Trends in Polyethylene Design and Manufacturing Characteristics for Total Knee Arthroplasty: An Analysis From the American Joint Replacement Registry

Lower Associated Risk of Revision with All-Polyethylene Tibial Components in Total Knee Arthroplasty: An Analysis of the American Joint Replacement Registry

BACKGROUND

Despite the potential advantage of all-polyethylene tibial components, modular metal-backed component use predominates the market in the United States for total knee arthroplasty (TKA). This is partially driven by concerns about the associated revision risk due to the lack of modularity with all-polyethylene components. This study utilized the American Joint Replacement Registry (AJRR) to compare the associated risk of all-cause revision and revision for infection for all-polyethylene versus modular metal-backed tibial components.

METHODS

An analysis of primary TKA cases in patients aged 65 years and older was performed with AJRR data linked to Centers for Medicare and Medicaid Services data from 2012 to 2019. Analyses compared all-polyethylene to modular metal-backed tibial components. We identified 485,024 primary TKA cases, consisting of 479,465 (98.9%) metal-backed and 5,559 (1.1%) all-polyethylene. Cox proportional hazard regression analyses created hazard ratios (HRs) to evaluate the association of design and the risk of all-cause revision while adjusting for sex, age and the competing risk of mortality. Event-free survival curves evaluate time to revision.

RESULTS

The all-polyethylene tibia group demonstrated a decreased risk for all-cause revision (HR = 0.37, 95% CI [confidence interval]: 0.24 to 0.55, P < 0.0001) and revision for infection (HR = 0.41, 95% CI: 0.22 to 0.77, P < 0.0001). Event-free survival curves demonstrated a decreased risk of all-cause revision that persisted across time points until 8 years post-TKA.

CONCLUSION

In the United States, all-polyethylene tibial component use for TKA remains low compared to modular metal-backed designs. A decreased associated risk for revision should ease concerns about the use of all-polyethylene components in patients aged 65 years or older, and future investigations should investigate the potential cost and value savings associated with expanded use in this population.

Ultracongruent Polyethylene Liners Do Not Affect Survival of Total Knee Arthroplasty for Valgus Deformity

BACKGROUND

Valgus knee deformity is observed in nearly 10% of patients undergoing total knee arthroplasty (TKA). The degree of polyethylene constraint required to balance a valgus knee remains controversial, and historically, posterior-stabilized (PS) designs have been favored. This study evaluated the survivorship of TKA done in valgus knees based on implant design and specifically compared posterior-stabilized (PS) and ultracongruent (UC) liners.

METHODS

A total of 549 primary TKAs performed on valgus knees by fellowship-trained arthroplasty surgeons from 2013 to 2019 were reviewed. Demographics, comorbidities, degrees of preoperative deformity, implants used, and all-cause revisions until final follow-up were recorded. Cox regression analyses evaluated survival to all-cause revision in each cohort. The mean follow-up was 4.9 years (range, 2 to 9).

RESULTS

There were 403 UC liners compared to 146 PS liners. There was no difference in patient age (68 versus 67 years; P = .30), body mass index (30.9 versus 30.4; P = .36), or degree of deformity (8.6 versus 8.8 degrees; P = .75) between the cohorts. At final follow-up, there were 5 revisions in the PS cohort (3.4%) versus 11 revisions in the UC cohort (2.7%) (P = .90). The most common reason for revision in both cohorts was periprosthetic joint infection (4 PS; 8 UC). Multivariable regression analyses controlling for age, body mass index, Elixhauser comorbidity score, sex, and degree of deformity demonstrated UC polyethylene liners were not associated with revision (hazard ratio 0.76; 95% confidence interval [CI] 0.26 to 2.21; P = .62). There was no difference in eight-year survivorship to all-cause revision, including aseptic and septic failure.

CONCLUSIONS

Alternative polyethylene liners from the historically utilized PS liners for TKA for valgus deformity did not reduce survivorship. With modern polyethylene designs, UC inserts can be utilized for this deformity without increasing the risk of failure.

Ultracongruent Designs Compared to Posterior-Stabilized and Cruciate-Retaining Tibial Inserts - What Does the Evidence Tell Us? A Systematic Review and Meta-Analysis

BACKGROUND

Posterior-stabilized (PS) and cruciate-retaining (CR) have been the most common tibial designs used in total knee arthroplasty. Ultra-congruent (UC) inserts are becoming popular because they preserve bone without relying on the posterior cruciate ligament balance and integrity. Despite increasing use, there is no consensus on how UC inserts perform versus PS and CR designs.

METHODS

A comprehensive literature search of 5 online databases was performed for articles from January 2000 to July 2022 comparing the kinematic and clinical outcomes of PS or CR tibial inserts to UC inserts. There were nineteen studies included. There were 5 studies comparing UC to CR and 14 comparing UC to PS. Only one randomized controlled trial (RCT) was rated "good quality".

RESULTS

For CR studies, pooled analyses showed no difference in knee flexion (n = 3, P = .33) or Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores (n = 2, P = .58). For PS studies, meta-analyses showed better anteroposterior stability (n = 4, P < .001) and more femoral rollback (n = 2, P < .001) for PS but no difference in knee flexion (n = 9, P = .55) or medio-lateral stability (n = 2, P = .50). There was no difference with WOMAC (n = 5, P = .26), Knee Society Score (n = 3, P = .58), Knee Society Knee Score (n = 4, P = .76), or Knee Society Function Score (n = 5, P = .51).

CONCLUSION

Available data demonstrates there are no clinical differences between CR or PS and UC inserts in small short-term studies ending around 2 years after surgery. More importantly, high-quality research comparing all inserts is lacking, demonstrating a need for more uniform and longer-term studies beyond 5 years after surgery to justify increased UC usage.

Identifying Trends and Quantifying Growth for Technological Innovation in Knee Arthroplasty: An Analysis of a Patent Database (1990 to 2020)

Technological innovation is the key for surgical progress in knee arthroplasty and improvement in patient outcomes. Exploring patented technologies can help elucidate trends and growth for numerous innovative technologies. However, patent databases, which contain millions of patents, remain underused in arthroplasty research. Therefore, the present study aimed to: (1) quantify patent activity; (2) group patents related to similar technologies into well-defined clusters; and (3) compare growth between technologies in the field of knee arthroplasty over a 30-year period. An open-source international patent database was queried from January 1990 to January 2020 for all patents related to knee arthroplasty A search strategy identified 70,154 patents, of which 24,425 were unique and included analysis. Patents were grouped into 14 independent technology clusters using Cooperative Patent Classification (CPC) codes. Patent activity was normalized via a validated formula adjusting for exponential growth. Compound annual growth rates (CAGR) were calculated (5-year, 10-year, and 30-year CAGR) and compared for each cluster. Overall yearly patent activity increased by 2,023%, from 104 patents in 1990 to 2,208 patents in 2020. The largest technology clusters were "drugs" (n = 5,347; 23.8%), "components" (n = 4,343; 19.0%), "instruments" (n = 3,130; 13.7%), and "materials" (n = 2,378; 10.4%). The fastest growing technologies with their 5-year CAGR were: "user interfaces for surgical systems" (58.1%); "robotics" (28.6%); "modularity" (21.1%); "navigation" (15.7%); and "computer modeling" (12.5%). Since 1990, overall patent growth rate has been greatest for "computer modeling" (8.4%), "robotics" (8.0%), "navigation" (7.9%), and "patient-specific instrumentation" (6.4%). Most patents in knee arthroplasty for the last 30 years have focused on drugs, components, instruments, and materials. Recent exponential growth was mainly observed for user interfaces for surgical systems, robotics, modularity, navigation, and computer-assisted technologies. Innovation theory would suggest that these rapidly growing technologies are experiencing high innovation output, increased resource investments, growing adoption by providers, and significant clinical impact. Periodic monitoring of technological innovation via patent databases can be useful to establish trends and future directions in the field of knee arthroplasty.

A Review of Early In Vivo Performance of Antioxidant Stabilized Polyethylene for Total Knee Arthroplasty

BACKGROUND

The incorporation of antioxidants into highly cross-linked polyethylene (HXLPE) has emerged as an alternative to postirradiation thermal treatments for improving oxidation resistance. Currently, use of antioxidant stabilized HXLPE (AO-XLPE) in total knee arthroplasty (TKA) is increasing. In this literature review, we asked: (1) How does the clinical performance of AO-XLPE compare to conventional ultra-high molecular weight polyethylene (UHMWPE) or HXLPE for TKA? (2) What material changes occur in vivo for AO-XLPE in TKA? and (3) What is the risk of revision for AO-XLPE in TKA?

METHODS

We performed a search of the literature according to the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines using PubMed and Embase. Included studies reported the in vivo behavior of vitamin E-doped polyethylene in TKA. We reviewed 13 studies.

RESULTS

Across the studies, clinical results including revision rates, patient-reported outcome measurement scores, and the occurrence of osteolysis or radiolucent lines tended to be similar for AO-XLPE as compared to conventional UHMWPE or HXLPE controls. In retrieval analyses, AO-XLPE exhibited excellent resistance to oxidation and typical surface damage. Survival rates were positive and not significantly different from conventional UHMWPE or HXLPE. There were no cases of osteolysis for AO-XLPE and no revision due to polyethylene wear reported.

CONCLUSION

The purpose of this review was to provide a comprehensive overview of the literature regarding the clinical effectiveness of AO-XLPE in TKA. Overall, the results of our review indicated positive early-to mid-term clinical performance for AO-XLPE in TKA and similar outcomes as compared to conventional UHMWPE and HXLPE.

No Reduction in Revision Risk Associated With Highly Cross-linked Polyethylene With or Without Antioxidants Over Conventional Polyetheylene in TKA: An Analysis From the American Joint Replacement Registry

BACKGROUND

Highly cross-linked polyethylene (HXLPE) can improve wear properties in TKA, but it can also lead to decreased mechanical properties. Antioxidants were added to HXLPE to improve its mechanical properties while retaining the improved wear characteristics. However, it remains unclear whether these modifications to conventional polytheylene used in TKA have resulted in a change in the revision risk.

QUESTIONS/PURPOSES

We used American Joint Replacement Registry data to ask: (1) Is there a difference in all-cause revision in patients who underwent TKA using HXLPE with or without an antioxidant doping compared with conventional polyethylene? (2) Is there a difference in revision for aseptic failure in patients who underwent TKA using HXLPE with or without an antioxidant doping compared with conventional polyethylene?

METHODS

We analyzed American Joint Replacement Registry data from 2012 to 2019. We identified 339,366 primary TKAs over the study period in patients older than 65 years and linked procedures to supplemental Centers for Medicare & Medicaid data where available. Patient total number of reported comorbidities, gender, age, region, polyethylene characteristics, procedure dates, and indication for revision were recorded. Median follow-up was 34 months. We compared HXLPE with or without antioxidants to conventional polyethylene. Event-free percent survival curves and Cox proportional hazard regression modeling was used for all-cause revision and revision for aseptic failure.

RESULTS

Compared with conventional polyethylene, there was no difference in all-cause revision with HXLPE with an antioxidant (HR 1.06 [95% CI 0.98 to 1.14]; p = 0.13) or HXLPE without an antioxidant (HR 1.04 [95% CI 0.97 to 1.11]; p = 0.28). Compared with conventional polyethylene, there was no difference in revision for aseptic failure with HXLPE with an antioxidant (HR 1.07 [95% CI 0.99 to 1.14]; p = 0.08) or HXLPE without an antioxidant (HR 1.03 [95% CI 0.97 to 1.01]; p = 0.30).

CONCLUSION

We found no difference in revision risk between HXLPE with or without an antioxidant and conventional polyethylene during this time frame. HXLPE polyethylene, with or without an antioxidant, should not be widely adopted until or unless it is shown to be superior to conventional polyethylene in TKA.

LEVEL OF EVIDENCE

Level III, therapeutic study.