A quantitative assessment of varus thrust in patients with medial knee osteoarthritis

Varus thrust is an abnormal lateral knee motion frequently seen in patients with medial knee osteoarthritis (OA) during gait. It is a worsening of the alignment in the stance phase of the gait cycle and closely relates to disease progression. In this study, we measured the thrust quantitatively using skin markers and examined the relationship to other static and dynamic parameters. Forty-four knees in 32 patients (mean age, 72 years; range, 64–81 years) who exhibited the radiographic OA at least grade 2 according to the Kellgren–Lawrence (K–L) scale were enrolled. Gait analysis was performed for each patient to measure the amount of thrust and knee adduction moment. The amounts of thrust in subjects with K–L grades 2 (25 knees), 3 (13 knees), and 4 (6 knees) were 2.4°(± 1.3°), 2.8°(± 1.4°), and 7.2°(± 5.3°), respectively and the knee adduction moments were 3.6(± 1.5) %BW   Ht, 3.9(± 1.2) %BW   Ht and 6.9(± 2.2%) BW   Ht, respectively. The amount of thrust also exhibited significant correlation to static radiographic alignment ( R = 0.47: 95% confidence interval 0.67–0.21, p = 0.0038) and showed greater correlation to the knee adduction moment ( R = 0.73: 95% confidence interval 0.84–0.55, p < 0.001), which has been identified as an important dynamic index of the disease. The amount of thrust, which is able to be measured by simple inexpensive equipment, correlated to static and dynamic parameters and may offer an important clinical index for knee OA.