Wear-pattern analysis in retrieved tibial inserts of mobile-bearing and fixed-bearing total knee prostheses

A Polished Cobalt-Chrome Baseplate is not Associated With a Lower Revision Rate Than Matt Titanium in a Single Total Knee Arthroplasty Implant System With Identical Baseplate Design

BACKGROUND

Polished baseplates were introduced into total knee arthroplasty (TKA) systems to reduce the incidence of backside wear. In 2004, a fixed-bearing knee arthroplasty system underwent a change in baseplate material from matt titanium to polished cobalt-chrome (CoCr) with the intention to reduce backside wear. Other design aspects were left unchanged. The aim of this study was to compare these implants with each baseplate using data from the Australian Orthopaedic Association National Joint Replacement Registry.

METHODS

Primary TKA procedures performed between January 2010 and December 2021 for osteoarthritis, using a single design with cross-linked polyethylene inserts and matt titanium or polished CoCr baseplates, were analyzed. The primary outcome was all-cause revision, summarized using Kaplan-Meier estimates, with age- and sex-adjusted hazard ratios estimated from Cox proportional hazards models. In total, there were 2,091 procedures with matt titanium and 2,519 procedures with polished CoCr baseplates.

RESULTS

The 9-year cumulative percent revision was 2.5% (95% confidence interval [CI] 1.8 to 3.5%) and 4.2% (95% CI 3.1 to 5.6%) for the matt titanium and CoCr groups, respectively. Compared to matt titanium, the revision rate of CoCr baseplates was not significantly higher (hazard ratio 1.44; 95% CI 0.96 to 2.15; P = .076).

CONCLUSIONS

Polished CoCr baseplates in a single TKA system were not associated with reduced all-cause revision rates compared to matt titanium up to 11 years post-TKA. Our results suggest that the predicted reduction in wear particle debris production from polished CoCr baseplates may not correlate with reduced revision rates in vivo, but further evaluation is required.

Outcomes of Total Ankle Arthroplasty After Periprosthetic Cyst Curettage and Bone Grafting

Total ankle arthroplasty (TAA) has become a popular management option for ankle arthritis. Periprosthetic osteolysis is one of the most common causes for reoperation in TAA. A CT scan should be done in all suspected osteolysis cases to confirm location, quantify size and aid in surgical planning. These patients are often asymptomatic with limited evidence regarding appropriate management. Smaller lesions should be monitored for progression in size. Periprosthetic cysts measuring 10-15mm in all three axes should be considered for debridment and curettage with autogenous bone grafting. The authors believe that bone grafting of large asymptomatic periprosthetic cysts could prevent implant failure.

Less wear in deep-dished mobile compared to fixed bearing total knee arthroplasty of the same design at 5-year follow-up: a randomised controlled model-based Roentgen stereophotogrammetric analysis trial

PURPOSE

The aim of this prospective randomised controlled study was to compare wear characteristics and functional outcome between deep-dished mobile bearing (MB) and fixed bearing (FB) cemented total knee arthroplasty (TKA). We hypothesised that deep-dished MB reduces polyethylene wear and improves patient-reported outcome measures.

METHODS

A total of 50 patients were randomised to receive a MB or FB tibia component of the same cemented TKA design. Patients were evaluated over a 5-year follow-up period. Medial and lateral wear were assessed using model-based Roentgen Stereophotogrammetric Analysis (RSA) and compared with the direct postoperative minimal joint space measurement. Functional outcome was assessed by the clinician-derived KSS and OKS, WOMAC, LEAS, and FJS-12. All data were derived using a general linear mixed model.

RESULTS

At 5-year follow-up, decreased wear in the MB compared to the FB group was observed on the lateral side (0.07 ± 0.17 mm, p = 0.026), but not on the medial side (0.31 ± 0.055 mm, p = 0.665). Functional outcomes improved with a statistical significant effect over time, with no significant differences between groups (all p > 0.17).

CONCLUSION

This model-based RSA study with 5-year follow-up showed that cemented deep-dished MB reduced lateral polyethylene wear as compared to FB in a single TKA system, whilst clinical outcomes were comparable. Longer follow-up is needed to establish clinical implications of these altered wear patterns and determine type of wear.

LEVEL OF EVIDENCE

Level 1 randomised controlled trial.

Wider translations and rotations in posterior-stabilised mobile-bearing total knee arthroplasty compared to fixed-bearing both implanted with mechanical alignment: a dynamic RSA study

PURPOSE

The purpose of this study was to investigate the in vivo kinematics of the same femoral design mechanically aligned posterior-stabilised (PS) total knee arthroplasty (TKA) with either fixed-bearing (FB) or mobile-bearing (MB) inlay, implanted by the same surgeon, using model-based dynamic radiostereometric analysis (RSA). The hypothesis of the present study was that the MB design would show wider axial rotation than the FB design, without affecting the clinical outcomes.

MATERIALS AND METHODS

A cohort of 21 non-randomised patients (21 DePuy Attune PS-FB) was evaluated by dynamic RSA analysis at a minimum 9-month follow-up, while performing differently demanding daily living activities such as sit to stand (STS) and deep knee lunge (DKL). Kinematic data were compared with those of a cohort of 22 patients implanted with the same prosthetic design but with MB inlay. Anterior-posterior (AP) translations, varus-valgus (VV) and internal-external (IE) rotations of the femoral component with respect to the tibial baseplate were investigated. Translation of medial and lateral compartment was analysed using the low point method according to Freeman et al. Questionnaires to calculate objective and subjective clinical scores were administered preoperatively and during follow-up visit by the same investigator.

RESULTS

The FB TKA design showed lower AP translation during STS (6.8 ± 3.3 mm in FB vs 9.9 ± 3.7 mm in MB, p = 0.006*), lower VV rotation (1.9 ± 0.8° in FB vs 5.3 ± 3.3° in MB, p = 0.005) and lower IE rotation (2.8 ± 1.1° in FB vs 9.5 ± 4.3° in MB, p = 0.001) during DKL than the mobile-bearing TKA design. Posterior-stabilised FB group showed significant lower translation of the low point of the medial compartment than the MB group (p = 0.008). The percentage of patients performing medial pivot in the FB group was higher compared to MB group in the examined motor tasks. No significant differences in post-operative range of motion (117° ± 16° for FB group and 124° ± 13° for MB group) and in clinical outcomes emerged between the two cohort.

CONCLUSIONS

The FB and MB designs differed in AP translations, VV rotations and IE rotations of the femoral component with respect to the tibial component in STS and DKL. Furthermore, FB cohort reported a significant higher percentage of medial pivot with respect to MB cohort. Despite this, no differences in clinical outcomes were detected between groups. Both designs showed stable kinematics and represent a viable option in primary TKA.

LEVEL OF EVIDENCE

Prospective cohort study, II.

A Postmortem Analysis of Polyethylene Damage and Periprosthetic Tissue in Rotating Platform and Fixed Bearing Tibial Inserts

BACKGROUND

Mobile bearing designs are intended to reduce wear, but mixed results were reported from retrieval analyses. Postmortem evaluation (PM) provides the opportunity to assess polyethylene damage in successful implants. We compared damage patterns, MRI presentation, and histology between mobile-bearing and fixed tibial inserts retrieved postmortem and compared these results to our prior findings from implants retrieved at revision.

METHODS

Eleven postmortem knees with rotating platform (RP) implants and 13 with fixed bearing (FB) implants were examined. All were MRI scanned, and tissue samples were collected from standardized regions for histology. Polyethylene inserts were subjectively scored to assess articular, backside, and PS post surfaces for damage modes and severity.

RESULTS

Average duration of implantation was 9.3 years (1.7-19.6 years). Surface burnishing was the most common polyethylene damage mode. Average damage scores were higher for RP (53.4) compared to FB inserts (34.4) due to greater backside damage (13.4 for RP vs 1.4 for FB). A minimal difference in damage was observed on the articular surfaces (37.4 RP vs 30.0 FB). Mild innate macrophage reactions were seen in 8 (72.7%) RP and 5 (45.5%) FB specimens. Polyethylene particles were identified in 7 (63.6%) RP and 3 (27.7%) FB specimens.

CONCLUSIONS

Postmortem inserts showed low damage levels and mild tissue reactions compared to those reported for implants removed at revision arthroplasty. Nonetheless, trends in comparing RP and FB inserts were consistent with those seen in retrieval analyses, demonstrating the usefulness of retrieval studies in capturing performance differences among TKA designs.

No significant clinical and radiological differences between fixed versus mobile bearing total knee replacement using the same semi-constrained implant type: a randomized controlled trial with mean 10 years follow-up

PURPOSE

The aim of this study was to compare the long-term clinical and radiological results between fixed (FB) and mobile bearing (MB) implants with identical design from the same manufacturer.

METHODS

From March 2007 to May 2009, we recruited 160 patients in a prospective, single centered, randomized controlled trial. The authors compared 81 FB total knee arthroplasty (TKA) versus 79 MB with medial compartment osteoarthritis. The same posterior stabilized HLS Noetos knee prosthesis (CORIN) was used in all patients. The two groups only differed by the tibial insert (fixed or mobile). The authors compared the postoperative Knee Society Score (KSS), the passive clinical and active radiological knee flexion, the implant survivorship, the complications, and the presence of radiolucent lines.

RESULTS

At mean 10.5 years' follow-up (range 8-12.1 years) no significant differences were found in clinical scores (KSS (p = 0.54), pain score (p = 0.77), stair climbing (p = 0.44), passive maximum flexion (p = 0.5)) or for radiological analyses (maximum active radiological flexion (p = 0.06), presence of progressive radiolucent lines (5 (MB group) versus 6 (FB group); p = 0.75)) between groups. No significant difference was found in overall implant survivorship (82% (MB group) versus 78% (FB group) p = 0.58) or complication rate (p = 0.32) at the last follow-up.

CONCLUSION

No significant clinical and radiological differences were found between fixed and mobile bearing TKA using the same semi-constrained implant type with comparable overall survivorship. The choice between a fixed or mobile bearing implant should be based on surgeon preference and experience with the selected implant.

LEVEL OF EVIDENCE

Prospective randomized controlled trial, Level II.

Effect of material selection on tibial post stresses in posterior-stabilized knee prosthesis

Aims

The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated.

Methods

Three different grades of polyethylene were compared in this study; conventional ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE). In addition, tibial baseplates with a fixed-bearing and a mobile-bearing insert were evaluated to understand differences in the contact properties. The inserts were implanted in neutral alignment and with a 10° internal malrotation. The contact stress, von Mises stress, and equivalent plastic strain (PEEQ) on the tibial posts were extracted for comparison.

Results

The stress and strain on the tibial post for the three polyethylenes greatly increased when the insert was placed in malrotation, showing a 38% to 56% increase in von Mises stress and a 335% to 434% increase in PEEQ. The VEPE insert had the lowest PEEQ among the three materials. The mobile-bearing design exhibited a lower increase in stress and strain around the tibial posts than the fixed-bearing design.

Conclusion

Using VEPE for the tibial component potentially eliminates the risk of material permanent deformation. The mobile-bearing insert can help to avoid a dramatic increase in plastic strain around the tibial post in cases of malrotation. The mobility allows the pressure to be distributed on the tibial post and demonstrated lower stresses with all three polyethylenes simulated.

Cite this article: Bone Joint Res 2020;9(11):768–777.

Bearing Thickness Is Not a Predictive Factor for Damage and Penetration in Oxford Unicompartmental Knee Arthroplasty-A Retrieval Analysis

The medial Oxford unicompartmental knee arthroplasty (OUKA) shows good survivorship, as well as clinical results. Aseptic loosening, however, remains one of the main reasons for revision and polyethylene debris is known to cause aseptic loosening. The role of bearing thickness in total as well as unicondylar knee arthroplasty has been the subject of controversial discussions, especially the longevity of lower thickness bearings in total knee arthroplasty was questioned. The purpose of this study was to assess the influence of bearing thickness on time to revision, damage pattern, penetration, and volumetric material loss. A cohort of 47 consecutively retrieved medial OUKA bearings was analyzed with conventional direct light microscopy applying the Hood damage analysis, as well as measuring the penetration depth. In this retrieval cohort, a difference on survival time, damage, penetration, as well as volumetric material loss could not be seen. We conclude that low as well as high thickness bearings can safely be used in OUKA without any relevant differences in terms of wear and damage.

Retrieval analysis of TiN (titanium nitride) coated knee replacements: Coating wear and degradation in vivo

INTRODUCTION

Titanium nitride (TiN) coatings are used in joint arthroplasty to minimize wear and reduce the allergenic potential of metal implants, yet little is known about their performance in knee arthroplasty. This retrieval study examined TiN coated knee replacements to verify in vivo wear and degradation of the coating.

MATERIALS AND METHODS

This study included total and unicompartmental mobile bearing knee replacements retrieved from five patients (eight components) after 13-21 months due to aseptic loosening or infection. Implants were examined using scanning (SEM) and optical microscopy, surface damage was assessed using a semiquantitative scoring system, adhesion was determined using indentation technique testing, surface roughness was measured using contact profilometry.

RESULTS

Although good coating adhesion and no gross failure were observed on all retrievals, coating wear and roughening were evident on tibial bearing surfaces. Multiple microscopic defects (pinholes, craters, titanium droplets) were observed on all samples in SEM studies. Microscopic wear scars indicated that particulate defects significantly contributed to coating wear, acting as third bodies.

CONCLUSION

TiN coatings of knee replacements undergo wear and degradation related to presence of third bodies and microscopic defects on their surface. Since coating integrity may be compromised in vivo, such implants should be used with caution in metal sensitive patients.

Peri-prosthetic bone cysts after total ankle replacement. A systematic review and meta-analysis

BACKGROUND

Periprosthetic cystic osteolysis is a well-known complication of total ankle replacement. Several theories have been proposed for its aetiology, based on individual biomechanical, radiological, histopathology and outcome studies.

METHODS

Studies that met predefined inclusion/exclusion criteria were analysed to identify literature describing the presence of peri-prosthetic ankle cystic osteolysis. Quantitative data from the selected articles were combined and statistically tested in order to analyse possible relations between ankle peri-prosthetic bone cysts and specific implant characteristics.

RESULTS

Twenty-one articles were elected, totalizing 2430 total ankle replacements, where 430 developed peri-prosthetic cystic osteolysis. A statistically significant association (P<.001) was found between the presence of bone cysts and non-anatomic implant configuration, hydroxyapatite-coating, mobile-bearing and non tibial-stemmed implants. No significant association existed between the type of constraining and the presence of cysts (P>.05).

CONCLUSIONS

Non-anatomic, mobile-bearing, hydroxyapatite-coated and non tibial-stemmed total ankle replacements are positively associated with more periprosthetic bone cysts.

Comparison of ISO 14243-1 to ASTM F3141 in terms of wearing of knee prostheses

BACKGROUND

The wear properties of knee implants need to be thoroughly evaluated prior to clinical use to ensure implant longevity. ISO 14243-1:2009 and ASTM F3141-17 are the two standards typically used for evaluating wear, with the ISO standard being more common; ASTM F3141-17 was first released in 2015. The aim of this study is to compare differences between these two standards in terms of wearing on a knee prosthesis.

METHODS

Using finite element analysis based on Archard's law, this study evaluated anterior-posterior and internal-external motion, contact area, contact force, contact stress, volumetric wear rate, wear depth, and wear distribution on the knee prosthesis.

FINDINGS

The results show that simulations performed according to ASTM F3141 produced knee kinematics that were more similar to human gait. The maximum wear depth occurred on the medial side of the tibia. However, the region of peak contact stress did not always correspond with the region of the maximum wear depth, indicating that considering the contact stress alone is not sufficient for evaluating wear as the sliding distance also plays an important role. The resulting wear region from the ASTM F3141 simulation was smaller but deeper than the wear region from the simulation per ISO 14243-1. However, the volumetric wear rates were very similar, with 13.48-55.26 mm³/million for ASTM F3141 and 13.64-54.9 mm³/million for ISO 14243-1.

INTERPRETATION

The resulting rate of wear is almost identical between ISO 14243-1 and ASTM F3141. However, there are differences in wear contours and wear depth.

A randomized prospective study comparing mobile-bearing against fixed-bearing PFC Sigma cruciate-retaining total knee arthroplasties with ten-year minimum follow-up

AIMS

This study compares the PFC total knee arthroplasty (TKA) system in a prospective randomized control trial (RCT) of the mobile-bearing rotating-platform (RP) TKA against the fixed-bearing (FB) TKA. This is the largest RCT with the longest follow-up where cruciate-retaining PFC total knee arthroplasties are compared in a non-bilateral TKA study.

PATIENTS AND METHODS

A total of 167 patients (190 knees with 23 bilateral cases), were recruited prospectively and randomly assigned, with 91 knees receiving the RP and 99 knees receiving FB. The mean age was 65.5 years (48 to 82), the mean body mass index (BMI) was 29.7 kg/m² (20 to 52) and 73 patients were female. The Knee Society Score (KSS), Knee Society Functional Score (KSFS), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), and 12-Item Short-Form Health Survey Physical and Mental Component Scores (SF-12 PCS, SF-12 MCS) were gathered and recorded preoperatively, at five-years' follow-up, and at ten years' follow-up. Additionally, Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected at five- and ten-year follow-ups. The prevalence of radiolucent lines (RL) on radiographs and implant survival were recorded at five- and ten-year follow-ups.

RESULTS

At the ten-year follow-up, the RP group (n = 39) had a statistically significant superior score in the OKS (p = 0.001), WOMAC (p = 0.023), SF-12 PCS (p = 0.019), KOOS Activities of Daily Living (ADL) (p = 0.010), and KOOS Sport and Recreation (Sport/Rec) (p = 0.006) compared with the FB group (n = 46). The OKS, SF-12 PCS, and KOOS Sport/Rec at ten years had mean scores above the minimal clinically important difference (MCID) threshold. There was no significant difference in prevalence of radiolucency between groups at five-years' follow-up (p = 0.449), nor at ten-years' follow-up (p = 0.08). Implant survival rate at 14 years postoperative was 95.2 (95% CI 90.7 to 99.8) and 94.7 (95% CI 86.8 to 100.0) for the RP and FB TKAs, respectively.

CONCLUSION

At ten-year follow-up, the mobile-bearing knee joint arthroplasty had statistically and clinically relevant superior OKS, SF-12 PCS, and KOOS (Sport/Rec) than the fixed-bearing platform. No difference was seen in prevalence of radiolucent lines. There was a greater than 94% implant survival rate for both cohorts at 14 years. Cite this article: Bone Joint J 2018;100-B:1336-44.

No differences between fixed- and mobile-bearing total knee arthroplasty

PURPOSE

For years, numerous studies have been performed to determine whether mobile-bearing total knee arthroplasty (MB-TKA) or fixed-bearing total knee arthroplasty (FB-TKA) is the preferential design in total knee arthroplasty. Reviews and meta-analyses on this subject have focused on a relatively small number of randomised controlled trials, possibly missing important results of smaller studies. The goal of this review was to provide a comprehensive overview of all literature comparing MB-TKA and FB-TKA in the treatment of osteoarthritis of the knee.

METHODS

An extensive literature search was performed in the PubMed database. All studies that compared MB-TKA with FB-TKA and looked at one of four theorised advantages (insert wear, signs of loosening, survival rate of the prosthesis and clinical outcome) were included.

RESULTS

The initial search yielded 258 articles, of which 127 were included after the first screening. The included studies consisted of 9 meta-analyses, 3 systematic reviews, 48 RCT's, 44 comparative studies, 10 reviews and 13 studies that examined patients who received bilateral TKA (one MB-TKA and one FB-TKA). Combining the results of all studies showed that almost all studies found no difference between MB-TKA and FB-TKA.

CONCLUSIONS

Even when examining all different types of studies on MB-TKA and FB-TKA, the results of this review showed no difference in insert wear, risk of loosening, survivorship or clinical outcome. In daily practice, the choice between MB-TKA and FB-TKA should be based on the experience and judgment of the surgeon, since no clear differences are observed in the scientific literature.

LEVEL OF EVIDENCE

III.

[Effectiveness comparison of mobile-bearing and fixed-bearing prostheses in total knee arthroplasty for ten years follow-up]

Objective

To compare the clinical results of mobile-bearing and fixed-bearing prostheses in total knee arthroplasty (TKA) during 10 years follow-up so as to provide a reference for clinical selection of TKA prosthesis.

Methods

Between January 2002 and December 2005, 113 patients with osteoarthritis of the knee joint underwent primary TKA, and the clinical data were retrospectively analyzed. Mobile-bearing prosthesis was used in 47 cases (group A) and fixed-bearing prosthesis in 66 cases (group B). There was no significant difference in age, gender, body mass index, varus and flexion deformity of the knee, range of motion (ROM) of the knee, knee society score (KSS), and Western Ontario and McMaster University Osteoarthritis Index (WOMAC) between 2 groups before operation ( P>0.05), so the data were comparable.

Results

The operation time of groups A and B was (88.1±6.5) and (90.3±7.2) minutes respectively, showing no significant difference ( t=1.666, P=0.099). The wounds healed by first intention in all patients of both groups, and no postoperative early complications of incision infection and deep venous thrombosis occurred. The follow-up time was 10.2-12.3 years (mean, 10.8 years) in group A, and was 10.2-12.6 years (mean, 11.3 years) in group B. Revision was performed in 3 cases of group A and 4 cases of group B; the survival rates of prosthesis were 93.6% and 93.9% in groups A and B respectively, showing no significant difference ( χ²=0.005, P=0.944). The postoperative knee ROM, KSS score, and WOMAC score were significantly improved when compared with preoperative ones ( P<0.05). The knee ROM and KSS score of group B were significantly better than those of group A at 6 weeks after operation ( P<0.05), but no significant difference was found between 2 groups at 1, 3, and 10 years after operation ( P>0.05). The WOMAC score of group A was significantly better than that of group B at 10 years after operation ( t=2.086, P=0.037), but no significant difference was shown at 6 weeks, 1 year, and 3 years after operation ( P>0.05). At 10 years after operation, the excellent and good rate of KSS score was 87.2% in group A and was 84.8% in group B, showing no significant difference ( χ²=0.018, P=0.893).

Conclusion

Good medium- and long-term clinical results can be achieved in TKA with both mobile-bearing and fixed-bearing prostheses. The TKA with fixed-bearing prosthesis is relatively simple with better early effectiveness of rehabilitation; and the TKA with mobile-bearing prosthesis could provide better long-term degree of satisfaction in WOMAC score, but a higher surgical skill and soft tissue balance techniques are needed.

Comparison of Tibial Insert Polyethylene Damage in Rotating Hinge and Highly Constrained Total Knee Arthroplasty: A Retrieval Analysis

This study compared the damage scores and damage patterns in 19 tibial inserts from rotating hinge (RH) implants with 19 inserts from highly constrained (HC) implants. Each insert was divided into 16 damage zones and each zone was subjectively graded from a scale of 0-3 for seven different damage modes. The overall damage scores were comparable for the two groups (RH: 64.1 ± 15.4; HC: 66.1 ± 29.0; P = 0.59). The HC group, however, had greater post damage (compared to the post-hole of RH) while the RH group had greater backside damage. The pattern of damage was also different, with burnishing and cold flow being more common in HC group while pitting, scratching and embedded debris were more common in the RH group.

The potential role of strontium ranelate in treating particle-induced osteolysis

Ultra high molecular weight polyethylene (UHMWPE) wear-particle-induced osteolysis is one of the major issues affecting the long-term survival of total joint prostheses. Currently, there are no effective therapeutic options to prevent osteolysis from occurring. The aim of this study was to evaluate the role of strontium ranelate (SR) in reducing the risk of particle-induced osteolysis. Forty-eight C57BL/6J ultra-high molecular weight polyethylene (UHMWPE) particle-induced murine calvarial osteolysis models were used. The mice were randomized into four groups as: sham (Group 1), UHMWPE particles (Group 2), and SR with UHMWPE particles (Group 3 and Group 4). Groups 1 to 3 were sacrificed at two weeks and group 4 was sacrificed at the fourth week. The skulls were then analyzed with a high-resolution micro-CT. Histological evaluation was then conducted and osteoclast numbers were analyzed for comparison. Based on the micro-CT, percentage bone volume and trabecular thickness were found to be significantly higher in Group 4 than in Group 2 (p<0.001). Osteoclast numbers in SR treated groups (Group 3 and Group 4) were reduced when compared to groups that did not receive SR treatment (Group 2). These results indicated that SR treatment helps to increase bone volume percentage and trabecular thickness and also suppresses osteoclast proliferation. It is suggested that oral SR treatment could serve as an alternative therapy for preventing particle-induced osteolysis.

In vivo biological response to highly cross-linked and vitamin e-doped polyethylene--a particle-Induced osteolysis animal study

Polyethylene particle-induced osteolysis is the primary limitation in the long-term success of total joint replacement with conventional ultra high molecular weight polyethylene (UHMWPE). Highly cross-linked polyethylene (HXLPE) and vitamin E-doped cross-linked polyethylene (VE-HXLPE) have been developed to increase the wear resistance of joint surfaces. However, very few studies have reported on the incidence of particle-induced osteolysis for these novel materials. The aim of this study was to use a particle-induced osteolysis animal model to compare the in vivo biological response to different polymer particles. Three commercially available polymers (UHMWPE, HXLPE, and VE-HXLPE) were compared. Osseous properties including the bone volume relative to the tissue volume (BV/TV), trabecular thickness (Tb. Th), and bone mineral density (BMD) were examined using micro computed tomography. Histological analysis was used to observe tissue inflammation in each group. This study demonstrated that the osseous properties and noticeable inflammatory reactions were obviously decreased in the HXLPE group. When compared with the sham group, a decrease of 12.7% was found in BV/TV, 9.6% in BMD and 8.3% in Tb.Th for the HXLPE group. The heightened inflammatory response in the HXLPE group could be due to its smaller size and greater amount of implanted particles. Vitamin E diffused in vivo may not affect the inflammatory and osteolytic responses in this model. The morphological size and total cumulative amount of implanted particles could be critical factors in determining the biological response.

Does increased topside conformity in modular total knee arthroplasty lead to increased backside wear?

BACKGROUND

Modular metal-backed tibia components allow surgeons intraoperative flexibility. Although it is known that modular tibia components introduce the possibility for backside wear resulting from relative motion between the polyethylene insert and the tibial baseplate, it is not known to what degree variability in the conformity of the tibial polyethylene liner itself might contribute to backside wear.

QUESTIONS/PURPOSES

The purpose of this study was to determine whether a flat, cruciate-retaining tibial polyethylene bearing generates less backside wear than a more conforming (curved) tibial polyethylene bearing in an analysis of specimens explanted during revision surgery.

METHODS

The study included 70 total knee inserts explanted at revision surgery, all implanted and explanted by the same surgeon. Two different cruciate-retaining insert options in an otherwise similar knee system were used: one with a curved-on-flat (17) articular geometry and one with a highly conforming curved-on-curved design (53); both groups were sequential cohorts. The composite backside wear depth for the insert as well as the volume of backside wear was measured and compared between groups.

RESULTS

The median linear backside-normalized wear for the posterior lipped inserts was 0.0063 mm/year (range, 0-0.085 mm/year), which was lower than for the curved inserts at 0.05 mm/year (range, 0.00003-0.14 mm/year) (p<0.001). The median calculated volumetric backside-normalized wear for the posterior lipped inserts was 14.2 mm3/year (range, 0-282.8 mm3/year) compared with 117 mm3/year (range, 2.1-312 mm3/year) for the curved inserts (p<0.001).

CONCLUSIONS

In this retrieval study, more conforming tibial inserts demonstrated more backside-normalized wear than the flatter designs. This suggests that in this modular total knee arthroplasty design, higher articular conformity to address the issues of high bearing contact stress comes at a price: increased torque transmitted to the backside insert-to-tray interface. We suggest further work be undertaken to examine newer insert designs to evaluate if our conclusions hold true with the newer generation locking mechanism, tibial tray finish and polyethylene designs, as more highly conforming tibial inserts are introduced into the market.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Assessment of reactive synovitis in rotating-platform posterior-stabilized design: a 10-year prospective matched-pair MRI study

This is the first long-term (mean 11.6 years), prospective, matched-pair study (based on age, gender, BMI and UCLA scores) using MAVRIC (multi-acquisition variable-resonance image combination) magnetic resonance imaging to analyze reactive synovitis and osteolysis between rotating-platform posterior-stabilized (RP-PS), fixed-bearing metal-back (FB-MB), and all-polyethylene tibial (APT) in active patients (24 total, 8 in each group, mean age of 64 years, mean UCLA of 8.5) with identical femoral component and polyethylene. Reactive synovitis was observed in 6 RP-PS (75%), all 8 FB-MB (100%), and 6 APT (75%). There was a significant difference between the RP-PS and FB-MB knees in volumetric synovitis (P=0.023). Osteolysis with bone loss more than 4mm was seen in 3 FB-MB, 2 APT and none for RP-PS. These were not statistically significant.

Intermediate outcome of a cruciate-retaining tibia

The use of an all-polyethylene tibia in total knee arthroplasty is being revisited as a means to decrease backside polyethylene wear and lessen cost. The Depuy Sigma all-polyethylene tibia (Depuy Orthopedics, Warsaw, Indiana) has been reported with good outcomes at a greater than 10-year interval, whereas the Biomet AGC I beam design (Biomet, Warsaw, Indiana) has had a high failure rate at an early interval. This is a retrospective review of another design. One hundred seventy patients (190 cruciate-retaining total knee replacements) with a Scorpio (Stryker, Mahwah, New Jersey) all-polyethylene implant and tibia were identified in the authors' registry. This implant was chosen for all octogenarians deemed fit for a cruciate-retaining knee and a few septuagenarians who were deemed likely to remain inactive postoperatively for reasons other than knee arthritis. Mean follow-up was 38 months (range, 24-83 months). Mean patient age was 83.1 years (range, 72.7-93.8 years). Twenty-seven patients (29 knees) were lost to follow-up. Nineteen patients (24 knees) died before 24-month follow-up; all implants were in place, and no deaths were associated with the index procedure. Fifty-one patients (55 knees) were followed by telephone interview only and 75 patients (81 knees) by an office visit with radiograph analysis. One tibia revision was performed 2 months postoperatively for an implant placed in extension and varus. No infections, component wear, radiolucent lines, or impending revisions of the remaining cohort occurred. Lower Extremity Activity Scale scores ranged from 2 to 10 (mean score, 6.8), which demonstrated success even in patients with an active lifestyle. This previously unreported design is a promising all-polyethylene tibia alternative for total knee arthroplasty in older patients.

The 2012 Mark Coventry award: a retrieval analysis of high flexion versus posterior-stabilized tibial inserts

BACKGROUND

High flexion (HF) implants were introduced to increase ROM and patient satisfaction, but design changes to the implant potentially have deleterious effects on polyethylene wear. It is unclear whether the HF implants affect wear.

QUESTIONS/PURPOSES

We therefore examined whether the design changes between HF and posterior-stabilized (PS) tibial inserts would affect overall damage or damage on their articular surface, backside, and tibial post and whether flexion angle achieved related to damage.

METHODS

We matched 20 retrieved HF inserts to 20 retrieved PS inserts from the same implant system on the basis of duration of implantation, body mass index, and age. Inserts were divided into 16 zones and a microscopic analysis of surface damage was carried out. Five inserts were scanned using micro-CT to further quantify instances of severe post notching. We determined overall damage with a scoring system.

RESULTS

We found greater backside and post damage in the HF group but no difference in the articular surface or overall damage scores. Backside and post damage scores correlated to flexion angle in the HF group. There was no flexion/damage correlation in the PS group. Notch depths around the post in both groups ranged from 0.6 to 1.9 mm.

CONCLUSIONS

HF inserts are more susceptible to post damage, possibly as a result of higher contact stresses from greater flexion. The increased backside damage was unexpected because the two groups have the same tibial component, locking mechanism, and sterilization method.

CLINICAL RELEVANCE

The introduction of a highly crosslinked HF insert will require close scrutiny as a result of the potential for post damage demonstrated in this series.

Can microcomputed tomography measure retrieved polyethylene wear? Comparing fixed-bearing and rotating-platform knees

BACKGROUND

Wear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear.

QUESTIONS/PURPOSES

We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear.

METHODS

We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52 months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear.

RESULTS

The average total wear was 254 ± 248 mm(3). The average wear rate was 58 ± 41 mm(3)/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm(3)/year and the fixed-bearing rate was 74 ± 49 mm(3)/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate.

CONCLUSIONS

Micro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.

Influence of time in-situ and implant type on fixation strength of cemented tibial trays - a post mortem retrieval analysis

BACKGROUND

Loosening of the tibial tray is cited as the most common cause of failure in total knee arthroplasty but the mechanism remains unclear. Post mortem specimens provide a unique opportunity to investigate the clinical condition.

METHODS

Twenty two cemented components were serially retrieved in situ at autopsy from a university clinic. They were investigated for mechanical stability by pull-out, which was related to cement morphology and bone quality from CT scans, and to polyethylene wear by score analysis. Implants were grouped into three types: a particular fixed bearing design (n=8), a particular rotating platform design (n=5) and other mixed designs (n=9).

FINDINGS

Trends were observed for pull-out force to decrease with time in situ and increase with cement penetration but was unrelated to bone density or polyethylene wear. For the fixed bearing implants decreasing pull-out strength was related to an increasing proportion of failure at the bone-cement interface. For the mixed designs the opposite was observed. The rotating platform implants failed at the implant-cement interface.

INTERPRETATION

The analysis demonstrated that interface failure is dependent on the implant design, but that both the stem and the bone interfaces weaken with time in situ. Published findings for laboratory implantations have demonstrated that greater cement penetration improves fixation and this was reflected for clinical samples in this study.

In vivo kinematics of high-flex mobile-bearing total knee arthroplasty, with a new post-cam design, in deep knee bending motion

PURPOSE

The objective of this study was to evaluate the in vivo knee kinematics to assess the available functional motion of the characteristic mobile-bearing prosthesis design and to examine whether the artificial joint would work in vivo according to its design concept.

METHODS

We studied 14 knees (11 patients) implanted with the Vanguard RP Hi-Flex prosthesis. This prosthesis has a highly original form of post-cam called a PS saddle design with high compatibility, and with a rotating plate mobile-bearing mechanism. The cylinder-type post-cam is designed to enable contact in early flexion ranges, and to prevent paradoxical anterior femoral component movement. Each patient performed weight-bearing deep knee bending under fluoroscopic surveillance. Motion between each component including the polyethylene insert was analyzed using the 2D/3D registration technique.

RESULTS

The mean range of motion was 122.0°. The mean femoral component rotation for the tibial tray was 5.0°. No paradoxical anterior movement of the nearest point was confirmed between the femoral component and the tibial tray in the early flexion ranges. Initial contact of the post-cam was confirmed at a knee flexion angle of 33.8°. Subsequently, the wide contact of the post-cam was maintained until flexion reached 120° in all knees, but disengagement of the post-cam was observed in two knees when flexion was ≥130°.

CONCLUSIONS

The results of this study demonstrated that the prosthesis design generally works in vivo as intended by its design concept. The present kinematic data may provide useful information for improvement of high-flex type prostheses.

Knee wear measured in retrievals: a polished tray reduces insert wear

BACKGROUND

Polyethylene wear is often cited as the cause of failure of TKA. Rotating platform (RP) knees show notable surface damage on the rotating surface raising concerns about increased wear compared to fixed bearing inserts.

QUESTIONS/PURPOSES

We therefore addressed the following questions: Is wear in RP inserts increased compared to that in fixed bearing inserts? Does the surface roughness of the tibial tray have a measurable impact on in vivo wear of modular knees? And does wear rate differ between posterior stabilized (PS) and cruciate retaining (CR) knees?

METHODS

We compared wear in two series of retrieved knee devices: 94 RP mobile bearings with polished cobalt-chrome (CoCr) trays and 218 fixed bearings with both rough titanium (Ti) and polished CoCr trays. Minimum implantation time was 0.4 months (median, 36 months; range, 0.4-124 months) and 2 months (median, 72 months; range, 2-179 months) for the RP and fixed bearing series, respectively.

RESULTS

Wear rate was lower for RP inserts than for fixed bearing inserts. Backside wear rate was lower for fixed bearing inserts mated to polished CoCr trays than for inserts from rough Ti trays. Inserts against polished trays (RP or fixed bearing) showed no increase in wear rate increase over time. Wear rate of PS knees was similar to that of CR knees.

CONCLUSIONS

We found mobile bearing knees have reduced wear rate compared to fixed bearings, likely due to the polished CoCr tibial tray surface. Fixed bearing inserts in polished CoCr trays wear less than their counterparts in rough Ti trays, and the wear rate of inserts from polished CoCr trays does not appear to increase with time.

The Rotaglide mobile bearing knee arthroplasty A 10- to 13-year review from an independent centre

The Rotaglide knee arthroplasty has a highly congruent mobile meniscal bearing allowing both rotation and antero-posterior translation. We reviewed 137 consecutive primary arthroplasties in 120 patients at mean 11.1 years (10-12.9) following surgery. No cases were lost to follow-up. Hospital for Special Surgery (HSS) and American Knee Society (AKSS) scores were recorded at a review clinic. Radiographs were assessed using the Knee Society's roentgenographic evaluation system. Forty-two patients had died, leaving 78 patients (87 knees) available for review. Sixty-four patients (70 knees) were assessed at a clinic and in 14 (17 knees) clinical outcomes were obtained via telephone and their most recent radiographs were assessed. There were three cases of aseptic loosening and one deep infection requiring revision surgery. Two meniscal bearings were replaced with thicker inserts, one following bearing fracture and one following bearing dislocation. Survival at 11 years for aseptic loosening was 97.6% (95% CI 94.3 to 1.0) and survival using re-operation for any cause was 95.3% (95% CI 90.8 to 99.8). The Rotaglide mobile-bearing total knee replacement demonstrates good survivorship and outcome scores at 11 years following surgery.

Wear damage in mobile-bearing TKA is as severe as that in fixed-bearing TKA

BACKGROUND

Mobile-bearing TKAs reportedly have no clinical superiority over fixed-bearing TKAs, but a potential benefit is improved polyethylene wear behavior.

QUESTIONS/PURPOSES

We asked whether extent of damage and wear patterns would be less severe on retrieved mobile-bearing TKAs than on fixed-bearing TKAs and if correlations with patient demographics could explain differences in extent or locations of damage.

METHODS

We performed damage grading and mapping of 48 mobile-bearing TKAs retrieved due to osteolysis/loosening, infection, stiffness, instability or malpositioning. Visual grading used stereomicroscopy to identify damage, and a grade was assigned based on extent and severity. Each damage mode was then mapped onto a photograph of the implant surface, and the area affected was calculated.

RESULTS

Marked wear damage occurred on both surfaces, with burnishing, scratching, and pitting the dominant modes. Damage occurred over a large portion of both surfaces, exceeding the available articular borders in nearly 30% of implants. Wear of mobile-bearing surfaces included marked third-body debris. Damage on tibiofemoral and mobile-bearing surfaces was not correlated with patient BMI or component alignment. Damage on mobile-bearing surfaces was positively correlated with length of implantation and was greater in implants removed for osteolysis or instability than in those removed for stiffness or infection.

CONCLUSIONS

Each bearing surface in mobile-bearing implants was damaged to an extent similar to that in fixed-bearing implants, making the combined damage score higher than that for fixed-bearing implants. Mobile-bearing TKAs did not improve wear damage, providing another argument against the superiority of these implants over fixed-bearing implants.