Patellar Component Research Articles

Polyethylene Failure of the Patellar Component in New Jersey Low-Contact Stress Total Knee Arthroplasties

In a postoperative 5- to 12-year follow-up study of 598 New Jersey low-contact stress total knee arthroplasties, 32 required revision. All retrieved patellar components were examined for polyethylene damage. These 32 cases had 3 types of failure: split rupture (7 cases), peripheral wear (21), and cantilevering breakage (4), respectively 75%, 64.3%, and 100% of which showed subluxation and/or tilting of the patellar component on the prerevision roentgenograms. Misalignment at the joint contact surfaces and rotational blockage of the mobile patellar component were considered the major causes of the failure. A design of a flatter metallic button (giving larger focal thickness of the polyethylene) and a dome-shaped polyethylene (reducing stress concentration at the pinnacle) may alleviate the failure driving mechanism should subluxation or tilting of the patellar component take place.

Removal of Solidly Fixed Implants During Revision Hip and Knee Arthroplasty

The removal of solidly fixed implants during revision hip and knee arthroplasty is a technically challenging procedure with the potential for a large amount of bone loss during component removal. This bone loss may compromise the subsequent reconstruction. Careful preoperative planning is essential before undertaking removal of solidly fixed implants. The surgeon should determine the type and size of the implants and be familiar with any specialized removal equipment that may be available. For both the hip and knee, extensive exposure is often necessary. Removal of a well-fixed femoral component often requires an extended trochanteric osteotomy. The most difficult component to remove from the knee is a well-fixed cementless patellar component. The primary goal in removing well-fixed components is to minimize loss of surrounding bone, which requires effective planning and often access to specialized tools and techniques.

Uncemented Rotating-Platform Total Knee Replacement

Mobile-bearing knee designs represent an alternative to conventional fixed-bearing total knee arthroplasty. We present the results of a prospective, intermediate-term clinical follow-up study of the bicruciate ligament-sacrificing porous-coated Low Contact Stress rotating-platform total knee design. Between February 1984 and January 1994, 528 uncemented primary knee replacements were performed in 421 patients. All patellae were resurfaced with use of the Low Contact Stress rotating patellar component. The average age of the patients at the time of the index procedure was sixty-nine years. The study group included 261 women and 160 men. Patients were evaluated at three months, six months, and yearly thereafter with use of the 100-point New Jersey Orthopaedic Hospital knee-scoring system. In addition, a radiographic analysis of the tibial, femoral, and patellar components was performed at each interval. There were twenty-nine failures that resulted in revision. The Kaplan-Meier estimate of implant survival at twelve years was 89.5% (95% confidence interval, 83.4% to 95.6%). The total clinical scores improved significantly compared with the preoperative scores for the first twelve months postoperatively and then plateaued. Three hundred and twenty-one knees had adequate radiographic follow-up (average, 8.1 years; range, five to twelve years). Zonal radiographic analysis revealed ninety-three instances of radiolucent lines (eighty-two of which measured <1 mm in width), with the greatest number of radiolucent lines (thirty-nine) being located around the tibial tray stem. None of these lines were deemed to be progressive, and no knee with a radiolucent line that measured >2 mm was revised because of failure. This first-generation uncemented, mobile-bearing, bicruciate ligament-sacrificing knee replacement was associated with a good survival rate and demonstrated clinical efficacy during the five to twelve-year follow-up interval. .

Patellofemoral forces after total knee arthroplasty: effect of extensor moment arm

Total knee arthroplasty implant designs with larger extensor moment arms theoretically should generate lower extensor forces for the same externally applied loads. This study measured knee kinematics, quadriceps forces, and patellofemoral forces under conditions of dynamic knee extension under load in two knee designs with differing quadriceps moment arms. Six human cadaver knees were tested both before implantation and after sequential implantation with two posterior cruciate retaining designs. The extensor moment arm of the LMA (long extensor moment arm design, Scorpio, Howmedica Osteonics, Rutherford, NJ) was approximately 1 cm longer than that of the Control design (7000, Howmedica Osteonics). Quadriceps tension was measured during dynamic closed kinetic chain knee extension. Patellar compressive and shear forces were also recorded using a patellar component instrumented with a custom triaxial load transducer. Knee kinematics were monitored using a three-dimensional electromagnetic tracking device. Both designs produced similar patterns of femoral rollback and tibial rotation. Quadriceps tension was lower in the LMA design compared with the Control design. Patellofemoral compressive forces were also significantly reduced in the LMA design when compared with Control (8–18% lower at angles greater than 50° flexion). The design with the longer extensor moment arm required less quadriceps force to extend the knee under load and reduced patellofemoral compressive forces. Reduced quadriceps forces may facilitate postoperative rehabilitation and activities such as stair climbing. Reduction in patellofemoral forces could reduce patellar complications such as anterior knee pain, component wear, and loosening.

Patellar resurfacing reduces pain after TKA for juvenile rheumatoid arthritis.

Influence of patellar resurfacing after knee replacement and the frequency of patella infera and its relation to the postoperative appearance of the knee pain were assessed in patients with juvenile rheumatoid arthritis. Seventy-seven total knee arthroplasties using the AGC prosthesis with nonconstrained components were done on 52 patients with a mean followup of 7.3 years (range, 3-13 years). Anterior knee pain was present in 14 of 30 patients (47%) with an unreplaced patella and in two of 18 patients (11%) with patella resurfacing. The patella was replaced in 18 patients (35%) and in 23 of 77 knees (30%). Neither revision surgery of implanted patellar components nor any later resurfacing of an unreplaced patella were done during the followup. Preoperatively using the Insall-Salvati ratio, the majority of knees (54 of 77) had a low-riding patella. Patella infera occurred commonly in patients with juvenile rheumatoid arthritis. No connection between patella infera and anterior knee pain was found.

Explicit finite element modeling of total knee replacement mechanics

Joint kinematics and contact mechanics dictate the success of current total knee replacement (TKR) devices. Efficient computer models present an effective way of evaluating these characteristics. Predicted contact stress and area due to articulations at the tibio-femoral and patello-femoral interfaces indicate potential clinical performance. Previous finite element (FE) knee models have generally been used to predict contact stresses and/or areas during static or quasi-static loading conditions. Explicit dynamic FE analyses have recently been used to efficiently predict TKR kinematics and contact mechanics during dynamic loading conditions. The objective of this study was to develop and experimentally validate an explicit FE TKR model that incorporates tibio-femoral and patello-femoral articulations. For computational efficiency, we developed rigid body analyses that can reasonably reproduce the kinematics, contact pressure distribution, and contact area of a fully deformable system. Results from the deformable model showed that the patello-femoral and tibio-femoral kinematics were in good agreement with experimental knee simulator measurements. Kinematic results from the rigid body analyses were nearly identical to those from the fully deformable model, and the contact pressure and contact area correlation was acceptable given the great reduction in analysis time. Component mesh density studied had little effect on the predicted kinematics, particularly for the patellar component, and small effects on the predicted contact pressure and area. These analyses have shown that, at low computational cost, a force-control dynamic simulation of a gait cycle can yield useful and predictable results.

Rebar Technique for Revision of the Failed Patellar Component

Rebar Technique for Revision of the Failed Patellar Component

Wear and Structural Fatigue Simulation of Crosslinked Ultra-High Molecular Weight Polyethylene for Hip and Knee Bearing Applications

Abstract There have been increasing concerns about the structural fatigue resistance of crosslinked UHMWPE devices due to deterioration of certain mechanical properties. However, due to the lack of clear correlation between specific mechanical properties and clinical performance, these concerns remain theoretical. In order to evaluate the potential benefits and risks of various crosslinked polyethylene materials for hip and knee bearing applications, two clinically relevant worst-case scenarios were simulated on functional devices. In the first worst-case scenario, cemented all-poly patellar components were tested under simulated stair-climbing conditions with rotational misalignment. In the second worst-case scenario, metal-backed thin acetabular liners were tested in a hip joint simulator under rim-loading conditions. Various types of crosslinked UHMWPE were prepared according to published process descriptions of commercial materials. While significant levels of volumetric wear reduction were confirmed by both the patellar and hip simulator tests, mixed results were obtained on the structural integrity of the devices. The latter was more significantly affected by the post-irradiation thermal treatment history than by the total dose of irradiation. Re-melting following irradiation led to catastrophic fractures of both rim-loaded liners and rotational-malaligned patellar pegs. The key mechanical property that was positively identified to correlate with the structural fatigue performance of crosslinked polyethylene materials was the ultimate tensile strength, whereas tensile elongation within 250% and 400% range had no effect on structural integrity. However, the results presented in this study should not be misconstrued with respect to the potential clinical performance of irradiation crosslinked and re-melted polyethylene liners with proper designs. In fact, the true outcome of all the crosslinked materials can only be revealed by long-term clinical follow-up.

Analysis of Early Failures in Total Knee Arthroplasty

Purpose: To analyze the cause of failure and average period in patients who had revision surgery within 5 years of their primary total knee arthroplasty (TKA). Materials and Methods: 786 total knee arthroplasties were performed between August 1994 and May 2003. During the period, there were 38 cases, 36 females and 2 males, of revision surgery within 5 years. The mean age was 66 years. The most common causes of disease in revision were degenerative arthritis. We analyzed the reasons for early failure retrospectively. Results: Revision TKA were performed at average 2 years after primary TKA. The causes of revision were polyethylene wear in 18 cases (47.4%), deep infection in 16 (42.1%), instability in 2, and aseptic loosening in 1, dissociation of patella component in 1. The degree of varus in tibial cutting was in average in polyethylene wear group. The obliquity of the tibial joint line was more than varus in 14 cases (82.4%). Most patients had their knee in hyperflexion and squatting position during activities of daily living. Conclusion: Thirty eight cases (4.8%) were performed revision surgery within 5 years of primary TKA. Polyethylene wear and deep infection were the common causes of early failure of primary TKA. The component malalignment, hyperflexion and squatting position during activities of daily living may be related to polyethylene wear. Diabetes mellitus and long term steroid application, may be related to infection.

Patellar options in revision total knee arthroplasty.

There are numerous options that need to be considered by the surgeon at the time of revision total knee arthroplasty (TKA). One needs to consider the reason for the revision, the type of patella in place, and the length of time the patella has been in place. The surgeon also needs to consider the status of the patellar bone stock, the stability of the patellar component (well-fixed or loose), and the component type (cemented or metal-backed). Assuming that the existing prosthesis is not metal-backed and has minimal PE wear, then it is preferable to retain a well-fixed all-PE cemented patellar button. However, if the button is metal-backed, then it probably is best to remove the button and replace it with an all-PE domed patellar component. Assuming more than 8 mm of patellar bone stock is remaining, it usually is best to cement an all-PE dome-shaped patella. However, if less than 8 mm is remaining, then that patient can be left with a patelloplasty, recognizing that this individual is going to continue with a high likelihood of anterior knee pain, subluxation, and poor functional results. In that situation, it may be preferable to consider a bone stock augmentation.

Dissemination of metals from a failed patellar component made of titanium-base alloy

Complications related to the patella are the most common problems in total knee arthroplasty and major reasons for revision surgery. Among patellofemoral problems, metal-to-metal contact between patellar and femoral components is the worst. We measured levels of titanium, aluminum, and vanadium in serum and urine samples and compared these measures from cases in which metal-to-metal contact of the patellar component occurred with those in cases in which only polyethylene wear occurred. Serum levels of the metals in cases with metal-to-metal contact were over 10 times higher than those in cases without metal-to-metal contact. This suggests that different ranges of serum metal ion levels could eventually be correlated with a variety of mechanisms of patellar failure. Therefore, cases with metal-to-metal contact should be distinguished from cases without metal-to-metal contact. These should not be considered as a single group in patellar component failure.

Bilateral patellar component dissociation in a patient with total knee arthroplasties

We present a case of bilateral patellar component dissociation 6 years after bilateral total knee arthroplasty. The patient had undergone arthroscopic lateral releases bilaterally for patellar maltracking. After repetitive trauma, the patient experienced patellar component dissociation, which was treated arthroscopically by removing the patellar components and leaving the patellae unresurfaced. The patient’s symptoms improved substantially. Our case highlights certain features of the etiology as well as the management of patellar component dissociation in the total knee arthroplasty, showing the important role of arthroscopy.

Mechanical properties and fatigue performance of crosslinked polyethylene in total knee applications

Abstract There has been increasing concern about the structural fatigue resistance of crosslinked ultra-high molecular weight polyethylene (UHMWPE) components due to deterioration of certain mechanical properties. However, due to the lack of clear correlation between specific mechanical properties and clinical performance, these concerns remain theoretical. To mimic clinical use and thus evaluate the potential risks and benefits of various crosslinked polyethylene materials for knee and hip bearing applications, two clinically relevant, worst-case scenarios were simulated on functional devices. In the first scenario, cemented all-polyethylene patellar components were tested under simulated stair-climbing conditions with femoral component rotational malalignment. In the second scenario, thin, metal-backed, polyethylene acetabular liners were tested in a hip joint simulator under rim-loading conditions. To compare the mechanical properties of these materials, various types of crosslinked UHMWPE were prepared according to published process descriptions of commercial materials. These materials were then subjected to standardized tensile strength testing. The results indicated that material performance was more significantly affected by the postirradiation thermal treatment history than by the total dose of irradiation. Remelting following irradiation led to catastrophic fractures of the pegs of the rotationally malaligned patellar components and the rim-loaded liners. The ultimate tensile strength appeared to be the key mechanical property that correlated with the structural fatigue performance of crosslinked polyethylene materials, whereas tensile elongation within the 250 to 400% range had no effect on structural integrity.

Excisional arthroplasty for patellar loosening in total knee arthroplasty

Four thousand two hundred eighty-seven cases of Anatomic Graduated Components total knee replacements with a cemented, single-peg, all-polyethylene patellar component were performed at our institution over the past 15 years. One hundred eighty cases of patellar component loosening were found. Eleven knees (0.3%) in 11 patients required isolated patellar component reoperation. In all cases, the patellar component was excised and not reimplanted. The average follow-up for the 11 patients was 2.2 years. Five had a complete minimum follow-up of 2 years following reoperation. Pain and function were improved. Complications included infection in 3 knees and extensor lag in 1 knee. Because of the complication rate associated with isolated patellar component excision caused by a loose patellar component, we recommend surgical removal of the patellar component only in cases of severe pain and/or prominence of the component.

Periprosthetic fractures complicating total knee arthroplasty

Abstract Periprosthetic fractures complicating total knee arthroplasty (TKA) occur in rare cases. However, the rate of TKA continues to rise. Given the increase in demand, orthopedists, more than ever, will be responsible for evaluating and treating these fractures. In order to properly treat periprosthetic fractures, a level of comfort with the basic principles on this topic is critical. This article will discuss fractures affecting the femoral, tibial and patellar components along with the respective classification systems. The potential patient risk factors and post-operative rehabilitation guidelines are also discussed.

Patellar position after total knee arthroplasty: Influence of femoral component malposition

Patellar shift, tilt, and rotation were analyzed in 7 cadaveric knee specimens during simulated quadriceps loading, in the intact knee, and after implant reconstruction. Femoral component medialization, lateralization, and external rotation were also investigated. Relative motion of the patella with respect to the femur was measured using an electromagnetic tracking system. The spatial position of the patella did not change with standardized total knee arthroplasty ( P < .05). After malpositioning of the femoral component, patellar rotation also did not change ( P > .05); however, patellar tilt was altered by femoral component external rotation malposition ( P < .05), and patellar shift was affected by all femoral component malpositions ( P < .05). The spatial position of the patella relative to the femoral shaft was changed with any femoral component malposition, suggesting that the soft tissues were abnormally tensioned. This could result in subsequent wear on the patellar component and, therefore, early failure.

Metal-backed patellar component failure in total knee arthroplasty presenting as a giant calf mass

Failure of total knee arthroplasty (TKA) caused by wear of the polyethylene-bearing surface of a metal-backed tibial platform or a metal-backed patellar component is a recognized complication. We present a case of a 78-year-old woman with a cystic mass in the left calf caused by metal wear debris from the failure of a Miller-Galante I TKA. The patient received a left TKA to treat advanced osteoarthritis in July 1990 and was lost to follow-up immediately after the operation. In December 1998, she presented at our clinic 2 days before admission, when an originally silent mass over the calf turned intolerably painful. A series of examinations revealed a calf mass caused by wear debris of total knee prosthesis and subsequent inflammation of the knee joint. Curettage of the cyst and simultaneous revision TKA were successful in relieving her symptoms. Copyright 2003, Elsevier Science (USA). All rights reserved.

Factors affecting the durability of primary total knee prostheses.

Failure of total knee arthroplasty is problematic. The purpose of this study was to evaluate the factors that influence the durability of a primary total knee prosthesis. A survivorship analysis of 11,606 primary total knee arthroplasties carried out between January 1, 1978, and December 31, 2000, was performed. An analysis of patient and implant-related factors affecting survivorship was done with use of a multivariate Cox model. The survivorship was 91% (95% confidence interval, 90% to 91%) at ten years (2943 knees), 84% (95% confidence interval, 82% to 86%) at fifteen years (595 knees), and 78% (95% confidence interval, 74% to 81%) at twenty years (104 knees) following the surgery. Prosthetic survivorship at ten years was 83% for patients fifty-five years of age or less compared with 94% for those older than seventy years of age (p < 0.0001), 90% for those with a diagnosis of osteoarthritis compared with 95% for those with inflammatory arthritis (p < 0.005), and 91% for those with retention of the posterior cruciate ligament compared with 76% for those with substitution of the posterior cruciate ligament (a posterior stabilized prosthesis) (p < 0.0001). Survivorship at ten years was 92% for nonmodular metal-backed tibial components, 90% for modular metal-backed tibial components, and 97% for all-polyethylene tibial components (p < 0.0001). Survivorship at ten years was 92% for prostheses fixed with cement compared with 61% for those fixed without cement (p < 0.0001). Significant risk factors for failure of total knee arthroplasty were the type of implant, age and gender of the patient, diagnosis, type of fixation, and design of the patellar component. In the ideal situation-treatment of a woman over the age of seventy years who has inflammatory arthritis with a nonmodular, metal-backed tibial component, cement fixation, an all-polyethylene patellar component, and retention of the posterior cruciate ligament-the ten-year survivorship of the prosthesis was estimated to be 98% (95% confidence interval, 97% to 99%).

Fate of the unrevised all-polyethylene patellar component in revision total knee arthroplasty.

During revision total knee arthroplasty, the alternatives for addressing the well-positioned and secure all-polyethylene patellar component with minimal or no wear include retention, revision, and resection. The purpose of the present study was to determine the intermediate-term fate of all-polyethylene patellar components that were left in situ at the time of revision tibiofemoral arthroplasty. We retrospectively reviewed the results of 202 revision total knee arthroplasties, performed at four centers, in which a well-fixed, well-positioned all-polyethylene patellar component with minimal wear was retained. Clinical evaluation was performed to identify the presence of anterior knee symptoms or patellar failures, and the Knee Society clinical scores were recorded. Sixty-eight percent of the revision tibiofemoral components were from a different manufacturer than the retained patellar component. Twenty-one patients (twenty-one knees; 10%) reported anterior knee pain at a mean duration of follow-up of seven years (range, two to fourteen years). Eleven of the twenty-one knees with anterior knee pain had evidence of component loosening, excessive wear, or delamination either on follow-up radiographs or on direct inspection at the time of reoperation. In the other ten knees, the findings were attributable to osseous impingement on the femoral component or soft-tissue dysfunction (including soft-tissue impingement, subluxation, and scarring). Seventeen of the twenty-one patients with anterior knee pain underwent additional surgery to address the source of the pain. Failures due to loosening or wear occurred only in patients in whom the patellar component had been sterilized with gamma irradiation in air; these failures occurred at a mean 7.3 years after revision (eleven years after primary total knee arthroplasty). The likelihood of patellar component failure was significantly greater when the component had been gamma irradiated in air than when it had been sterilized with another method (p = 0.0008). The average knee score increased from 42 to 86 points, and the average function score increased from 46 to 70 points. Retaining a well-positioned, stable all-polyethylene patellar component at the time of revision tibiofemoral arthroplasty can be successful, provided that the polyethylene has not oxidized. Manufacturing mismatch is acceptable with most contemporary designs provided that the patellar component articulates appropriately with the femoral implant. Therapeutic study, Level IV (case series [no, or historical, control group]). See p. 2 for complete description of levels of evidence.

POLYETHYLENE DAMAGE IN TOTAL KNEES AND USE OF HIGHLY CROSSLINKED POLYETHYLENE

Tibial inserts and patellar components used in total knee arthroplasty (TKA) are made of ultra-high molecular weight polyethylene. (In the present article, UHMWPE and terminology will be used interchangeably to refer to the same polymer, i.e., ultra-high molecular weight polyethylene.) The mechanisms of damage at the tibiofemoral and patellofemoral articulations consist of delamination, adhesive wear, and abrasive wear of the polyethylene component. These damage mechanisms contribute to the formation of a visible scar on the articular surfaces of the tibial insert and the patellar component. Creep and plastic deformation, both of which induce permanent deformation, also contribute to the scar on the articular surfaces and on the backside of modular polyethylene components. Creep accumulates for approximately the first two years of in vivo use and then reaches a steady state. Plastic deformation occurs rapidly due to the yielding of the polyethylene surface when the joint is loaded. Among these damage modes, delamination is the primary cause of most polyethylene-related total knee failures. Delamination can result in the loss of geometric conformity, can alter the pattern of load distribution, and can eventually result in accelerated implant failure by disengagement or fracture of the tibial insert or wear-through. To a lesser extent, adhesive/abrasive wear contributes to implant failure mainly by generating particulate debris that results in periprosthetic osteolysis1-11. In some instances, the amount of bone loss after TKA is great, leading to component loosening or fracture9. Revision surgery in these cases is particularly difficult, often requiring special component augments or bone grafts12. The causes of delamination and adhesive/abrasive wear are multifactorial. These damage mechanisms are influenced by the extent of oxidative embrittlement of the polyethylene resulting from gamma sterilization in air13-15 and the stress state of the components16, …