Is Computer Navigation Necessary for Acetabular Component Positioning?
Since 1992, orthopaedic surgeons have used computer navigation when performing total hip arthroplasty (THA).
One of the drivers of this and other new technology intended to improve outcomes in THA is the issue of inadequate component positioning during the procedure, which may lead to wear, lysis, and instability – all major causes of THA failure.
Proponents of navigation say that it helps with proper placement of the acetabular component in the so-called “safe zone,” defined by Lewinneck in 1978 as an abduction angle of 30-50° and anteversion of 5-25°. This, they say, prevents the high number of hip dislocations that occur when the cup not placed in the safe zone.
Dr. Rafael Sierra is not one of the advocates for computer navigation in THA. Speaking at ICJR’s annual Winter Hip & Knee Course, Dr. Sierra asked, what really is the safe zone for acetabular cup placement? Research has not unequivocally shown that placing the cup in the safe zone via computer navigation provides better function or decreased dislocation rates compared with manual implantation. Subsequent research papers, in fact, have both proven and refuted Lewinneck’s definition of the safe zone.
Dr. Sierra believes cup positioning needs to be individualized for the patient based on a number of factors, including:
- Femoral component version
- Spinal deformities, which are associated with a higher risk for dislocation after THA
- Soft tissue structures around the hip
He uses what he terms “poor man’s navigation” for acetabular component positioning, starting with templating pre-operatively so that he knows going into the procedure:
- The size of the cup he’s going to use
- Whether he has to remove any anterior or posterior osteophytes
- How medially he wants to place the cup
- How much bone he will have to remove
- How much uncovering of the acetabular component from the bone he will have, which helps him estimate the abduction angle
- How much he will need to cut the femoral neck to restore the offset
Intraoperatively, he uses anatomic landmarks to position the cup, including the lateral acetabular rim for the abduction angle and the anterior wall, the posterior wall, and the transverse ligament for version. Research has shown that placing the cup parallel to the transverse ligament should reduce the dislocation rate to less than 1%.
With appropriate preoperative planning and an anatomic approach, Dr. Sierra believes manual implantation of THA components is reliable and does not require navigation.
Dr. Sierra’s presentation can be found here.