title: Joint line reconstruction in medial unicompartmental knee arthroplasty: development and validation of a measurement method.
abstract: OBJECTIVE
  Preservation of the joint line in total knee arthroplasty (TKA) has shown to be an important factor for the long-term outcome, especially in revision TKA. For unicompartmental knee arthroplasty (UKA), the role of the joint line has neither been investigated nor is it consciously respected during implantation. Thus, the aim was to establish and validate a standardised measurement method to determine the joint line in UKA.
  
  
  METHODS
  As there is no established method to evaluate changes in the joint line radiologically, we introduced two methods and correlated them. The methods were first validated in a cadaver model by a controlled rotational study. Then, the joint line of 29 patients with an UKA (Oxford, Biomet, Bridgend, UK) was determined on pre- and post-operative radiographs. Both methods were tested by intra- and inter-rater reliability.
  
  
  RESULTS
  Both methods showed a good intra- and inter-rater reliability. Furthermore, there was only little bias in agreement between both methods and raters. Measurements of the 29 UKA patients revealed that the joint line was more distally by a mean of 4.4 ± 1.2 mm after surgery.
  
  
  CONCLUSIONS
  The study provides for the first time a reliable and standardised measurement tool to determine the changes in the joint line after implantation of an UKA. The instrument should be used in further studies to evaluate the impact of the joint line on the long-term outcome, the load in the two non-replaced knee compartments and on the ligaments.
authors.affiliation: Department of Orthopaedic Surgery, Ludwig-Maximilians-University, Campus Grosshadern, Marchioninistr. 15, 81377, Munich, Germany, patrick.weber@med.uni-muenchen.de.
authors.forename: Patrick
authors.initials: P
authors.lastname: Weber
authors.forename: Christian
authors.initials: C
authors.lastname: Schröder
authors.forename: Rüdiger Paul
authors.initials: RP
authors.lastname: Laubender
authors.forename: Andrea
authors.initials: A
authors.lastname: Baur-Melnyk
authors.forename: Christoph
authors.initials: C
authors.lastname: von Schulze Pellengahr
authors.forename: Volkmar
authors.initials: V
authors.lastname: Jansson
authors.forename: Peter E
authors.initials: PE
authors.lastname: Müller
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D017760:Bone Malalignment / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging* / Q000601:surgery; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D011859:Radiography; D015203:Reproducibility of Results; D012399:Rotation