Polyethylene wear is influenced by manufacturing technique in modular TKA

Results of a Highly Porous Metal-Backed Cementless Patella Implant: A Minimum 5-Year Follow-Up

Initial design cementless metal-backed patellar implants failed due to multiple reasons including implant design, use of first-generation polyethylene, and surgical technique. This study evaluates clinical outcomes and survivorship of total knee arthroplasty (TKA) using a current generation highly porous metal-backed patellar component. One-hundred twenty-five consecutive primary cementless TKAs with a compression molded highly porous metal-backed patella were reviewed. One-hundred three TKAs (82.4%) with 5-year clinical and radiographic follow-up were available for review. These were matched with 103 consecutive TKAs using a cemented patella of the same implant design. The cementless cohort had a mean age of 65.5 years, body mass index (BMI) of 33.0, and follow-up of 64.4 months. Indications for cementless TKA were based on multiple factors including age, BMI, and bone quality. There were no revisions for loosening or mechanical failure of the cementless patella compared with two cemented patellae revised for aseptic loosening. Eight patients required revisions in the cementless cohort: three for prosthetic joint infection (PJI), two for instability, one periprosthetic femur fracture, one for patella instability, and one for extensor mechanism rupture. Five patients required revisions in the cemented cohort: two for aseptic patellar loosening, one for aseptic femoral loosening, one for PJI, and one for instability. All-cause survivorship at 5 years was 92.2 and 95.1% for the cementless metal-backed implant and cemented implant cohorts, respectively. Use of a compression molded highly porous metal-backed patella component demonstrated excellent clinical and radiographic results at 5-year follow-up. Longer follow-up is required to evaluate the ability of highly porous cementless patella implants to provide durable long-term fixation.

The impact of postoperative inclination of the joint line on clinical outcomes in total knee arthroplasty using a prosthesis with anatomical geometry

The goal of this study was to investigate the impact of postoperative inclination of the joint line on clinical results after total knee arthroplasty (TKA) using a prosthesis with anatomical geometry. This study included 145 primary cruciate-retaining type of knee prosthesis with anatomical geometry. Three years postoperatively, clinical outcomes including the patient-reported outcomes (PROs) were recorded. Limb alignment was evaluated by the hip-knee-ankle (HKA) axis and inclination of the joint line was assessed by the joint line orientation angle (JLOA). Knees were divided into two groups according to the HKA: in-range (- 3 to 3°) and outlier group (< - 3° or > 3°) or the JLOA: in-range (2-4°) and outlier group (< 2° or > 4°), and clinical outcomes were compared between the groups. Postoperative Knee Society Function Score (KS-FS) was significantly higher in the HKA in-range group than the outlier group (p = 0.01). The Knee Society Knee Score and all subscales of the Knee injury Osteoarthritis Outcome Score were comparable between the groups. A multivariate analysis revealed a significant association between age at operation and postoperative KS-FS > of 80 points. Neither HKA in-range nor JLOA in-range were associated with the higher knee function. In conclusion, TKA-postoperative inclination of the joint line was not relevant to the short-term PROs. Treatment strategies that attempt to make joint line inclination in order to improve postoperative PROs should be avoided, and alignment goals such as kinematic alignment should be considered carefully.

Osteolysis Complicating Total Knee Arthroplasty

Osteolysis is a process mounted by the host immune system that relies on several variables, including patient-related factors, type of insert material, modes of wear, and implant design. Imaging techniques such as radiography, computed tomography (CT) scans, magnetic resonance imaging (MRI), and tomosynthesis aid in diagnosing osteolysis. Surgical options for the treatment of osteolysis include the insertion of bone grafts, bone cement, and prosthetic augmentation. Although no approved pharmacological therapies for the specific treatment of osteolysis exist, the use of bisphosphonates and statins decreases the risk of osteolysis.

Comparison of patellofemoral outcomes after TKA using two prostheses with different patellofemoral design features

PURPOSE

The purpose of the present study was to compare the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, including outcomes related to compatibility of the patellofemoral joint.

METHODS

The clinical and radiographic results of 81 patients (100 knees) who underwent TKA using the specific prosthesis (group A) were compared with those in a control group who underwent TKA using the other prosthesis (group B). The presence of anterior knee joint pain, patellar crepitation, and patellar clunk syndrome was also checked.

RESULTS

The function score and maximum flexion angle at the last follow-up were slightly better in group A than those in group B (92.0 ± 2.3 vs. 90.6 ± 4.2) (133.6° ± 8.4° vs. 129.6° ± 11.4°). Anterior knee pain was observed in 6 knees and patellar crepitation in four knees in group A. In group B, these symptoms were observed in 22 knees and 18 knees, respectively. There was no patellar clunk syndrome in either group. The alignment was corrected with satisfactory positioning of components. The patellar height remained unchanged after TKA in the two groups. The differences between preoperative and postoperative patellar tilt angle and patellar translation were small.

CONCLUSION

When comparing the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, TKA using the specific prosthesis provided satisfactory results with less clinical symptoms related to the patellofemoral kinematics with TKA using the other prosthesis.

LEVEL OF EVIDENCE

III.

Current Total Knee Designs: Does Baseplate Roughness or Locking Mechanism Design Affect Polyethylene Backside Wear?

BACKGROUND

Tibial baseplate roughness and polyethylene-insert micromotion resulting from locking-mechanism loosening can lead to polyethylene backside wear in TKAs. However, many retrieval studies examining these variables have evaluated only older TKA implant designs.

QUESTIONS

We used implant-retrieval analysis to examine if there were differences in: (1) backside damage scores, (2) backside damage modes, and (3) backside linear wear rates in five TKA implant designs owing to differing baseplate surface roughness and locking mechanisms. Additionally, we examined if (4) patient demographics influence backside damage and wear.

METHODS

Five TKA implant models (four modern and one historical design) were selected with different tibial baseplate and/or locking mechanism designs. Six tibial inserts retrieved at the time of revision from each TKA model were matched for time in vivo, age of the patient at TKA revision, BMI, sex, revision number, and revision reason. Each insert backside was analyzed for: (1) visual total damage score and (2) individual visual damage modes, both by two observers and with an intraclass correlation coefficient of 0.66 (95% CI, 0.39-0.92), and (3) linear wear rate measured by micro-CT. Median primary outcomes were compared among the five designs. For our given sample size among five groups we could detect with 80% power a 10-point difference in damage score and an 0.11-mm per year difference in wear rate.

RESULTS

The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint showed a lower total damage score compared with the nonpolished tibial design with only a complete peripheral-rim locking mechanism (median, 12.5; range, 9.5-18.0; 95% CI, 9.58-16.42 versus median, 22.3; range, 15.5-27.0; 95% CI, 17.5-26.5; p = 0.019). The polished baseplate with a tongue-in-groove locking mechanism showed more abrasions than the nonpolished baseplate with a peripheral-rim capture and antirotational island (median, 7.25; range, 0.5-8.0; 95% CI, 2.67-8.99 versus median, 0.75; range, 0-1.5; 95% CI, 0.20-1.47; p = 0.016)). Dimpling was a unique wear mode to the nonpolished baseplates with the peripheral-rim capture and antirotational island (median, 5.5; range, 2.0-9.0; 95% CI, 2.96-8.38) and the peripheral-rim capture alone (median, 9.0; range, 6.0-10.0; 95% CI, 7.29-10.38). Overall, the linear wear rate for polished designs was lower than for nonpolished designs (0.0102 ± 0.0044 mm/year versus 0.0224 ± 0.0119 mm/year; p < 0.001). Two of the polished baseplate designs, the partial peripheral capture with anterior constraint (median, 0.083 mm/year; range, 0.0037-0.0111 mm/year; 95% CI, 0.0050-0.0107 mm versus median, 0.0245 mm/year; range, 0.014-0.046 mm/year; 95% CI, 0.0130-0.0414 mm; p = 0.008) and the tongue-in-groove locking mechanism (median, 0.0085 mm/year; range, 0.005-0.015 mm/year; 95% CI, 0.0045-0.0138 mm; p = 0.032) showed lower polyethylene linear wear rates compared with the nonpolished baseplate design with only a peripheral-rim capture.

CONCLUSIONS

Total damage scores and linear wear rates were highest involving the nonpolished design with only a peripheral rim capture. There were no differences among the other TKA designs regarding damage and wear, but this finding should be considered in the setting of a relatively small sample size.

CLINICAL RELEVANCE

Our study showed that in the complex interplay between baseplate surface finish and locking mechanism design, a polished baseplate with a robust locking mechanism had the lowest backside damage and linear wear. However, improvements in locking mechanism design in nonpolished baseplates potentially may offset some advantages of a polished baseplate. Further retrieval analyses need to be done to confirm such findings, especially analyzing current crosslinked polyethylene. Additionally, we need mid- and long-term studies comparing TKA revisions attributable to wear and osteolysis among implants before understanding if such design differences are clinically relevant.

Peripheral snap-fit locking mechanisms and smooth surface finish of tibial trays reduce backside wear in fixed-bearing total knee arthroplasty

Background and purpose - Severe backside wear, observed in older generations of total knee replacements (TKRs), led to redesign of locking mechanisms to reduce micromotions between tibial tray and inlay. Since little is known about whether this effectively reduces backside wear in modern designs, we examined backside damage in retrievals of various contemporary fixed-bearing TKRs. Patients and methods - A consecutive series of 102 inlays with a peripheral (Stryker Triathlon, Stryker Scorpio, DePuy PFC Sigma, Aesculap Search Evolution) or dovetail locking mechanism (Zimmer NexGen, Smith and Nephew Genesis II) was examined. Articular and backside surface damage was evaluated using the semiquantitative Hood scale. Inlays were examined using scanning electron microscopy (SEM) to determine backside wear mechanisms. Results - Mean Hood scores for articular (A) and backside (B) surfaces were similar in most implants-Triathlon (A: 46, B: 22), Genesis II (A: 55, B: 24), Scorpio (A: 57, B: 24), PFC (A: 52, B: 20); Search (A: 56, B: 24)-except the NexGen knee (A: 57, B: 60), which had statistically significantly higher backside wear scores. SEM studies showed backside damage caused by abrasion related to micromotion in designs with dovetail locking mechanisms, especially in the unpolished NexGen trays. In implants with peripheral liner locking mechanism, there were no signs of micromotion or abrasion. Instead, "tray transfer" of polyethylene and flattening of machining was observed. Interpretation - Although this retrieval study may not represent well-functioning TKRs, we found that a smooth surface finish and a peripheral locking mechanism reduce backside wear in vivo, but further studies are required to determine whether this actually leads to reduced osteolysis and lower failure rates.

Factors Affecting Wear of Constrained Polyethylene Tibial Inserts in Total Knee Arthroplasty

BACKGROUND

Wear in posterior-stabilized (PS) polyethylene tibial inserts depends on component position, limb alignment, and ligament balancing. Valgus-varus constrained (VVC) inserts are likely to be affected similarly. We aimed to compare wear characteristics of VVC and PS inserts and identify associated factors.

METHODS

This was a retrieval analysis (macroscopic and radiographic) of all 18 VVC liners collected from patients who underwent revision surgery from 1999 to 2011. These patients were matched to another group with PS inserts who underwent revision in the same time period.

RESULTS

There was significantly more damage in the posts of the VVC group (13.0 ± 5.0, compared to 4.7 ± 1.9 in the PS group; P < .001). Within the VVC group, the total damage score and cold flow damage were significantly higher with excessive joint line changes (≥5 mm; P = .01). The excessive joint line elevation was associated with rotational wear pattern of the post (P = .004). Damage scores were increased with femoral component malposition (P = .04), anterior tibial slope (P = .04), and tibial component malposition (P = .04).

CONCLUSION

Joint line elevation, femoral and tibial component malposition, and anterior tibial slope resulted in significantly more wear in the VVC inserts. Joint line elevation of >5 mm resulted in wear of the medial and lateral aspects of the post, femoral valgus resulted in cold flow wear of the anterior post, and tibial valgus and anterior slope resulted in wear of lateral aspect of the post.

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.

Changes in surface topography at the TKA backside articulation following in vivo service: a retrieval analysis

PURPOSE

With the advent of modular total knee arthroplasty (TKA) systems, backside wear at the articulation between the ultra-high-molecular-weight-polyethylene (UHMWPE) component undersurface and the tibial baseplate has received increasing attention as a source of clinically significant polyethylene wear debris. The aim of this study was to investigate the reciprocating interface at the TKA undersurface articulation using profilometry after in vivo service. Our null hypothesis was that there would be no discernible pattern or relationship between the metal tibial baseplate and UHMWPE surface profile.

METHODS

A nanoscale analysis of thirty retrieved fixed-bearing TKA explants was performed. Surface roughness (Sa) and skewness (Ssk) were measured on both the UHMWPE component undersurface and the tibial baseplate of explants using a non-contacting profilometer (1 nm resolution). Four pristine unimplanted components of two different designs (Stryker Kinemax and DePuy PFC) were examined for control purposes.

RESULTS

Mean explant baseplate surface roughness was 1.24 μm (0.04-3.01 μm). Mean explant UHMWPE undersurface roughness was 1.16 μm (0.23-2.44 μm). Each explant had an individual roughness pattern with unique baseplate and undersurface UHMWPE surface roughness that was different from, but closely related to, surface topography observed in control implants of the same manufacturer and design. Following in vivo service, UHMWPE undersurface showed changes towards a negative skewness, demonstrating that wear is occurring at the backside interface.

CONCLUSION

In vivo loading of the TKA prosthesis leads to measurable changes in surface profile at the backside articulation, which appear to be dependent on several factors including implant design and in vivo duration. These findings are consistent with wear occurring at this surface. Findings of this study would support the use of a polished tibial tray over an unpolished design in total knee arthroplasty with the goal of reducing PE wear by means of providing a smoother backside countersurface for the UHMWPE component.

Better survival of total knee replacement in patients older than 70 years: a prospective study with 8 to 12 years follow-up

BACKGROUND

Modern knee designs have popularized its use in younger patients due to its better performance. There remains uncertainty whether higher demands of these patients can affect implant survivorship.

PURPOSE

To assess whether modern knee designs have provided similar results in patients younger than 70 years versus older patients.

METHODS

We included 203 consecutive patients (236 knees) who underwent knee replacement for osteoarthritis with a mean follow-up of 11.4 years (range: 8.8 to 12). The mean age was 70 years (range: 31 to 85). Knee replacements were stratified into two groups: 109 were younger than 70 years and 127 were older than 70 years (70 years of age is the mandatory retirement age).

RESULTS

There were no significant pre-operative differences between groups with regards to knee alignment, alpha or beta angles, knee score or function score. Fourteen implants were radiographically loose at last follow up visit. Groups were matched in terms of demographic data. We found that patients older than 70 years had significantly better mean survivorship at 12 years. (97% vs. 88%; P=0.010). Patients under 70 years presented with a higher rate of polyethylene wear which was further associated with radiolucent lines in the femur and tibia as well as the presence of osteolysis. There was also an association between migration and presence of osteolysis.

CONCLUSIONS

Patients over 70 years old undergoing cemented total knee replacement for osteoarthritis showed better implant survivorship versus patients under 70 years old.

Polished trays reduce backside wear independent of post location in posterior-stabilized TKAs

BACKGROUND

Backside damage of the polyethylene in TKA is a potential source of debris. The location of the tibial post in posterior-stabilized implants may influence micromotion, and thus affect backside damage, as may surface roughness.

QUESTIONS

We used implant retrieval analysis to (1) examine if there were differences in backside damage among three modern posterior-stabilized implants attributable to variable surface roughness; (2) determine if the location of damage on the tibial post affected the pattern of backside damage; and (3) determine if demographics influenced backside damage.

METHODS

We identified 403 posterior-stabilized tibial retrieved inserts (147 NexGen(®), 152 Optetrak(®), 104 Genesis(®) II). The damage on the surfaces of the tibial posts was previously graded. The backside of the inserts (divided into quadrants) were scored for evidence of damage. The total quadrant damage was compared for each implant group, the relationship between post face damage and location of damage on the backside was determined for each implant group, and total backside damage was compared among the three implant groups.

RESULTS

No correlation was found between the location of damage on the post and location of damage on the backside of the implant for any of the three groups. The Genesis(®) II polyethylene implants, which articulate with a highly polished tibial tray, showed a significantly lower total backside damage score (p < 0.01) when compared with the other two implant groups. The Genesis(®) II and Optetrak(®) showed significantly more damage in the posterior quadrants of the implants (p < 0.01) when compared with the anterior quadrants. A linear regression analysis revealed that lower tibial tray surface roughness was correlated with decreased damage.

CONCLUSIONS

An implant design with a highly polished tibial tray was associated with decreased backside damage. However, tibial post design and location did not influence the location of backside damage.

CLINICAL RELEVANCE

Our study showed that a highly polished tibial tray was associated with decreased damage to the backside of polyethylene inserts independent of post design and location. These findings should be taken into consideration when new generations of implants are designed.

Comparison of conventional polyethylene wear and signs of cup failure in two similar total hip designs

Multiple factors have been identified as contributing to polyethylene wear and debris generation of the acetabular lining. Polyethylene wear is the primary limiting factor in the functional behavior and consequent longevity of a total hip arthroplasty (THA). This retrospective study reviewed the clinical and radiographic data of 77 consecutive THAs comparing in vivo polyethylene wear of two similar acetabular cup liners. Minimum follow-up was 7 years (range 7-15). The incidence of measurable wear in a group of machined liners sterilized with ethylene oxide and composed of GUR 1050 stock resin was significantly higher (61%) than the compression-molded, GUR 1020, O2-free gamma irradiation sterilized group (24%) (P = 0.0004). Clinically, at a 9-year average followup, both groups had comparable HHS scores and incidence of thigh or groin pain, though the machined group had an increased incidence of osteolysis and annual linear wear rate.

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.

The influence of sterilization method on articular surface damage of retrieved cruciate-retaining tibial inserts

This observational study was designed to determine the importance of sterilization method and insert thickness as predictors of articular damage of cruciate-retaining polyethylene components used in total knee arthroplasty. Ninety-nine explanted tibial inserts were evaluated for surface damage. Severe damage modes were observed in 36 of 52 of γ-irradiated inserts but none of those sterilized by ethylene oxide. Articular damage significantly correlated to time in vivo but not to insert thickness. Inserts sterilized by ethylene oxide gas in gas-permeable packaging exhibited a significantly lower damage accumulation rate compared with inserts sterilized by γ radiation and stored in air or an inert environment. γ irradiation and storage in argon instead of air reduced the frequency of severe damage such as delamination but not the overall damage rate.

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

Components from 73 failed knee replacements (TKRs) consisting of rotating-platform, mobile-bearing and fixed-bearing implants were examined to assess the patterns of wear. The patterns were divided into low-grade (burnishing, abrasion and cold flow) and high-grade (scratching, pitting/metal embedding and delamination) to assess the severity of the wear of polyethylene. The rotating-platform group had a higher incidence of low-grade wear on the upper surface compared with the fixed-bearing group. By contrast, high-grade wear comprising scratching, pitting and third-body embedding was seen on the lower surface. Linear regression analysis showed a significant correlation of the wear scores between the upper and lower surfaces of the tibial insert (R(2) = 0.29, p = 0.04) for the rotating-platform group, but no significant correlation was found for the fixed-bearing counterpart. This suggests that high-grade wear patterns on the upper surface are reduced with the rotating-platform design. However, the incidence of burnishing, pitting/third-body embedding and scratching wear patterns on the lower surface was higher compared with that in the fixed-bearing knee.