title: Results of revision surgery and causes of unstable total knee arthroplasty.
abstract: BACKGROUND
  The aim of this study was to evaluate causes of unstable total knee arthroplasty and results of revision surgery.
  
  
  METHODS
  We retrospectively reviewed 24 knees that underwent a revision arthroplasty for unstable total knee arthroplasty. The average follow-up period was 33.8 months. We classified the instability and analyzed the treatment results according to its cause. Stress radiographs, postoperative component position, and joint level were measured. Clinical outcomes were assessed using the Hospital for Special Surgery (HSS) score and range of motion.
  
  
  RESULTS
  Causes of instability included coronal instability with posteromedial polyethylene wear and lateral laxity in 13 knees, coronal instability with posteromedial polyethylene wear in 6 knees and coronal and sagittal instability in 3 knees including post breakage in 1 knee, global instability in 1 knee and flexion instability in 1 knee. Mean preoperative/postoperative varus and valgus angles were 5.8°/3.2° (p = 0.713) and 22.5°/5.6° (p = 0.032). Mean postoperative α, β, γ, δ angle were 5.34°, 89.65°, 2.74°, 6.77°. Mean changes of joint levels were from 14.1 mm to 13.6 mm from fibular head (p = 0.82). The mean HSS score improved from 53.4 to 89.2 (p = 0.04). The average range of motion was changed from 123° to 122° (p = 0.82).
  
  
  CONCLUSIONS
  Revision total knee arthroplasty with or without a more constrained prosthesis will be a definite solution for an unstable total knee arthroplasty. The solution according to cause is very important and seems to be helpful to avoid unnecessary over-constrained implant selection in revision surgery for total knee instability.
authors.affiliation: Department of Orthropaedic Surgery, Sun General Hospital, Daejeon, Korea.
authors.forename: In-Soo
authors.initials: IS
authors.lastname: Song
authors.affiliation: Department of Orthropaedic Surgery, Sun General Hospital, Daejeon, Korea.
authors.forename: Doo-Hoon
authors.initials: DH
authors.lastname: Sun
authors.affiliation: Department of Orthropaedic Surgery, Sun General Hospital, Daejeon, Korea.
authors.forename: Jae-Gyun
authors.initials: JG
authors.lastname: Chon
authors.affiliation: Department of Orthropaedic Surgery, Sun General Hospital, Daejeon, Korea.
authors.forename: Sung-Won
authors.initials: SW
authors.lastname: Jang
authors.affiliation: Department of Orthropaedic Surgery, Sun General Hospital, Daejeon, Korea.
authors.forename: Dong-Hyuk
authors.initials: DH
authors.lastname: Sun
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure; D012086:Reoperation; D012189:Retrospective Studies
keywords: Revision arthroplasty; Total knee instability; Unstable total knee