A distractor instrument for use in knee joint surgery is provided that includes a tibial plate, a femoral plate, a tibial arm having a plate end and a control end, wherein the tibial plate is fastened to the plate end of the tibial arm at its anterior edge, and wherein, when the tibial plate is engaged with the tibia, the tibial arm is configured to extend from the tibial plate generally medially or laterally of the knee joint. The distractor instrument also includes a femoral arm having a plate end and a control end, wherein the femoral plate is fastened to the plate end of the femoral arm, and wherein, when the femoral plate is engaged with the femur, the femoral arm extends from the femoral plate generally aligned with the tibial arm. The tibial arm and the femoral arm are pivotably connected to one another at a point between their respective plate and control ends so that pivotal movement of the femoral arm relative to the tibial arm reduces the distance between their control ends and causes the distance between the tibial plate end and the femoral plate end to increase.