The distribution of implant fixation for femoral components of TKA: a postmortem retrieval study

Bond strength of metal-free polyether-ether-ketone knee prostheses compared to metal knee prostheses with bone cement: A preliminary in vitro study

BACKGROUND

Total knee arthroplasty is the most effective treatment for advanced-stage knee arthritis, and the majority of knee prostheses are made of metal. Nevertheless, metal prostheses still have several problems. The objective of this study is to introduce new metal-free knee prostheses made of polyether-ether-ketone (PEEK) and to compare their cement bond strength with metal prostheses.

METHODS

Twelve sets of knee prostheses were divided into four groups (unloaded PEEK, unloaded Metal, 10 million cycles (MC) PEEK, 10 MC Metal, N = 3 each), and then attached to composite bones using bone cement. Both the 10 MC PEEK and 10 MC Metal groups were subjected to dynamic gait simulations of 10 MC, whereas the other two sets were not. Afterwards, a pull-off strength test was performed on the femoral prostheses and a shear strength test was performed on the tibial prostheses.

RESULTS

No apparent cracks were observed in the bone cement after subjecting the PEEK and Metal groups to 10 million cycles of dynamic simulation. No statistically significant differences were observed (p > .05) in the strength tests for unloaded PEEK vs. unloaded Metal, 10 MC PEEK vs.10 MC Metal in the femoral pull-off test, and for unloaded PEEK vs. unloaded Metal in the tibial shear test. The shear strength of 10 MC PEEK was significantly lower (p < .05) compared to that of 10 MC Metal.

CONCLUSIONS

By comparing the force analysis of previous investigations on knee prostheses with the failure pattern observed in the PEEK knee prosthesis of this study, which replicates that of the metal prosthesis. We believe that the combination of the peek knee prosthesis with bone cement is reliable. We anticipate that metal-free PEEK knee prostheses will find application in Total Knee Arthroplasty (TKA) in the future, thereby benefiting patients.

The effects of tourniquet on cement penetration in total knee arthroplasty

PURPOSE

Aseptic loosening is a common cause of implant failure following total knee arthroplasty (TKA). Cement penetration depth is a known factor that determines an implant's "strength" and plays an important role in preventing aseptic loosening. Tourniquet use is thought to facilitate cement penetration, but its use has mixed reviews. The aim of this study was to compare cement penetration depth between tourniquet and tourniquet-less TKA patients.

METHODS

A multicenter retrospective review was conducted. Patients were randomized preoperatively to undergo TKA with or without the use of an intraoperative tourniquet. The variables collected were cement penetration measurements in millimeters (mm) within a 1-month post-operative period, length of stay (LOS), and baseline demographics. Measurements were taken by two independent raters and made in accordance to the zones described by the Knee Society Radiographic Evaluation System and methodology used in previous studies.

RESULTS

A total of 357 TKA patients were studied. No demographic differences were found between tourniquet (n = 189) and tourniquet-less (n = 168) cohorts. However, the tourniquet cohort had statistically, but not clinically, greater average cement penetration depth [2.4 ± 0.6 mm (range 1.2-4.1 mm) vs. 2.2 ± 0.5 mm (range 1.0-4.3 mm, p = 0.01)]. Moreover, the tourniquet cohort had a significantly greater proportion of patients with an average penetration depth within the accepted zone of 2 mm or greater (78.9% vs. 67.3%, p = 0.02).

CONCLUSION

Tourniquet use does not affect average penetration depth but increases the likelihood of achieving optimal cement penetration depth. Further study is warranted to determine whether this increased likelihood of optimal cement penetration depth yields lower revision rates.

Migration of the femoral component and clinical outcomes after total knee replacement: a narrative review

Loosening is considered as a main cause of implant failure in total knee replacement (TKR). Among the predictive signs of loosening, migration is the most investigated quantitative parameter. Several studies focused on the migration of the tibial component in TKR, while no reviews have been focused on the migration of the femoral component and its influence on patients' clinical outcomes. The aim of this narrative review was (1) to provide information about of the influence of migration in femoral component of TKR prostheses, (2) to assess how migration may affect patient clinical outcomes and (3) to present alternative solution to the standard cobalt-chrome prostheses. A database search was performed on PubMed Central® according to the PRISMA guidelines for studies about Cobalt-Chrome femoral component migration in people that underwent primary TKR published until May 2020. Overall, 18 articles matched the selection criteria and were included in the study. Few studies investigated the femoral component through the migration, and no clear migration causes emerged. The Roentgen Stereophotogrammetric Analysis has been mostly used to assess the migration for prognostic predictions. An annual migration of 0.10 mm seems compatible with good long-term performance and good clinical and functional outcomes. An alternative solution to cobalt-chrome prostheses is represented by femoral component in PEEK material, although no clinical evaluations have been carried out on humans yet. Further studies are needed to investigate the migration of the femoral component in relation to clinical outcomes and material used.

Investigation of the effect of the angle between femoral and prosthesis mechanical axes on bone remodeling of femur in total knee arthroplasty

The bone remodeling is the process in which the bone adapts its structure to the variation of environmental loads. The joint might be broken or damaged as a result of aging or an accident. To remedy this situation, Total Knee Arthroplasty (TKA) and prosthesis implantation is recommended. The main goal of this research is to investigate the effects of femur implanting angle on the bone remodeling process after TKA in the Coronal, Sagittal and horizontal planes over seven years. First, the 3D CAD model from CT images is created then the bone behavior is simulated using a model with a USDFLD subroutine. The results show that as the implant rotates in one direction, the stress and density distribution increases in the same direction whereas the load and consequently the bone density decrease substantially in the opposite direction. Consequently, the bone density might even decrease 77 and 31 percent in the coronal and sagittal plane respectively, so in the total knee arthroplasty, the mechanical axes of prosthesis and femur should be parallel. The active bone which occurs as a result of mechanical axes of prosthesis and femur parallelism and consequently uniform load distribution, can protect the implant from prosthesis loosening and fracture.

Cementing technique affects the rate of femoral component loosening after high flexion total knee arthroplasty

BACKGROUND

The purpose of this study was to determine the effects of different cementing techniques on the rate of early femoral loosening of high-flexion total knee arthroplasties (TKAs).

METHODS

A total of 734 knees from 486 patients treated with high-flexion design TKA between July 2001 and July 2010 were divided into two groups based on the cementing technique used. For 403 knees (group N), cement was applied onto the distal and anterior cut surfaces of the femur and the posterior flanges of the femoral component without pressurization. For 331 knees (group P), cement was applied onto distal and anterior femoral cut surfaces with digital pressurization and whole cement surfaces of the femoral component. Two groups were subjected to clinical and radiological evaluation with a minimum five year follow-up period. Cox proportional hazards model with revision surgery of the prosthesis or radiological loosening as an endpoint was used to evaluate the effect of the cementing technique and other covariates.

RESULTS

The pressurizing and bi-surface cementing technique resulted in significant reduction in femoral radiological loosening incidence compared to that without pressurization (0.3% vs. 2.5%, P=0.015) and revision rate for aseptic causes (0.9% vs. 3.2%, P=0.032). Cox proportional hazard regression analysis revealed a significant difference in component survival rate between the two groups if femoral radiological loosening was considered as failure (hazard ratio, 4.229, 95% confidence interval (CI): 1.256-14.243, P=0.020).

CONCLUSION

Pressurizing and bi-surface cementation can reduce the occurrence rate of early loosening around the femoral component in high-flexion TKAs.

Trabecular resorption patterns of cement-bone interlock regions in total knee replacements

With in vivo service, there is loss of mechanical interlock between trabeculae and PMMA cement in total knee replacements. The mechanisms responsible for the loss of interlock are not known, but loss of interlock results in weaker cement-bone interfaces. The goal of this study was to determine the pattern of resorption of interdigitated bone using a series of 20 postmortem retrieved knee replacements with a wide range of time in service (3-22 years). MicroCT scans were obtained of a segment of the cement-bone interface below the tibial tray for each implant. Image processing methods were used to determine interface morphology and to identify supporting, interdigitated, resorbed, and isolated bone as a function of axial position. Overall, the amount of remaining interdigitated bone decreased with time in service (p = 0.0114). The distance from the cement border (at the extent of cement penetration into the bone bed) to 50% of the interdigitated volume decreased with time in service (p = 0.039). Isolated bone, when present, was located deep in the cement layer. Overall, resorption appears to start at the cement border and progresses into the cement layer. Initiation of trabecular resorption near the cement border may be a consequence of proximity to osteoclastic cells in the adjacent marrow space.

CLINICAL SIGNIFICANCE

Aseptic loosening of joint replacements remains an important clinical problem. This work explores the process and pattern of trabecular bone resorption responsible for loss of interface fixation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2773-2780, 2017.

The mechanical response of a polyetheretherketone femoral knee implant under a deep squatting loading condition

The current study was designed to investigate the mechanical response of a polyetheretherketone-on-polyethylene total knee replacement device during a deep squat. Application of this high-demand loading condition can identify weaknesses of the polyetheretherketone relative to cobalt-chromium. This study investigated whether the implant is strong enough for this type of loading, whether cement stresses are considerably changed and whether a polyetheretherketone femoral component is likely to lead to reduced periprosthetic bone loss as compared to a cobalt-chromium component. A finite element model of a total knee arthroplasty subjected to a deep squat loading condition, which was previously published, was adapted with an alternative total knee arthroplasty design made of either polyetheretherketone or cobalt-chromium. The maximum tensile and compressive stresses within the implant and cement mantle were analysed against their yield and fatigue stress levels. The amount of stress shielding within the bone was compared between the polyetheretherketone and cobalt-chromium cases. Relative to its material strength, tensile peak stresses were higher in the cobalt-chromium implant; compressive peak stresses were higher in the polyetheretherketone implant. The stress patterns differed substantially between polyetheretherketone and cobalt-chromium. The tensile stresses in the cement mantle supporting the polyetheretherketone implant were up to 33% lower than with the cobalt-chromium component, but twice as high for compression. Stress shielding was reduced to a median of 1% for the polyetheretherketone implant versus 56% for the cobalt-chromium implant. Both the polyetheretherketone implant and the underlying cement mantle should be able to cope with the stress levels present during a deep squat. Relative to the cobalt-chromium component, stress shielding of the periprosthetic femur was substantially less with a polyetheretherketone femoral component.

Peri-Implant Distribution of Polyethylene Debris in Postmortem-Retrieved Knee Arthroplasties: Can Polyethylene Debris Explain Loss of Cement-Bone Interlock in Successful Total Knee Arthroplasties?

BACKGROUND

Loss of mechanical interlock between cement and bone with in vivo service has been recently quantified for functioning, nonrevised, cemented total knee arthroplasties (TKAs). The cause of interlocking trabecular resorption is not known. The goal of this study is to quantify the distribution of PE debris at the cement-bone interface and determine if polyethylene (PE) debris is locally associated with loss of interlock.

METHODS

Fresh, nonrevised, postmortem-retrieved TKAs (n = 8) were obtained en bloc. Laboratory-prepared constructs (n = 2) served as negative controls. The intact cement-bone interface of each proximal tibia was embedded in Spurr's resin, sectioned, and imaged under polarized light to identify birefringent PE particles. PE wear particle number density was quantified at the cement-bone interface and distal to the interface, and then compared with local loss of cement-bone interlock.

RESULTS

The average PE particle number density for postmortem-retrieved TKAs ranged from 8.6 (1.3) to 24.9 (3.1) particles/mm2 (standard error) but was weakly correlated with years in service. The average particle number density was twice as high as distal (>5mm) to the interface compared to at the interface. The local loss of interlock at the interface was not related to the presence, absence, or particle density of PE.

CONCLUSION

PE debris can migrate extensively along the cement-bone interface of well-fixed tibial components. However, the amount of local bone loss at the cement-bone interface was not correlated with the amount of PE debris at the interface, suggesting that the observed loss of trabecular interlock in these well-fixed TKAs may be due to alternative factors.