title: Painful patellar clunk or crepitation of contemporary knee prostheses.
abstract: BACKGROUND
  Painful patellar clunk or crepitation (PCC) is a resurgent complication of contemporary posterior-stabilized TKA. The incidence, time to presentation, causes, and treatment of PCC still remain controversial.
  
  
  OBJECTIVE
  We therefore (1) compared the incidence of PCC with five contemporary TKA designs, (2) evaluated the time to presentation, (3) identified possible etiologies, and (4) determined recurrence rate and change in knee functional scores after treatment for PCC.
  
  
  METHODS
  We reviewed 580 patients who had 826 posterior-stabilized TKAs involving five different designs. The incidences of PCC were compared among the prostheses. The knees were divided into two groups depending on the development of PCC, and possible etiologic factors of PCC, including prosthesis design and surgical or radiographic variables, were compared between groups. We investigated the onset time of PCC and evaluated treatment results by knee outcome scores. Minimum followup was 2.0 years (mean, 3.9 years; range, 2.0-9.8 years).
  
  
  RESULTS
  The PCC incidence was higher in the Press-Fit Condylar(®) Sigma(®) Rotating Platform/Rotating Platform-Flex Knee System (11 of 113 knees, 9.7%) than in the others (seven of 713 knees, 1.0%). Increased risk of PCC was associated with using a specific prosthesis and patellar retention. PCC occurred in all cases within a year after TKA (mean, 7.4 months). Arthroscopic treatment (16 knees) and patellar replacement (two knees) improved knee scores, with no recurrence observed over an average followup of 29 months.
  
  
  CONCLUSIONS
  Prosthesis design and patellar retention were associated with PCC. Surgery resolved the PCC.
authors.affiliation: Department of Orthopaedic Surgery, CHA Bundang Medical Center, CHA University School of Medicine, Seongnam, Korea.
authors.forename: Won Chul
authors.initials: WC
authors.lastname: Choi
authors.forename: Keun-Jung
authors.initials: KJ
authors.lastname: Ryu
authors.forename: Sahnghoon
authors.initials: S
authors.lastname: Lee
authors.forename: Sang Cheol
authors.initials: SC
authors.lastname: Seong
authors.forename: Myung Chul
authors.initials: MC
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation*; D001182:Arthroscopy; D001696:Biomechanical Phenomena; D016009:Chi-Square Distribution; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D015994:Incidence; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010147:Pain Measurement; D010149:Postoperative Pain / Q000175:diagnosis / Q000453:epidemiology* / Q000601:surgery; D010329:Patella / Q000601:surgery*; D011474:Prosthesis Design; D011859:Radiography; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012008:Recurrence; D012086:Reoperation; D056910:Republic of Korea; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome