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Key to management of bone defects is to address bone loss
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Managing bone loss during revision total knee arthroplasty has vastly changed, according to one orthopedic surgeon.
“Certainly, severe metaphyseal bone loss results in fixation issues and revisions,” Wayne G. Paprosky, MD, FACS, of Rush Medical University Medical Center in Chicago, said. “I think this is the main issue and this is where I think failure occurs.”
Causes of bone defect vary from chronic inflammation (secondary to polyethylene particles and debris) to infection to severe osteolysis and malunited fractures. Paprosky said the growing number of younger and active patients opting for total knee arthroplasty (TKA) creates a need for stable, early weight-bearing devices. Coupled with poor-quality bones in elderly individuals, especially after previous revisions, and an obese population overall, “we need a changing environment,” he said.
The keys to success in managing bone defects are to address bone loss Paprosky said.
“We’ve used metal, bone graft and cement for smaller defects. Achieving metaphyseal stability, balancing the knee and maximizing the implant’s stability is crucial,” Paprosky told Orthopedics Today.
Also tantamount is protecting these reconstructions with a stem, “whether it is a cemented stem or canal-filling cementless stem,” said Paprosky, who spoke at the Current Concepts in Joint Replacement 2010 Winter Meeting. “I don’t think there is any difference in results, providing it is done correctly.”
Paprosky said bone loss is now the biggest problem with revision surgery. He also suspects aseptic loosening is the number one cause. However, “a lot of bone loss occurs during removal of well-fixed devices, especially cementless devices. Cementless metaphyseal fixation is necessary for re-implantation where large defects have occurred.”
For minor defects, the standard treatment is probably a medial tibial metal augment that can be cemented to the bone, “providing the bone still has some structural integrity,” Paprosky said. The use of large allografts to treat defects, on the other hand, “has been a mainstay for years. But a structural graft can resorb and is very difficult to do. It requires more time in the OR.”
During the past 5 years, Paprosky has increasingly relied on porous tantalum augments (Trabecular Metal, Zimmer) to correct major defects.
“Although follow-up time is limited, I think these augments show extreme promise,” he said. “Standard augments can be used when possible, but porous tantalum augments are wonderful cementless devices. The tantalum is placed against the host bone rather than being cemented to the host bone itself.”
Paprosky said that failure in revision knees is caused by large metaphyseal defects not responding well to cement bonding. Trabecular metal (TM) consists of various types of cones that are press fit into the defect, as opposed to filling in contained or semi-uncontained defects with cancellous bone.
“The cement is placed around the inside of the device, and the actual component is cemented with a cement metal-metal bond,” Paprosky said. Supplemental fixation is preferably provided with a press-fit cementless stem.
Paprosky applies cement to the stem in those cases where he feels adequate cementless fixation is not possible, due to excessive offset or questionable metaphyseal fixation. In a study of 38 TM augments in 26 patients, most of whom were for aseptic loosening, 88% of the patients “still had their TM augment in place at a mean follow-up of 37 months,” Paprosky reported. Clinical results showed significant improvement in Knee Society scores. All radiolucent lines that occurred were also stable and nonprogressive.
“I think you can adapt the shape of these augments to the individual,” Paprosky said. “Metaphyseal ingrowth of the cone and augments provide superior fixation over cement.”– by Bob Kronemyer
Reference:
- Paprosky WG. Management of bone loss: Is it a changing world? Paper #107. Presented at the Current Concepts in Joint Replacement 2010 Winter Meeting. Dec. 8-11. Orlando, Fla.
- Wayne G. Paprosky, MD, FACS, can be reached at Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612; 630-682-5653; email: parp1210@gmail.com.
- Disclosure: Paprosky receives monetary compensation/consulting fees for design consulting from Zimmer, Inc.
