title: The identification and quantification of instability in a primary total knee replacement prior to revision.
abstract: Instability is the reason for revision of a primary total knee replacement (TKR) in 20% of patients. To date, the diagnosis of instability has been based on the patient's symptoms and a subjective clinical assessment. We assessed whether a measured standardised forced leg extension could be used to quantify instability. A total of 25 patients (11 male/14 female, mean age 70 years; 49 to 85) who were to undergo a revision TKR for instability of a primary implant were assessed with a Nottingham rig pre-operatively and then at six and 26 weeks post-operatively. Output was quantified (in revolutions per minute (rpm)) by accelerating a stationary flywheel. A control group of 183 patients (71 male/112 female, mean age 69 years) who had undergone primary TKR were evaluated for comparison. Pre-operatively, all 25 patients with instability exhibited a distinctive pattern of reduction in 'mid-push' speed. The mean reduction was 55 rpm (sd 33.2). Post-operatively, no patient exhibited this pattern and the reduction in 'mid-push' speed was 0 rpm. The change between pre- and post-operative assessment was significant (p < 0.001). No patients in the control group exhibited this pattern at any of the intervals assessed. The between-groups difference was also significant (p < 0.001). This suggests that a quantitative diagnostic test to assess the unstable primary TKR could be developed.
authors.affiliation: University of Edinburgh, FU413, Chancellor's Building, 49 Little France Crescent, Edinburgh, EH16 4SB, UK.
authors.forename: D F
authors.initials: DF
authors.lastname: Hamilton
authors.affiliation: University of Edinburgh, Department of Trauma and Orthopaedics, Edinburgh, EH16 4SB, UK.
authors.forename: R
authors.initials: R
authors.lastname: Burnett
authors.affiliation: University of Edinburgh, Department of Trauma and Orthopaedics, Edinburgh, EH16 4SB, UK.
authors.forename: J T
authors.initials: JT
authors.lastname: Patton
authors.affiliation: University of Edinburgh, Department of Trauma and Orthopaedics, Edinburgh, EH16 4SB, UK.
authors.forename: C R
authors.initials: CR
authors.lastname: Howie
authors.affiliation: University of Edinburgh, Department of Trauma and Orthopaedics, Edinburgh, EH16 4SB, UK.
authors.forename: A H R W
authors.initials: AH
authors.lastname: Simpson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D011183:Postoperative Complications / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery; D057234:Preoperative Period; D011379:Prognosis; D011475:Prosthesis Failure; D016059:Range of Motion, Articular; D012086:Reoperation; D012189:Retrospective Studies; D012720:Severity of Illness Index
keywords: Instability; Revision surgery; Total knee replacement