title: Do jumbo cups cause hip center elevation in revision THA? A computer simulation.
abstract: BACKGROUND
  Acetabular revision THA with use of a large (jumbo) cup is an effective treatment for many cavitary and segmental peripheral bone defects. However, the jumbo cup may result in elevation of the hip center and protrusion through the anterior acetabular wall as a result of the oversized geometry of the jumbo cup compared with the physiologic acetabulum.
  
  
  OBJECTIVE
  The purpose of this computer simulation was to determine how much elevation of the hip center and anterior wall protrusion occurs in revision THA with use of a jumbo cup technique in which the inferior edge of the jumbo cup is placed at the inferior acetabular rim and the superior edge of the jumbo cup is placed against host bone at the superior margin of a posterosuperior bone defect.
  
  
  METHODS
  Two hundred sixty-five pelvic CT scans were analyzed by custom CT analytical software. The computer simulated oversized reaming. The vertical and anterior reamer center shifts were measured, and anterior column bone removal was determined.
  
  
  RESULTS
  The computer simulation demonstrated that the hip center shifted 0.27 mm superiorly and 0.02 mm anteriorly, and anterior column bone removal increased 0.86 mm for every 1-mm increase in reamer diameter.
  
  
  CONCLUSIONS
  Our results indicate that the jumbo cup technique results in hip center elevation despite placement of the cup adjacent to the inferior acetabulum. For a hypothetical increase from a 54-mm socket to a 72-mm socket, as one might see in the context of the revision of a failed THA, our model would predict an elevation of the hip center of approximately 5 mm and loss of approximately 15 mm of anterior column bone. This suggests that an increase in femoral head length may be needed to compensate for the hip center elevation caused by the use of a large jumbo cup in revision THA. A jumbo cup may also result in protrusion through the anterior wall.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: Chima
authors.initials: C
authors.lastname: Nwankwo
authors.forename: Nick N
authors.initials: NN
authors.lastname: Dong
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Heffernan
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ries
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D005270:Femur Head / Q000601:surgery; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011857:Radiographic Image Interpretation, Computer-Assisted; D012086:Reoperation; D012984:Software; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome