Mobile-bearing Knee Research Articles

Fixed or mobile-bearing total knee arthroplasty

Fixed and mobile-bearing in total knee arthroplasty are still discussed controversially. In this article, biomechanical and clinical aspects in both fixed and mobile-bearing designs were reviewed. In biomechanical aspect, the mobile-bearing design has proved to provide less tibiofemoral contact stresses under tibiofemoral malalignment conditions. It also provides less wear rate in in-vitro simulator test. Patients with posterior stabilized mobile-bearing knees had more axial tibiofemoral rotation than patients with posterior stabilized fixed-bearing knees during gait as well as in a deep knee-bend activity. However, in clinical aspect, the mid-term or long-term survivorship of mobile-bearing knees has no superiority over that of fixed-bearing knees. The theoretical advantages for mobile-bearing design to provide a long-term durability have not been demonstrated by any outcome studies. Finally, the fixed-bearing design with all-polyethylene tibial component is suggested for relatively inactive, elder people. The mobile-bearing design is suggested for younger or higher-demand patients due to the potential for reduced polyethylene wear and more normal kinematics response after joint replacement. For younger surgeon, the fixed-bearing design is suggested due to less demand for surgical technique. For experienced surgeon, one familiar surgical protocol and instrumentation is suggested rather than implant design, either fixed-bearing or mobile-bearing.

Limited rotation of the mobile-bearing in a rotating platform total knee prosthesis

The hypothesis of this study was that the polyethylene bearing in a rotating platform total knee prosthesis shows axial rotation during a step-up motion, thereby facilitating the theoretical advantages of mobile-bearing knee prostheses. We examined 10 patients with rheumatoid arthritis who had a rotating platform total knee arthroplasty (NexGen LPS mobile, Zimmer Inc. Warsaw, USA). Fluoroscopic data was collected during a step-up motion six months postoperatively. A 3D–2D model fitting technique was used to reconstruct the in vivo 3D kinematics. The femoral component showed more axial rotation than the polyethylene mobile-bearing insert compared to the tibia during extension. In eight knees, the femoral component rotated internally with respect to the tibia during extension. In the other two knees the femoral component rotated externally with respect to the tibia. In all 10 patients, the femur showed more axial rotation than the mobile-bearing insert indicating the femoral component was sliding on the polyethylene of the rotating platform during the step-up motion. Possible explanations are a too limited conformity between femoral component and insert, the anterior located pivot location of the investigated rotating platform design, polyethylene on metal impingement and fibrous tissue formation between the mobile-bearing insert and the tibial plateau.

Dislocation of posterior-stabilized mobile-bearing knee prosthesis: A case report

Spin-out of mobile-bearing knees is a significant early complication of mobile-bearing total knee arthroplasty. Dislocation of the cam-post mechanism of fixed-bearing posterior-stabilized knees occurs more rarely. We have observed an unusual case of dislocation of posterior-stabilized rotating-platform total knee arthroplasty, which has both a cam-post mechanism and rotating platform. A 65-year-old man with knee osteoarthritis and cervical spondylotic myelopathy underwent total knee arthroplasty using a mobile-bearing prosthesis. The dislocation, which occurred 4 days postoperatively, could not be reduced by closed manipulation. However, spontaneous reduction occurred 6 days after the dislocation, which did not recur. A gap mismatch or trapezoidal-shaped gaps may lead to dislocation or spin-out of the bearing insert. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur, and both quadriceps deficiency and ligament laxity may contribute to the risk of dislocation.

A kinematic comparison of fixed- and mobile-bearing knee replacements

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur. We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.

Mobile Bearings Do Not Improve Fixation in Cemented Total Knee Arthroplasty

Mobile bearings were introduced to improve wear and knee kinematics. By uncoupling the forces generated at the articulation from the implant-bone interface this would, theoretically, also improve the fixation of the implant to bone. We did this study to evaluate whether mobile bearings improve the fixation of the tibial component to bone. Fifty-two consecutive knees in 47 patients (average age, 72 years; range, 62-84 years) with primary osteoarthrosis were randomized into two groups to receive a cemented total knee arthroplasty with either a fixed-bearing or mobile-bearing tibial component. The quality of fixation was analyzed with radiostereometric analysis for up to 2 years. Mobile bearings did not improve fixation. Both magnitudes and directions of component rotations were similar, and the number of implants with continuous migration was almost identical. Both implant types had a combination of subsidence and lift-off, but where the mobile bearing implants displayed more of subsidence, the fixed bearing knees showed more lift-off. It might be that the somewhat stiffer cobalt-chromium baseplate or the different joint conformity used in the mobile-bearing knees counteracts any potential effects of the mobile bearing. Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

A Mobile-bearing Knee Prosthesis Can Reduce Strain at the Proximal Tibia

Mobile and fixed-bearing knee prostheses are likely to generate distinct strain gradients in the proximal tibia. The resulting strain distribution in the proximal tibia governs bone remodeling and affects implant integration and stability. We determined the effects of fixed and mobile-bearing total knee prostheses on strain distribution at the proximal tibia. This mobile-bearing prosthesis was evaluated in cadaveric specimens under axial and torsional loading. Strain on the proximal tibial cortex was measured with rosette strain gages and an optical full-field strain acquisition system. Tibial torsion in response to combined axial and torsional loading was documented. There was no difference in cortex strain between the fixed and the mobile-bearing prostheses under 1.5 kN axial loading. Superimposing 10 degrees tibial internal rotation induced 22% less compressive strain in the mobile-bearing prosthesis compared with the fixed-bearing prosthesis. Under 10 degrees tibial external rotation, the mobile-bearing prosthesis induced 33% less compressive strain than the fixed-bearing prosthesis. Optically acquired strain fields showed peak compressive strain at the anteromedial aspect 30 mm below the joint line. The mobile-bearing prosthesis reduced torque in the proximal tibia during knee rotation by 68-73% compared with the fixed-bearing prosthesis. Our data suggest that the particular mobile-bearing prosthesis tested potentially reduces elevated strain levels in the proximal tibia.

Wear pattern analysis of tibial polyethylene inserts from failed total knee arthroplasty—a comparison of mobile-bearing and fixed-bearing knees

Wear pattern analysis of tibial polyethylene inserts from failed total knee arthroplasty—a comparison of mobile-bearing and fixed-bearing knees

Comparison of Range of Motion of High-Flexion Prosthesis and Mobile-Bearing Prosthesis in Total Knee Arthroplasty

The purpose of this study was to compare the range of motion (ROM) of conventional total knee arthroplasty (TKA) using high-flexion, posterior cruciate ligament (PCL) stabilized prostheses and the ROM of conventional knee arthroplasty using navigation-assisted TKA, with mobile-bearing, cruciate ligament-retaining knees. Fifty conventional TKAs with high-flexion knees and 50 navigation-assisted TKAs with mobile-bearing knees were included in this study. The ROM and number of knees that allowed comfortable kneeling and cross-legged sitting 2 years postoperatively were evaluated and compared. Functional outcomes of the two groups were assessed with the Hospital for Special Surgery (HSS) scores. The authors found no difference between the ROM and functional outcomes of conventional TKA with high-flexion knees and navigation-assisted TKA with mobile-bearing knees.

Secondary Resurfacing of the Patella in Mobile-Bearing Total Knee Arthroplasty

Objective: We aim to evaluate the impact of secondary patellar resurfacing in patients with patellar-related anterior knee pain who have undergone a mobile-bearing primary knee arthroplasty without resurfacing. Materials: A total of 2950 primary Low Contact Stress (DePuy, Warsaw, Ind) mobile-bearing knee arthroplasties without patellar resurfacing were carried out between March 1992 and March 2003. Thirteen patients (0.4%) underwent secondary patellar resurfacing for patellar-related anterior knee pain. The mean age of the patients was 67.8 years. There was a mean time of 28 months to the secondary resurfacing procedure. Results: Only 4 patients had an unequivocal improvement in their symptoms at a mean follow-up of 45 months (range, 3-92 months). No morbidity was noted from the procedure. Conclusion: The success rate of secondary patellar resurfacing is poor and patients should be counseled carefully.

Benefits of Mobile-Bearing Knee Implants Unclear

Benefits of Mobile-Bearing Knee Implants Unclear

A Study of the Effect of Tibial Tray Rotation on a Specific Mobile Bearing Total Knee Arthroplasty

We presumed that a particular mobile-bearing knee prosthesis would cope with tibial tray rotation about its longitudinal axis. We studied the tibiofemoral and patellofemoral joints to assess this. The prosthesis was mounted on a specially designed jig. The tray was externally rotated in 5° increments and put through a range of flexion. We found that increasing tibial tray rotation caused excessive polyethylene loading and, eventually, medial femoral component liftoff. The patellofemoral joint showed increasing lateral patella facet contact. Surprisingly, this mobile-bearing prosthesis could not cope with tibial tray rotation. It required the tibial tray to be neutrally aligned to the femoral component to avoid excessive polyethylene loading.

Real In Vivo Kinematic Differences between Mobile-Bearing and Fixed-Bearing Total Knee Arthroplasties

We did an in vivo fluoroscopic study comparing the sagittal plane kinematics of mobile-bearing and fixed-bearing total knee arthroplasties in a unique group of patients. These patients were part of a larger bilateral randomized controlled outcome trial with each patient having received both types of total knee arthroplasties. Invited patients did three exercises with each of their different knee replacements; extension against gravity, flexion against gravity, and a step-up. These exercises were recorded using video fluoroscopy, and a series of still digital images over the flexion range were retrieved. The relationship of patella tendon angle to knee flexion angle for each patient was derived. The patella tendon angle to knee flexion angle of the mobile-bearing knee behaved in a linear manner more closely replicating the normal knee, whereas the fixed-bearing knee behaved in a nonlinear, more variable manner. This pattern of results was similar for all three exercises with each patient having one knee replacement that behaved differently in the sagittal plane when compared with their other knee replacement. These kinematic differences may explain the clinical differences observed in the randomized controlled trials that compared these two total knee arthroplasties.

Comparison of micromotion in mobile bearing and posterior stabilized total knee prostheses

Background On theoretical grounds mobile bearing total knees should reduce the micromotion of the tibial component relative to the bone.Patients and methods We used radiostereometric analysis to measure the three-dimensional micromotion in 42 tibial components during 2 years of follow-up. The patients had been randomized as to whether they would receive a mobile bearing (MB) or posterior stabilized (PS) design. We expected that the MB knee would facilitate dissipation of forces from the prosthesis-bone interface by the motion of the bearing and by load sharing with the soft tissues, leading to less micromotion. In the PS designs, limited free rotation caused by the campost articulation might cause additional stress at the bone-prosthesis interface.Results We found no significant differences between the MB and PS group at the 2-year follow-up evaluation with respect to Knee Society scores and radiographic results. The PS group had a higher variability in subsidence and anterior-posterior tilting of the component than the MB group.Interpretation The low variability of the data in the MB knee prosthesis group suggests that this design is more predictable and forgiving with respect to micromotion of the tibial component.

Wear, Debris, and Biologic Activity of Cross-linked Polyethylene in the Knee

Cross-linked polyethylene currently is being introduced in knee prostheses. The wear rates, wear debris, and biologic reactivity of non cross-linked, moderately cross-linked, and highly cross-linked polyethylene have been compared in multidirectional wear tests and knee simulators. Multidirectional pin-on-plate wear studies of noncross-linked, moderately cross-linked (5 Mrad), and highly cross-linked (10 Mrad) polyethylene showed a 75% reduction in wear with the highly cross-linked material under kinematics found in the hip, but only a 33% reduction under wear in kinematics representative of the knee. In knee simulator studies, with the fixed-bearing press-fit, condylar Sigma cruciate-retaining knee under high kinematic input conditions, the wear of 5 Mrad moderately cross-linked polyethylene was 13 +/- 4 mm per 1 million cycles, which was lower (p < 0.05) than the wear of clinically used, gamma vacuum foil GUR 1020 polyethylene (23 +/- 6 mm/1 million cycles). For the low-contact stress mobile-bearing knee, the wear of moderately cross-linked polyethylene was 2 +/- 1 mm per 1 million cycles, which was lower (p < 0.05) than GVF GUR 1020 polyethylene (5 +/- 2 mm/1 million cycles). The wear debris isolated from the fixed-bearing knees showed the moderately cross-linked material had a larger percentage volume of particles smaller than 1 mum in size, compared with GVF GUR 1020 polyethylene. Direct cell culture studies of wear debris generated in sterile wear simulators using multidirectional motion showed a increase (p < 0.05) in tumor necrosis factor-alpha levels and reactivity for GUR 1050 cross-linked polyethylene debris compared with an equivalent volume of noncross-linked GUR 1050 polyethylene. The use of cross-linked polyethylene in the knee reduces the volumetric wear rate. However, the clinical significance of reduced fracture toughness, elevated wear in abrasive conditions, and the elevated tumor necrosis factor-alpha release from smaller more reactive particles warrant further investigation.

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. .

2003 Hap Paul Award paper of the International Society for Technology in Arthroplasty: Design and activity dependence of kinematics in fixed and mobile-bearing knee arthroplasties

Knee arthroplasty implants are designed with features that provide varying articular constraint over the range of flexion such that the pattern of knee motion may also vary. Because the motions of total knee implants have a direct influence on patient function and device longevity, it is important to understand how knee implants based on a variety of design philosophies perform in vivo. Fifty-nine knees in patients with 5 designs of implants were studied with fluoroscopic imaging during gait and stair-climbing activities. Many knees showed significantly different kinematics between the gait and stair activities, as well as differences from knees having other implant designs. The measured motions were consistent with the intrinsic constraint provided by the implant components and the variation in constraint over the flexion range.

Mobile-bearing total knee prosthesis: A 5- to 9-year follow-up of the first 110 consecutive arthroplasties

This study regards the total articulating cementless knee. This is a mobile-bearing knee, the tibial component of which consists of 2 parts: a highly conforming polyethylene insert freely rotating on a metal tray. Our case study relating to the implant of the first 110 knees operated on consecutively from 1991 to 1995 is reported, with an average follow-up of 6.3 years (range, 5–9 years). The average preoperative Knee Society Score was 78 points, and the average postoperative score was 156 points. The complications specifically related to the prosthetic components and which required revision surgery were 4: 2 cases of instability, 1 aseptic loosening of the tibial tray, and 1 traumatic dislocation of the tibial insert. A further 3 patients underwent reoperation for causes not strictly related to the implant: 2 because of intractable patellar pain and 1 because of periprosthetic ossifications that limited flexion. All of the complications were observed in patients operated on during the first 3 years of our experience, thus suggesting a definite learning curve with this prosthesis. No evidence of progressive radiographic periprosthetic osteolysis was recorded, and no relevant polyethylene wear was observed over time. Kaplan-Meier survival curves show the probability of survival to be 93.7% with revision surgery for any reason as an endpoint, and 96.3% with revision surgery for a mechanical reason as an endpoint. Certainty that mobile-bearing total knees are able to assure a longer life of the implant than the conventional models would require an evaluation of results over 15 to 20 years. However, in the meantime, these good preliminary results at least justify continuing the use of this type of prosthesis, which still awaits confirmation of the, as-yet-theoretical, advantage compared with fixed-bearing total knees.

Implant design affects knee arthroplasty kinematics during stair-stepping.

Knee implant motions have a direct influence on patient function and implant longevity. The purpose of this study was to determine if there were consistent differences in knee motions among three groups of knee implants. Two hundred thirteen knees in 173 patients, with 25 implant designs, were studied using fluoroscopy during stair-stepping. All knee implants were assigned to one of three groups based on the design: fixed-bearing posterior-stabilized, fixed-bearing posterior cruciate-retaining, and mobile-bearing. All types of implants had the same pattern of internal/external rotations, but different designs had different anteroposterior translations. Seventy-five percent of posterior-stabilized knee implants had a medial center of rotation, indicating posterior femoral translation with flexion. Sixty-three percent of cruciate-retaining fixed-bearing knee implants had a lateral center of rotation. Eighty-six percent of mobile-bearing knee implants had a lateral center of rotation, indicating anterior femoral translation with flexion. Knee motion in patients with successful total knee arthroplasties is related directly to the constraints of the implant design.

Mobile-bearing knee arthroplasty: Rotation is our salvation!

Rotating-platform knee arthroplasties have enjoyed an outstanding clinical history since their introduction in 1978. Mechanical complications requiring further surgery have been identified and include loosening, bearing dislocation, bearing wear, and osteolysis. No structural, metallic failures were reported, although extreme bearing wear was noted to cause metal surface damage sufficient to require revision in isolated cases. Survivorship of primary LCS cemented rotating-platform knee arthroplasties using an endpoint of revision of any component for any reason was 97.7% at the 20-year interval. Survivorship of primary LCS cementless rotating-platform knee arthroplasties using the same endpoint was 98.3% at the 18-year interval.

In vivo kinematics of mobile-bearing knee arthroplasty in deep knee bending motion

The current study aimed to analyze kinematics during deep knee bending motion by subjects with fully congruent mobile-bearing total knee arthroplasties allowing axial rotation and anteroposterior (AP) gliding. Twelve subjects were implanted with Dual Bearing Knee prostheses (DBK, slot type: Finsbury Orthopaedics, Surrey, UK). These implants include a mobile-bearing insert that is fully congruent with the femoral component throughout flexion and allows axial rotation and limited AP translation. Sequential fluoroscopic images were taken in the sagittal plane during loaded knee bending motion. In vivo kinematics were analyzed using a two- to three-dimensional registration technique, which uses computer-assisted design models to reproduce the spatial position of femoral and tibial components from single-view fluoroscopic images. The average femoral component demonstrated 13.4° external axial rotation for 0–120° flexion. On average, the medial condyle moved anteriorly 6.2 mm for 0–100° flexion, then posteriorly 4.0 mm for 100–120° flexion. On average, the lateral condyle moved anteriorly 1.0 mm for 0–40° flexion, then posteriorly 8.7 mm for 40–120° flexion. The typical subject exhibited a lateral pivot pattern from extension to 60° flexion and a central pivot pattern from 60° to 100° flexion, patterns that are not usually observed in normal knees. Subsequently from 100° to 120° flexion, a rollback pattern was reproduced in which bilateral condyles moved backward.