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From March 2006 to August 2008, 93 subjects (186 knees) underwent simultaneous bilateral total knee arthroplasty performed by eight surgeons at North American centers. This randomized study was conducted to determine whether non-weight-bearing passive flexion was superior for knees receiving a posterior stabilized high flexion device compared to a posterior stabilized standard device in the contra-lateral knee. Weight-bearing single leg active flexion was one secondary endpoint. Follow-up compliance was 92.5%. Results show small, but significant superiority in the motion metrics for the high flexion device compared to the standard device 12 months after surgery, especially for a subgroup of patients with pre-operative flexion less than 120° in both knees. Thus, the ideal candidate for the high flexion device may be one with lesser pre-operative flexion., (Copyright © 2013 Elsevier Inc. All rights reserved.)

An 11.1% incidence of femoral osteolysis (30 cases in 28 patients) was identified in a series of 271 primary total knee arthroplasties. Two minimally constrained total knee designs (Synatomic [Depuy, Warsaw, IN] and Porous-Coated Anatomic [PCA, Howmedica, Rutherford, NJ] were used in this patient population. Femoral osteolysis was observed in 26 Synatomic and 4 PCA knees. The average follow-up period was 52 months (range, 24-96 months). Osteolytic lesions were identified radiographically, adjacent to the nonporous-coated (smooth) regions of the anterior and posterior flanges of the Synatomic and PCA femoral components. The average time to the diagnosis of femoral osteolysis was 31 months (range, 7-96 months). The average patient age at the time of primary total knee arthroplasty was 63 years (range, 43-83 years) and the average weight was 180 lb. (range, 107-278 lb.). Sixteen of the 30 cases were in men. All of the cases with femoral osteolysis had cementless implantation. Tissue specimens were obtained from the 18 cases requiring revision. Implants remained in situ an average of 66 months (range, 15-96 months) prior to revision. In 16 of the 18 cases revised, the femoral component was clinically and radiographically stable. Six of 18 cases were revised for severe osteolysis. The remaining 12 cases were revised for failed metal-backed patellae, failed cementless tibial fixation, or advanced polyethylene wear. Wear of the thin tibial inserts and patellar components were the two sources of particulate polyethylene. Polyethylene debris was observed in all tissue specimens. In cases with failed metal-backed patellae or impingement of the tibial locking pin-and-clip, fine metallic debris was also noted in tissue specimens. Microscopic evaluation of the osteolytic tissue revealed a florid histiocytic response with occasional giant cells. Intracellular submicron particulate polyethylene was identified with polarized light microscopy and oil-red-O staining techniques. In the study population, statistically significant factors associated with femoral osteolysis included male gender (P < .05), younger age (P < .05), increased patient weight (P < .05), positive tibial osteolysis (P < .001), osteoarthritis (P < .07), and length of time in situ (P < .001). In addition, patients with a Synatomic prosthesis were at increased risk for osteolysis compared to patients with a PCA device (P < .02). The authors postulate that histiocytic granuloma gained access to the proximal femur primarily via the unbonded interface between the smooth metal and bone.

The prevalence and characteristics of osteolysis were studied after 174 consecutive total knee arthroplasties, performed without cement; 16 per cent (twenty-seven) of the implants (in twenty-six patients) were identified as being associated with osteolysis. The diagnosis was made an average of thirty-five months after the operation. Fifteen (56 per cent) of the twenty-seven prostheses were revised after an average of forty-five months in situ. The remaining twelve implants were still in situ five years or more postoperatively. In the patients who were managed with revision, six implants were judged to be stable radiographically and intraoperatively. The remaining nine implants were loose. The average age of the patients who had osteolysis was sixty-three years, and the average weight was seventy-six kilograms (168 pounds). Eighteen of the twenty-six patients who had osteolysis were women. The medial aspect of the tibial metaphysis was the most common site for resorption of bone (twenty-four knees). Sequential radiographs demonstrated progressive extension of the osteolytic process around the tibial base-plate of the prosthesis and distally into the tibial metaphysis along the screw-bone interface in all patients. Histological evaluation of tissue obtained at the revision procedures revealed sheets of histiocytes and occasional giant cells. Intracellular particulate polyethylene and metal were found; most particles were less than one micrometer in size, although particles as large as three micrometers were identified. Mechanical failure of the thin, modular, polyethylene tibial insert; excessive abrasion of the prominent polyethylene tibial eminence, with secondary wear and impingement of the pin on the femoral component; and failure of the metal-backed patellar component all contributed to the extensive amount of polyethylene and the variable amount of metal debris that were generated. Corrosion between the angulated titanium screws and the cobalt-chromium base-plate also contributed particulate metal to the osteolytic process locally. This study demonstrated that osteolysis occurs in association with cementless total knee replacement.

This study analyzed data from 313 posterior-cruciate-sparing total knee replacements to determine the influence of preoperative flexion on postoperative flexion. The patients with limited flexion preoperatively demonstrated an improvement in flexion postoperatively. By contrast, patients with more than 105 degrees of flexion preoperatively demonstrated a decrease in flexion postoperatively. The study indicated a migration towards the mean range of motion. These findings were true for the total pool of patients and for each subgroup of patients based on diagnosis, cement status of the tibia, and implant type. The data suggests that flexion does not change beyond the first postoperative year.

We examined 86 polyethylene inserts, retrieved from total and unicompartmental knee prostheses after an average of 39.5 months in situ, grading them from 0 to 3 for seven modes of polyethylene degradation. Severe wear, with delamination or deformation, was observed in 51% of the implants, and was associated with time in situ, lack of congruency, thin polyethylene, third-body wear debris, and heat-pressed polyethylene. Significant under-surface cold flow was identified in some areas of unsupported polyethylene, and was associated with delamination in the load-bearing areas of thin inserts above screw holes in the underlying metal tray. We recommend the use of thicker polyethylene inserts, particularly in young, active patients and in designs with screw holes in the tibial baseplate. Thin polyethylene inserts which are at risk for accelerated wear and premature failure should be monitored radiographically at annual intervals.