title: Is unicompartmental arthroplasty an acceptable option for spontaneous osteonecrosis of the knee?
abstract: BACKGROUND
  The literature suggests survivorship of unicompartmental knee arthroplasties (UKAs) for spontaneous osteonecrosis of the knee ranges from 93% to 97% at 10 to 12 years. However, these data arise from small series (23 to 33 patients), jeopardizing meaningful conclusions.
  
  
  OBJECTIVE
  We determined (1) the longer-term survivorship of UKAs in a larger group of patients with spontaneous osteonecrosis of the knee; (2) their subjective, symptomatic, and functional outcomes; and (3) the percentage of failures and reasons for failures to identify relevant indications, contraindications, and technical parameters for treatment with a modern implant design.
  
  
  METHODS
  We retrospectively evaluated all 84 patients with late-stage spontaneous osteonecrosis of the knee who had a medial UKA from 1998 to 2005. All patients had preoperative MRI to confirm the diagnosis, exclude metaphyseal involvement, and confirm the absence of major degenerative changes in the lateral and patellofemoral compartments. The mean age of the patients at surgery was 66 years and mean BMI was 28.9. We conducted Kaplan-Meier survival analysis using revision for any reason as the end point. Minimum followup was 63 months (mean, 98 months; range, 63-145 months).
  
  
  RESULTS
  Ten-year survivorship was 89%. Ten revisions were performed; the most common reasons were subsidence of the tibial component (four) and aseptic loosening of the tibial component (three). No patient underwent revision for progression of osteoarthritis in the lateral or patellofemoral compartments.
  
  
  CONCLUSIONS
  Our data suggest spontaneous osteonecrosis of the knee may be an indication for UKA, provided secondary osteonecrosis of the knee is ruled out, preoperative MRI documents the absence of disease in other compartments, and there is no overcorrection in any plane.
  
  
  METHODS
  Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: 3rd Orthopaedics and Traumatologic Clinic, Rizzoli Orthopaedic Institute, Via Pupilli 1, 40136 Bologna, Italy. d.bruni@biomec.ior.it
authors.forename: Danilo
authors.initials: D
authors.lastname: Bruni
authors.forename: Francesco
authors.initials: F
authors.lastname: Iacono
authors.forename: Giovanni
authors.initials: G
authors.lastname: Raspugli
authors.forename: Stefano
authors.initials: S
authors.lastname: Zaffagnini
authors.forename: Maurilio
authors.initials: M
authors.lastname: Marcacci
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010020:Osteonecrosis / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D011475:Prosthesis Failure; D011859:Radiography; D012086:Reoperation; D012189:Retrospective Studies; D015996:Survival Rate