Fang-Yuan Ho

Long-term results of low contact stress mobile-bearing total knee replacements.

Five hundred ninety-eight consecutive primary low contact stress total knee replacements were done in 502 patients between 1985 and 1990. Clinical review was available for 495 knees (406 patients), 228 knees with meniscal-bearing prostheses and 267 knees with rotating-platform prostheses. The average followup was 12 years (range, 10–15 years). The average postoperative knee and functional scores were 87 points and 75 points, respectively. The average postoperative range of motion was 110°. Fifty-six knees (11%) required revision for excessive wear of the tibial insert (41), dislocation (10), patellar polyethylene breakage (one), component loosening (one patellar, one tibial), and infection (two). During revision, osteolysis (20 knees), patellar polyethylene failure (33), and femoral component fracture (one) were seen. The overall survivorship was 88.1% at 15 years using Kaplan-Meier analysis. The survival rate was 83% for the meniscal-bearing prostheses and 92.1% for the rotating-platform prostheses. The Low Contact Stress mobile-bearing knee prosthesis has no superiority over that of fixed-bearing knees, especially for the meniscal-bearing design in prevention of polyethylene failure or revision. Based on the results of this study, the use of the LCS meniscal-bearing prosthesis does not appear to be justified.

Osteolysis in Failed Total Knee Arthroplasty: A Comparison of Mobile-Bearing and Fixed-Bearing Knees

Background: Osteolysis is an important complication associated with total knee arthroplasty. The purpose of this study was to compare the prevalence of osteolysis after failed total knee arthroplasty with a mobile-bearing prosthesis and after failed arthroplasty with a fixed-bearing prosthesis.Methods: Eighty revision total knee arthroplasties performed between 1995 and 1998 were included in this study. All had radiographic evidence of advanced polyethylene wear. The mobile-bearing group consisted of thirty-four knees with a Low Contact Stress implant, and the fixed-bearing group included forty-six knees. The average time (and standard deviation) from the primary operation to the revision was 102.8 ± 26.5 months in the mobile-bearing group and 96.0 ± 30.1 months in the fixed-bearing group. The prerevision radiographs and operative findings were reviewed.Results: The prevalence of osteolysis was significantly higher in the mobile-bearing group (47%; sixteen of thirty-four knees) than in the fixed-bearing group (13%; six of forty-six knees) (p = 0.003). The distal part of the femur was involved in thirteen knees in the mobile-bearing group and in four knees in the fixed-bearing group. Seventeen knees had osteolysis in the posterior aspect of the femoral condyle, which was the most common site of osteolysis; however, twelve of them had no evidence of osteolysis on prerevision radiographs.Conclusions: The prevalence of osteolysis was higher in the knees with a mobile-bearing prosthesis than in those with a fixed-bearing prosthesis. The osteolysis was predominantly on the femoral side, adjacent to the posterior aspect of the condyle. Radiographic evaluation of osteolysis in the distal part of the femur may not be reliable and usually leads to an underestimation of the degree of osteolysis.

Particle size and morphology of UHMWPE wear debris in failed total knee arthroplasties—a comparison between mobile bearing and fixed bearing knees

Osteolysis induced by ultrahigh molecular weight polyethylene wear debris has been recognized as the major cause of long‐term failure in total joint arthroplasties. In a previous study, the prevalence of intraoperatively identified osteolysis during primary revision surgery was much higher in mobile bearing knee replacements (47%) than in fixed bearing knee replacements (13%). We postulated that mobile bearing knee implants tend to produce smaller sized particles. In our current study, we compared the particle size and morphology of polyethylene wear debris between failed mobile bearing and fixed bearing knees. Tissue specimens from interfacial and lytic regions were extracted during revision surgery of 10 mobile bearing knees (all of the low contact stress (LCS) design) and 17 fixed bearing knees (10 of the porous‐coated anatomic (PCA) and 7 of the Miller/Galante design). Polyethylene particles were isolated from the tissue specimens and examined using both scanning electron microscopy and light‐scattering analyses. The LCS mobile bearing knees produced smaller particulate debris (mean equivalent spherical diameter: 0.58 μm in LCS, 1.17 μm in PCA and 5.23 μm in M/G) and more granular debris (mean value: 93% in LCS, 77% in PCA and 15% in M/G).

Late dislocation of rotating platform in New Jersey Low-Contact Stress knee prosthesis.

Five patients with late rotational dislocation of the rotating platform bearing in the New Jersey Low-Contact Stress total knee arthroplasty are reported. The prostheses had functioned well for 8 to 12 years before failure. Preoperative radiographs showed asymmetric femorotibial joint spaces. Entrapment of the dislocated bearing in three patients and spontaneous reduction of the dislocated bearing in another two patients were seen at revision. Femorotibial ligamentous instability was found after reduction. The retrieved polyethylene bearings showed advanced wear and cold flow deformities and the thickness was reduced. The revision arthroplasty was accomplished by replacement with a thicker bearing element. Progressive femorotibial ligament laxity and reduction of the thickness of polyethylene with wearing break down the originally well-balanced soft tissue tension of the knee. The rotational degree of the rotating platform bearing is unrestricted, which may result in late dislocation. Polyethylene wear is unavoidable in knee prostheses using metal contact with polyethylene even with a mobile-bearing design. Efforts to reduce polyethylene wear are mandatory.

The effect of the design of the femoral component on the conformity of the patellofemoral joint in total knee replacement

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58 degrees ; 0.14 degrees to 29.9 degrees ) and with its own patellar component (mean 11.36 degrees ; 0.55 degrees to 39.19 degrees ). In the other four prostheses, the conformity was better (mean 2.25 degrees ; 0.02 degrees to 10.52 degrees ) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51 degrees ; 0.07 degrees to 9.89 degrees ) than the Miller-Galante II prosthesis (mean 11.20 degrees ; 5.80 degrees to 16.72 degrees ) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57 degrees ; 1.40 degrees to 4.56 degrees ) or high angles of flexion (mean 4.54 degrees ; 0.91 degrees to 9.39 degrees ), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39 degrees ; 0.04 degrees to 4.56 degrees ). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation.

Mobile-bearing knees reduce rotational asymmetric wear.

Polyethylene wear of bearing components is the most common long-term complication in total knee arthroplasty. One would anticipate differing kinematics would generate different wear patterns (including wear type, degree, and symmetry) on the articulating surface of mobile-bearing and fixed-bearing inserts. Because mobile-bearing designs facilitate movement of the insert relative to the tray when the knee rotates, we hypothesized mobile-bearing designs would reduce the incidence of rotational asymmetric wear. We examined 51 worn tibial inserts, including 15 from mobile-bearing rotating-platform posterior-cruciate-sacrificing dished prostheses and 36 from fixed-bearing posterior-cruciate-retaining flat prostheses, which were retrieved at revision surgery with an average implantation time of 115 months. We divided wear types into low-grade wear (burnishing, abrasion, and cold flow) and high-grade wear (scratching, pitting, metal embedding, and delamination) to assess wear degree of polyethylene. To assess symmetry of wear, the insert surface was divided into medial and lateral sides and each side was further divided into three equal zones along the anteroposterior direction. Low-grade wear was more common in mobile-bearing knees, whereas high-grade wear was more common in fixed-bearing knees. We identified no internal/external rotational asymmetric wear or anteroposterior asymmetric wear in mobile-bearing knees.

Wear-pattern analysis in retrieved tibial inserts of mobile-bearing and fixed-bearing total knee prostheses

Components from 73 failed knee replacements (TKRs) consisting of rotating-platform, mobile-bearing and fixed-bearing implants were examined to assess the patterns of wear. The patterns were divided into low-grade (burnishing, abrasion and cold flow) and high-grade (scratching, pitting/metal embedding and delamination) to assess the severity of the wear of polyethylene. The rotating-platform group had a higher incidence of low-grade wear on the upper surface compared with the fixed-bearing group. By contrast, high-grade wear comprising scratching, pitting and third-body embedding was seen on the lower surface. Linear regression analysis showed a significant correlation of the wear scores between the upper and lower surfaces of the tibial insert (R(2) = 0.29, p = 0.04) for the rotating-platform group, but no significant correlation was found for the fixed-bearing counterpart. This suggests that high-grade wear patterns on the upper surface are reduced with the rotating-platform design. However, the incidence of burnishing, pitting/third-body embedding and scratching wear patterns on the lower surface was higher compared with that in the fixed-bearing knee.

Hemarthrosis Associated with Failure of a Mobile Meniscal-Bearing Total Knee Arthroplasty

The New Jersey Low Contact Stress (LCS) knee system (DePuy, Warsaw, Indiana) was introduced in the late 1970s by Buechel and Pappas1,2. Two types of mobile bearings are available: a meniscal-bearing system and a rotating-platform system. In a previous study, we reported eight cases of symptomatic polyethylene failure in patients who had received a meniscal-bearing knee replacement3. Previous authors have reported direct vascular injury as a result of total knee arthroplasty4-10, and one group of investigators reported a case in which vascular injury was caused by the prosthesis itself11. However, vascular injury caused by failure of a polyethylene meniscal bearing has never been reported, to our knowledge. We report the case of a patient in whom hemarthrosis and calf hematoma occurred in association with the failure of a polyethylene meniscal bearing of an LCS knee replacement. The patient was informed that data concerning her case would be submitted for publication. A seventy-year-old woman with severe osteoarthritis underwent a left total knee arthroplasty with a meniscal-bearing LCS knee implant that was fixed with cement in 1990. She did well until eight years after surgery, when she noted the sudden development of pain, a catching sensation, and varus instability of the knee. Radiographs showed dislodgment of the medial meniscal bearing. At the time of revision, a fracture of the medial meniscal bearing was found (Fig. 1). Only the polyethylene bearing was replaced. The knee functioned well after the revision. However, four years later, the …