Conventional knee films hamper accurate knee alignment determination in patients with varus osteoarthritis of the knee.

Surgical therapeutic procedures such as knee osteotomy and knee replacement depend on proper knee alignment assessment. The aim of this study was to evaluate if femorotibial (FT) measurement on short knee films may be used in clinical settings. The study population comprised 68 patients with symptomatic medial compartmental knee osteoarthritis. We measured the FT angle with the use of mid-diaphyseal lines (FTa), and the knee joint centre (FTb) to determine anatomical knee alignment on a short knee image. Then, the accuracy of alignment was compared to the gold standard Hip-Knee-Ankle (HKA) angle on a full-limb view. FTa angle assessment correlated well (r=0.65) with the HKA angle. However, this method showed poor inter-observer agreement (ICC=0.37). 3% of patients were incorrectly classified as having valgus alignment. Good intra- and inter-observer agreements were observed for FTb angle measurement (ICC=0.89 and 0.79; respectively). But correlation between HKA and FTb angles was low (r=0.34). 15% of patients were incorrectly classified as having valgus alignment. Short knee images cannot substitute whole leg views when accurate assessment of knee alignment is essential.