title: All-polyethylene and metal-backed tibial components are equivalent with BMI of less than 37.5.
abstract: BACKGROUND
  Modular, metal-backed tibial (MBT) components are associated with locking mechanism dysfunction, breakage, backside wear, and osteolysis, which compromise survivorship. All-polyethylene tibial (APT) components eliminate problems associated with MBTs, but, historically, APT utilization has generally been limited to older, less active patients. However, it is unclear whether APT utilization can be expanded to a nonselected patient population.
  
  
  OBJECTIVE
  We therefore determined the survivorship of APT components compared with MBT components in a non-age- or activity-selected population who underwent TKA.
  
  
  METHODS
  Using a longitudinal database, we identified 775 patients with primary TKAs utilizing a single implant design between 1999 and 2007. Of these, 558 (72%) patients had APT components (APT2), while 217 (28%) patients with tibial bone loss or defects, contralateral MBT components, or a BMI of greater than 37.5 received MBT components. We determined the survivorship in the two groups. The minimum followup was 2 years for both groups (mean ± SD: MBT, 80 ± 29 months; APT, 63 ± 27 months). The APT group was older (average age: APT2, 70 years; MBT, 64.7 years) and had a lower BMI than the MBT group (APT2, 30.8; MBT, 33.8).
  
  
  RESULTS
  Survivorship, as defined by revision for any reason, was 99% for the APT group and 97% for the MBT group. There were four (2%) tibial failures in the MBT group in patients with a BMI of greater than 40. There were no revisions for loosening or osteolysis in the APT group.
  
  
  CONCLUSIONS
  APT implants perform as well as MBT implants in a non-age- or activity-selected TKA population with a BMI of less than 37.5.
authors: Department of Orthopaedic Surgery, Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA 01805, USA.
authors: Jared
authors: J
authors: Toman
authors: Richard
authors: R
authors: Iorio
authors: William L
authors: WL
authors: Healy
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods*; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000601:surgery; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000601:surgery; D010147:Pain Measurement; D020959:Polyethylene / Q000737:chemistry*; D011182:Postoperative Care / Q000379:methods; D011300:Preoperative Care / Q000379:methods; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D020127:Recovery of Function; D012189:Retrospective Studies; D018570:Risk Assessment; D012737:Sex Factors; D013977:Tibia / Q000601:surgery; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D020959:Polyethylene