A computer assisted surgical navigation system for registering the position of prosthetic hip joint components, the system comprising: a first reference element configured to be applied to the pelvis and to generate a first three-dimensional dynamic reference array, which is configured to be independently registered in the system; a second reference element configured to be applied to the femur and to generate a second three-dimensional dynamic reference array, which is configured to be independently registered in the system; a computer configured for determining, from the first and second dynamic arrays, a three-dimensional dynamic reference point representing the native anatomical joint center that is independently registered in the system; a single tracking device configured to generate a third three-dimensional dynamic reference array, which is configured to be independently registered in the system, wherein the single tracking device has a ball with a pre-determined shape and dimensions configured to precisely articulate with an acetabular component so that the computer determines a center of the acetabular component, said pre-determined shape being at least one fourth of a sphere, the ball comprising a trunion hole with a shape and dimensions configured to independently articulate precisely with a neck portion of a femoral component so that the computer determines an axis of the femoral component, the center of the ball representing a prosthetic joint center independently registered in the system prior to any reduction of the prosthetic joint; and wherein the computer is configured to concurrently register the three dimensional positions of the femoral and acetabular prosthetic components, the prosthetic joint center and the native anatomical joint center, respectively, to intraoperatively represent alterations in three dimensional location of the leg length and offset prior to any reduction of the prosthetic joint. a first reference element configured to be applied to the pelvis and to generate a first three-dimensional dynamic reference array, which is configured to be independently registered in the system; a second reference element configured to be applied to the femur and to generate a second three-dimensional dynamic reference array, which is configured to be independently registered in the system; a computer configured for determining, from the first and second dynamic arrays, a three-dimensional dynamic reference point representing the native anatomical joint center that is independently registered in the system; a single tracking device configured to generate a third three-dimensional dynamic reference array, which is configured to be independently registered in the system, wherein the single tracking device has a ball with a pre-determined shape and dimensions configured to precisely articulate with an acetabular component so that the computer determines a center of the acetabular component, said pre-determined shape being at least one fourth of a sphere, the ball comprising a trunion hole with a shape and dimensions configured to independently articulate precisely with a neck portion of a femoral component so that the computer determines an axis of the femoral component, the center of the ball representing a prosthetic joint center independently registered in the system prior to any reduction of the prosthetic joint; and wherein the computer is configured to concurrently register the three dimensional positions of the femoral and acetabular prosthetic components, the prosthetic joint center and the native anatomical joint center, respectively, to intraoperatively represent alterations in three dimensional location of the leg length and offset prior to any reduction of the prosthetic joint. <EOS>