title: Long-term absorption of beta-tricalcium phosphate poly-L-lactic acid interference screws.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the long-term in vivo degradation of biodegradable interference screws made of poly-L-lactic acid (PLLA) and beta-tricalcium phosphate (beta-TCP).
  
  
  METHODS
  Twenty patients undergoing patellar tendon autograft anterior cruciate ligament reconstruction fixed at both the femur and tibia with beta-TCP-PLLA screws at least 44 months earlier were evaluated by physical, radiographic, and computed tomography (CT) evaluations. This study was approved by the institutional review board. Lysholm, Tegner, Cincinnati, and International Knee Documentation Committee scores were also obtained. CT data were measured in Hounsfield units.
  
  
  RESULTS
  We evaluated 13 male and 7 female patients at a mean of 50 months after surgery (range, 44 to 56 months). CT scans and radiographs showed the bone plug fused to the tunnel wall with no beta-TCP-PLLA screw remaining. The screws were replaced with clearly calcified non-trabecular material, denser than soft tissue. Osteoconductivity was present in 75% of the tunnels and complete in 10%. No positive pivot-shift tests were found. Lysholm, Tegner, and Cincinnati scores improved from 60.4, 3.7, and 53.3, respectively, preoperatively to 90.8, 5.8, and 86.4, respectively, at follow-up. The mean side-to-side difference determined by use of the KT arthrometer (MEDmetric, San Diego, CA) was 0.4 mm.
  
  
  CONCLUSIONS
  The beta-TCP-PLLA interference screw (Bilok; ArthroCare, Sunnyvale, CA) completely degraded, and no remnant was present 4 years after insertion. Osteoconductivity was confirmed by CT scans at 75% of the screw sites and completely filled the site in 10%. The addition of beta-TCP to PLLA results in a biocomposite interference screw that is osteoconductive.
  
  
  METHODS
  Level IV, therapeutic case series.
authors: Plano Orthopedic and Sports Medicine Center, Plano, Texas 75093, USA.
authors: F Alan
authors: FA
authors: Barber
authors: William D
authors: WD
authors: Dockery
mesh_terms: D020341:Absorbable Implants; D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging / Q000601:surgery*; D001182:Arthroscopy / Q000379:methods; D001672:Biocompatible Materials / Q000493:pharmacokinetics; D001863:Bone Screws; D002130:Calcium Phosphates / Q000493:pharmacokinetics* / Q000494:pharmacology; D015331:Cohort Studies; D005069:Evaluation Studies as Topic; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging / Q000601:surgery; D019344:Lactic Acid / Q000493:pharmacokinetics* / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D017847:Patellar Ligament / Q000637:transplantation; D011091:Polyesters; D011108:Polymers / Q000493:pharmacokinetics* / Q000494:pharmacology; D019651:Plastic Surgery Procedures / Q000295:instrumentation* / Q000379:methods; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014182:Transplantation, Autologous; D016896:Treatment Outcome
chemical_list: D001672:Biocompatible Materials; D002130:Calcium Phosphates; D011091:Polyesters; D011108:Polymers; C485817:beta-tricalcium phosphate; D019344:Lactic Acid; C033616:poly(lactide)