Component In Total Knee Replacement Research Articles

Dynamic simulation of a displacement-controlled total knee replacement wear tester

This paper presents a dynamic finite element method (FEM) model of a commercial displacement-controlled total knee replacement (TKR) wear tester. The first goal of the study was to validate the model, which included both the wear tester and the TKR components. Convergence simulations and experimental testing were performed. These included a novel experimental determination of the coefficient of friction and an evaluation of predicted joint contact areas by comparing simulation results with experimental data collected using pressure-sensitive film. The second goal of this study was to develop a procedure for implementing force-based testing protocols on a displacement-controlled TKR wear tester. A standard force-based cyclic wear-testing protocol was simulated using the FEM model and resulting displacement waveforms were extracted. These were used as control inputs to the physical wear tester and an experimental wear test was performed. Reaction loads on the tibial components were measured and compared with the simulated results. The model was capable of accurately predicting the tibial loads throughout the test cycle, verifying the model's contact mechanics. The study demonstrated the use of computational modelling to convert a force-based testing protocol into displacement-based control parameters for use in a displacement-controlled mechanical testing system.

Long-term implant—bone fixation of the femoral component in total knee replacement

Success of total knee replacement (TKR) depends on the prosthetic design. Aseptic loosening of the femoral component is a significant failure mode that has received little attention. Despite the clinical relevance of failures, no protocol is available to test long-term implant-bone fixation of TKR in vitro. The scope of this work was to develop and validate a protocol to assess pre-clinically the fixation of TKR femoral components. An in vitro protocol was designed to apply a simplified but relevant loading profile using a 6-degrees-of-freedom knee simulator for 1,000000 cycles. Implant-bone inducible micromotions and permanent migrations were measured at three locations throughout the test. After test completion, fatigue damage in the cement was quantified. The developed protocol was successfully applied to a commercial TKR. Additional tests were performed to exclude artefacts due to swelling or creep of the composite femur models. The components migrated distally; they tilted towards valgus in the frontal plane and in extension in the sagittal plane. The migration patterns were consistent with clinical roentgen-stereophotogrammetric recordings with TKR. Additional indicators were proposed that could quantify the tendency to loosen/stabilize. The type and amount of damage found in the cement, as well as the migration patterns, were consistent with clinical experience with the specific TKR investigated. The proposed pre-clinical test yielded repeatable results, which were consistent with the clinical literature. Therefore, its relevance and reliability was proved.

Computational assessment of constraint in total knee replacement

Anterior–posterior (AP) and internal–external (IE) rotational constraint of total knee replacement (TKR) components is frequently assessed experimentally in a multi-axis loading machine. This constraint is of clinical interest because it represents the contribution of the implants to passive joint constraint following surgery. A standard has been published to establish a uniform protocol of constraint testing (American Society of Testing and Materials (ASTM) International, 2005; Designation: F 1223-05. Standard Test Method for Determination of Total Knee Replacement). In the present study a dynamic computer simulation of a posterior-substituting TKR design undergoing an AP and IE range of constraint test was developed and tested. Implant surfaces in the simulation were specified based on the manufacturer's CAD representations, and contact between implants was computed using a rigid-body-spring-model formulation. Predictions of constraint force compared favorably to experimental values when the compliance of the testing frame was modeled. The simulated constraint test was then used to evaluate the selective locking of secondary degrees of freedom (motions other than AP displacement and IE rotation) during constraint testing. The published ASTM standard does not clearly define either the design of the testing machine to accommodate secondary motions or which coupled motions should be allowed. Predicted component constraint for a posterior cruciate-retaining TKR design was sensitive to both varus–valgus joint location and the combinations of allowed secondary motions. Computational prediction of implant constraint can expedite the design cycle and allow an objective comparison between TKR components tested in different locations.

Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer‐based navigation system

To improve the anatomy-based alignment of prosthetic components in total knee replacement, surgical navigation systems have recently been developed, based on anatomical reference frame definitions through landmark digitations and functional calibration. In this study, femoral and tibial resection plane alignments, obtained by conventional tecnique, were measured intraoperatively during total knee replacements by a navigation system to quantify potential errors in conventional bone preparation techniques. Femoral and tibial resection plane alignments, obtained by conventional femoral intramedullary and tibial extramedullary cutting guides, were measured intraoperatively in 25 primary total knee replacements by a navigation system. This system enabled the surgeon to calculate, before definitive bone sawing, the final position and orientation of all resection planes. The measurements revealed unsatisfactory alignments in nearly all anatomical planes. Except for tibial varus/valgus, final plane orientations were considerably different from those targeted by the surgeon via the navigation system, respectively 7 degrees, 8 degrees and 10 degrees apart in varus-valgus and flexion-extension at the femur, and in flexion-extension at the tibia. Modern computer-aided surgery in total knee replacement, once relevant precision has been established in all femur and tibia anatomical planes, can in the future limit the current critical component misalignments.

Alignment and orientation of the components in total knee replacement with and without navigation support

Bilateral sequential total knee replacement was carried out under one anaesthetic in 100 patients. One knee was replaced using a CT-free computer-assisted navigation system and the other conventionally without navigation. The two methods were compared for accuracy of orientation and alignment of the components. There were 85 women and 15 men with a mean age of 67.6 years (54 to 83). Radiological and CT imaging was carried out to determine the alignment of the components. The mean follow-up was 2.3 years (2 to 3). The operating and tourniquet times were significantly longer in the navigation group (p < 0.001). There were no significant pre- or post-operative differences between the knee scores of the two groups (p = 0.288 and p = 0.429, respectively). The results of imaging and the number of outliers for all radiological parameters were not statistically different (p = 0.109 to p = 0.920). In this series computer-assisted navigated total knee replacement did not result in more accurate orientation and alignment of the components than that achieved by conventional total knee replacement.

Fixation strength comparison of onlay and inset patellar implants

Patellar implant fixation continues to be one of the most troublesome areas in total knee arthroplasty (TKA). It has been reported that patellofemoral complications in TKA are responsible for almost half of all re-operations. The literature review revealed the rate of primary all-polyethylene patellar implant loosening ranging 1%–4.2% [Berend ME, Ritter MA, Keating EM, Faris PM, Crites BM. The failure of all-polyethylene patellar components in total knee replacement. Clin Orthop 2001;388:105–11, Chew JT, Stewart NJ, Hanssen AD, Luo ZP, Rand JA, An KN. Differences in patellar tracking and knee kinematics among three different total knee designs. Clin Orthop 1997;345:87–98, Barrack RL, Wolfe MW, Waldman DA, et al. Patellar resurfacing in total knee arthroplasty: a five to seven year follow-up of prospective, randomized, double-blind study. Proceedings of Sixty-Seventh Annual Meeting of the American Academy of Orthopaedic Surgeons 2000. p. 547]. The loosening rates for metal-backed or following patellar component revisions were considerably higher [Chew JT, Stewart NJ, Hanssen AD, Luo ZP, Rand JA, An KN. Differences in patellar tracking and knee kinematics among three different total knee designs. Clin Orthop 1997;345:87–98, Jordan LR, Sorrells RB, Jordan LC, Olivo JL. The long-term results of a metal-backed mobile bearing patella. Clin Orthop 2005;436:111–8, Berger RA, Lyon, JH, Jacobs JJ, Barden RM, Berkson EM, Sheinkop MB, et al. Problems with cementless total knee arthroplasty at 11 years followup. Clin Orthop 2001;392:196–207, Ritter MA, Pierce MJ, Zhou H, Meding JB, Faris PM, Keating EM. Patellar complications (total knee arthroplasty). Effect of lateral release and thickness. Clin Orthop 1999;367:149–57] Onlay and inset patellar components with variable fixation surface geometry are currently available for clinical use. The purpose of this study was to quantify the shear disassociation strength for both onlay and inset patellar fixation techniques. The variation in host material was minimized by the use of synthetic patellae, which has been previously validated in implant fixation studies. The testing revealed that inset patellar fixation resistance to shear disassociation was 25% higher than onlay patellae ( p = 0.0002).

Role of tibial constraint on knee joint biomechanics under muscle loads

In connection with technological advances in the manufacturing of medical ceramics, a newly developed ceramic femoral component was introduced in total knee arthroplasty. We generated an explicit finite-element-model to calculate the stresses developed under the highly dynamic intraoperative impaction with regard to cobalt–chromium and ceramic implant material as well as application of a silicone cover in order to reduce stress.The impaction was calculated with the hammer hitting the backside of the impactor at previously measured initial velocities. Subsequently the impactor, consisting of a steel handhold and a polyoxymethylene head, hit the femoral component. Instead of modelling femoral bone, the implant was mounted on four spring elements with spring constants previously determined in an experimental impaction model. The maximum principal stresses in the implants were evaluated at 8000 increments during the first 4 ms of impact.The ceramic implant showed principal stresses 10% to 48% higher than the cobalt chromium femoral component. The simulation of a 5 mm thick silicone layer between the impactor and the femoral component showed a strong decrease of vibration resulting in a reduction of 54% to 68% of the maximum stress amounts. The calculated amounts of principal stress were beneath the ultimate bending strengths of each material.Based on the results, intraoperative fracture of femoral components in total knee replacement may not be caused solely by impaction, but also by contributing geometrical factors such as inadequate preparation of the distal femur. In order to minimize the influence of impaction related stress peaks we recommend limiting the velocity as well as the weight of the impaction hammer when inserting femoral components. The silicone cover seems to deliver a strong decrease of implant stress and should be considered in surgery technique in the future.

A contemporary snapshot of the use of hydroxyapatite coating in orthopaedic surgery

The capacity for biological materials to combine with inorganic salts is well established. Bio-mineralisation was an evolutionary milestone, and a key contributor to the ‘cladogenesis of life’ which occurred in the early Cambrian period, 570 million years ago.[1][1] A protracted ice age in the

Rotational Alignment of the Femoral Component in Total Knee Replacement: Ligament Balance, Tibial Reference, and Femoral Component Sizing

Rotational Alignment of the Femoral Component in Total Knee Replacement: Ligament Balance, Tibial Reference, and Femoral Component Sizing

Nanotribology of CoCr–UHMWPE TJR prosthesis using atomic force microscopy

Ultra high molecular weight polyethylene (UHMWPE) submicron wear debris particles in total joint replacement (TJR) prosthesis have been observed clinically to cause osteolysis. In this study, the formation of UHMWPE submicron wear debris was investigated by modeling a nanoscale asperity on the surface of a CoCr femoral component of a total knee replacement (TKR) prosthesis using a Si 3N 4 AFM commercial tip. Contact mode atomic force microscope (AFM) was used as a tribosystem to represent CoCr–UHMWPE asperity contact in TKR prostheses in order to evaluate nanoscale coefficient of friction ‘ μ’. Nanoindentation was used to understand the mechanical response of the TJR prosthesis components. Moreover, the threshold for UHMWPE plastic deformation and subsequently wear as a function of frictional and normal load at a nanoscale between CoCr alloy and UHMWPE asperity-to-asperity contact was investigated. Results from energy dispersive X-ray (EDX) analysis and back scattering energy (BSE) technique illustrated the presence of silicon carbide (SiC) particles in the polished surface of a femoral component of total knee replacement (TKR) prosthesis. Sliding of the model asperity on direct compression moulded UHMWPE for a total normal load range of 1–11 nN caused contact pressures ranging from 14 to 80 MPa which resulted in the dynamic ‘ μ’ at the interface of the nanotribocontact equal to 0.22±0.01. Transients in frictional response of the UHMWPE as a function of normal load range (17–340 nN) during sliding against the modeled CoCr asperity were observed. The first transient in frictional force was observed at a normal load of 197±9 nN, corresponding to a contact pressure of 462±9 MPa. The second transient in the frictional force was observed at a normal load of 288±13 nN corresponding to a contact pressure of 518±13 MPa. Following the second transition in frictional response for the normal load range selected, plowing of the UHMWPE surface by the hard asperity was observed. This indicated that the deep scratches noticed in retrieved TJR prosthesis could be due to the abrasion from protruding hard carbide asperities that exist within the cast CoCr alloy of TJR prosthesis. From this study it can be stated that the plastic deformation of UHMWPE under multiaxial loading conditions (normal and shear) during sliding can be used to explain the initiation of failure of the UHMWPE insert in TJR prosthesis eventually leading to submicron wear debris generation.

Analysis of polyethylene thickness of tibial components in total knee replacement.

Excessive wear of the polyethylene bearing surfaces of tibial components has become an important factor in early failure of total knee arthroplasty. Inadequate thickness of the polyethylene insert is one cause of excessive wear, and various minimum thicknesses have been recommended in order to reduce contact stresses within the polyethylene. However, the true thicknesses of modular polyethylene tibial inserts typically are not stated accurately by the manufacturers in their product information. The purpose of this study was to determine whether the information about the thickness of tibial inserts supplied by the manufacturers is adequate. Five of the thinnest available polyethylene tibial inserts from five different manufacturers were selected. The minimum thickness of each was measured with use of a Sigma electronic micrometer comparator to an accuracy of +/-0.005 mm. The stated thicknesses of the polyethylene tibial inserts were 8, 9, and 10 mm, values that differed markedly from the actual minimum thicknesses, which ranged from 5.5722 to 6.2048 mm (mean values). The thickness of polyethylene tibial inserts has been implicated as a potential cause of excessive wear and early failure of total knee replacements. This paper highlights the fact that the information supplied by the manufacturers is inaccurate and potentially misleading; in one case, the true thickness was much less than the recommended minimum thickness. We recommend that the minimum thickness of the tibial components as well as the combined thickness of the polyethylene insert and the metal tibial tray be specified in the product information and on the packaged insert.

The Failure of All-Polyethylene Patellar Components in Total Knee Replacement

The patellar component of total knee replacement is the most frequent source of nonseptic complications after total knee arthroplasty. The purpose of the current study was to review the radiographic factors associated with loosening of all-polyethylene patellar components. Four thousand five hundred eighty-three cases of Anatomic Graduated Components total knee replacements were performed at the authors' institution during the past 15 years. Radiographs were reviewed and loosening was defined as global radiolucency or component migration. Four thousand two hundred eighty-seven allpolyethylene patellar components were implanted. There were 180 (4.2%) loose all-polyethylene patellar components. The mean time to loosening was 2.6 years (+/- 1.75 years). Fifteen (0.3%) patellar components required revision. Five radiographic features were associated with failure. The incidence and mean time of appearance were recorded: (number; incidence; time) (1) Bone-cement radiolucency, n = 174, 96.7%, 1.4 years; (2) increased density, n = 118, 65.6%, 1.8 years; (3) trabecular collapse of the bone, n = 160, 88.9%, 2.3 years; (4) patella fracture and fragmentation, n = 133, 73.9%, 2.5 years; and (5) lateral subluxation of the residual patella bone, n = 146, 81.1%, 2.9 years. Lateral retinacular release was associated with an increased rate of patellar loosening. Loosening of the allpolyethylene patella component is an avascular process strongly associated with lateral retinacular release and for which the patient infrequently requires revision surgery.

The outcome of cemented vs. cementless fixation of a femoral component in total knee replacement (TKR) with the identification of radiological signs for the prediction of failure

A survival analysis and radiological review were performed on a series of femoral total knee arthroplasty (TKA) prostheses either cemented (150 cases) or cementless, press-fit (201 cases). The internal surface of the femoral components were shot-blast CoCr alloy. The incidence of loosening of the femoral component at 6 years was 9.8% with cementless fixation and 0.6% with cement ( P<0.05) at 6 years. Amongst uncemented prostheses, there was no difference in the survival or radiological outcome with the use of a stem as against two condylar pegs. The clinical need for revision may be predicted radiologically 3 years after operation in symptomless patients by noting a change in component position combined with progressive radiolucent lines and osteolysis. Thus, radiological follow-up should be continued for a minimum of 3 years after knee replacement. The use of a stem enabled the detection of radiolucent lines which we believe were missed around prostheses with condylar pegs. Thus, the use of a stem improves the prediction of failure (but does not improve fixation).

Controlling the Motion of Total Knee Replacements using Intercondylar Guide Surfaces

Total knee replacements using intercondylar cams, such as posterior stabilized types, have been in use for many years. In a previous study, software was written to analyze an alternative shape of the intercondylar cams. The goal of the current study was to investigate in a more general way the potential of intercondylar cams, or guide surfaces, for reproducing the anterior-posterior motion of the natural knee throughout the flexion range. Typical sagittal outlines for the femoral and tibial bearing surfaces were defined, and a parametrized shape for the femoral guide surface was defined to produce a wide range of shapes. Software was written in which the femoral component was flexed in increments, with the posterior translation defined as a function of the flexion angle. The shape of the tibial guide surface was derived from the locus of the femoral guide surface at its multiple flexion positions. By iterating methodically through possible shapes of femoral guide surfaces, several types of total knee replacement components in common use today were identified, as well as other configurations of potential interest. For quantification of a given design, the software calculated the anterior and posterior laxity at each flexion angle. Laxity was defined as the motion before the femoral guide surface impacted the tibial guide surface or until the contact point of the bearing surfaces reached a specified slope. Convex femoral and concave saddle-shaped tibial guide surfaces produced small laxities in both directions over most of the flexion range. A saddle design with small laxities in the first half of flexion, combined with a posterior stabilized feature, was an interesting combination. Potential improvements to the currently used designs were shown in this study, and new shapes of intercondylar guide surfaces were derived that could be considered for application.

Controlling the motion of total knee replacements using intercondylar guide surfaces.

Total knee replacements using intercondylar cams, such as posterior stabilized types, have been in use for many years. In a previous study, software was written to analyze an alternative shape of the intercondylar cams. The goal of the current study was to investigate in a more general way the potential of intercondylar cams, or guide surfaces, for reproducing the anterior-posterior motion of the natural knee throughout the flexion range. Typical sagittal outlines for the femoral and tibial bearing surfaces were defined, and a parametrized shape for the femoral guide surface was defined to produce a wide range of shapes. Software was written in which the femoral component was flexed in increments, with the posterior translation defined as a function of the flexion angle. The shape of the tibial guide surface was derived from the locus of the femoral guide surface at its multiple flexion positions. By iterating methodically through possible shapes of femoral guide surfaces, several types of total knee replacement components in common use today were identified, as well as other configurations of potential interest. For quantification of a given design, the software calculated the anterior and posterior laxity at each flexion angle. Laxity was defined as the motion before the femoral guide surface impacted the tibial guide surface or until the contact point of the bearing surfaces reached a specified slope. Convex femoral and concave saddle-shaped tibial guide surfaces produced small laxities in both directions over most of the flexion range. A saddle design with small laxities in the first half of flexion, combined with a posterior stabilized feature, was an interesting combination. Potential improvements to the currently used designs were shown in this study, and new shapes of intercondylar guide surfaces were derived that could be considered for application.

Current concepts review: Symmetry versus asymmetry in the design of total knee femoral components—An unresolved controversy

Despite the excellent success of earlier total knee replacement designs such as the Total Condylar Knee (Johnson & Johnson, Raynham, MA), which had a symmetrical femoral component, the majority of modern designs feature a more anatomic and asymmetric femoral prosthesis. A raised lateral phalange, an angled trochlear groove, or both are thought to improve patellar tracking. Laboratory studies, however, suggest that surgical technique may be the dominant factor in determining patellofemoral kinematics. Component design has not been proven to be significant. A prosthesis with asymmetric femoral components may cost more. The literature reviewed in this article finds no advantage to the use of asymmetric versus symmetrical femoral components in total knee replacement.

Effects of fixation technique on displacement incompatibilities at the bone-implant interface in cementless total knee replacement in a canine model.

Bone-implant displacements can be caused by rigid body motion and by differences in material properties of the implant and bone. In the present study of the tibial component in total knee replacement, we tested a series of tibial component fixation designs to determine how certain design features influenced the magnitude of the tangential displacement between the component and supporting bone in a canine model. The transverse expansion of the proximal tibia under static axial loading was measured in the intact tibia and then in the same bone following implantation of tibial components with different interface characteristics: cementless flat smooth, cementless flat porous-coated, cementless flat porous-coated with screws, cementless pegged porous-coated, cementless pegged porous-coated with screws, cemented pegged, and cemented pegged with screws. In all cases, the magnitude of the transverse expansion increased with higher applied loads. When the statistical analysis was restricted to the cementless interfaces, the presence/absence of the porous coating, the presence/absence of pegs, and the use of screws had no significant influence on tibial expansion. However, in an analysis including the cemented and cementless pegged components, tibial expansion was reduced with the use of screws. The magnitude of the interface motion due to these displacement incompatibilities was approximately fivefold lower than the amount of interface motion related to rigid body motion found in a separate study with the canine model. The measured expansion was similar in the intact tibiae and the implanted tibiae, suggesting that the transverse constraint in the canine proximal tibia must be provided by the surrounding cortical ring rather than the subchondral bone.

Soft-tissue balancing at the time of knee replacement: rationale and method

A retrospective survey of knee arthroplasties has shown signs of persistent soft-tissue imbalance and has led to the development of specific instrumentation to measure soft-tissue balance during knee replacement. This instrumentation has been used to develop a sequential method of soft-tissue balancing during such surgery. Further analysis of mechanical failures amongst the total knee replacement components has shown them to be statistically associated with persistent soft-tissue imbalance as well as with other factors such as age, weight, activity and the severity of pre-operative deformity. Correction of soft-tissue imbalance at the time of knee arthroplasty is critical if proper limb alignment is to be achieved. Care in achieving both balance and proper alignment should minimize the potential for long-term component failure. The effective correction of imbalance cannot be achieved without properly designed instruments which apply equal tension to the soft tissues to be measured while at the same time registering the relative lengths of the distracted soft tissues.

Consequences of an interference fit on the fixation of porous-coated tibial components in total knee replacement.

A linearly elastic, axisymmetrical finite-element model was developed in an attempt to explain observed long-term patterns of growth of bone into tibial components. This model, which represents a portion of the tibial tray, one peg, and the surrounding cancellous bone, was used to examine two conditions of fixation in the immediate postoperative period. The first was characterized by the use of an interference fit for initial fixation of the component and the second, by the use of an interference fit with the hole in the bone deeper than the length of the peg. Two conditions of long-term fixation were also examined. In one, the bone was assumed to have grown into all of the porous coating. In the other, the bone was assumed to have grown only into the peg, and a layer of fibrous tissue was assumed to have developed between the tray and the bone. An interference fit between the peg and the cancellous bone produced considerable residual radial stresses in the bone. These stresses provide conditions that are favorable for ingrowth of bone into the pegs because the bone at the interface is stressed, and these stresses inhibit relative motion at the bone-peg interface. However, the interference fit of the peg relieved the stresses in the cancellous bone under the tray of the implant. Lack of stress at this interface is consistent with relative motion and subsequent formation of a layer of fibrous tissue. Deepening of the hole for the peg in the cancellous bone did not diminish the effects of the interference fit. Stresses in the bone under the metal tray were relieved when a layer of fibrous tissue under the tibial tray was represented in the model.

Failure of carbon fiber-reinforced polyethylene total knee-replacement components. A report of two cases.

Wright, T M; Astion, D J; Bansal, M; Rimnac, C M; Green, T; Insall, J N; Robinson, R P Author Information