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Simple tool provides fast, easy method of orienting acetabular cups

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ORLANDO, Fla. — Some surgeons are reporting good results placing acetabular cups with a hand-held mechanical sextant rather than freehand or with optical navigation.

It takes about 2 minutes to use the three-legged navigation tool in primary or revision cases, Stephen B. Murphy, MD, said at the 26th Annual Current Concepts in Joint Replacement Winter Meeting, here.

“We developed a hip sextant that has a simple, easy-to-use and rapid method of determining acetabular component orientation during surgery,” he said.

The device requires acquiring CT scans preoperatively so that an individualized surgical plan can be created.

Comparable to controls

At the meeting, Murphy reviewed his initial clinical results with the device (Hip Sextant, Surgical Planning Associates). For an institutional review board-approved study, he implanted 46 acetabular cups with the instrument and compared their positions to those of 146 control cups implanted with a CT-based optical navigation system.

The mean cup abduction using the sextant was 44.9° compared to 43.5° using the CT-based optical navigation system.

The mean cup anteversion measured 26.4° with the sextant compared to 25.7° with the CT-based optical navigation system.

“Virtually all of the 73 cases, which is our initial experience, were in the safe zone,” Murphy said.

Positioning aid

Prior to cup implantation, the surgeon places a leg of the sextant on the patient’s ischium, anterior superior iliac spine and a flat surface. The device determines the intraoperative position of the patient’s pelvis at the time of surgery and helps the surgeon achieve more accurate component positioning than with other techniques that rely on earlier-acquired images.

The technique reduces the risks of malposition leading to hip instability, Murphy said.

Using the sextant with preoperative radiographs alone may soon be possible, he added.

• Reference:

Murphy SB. The hip sextant: Navigating acetabular cup placement. Paper #46. Presented at the 26th Annual Current Concepts in Joint Replacement Winter Meeting. Dec. 9-12, 2009. Orlando, Fla.

Murphy receives grant/research support from and is a consultant to Wright Medical Technology. He is a major stockholder in Surgical Planning Associates.