RESULTS OF NONMETAL-BACKED, HIGH-DENSITY POLYETHYLENE, BICONVEX PATELLAR PROSTHESES - A 5-7-YEAR FOLLOW-UP EVALUATION

This study evaluates the clinical and radiographic results of an all-p olyethylene, biconvex, dome-shaped patellar prosthesis with precise in strumentation implanted in 53 knees with a minimum follow-up period of 5 years (average, 6.3 years; range, 5.0-7.1 years). The mean patient age was 70.9 years (range, 18.0-89.0 years). The mean Hospital for Spe cial Surgery knee rating score was 63.6 before surgery and 83.4 after surgery. There was no fracture of the patella, no implant failure, or radiographic loosening of the prosthesis. Patellar complications consi sted of two dislocations secondary to trauma and one case of patellar subluxation. Several radiographic param eters were measured. Means and SDs were computed for: (1) patellar tilt, as measured from a line bet ween the anterior limits of the femoral condyles and the patella, whic h showed no significant difference after surgery (3.01 degrees +/- 5.1 2 degrees) compared to before surgery (3.73 degrees =/- 5.44 degrees); (2) the angle between the patellar component and the residual bone wa s -0.04 degrees +/- 2.04 degrees, with every case in the normal range (+/- 5 degrees); (3) there was no significant difference between pre- and postoperative patellar length, patellar thickness, or articular le ngth of the patella; (4) the patellar height showed a small but statis tically significant difference after surgery (2.69 +/- .64 cm) and bef ore surgery (2.94 =/- .72 cm); (5) the distance from the tibial tuberc le to the joint line did not differ significantly between preoperative (2.73 +/- 0.34 cm) and postoperative (3.06 +/- 0.36 cm) measurements; and (6) the distance from the center of the tibial plateau to the cen ter line of the tibial prosthesis was 1.34 +/- 0.32 cm. These results are superior to previously reported series.