Osteolysis around total knee arthroplasty components has been
described predominantly in association with posterior cruciate ligament-retaining
knee designs1-4. Most of these
implants had been inserted without bone cement and had relatively
nonconforming articular surfaces and a thin tibial polyethylene
insert5-9. In contrast, to our
knowledge, neither clinically apparent wear of the polyethylene
of the tibial component nor extensive osteolysis has been reported
in association with the classic posterior stabilized total knee
prosthesis (Insall-Burstein; Zimmer, Warsaw, Indiana)10,11.
The posterior stabilized prosthesis incorporates a post-and-cam
mechanism that provides for controlled rollback of the femur when
the knee is flexed and that incorporates moderate conformity of
the tibiofemoral articulation in both the sagittal and the coronal
plane. That conformity reduces stress on the polyethylene bearing
surface and may account for the favorable wear characteristics of
the prosthesis12-16. Recently,
concerns have emerged about the potential for marked wear occurring
on the nonarticular surface of modular tibial polyethylene inserts17-19. A 1997 report linked wear of
the nonarticular surface of the tibial polyethylene insert with
tibial metaphyseal osteolysis after total knee arthroplasty without
cement19.
We report the case of a patient who had marked tibial osteolysis
in association with a cemented, posterior stabilized total knee
replacement with a modular tibial tray; the nonarticular surface
of the tibial polyethylene insert appeared to be the source of wear
debris.
A fifty-five-year-old woman with marked degenerative arthritis
of the medial compartment of the left knee had a cemented, modular,
posterior stabilized total knee (Insall-Burstein II) prosthesis
with a 10-mm tibial polyethylene insert implanted in August 1991.
The intraoperative course was uneventful.
The tibiofemoral angle measured 5° of valgus on the early postoperative
radiographs. The patient did well postoperatively and was seen on
a yearly basis. She reported no pain or problems with the knee until
June 1997, when she returned because of a sudden onset of pain in
the knee. On examination, the knee was stable in all planes, with
no effusion, and it had a range of motion from 0° to 115°. She had
pain on palpation of the proximal-medial aspect of the tibia but
no erythema or warmth in that region. Radiographs revealed a marked
osteolytic lesion of the medial tibial condyle (Fig. 1-A). The tibiofemoral
angle measured 5° of valgus on these radiographs. Laboratory tests,
including complete blood-cell count, measurement of the erythrocyte
sedimentation rate and C-reactive protein level, and gram stain
and culture of knee-joint aspirate, were negative for infection.
A technetium-labeled white-blood-cell scan revealed no evidence
of infection. A computed tomography scan made through the proximal
aspect of the tibia revealed a cystic area 2.6 1.8 cm beneath the
tibial tray medially (Fig. 1-B). A presumptive diagnosis of osteolysis
was made.
Because of the size of the lesion and its rapid onset, the tibial component
was revised in September 1997. The tibial component was removed
with use of an oscillating saw, osteotomes, and a base-plate extractor
tool. A small amount of motion was seen between the tibial polyethylene
insert and the tray. The tibial tray locking mechanism was intact.
The underlying medial tibial defect was exposed and was found to
be filled with fibrous tissue. Examination of frozen intraoperative
sections and gram stain revealed no evidence of acute inflammation.
The cystic region was thoroughly curetted. The tibial canal was
prepared for insertion of a stemmed tibial component. With the trial
tibial stem in place, the medial tibial defect was packed with morselized
cancellous autograft and demineralized bone matrix. A 59-mm Insall-Burstein
II tibial tray with a 10 75-mm stem extension and a 15-mm tibial polyethylene
insert was then cemented into place.
Range of motion of the knee was encouraged immediately, and partial
weight-bearing was allowed for the first six weeks postoperatively.
Two years postoperatively, the patient was walking well with minimal
pain in the knee, which had a range of motion from 0° to 120°. Radiographs
revealed incorporation of the bone graft and a well-fixed tibial
component. Histological analysis showed fibrovascular tissue with
a histiocytic reaction and a foreign-body giant-cell reaction with
chronic inflammatory cells. Polarized light microscopy showed macrophages engulfing
polyethylene particles.
A retrieval analysis of the tibial base-plate and the polyethylene
liner was performed. Wear of the articular surface of the polyethylene
was quantified with a digital camera and Optimas image-analysis
software (Media Cybernetics, Silver Spring, Maryland). Calculation
of the wear of the nonarticular polyethylene surface with use of
data points from a coordinate measuring machine showed a minimal
amount of wear. The stabilizing polyethylene post showed a small
degree of cold flow deformation posteriorly. The nonarticular surface
of the polyethylene had marked burnishing, with 13 mm3 estimated to have been worn. Cross-sectional
analysis revealed bands and unconsolidated particles. Analysis of
the material properties of the polyethylene showed a gamma-sterilized,
mildly oxidized polyethylene insert. The polyethylene had been manufactured
with ram-extruded bar stock from 4150 resin that was then machined
to its final shape. No atypical findings were seen in the polyethylene.