"Backside" polyethylene deformation in total knee arthroplasty

Global mapping of institutional and hospital-based (Level II-IV) arthroplasty registries: a scoping review

PURPOSE

Four joint arthroplasty registries (JARs) levels exist based on the recorded data type. Level I JARs are national registries that record primary data. Hospital or institutional JARs (Level II-IV) document further data (patient-reported outcomes, demographic, radiographic). A worldwide list of Level II-IV JARs must be created to effectively assess and categorize these data.

METHODS

Our study is a systematic scoping review that followed the PRISMA guidelines and included 648 studies. Based on their publications, the study aimed to map the existing Level II-IV JARs worldwide. The secondary aim was to record their lifetime, publications' number and frequency and recognise differences with national JARs.

RESULTS

One hundred five Level II-IV JARs were identified. Forty-eight hospital-based, 45 institutional, and 12 regional JARs. Fifty JARs were found in America, 39 in Europe, nine in Asia, six in Oceania and one in Africa. They have published 485 cohorts, 91 case-series, 49 case-control, nine cross-sectional studies, eight registry protocols and six randomized trials. Most cohort studies were retrospective. Twenty-three per cent of papers studied patient-reported outcomes, 21.45% surgical complications, 13.73% postoperative clinical and 5.25% radiographic outcomes, and 11.88% were survival analyses. Forty-four JARs have published only one paper. Level I JARs primarily publish implant revision risk annual reports, while Level IV JARs collect comprehensive data to conduct retrospective cohort studies.

CONCLUSIONS

This is the first study mapping all Level II-IV JARs worldwide. Most JARs are found in Europe and America, reporting on retrospective cohorts, but only a few report on studies systematically.

Computational wear of knee implant polyethylene insert surface under continuous dynamic loading and posterior tibial slope variation based on cadaver experiments with comparative verification

Background

The effect of posterior tibial slope on the maximum contact pressure and wear volume of polyethylene (PE) insert were not given special attention. The effects of flexion angle, Anterior-Posterior (AP) Translation, and Tibial slope on the max contact pressure and wear of PE insert of TKR were investigated under loadings which were obtained in cadaver experiments by using Archard’s wear law. This study uses not only loads obtained from cadaver experiments but also dynamic flexion starting from 0 to 90 degrees.

Method

Wear on knee implant PE insert was investigated using a 2.5 size 3 dimensional (3D) cruciate sacrificing total knee replacement model and Finite Element Method (FEM) under loadings and AP Translation data ranging from 0 to 90 flexion angles validated by cadaver experiments. Two types of analyses were done to measure the wear effect on knee implant PE insert. The first set of analyses included the flexion angles dynamically changing with the knee rotating from 0 to 90 angles according to the femur axis and the transient analyses for loadings changing with a certain angle and duration.

Results

It is seen that the contact pressure on the PE insert decreases as the cycle increases for both Flexion and Flexion+AP Translation. It is clear that as the cycle increases, the wear obtained for both cases increases. The loadings acting on the PE insert cannot create sufficient pressure due to the AP Translation effect at low speeds and have an effect to reduce the wear, while the effect increases with the wear as the cycle increases, and the AP Translation now contributes to the wear at high speeds. It is seen that as the posterior tibial slope angle increases, the maximum contact pressure values slightly decrease for the same cycle.

Conclusions

This study indicated that AP Translation, which changes direction during flexion, had a significant effect on both contact pressure and wear. Unlike previous similar studies, it was seen that the amount of wear continues to increase as the cycle increases. This situation strengthens the argument that loading and AP Translation values that change with flexion shape the wear effects on PE Insert.

Tibial tray debonding from the cement mantle is associated with deformation of the backside of polyethylene tibial inserts

AIMS

The aim of this study was to investigate whether wear and backside deformation of polyethylene (PE) tibial inserts may influence the cement cover of tibial trays of explanted total knee arthroplasties (TKAs).

METHODS

At our retrieval centre, we measured changes in the wear and deformation of PE inserts using coordinate measuring machines and light microscopy. The amount of cement cover on the backside of tibial trays was quantified as a percentage of the total surface. The study involved data from the explanted fixed-bearing components of four widely used contemporary designs of TKA (Attune, NexGen, Press Fit Condylar (PFC), and Triathlon), revised for any indication, and we compared them with components that used previous generations of PE. Regression modelling was used to identify variables related to the amount of cement cover on the retrieved trays.

RESULTS

A total of 114 explanted fixed-bearing TKAs were examined. This included 76 used with contemporary PE inserts which were compared with 15 used with older generation PEs. The Attune and NexGen (central locking) trays were found to have significantly less cement cover than Triathlon and PFC trays (peripheral locking group) (p = 0.001). The median planicity values of the PE inserts used with central locking trays were significantly greater than of those with peripheral locking inserts (205 vs 85 microns; p < 0.001). Attune and NexGen inserts had a characteristic pattern of backside deformation, with the outer edges of the PE deviating inferiorly, leaving the PE margins as the primary areas of articulation.

CONCLUSION

Explanted TKAs with central locking mechanisms were significantly more likely to debond from the cement mantle. The PE inserts of these designs showed characteristic patterns of deformation, which appeared to relate to the manufacturing process and may be exacerbated in vivo. This pattern of deformation was associated with PE wear occurring at the outer edges of the articulation, potentially increasing the frictional torque generated at this interface. Cite this article: Bone Joint J 2021;103-B(12):1791-1801.

Joint line elevation and tibial slope are associated with increased polyethylene wear in cruciate-retaining total knee replacement

The purpose of this retrieval study was to determine the effect of implant positioning on wear, taking patient-related factors into account. Therefore, the volumetric material loss of 59 retrieved tibial liners was quantitatively determined using a coordinate measuring-machine. All retrievals were made of the same polyethylene and design by a single manufacturer. Using time in-situ and linear regression, a wear rate for each liner was determined and corrected for bedding-in. Backside damage was qualitatively scored. The following implant positioning parameters were obtained from radiographs: anatomical lateral-distal femoral angle, anatomical medial-proximal tibial angle, femoral tilt angle, and posterior tibial slope. The patella position was assessed by the Blackburne-Peel index and the Insall-Salvati ratio. Unlike the Insall-Salvati ratio, the Blackburne-Peel index is known to detect surgical joint line elevation. Using general linear modeling the most impactful factors on wear rate and backside damage was determined, thereby taking patient demographic factors into account. The mean volumetric wear rate was 11.6 mm³ /y. Wear decreased with older age (P = .021) and female sex (P = .001). The wear rate increased with joint line elevation as indicated from a decreased Blackburne-Peel index (P = .019), and increased with increased posterior tibial slope (P = .026). The backside damage score also increased with joint line elevation (P = .036). A Blackburne-Peel index decrease of 0.1, signifying joint line elevation, was found to increase the wear rate by 1.8 mm³ /y and increase back-sided wear. A high tibial slope (>7°) led to a 9.3 mm³ /y increase in wear rate compared with a low tibial slope (<3°). The results of this study demonstrate that tibial liner positioning has a significant impact on polyethylene wear with potential implications on osteolysis over time.

Popliteal Skin Lesion due to Wear Disease in Total Knee Arthroplasty: A Case Report

CASE

An 87-year-old woman presented with a popliteal skin lesion due to polyethylene wear 13 years following a left total knee arthroplasty. Excisional biopsy through a posterior approach was performed. Histology showed inflammation with granulomas and birefringent foreign body particles in the skin. Cultures remained negative, and revision knee arthroplasty was performed.

CONCLUSIONS

A popliteal skin lesion due to polyethylene wear disease in total knee arthroplasty has not previously been described. Patients with an atypical inflammation of the skin with an underlying joint implant should be referred to an orthopaedic surgeon, and dermal biopsies should be checked for birefringent material.

LEVEL OF EVIDENCE

Level V.

Severe metallosis following total knee arthroplasty: a case report and review of radiographic signs

Metallosis is an uncommon complication following total knee arthroplasty that leads to osteolysis and implant loosening due to chronic inflammatory reaction. Abrasion between the metallic surfaces of the implant releases metallic debris that interacts with the periprosthetic soft tissues and causes chronic synovitis. Here we present a case of a 65-year-old man who had undergone total knee arthroplasty 10 years ago and developed implant loosening associated with severe metallosis and varus instability. Radiographs show the three typical signs of metallosis: metal-line sign, bubble sign, and cloud sign. This patient was subjected to revision surgery consisting of debridement and primary implant replacement by a hinged endoprosthesis. Knowledge of the typical radiographic and clinical findings of metallosis is important to rapidly diagnose this complication and avoid progressive joint destruction.

Retrieval analysis of modular total knee replacements: factors influencing backside surface damage

Retrieved knee implants were examined to investigate the influence of patient and implant related factors on backside damage. Fifty-two implants of three different models were examined that all had cemented tibial trays without screw holes. A semi-quantitative grading system supplied backside damage scores (BDS) for each polyethylene (PE) tibial insert. Evidence was obtained to support the use of a constraining partial-peripheral locking mechanism and polished tibial tray surface (particularly for male patients) to reduce backside damage. Overall, male patients in the present study were associated with higher body mass and higher BDS compared with female patients. Furthermore, PE inserts sterilized by gamma-in-air had higher BDS than PE inserts sterilized in inert environments (gas-plasma or ethylene-oxide). Also, the proximal surfaces of tibial trays that had been grit-blasted showed embedded particles that may have increased backside damage. While none of these overall findings was unexpected, the present study provided detailed supporting analysis based on data from clinical retrievals, which may further support the use of a polished tibial tray combined with partial-peripheral locking mechanism to reduce BDS.

Prediction of backside micromotion in total knee replacements by finite element simulation

The micromotion at the interface between the polyethylene tibial insert and metal tibial tray [corrected] in modular total knee replacements [corrected] has been shown to contribute to wear particle-induced osteolysis and may [corrected] cause implant failure. Therefore, studying the design parameters that are involved in the backside wear process is an important task that may lead to improvement in new total knee replacements. In the present study, a finite element model was developed to predict the backside micromotion along the entire modular interface. Both the linear elastic constitutive model and non-linear J2-plasticity constitutive model were considered in the finite element model for polyethylene and were corroborated against published results obtained from displacement controlled knee simulator wear tests. The finite element simulation with the non-linear J2-plasticity constitutive model was able to predict backside micromotion [corrected] more accurately than the simulation with the linear elastic constitutive model. [corrected] The developed finite element model (including the non-linear J2-plasticity constitutive model) was then applied to assess the effects of the tibial tray locking mechanism design (dovetails versus fullperipheral [corrected] design) and different levels of interference fit on insert micromotion. The developed finite element model, implementing the non-linear J2-plasticity constitutive model, was shown to successfully predict clinical amounts of backside micromotion and could be used for the design and development of total knee replacements for the reduction of backside micromotion and polyethylene [corrected] wear.

Oxidation and fusion defects synergistically accelerate polyethylene failure in knee replacement

We have previously reported upon a cohort of patients with premature failure of such material and postulated upon the impact of abnormally high concentrations of type 2 fusion defects whereby there is a lack of particle cohesion due to incomplete diffusion. In vivo oxidation has been purported to underscore the premature failure of polyethylene. The mechanism of such remains poorly delineated. New data has now been obtained by determining substrata oxidative profiles of 10 failed Kinemax Plus modular tibial insert analyses in conjunction with fusion defect detection. The full thickness of a series of cores was analysed using infra-red spectroscopy to identify higher levels of oxidation in loaded used material at both the articulating and non-articulating regions. A comparison was made to an unused control. Articulating, loaded, areas exhibited greater local concentrations of oxidised material and wider variation of such consistent with the higher presence of fusion defects. Subsurface analysis confirmed the presence of a major oxidative peak 2mm below the surface for all loaded areas irrespective of wear. Additionally we were able to identify a second major oxidative focus about halfway between the inferior (tibial baseplate) surface and the articulating area. We believe that the combination of high oxidation and fusion defects represents a second high stress zone consistent with the observation of tibial baseplate polyethylene dissociation and backside wear with resultant catastrophic material failure.

Second-generation locking mechanisms and ethylene oxide sterilization reduce tibial insert backside damage in total knee arthroplasty

This study evaluated the effects of polyethylene quality and locking mechanism on damage to the nonarticulating (backside) surface of retrieved tibial inserts in total knee arthroplasty. Inserts with peripheral capture (PC) locking mechanisms and ethylene oxide (EtO)-sterilized polyethylene were hypothesized to prevent major backside damage. A total of 156 inserts were sorted by locking mechanism and sterilization method and analyzed by damage scoring methods. Ninety-seven specimens exhibited burnishing. Significant positive linear correlations were observed between damage score and age in vivo for all combinations, but damage occurred at a significantly lower rate for second-generation PC implants with EtO sterilization. Most specimens in this group were undamaged (46/72), with others exhibiting only burnishing. Sex, body mass index, and weight did not influence backside damage.

Wear debris pseudotumor following total knee arthroplasty: a case report

INTRODUCTION

In patients who have undergone a total joint replacement, any mass occurring in or adjacent to the joint needs thorough investigation and a wear debris-induced cyst should be suspected.

CASE PRESENTATION

An 81-year-old man presented with a painful and enlarging mass at the popliteal fossa and calf of his right knee. He had had a total right knee replacement seven years previously. Plain radiographs showed narrowing of the medial compartment. Magnetic resonance imaging showed a cystic lesion at the postero-medial aspect of the knee joint mimicking popliteal cyst or soft tissue sarcoma. Fine needle aspiration was non-diagnostic. A core-needle biopsy showed metallosis. Intraoperative findings revealed massive metallosis related to extensive polyethylene wear, delamination and deformation. Revision knee and patella arthroplasty was carried out after a thorough debridement of the knee joint.

CONCLUSION

Long-term follow-up is critical for patients with total joint replacement for early detection of occult polyethylene wear and prosthesis loosening. In these cases, revision arthroplasty may provide a satisfactory knee function.

Pre-surgical radiologic identification of peri-prosthetic osteolytic lesions around TKRs: a pre-clinical investigation of diagnostic accuracy

BACKGROUND

Emerging longitudinal data appear to demonstrate an alarming trend towards an increasing prevalence of osteolysis-induced mechanical failure, following total knee replacement (TKR). Even with high-quality multi-plane X-rays, accurate pre-surgical evaluation of osteolytic lesions is often difficult. This is likely to have an impact on surgical management and provides reasonable indication for the development of a model allowing more reliable lesion assessment. The aim of this study, using a simulated cadaver model, was to explore the accuracy of rapid spiral computed tomography (CT) examination in the non-invasive evaluation of peri-prosthetic osteolytic lesions, secondary to TKR, and to compare this to conventional X-ray standards.

METHODS

A series of nine volume-occupying defects, simulating osteolytic lesions, were introduced into three human cadaveric knees, adjacent to the TKR implant components. With implants in situ, each knee was imaged using a two-stage conventional plain X-ray series and rapid-acquisition spiral CT. A beam-hardening artefact removal algorithm was employed to improve CT image quality.After random image sorting, 12 radiologists were independently shown the series of plain X-ray images and asked to note the presence, anatomic location and 'size' of osteolytic lesions observed. The same process was repeated separately for review of the CT images. The corresponding X-ray and CT responses were directly compared to elicit any difference in the ability to demonstrate the presence and size of osteolytic lesions.

RESULTS

Access to CT images significantly improved the accuracy of recognition of peri-prosthetic osteolytic lesions when compared to AP and lateral projections alone (P = 0.008) and with the addition of bi-planar oblique X-rays (P = 0.03). No advantage was obtained in accuracy of identification of such lesions through the introduction of the oblique images when compared with the AP and lateral projections alone (P = 0.13)

CONCLUSION

The findings of this study suggest that peri-prosthetic osteolytic lesions can be reliably described non-invasively using a simple, rapid-acquisition CT-based imaging approach. The low sensitivity of conventional X-ray, even with provision of supplementary bi-planar 45 degrees oblique views, suggests a limited role for use in situ for TKR implant screening where peri-prosthetic osteolytic lesions are clinically suspected. In contrast, the accuracy of CT evaluation, linked to its procedural ease and widespread availability, may provide a more accurate way of evaluating osteolysis around TKRs, at routine orthopaedic follow up. These findings have direct clinical relevance, as accurate early recognition and classification of such lesions influences the timing and aggressiveness of surgical and non-operative management strategies, and also the nature and appropriateness of planned implant revision or joint-salvaging osteotomy procedures.

Distal leg wear debris mass from a rotating hinged knee prosthesis

An 18-year-old woman presented with a gradually increasing distal leg mass 8 years after wide resection for an osteosarcoma and reconstruction of the proximal left tibia with a rotating hinged knee megaprosthesis. Open biopsy of the distal leg mass showed necrobiotic tissue, metallosis, fibroblasts, osteoblasts, histiocytes, and multinucleated giant cells. The patient underwent debridement of the distal leg mass, metallosis, and wear debris surrounding the tibial component, followed by revision of the destructed polyethylene-bearing components. At the latest follow-up, 4 years after the revision surgery, the patient is alive and tumor-free, asymptomatic, and has no clinical or imaging evidence of wear and metallosis.

Quantification of polyethylene degradation in mobile bearing knees: a retrieval analysis of the Anterior-Posterior-Glide (APG) and Rotating Platform (RP) Low Contact Stress (LCS) knee

BACKGROUND

Routine qualitative observations of more than 850 polyethylene fixed and mobile bearings at our institution have noted minimal wear of mobile bearings. The APG mobile bearing is the most recent design variant of the LCS knee, allows multi-directional movement at the tibiofemoral articulation, and is posterior cruciate sparing. Even though it is difficult to perform, quantitative wear measurement is important in determining the likely longevity of new arthroplasty devices, and is especially relevant because of increasing numbers of new mobile bearing designs.

PATIENTS AND METHODS

We analyzed 10 retrieved APG and 7 retrieved RP tibial bearings (De Puy) with a mean implantation period of 33 (9-70) months. We used coordinate-measuring techniques to quantitatively determine linear penetration, and optical and scanning electron microscopy to assess wear mechanisms qualitatively.

RESULTS

The mean total volume loss (superior and inferior articulations) of the APG and RP designs was 85 mm((3))/year and 77 mm((3))/year, respectively. Burnishing was the predominant wear mechanism, and to a lesser extent scratching, abrasion and pitting. Multidirectional scratching and abrasion were noted on the APG inserts inferiorly, whereas there was circumferential scratching on the RP inserts.

INTERPRETATION

Our short-term results for the APG and RP mobile bearing designs are similar and compare more than favorably with reported values for fixed-bearing designs. However, increased backside wear due to multidirectional movement may predispose the APG design to greater wear in the long term.

Backside damage corresponding to articular damage in retrieved tibial polyethylene inserts

Although motion between the polyethylene insert and tibial baseplate is one probable cause of backside wear, articular contact stresses and kinematic conditions may be additional factors. However, comparisons of articular and backside damage patterns are limited. We report the effect of physiologic loading on the modular capture mechanism and distribution of articular and backside surface damage patterns on retrieved tibial components. We evaluated damage patterns on 37 tibial inserts with a full peripheral rim capture mechanism, including six autopsy-retrieved components that were not previously disassembled and were available for mechanical testing. The duration of physiologic loading affected the modular capture mechanism and damage patterns. Backside damage revealed evidence of a mechanical interlock between the polyethylene insert and tibial tray consistent with the measured insert motion. In autopsy components retrieved after 2 to 6 years, inserts with the least motion had the longest duration of in vivo function and the largest backside damage area. The backside damage area and location corresponded to articular damage with damage patterns concentrated on the posterior half of the polyethylene inserts. Substantial differences between the articular and backside damage modes suggest different wear mechanisms exist at the two interfaces during physiologic loading.

Should we reconsider all-polyethylene tibial implants in total knee replacement?

The role of modular tibial implants in total knee replacement is not fully defined. We performed a prospective randomised controlled clinical trial using radiostereophotogrammetric analysis to compare the performance of an all-polyethylene tibia with a metal-backed cruciate-retaining condylar design, PFC-∑ total knee replacement for up to 24 months. There were 51 patients who were randomised into two treatment groups. There were 10 subsequent withdrawals, leaving 21 all-polyethylene and 20 metal-backed tibial implants. No patient was lost to follow-up. There were no significant demographic differences between the groups. At two years one metal-backed implant showed migration > 1 mm, but no polyethylene implant reached this level. There was a significant increase in the SF-12 and Oxford knee scores after operation in both groups.

In an uncomplicated primary total knee replacement the all-polyethylene PFC-∑ tibial prosthesis showed no statistical difference in migration from that of the metal-backed counterpart. There was no difference in the clinical results as assessed by the SF-12, the Oxford knee score, alignment or range of movement at 24 months, although these assessment measures were not statistically powered in this study.

Clinical performance of contemporary tibial polyethylene components

A postclinical retrieval analysis was performed on 43 polyethylene tibial components of a contemporary total knee arthroplasty system with implantation duration between 12 and 80 months. Components were scored for 8 potential modes of surface wear or damage on the top and back surfaces. Moderate backside wear of 4.1 microm/y was documented by measuring the extent of manufacturer's engraved lettering removal. Neither the topside nor backside score correlated with duration of in vivo function. No component experienced topside or backside delamination, cracking, or significant deformation. The greatest contribution to wear and damage score was pitting and scratching secondary to bone cement debris. The extent of both wear and damage experienced by these components was moderate, in comparison with that previously reported with older implant systems.

Sports after total joint replacement

Today's patients require additional guidance in their expectations after replacement surgery. Failure rates for shoulder, hip, and knee replacements across most studies are approximately 0.5% to 1% per year, including infection, loosening, and wear of the parts. Elbow and ankle replacements will likely require more restrictions and have slightly higher revision rates.