An accelerometric method was performed on 30 normal and 148 osteoarthritic (OA) knees to clarify sideways movement of the knee (lateral thrust) which occurs suddenly in the early stance phase of walking. Three thrust patterns were observed: (1) lateral thrust (LT) pattern, (2) medial thrust (MT) pattern, (3) unclassifiable (U) pattern. LT, MT and U patterns were observed in 66.7, 26.6, 6.7% respectively of the 30 normal knees; 76.6, 0, 23.4% of the 137 medial compartmental OA knees, and 0, 45.5, 54.5% of the 11 lateral compartmental OA knees. Descending steps and slope, increased walking speed, and walking with a heavy (20 Kg) object on the shoulders, all significantly increased the first peak of acceleration compared with the usual level walking in both normal and OA knees. However, the rate of increase was significantly greater in OA than in normal knees. A laterally elevated wedged-insole (LWI) decreased the first peak of lateral acceleration, whereas a medially elevated wedged-insole (MWI) increased it. In OA knees, effectiveness of the insole was well correlated with a degree of a reduction in the first peak value of acceleration. Although the LWI caused changes in the magnitude of the lateral acceleration, none of the insoles changed the accelerographic patterns, suggesting their limited effects on the lateral thrust. Clinically properly performed high tibial osteotomy (HTO) showed much greater restraining effects on the lateral thrust of the knee than any insoles, since HTO changed the LT pattern of the 25 medial OA knees to either the MT pattern (72%) or U pattern (28%).