Coronal alignment on the single-limb stance radiograph in posterolateral rotatory instability, osteoarthritis and healthy knees.

Background: We aimed to determine whether coronal alignment measured on the single-limb stance (SLS) radiographs differs from those on the double-limb stance (DLS) images. We also investigated whether the size of such differences was affected by the knee pathology, lower limb alignment, and geometry of the tibia or femur.

Methods: We measured coronal alignment with mechanical tibiofemoral angle (MTFA) on the DLS and SLS radiographs in patients with posterolateral rotatory instability (PLRI, 30 knees), osteoarthritis (OA) with varus deformity who were scheduled for high tibial osteotomy (HTO) (60 knees), and in normal control (60 knees). The measurements on the SLS radiographs were compared with those on DLS images and the size of the differences were compared between the three groups. The correlation between the radiograph-related differences of coronal alignment and the limb alignment or geometry of tibia/femur was investigated. In the OA group, the size of the radiograph-related differences before HTO were compared with those after surgery.

Results: The coronal alignment on the SLS radiographs indicated varus accentuation compared to those on the DLS radiographs in the PLRI and OA groups (1.6 and 2.4°, respectively), while it was negligible in the normal group. Greater varus inclination of the tibial plateau was related to greater varus accentuation (r=0.249). The HTO decreased the extent of varus accentuation in the OA group (reduction of varus accentuation=1.5°).

Conclusions: Coronal alignment on the SLS radiograph is different from static alignment measured on the DLS radiograph, which may reflect dynamic alignment.