title: A sliding stem in revision total knee arthroplasty provides stability and reduces stress shielding.
abstract: OBJECTIVE
  In the reconstruction of unicondylar femoral bone defects with morselized bone grafts in revision total knee arthroplasty, a stem extension appears to be critical to obtain adequate mechanical stability. Whether stability is still assured by this reconstruction technique in bicondylar defects has not been assessed. The disadvantage of relatively stiff stem extensions is that bone resorption is promoted due to stress shielding. We therefore designed a stem that would permit axial sliding movements of the articulating part relative to the intramedullary stem.
  
  
  METHODS
  This stem was used in the reconstruction with impaction bone grafting (IBG) of 5 synthetic distal femora with a bicondylar defect. A cyclically axial load was applied to the prosthetic condyles to assess the stability of the reconstruction. Radiostereometry was used to determine the migrations of the femoral component with a rigidly connected stem, a sliding stem, and no stem extension.
  
  
  RESULTS
  We found a stable reconstruction of the bicondylar femoral defects with IBG in the case of a rigidly connected stem. After disconnecting the stem, the femoral component showed substantially more migrations. With a sliding stem, rotational migrations were similar to those of a rigidly connected stem. However, the sliding stem allowed proximal migration of the condylar component, thereby compressing the IBG.
  
  
  CONCLUSIONS
  The presence of a functional stem extension is important for the stability of a bicondylar reconstruction. A sliding stem provides adequate stability, while stress shielding is reduced because compressive contact forces are still transmitted to the distal femoral bone.
authors.affiliation: Department of Orthopaedics, Radboud University Nijmegen Medical Centre, Nijmegen. hjmeijerink@hotmail.com
authors.forename: Huub J
authors.initials: HJ
authors.lastname: Meijerink
authors.forename: Corné J M
authors.initials: CJ
authors.lastname: van Loon
authors.forename: Maarten C
authors.initials: MC
authors.lastname: de Waal Malefijt
authors.forename: Albert
authors.initials: A
authors.lastname: van Kampen
authors.forename: Nico
authors.initials: N
authors.lastname: Verdonschot
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods; D016025:Bone Transplantation; D005269:Femur / Q000502:physiology / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D010780:Photogrammetry; D011475:Prosthesis Failure; D012086:Reoperation; D012399:Rotation
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