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Friday, March 17, 2000

Loosening, osteolysis can occur in younger, active TKR patients

Posterior cruciate-substituting total knee replacement is being used more frequently, and in younger or more active patients. Although uncommon, loosening and osteolysis do occur with posterior cruciate-substituting knees, say researchers in a study presented in poster exhibit 140.

They found that patients at risk are relatively young with well functioning knees, have cementless femurs and a history of synovitis. The majority of wear occurs from the intended motion of the knee, but they say, there are other sources of wear particles. They recommend annual and semi-annual clinical and radiographic evaluations.

The study involves 513 posterior cruciate-substituting primary total knee replacements implanted by a single surgeon. All components were fixed with cement except for 83 uncemented femurs. All patellae were resurfaced with an all-polyethylene component. Minimum four-year follow-up (maximum nine years) was available on 513 knees.

At an average of 47 months (range: 20-73 months), 13 knees (2.5 percent) have been revised for aseptic loosening or osteolysis; two for isolated tibial loosening; three for tibial and femoral loosening; three for femoral loosening and tibial osteolysis (one uncemented femur); one for tibial loosening and femoral osteolysis; and five with osteolysis around well-fixed components (three uncemented femurs). Average age of the patients was 62 years.

All knees had good to excellent function at one year with an average KSS of 93. All knees had at least a brief period of synovitis prior to the radiographic appearance of loosening or osteolysis.

The superior surface of the tibial polyethylene components had varying degrees of burnishing, pitting and scratching, but no delamination or edge wear. Wear also occurred on the posterior aspect of the cruciate-substituting post and in two cases on the anterior aspect of the post. Grossly apparent backside wear occurred in eight knees. The pattern of backside wear indicates rotational motion between the polyethylene and the baseplate, which is under further investigation.

Co-authors of the study are Thomas P. Schmalzried, MD, Joint Replacement Institute, Los Angeles; and Ormande M. Mahoney, MD, Athens Orthopaedic Clinic, Athens, Ga.

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Last modified 23/February/2000 by IS