Highly conforming polyethylene inlays reduce the in vivo variability of knee joint kinematics after total knee arthroplasty

Survivorship and Patient Outcomes of Conforming Bearings in Modern Primary Total Knee Arthroplasty: Mean 3.5 Year Follow-Up

BACKGROUND

The use of conforming and congruent bearings in total knee arthroplasty (TKA) have rapidly increased due to the benefits of increased stability and the potential for replicating normal knee kinematics. However, limited data exist for these newly available bearings. This study evaluated revision-free survivorship and patient-reported outcome measures (PROMs) of a large granular database of primary TKAs using a single conforming bearing design.

METHODS

A total of 1,306 consecutive primary TKAs performed using a single conforming bearing design (85% cemented and 15% cementless) were retrospectively reviewed. Kaplan-Meier survivorship estimates were calculated based on the latest clinical follow-up. The PROMs and minimal clinically important differences were evaluated. A total of 93% of cases achieved minimum 1-year clinical follow-up (mean 3.5 years; range, 1 to 7), with a subset of 261 cases that achieved minimum 5-year follow-up (mean 5.8 years; range, 5 to 7).

RESULTS

All-cause and aseptic Kaplan-Meier survivorship estimates were 97.6 (95% CI [confidence interval], 97 to 99) and 98.1% (95% CI, 97 to 99) at 7.0 years. Revision-free survivorship did not differ by cemented or cementless fixation (98 versus 97%, P = .163). All PROM scores significantly improved from preoperative baseline (P < .001), and ≥ 86% of patients achieved minimal clinically important differences for Knee Society pain and Knee Injury and Osteoarthritis Outcome Score for Joint Replacement total scores. A total of 89% of cases reported their knees to 'sometimes or always' feel normal. For cases with minimum 5-year PROMs, 93% were 'very satisfied' or 'satisfied.'

CONCLUSIONS

Conforming-bearing TKA demonstrated excellent survivorship up to 7.0 years. In addition, PROMs were comparable to other designs reported in the literature. While mid-term (mean 3.5-year) results are promising, long-term data are warranted on survivorship due to potential polyethylene wear in conforming bearings with more surface area in contact with articulating surfaces.

LEVEL OF EVIDENCE

IV.

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.

Modern Total Knee Arthroplasty Bearing Designs and the Role of the Posterior Cruciate Ligament

The role of the posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) surgery continues to be a source of debate among the adult reconstruction community. In native knee flexion, the PCL is comprised of an anterolateral and posteromedial bundle that work together to limit posterior tibial translation and allow adequate femoral rollback for deep flexion. In the arthritic knee, the PCL can often become dysfunctional and attenuated, which led to the development of posterior stabilized (PS) TKA bearing options. PS TKAs implement a cam-post construct to functionally replace a resected PCL. While PS designs may facilitate balancing knees with significant deformity, they are associated with complications such as postfracture, increased wear, and patellar clunk/crepitus. In recent years, newer designs have been popularized with greater degrees of congruency and incorporation of medial and lateral pivoting to better recreate native knee kinematics. The American Joint Registry has confirmed the recent predilection for ultra-congruent and cruciate-retaining TKA inserts over PS TKAs during the last decade. Studies have failed to identify an overall clinical superiority between the cruciate substituting and sacrificing designs. The literature has also failed to identify clinical consequences from PCL resection with modern, more conforming TKA designs. In this article, we review modern PCL sacrificing designs and discuss the impact of each on the kinematics after TKA. We also will delineate the role of the PCL in modern TKA in the hopes to better understand the recent surge in sacrificing but not substituting knee implants.

Equivalent outcomes of ultra-congruent and standard cruciate-retaining inserts in total knee arthroplasty

PURPOSE

No systematic review has compared the clinical outcome of anterior stabilized ultra-congruent and standard cruciate-retaining inserts in fixed-bearing primary total knee arthroplasty. This study aimed to compare the outcomes and establish the superiority or equivalence of these inserts.

METHODS

Pubmed, EMBASE, Medline, AMED, ERIC, and Proquest databases were searched electronically. PRISMA guidelines were followed in the conduct of the study. The clinical outcomes compared in the meta-analysis were overall knee score, WOMAC, score for knee function, score for knee pain, SF-12 PCS, knee flexion, manipulation under anaesthesia for postoperative knee stiffness, revision total knee arthroplasty or change of polyethylene insert for post-operative instability (relative risk [RR]) and survivorship. Study quality was evaluated using the Newcastle Ottawa Scale and the Modified Jadad scale.

RESULTS

Fourteen studies comprising 9989 knees (three RCTs and 11 comparative case-cohort studies) were included for qualitative and quantitative analysis. The pooled analysis of the ultracongruent insert and the standard cruciate retaining insert was based on a cohort of 2860 and 7129 TKA, respectively. Knee pain was significantly better in patients that had standard inserts (p = 0.02; 95% CI - 1.06 to - 0.10), and the physical component of health-related quality of life was also significantly better in patients that had standard inserts (p = 0.02; 95% CI - 6.43 to - 0.64). There was a 72% lesser chance of revision TKA or change of insert for postoperative instability in knees that had been implanted with ultracongruent inserts (RR = 0.28; p = 0.0002; 95% CI 0.15-0.55). There was no difference in the otheroutcome measures. There was no significant difference between the two inserts, considering the minimal clinically important difference or absolute ratio.

CONCLUSION

Differences observed between the two types of inserts were not clinically significant. Therefore, based on current evidence, arthroplasty surgeons can use either of these inserts with cruciate-retaining knee prosthesis.

LEVEL OF EVIDENCE

Therapeutic study, Level II.

In vivo kinematic comparison between an ultra-congruent and a posterior-stabilized total knee arthroplasty design by RSA

PURPOSE

The aim of the present study was to compare the in vivo under weight-bearing kinematic behavior of a posterior-stabilized (PS) and an ultra-congruent (UC) total knee arthroplasty (TKA) model during a sit-to-stand motor task, a common activity of daily life.

METHODS

A cohort of 16 randomly selected patients (8 PS Persona Zimmer, 8 UC Persona Zimmer) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit-to-stand. The anteroposterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student's t test (p < 0.05).

RESULTS

A significantly greater anterior translation of the femoral component was found for the PS group compared to the UC group. The flexion interval where statistical significance was found was between 30° and 0° (p = 0.017). Both groups showed a significantly greater anterior translation of the low point of the lateral compartment with respect to the medial one (PS: p = 0.012, UC: p = 0.018). This was consistent with a medial-pivot pattern. Furthermore, a significantly greater anterior translation of the medial compartment was found in the PS group compared to the UC group (p = 0.001). The same pattern was observed for the lateral compartment (p = 0.006).

CONCLUSIONS

The TKA designs evaluated in the present study showed comparable in-vivo kinematics with regards to medial pivot pattern but differences in absolute AP translation. Specifically, the UC design showed greater AP stability than the PS design. This finding could be positive in terms of implant stability, but negative in terms of premature polyethylene wear and thus implant failure. This remains to be verified in studies with a larger sample size and longer follow-up.

LEVEL OF EVIDENCE

IV.

Comparative Analysis of Contemporary Fixed Tibial Inserts: A Systematic Review and Network Meta-analysis of Randomized Controlled Trials

Background

Multiple options are available for the tibial insert in total knee arthroplasty (TKA). A systematic review (SR) and network meta-analysis (NMA) to compare available randomized controlled trials (RCTs) could assist with decision making. We aim to show that designs with increased conformity may improve function and satisfaction without an increase in complications though posterior stabilized (PS) inserts will likely have more flexion.

Methods

A search of MEDLINE, EMBASE, and the Cochrane Library was performed. Studies were limited to RCTs evaluating cruciate retaining (CR), PS, anterior stabilized (AS), medial pivot (MP), bicruciate retaining (BR), and bicruciate stabilizing (BCS) inserts. Mean differences (MD) were used for patient reported outcome measures (PROMs) and odds ratios (OR) for reoperation rates and MUA. A systematic review was performed for satisfaction.

Results

27 trials were identified. The NMA showed no difference from a statistical or clinical standpoint for PROMs evaluated. There was a statistical difference for increased flexion for PS knees (3 degrees p 0.04). There were no differences in the MUA or reoperation rates. There was insufficient information to determine if a specific insert improved satisfaction.

Discussion

The results of this NMA show no statistical or clinical difference in PROMs. There was higher flexion for PS knees though the amount was not clinically significant. There was insufficient data for conclusions on patient satisfaction. Therefore, the surgeon should evaluate the clinical situation to determine the best insert rather than choose and insert based on functional scores, patient satisfaction, or complication rates.

The Effect of Posterior Cruciate Ligament Release on Kinematics and Outcomes in Primary Total Knee Arthroplasty With a Dual-Pivot Conforming Polyethylene

BACKGROUND

Ultracongruent bearings are increasingly utilized in total knee arthroplasty (TKA); however, implications of surgical technique on knee kinematics and outcomes with these bearings are not well understood. This study's purpose was to evaluate the relationship of 3-dimensional knee kinematics and patient-reported outcome measures (PROMs) in a dual-pivot congruent bearing TKA with and without posterior cruciate ligament (PCL) release.

METHODS

Forty patients undergoing TKA with an asymmetric ultracongruent bearing were prospectively enrolled for gait analysis preoperatively and 4 months postoperatively. Three-dimensional gait analysis was performed utilizing infrared motion capture. Knee kinematic data and PCL disposition were analyzed for correlations with PROMs.

RESULTS

The PCL was fully released in 52.5% (21/40) of cases. Greater maximum anteroposterior femoral translation correlated with lower Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (rho = -0.596, P = .012), greater Knee Society Score pain with level walking (rho = 0.411, P = .101), and greater Knee Society Score pain while climbing stairs (rho = 0.469, P = .058) at 4-month follow-up. The PCL-release group was associated with greater maximum femoral anteroposterior translation (9.8 vs 5.5 mm, P = .053) and greater maximum internal tibial rotation (-6.2° vs -3.0°, P = .040), supporting a more anterior-based position of the medial condyle. The PCL released group had lower median Knee Injury and Osteoarthritis Outcome Score for Joint Replacement scores (70.7 vs 76.3, P = .031) and reported that their knees "sometimes or always" feel normal less frequently (81.8% vs 92.3%, P = .576).

CONCLUSION

With this asymmetric ultracongruent bearing TKA, preservation or partial titration release of the PCL, as opposed to full PCL release, appears to minimize deleterious anterior femoral translation and internal tibial rotation, which is correlated with optimized patient-reported outcomes.

LEVEL OF EVIDENCE

II.

Biomechanics and Outcomes of Modern Tibial Polyethylene Inserts

PURPOSE OF REVIEW

There have been many attempts to use variations in tibial polyethylene design to better recreate normal knee kinematics in the total knee arthroplasty. The goal of this review is to provide an overview of the various types of tibial inserts that exist and review the theoretical mechanics versus what was demonstrated in vivo.

RECENT FINDINGS

Many polyethylene inserts have been attempted to re-create normal knee kinematics, but none have been able to successfully do so. Previously the only two types of inserts were posterior stabilized (PS) and cruciate retaining (CR) polyethylene inserts. Both of these have shown excellent long-term survival but neither has demonstrated native kinematics. Initially, it was thought that retention of the posterior cruciate ligament (PCL) would allow for more native kinematics, but fluoroscopic evidence has shown that the PCL alone cannot accomplish this. Newer inserts try to restore femoral roll back and the screw home mechanism. The bicruciate retaining total knee inserts are having the most "normal" kinematics, suggesting the importance of both the ACL and PCL in knee biomechanics. Modern polyethylene inserts show favorable short-term data with bicruciate retaining inserts having the best kinematics; however, long-term studies are still needed to determine if survivorship and patient outcomes remain favorable.

Press-Fit Dual-Pivot Total Knee Arthroplasty: Early Results With a Minimum 2-Year Follow-Up

BACKGROUND

Ultracongruent (UC) tibial bearings are being used with increasing frequency in the United States. Evidence suggests that the use of certain UC bearings may lead to improved patient satisfaction when compared with using conventional inserts. However, little is known as to what effect the use of UC tibial inserts has on bone ingrowth in uncemented total knee arthroplasty (TKA). The purpose of this study was to determine the early clinical and radiographic results of TKA using a press-fit dual-pivot design.

METHODS

Between 2017 and 2019, a consecutive series of 232 TKAs were implanted using a press-fit tibial and femoral component and a UC dual-pivot tibial insert. Sixty-two percent of patients were male. The average age was 56 years. Patients were followed for a minimum of 2 years (range, 24-42 months) using KOOS-JR and Knee Society clinical and radiographic evaluation.

RESULTS

No patient had more than mild knee stiffness at the final follow-up. Two patients reported moderate knee pain with stair climbing. All other patients reported either mild or no pain with activity. Knee Society pain scores averaged 42 points. Flexion averaged 118 degrees. Three knees (1.3%) were revised (one each for flexion instability, tibial plateau fracture, and suspected femoral component loosening). No other cases of femoral or tibial loosening were identified.

CONCLUSION

Although the success of uncemented TKA is determined by a variety of factors, the use of this dual-pivot knee design did not appear to influence tibial or femoral component fixation at early follow-up, yielding acceptable clinical and radiographic outcomes.

Midterm Outcomes of a Bicruciate-Retaining Compared With the Bicruciate-Sacrificing Knee System

BACKGROUND

The purpose of this study is to report midterm outcomes and survivorship of a bicruciate retaining knee arthroplasty compared with a bicruciate sacrificing anterior stabilized knee arthroplasty.

METHODS

A retrospective comparative cohort analysis was performed of all patients who underwent primary total knee arthroplasty with the bicruciate retaining (XP) knee arthroplasty compared with an anterior stabilized (AS) cruciate sacrificing bearing. The XP system was used in 195 knees and was compared with 1471 knees in which the AS bearing was used. Patients were included in analysis if they had minimum 2-year follow-up or had a revision at any point. Preoperative and postoperative range of motion, Knee Society Scores, complications, and reoperations were evaluated. Unpaired t-test and chi-square analysis were performed. Kaplan-Meier survival analysis was performed for all-cause and aseptic survival.

RESULTS

At an average of 5.2-year follow-up, 22 (11.3%) XP knees had been revised, compared with 23 (1.6%) AS knees (P < .001). Nineteen (9.7%) XP knees were revised for aseptic tibial loosening; one (0.1%) of the AS knees was revised for the same (P < .001). Nineteen of the XR revision surgeries (86.4%) were for aseptic tibial loosening. Compared with AS knees, the XP knees had significantly lower improvement in range of motion (3.2 deg vs 2.2 deg, P < .001), Knee Society (KS) pain scores (39 vs 35.7, P = .014), KS clinical scores (52.4 vs 46, P < .001), and KS functional scores (20.9 vs 15.5, P = .01).

CONCLUSION

The bicruciate retaining Vanguard XP Total Knee System demonstrated an unacceptably high rate of aseptic tibial loosening without conferring the benefit of improved postoperative function relative to other available bearings.

Bicompartmental, medial and patellofemoral knee replacement might be able to maintain unloaded knee kinematics

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are standard procedures for treating knee joint arthritis. Neither UKA nor TKA seems to be optimally suited for patients with bicompartmental osteoarthritis that affects only the medial and patellofemoral compartments. A bicompartmental knee arthroplasty (BKA) was designed for this patient group. This study aimed to compare the effectiveness of a BKA and TKA in restoring the kinematics of the knee joint.

MATERIALS AND METHODS

In this in vitro study, three types of knee arthroplasties (BKA, posterior cruciate ligament-retaining, and posterior cruciate ligament-resecting TKA) were biomechanically tested in six freshly frozen human cadaveric specimens. Complete three-dimensional kinematics was analyzed for each knee arthroplasty during both passive and loaded conditions in a validated knee kinematics rig. Infrared motion capture cameras and retroreflective markers were used for recording data.

RESULTS

No significant differences could be found between the three types of arthroplasties. However, similar kinematic changes between BKA and a native knee joint were documented under passive conditions. However, in a weight-bearing mode, a significant decrease in femoral rotation during the range of motion was found in arthroplasties compared to the native knee, probably caused by contraction of the quadriceps femoris muscle, which leads to a decrease in the anterior translation of the tibia.

CONCLUSIONS

Kinematics similar to that of the natural knee can be achieved by BKA under passive conditions. However, no functional advantage of BKA over TKA was detected, which suggests that natural knee kinematics cannot be fully imitated by an arthroplasty yet. Further prospective studies are required to determine the anatomic and design factors that might affect the physiologic kinematics.

Survivorship Comparisons of Ultracongruent, Cruciate-Retaining and Posterior-Stabilized Tibial Inserts Using a Single Knee System Design: Results From the Australian Orthopedic Association National Joint Replacement Registry

BACKGROUND

Ultracongruent (UC) tibial inserts can increase knee replacement stability, but how survivorship compares to cruciate retaining (CR) or posterior stabilized (PS) inserts is unclear.

METHODS

Data from a large joint registry were used to calculate the cumulative percent revision of a single popular knee design used with different inserts. There were 67,523 procedures, of which 12,434 were UC, 21,635 CR, and 33,454 PS. Revision rates and reasons for revision were analyzed.

RESULTS

The cumulative percent revision at 18 years was 8.3% for UC, 9.2% for CR, and 8.9% for PS. There was no difference when UC was compared to CR, but PS had a higher risk of revision. Revision reasons were similar.

CONCLUSION

Compared to the CR, an UC insert did not increase revision rates and was actually lower than a PS insert. An UC insert does not compromise long-term total knee arthroplasty survivorship in the Genesis II prosthesis.

Primary Total Knee Arthroplasty Revised for Instability: A Detailed Registry Analysis

BACKGROUND

Instability after total knee arthroplasty is a common but poorly understood complication.

METHODS

Data from a large national registry was used to study patient and prosthesis characteristics of 2605 total knee arthroplasty revisions for instability. The cumulative percent revision was calculated using Kaplan-Meier estimates, and Cox proportional models used to compare revision rates. The rate of further revision was analyzed with regard to prostheses used in the first revision.

RESULTS

Instability increased from 6% of all first revision procedures in 2003 to 13% in 2019. The revision risk was lower for minimally stabilized prostheses, males, and patients aged ≥65 years. Polyethylene insert exchange was used for 55% of revision procedures, using a thicker insert in 93% and a change in insert conformity in 24% of cruciate-retaining knees. The increase in either thickness or conformity had no effect on the rate of further revision. After a revision for instability, 24% had a second revision by 14 years. Recurrent instability accounted for 32% of further revisions. A lower second revision rate was seen after revision of both femoral and tibial components, and where constrained components were used.

CONCLUSION

Revision for instability is increasing. Revising both femoral and tibial components led to a lower rate of second revision compared to a change in insert alone. Recurrent instability was common.

No kinematical difference between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment: an in vivo dynamic RSA study

PURPOSE

To explore in vivo kinematical behavior of the same total knee arthroplasty (TKA) cruciate-retaining (CR) femoral design with either medial-congruent (MC) or ultra-congruent (UC) inlay using model-based dynamic radiostereometric analysis (RSA). The hypothesis was that there would be comparable kinematics between the two groups.

METHODS

A cohort of 16 randomly selected patients (8 MC Persona Zimmer, 8 UC Persona Zimmer) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit-to-stand. The antero-posterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student's t test (p < 0.05).

RESULTS

Both groups showed a medial pivot behavior, with a significantly greater anterior translation of the Low Point of the lateral compartment with respect to the medial compartment (MC medial range: 2.4 ± 2.4 mm; MC lateral range: 7.7 ± 3.0 mm; p < 0.001 - UC medial range: 3.3 ± 3.3 mm; UC lateral range: 8.0 ± 3.2 mm; p < 0.001). A statistically significant greater degree of flexion was clinically recorded at follow-up visit in the MC group respect to the UC group (126° vs 101°-p = 0.003).

CONCLUSION

The present study did not show difference in the medial pivot behavior between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment; however, the MC group demonstrated a greater degree of flexion. The MC design examined is a valid alternative to the UC design, allowing to achieve a screw-home movement restoration combined with a high flexion.

LEVEL OF EVIDENCE

IV.

Conforming Polyethylene Inserts in Total Knee Arthroplasty: Beyond the Posterior-Stabilized and Cruciate-Retaining Debate

Total knee arthroplasty continues to be one of the most commonly performed surgical procedures worldwide. However, considerable controversy exists regarding the optimal implant design. Total knee implants with both posterior-stabilized and cruciate-retaining designs have excellent long-term outcomes with inadequate data demonstrating superiority of either design. Recently, the popularity of total knee designs with more conforming polyethylene liners has increased. These polyethylene inserts prevent paradoxical anterior translation of the femur, without relying on a cam and post mechanism, and promote more physiologic native knee kinematics. This review summarizes the design rationale of several commercially available implants, discusses the kinematic data of several designs, and reviews the available clinical data.

Tibial baseplate position and posterior cruciate ligament status impact patient-reported outcomes in conforming dual-pivot bearing total knee arthroplasty

Background

In an effort to optimize clinical outcomes and enhance stability, ultracongruent bearings have been increasingly used in primary total knee arthroplasty (TKA). The importance of the posterior cruciate ligament (PCL) and optimal sagittal tibial baseplate position in ultracongruent bearing TKA remains unknown. This study sought to determine whether these modifiable, surgical-technique-dependent variables meaningfully impact patient-reported outcome measures.

Methods

A total of 759 primary TKAs of the same dual-pivot design performed using a consistent surgical technique between January 2016 and April 2019 were retrospectively reviewed. PCL status was recorded, and anteroposterior (AP) tibial baseplate position and posterior tibial slope were measured by two independent blinded raters. Patient-reported outcomes related to pain, function, satisfaction, and activity level were analyzed in relationship to PCL status, posterior tibial slope, and AP tibial baseplate position, in addition to other pertinent covariates.

Results

Median age and body mass index of the cohort were 68.3 years and 33.4 kg/m², respectively, with 73% being female. In multivariate analysis, partial or full release of the PCL was predictive of a knee “always” feeling normal (odds ratio 1.42, P = .041). Furthermore, tibial baseplate position closer to the middle of the tibia was associated with greater improvements in pain with level walking, pain while climbing stairs, and Knee Injury and Osteoarthritis Outcome Score for Joint Replacement total scores (P ≤ .079).

Conclusion

In congruent dual-pivot bearing TKA, partially or fully releasing the PCL and AP tibial baseplate position closer to the middle of the tibia may provide greater improvement in pain and function scores at minimum 1-year follow-up.

No differences in clinical outcomes or isokinetic performance between cruciate-substituting ultra-congruent and posterior stabilized total knee arthroplasties: a randomized controlled trial

PURPOSE

Whether ultra-congruent (UC) or posterior cruciate ligament-stabilized (PS) inserts should be used in posterior cruciate ligament (PCL)-sacrificing total knee arthroplasty (TKA) remains debatable. Therefore, the aim of this prospective randomized controlled study was to compare the isokinetic performance and clinical outcomes of these inserts in PCL-sacrificing TKA.

METHODS

Sixty-six patients diagnosed with primary knee osteoarthritis were randomly assigned to either the UC or the PS group. There were no significant differences between the groups in terms of age, body mass index or sex. The Knee Society score (KSS) and isokinetic performance results for each patient were recorded preoperatively and at 3, 6 and 12 months postoperatively. The physiatrist that performed the isokinetic tests and the patients were blinded to the study groups.

RESULTS

There were no significant differences between the groups in terms of the preoperative KSS or isokinetic performance. Gradual improvement in the KSS was observed in both groups, but no significant differences were detected between the groups during the whole follow-up period. The UC and PS groups exhibited similar peak extension and flexion torque values normalized to body weight at 3, 6 and 12 months postoperatively (p > 0.05).

CONCLUSION

The use of UC or PS inserts in TKA did not affect the clinical outcomes or isokinetic performance.The clinical relevance of this study is that the potential differences in clinical outcomes and isokinetic performance between UC and PS inserts do not need to be considered when sacrificing the PCL in TKA.

LEVEL OF EVIDENCE

I.

Comparison of Functional Outcomes, Femoral Rollback and Sagittal Stability of Anterior-Stabilized Versus Posterior-Stabilized Total Knee Arthroplasty: A Systematic Review and Meta-analysis of Randomized Controlled Trials

PURPOSE

Total knee arthroplasty (TKA) has improved leaps and bounds in terms of design to improve clinical outcomes and achieve better rehabilitation of the patients. Ultra-congruent inserts (UC) were designed to replace the need for posterior stabilized (PS) implants. The purpose of this review was to evaluate clinical outcomes, femoral rollback, functional scores, range of motion, sagittal laxity, complication rates, and isokinetic performance between UC and PS TKA among RCTs.

METHODS

Electronic databases such as PubMed, Scopus, opengrey, and Cochrane were searched from date of inception up to mid-April 2021, and meta-analysis was performed following PRISMA guidelines. This study analyzed outcomes, femoral rollback, tibial sagittal laxity and isokinetic performance.

RESULTS

Ten RCTs identified 852 knees, of which 420 underwent UC TKAs and 432 underwent PS TKA. Compared to UC TKA, a significantly better sagittal stability (p = 0.17) and femoral rollback (p < 0.00001) in PS TKAs was noted, although no statistically significant difference was found in the assessment of the range of motion (p = 0.19) and functional scores. Both the groups had similar isokinetic performance with extensor torque (p = 0.97) and flexor torque (p = 0.37).

CONCLUSIONS

We conclude with the current meta-analysis that there are no added benefits for UC over PS inserts and these inserts have a higher sagittal laxity and less femoral roll back in cruciate sacrificing UC knee. But since there are no long-term wear data, UC inserts with CS technique should be used cautiously and may be used only when the PCL cannot be balanced adequately. There is no evidence or only a few to support the superiority of the AS TKA in terms of clinical outcomes or isokinetic performance or femoral external rotation over PS TKA.

LEVEL OF EVIDENCE

Level I, Systematic review and meta-analysis of RCTs.

The effect of sacrificing the posterior cruciate ligament on total knee arthroplasty with cruciate retaining highly congruent rotating platform prosthesis

Objective

To analyze the effect of sacrificing the posterior cruciate ligament (PCL) on the early postoperative outcome of cruciate retaining (CR) highly congruent rotating platform TKA.

Methods

From May 2018 to September 2019, 105 cases of total knee arthroplasty (TKA) with CR highly congruent rotating platform prosthesis were retrospectively analyzed. According to the tension of posterior cruciate ligament, they were divided into sacrifice group (29 cases, 27.6%) and retention group (76 cases, 72.4%). Preoperative and postoperative The Hospital for Special Surgery (HSS) score, range of motion (ROM) were compared between the two groups. In addition, postoperative infection, prosthesis loosening, bearing dislocation, and other complications were also compared.

Results

All patients were followed up for 11~24 months (mean 18.14 ± 3.52) months. There was no significant difference in general data, preoperative HSS score, and ROM between the two groups (P > 0.05). At the last follow-up, HSS score and ROM of the two groups were better than those before operation (P < 0.05). However, there was no significant difference between the two groups (P > 0.05). Moreover, there were no complications such as infection, loosening of prosthesis, and bearing dislocation in all cases.

Conclusion

In CR, highly congruent rotating platform TKA with or without tension of the PCL can achieve satisfactory outcomes. Tension-free PCL do not cause joint instability.

Comparing patient reported outcomes in depuy sigma curved versus curved plus polyethylene inserts in cruciate retaining total knee arthroplasty

Total knee designs have evolved to allow more motion with compromising stability. The purpose of this study is to compare standard congruency and anterior lipped liners' effects on patient reported outcomes after TKA. 68 patients were retrospectively reviewed, and their SF-12 and KOOS scores were assessed preoperatively and one year post-operatively. Two-sample t-tests were used to compare differences between groups. The CVD design had a statistically significant greater improvement in KOOS-Pain compared to CVD+. No statistical difference was observed in the outcomes. The results may suggest that higher congruency designs lead to less physiological joint kinematics and pain.

Progressive Tibial Bearing Sagittal Plane Conformity in Cruciate-Retaining Total Knee Arthroplasty

BACKGROUND

We hypothesized that when the posterior cruciate ligament (PCL) is found deficient at total knee arthroplasty (TKA), using an anterior-stabilized (AS) tibial insert would provide similar function and survivorship when compared to using a more traditional cruciate-retaining (CR) bearing when the (PCL) is balanced.

METHODS

A total of 1731 TKAs were performed using the same TKA design. Of them, 868 TKAs had a standard CR insert implanted (CR-S), 480 TKAs used a lipped CR insert (CR-L), and 383 TKAs used an AS insert. If the PCL was considered nonfunctional or absent, an AS bearing was placed. When the PCL was balanced, a CR-S or CR-L bearing was used. Follow-up was performed using the Knee Society scoring system. Kaplan-Meier survivorship was used with failure defined as aseptic loosening.

RESULTS

At final follow-up, there were no significant differences in knee flexion, pain, function, or stair scores. Walking scores were significantly lower in the AS group. Posterior instability was higher in the CR-S group, whereas the manipulation rate was highest in the CR-L group (1.7%, 1.3%, and 0% for CR-L, CR-S, and AS groups, respectively). Kaplan-Meier survivorship at 5 years demonstrated no significant difference between the 3 groups (99% 100%, and 99% for CR-S, CR-L, and AS groups, respectively).

CONCLUSION

Using an AS insert provided similar function and 5-year survivorship as compared to using a CR-S and CR-L tibial insert when the PCL was balanced. Using an ultracongruent AS dished tibial component appears to be a reasonable option when the PCL is completely released or found deficient at operation.

Anterior-stabilized TKA is inferior to posterior-stabilized TKA in terms of postoperative posterior stability and knee flexion in osteoarthritic knees: a prospective randomized controlled trial with bilateral TKA

PURPOSE

To determine whether knee stability, range of motion (ROM) and clinical scores differ between anterior-stabilized (AS) and posterior-stabilized (PS) total knee arthroplasty (TKA).

METHODS

This prospective randomized controlled trial included 34 patients with severe bilateral knee osteoarthritis who underwent bilateral TKA between June 2010 and July 2011 using AS and PS designs of a single-implant system. AS TKA with ultracongruent inserts was performed in one knee and PS TKA with a cam-post mechanism was performed in the other knee in each patient. Clinical and radiological data from a mean follow-up period of 5 years, including ROM, clinical scores, peak knee torque determined by isokinetic test, knee joint laxity determined by Telos stress views, tourniquet time and subjects' preference were analyzed.

RESULTS

The mean postoperative knee flexion angle did not differ between groups until 1 year. Beginning 2 years postoperatively, the knee flexion angle decreased slightly in the AS group and was smaller than that in the PS group (p = 0.004). The mean Knee Society knee score was higher in the PS group than in the AS group after 2 years. The quadriceps strength did not differ between groups. The mean posterior laxity after TKA was 6-8 mm greater in the AS group than in the PS group. No radiological loosening was observed in either group. More subjects preferred PS knees to AS knees. However, this difference was not significant.

CONCLUSION

AS primary TKA was inferior to PS TKA in terms of posterior knee stability, postoperative knee flexion and clinical scores after 2 years.

LEVEL OF EVIDENCE

Therapeutic study, Level 1.

Sagittal radius of curvature, trochlea design and ultracongruent insert in total knee arthroplasty

Multi radius (MR) total knee arthroplasty (TKA) has been associated with mid-flexion instability.

Single radius (SR) TKA may provide better anteroposterior stability through single flexion axis and biomechanical advantage for quadriceps function.

Medial pivot (MP) TKA and gradually reducing (GR) radius TKA produce better knee kinematics.

Clinical outcomes are equivalent for SR, MR and MP TKA.

Short-term studies have shown better clinical outcomes and kinematics for GR TKA.

Thinner and narrow anterior flange, deeper trochlea groove and more anatomical trochlea design reduces patellofemoral complications in TKA

Ultracongruent inserts provide comparable clinical outcomes to posterior-stabilized TKA and cruciate retaining TKA.

Cite this article: EFORT Open Rev 2019;4:519-524. DOI: 10.1302/2058-5241.4.180083

The Effect of Sacrificing the Posterior Cruciate Ligament in Total Knee Arthroplasties That Use a Highly Congruent Polyethylene Component

BACKGROUND

There is continued debate regarding retention versus sacrificing of the posterior cruciate ligament (PCL) in total knee arthroplasty (TKA). We sought to determine if there was a difference in range of motion (ROM) after TKA between patients with PCL sacrifice versus PCL retention when using a highly congruent polyethylene insert.

METHODS

We conducted an Institutional Review Board approved retrospective study of consecutive patients receiving TKA using the same implant with a highly congruent polyethylene component implanted by one surgeon from November 2013 to January 2016. Patients were placed in 2 groups based on whether the PCL was intact or released at the time of surgery. Patient charts were reviewed for age, body mass index, PCL status at surgery (incompetent, kept intact, or released), and preoperative/postoperative knee ROM.

RESULTS

Both groups were similar in average age (60.5 vs 60.6, respectively) and body mass index (33.3 vs 32.6, respectively). Postoperative tibial slope (5.5° PCL release, 6.6° PCL retained, P = .028) was the only alignment variable reaching significance; all other alignment and motion variables were similar.

CONCLUSION

Results indicate that the PCL can be successfully retained with the use of a congruent bearing design, with no evident limitation in postoperative ROM or loss of stability due to the bearing in comparison to patients who undergo PCL release.

How prosthetic design influences knee kinematics: a narrative review of tibiofemoral kinematics of healthy and joint-replaced knees

INTRODUCTION

To improve the total knee arthroplasty (TKA) prosthesis design, it is essential to study the kinematics of the tibiofemoral joint. Many studies have been conducted in this area; however, conflicting results and incomparable testing methods make it difficult to draw definitive conclusions or compare research from studies. The goal of this article is to introduce what is known about both healthy and prosthetic tibiofemoral joint kinematics.

AREAS COVERED

Healthy tibiofemoral joint kinematics are reviewed in vivo by different activities, and the kinematics of existing knee prosthetic design features are considered separately. These features include but are not limited to cruciate retaining, posterior cruciate substituting, mobile-bearing, and high flexion.

EXPERT COMMENTARY

The type of activity that is being performed has a great influence on the kinematics of healthy knees, and the influences of different TKA prosthetic design features on the kinematics are complex and varied. Moreover, the TKA postoperative functional performance is influenced by many factors, and prosthetic design is among them, but not the only one that defines the performance.

Posterior-stabilized inserts are preferable to cruciate-substituting ultracongruent inserts due to more favourable kinematics and stability

PURPOSE

It is unknown whether the conforming superiority of ultracongruent (UC) inserts over posterior stabilized (PS) inserts, due to an increased anterior lip for prevention of anterior displacement of the condyles during knee flexion, leads to better knee scores or greater knee stability in arthroplasty patients. This meta-analysis compared clinical outcomes, intraoperative kinematics, sagittal stability, and range of motion (ROM) between groups with either UC or PS inserts in primary total knee arthroplasty (TKA).

METHODS

Studies that recorded clinical outcomes, intraoperative kinematics, sagittal stability, and ROM in patients who underwent primary TKA with UC or PS inserts were included in the meta-analysis. Subgroup analyses based on differences in flexion angles were performed for intraoperative kinematics.

RESULTS

Thirteen studies met the criteria for inclusion in the meta-analysis. The UC and PS insert groups reported similar pain scores (95% CI - 0.15 to 0.16; n.s.) and function scores (95% CI - 0.30 to 0.14; n.s.). In contrast, femoral rotation during flexion (95% CI - 0.06 to 6.35; p = 0.05), posterior femoral translation during flexion (95% CI - 2.74 to - 0.15; p = 0.03), tibial sagittal laxity at 90° (95% CI 2.91 to 7.72; p < 0.0001), and ROM (95% CI - 4.84 to - 1.53; p = 0.0002) differed significantly between the groups. Subgroup analyses revealed that the pooled data for femoral rotation were significantly different between groups: 60°, 4.09 (p < 0.00001); 90°, 7.94 (p < 0.00001); and 120°, 8.16 (p < 0.00001). Furthermore, pooled data for posterior femoral translation were significantly different between groups: 90°, - 3.70 (p < 0.00001); and 120°, - 3.96 (p < 0.00001).

CONCLUSIONS

There were no significant differences in clinical outcomes between the groups with UC and PS inserts. However, the UC insert group showed significantly greater external femoral rotation, less posterior femoral translation, greater tibial laxity in the sagittal plane, and less ROM than the PS insert group. Based on the results of the current meta-analysis, in substituting the PCL, PS inserts are preferable to UC inserts due to more favourable kinematics and stability, even though both inserts have equivalent clinical outcomes.

LEVEL OF EVIDENCE

Therapeutic study, Level II.

Variable tibiofemoral articular contact stress in fixed-bearing total knee arthroplasties

BACKGROUND

Rotational allowance at the tibiofemoral joint would be required during deep flexion. However, the amount of flexion and rotation has not been investigated in modern total knee arthroplasty (TKA) designs. The present study aimed to determine the contact stress in five posterior-stabilized fixed-bearing TKA designs.

HYPOTHESIS

We hypothesized that the contact area and stresses at the tibiofemoral articular surfaces vary according to the type of implant design and tested condition.

MATERIALS AND METHODS

The contact area and mean and peak contact stresses at the tibiofemoral articular surfaces were determined when a compressive load of 1200N was applied to a NexGen LPS Flex, Scorpio NRG, Genesis II, PFC Sigma, and Foundation implant. Measurements were performed at 0° and 45° flexion with 0°, 5°, 10°, and 15° rotation, and at 90° and 135° flexion with 0, 5°, 10°, 15°, and 20° rotation.

RESULTS

The LPS Flex showed that the femoral component could not achieve 20° rotation at 135° flexion. The Scorpio NRG showed less than 20MPa of contact stress at all conditions. The Genesis II showed higher contact stress than 20MPa at 135° flexion with 20° rotation. The PFC Sigma showed that the femoral component could not achieve >10° rotation at any flexion angle. The Foundation showed more than 20MPa of contact stress at 90° flexion with 20° rotation and at 135° flexion with 10°, 15°, and 20° rotation.

DISCUSSION

Surgeons should be more aware of the variable contact conditions of the tibiofemoral articular surfaces in individual TKA designs.

LEVEL OF EVIDENCE

Level IV, basic science study.

Satisfactory Short-Term Results of Navigation-Assisted Gap-Balancing Total Knee Arthroplasty Using Ultracongruent Insert

BACKGROUND

The use of highly conforming ultracongruent (UC) polyethylene insert is bone-preserving and became a relatively common alternative to the conventional posterior stabilized total knee arthroplasty (TKA) design. The purpose of this study was to analyze the short-term clinical and radiologic results of UC insert TKA using the navigation-assisted gap-balancing technique.

METHODS

Two hundred thirty-three knees were operated with a mean follow-up period of 8.1 years (minimum of 5 years). Radiologic and clinical outcomes were assessed before operation and at latest follow-up using the Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index score. For statistical analysis, paired sample t-test and analysis of variance were used. Significance was considered as P < .05.

RESULTS

According to the preoperative deformities (valgus, mild varus, and moderate varus), there were 23 cases (9.9%) of valgus deformity, 180 cases (77.3%) of mild varus deformity, and 30 cases (12.9%) of moderate varus deformity. Overall, the results at mean 8.1 years revealed an improvement in mean Knee Society Score (54 ± 12 to 92 ± 3) and mean Western Ontario and McMaster Universities Osteoarthritis Index scores (62 ± 14 to 17 ± 3). Overall, 220 of 233 cases (94.4%) were in neutral alignment (between -3° and +3°) at latest follow-up. There were no migrating or shifting prosthesis that should be considered as possible failure. There was 0% component revision rate.

CONCLUSION

Navigation-assisted gap-balancing technique using UC insert TKA had satisfactory short-term outcome. Strict gap-balancing technique using the offset-type-force-controlled-spreader-system aided in the satisfactory results.

Different intraoperative kinematics with comparable clinical outcomes of ultracongruent and posterior stabilized mobile-bearing total knee arthroplasty

PURPOSE

There remains no consensus as to whether mobile total knee arthroplasty (TKA) should use a posterior cruciate ligament-sacrificing ultracongruent (UC) or a posterior cruciate ligament-substituting posterior stabilized (PS) prosthesis. The purpose of this study was to assess intraoperative kinematics and clinical outcomes of UC and PS rotating platform mobile-bearing TKA.

METHODS

In this randomized controlled study, mobile UC TKA prostheses (n = 45) were compared with mobile PS TKA prostheses (n = 45) with regard to intraoperative kinematics and clinical outcomes. The passive kinematic study using intraoperative navigation system included anterior/posterior translation, varus/valgus alignment and rotation of femur during flexion. The patients were clinically and radiographically evaluated over a 3-year follow-up.

RESULTS

Paradoxical anterior translation of the femur was 10.8 ± 5.2 mm in the UC knee from 0° to 82° of knee flexion and 8.7 ± 3.0 mm in the PS knee from 0° to 70° of knee flexion (p = 0.027). Paradoxical internal rotation of the femur was 5.8° in the UC knees and 9.9° in the PS knees (p = 0.003). But, there was no significant difference between the groups in regard to the coronal alignment. There was no significant difference in the range of motion, KS knee scores, KS function scores, and WOMAC index scores.

CONCLUSIONS

Despite different intraoperative kinematics between mobile UC and mobile PS TKA, neither design reproduced physiologic knee kinematics and there was no difference in clinical outcomes between the two groups. The clinical relevance of the study is that despite different intraoperative kinematics, UC design can be a considerable alternative to PS design in mobile-bearing TKA in respect of clinical outcomes.

LEVEL OF EVIDENCE

II.

Cruciate retaining and cruciate substituting ultra-congruent insert

The posterior cruciate ligament (PCL) conservation and the polyethylene insert constraint in total knee arthroplasty (TKA) are still debated. The PCL is one of the primary stabilizers of the joint, but cruciate retaining (CR) implants have the disadvantage of a difficult balancing of the PCL. Postero-stabilized (PS) implants were introduced to reduce this problem. However, also the PS implants have some disadvantages, due to the cam-mechanism, such as high risk of cam-mechanism polyethylene wear. To minimize the polyethylene wear of the cam-mechanism and the bone sacrifice due to the intercondylar box, different types of inserts were developed, trying to increase the implant conformity and to reduce stresses on the bone-implant interface. In this scenario ultra-congruent (UC) inserts were developed. Those inserts are characterized by a high anterior wall and a deep-dished plate. This conformation should guarantee a good stability without the posterior cam. Few studies on both kinematic and clinical outcomes of UC inserts are available. Clinical and radiological outcomes, as well as kinematic data are similar between UC mobile bearing (MB) and standard PS MB inserts at short to mid-term follow-up. In this manuscript biomechanics and clinical outcomes of UC inserts will be described, and they will be compared to standard PS or CR inserts.

Functional Outcomes of a New Mobile-Bearing Ultra-Congruent TKA System: Comparison With the Posterior Stabilized System

We determined whether a new mobile-bearing ultra-congruent (UC) TKA system provides better functional outcomes than an established posterior-stabilized (PS) prosthesis. The functional outcomes (motion arc, AKS scores, WOMAC Index, and SForm-36 scores evaluated at 1 and 2 years postoperatively), satisfaction and incidences of adverse events were compared between the knees implanted with mobile-bearing UC prosthesis (n=103) and the mobile-bearing PS prosthesis (n=99). At 2 years, mobile-bearing UC TKAs showed similar functional outcomes and satisfaction, but smaller motion arc compared to mobile-bearing PS TKAs (126° vs. 131°). There were no differences in the incidence of adverse events. Mobile-bearing UC prosthesis can be considered a safe and viable alternative to the PS design, with an expectation of smaller postoperative maximum flexion.

Cruciate-sacrificing total knee arthroplasty and insert design: A radiologic study of sagittal laxity

INTRODUCTION

Ultracongruent inserts avoid some of the drawbacks of central spine postero-stabilized inserts. However, early wear has been reported, and may be due to increased sagittal laxity. The principal objective of the present study was to compare sagittal laxity in rotating platform total knee replacements (TKR) according to insert design: ultracongruent versus central spine. The principal hypothesis was that insert design influences global sagittal laxity.

MATERIAL AND METHODS

A retrospective comparative study recruited 3 consecutive series of patients treated for primary osteoarthritis of the knee, with a minimum 1 year's follow-up. The UC series comprised 35 knees in 34 patients, receiving a Total Knee Triathlon™ (Stryker Orthopaedics, Mahwah, NJ) TKR with ultracongruent insert, at a mean 2.0 years' follow-up. The UC+ series comprised 36 knees in 34 patients, receiving the BalanSys™ (Mathys Ltd, Bettlach, Switzerland) TKR with ultracongruent insert, at a mean 2.5 years' follow-up; in this model, the anterior edge of the insert is higher than in the UC series ("deep-dish" design). The PS series comprised 43 knees in 40 patients, receiving a Total Knee Triathlon™ (Stryker Orthopaedics, Mahwah, NJ) TKR with central spine posterior stabilization, at a mean 1.5 years' follow-up. The principal assessment criterion was sagittal laxity at 90° flexion as measured by the Telos Stress Device® (Metax GmbH, Hungen, Germany).

RESULTS

Sagittal laxity did not significantly differ between the UC and UC+ series: mean 8.2mm (range: 0-19.5mm) and 8.4mm (4.5-15.8mm), respectively. Sagittal laxity in the PS series was significantly less: 1.4mm (0.2-3.9) (P<0.0001).

CONCLUSION

Sagittal laxity was greater in ultracongruent than central spine posterior stabilized TKR. This anteroposterior movement may induce polyethylene wear. The ideal degree of sagittal laxity for ultracongruent inserts remains to be determined.

LEVEL OF EVIDENCE

IV - retrospective study.

Does Insert Type Affect Clinical and Functional Outcome in Total Knee Arthroplasty? A Randomised Controlled Clinical Trial With 5-Year Follow-Up

New insert types have been developed to improve clinical and functional outcome in mobile bearing (MB-TKA) and fixed bearing total knee arthroplasty (FB-TKA). A prospective single blinded randomised controlled clinical trial was performed to evaluate 2 types of MB-TKA inserts and 2 types of FB-TKA inserts of the Genesis II prosthesis (Smith & Nephew) in 146 patients with 5-years follow-up. A significant difference (P=.042) between the MB-TKA inserts was found in KSS function scores, but clinical significance is expected to be limited. Goniometry, temporal gait parameters and QoL were similar in all groups. Survival was significantly better (P=.047) for FB-TKA. The comparable outcome and higher revision rate in MB-TKA indicate that FB-TKA may be preferential for the Genesis II implant system.

The role of the deep medial collateral ligament in controlling rotational stability of the knee

PURPOSE

The tibial insertion of the deep medial collateral ligament (dMCL) is frequently sacrificed when the proximal tibial cut is performed during total knee arthroplasty. The role of the dMCL in controlling the knee's rotational stability is still controversial. The aim of this study was to quantify the rotational laxity induced by an isolated lesion of the dMCL as it occurs during tibial preparation for knee arthroplasty.

METHODS

An isolated resection of the deep MCL was performed in 10 fresh-frozen cadaver knees. Rotational laxity was measured during application of a standard 5.0 N.m rotational torque. Maximal tibial rotation was measured at different knee flexion angles using an image-guided navigation system (Medivision Surgetics system, Praxim, Grenoble, France) before and after dMCL resection.

RESULTS

In all cases, internal and external tibial rotation increased after dMCL resection. Total rotational laxity increased significantly for all knee flexion angles, with an average difference of +7.8° (SD 5.7) with the knee in extension, +8.9° (SD 1.9) in 30° flexion, +7° (SD 2.9) in 60° flexion and +5.3° (SD 2.8) in 90° flexion.

CONCLUSIONS

Sacrificing the tibial insertion of the deep MCL increases rotational laxity of the knee by 5°-9°, depending on the knee flexion angle. Based on our findings, new surgical techniques and implants that preserve the dMCL insertion such as tibial inlay components should be developed. Further clinical evaluations are necessary.

Articular contact kinematics of the knee before and after a cruciate retaining total knee arthroplasty

Accurate knowledge of tibiofemoral articular contact kinematics of the knee after total knee arthroplasty (TKA) is important for understanding the intrinsic knee biomechanics and improving the longevity of the components. The objective of this study was to compare the in vivo articular contact kinematics of the knees with end-stage medial osteoarthritis (OA) during a weight-bearing, single leg lunge activity before and after a posterior cruciate retaining TKA (CR-TKA) using a dual fluoroscopic imaging technique. We found that the CR-TKA resulted in more posterior contact positions on the tibial surface and a reduced range of motion in the medial and lateral compartments. The distances between medial and lateral contact locations in the CR-TKA knees were statistically larger than the OA knees. The articular contact centers have shifted from medial side of the tibial plateau pre-operatively to the lateral side after operation. This study indicated that the CR-TKA resulted in significant changes in contact kinematics of the knees in both anteroposterior and mediolateral directions. Further studies are needed to determine the influence of the altered in vivo contact kinematics on the longevity of polyethylene liner and long term clinical outcomes of the TKA.

Posterior stabilized versus cruciate retaining total knee arthroplasty designs: conformity affects the performance reliability of the design over the patient population

Commercially available fixed bearing knee prostheses are mainly divided into two groups: posterior stabilized (PS) versus cruciate retaining (CR). Despite the widespread comparative studies, the debate continues regarding the superiority of one type over the other. This study used a combined finite element (FE) simulation and principal component analysis (PCA) to evaluate "reliability" and "sensitivity" of two PS designs versus two CR designs over a patient population. Four fixed bearing implants were chosen: PFC (DePuy), PFC Sigma (DePuy), NexGen (Zimmer) and Genesis II (Smith & Nephew). Using PCA, a large probabilistic knee joint motion and loading database was generated based on the available experimental data from literature. The probabilistic knee joint data were applied to each implant in a FE simulation to calculate the potential envelopes of kinematics (i.e. anterior-posterior [AP] displacement and internal-external [IE] rotation) and contact mechanics. The performance envelopes were considered as an indicator of performance reliability. For each implant, PCA was used to highlight how much the implant performance was influenced by changes in each input parameter (sensitivity). Results showed that (1) conformity directly affected the reliability of the knee implant over a patient population such that lesser conformity designs (PS or CR), had higher kinematic variability and were more influenced by AP force and IE torque, (2) contact reliability did not differ noticeably among different designs and (3) CR or PS designs affected the relative rank of critical factors that influenced the reliability of each design. Such investigations enlighten the underlying biomechanics of various implant designs and can be utilized to estimate the potential performance of an implant design over a patient population.

Comparison of total knee arthroplasty with highly congruent anterior-stabilized bearings versus a cruciate-retaining design

BACKGROUND

The use of a highly conforming, anterior-stabilized bearing has been associated with clinical success in a limited number of studies.

QUESTIONS/PURPOSES

We compared Knee Society scores, radiographic results, complication rates, and revision rates with the use of anterior-stabilized bearings compared with cruciate-retaining (CR) bearings.

METHODS

A series of 382 patients with 468 primary total knee arthroplasties (TKAs) between 2003 and 2008 with minimum 2-year followup were reviewed. Anterior-stabilized bearings comprised 49% (n = 228) of the sample and CR bearings consisted of 51% (n = 240). The decision to use an anterior-stabilized bearing was based on integrity of the posterior cruciate ligament (PCL) intraoperatively or after sacrifice of the PCL to achieve soft tissue balance. The tibial and femoral component designs were the same regardless of bearing choice. Outcomes were measured with Knee Society scores, complications, revision TKA, and survival. Radiographs were analyzed for component alignment and evidence of loosening.

RESULTS

There was no difference in Knee Society knee scores, radiographic alignment, component loosening, manipulation rate, major complications, or time to revision for patients between the two groups. However, the CR group had significantly more revisions than the anterior-stabilized group (21 CR [1.5%] versus seven anterior-stabilized [4.6%], p = 0.03) at a minimum followup of 5 months (mean, 42 months; range, 5-181 months).

CONCLUSIONS

The use of a highly congruent anterior-stabilized bearing for PCL substitution has comparable clinical and radiographic results to traditional CR TKA. These results suggest that this approach is an effective method to achieve stability without the PCL in primary TKA.

Constraints in posterior-stabilised TKA kinematics: a comparison of two generations of an implant

PURPOSE

This study tests the hypothesis that the design changes incorporated in the newer generation Triathlon posterior-stabilised TKA design result in kinematics that more closely reproduce the kinematics observed in healthy knees than those achieved by the older generation Scorpio posterior-stabilised TKA design.

METHODS

Eleven patients with Triathlon posterior-stabilised TKA, twelve patients with Scorpio posterior-stabilised TKA, and 22 subjects with normal asymptomatic knees underwent fluoroscopic assessment of the knee during a step-up exercise and a weight-bearing deep knee bend. Two-dimensional and three-dimensional knee kinematics were assessed including the maximum flexion, the patella tendon angle (PTA), the patella flexion angle (PFA), the minimum distance between cam and post, and the tibio-femoral contact positions.

RESULTS

The average maximum flexion achieved was 114° (SD 3°), 91° (SD 10°), and 143° (SD 14°) for the Triathlon, Scorpio, and Normal groups. The average cam/post mechanism engagement was at 63° (SD 24°) and 82° (SD 16°) for the Triathlon and Scorpio groups. The condylar contact points showed a paradoxical anterior slide for the Scorpio group which was not present in the Triathlon group. The PTA and PFA values of both implants showed significant differences from normal.

CONCLUSION

Overall, the Triathlon implant design, as compared to Scorpio TKA, produced kinematics closer to that of normal knees as proposed by the hypothesis. However, despite being closer to normal, the kinematics exhibited by the Triathlon group were still different from normal. A comparison of kinematic performance, taking into account altered design parameters, will contribute to improved understanding and future design considerations.

Preservation of the posterior cruciate ligament is not helpful in highly conforming mobile-bearing total knee arthroplasty: a randomized controlled study

PURPOSE

The purpose of this study is to investigate whether the preservation of the posterior cruciate ligament (PCL) can be helpful for improving kinematics and clinical outcome in highly conforming mobile-bearing total knee arthroplasty (TKA).

METHODS

Ninety osteoarthritic knees were randomly allocated to either the PCL-preserving group or the PCL-sacrificing group. Passive kinematics was recorded with a navigation system immediately after implantation. Three parameters (anterior/posterior translation, varus/valgus rotation, and internal/external rotation) were analysed from 0° to 120° flexion.

RESULTS

The PCL-preserving group (42 knees) had more varus rotation over 90° flexion (p < 0.05) and more anterior translation of the femur in all ranges of flexion (p < 0.05) than those in the PCL-sacrificing group (44 knees). There was no difference in the internal/external rotation (p > 0.05). The range of motion, functional scores, and radiographic results did not significantly differ between the two groups at the final follow-up. Three knees in the PCL-preserving group were revised: two presented with instability caused by traumatic attenuation of the PCL and one with subluxation of the insert due to a tight PCL.

CONCLUSION

The preservation of the PCL was not helpful for improving kinematics and clinical outcome in highly conforming mobile-bearing TKA.

Which total knee replacement implant should I pick?

Debate has raged over whether a cruciate retaining (CR) or a posterior stabilised (PS) total knee replacement (TKR) provides a better range of movement (ROM) for patients. Various sub-sets of CR design are frequently lumped together when comparing outcomes. Additionally, multiple factors have been proven to influence the rate of manipulation under anaesthetic (MUA) following TKR. The purpose of this study was to determine whether different CR bearing insert designs provide better ROM or different MUA rates. All primary TKRs performed by two surgeons between March 2006 and March 2009 were reviewed and 2449 CR-TKRs were identified. The same CR femoral component, instrumentation, and tibial base plate were consistently used. In 1334 TKRs a CR tibial insert with 3° posterior slope and no posterior lip was used (CR-S). In 803 there was an insert with no slope and a small posterior lip (CR-L) and in 312 knees the posterior cruciate ligament (PCL) was either resected or lax and a deep-dish, anterior stabilised insert was used (CR-AS). More CR-AS inserts were used in patients with less pre-operative ROM and greater pre-operative tibiofemoral deformity and flexion contracture (p < 0.05). The mean improvement in ROM was highest for the CR-AS inserts (5.9° (-40° to 55°) vs CR-S 3.1° (-45° to 70°) vs CR-L 3.0° (-45° to 65°); p = 0.004). There was a significantly higher MUA rate with the CR-S and CR-L inserts than CR-AS (Pearson rank 6.51; p = 0.04). Despite sacrificing or not substituting for the PCL, ROM improvement was highest, and the MUA rate was lowest in TKRs with a deep-dish, anterior-stabilised insert. Substitution for the posterior cruciate ligament (PCL) in the form of a PS design may not be necessary even when the PCL is deficient.

Cite this article: Bone Joint J 2013;95-B, Supple A:129–32.