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Computer-assisted surgery may help avoid impingement after hip arthroplasty
Using CAD implants, an orthopedist investigates which implant positions result in impingement.
As computer-navigated surgery becomes more widespread, surgeons are calling for its use in data gathering and ensuring accurate implant placement to avoid complications, such as impingement.
David J. Mayman, MD, suggested that a combination of data gathering and computer-assisted surgery using navigation could help avoid acetabular impingement during total hip arthroplasty (THA).
He and his colleagues are evaluating whether computer navigation can help orthopedic surgeons obtain accurate placement of components, based on normal hip range of motion (ROM), to avoid impingement.
“Impingement probably leads to increased rates of dislocation and it definitely has effects on wear of the liners, and with new hard-bearing surfaces, it probably has a larger effect than it did with standard polyethylene,” Mayman said at Orthopedics Today New York 2006, A Comprehensive CME Course.
Frequency of impingement
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Impingement of the implant neck along the rim of the acetabulum typically occurs in extension and external rotation. In flexion and internal rotation, it can lead to posterior dislocation or acetabular liner wear, Mayman said.
In one study, Eduardo Salvati, MD, and colleagues found impingement in 56% of 162 retrieved acetabular implants. Of the acetabular liners removed for recurrent dislocation, 94% showed signs of impingement, Mayman said.
In a 2001 study, Yamaguchi and colleagues found 39% of 111 retrieved acetabular components showed signs of impingement. “All of that impingement was posterior, suggesting that there was increased anteversion of the cup, trying to minimize the risk of posterior dislocation,” Mayman said.
More alarming: studies on current-day implants, including ceramic-on-ceramic and cross-linked polyethylene components, have shown cracks in the liner related to impingement. “With hard-bearing surfaces, impingement is definitely one of the problems,” Mayman said.
For some time, surgeons have been placing hip components according to established guidelines, such as providing 15° to 20° of anteversion in every patient, Mayman said. However, he and his colleagues took a step back and evaluated the normal hip ROM in an uninjured adult.
Lacking normal hip ROM data
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Images: Mayman DJ |
“If you look at people who do normal activities of daily living, do we have any data of what normal hip motion is?” Mayman asked. “Surprisingly, we don’t.”
What’s more, “There’s also a lot of data out there [on] different implants and the motion of those implants, but nothing that shows actual motion between the pelvis and the femur in a normal adult,” he said.
In an effort to understand the normal hip ROM, Mayman and his colleagues evaluated 20 healthy volunteers with no hip, lower spine or knee pathologies.
Through gait analysis, they measured the patients’ motions during regular walking; rising from a low chair; tying a shoelace, to allow crossover for maximum flexion, internal rotation and abduction; and walking while cutting 90°, a typical move that risks posterior impingement.
Tight positioning required
After determining normal hip ROM, “The next question is, can we take that, go to the lab and position implants and look at whether we can actually obtain that ROM without impingement, using current-day implants?” he said.
Mayman and his colleagues are trying to answer that question. They recently created a CT model of the pelvis and femur that shows impingement through ROM. Next, they implanted computer-assisted designs of acetabular and femoral components in various positions. The researchers put the hips through ROM in each of the different positions to determine which ones cause impingement.
“The early data show that … you have to have tight component positioning … to obtain maximum flexion, internal rotation and abduction, and maximum extension and external rotation without impinging using current-day implants,” Mayman said.
Of note, he said, the researchers are using standard 28-mm heads, but most surgeons have been using larger heads in THA to allow more ROM.
“The next step is to take this to the operating room with computer navigation to see whether we’re able to obtain accurate-enough placement of components to avoid impingement,” Mayman said.
For more information:
- Mayman DJ. Acetabular position and impingement. Presented at Orthopedics Today NY 2006, A Comprehensive CME Course. Nov. 11-12, 2006. New York.
- David J. Mayman, MD, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021; 212-774-2024; maymand@hss.edu. He has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.