Biomedical subjects

A Tsao

Publications and source records attributed to A Tsao.

20 records · Page 2Linked to original sources

PubMed1993

Failure of the porous-coated anatomic prosthesis in total knee arthroplasty due to severe polyethylene wear.

Four hundred and eighty-seven total knee arthroplasties were performed by a single surgeon with use of a porous-coated anatomic prosthesis between 1982 and 1989. There were thirty-two clinical failures (7 per cent) due to severe wear of the surfaces of the tibial and patellar polyethylene components. Thirty patients had a revision. The average time to failure of the implant was four and one-half years. The initial clinical symptoms of failure by wear consisted of a painless effusion with a decreased range of motion. Subsequent pain was considered as the criterion for failure necessitating operative intervention. Increased weight and decreased age of the patient and a thinner tibial component were significant predictors of an increased risk of failure (p < 0.01). Examination of retrieved tibial components revealed extensive delamination caused by fracture of the polyethylene at a depth of about one millimeter below the surface. Cracks that had propagated in from the medial and lateral peripheries of the tibial component toward the center of the condyles were also a common finding. It appears that the design of the implant as well as clinical factors (the age and weight of the patient) contributed to the mechanical failure of the polyethylene of these implants.

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PubMed1988

Failure mechanisms of metal-backed patellar components.

A specific type of failure of a metal-backed patella occurred, consisting of a separation of the polyethylene from the metal backing. This dissociation is followed by wearing of the metal backing against the femoral component. This produces clinical signs and symptoms that usually require revision. This failure occurred in 16 knees of 14 patients. Average time to failure was 14 months. Failure was associated with patellar implant design, surgical technique, patient characteristics, and femoral component design. The plastic of the metal-backed patellae was thin at the periphery. The metal plate did not extend to the edge of the plastic and acted like a sharp edge that cut the thin plastic. The plastic dome was not bonded to the plate and became separated from the plate once the plastic tore. The plate became deformed. Failure was more likely with a subluxated, tilted, or excessively thick patella or flexed femoral component. The typical patient was a large, active male who had achieved more than 115 degrees of flexion. A prominent edge on the lateral intercondylar ridge of the femoral component resulted in a concentrated load being applied to the plastic dome and favored rapid wear of the patella. Until a greater understanding of patello-femoral loading is acquired, caution in the use of metal-backed patellae is recommended.

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