Background: The Bisurface knee prosthesis
was designed in 1989 to improve knee flexion without affecting the durability
of the prosthesis. The prosthesis has a unique ball-and-socket joint
in the midposterior portion of the femoral and tibial components, which
functions as a posterior stabilizing cam mechanism and causes femoral
rollback. The femoral component was made of alumina ceramic. The
purpose of this study was to review the clinical results of the
first 223 arthroplasties performed with this prosthesis in order
to assess whether this new implant had achieved its design objectives.
Methods: From December 1989 to May 1994, all
patients who were scheduled for primary total knee arthroplasty
were enrolled in a prospective study of the Bisurface knee. The
patients were evaluated clinically according to The Hospital for
Special Surgery knee-rating system and with a self-administered
questionnaire, and they were evaluated radiographically according
to the system of the Knee Society. Kaplan-Meier survivorship analysis
was performed with revision of the knee or recommendation for revision
as the end point.
Results: One hundred and sixty-six patients
treated with a total of 223 consecutive primary total knee arthroplasties
were enrolled in the study, and 182 knees were followed for 3.9
to 9.0 years (mean, 5.8 years). Preoperatively, the mean Hospital
for Special Surgery knee score was 44.5 points. At the time of latest
follow-up, the mean knee score was 86.3 points. The mean preoperative
and postoperative ranges of flexion were 119 and 124 degrees, respectively.
The patients, even those with a good preoperative range of motion,
rarely lost deep flexion of the knee after the procedure. A revision
operation was performed in eight knees (because of infection in
five, instability in two, and breakage of the peg of the patellar
component in one). Two knees had recurrent medial-lateral subluxations
of the femorotibial articulation, which were treated nonoperatively.
No prosthesis had loosened aseptically and no alumina ceramic femoral
component had broken by the time of latest follow-up. The rate of
survival of the implant was 94 percent (95 percent confidence interval,
90 to 98 percent) at six years. According to the patient questionnaires, 20
percent of the knees sometimes felt loose in daily living activities,
which prompted us to improve the intrinsic stability of the prosthesis
by improving the congruity of the ball-and-socket joint.
Conclusions: Total knee arthroplasty with the
Bisurface prosthesis resulted in an excellent range of motion and a
high level of satisfaction with the operation; the durability of
the prosthesis is promising.