Metal-backed and all-polyethylene tibial components in total knee replacement.

One hundred seventy-five patients with 243 consecutive primary Press Fit Condylar cruciate-substituting total knee replacements were evaluated at a mean of 5.5 years. One hundred thirteen knees had modular metal-backed tibial components and 130 had all-polyethylene tibial components. The mean knee score and functional score for the patients with unrevised components was not significantly different. The incidence of osteolysis and synovitis was higher in patients in the modular metal-backed tibia group (5%; five patients, six knees). No patients in the all-polyethylene tibia group had osteolysis or synovitis. Five revision operations were necessary: four for osteolytic defects and one for synovitis, all in patients in the modular metal-backed tibia group. All of the retrieved polyethylene inserts had evident backside wear. The best case rate of survival of the all-polyethylene tibial components was 96%+/-0.8% at 7 years and for the modular metal-backed components it was 75%+/-10% at 7 years. Metal backing and modularity were added to the Press Fit Condylar total knee replacement design to improve fixation durability. However, the superiority of the modular metal-backed implants remains in question.     

Failure of the all-polyethylene patellar component after total knee arthroplasty

From 1991 to 1996, 953 cases of porous-coated anatomic modular knee prostheses with all-polyethylene patellar components were implanted. Among them, 4 cases had breakage of the patellar component at the peg-button interfaces. One had loosening of the patellar component by cutting out the patellar bony bed. Heavy body weight, weakness of the pegs of the all-polyethylene patellar component, and osteonecrosis of the patella were conceived as the causes of failure.     

Metal-backed versus all-polyethylene tibial components in primary total knee arthroplasty

Background and purpose

The choice of either all-polyethylene (AP) tibial components or metal-backed (MB) tibial components in total knee arthroplasty (TKA) remains controversial. We therefore performed a meta-analysis and systematic review of randomized controlled trials that have evaluated MB and AP tibial components in primary TKA.

Methods

The search strategy included a computerized literature search (Medline, EMBASE, Scopus, and the Cochrane Central Register of Controlled Trials) and a manual search of major orthopedic journals. A meta-analysis and systematic review of randomized or quasi-randomized trials that compared the performance of tibial components in primary TKA was performed using a fixed or random effects model. We assessed the methodological quality of studies using Detsky quality scale.

Results

9 randomized controlled trials (RCTs) published between 2000 and 2009 met the inclusion quality standards for the systematic review. The mean standardized Detsky score was 14 (SD 3). We found that the frequency of radiolucent lines in the MB group was significantly higher than that in the AP group. There were no statistically significant differences between the MB and AP tibial components regarding component positioning, knee score, knee range of motion, quality of life, and postoperative complications.

Interpretation

Based on evidence obtained from this study, the AP tibial component was comparable with or better than the MB tibial component in TKA. However, high-quality RCTs are required to validate the results.The design of the tibial component is an important factor for implant failure in total knee arthroplasty (TKA) (Pagnano et al. 1999, Forster 2003, Gioe et al. 2007b, Willie et al. 2008, Garcia et al. 2009, KAT Trial Group 2009). The metal-backed (MB) design of tibial component has become predominant in TKA because it is thought to perform better than the all-polyethylene (AP) design (Muller et al. 2006, Gioe et al. 2006, 2007a,b). In theory, the MB tibial component reduces bending strains in the stem, reduces compressive stresses in the cement and cancellous bone beneath the baseplate (especially during asymmetric loading), and distributes load more evenly across the interface (Bartel et al. 1982, 1985, Taylor et al. 1998). However, critics of the MB tibial component claim that there are expensive implant costs, reduced polyethylene thickness with the same amount of bone resection, backside wear, and increased tensile stresses at the interface during eccentric loading (Bartel et al. 1982, 1985, Pomeroy et al. 2000, Rodriguez et al. 2001, Li et al. 2002, Muller et al. 2006, Blumenfeld and Scott 2010, Gioe and Maheshwari 2010).In the past decade, several randomized controlled trials (RCTs) have been performed to assess the effectiveness of the MB tibial component (Adalberth et al. 2000, 2001, Gioe and Bowman 2000, Norgren et al. 2004, Hyldahl et al. 2005a, b, Muller et al. 2006, Gioe et al. 2007, Bettinson et al. 2009, KAT Trial Group 2009). However, data have not been formally and systematically analyzed using quantitative methods in order to determine whether the MB tibial component is indeed optimal for patients in TKA. In this study, we wanted (1) to determine the scientific quality of published RCTs comparing the AP and MB tibial components in TKA using Detsky score (Detsky et al. 1992) and (2) to conduct a meta-analysis and systematic review of all published RCTs that have compared the effects of AP and MB tibial components on the radiographic and clinical outcomes of TKA.     

Metal-backed versus all-polyethylene tibial components in primary total knee arthroplasty

Background and purpose The choice of either all-polyethylene (AP) tibial components or metal-backed (MB) tibial components in total knee arthroplasty (TKA) remains controversial. We therefore performed a meta-analysis and systematic review of randomized controlled trials that have evaluated MB and AP tibial components in primary TKA.

Methods The search strategy included a computerized literature search (Medline, EMBASE, Scopus, and the Cochrane Central Register of Controlled Trials) and a manual search of major orthopedic journals. A meta-analysis and systematic review of randomized or quasi-randomized trials that compared the performance of tibial components in primary TKA was performed using a fixed or random effects model. We assessed the methodological quality of studies using Detsky quality scale.

Results 9 randomized controlled trials (RCTs) published between 2000 and 2009 met the inclusion quality standards for the systematic review. The mean standardized Detsky score was 14 (SD 3). We found that the frequency of radiolucent lines in the MB group was significantly higher than that in the AP group. There were no statistically significant differences between the MB and AP tibial components regarding component positioning, knee score, knee range of motion, quality of life, and postoperative complications.

Interpretation Based on evidence obtained from this study, the AP tibial component was comparable with or better than the MB tibial component in TKA. However, high-quality RCTs are required to validate the results.     

Midterm results of all-polyethylene tibial components in primary total knee arthroplasty

Our goal was to determine the 7-year survivorship of a total knee arthroplasty system with all-polyethylene tibial components. From June 1996 to December 1997, 129 consecutive patients (177 knees) (>/=70 years old) underwent such primary arthroplasty at 2 centers in the United States. The 88 patients (120 knees) with 7 years or more of follow-up were evaluated radiographically and functionally. Average results included: Knee Society Score, 93.7 points (SD, 8.1); Knee Society function score, 68.9 points (SD, 27.6); range of motion, 119 degrees (SD, 10.9); osteolysis, 0%; stress shielding, 6.6%; progressive radiolucencies, 2.5%; Kaplan-Meier survivorship (revision), 99.4% (95% confidence intervals, 98.2%-100.0%). At midterm follow-up, an all-polyethylene tibial component proved to be an excellent surgical option for total knee arthroplasty in an elderly patient population.     

Micromotion of conventionally cemented all-polyethylene tibial components in total knee replacements

Summary Micromotion of the tibial component in 27 knee arthroplasties for gonarthrosis, three of which were regarded as failures for reasons other than mechanical loosening, was studied using high-resolution roentgen stereophotogrammetric analysis (RSA). Migration over time was found in all cases, ranging from 0.2 to 2.1 mm. The majority of the cases showed migration during the first year only, while a minority migrated continuously during the period studied. The latter group showed more migration even after 1 year. All cases showed inducible displacement in response to external forces, ranging from 0.2 to 1.0 mm. The micromotion correlated with the age of the patient but not with other demographic parameters. Alignment or component position did not correlate with the micromotion. All cases but one had developed a radiolucent zone, and it was concluded that the micromotion occurred in the soft tissue interface between bone and cement. Such micromotion is a normal finding in cemented tibial components in knee arthroplasty.     

Edge loading of patellar components after total knee arthroplasty.

Patellofemoral joint kinematics, contact areas, contact pressures, and contact patterns were assessed after total knee arthroplasty (TKA) using human cadaver knees. Two contemporary TKA systems with anatomic patellofemoral joints were implanted and tested under anatomically based loading conditions. An electromagnetic tracking system was used to evaluate patellofemoral kinematics, and Fuji pressure-sensitive film was used to determine contact areas, pressures, and patterns. Edge loading of patellar components was observed at higher knee flexion angles with both TKA systems. Peak contact pressures seen at the regions of edge loading exceeded the yield strength of ultra-high-molecular weight polyethylene. Efforts to reduce edge loading and contact pressures may decrease the incidence of patellofemoral joint complications and component failure after TKA.     

A meta-analysis of patellar replacement in total knee arthroplasty

From individual randomized studies it is unclear whether the patella should be replaced during total knee replacement. We did a meta-analysis to provide quantitative data to compare patellar resurfacing with nonresurfacing during total knee arthroplasty. Only randomized, controlled trials reported between January 1966 and August 2003 comparing patellar replacement with patella retention were included for a total of 12 studies. Two reviewers assessed trial quality and extracted data from papers. The outcomes identified were reoperations for patellar problems, anterior knee pain, knee scores, stair climbing, and patient satisfaction. The resurfaced patella performed better, and we found an increased relative risk (defined by the ratio of the risk of the event in the resurfaced group on the risk of the event in the nonresurfaced group) for reoperation, for significant anterior knee pain, and for significant pain during stair climbing when the patella was left unresurfaced. No differences were observed between the two groups for International Knee Society function score, Hospital for Special Surgery score, and for patient satisfaction. Despite these general findings, forming a definitive conclusion is difficult because many confounding factors, such as component design, surgeon experience, and technical aspects of the surgery, might influence the result in a patient.     

Clinical comparison of all-polyethylene and metal-backed tibial components in total knee arthroplasty

Based primarily on in vitro biomechanical studies, most total knee arthroplasty (TKA) manufacturers have abandoned the all-polyethylene tibial component (APT) in favor of the metal-backed tibial component (MBT). There is little clinical evidence to support this decision. A retrospective review of cemented TKA using the total condylar prosthesis was performed. One hundred eighteen patients with 131 TKAs were evaluated. Sixty-two of these knee prostheses had tibial components made entirely of polyethylene while 69 had the MBT. There were 13 cases of bilateral TKA in which the APT was used for one knee and the MBT for the other. All patients were examined by the authors for an average follow-up period of six years. Hospital for Special Surgery knee scores and a comprehensive roentgenographic evaluation were obtained. No significant difference was noted between the patients with APT and those with MBT, raising serious doubt on the need for the MBT in patients being treated with primary, cemented TKA.     

The length of the patellar tendon after unicompartmental and total knee replacement.

Patella infera may occur after reconstruction of the anterior cruciate ligament (ACL), high tibial osteotomy and total knee replacement (TKR). Restriction of movement of the knee and pain may result. Our aim was to compare the incidence and to assess the effects of patella infera after TKR and unicompartmental knee replacement (UKR). We reviewed radiographs of the knees of 84 patients who had had either TKR or UKR as part of a randomised, controlled trial The length of the patellar tendon was measured on serial radiographs taken before, at eight months and at five years after operation. There was no significant change in the length of the patellar tendon after UKR, but a significant reduction was observed after TKR. Five years after the operation, the shortening of the tendon had increased to a mean of 3.5 mm. Of the knees with TKR reviewed at five years, 34% developed patella infera, defined as 10% or more of shortening, compared with 5% of those with UKR. Shortening was greatest in those knees which had required a lateral release; in this subgroup the mean shortening was 7.2 mm. Shortening correlated with restriction of movement and pain in the knee. Our study has shown that patella infera develops in most patients after TKR with lateral release, and in approximately 25% of patients after TKR without this additional procedure. Patella infera rarely occurs after UKR. It is associated with restriction of movement and pain in the knee. It may be an effect of the more extensive exposure required to perform TKR and may, in part, explain the better clinical results of UKR.     

Migration of all-polyethylene compared with metal-backed tibial components in cemented total knee arthroplasty

Background and purpose — With a rapidly increasing population in need of total knee arthroplasty (TKA), there is renewed interest in cost-saving all-polyethylene designs. Differences between metal-backed and all-polyethylene designs in initial component migration assessed by radiostereometric analysis (RSA), a proven predictor for late aseptic loosening, have been scantily reported. The purpose of this study was to compare implant migration and clinical outcomes of all-polyethylene tibial components versus metal-backed trays of similar geometrical shape.

Patients and methods — In this randomized controlled trial, 59 patients received a cemented Triathlon condylar-stabilizing implant (Stryker, Mahwah, NJ, USA) with either an all-polyethylene (n = 29) or a metal-backed tibial component (n = 30). RSA measurements and clinical scores (the Knee Society Score, Forgotten Joint Score, and Knee Osteoarthritis and Injury Outcome Score) were evaluated at baseline and postoperatively at 3, 12, and 24 months. A linear mixed-effects model was used to analyze the repeated measurements.

Results — A statistically significant difference in mean migration after 2 years was found in favor of the all-polyethylene group, with a mean maximum total point motion of 0.61?mm (95% CI 0.49–0.74) versus 0.81?mm (95% CI 0.68–0.96) for the cemented group (p = 0.03). However, this difference was smaller and not statistically significant after post hoc adjustment for surgeon effect. Both groups showed comparable improvements on all clinical outcome scores over time.

Interpretation — The Triathlon all-polyethylene tibial component showed less migration, suggesting a lower risk of late loosening as compared with its metal-backed counterpart. However, the found surgeon effect warrants further investigation.     

Comparison of metal-backed and all-polyethylene tibial components in cruciate condylar total knee arthroplasty

An evaluation of 78 knees in 63 patients using the cruciate-sparing total condylar prosthesis was performed. At a mean of 10 years following the arthroplasty there were 86% good or excellent results in knees with an all-polyethylene tibial component compared to 95% with a metal-backed tibial component (NS). Survivorship at 10 years using an endpoint of revision was 96% (NS) in both groups; using an endpoint of revision or poor knee score was 85% (NS) in the metal-backed compared to 92% (NS) in the all-polyethylene groups; using an endpoint of revision, poor knee score, or complete radiolucent line was 85% in the metal-backed compared to 90% (NS) in the all-polyethylene groups. There were no significant differences in the frequency of radiolucent lines at the last evaluation. Two percent of the tibial components in the metal-backed group had complete radiolucent lines compared to none in the allpolyethylene group. The cruciate-sparing total condylar prosthesis provides satisfactory results with no significant differences between the metal-backed or all-polyethylene tibial components at 10 years.     

Wear and deformation of patellar components in total knee arthroplasty

Clinical experience has shown that deformation of patella components can lead to loosening or excessive particulate debris, requiring revision. Factors affecting patella performance are the degree of congruity, the shear forces occurring due to tracking variations, and the excessive patellofemoral forces, particularly at higher flexion angles. A method was devised to load the patella with a constant force against the femoral component. The load was applied through a range of flexion. The deformation and wear patterns resembled those of retrieved clinical specimens. All-plastic components suffered from local deformation and underlying bone failure, whereas metal backing led to eventual penetration of the metal onto the femoral flange. Increased conformity of the patella component onto the femoral flange improved the situation for all-plastic and metal-backed designs by increasing the contact area and the available thickness of plastic.     

Surface damage of patellar components used in total knee arthroplasty

BACKGROUND: Patellofemoral complications are a common cause of failure of total knee replacement. In this study, we examined eighty-five patellar components that had been retrieved for a variety of reasons after a mean of 71.9 months in vivo. The objective of this study was to identify factors contributing to surface damage of patellar components in total knee replacements. METHODS: The retrieved patellar components were of three primary designs: dome-shaped, sombrero-shaped, and pseudo-anatomic. Five zones on each specimen were evaluated for five different types of damage (creep, pitting, delamination, abrasion, and burnishing). The severity of the damage was assigned a score of 0 to 4, with 0 indicating no damage and 4 indicating extreme damage. The extent of the damage was also assigned a score of 0 to 4, with 0 indicating 0% and 4 indicating 76% to 100%. An asymmetry ratio was calculated for each damage pattern to evaluate the uniformity of the distribution of the damage across each component. RESULTS: Eighty-six percent of the components had a damage score of > or =4 (product of the extent and severity scores) for at least one damage mechanism (creep for 38% of the components, pitting for 47%, delamination for 26%, abrasion for 49%, and burnishing for 76%). Components that had been in situ for more than two years had significantly more severe creep, delamination, and burnishing than components that had been in place for less than two years. Metal-backed designs had more severe damage than all-polyethylene components. Factors that reduced the occurrence and severity of polyethylene damage were a congruent patellar design (a non-dome-shaped component) and the use of an asymmetric femoral component. CONCLUSIONS: Damage to the patellar component was a common finding, particularly when the implant had been retrieved more than two years after implantation. Moreover, delamination was frequently found on the patellar components, as has been observed by others who examined retrieved tibial inserts. The results of this study suggest that the use of congruent patellar components may reduce damage.     

Retention of all-polyethylene acetabular components after femoral revision of a cemented total hip replacement.

BACKGROUND: This study was undertaken to provide a basis for decision-making when a well-fixed cemented cup is encountered at the time of a revision of a femoral component of a total hip replacement. It may be beneficial to retain the cup in some instances and thus reduce morbidity, complications, blood loss, operative time, and cost. METHODS: All patients who had a revision of the femoral component and retention of an all-polyethylene acetabular component from 1971 to 1996 were identified. Three hundred and seventy-four patients with a total of 395 cemented total hip replacements fit the inclusion criteria. The gender, date of and age at the index surgery, type of acetabular implant, and time of and reason for the revision of the femoral component were reviewed. The time to subsequent cup revision or latest surveillance was noted. The average age (and standard deviation) was 66.5 +/- 11.8 years at the time of the femoral revision, which was performed at an average of 8.0 +/- 4.4 years after the primary arthroplasty. For the purposes of this study, the end point for survival of the acetabular component was cup revision for any reason. RESULTS: At the time of the latest follow-up, at an average of nine years after the femoral revision and 17.3 years after the primary arthroplasty, 342 (86.6%) of the 395 cups remained in situ. Fifty-three cups (13.4%) in fifty-two patients had been revised, at an average of 10.0 +/- 5.7 years after the femoral revision and 16.7 +/- 5.3 years after the primary arthroplasty. The rate of survival of the retained acetabular components was 96.9% at five years, 89.3% at ten years, and 78.7% at fifteen years after the femoral revision and was 95.1% at fifteen years and 87.1% at twenty years after the primary arthroplasty. Increased age (p < 0.0001) and a shorter time-interval (less than 7.5 years) between the primary arthroplasty and the femoral revision (p = 0.05) were significantly associated with an increased likelihood of survival free of cup revision. Femoral head size, acetabular component design, gender, and primary diagnosis did not affect prosthetic survival in this sample of patients. CONCLUSIONS: The likelihood of survival of the unrevised cup was associated with patient age and duration of implantation, with the age of the patient being the more dominant factor predicting failure of the acetabular component.     

Mechanical failure modes in total knee replacement

Summary In an attempt to define failure modes, a study of 39 knees which failed mechanically has been carried out. In 7 cases failure occurred on the femoral side and in 32 on the tibial side. There was fracture of one femoral component. All femoral loosenings and/or sinkage occurred in malaligned components.Two main tibial failure modes were noted, lateral subluxation of the tibia on the femur leading to loosening and sinkage of the tibial component. Release of popliteus prevents lateral subluxation. Correct component alignment and the use of a large area tibial component resting on the cortices should decrease the incidence of tibial sinkage.