title: Changes of posterior condylar offset results in midflexion instability in single-radius total knee arthroplasty.
abstract: BACKGROUND
  There is no algorithm for the management of joint stability in midflexion up to now. Change in the joint line (JL) is considered to be the primary cause, although it only determines the extension gap. The purpose of this study was to determine the influence of the posterior condylar offsets (PCO), which defines the flexion gap, on midflexion instability.
  
  
  METHODS
  Forty-two knee joints (38 patients) were included in this study, patients undergoing navigated total knee arthroplasty due to primary osteoarthritis of the knee. Changes in the JL and the PCO were determined from the navigation data. A gap tensioning device was used to determine the width of the joint gap at -5°, 0°, 30° and 60° intraoperatively.
  
  
  RESULTS
  Within a range between 5 mm proximalization and 2 mm distalization, the JL had no influence on stability in midflexion. In contrast to this, both an increase and a decrease in PCO led to midflexion instability (R = 0.361, p = 0.019). In 16 cases (38%), the PCO was changed by more than 2 mm. This led to a midflexion instability of more than 2 mm in seven of these cases (44%).
  
  
  CONCLUSIONS
  Whereas the joint line can be displaced by up to 5 mm without measurable changes in joint stability, reconstruction of the posterior offset within a tight range of 2 mm is necessary to avoid midflexion instability.
authors.affiliation: Orthopedic Department, Friedrich-Schiller University, Campus Eisenberg, Jena, Germany. g.matziolis@krankenhaus-eisenberg.de.|Orthopedic Department, University Hospital Jena, Campus Eisenberg, Klosterlausnitzer Straße 81, 07607, Eisenberg, Germany. g.matziolis@krankenhaus-eisenberg.de.
authors.forename: Georg
authors.identifier: http://orcid.org/0000-0002-5105-5875
authors.initials: G
authors.lastname: Matziolis
authors.affiliation: Orthopedic Department, Friedrich-Schiller University, Campus Eisenberg, Jena, Germany.|Orthopedic Department, University Hospital Jena, Campus Eisenberg, Klosterlausnitzer Straße 81, 07607, Eisenberg, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Brodt
authors.affiliation: Orthopedic Department, Friedrich-Schiller University, Campus Eisenberg, Jena, Germany.|Orthopedic Department, University Hospital Jena, Campus Eisenberg, Klosterlausnitzer Straße 81, 07607, Eisenberg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Windisch
authors.affiliation: Orthopedic Department, Friedrich-Schiller University, Campus Eisenberg, Jena, Germany.|Orthopedic Department, University Hospital Jena, Campus Eisenberg, Klosterlausnitzer Straße 81, 07607, Eisenberg, Germany.
authors.forename: Eric
authors.initials: E
authors.lastname: Roehner
mesh_terms: D000368:Aged; D000465:Algorithms; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000601:surgery*; D017063:Outcome Assessment, Health Care / Q000379:methods; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology / Q000517:prevention & control; D016059:Range of Motion, Articular
keywords: Joint line; Midflexion instability; Posterior offset; Total knee arthroplasty