Skeletal Radiology

, Volume 47, Issue 4, pp 511–517 | Cite as

The posterior–anterior flexed view is better than the anterior–posterior view for assessing osteoarthritis of the knee

  • Kilian Rueckl
  • Friedrich Boettner
  • Noor Maza
  • Armin Runer
  • Ulrich Bechler
  • Peter Sculco
Scientific Article



The aim of this study is to determine whether the posterior–anterior (PA)-flexed view improves the radiographic assessment of patients with knee pain compared with the standard standing anterior–posterior radiograph.

Materials and methods

Three hundred and sixty-five patients with knee pain underwent anterior–posterior (AP), PA flexed, lateral, and Merchant radiographs of the knee. Knees were grouped as mild (Kellgren and Lawrence [K-L] 1–2) or severe (K-L 3–4) osteoarthritis (OA) and either varus (medial compartment), valgus (lateral compartment), or patellofemoral OA.


In knees with mild valgus OA on AP view (K–L 1–2), the PA flexed view was more sensitive than the AP view. The measured lateral minimal joint space width (minJSW) decreased more than 2 mm in 68% of the patients, resulting in an increase in K–L grade (3 or 4). In patients with severe valgus OA and in all patients with varus and patellofemoral OA, there was no difference between AP and PA flexed view with regard to radiographic measurements or KL grade. Based on the Medicare reimbursement rate using the PA flexed view alone instead of both views reduced imaging costs by 47%.


The PA flexed view better classifies the severity of lateral compartment disease in patients with mild valgus OA and provides comparable diagnostic sensitivity for joint space narrowing in varus- and patellofemoral OA. Using the PA flexed view alone was more cost effective than using the combination of AP and PA flexed imaging.


PA flexed view Assessment Osteoarthritis Cost Valgus 


Compliance with ethical standards

Conflicts of interest

Author Friedrich Boettner receives royalties from Smith&Nephew and Orthodevelopment and compensation from Smith&Nephew, Orthodevelopment, and DePuy. All other authors declare that they have no conflicts of interests.


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Copyright information

© ISS 2017

Authors and Affiliations

  • Kilian Rueckl
    • 1
  • Friedrich Boettner
    • 1
  • Noor Maza
    • 1
    • 2
  • Armin Runer
    • 1
  • Ulrich Bechler
    • 1
  • Peter Sculco
    • 1
  1. 1.Hospital for Special SurgeryNew YorkUSA
  2. 2.Icahn School of Medicine at Mount SinaiNew YorkUSA

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