title: Patient-specific guide for revision of medial unicondylar knee arthroplasty to total knee arthroplasty: beneficial first results of a new operating technique performed on 10 patients.
abstract: OBJECTIVE
  Unicompartmental to total knee arthroplasty revision surgery can be technically demanding. Joint line restoration, rotation, and augmentations can cause difficulties. We describe a new technique in which single-way fitting guides serve to position the knee system cutting blocks.
  
  
  METHODS
  Preoperatively, images of the distal femur and proximal tibia are taken using CT scanning. These images are used to create a patient-specific guide that fits in one single position on the contours of the bone and the prosthesis in situ. The guides are fixed with pins and then removed. The pins determine the position of the cutting blocks. 10 consecutive revisions were performed using this technique.
  
  
  RESULTS
  All guides fitted well. 7 of 10 femoral prostheses were within the desired AP and sagittal angle ± 3°. However, 1 proximal tibia did not have enough bone stock on the medial plateau for adequate fixation of the guide, so conversion to intramedular referencing was performed. This was to be expected after the preoperative planning. All tibial components were within the desired AP angle ± 3° and 7 of 10 were within the desired sagittal angle. Hip-knee-ankle angle was within 0 ± 3° in 8 of 10 cases.
  
  
  CONCLUSIONS
  This new technique makes preoperative planning and execution of this plan during surgery less demanding. Problems such as the need for augmentations can be predicted at the preoperative planning. The instrumentation must be redesigned in order to make this technique work in cases where there is minimal bone stock present.
authors.affiliation: Department of Orthopaedic Surgery, Maastricht University Medical Centre, Maastricht, the Netherlands. bartkerens@hotmail.com
authors.forename: Bart
authors.initials: B
authors.lastname: Kerens
authors.forename: Bert
authors.initials: B
authors.lastname: Boonen
authors.forename: Martijn
authors.initials: M
authors.lastname: Schotanus
authors.forename: Nanne
authors.initials: N
authors.lastname: Kort
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods; D017760:Bone Malalignment / Q000517:prevention & control*; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007430:Intraoperative Care / Q000295:instrumentation*; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome