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Increased incidence of patellar clunk/crepitation observed with high-flexion implants for primary TKA
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About 5% of patients undergoing primary total knee arthroplasty with high-flexion implants can expect to develop patellar clunk and/or crepitation, although only 25% of this small number will likely eventually require treatment for symptomatic discomfort, according to a retrospective review of 643 knees.
Primary study author Steven B. Ogden, MD, an orthopedic surgeon at the Texas Hip and Knee Center in Fort Worth, said he was inspired to undertake the study because he and one his partners had noticed that some of their implanted patients with flexion over 130° were starting to redevelop patellar clunk.
Ogden was not surprised that the incidence of patellar clunk was 5.3% (34 knees), with an average follow-up of 3.3 years. “One of my other partners has written a paper indicating a 0% rate of patellar clunk with advanced implants; however, we were observing a 4% to 5% incidence,” Ogden told Orthopedics Today.
Among the factors that influenced clunk were: gender, 72% of cases were in men; a larger femoral component; and high knee flexion with cases averaging 138°.
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Gender factor
“Men have larger femoral components than women and they tend to be slightly more aggressive with their knee,” Ogden said. “I believe men flex more than women. But both sex and size of the femoral component were independently important. A larger femoral box allows more room for tissue to get trapped inside.”
One of the surprising findings of the study, which was presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS) in New Orleans, was that the diagnosis of patellar clunk was most commonly observed at the second year of follow-up (65% of cases) as opposed to early on in the postoperative period.
“Clunk usually resolves on its own within the first year,” Ogden said. “However, many people achieve 3° to 5° of increased flexion over the first couple of years. So those initially flexing 125° and doing fine often come back in 2 years with a flexion of 130° or more. A small percentage of these patients have some clunk.”
To date, only about 25% of the knees with clunk (eight of 34 knees) have required any intervention, he said. “The typical knee scope to remove the scar tissue alleviated the pain.” The remaining 75% of the knees have been asymptomatic. “These patients notice the crepitation and feel the grinding, yet it does not cause any pain or limit their activities,” he said.
Technique related?
Ogden and his colleagues use a less-invasive, midvastus surgical approach with increased flexion implants. “Some people suggest that this particular approach may cause the clunk,” Ogden said. “But there is a well-researched paper that shows that if the right implant is chosen, our midvastus approach is not the culprit.”
Ogden predicts that patellar clunk/crepitation will become an increasingly common side effect among high-flexion implants because the market is implant-driven, “with younger and more-demanding patients. Even the elderly patients are more demanding of their knees and desire higher flexion. Over the years, we have increased flexion from around 117· to more than 130·. Unfortunately, this implant modification is not going to be acceptable for every patient.”
In the future, a successful implant to provide greater flexion needs to accommodate the tissues in the box better, by deepening the box, having a better transition and moving the box more posterior, according to Ogden, “so even with higher flexion, you are not getting that soft tissue impingement into the box. Hence, the incidence of clunk should be reduced.” Meanwhile, “these patients are happy with their knee and any symptomatic clunk is usually completely resolvable with a simple knee scope.” – by Bob Kronemyer
Reference:
- Ogden, SB; Weeden, SH. Patellar clunk/crepitation in patients with implants designed for increased flexion. Paper 160. Presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 9-13. New Orleans.
Steven B. Ogden, MD, can be reached at Texas Hip and Knee Center, 750 8th Ave. Suite 400, Fort Worth, TX 76104; 817-877-3432; e-mail: stevenogden@hotmail.com.
