title: A biomechanical analysis of the rheumatoid index finger after joint arthroplasty.
abstract: OBJECTIVE
  To determine the mechanisms responsible for the recurrence of ulnar drift after metacarpophalangeal joint arthroplasty in the rheumatoid hand.
  
  
  METHODS
  A three-dimensional biomechanical model of the index finger joints was used to predict the implant loads during several activities of daily living.
  
  
  BACKGROUND
  Post-operative clinical evaluation of Sutter metacarpophalangeal prostheses shows a high incidence of fracture and recurrent deformity.
  
  
  METHODS
  A six-component force transducer in conjunction with a six-camera motion analysis system were used to obtain kinematic and external loading data from eight patients with rheumatoid arthritis during several simulated activities. These data were used as input into a three-dimensional biomechanical model of the implant and interphalangeal joints of the index finger. Tendon lines of action and moment arms were obtained using a series of MRI scans and CAD modelling techniques.
  
  
  RESULTS
  Implant forces were oriented in a radial and dorsal direction to resist the ulnarpalmarly pull of tendons associated with the metacarpophalangeal joint.
  
  
  CONCLUSIONS
  The recurrence of ulnar drift is attributable to fatigue failure of the prostheses. After fracture the implant is unable to support the repetitive loading patterns experienced during activities of daily living.
  
  
  CONCLUSIONS
  Understanding the mechanisms responsible for the recurrence of ulnar drift and implant failure is a step towards improving the prosthesis design, surgical procedures and ultimately the patient's prognosis.
authors.affiliation: Bioengineering Unit, Wolfson Centre, University of Strathclyde, 106 Rottenrow, Glasgow, Scotland G4 ONW, UK. nicola.fowler@strath.ac.uk
authors.forename: N K
authors.initials: NK
authors.lastname: Fowler
authors.forename: A C
authors.initials: AC
authors.lastname: Nicol
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001172:Arthritis, Rheumatoid / Q000503:physiopathology / Q000601:surgery*; D001696:Biomechanical Phenomena; D005069:Evaluation Studies as Topic; D005260:Female; D005500:Follow-Up Studies; D006227:Hand Deformities, Acquired / Q000601:surgery; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008662:Metacarpophalangeal Joint / Q000503:physiopathology / Q000601:surgery*; D008875:Middle Aged; D011184:Postoperative Period; D011336:Probability; D016059:Range of Motion, Articular / Q000502:physiology*; D020127:Recovery of Function; D012720:Severity of Illness Index; D016896:Treatment Outcome