title: The significance of an asymmetric extension gap on routine radiographs after total knee replacement: A new sign and its clinical significance.
abstract: We investigated whether an asymmetric extension gap seen on routine post-operative radiographs after primary total knee replacement (TKR) is associated with pain at three, six, 12 and 24 months' follow-up. On radiographs of 277 patients after primary TKR we measured the distance between the tibial tray and the femoral condyle on both the medial and lateral sides. A difference was defined as an asymmetric extension gap. We considered three groups (no asymmetric gap, medial-opening and lateral-opening gap) and calculated the associations with the Western Ontario and McMaster Universities osteoarthritis index pain scores over time. Those with an asymmetric extension gap of ≥ 1.5 mm had a significant association with pain scores at three months' follow-up; patients with a medial-opening extension gap reported more pain and patients with a lateral-opening extension gap reported less pain (p = 0.036). This effect was still significant at six months (p = 0.044), but had lost significance by 12 months (p = 0.924). When adjusting for multiple cofounders the improvement in pain was more pronounced in patients with a lateral-opening extension gap than in those with a medial-opening extension gap at three (p = 0.037) and six months' (p = 0.027) follow-up.
authors.affiliation: University of Schleswig-Holstein Medical Centre, Kiel Campus, Department of Orthopaedic Surgery, Michaelisstr. 1, 24015 Kiel, Germany. liebs@liebs.eu
authors.forename: T R
authors.initials: TR
authors.lastname: Liebs
authors.forename: S-A
authors.initials: SA
authors.lastname: Kloos
authors.forename: W
authors.initials: W
authors.lastname: Herzberg
authors.forename: W
authors.initials: W
authors.lastname: Rüther
authors.forename: J
authors.initials: J
authors.lastname: Hassenpflug
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D015331:Cohort Studies; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery*; D010146:Pain / Q000000981:diagnostic imaging / Q000473:pathology; D010147:Pain Measurement; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000473:pathology; D011859:Radiography; D013997:Time Factors