title: Postoperative Increased Loading Leads to an Alteration in the Radiological Mechanical Axis After Total Knee Arthroplasty.
abstract: Standing long-leg radiographs allow assessment of the mechanical axis in the frontal plane before and after total knee arthroplasty (TKA). An alteration in loading, and hence in the forces acting on the knee joint, occurs postoperatively. We therefore postulated that the mechanical axis measured in the long-leg standing radiograph would change within the first year after TKA.
  
  
  
  Standing long-leg radiographs of 156 patients were performed 7 days, 3 months, and 12 months after TKA with determination of mechanical axis of the lower limb.
  
  
  
  Seven days after surgery, the mechanical axis amounted 0.8° ± 1.7° valgus. Three months after the operation, at 1.3° ± 1.3° varus, it was significantly different (P < .001) from the primary measurement. No further alteration in the mechanical axis occurred during the first year after TKA. This difference was even more pronounced (P < .001) in patients with a postoperative lack of complete extension. Seven days after surgery, they had a valgus axis deviation of 1.6° ± 1.6°; after 3 months, the measurement amounted 1.2° ± 1.3° varus.
  
  
  
  Measured by a standing long-leg radiograph, the frontal mechanical axis after TKA changes over time. The predictive power of a standing long-leg radiograph in the first week after surgery is limited because limb loading is altered because of pain and is therefore nonphysiological. The actual mechanical axis resulting after TKA can only be assessed in a standing long-leg radiograph at physiological loading.
authors.affiliation: Department of Orthopaedics and Traumatology, Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Robert Karl
authors.initials: RK
authors.lastname: Zahn
authors.affiliation: Department of Orthopaedics and Traumatology, Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Fussi
authors.affiliation: Department of Orthopaedics and Traumatology, Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: von Roth
authors.affiliation: Department of Orthopaedics and Traumatology, Center for Musculoskeletal Surgery, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Carsten F
authors.initials: CF
authors.lastname: Perka
authors.affiliation: Orthopedic Department, Hospital Märkisch Oderland, Wriezen, Germany.
authors.forename: Hagen
authors.initials: H
authors.lastname: Hommel
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D035002:Lower Extremity / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009038:Motion; D011184:Postoperative Period; D011187:Posture; D011859:Radiography; D013314:Stress, Mechanical; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013997:Time Factors
keywords: alteration in postoperative loading; long-leg radiograph; mechanical axis; physiological loading; total knee arthroplasty