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

Condylar-Stabilized Designs in Total Knee Arthroplasty: A Classification System and Review of Outcomes

BACKGROUND

The increasing use of condylar-stabilized (CS) bearing designs in primary total knee arthroplasty (TKA) can be attributed to bony preservation with the option for posterior cruciate ligament (PCL) resection without compromising kinematics. Although there are a variety of CS designs, there is no system of nomenclature for them, making comparisons challenging. This study proposes a comprehensive classification system of differing CS designs based on articular surface and femoral component geometries and kinematic principles. We also review the literature for functional outcomes and survivorship associated with each CS design.

MATERIALS AND METHODS

There were 31 CS designs noted from 21 manufacturers identified using a combination of literature reviews, web searches, surgeon input, and manufacturer correspondence. The designs were subsequently categorized into distinct groups based on their geometry, the location of polyethylene buildup, conformity compared to their CR counterparts, and the radius of the femoral component. A scoping review was conducted to evaluate patient-reported outcome measures (PROMs), ranges of motion (ROM), and survivorships associated with each category. After exclusion, we reviewed 91 studies in the PubMed, Ovid MEDLINE, Embase, Cochrane, Web of Science, and Scopus databases.

RESULTS

We established five distinct categories: 1) anterior-stabilized; 2) ultracongruent; 3) medial-stabilized; 4) medial-pivot; and 5) lateral-stabilized. There were 12 studies describing anterior-stabilized designs, 15 describing ultracongruent, two describing medial-stabilized, 55 describing medial-pivot, and three describing lateral-stabilized designs. All CS designs demonstrated significant improvements in PROMs and ROM postoperatively, with survivorship of at least 90% and follow-up ranging from two to 18 years in some designs.

CONCLUSIONS

The classification developed in this study will allow for appropriate grouping and comparison of distinct condylar-stabilized implants. As presented in this review, there are favorable short-term functional outcomes across all CS subcategories. Although the data associated with these designs appears promising, it is limited. Further research comparing different designs to understand how differing geometries impact kinematic function and clinical outcomes may potentially inform implant selection and future design.

A Comparison of Medial-congruent, Ultracongruent, and Cruciate-retaining Bearings Using a Single Cruciate-retaining Total Knee Design

Background

Improving outcomes has driven advancements in total knee arthroplasty (TKA) bearing design. The aim of this study was to compare medial-congruent (MC), ultracongruent (UC), and cruciate-retaining (CR) TKA utilizing a single CR total knee system.

Methods

Six surgeons performed 2883 primary TKAs from 2012 to 2022 using the same implant design, comprised of 708 MC, 799 UC, and 1376 CR bearings. Prospectively collected data on clinical and patient-reported outcome measures were compared. Data analyses utilized analysis of variance tests for continuous data, chi-square tests for categorical data, and Mantel-Cox tests for survivorship analysis. MC subjects were older (MC = 67.5 vs UC = 65.3 vs CR = 66.7 years; P < .001), had lower body mass index (MC = 32.4 vs UC = 33.1 vs CR = 33.2 kg/m2; P = .04), and had shorter mean follow-up (MC = 1.2 vs UC = 2.4 vs CR = 2.9 years; P < .001).

Results

All groups experienced similar rates of 90-day complications (MC = 26/708, 3.7% vs UC = 39/799, 4.9% vs CR = 52/1376, 3.8%; P = .38) and revisions (MC = 1/708, 0.1% vs UC = 4/799, 0.5% vs CR = 5/1376, 0.4%; P = .49). Survivorship was similar at 2 years (P = .41) and above 98% at 5 years for all groups. At the 1-year follow-up, MC bearings had significantly greater Patient-Reported Outcomes Measurement Information System Global Health Physical (MC = 47.1 vs UC = 41.5 vs CR = 42.8; P < .001) and mental scores (MC = 48.9 vs UC = 41.3 vs CR = 43.7; P < .001).

Conclusions

No differences in all-cause complications or revisions were observed for MC, UC, and CR bearings using the same total knee system. Clinically important differences favoring MC bearings were found with Patient-Reported Outcomes Measurement Information System Global Health Physical scores at 1 year; however, longer follow-up is necessary to determine if this trend holds.

Comparing Patient Preference for Highly Congruent Versus Cruciate-Retaining Inserts in Bilateral Knee Arthroplasties

INTRODUCTION

The purpose of this study was to determine if patients who had undergone bilateral total knee arthroplasty (TKA) with a cruciate-retaining (CR) bearing in one knee and a highly congruent bearing in the other had a preference between the two bearings.

METHODS

We retrospectively identified 104 patients who had bilateral TKAs performed an average of 15 months apart (range, simultaneous to 11 years apart) by the same surgeon using the same implant system, with each patient having a CR bearing in one knee and a highly congruent bearing in the other. The mean age at surgery was 62 years (range, 43 to 88), and 62% of patients were women. We assessed implant survival, reoperation rate, and range of motion (ROM). Patient knee preference, satisfaction, noise generation, subjective instability, and patient-reported outcome measures (PROM) were also analyzed. A power analysis revealed that 81 knees in each group were required to detect a difference in laterality preference of 20% (alpha = 0.05, beta = 0.80). Univariate analyses with alpha < 0.05 were used in comparisons between groups.

RESULTS

At a mean of 5.4 years, 27 patients (26%) preferred their CR knee, 25 patients (24%) preferred their highly congruent knee, and 52 patients (50%) had no preference (P = 0.9). There were 35 patients (34%) who preferred the first knee that was operated on versus 14% who preferred the second knee (P < 0.001). There was no difference in prosthesis survival (P = 0.4) or reoperations (P = 0.1) between groups. Additionally, there was no difference in overall patient satisfaction, knee flexion, or PROMs.

CONCLUSION

Patients who had a CR insert in one knee and a highly congruent insert in the other did not prefer one versus the other. There was no difference in survival, outcomes, or post-operative ROM between the two bearings, demonstrating both as reliable and adequate choices in TKA.

Ultracongruent Versus Posterior-Stabilized Polyethylene: No Difference in Anterior Knee Pain but Decreased Noise Generation

BACKGROUND

Noise generation and anterior knee pain can occur after primary total knee arthroplasty (TKA) and may affect patient satisfaction. Polyethylene design in cruciate-sacrificing implants could be a variable influencing these complications. The purpose of this study was to analyze the effect of polyethylene design on noise generation and anterior knee pain.

METHODS

We prospectively reviewed a cohort of patients who underwent primary TKA between 2014 and 2022 by a single surgeon using either a posterior-stabilized (PS) or ultracongruent (UC) polyethylene of the same implant design. The primary outcomes were measured through a noise generation questionnaire and the Knee Injury and Osteoarthritis Outcome Score-Patellofemoral score.

RESULTS

A total of 409 TKA procedures were included, 153 (37.4%) PS and 256 (62.6%) UC. No difference was noted in the Knee Injury and Osteoarthritis Outcome Score-Patellofemoral score between PS and UC designs (71.7 ± 26 versus 74.2 ± 23.2, P = 0.313). A higher percentage of patients in the PS cohort reported hearing (32.7% versus 22.3%, P = 0.020) or feeling noise (28.8 versus 20.3, P = 0.051) coming from their implant. No notable difference was observed in noise-related satisfaction rates. Independent risk factors of noise generation were age (OR, 0.96; P = 0.006) and PS polyethylene (OR, 1.61; P = 0.043). Noise generation was associated with decreased patient-reported outcome measure scores ( P < 0.001).

CONCLUSION

While there was no difference in anterior knee pain between PS and UC polyethylene designs, PS inserts exhibit higher rates of noise generation compared with UC. Noise generation had comparable satisfaction but was associated with decreased patient-reported outcome measure scores.

Do Ultracongruent Inserts Reproduce the Intraoperative Sagittal Plane Kinematics of Posterior Stabilized TKR? Assessment Using a Modern Robotic System

Background

Ultracongruent (UC) total knee replacement (TKR) designs, serving as alternatives to posterior stabilized (PS) and cruciate retaining (CR) designs, lack conclusive evidence regarding posterior femoral rollback. This study aimed to compare intraoperative posterior femoral rollback and maximal knee flexion between UC and PS inserts, addressing the paucity of literature on femoral rollback achieved with UC designs in total knee replacement.

Methods

A consecutive cohort of 20 patients undergoing robotic-assisted primary total knee replacement, posterior femoral rollback and maximal intraoperative knee flexion were assessed. Robotic imaging at varying flexion angles (0°, 45°, 90°, and 120°) was conducted after implanting femoral and tibial components with Ultracongruent and Posterior-Stabilized trial inserts. Femoral contact on the tibia was estimated as a percentage of the sagittal dimension of the tibial component with 0 representing the anterior edge and 100 representing the posterior edge of the tibial component.

Results

In extension, UC inserts exhibited a statistically significant posterior contact point versus PS inserts (56.3 + 4.3 vs 53.5 + 5.3, p = 0.003). Between 0 and 45° flexion, 13 of 20 UC inserts showed a paradoxical anterior translation exceeding 5%, unlike the PS group. At 90° flexion, both displayed consistent posterior femoral rollback, with PS inserts having a more posterior contact point (63.5 + 6.2 vs 67.2 + 5.1, p = .008). At 120° flexion, rollback was similar (70.1 + 8.4 vs 71.3 + 8.4, p = 0.128). Mean maximal flexion was 130° (SD = 6.87) and 133° (SD = 6.72) for UC and PS inserts, respectively (p = 0.0001).

Conclusions

The study indicates UC inserts achieve comparable posterior femoral rollback in deep flexion, supporting their alternative use, despite minor intraoperative flexion differences. However, paradoxical anterior translation in mid-flexion with UC inserts warrants further investigation into wear and clinical outcomes.

No difference in patient-reported outcomes or range of motion between ultracongruent and posterior stabilized total knee arthroplasty: A randomized controlled trial

Purpose

Ultracongruent (UC) inserts were designed to overcome potential issues with posterior stabilized (PS) inserts, including bone resection, post-breakage, and patellar clunk syndrome. However, there remains a shortage of high-quality studies directly comparing this insert design to the established PS Total Knee Arthroplasty (TKA). This prospective randomized controlled trial (RCT) aimed to compare clinical outcomes, range of motion, and complications of UC and PS TKA.

Methods

Ninety six patients with primary knee osteoarthritis were randomly assigned to either the PS or the UC group. There were no significant differences between the groups regarding age, body mass index, sex, or Osteoarthritis grade. The measured outcomes were Knee Injury and Osteoarthritis Outcome Score (KOOS) and Range of Motion (ROM), recorded preoperatively and at 3 and 6 months postoperative. Both the patient and interviewer were blinded to the allocation group.

Results

Eighty one patients were included in the analysis, with a mean follow-up of 1.3 years. Both groups exhibited a gradual improvement in KOOS. Still, no statistically significant differences were observed between the groups during the follow-up examinations at 3 or 6 months in KOOS or range of motion. No complication occurred in either group during the follow-up period.

Conclusion

Both designs demonstrated comparable positive outcomes, reinforcing the viability of UC designs as an alternative to the well-established PS TKA.

Levels of Evidence

Level l, randomized controlled trial.

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.

The Effect of Congruent Tibial Inserts in Total Knee Arthroplasty: A Network Meta-Analysis of Randomized Controlled Trials

Objective: The aim of this study was to determine whether modern congruent tibial inserts are associated with superior outcomes in total knee arthroplasty (TKA). Background: Ultracongruent fixed-bearing (UCFB) and medial congruent fixed-bearing (MCFB) inserts have been known to be effective in total knee arthroplasty with patient satisfaction. Nonetheless, no supporting evidence to date exists to rank the clinical outcomes of these various congruent inserts in TKA compared with other important considerations in TKA including cruciate-retaining fixed-bearing (CRFB) and posterior-stabilized fixed-bearing (PSFB) inserts. Methods: We searched PubMed, Embase, the Cochrane Central Register of Controlled Trials, Web of Science, and Scopus up to 15 May 2022. We selected studies involving an active comparison of UCFB or MCFB in TKAs. We performed a network meta-analysis (NMA) of randomized controlled trials (RCTs) and compared different congruent inserts. We ranked the clinical outcomes by SUCRA score with the estimate of the best treatment probability. Our primary outcomes were revision rates and radiolucent lines. Secondary outcomes were functional scores, including the range of motion (ROM), the Knee Society Score (KSS), the Oxford Knee Score (OKS), and WOMAC. Results: Eighteen RCTs with 1793 participants were analyzed. Our NMA ranked MCFB, CRFB, and UCFB with the lowest revision rates. CRFB and UCFB had the fewest radiolucent lines. UCFB had overall the best ROM. UCFB and MCFB had the best OKS score overall. Conclusions: The ranking probability for better clinical outcomes in congruent inserts demonstrated the superiority of congruent tibial inserts, including UCFB and MCFB. UCFB may be associated with better ROM and postoperative functional outcomes. However, integrating future RCTs for high-level evidence is necessary to confirm these findings.