range, 24 to 49 months). CT scans and radiographs showed the bone plug fused to the tunnel wall with no PLLA/PGA/β-TCP screw remaining. The screws were replaced with material that was calcified and non-trabecular. Osteoconductivity was present in 21 of 26 tunnels (81%) and complete (type 4 ossification) in 5 of 26 (19%). Mean screw site densities (femoral, 159 HU; tibial, 157 HU) were not different from the mean cancellous bone density (femoral, 146 HU; tibial, 140 HU). No positive pivot-shift tests were found. Lysholm, Tegner, and Cincinnati scores improved from 44, 3.7, and 37 preoperatively to 93, 6, and 87 at follow-up, respectively. The mean KT arthrometer (MEDmetric, San Diego, CA) difference was 0.8 mm.
  
  
  CONCLUSIONS
  The PLLA/PGA/β-TCP interference screw completely degraded, and no remnant was present 3 years after implantation for a bone-patellar tendon-bone graft ACL reconstruction. Osteoconductivity was confirmed in 21 of 26 screw sites (81%) and completely filled the site in 5 of 26 (19%). The PLLA/PGA/β-TCP biocomposite interference screw is osteoconductive.
  
  
  METHODS
  Level IV, therapeutic case series.
authors.affiliation: Plano Orthopedic Sports Medicine and Spine Center, Plano, Texas 75093, USA.
authors.forename: F Alan
authors.initials: FA
authors.lastname: Barber
authors.forename: W D
authors.initials: WD
authors.lastname: Dockery
authors.forename: Scott A
authors.initials: SA
authors.lastname: Hrnack
mesh_terms: D020341:Absorbable Implants; D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D001182:Arthroscopy; D001861:Bone Regeneration; D001863:Bone Screws; D050376:Bone-Patellar Tendon-Bone Grafting / Q000295:instrumentation*; D002130:Calcium Phosphates; D004357:Drug Synergism; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging; D005500:Follow-Up Studies; D006801:Humans; D019344:Lactic Acid; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011446:Prospective Studies; D013977:Tibia / Q000000981:diagnostic imaging; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D002130:Calcium Phosphates; C485817:beta-tricalcium phosphate; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid