Introduction: The position of the cup makes a major contribution to the success of total hip arthroplasty (THA). In conventional implantation of the prosthesis without navigation, the surgeon relies on the spatial position of the pelvis. However, iatrogenic manipulation of the pelvis during different surgical steps constantly changes the position of the pelvis during the operation. The position of the pelvis is substantial for the correct placement of the cup. The objective of this study was to investigate and visualize the course of this pelvic lift and correlate it to certain surgical steps.
Materials and methods: Pelvic lift was measured in 67 patients during implantation of a THA. This was done by measuring acceleration using the SensorLog app on a smartphone. It was placed on the patient's contralateral anterior superior iliac spine and recorded the movement of the pelvis throughout the whole surgical procedure. The position of the pelvis was allocated to each of eight relevant surgical steps during the operation. These surgical steps were normed over the time axis and transferred to a diagram.
Results: We found an average pelvic lift displacement of up to 14.9° upon placement in the figure-of-four position. This lift is particularly critical when exposing the acetabulum, as the true cup position can be unconsciously influenced. Average values of between 5.6° and 6.9° were found here.
Conclusions: When implanting a THA in supine position, the pelvis is not fixed on the operating table. Rather, the side to be operated on is lifted to a greater or lesser degree, depending on the surgical step to be performed. The retractor traction immediately before cup implantation should be minimized. Nevertheless, it should be taken into account that anteversion of the cup implant in relation to the table plane is systematically higher than in relation to the pelvic entry plane.
Keywords: Cup position; Pelvic lift; Pelvic motion; Total hip arthroplasty.