title: Revision of broken knee megaprostheses: new solution to old problems.
abstract: BACKGROUND
  Low-cost indigenous megaprostheses used in the developing world are prone to mechanical failure but the frequency and causes are not well established.
  
  
  OBJECTIVE
  We retrospectively analyzed the causes of failure, particularly design, and suggest changes to reduce the breakage. We also report our experience with revision surgery.
  
  
  METHODS
  We identified 28 breakages in 266 megaprosthetic knee arthroplasties performed between January 2000 and December 2006. Twenty-six breakages were revised to another prosthesis. The complications were studied and the function was evaluated. Prostheses were studied for failure by the computer-aided design program SolidWorks(®) and Hyperworks(®) for finite element analysis (FEA). Design improvements were performed based on these results.
  
  
  RESULTS
  In 21 cases, the failure occurred at the stem-collar junction, the point of maximum stress predicted by FEA. Stainless steel implants were prone to failure. There was one early and one late infection. Three patients died of metastatic disease. The most difficult surgical step involved the removal of the well-cemented broken stem from the intramedullary canal. Musculoskeletal Tumor Society scores varied from 27 to 29 after revision. FEA revealed stress could be reduced by filleting the stem-collar junction and by two-piece stems.
  
  
  CONCLUSIONS
  Revisions of broken total knee megaprostheses, though technically difficult, have allowed patients reasonable function. We recommend design analysis for custom prostheses to point to areas of weakness. Breakages can be reduced by using titanium stems and filleting the junction or by having two-piece inserted stems. Incorporating these changes has reduced the failures in our experience.
authors.affiliation: PD Hinduja National Hospital & Medical Research Centre, Veer Savarkar Marg, Mahim, Mumbai, 400016, India. mgagarwal@gmail.com
authors.forename: Manish
authors.initials: M
authors.lastname: Agarwal
authors.forename: Ashish
authors.initials: A
authors.lastname: Gulia
authors.forename: B
authors.initials: B
authors.lastname: Ravi
authors.forename: Rupesh
authors.initials: R
authors.lastname: Ghyar
authors.forename: Ajay
authors.initials: A
authors.lastname: Puri
mesh_terms: D000293:Adolescent; D000328:Adult; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation*; D001859:Bone Neoplasms / Q000401:mortality / Q000473:pathology / Q000601:surgery*; D017076:Computer-Aided Design; D003906:Developing Countries; D019544:Equipment Failure Analysis; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007194:India; D007720:Knee Prosthesis; D023821:Limb Salvage; D008297:Male; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D012189:Retrospective Studies; D013314:Stress, Mechanical; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult