ObjectiveTrunk movement is important but still little understood after total knee arthroplasty. The alternation of trunk movement was analyzed for use in a postoperative rehabilitation program in the short-term after arthroplasty.Materials and methodsThe subjects were 25 patients with knee osteoarthritis (4 males, 21 females). The femorotibial angle was evaluated on standing anteriorposterior radiographs and recorded at pre- and post-arthroplasty. Using three-dimensional motion capture, the gait parameters (cadence, walking speed, stride length, step length, step width), range of motion of lower extremity joints (hip, knee, and ankle), and trunk movement parameters (angle, speed, and displacement) were measured and compared between the pre- and 4th post-arthroplasty week.ResultsThe femorotibial angles of the arthroplasty side were improved from an average of 189° to 175° after arthroplasty. At the 4th post-arthroplasty week, the range of motion of the hip and knee flexion, hip adduction on the arthroplasty side, and ankle dorsiflexion on the non-arthroplasty side were significantly increased compared to pre-arthroplasty. Among gait parameters, only the stride length increased significantly. Regarding the trunk movement in the coronal plane, the maximal trunk speed to the non-arthroplasty side and maximal trunk displacement to the arthroplasty side were both reduced in a medio-lateral direction; the upward maximal trunk speed on the arthroplasty side increased and the maximal trunk displacement on the non-arthroplasty side decreased significantly in an up-down direction.ConclusionThe recovery of hip adduction during the standing phase caused by improvement of knee alignment contributed the reduction of trunk movement to the operated side. In the early post-arthroplasty period, the reduction of trunk movement in the coronal plane is beneficial to maintain trunk balance and prevent falls. Functional recovery of the lower extremities is a long-term process, and sustained functional training is necessary.