Ten-year results of an inset biconvex patella prosthesis in primary knee arthroplasty

Abstract

The inset biconvex patella component is an alternative form of patella resurfacing in knee arthroplasty. We retrospectively reviewed 433 patients in whom 521 patella prostheses were implanted before April 1997 to determine survivorship, factors associated with failure of the implant, incidence of anterior knee pain, and factors that may be associated with the latter. We had clinical results for 204 surviving patients (242 knees) without failure of their implants with a minimum 10-year followup (mean, 11.4 years; range, 10-17 years). For the remaining 229 patients we used chart or radiographic review to determine if failure of their implant or other complications had occurred. At latest followup, 14 patella components had been revised for aseptic reasons or were radiographically loose. The 10-year Kaplan-Meier survivorship for the entire cohort for aseptic failure was 97.0%. Aseptic failure of the patella component was associated with the presence of osteonecrosis and the absence of a superior rim of bone radiographically. The incidence of anterior knee pain in surviving patients without failure of their implants was 7.8%. No factor examined was associated with anterior knee pain. Survivorship and clinical and radiographic results are equivalent, but not clearly superior, to those reported for other forms of patella resurfacing.

Level of evidence: Level IV, therapeutic study.

Fig. 1A–B

(A) A side view and (B) a view of the underside of the biconvex inset patella implant are shown.

Fig. 2

Radiographic measures on a lateral radiograph are shown. A = measured thickness of patella (later corrected for magnification). B = articular surface patella. C = measured diameter of patella implant. Percent covered by implant = C/B × 100. Magnification of radiograph = C/actual diameter patella implant. Thickness of residual patella = A/(magnification) × 100.

Fig. 3

Radiographic measures on a skyline radiograph are shown. A = measured diameter of implant. B = articular surface patella. C = measured thickness patella. Percent covered by implant = A/B × 100. Magnification of radiograph = A/actual diameter patella implant. Thickness of residual patella = C/(magnification) × 100.

Fig. 4A–B

The diagrams show radiographic measurements of (A) tilt of the patella to the femur and (B) tilt of the implant to the patella.

Fig. 5A–B

The radiographs show the patella components (A) with no superior rim and (B) with an intact superior rim.

Fig. 6A–B

The radiographs show the patella components with (A) central tracking and (B) the lateral facet of the patella articulating with the femur.

Fig. 7A–B

Kaplan-Meier survivorship curves with (A) aseptic revision of the patella as the end point and (B) radiographic loosening or aseptic revision of the patella as the end point are shown. The data are based on the last available information available in the charts or most recent radiograph for the 213 patients either deceased or lost to followup, for whom only chart or radiographic followup was available. Dotted lines indicate 95% confidence intervals.