title: Are younger patients undergoing TKAs appropriately characterized as active?
abstract: BACKGROUND
  The use of TKAs in young patients is increasing. Demographic characteristics and activity levels among this patient group may affect implant selection, performance, and survivorship. Patient age (≤ 55 years) and preoperative diagnosis have been used to define this patient group, with the presumption that these patients are more active than older patients with similar indications for TKA.
  
  
  OBJECTIVE
  We questioned whether (1) demographic features of young patients support high activity expectations after TKA, and (2) preoperative or postoperative functional activity measures support projections that young patients are active after TKA.
  
  
  METHODS
  We retrospectively compared demographic characteristics (gender, BMI, diagnosis) and functional activity profile (as determined by preoperative and postoperative UCLA activity score and functional subscores of The Knee Society and WOMAC instruments) for 150 patients 55 years old or younger (181 TKAs) and 262 patients who were between 65 to 75 years old (314 TKAs) at the time of surgery.
  
  
  RESULTS
  Younger patients having TKAs were significantly more likely than older patients to be female (74% versus 60%, p < 0.001) and to have diagnoses other than osteoarthritis (18% versus 3%, p < 0.001). BMI was significantly greater among younger female patients than among other age and gender combinations (35 kg/m(2) versus 31 kg/m(2), p < 0.001). Male patients had higher mean postoperative UCLA activity scores (5.5 versus 4.4, p < 0.001), Knee Society function subscores (80.2 versus 66.4, p < 0.001), and WOMAC function subscores (82.8 versus 74.2, p < 0.01) compared with female patients, but these were not different in older versus younger patients.
  
  
  CONCLUSIONS
  Sustained high activity levels are not likely to be a principal cause of revision TKAs among younger patients when considering age and diagnosis alone. Determining the effect of activity on survivorship of prosthetic designs and techniques should be based on measured functional activity instead of using age and diagnosis as surrogates for activity.
  
  
  METHODS
  Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid, CB 8233, St Louis, MO, 63110, USA, keeneyj@wudosis.wustl.edu.
authors.forename: James A
authors.initials: JA
authors.lastname: Keeney
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Nunley
authors.forename: Rick W
authors.initials: RW
authors.lastname: Wright
authors.forename: Robert L
authors.initials: RL
authors.lastname: Barrack
authors.forename: John C
authors.initials: JC
authors.lastname: Clohisy
mesh_terms: D000367:Age Factors; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects; D001696:Biomechanical Phenomena; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010809:Physical Fitness; D011183:Postoperative Complications / Q000503:physiopathology / Q000601:surgery; D011475:Prosthesis Failure; D020127:Recovery of Function; D012086:Reoperation; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors; D013997:Time Factors; D016896:Treatment Outcome