Total knee replacement with retention of both cruciate ligaments

Complications of Bicruciate-Retaining Total Knee Arthroplasty: The Importance of Alignment and Balance

Bicruciate-retaining total knee arthroplasty (BCR TKA) results in kinematics closer to the native knee and in greater patient satisfaction but information concerning its outcome and complications is lacking.The goal of this study is to report the clinical and radiological outcomes of BCR prosthesis implanted using a spacer-based gap balancing technique and to assess if some preoperative factors are associated with a worse prognosis.A cohort of 207 knees in 194 patients who underwent BCR TKA, with a minimum 1-year follow-up, was retrospectively analyzed.Patients were followed at 6 weeks, 6 months, 1 year, and then every following year postoperatively, and filled questionnaires (Knee Society and Knee injury and Osteoarthritis Outcome Score) at every visit. Clinical and radiological assessments included range of motion, knee alignment, pain, and complications as defined by the Knee Society's Standardized list and definition of Complication of Total Knee Arthroplasty.Forty-three knees (20.8%) suffered major complications. Twenty-one knees (10.1%) underwent revision at an average of 32.1 months after the index procedure. Revision-free survival at 100 months was 85.7%. Revision was performed for aseptic tibial loosening in eight knees (3.9%) and stiffness in five knees (2.4%). There were 29 reoperations other than revision (14.0%), the most frequent procedure being manipulation under anesthesia in 14 knees (6.8%). Minor complications included tendonitis (20.8%), persistent synovitis (6.8%), and superficial wound infections (6.3%).All outcomes scores were greatly improved at the 1-year follow-up compared with preoperatively (p < 0.001). However, maximum flexion at the last follow-up was significantly reduced compared with preoperatively (mean maximum flexion ± standard deviation: 119.9 ± 15.6 vs. 129.9 ± 14.4, p < 0.001). Aseptic tibial loosening was associated with a hypercorrection in varus of preoperative valgus knees (p = 0.012).BCR TKA can give functional results similar to other types of prostheses but involves a substantial risk of complications. Important factors that can explain failed BCR TKA and guide its use were identified, more particularly knee alignment and its role in aseptic tibial loosening.

The function of cruciate ligaments in bi-cruciate retaining Total knee arthroplasty with asymmetrical design

BACKGROUND

Bi-cruciate retaining total knee arthroplasty with an asymmetrical design may improve knee function and clinical outcomes. This study aimed to compare the kinematics, anteroposterior laxity, and in situ forces of the anterior and posterior cruciate ligaments of knees subjected to this treatment with those of healthy knees.

METHODS

Seven fresh-frozen cadaveric knees were tested using a robotic/universal force-moment sensor system. The kinematics during passive flexion-extension motion and anteroposterior laxity for native knee, treated knee, and treated knee with cruciate ligament transection states were investigated. The motions of the intact and treated knees during each test were repeated after anterior/posterior cruciate ligament transection to calculate the in situ force in the ligaments.

FINDINGS

The screw-home movement of normal knees disappeared after treatment. The in situ force of the anterior cruciate ligament in treated knees was higher than that in intact knees at ˃15° during flexion and at 60° and 90° against an anterior force. The in situ force of the posterior cruciate ligament in treated knees was higher at 0°, 15°, and 30° during flexion and at all flexion angles against a posterior force.

INTERPRETATION

The screw-home movement of normal knees decreased, and the in situ force of the anterior and posterior cruciate ligaments increased after treatment.

Bicruciate-retaining total knee arthroplasty non-inferior to posterior-stabilized prostheses after 5 years: a randomized, controlled trial

PURPOSE

Bicruciate-retaining (BCR) prostheses may improve satisfaction of patient undergoing total knee arthroplasty (TKA). The objective of this randomized controlled trial was to assess whether BCR prostheses provide better clinical outcomes than posterior-stabilized (PS) prostheses.

MATERIALS AND METHODS

This is a randomized single-blind control trial involving a total of 77 patients with knee osteoarthritis, randomly assigned to undergo TKA with a BCR or PS implant between 2015 and 2019. Mean follow-up period was 39 months. Clinical and demographic data were extracted manually from medical records. Data acquisition included patient demographics, knee range of motion, and patient-reported outcomes via KSS, KOOS, WOMAC, and SF-12 scores.

RESULTS

A total of 38 patients were randomized to the PS group and 39 to the BCR group. At the 5-year follow-up, no statistical differences were noted for knee range of motion or patient-reported outcomes between the two groups, except for a greater knee flexion in the early follow-up period in the PS group. Five adverse events occurred in the BCR group compared to none in the PS group (p = 0.02).

CONCLUSION

BCR TKA yield similar clinical and patient-reported outcomes 5 years following the intervention compared with PS TKA. The BCR TKA had more complications.

LEVEL OF EVIDENCE

I (Randomized Controlled Trial).

Early outcomes of a novel bicruciate-retaining knee system: a 2-year minimum retrospective cohort study

INTRODUCTION

Bicruciate retaining (BCR) total knee arthroplasty (TKA) was designed to simulate natural knee kinematics and improve proprioception by retaining both the ACL and PCL. While the prospect of the design appears favorable to patients, previous designs have demonstrated modest survivorship rates compared to traditional designs. This study aims to report the early functional outcomes and implant survivorship of a novel BCR design.

MATERIALS AND METHODS

A multi-center, retrospective study was conducted identifying BCR TKA patients from 2016 to 2017. Patient demographics, quality outcomes, and post-operative complications were collected. A Kaplan-Meier analysis was used to evaluate revision-free survival.

RESULTS

One-hundred thirty-three patients with a mean follow-up time of 2.35 ± 0.25 years (range: 2.00-2.87 years) were identified. Patients receiving BCR TKA were, on average, 61.46 ± 9.27 years-old, obese (BMI = 31.80 ± 6.01 kg/m²), predominantly white (71.4%), and female (69.9%). The device was most often implanted using standard instruments (85.7%) compared to computer-assisted navigation (13.5%). Average length-of-stay was 1.77 ± 0.97 days. Six patients had a reoperation; three (2.5%) full revisions occurred for: infection (n = 1), arthrofibrosis (n = 1), and ACL rupture (n = 1); one (0.8%) tibial revision occurred for: arthrofibrosis; two (1.5%) liner exchanges occurred for: infection (n = 1) and arthrofibrosis (n = 1). Kaplan-Meier survivorship analysis of cumulative failure at 2-year showed a survival rate of 96.2% (95% confidence interval, 91.2-98.4%) for all-cause reoperation, 97.3% (91.6-99.1%) for aseptic revision, and 100% for mechanical failure.

CONCLUSION

Survivorship was 96.2% for all-cause reoperation, 97.3% for aseptic revision, and 100% for mechanical implant failure at 2-years. This novel BCR TKA demonstrated no implant-related complications and excellent survivorship outcomes over 2 years with comparable revision rates to those previously reported in the literature.

Fluoroscopic and radiostereometric analysis of a bicruciate-retaining versus a posterior cruciate-retaining total knee arthroplasty: a randomized controlled trial

AIMS

The aim of this study was to compare a bicruciate-retaining (BCR) total knee arthroplasty (TKA) with a posterior cruciate-retaining (CR) TKA design in terms of kinematics, measured using fluoroscopy and stability as micromotion using radiostereometric analysis (RSA).

METHODS

A total of 40 patients with end-stage osteoarthritis were included in this randomized controlled trial. All patients performed a step-up and lunge task in front of a monoplane fluoroscope one year postoperatively. Femorotibial contact point (CP) locations were determined at every flexion angle and compared between the groups. RSA images were taken at baseline, six weeks, three, six, 12, and 24 months postoperatively. Clinical and functional outcomes were compared postoperatively for two years.

RESULTS

The BCR-TKA demonstrated a kinematic pattern comparable to the natural knee's screw-home mechanism in the step-up task. In the lunge task, the medial CP of the BCR-TKA was more anterior in the early flexion phase, while laterally the CP was more posterior during the entire movement cycle. The BCR-TKA group showed higher tibial migration. No differences were found for the clinical and functional outcomes.

CONCLUSION

The BCR-TKA shows a different kinematic pattern in early flexion/late extension compared to the CR-TKA. The difference between both implants is mostly visible in the flexion phase in which the anterior cruciate ligament is effective; however, both designs fail to fully replicate the motion of a natural knee. The higher migration of the BCR-TKA was concerning and highlights the importance of longer follow-up.Cite this article: Bone Joint J 2023;105-B(1):35-46.

Proximal tibial morphology is associated with risk of trauma to the posteromedial structures during tibial bone resection reproducing the anatomical posterior tibial slope in bicruciate-retaining total knee arthroplasty

BACKGROUND

A tibial cut with the native posterior tibial slope (PTS) is a theoretical prerequisite in bicruciate-retaining total knee arthroplasty (BCRTKA) to regain physiological knee kinematics. The present study reveals tibial morphological risk factors of trauma to the posteromedial structures of the knee during tibial bone resection in BCRTKA.

METHODS

Fifty patients undergoing BCRTKA for varus knee osteoarthritis were analyzed. A three-dimensional tibial bone model was reconstructed using a computed tomography-based preoperative planning system, and the coronal tibial slope (CTS) and medial PTS (MPTS) were measured. Then, we set the simulated tibial cutting plane neutral on the coronal plane, posteriorly inclined in accordance with the MPTS on the sagittal plane, and 9 mm below the surface of the subchondral cortical bone (i.e., 11 mm below the surface of the cartilage) of the lateral tibial plateau. The association between the tibial morphology and the distance from the simulated cutting plane to the semimembranosus (SM) insertion (Dsm) was analyzed.

RESULTS

Of the 50 patients, 19 (38%) had negative Dsm values, indicating a cut into the SM (namely, below the posterior oblique ligament) insertion. The MPTS was negatively correlated with Dsm (r = -0.396, p = 0.004), whereas the CTS was positively correlated with Dsm (r = 0.619, p < 0.001). On multivariate linear regression analysis, the MPTS and CTS were independent predictors of Dsm.

CONCLUSION

In the setting of tibial cuts reproducing the native MPTS in BCRTKA, patients with larger PTS and smaller CTS had more risk of trauma to the posteromedial structures.

Posterior Tibial Slope Increases Anterior Cruciate Ligament Stress in Bi-Cruciate Retaining Total Knee Arthroplasty: In Vivo Kinematic Analysis

The study design involved here is experimental in nature. The resection of the anterior cruciate ligament (ACL) during conventional total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal in vivo knee kinematics. Bi-cruciate retaining (BCR) TKA designs allow the preservation of the ACL with the potential to restore native knee kinematics. This study aimed to investigate the effect of posterior tibial slope (PTS) on stress experienced by the ACL during weight bearing sit-to-stand (STS) and single-leg deep lunge. The ACL elongation patterns were measured in 30 unilateral BCR TKA patients during weight-bearing STS and single-leg deep lunge using a validated dual fluoroscopic tracking technique. The minimum normalized stress within the anteromedial (AM) and posterolateral (PL) bundle of the ACL during weight-bearing STS and single-leg deep lunge was found at a PTS of 3.7 degrees. The maximum AM and PL bundle stresses were observed at a PTS of 8.5 and 9.3 degrees, respectively during STS and at 8.4, and 9.1 degrees, respectively during single-leg deep lunge. There was a significant positive correlation between PTS and stress observed within the AM and PL bundle of the ACL during weight-bearing STS (R ² = 0.37; p < 0.01; R2  = 0.36; p = 0.01) and single-leg deep lunge (R ² = 0.42; p < 0.01; R ²= 0.40; p < 0.01). The study demonstrates that PTS of operated BCR TKA knees has a significant impact on the stress experienced by the preserved ACL during weight-bearing STS and single-leg deep lunge. This suggests that avoiding excessive PTS may be one of the surgical implant alignment factors to consider during surgery to minimize increased loading of the preserved ACL.

Bicruciate-retaining total knee arthroplasty: What’s new?

Primary total knee arthroplasty (TKA) is a widespread procedure to address end stage osteoarthritis with good results, clinical outcomes, and long-term survivorship. Although it is frequently performed in elderly, an increased demand in young and active people is expected in the next years. However, a considerable dissatisfaction rate has been reported by highly demanding patients due to the intrinsic limitations provided by the TKA. Bicruciate-retaining (BCR) TKA was developed to mimic knee biomechanics, through anterior cruciate ligament preservation. First-generation BCR TKA has not gained popularity due to its being a challenging technique and having poor survival outcomes. Thanks to implant design improvement and surgeon-friendly instrumentation, second-generation BCR TKA has seen renewed interest. This review will focus on surgical indications, kinematical basis, clinical results and latest developments of second-generation BCR TKA.

Anterior cruciate ligament intactness in osteoarthritic patients indicated for total knee arthroplasty: a systematic literature review and meta-analysis

Bi-cruciate retaining total knee arthroplasty (BCR TKA) is thought to result in more natural knee kinematics compared to conventional TKA designs. This may lead to a reduction in dissatisfied patients after TKA. An intact anterior cruciate ligament (ACL) is a prerequisite for implantation of a BCR TKA but the frequency of an intact ACL in patients indicated for TKA is not well known. The objective of this systematic literature review was to determine the presence of an intact ACL in patients undergoing TKA by intraoperative macroscopic or MRI assessment. A systematic literature review was conducted using PubMed™ and EMBASE™ in June 2020. The ACL of patients with knee osteoarthritis (OA) undergoing TKA was classified as present (including intact and degenerated) vs. absent, and as intact vs. not fully intact. Proportional meta-analyses were performed. 2840 articles were identified and screened. 135 full texts were analyzed and 18 studies met the inclusion criteria for subsequent qualitative and quantitative meta-analysis. Analysis of the status of the ACL when assessed intraoperatively during TKA showed that the ligament was present in 79.4% of patients (CI: 73.5-84.3%), from 14 studies with 2067 cases studied. The ACL was determined to be intact in 55.0% of patients (CI: 45.3-64.4%), from 14 studies with 1916 cases. Preoperative ACL assessment using MRI (2 studies) revealed it was present in 82.9% of 193 cases (CI: 76.9-87.6%), and intact in 56.8% of 176 cases (CI: 8.2-94.7%). This systematic literature review shows that the ACL is macroscopically intact in more than half of patients with knee OA undergoing TKA, based on intraoperative assessment of the ligament. The results suggest BCR TKA may be considered as an alternative to traditional TKA in a large number of TKA patients. More high-quality studies are needed to better understand the functional status of the ACL in TKA patients.Level of evidence III.

Cruciate ligament force of knees following mobile-bearing unicompartmental knee arthroplasty is larger than the preoperative value

We analyzed the implantation effects on cruciate ligament force in unicompartmental knee arthroplasty (UKA) and determined whether kinematics is associated with the cruciate ligament force. We examined 16 patients (17 knees) undergoing medial UKA. Under fluoroscopy, each participant performed a deep knee bend before and after UKA. A two-dimensional/three-dimensional registration technique was employed to measure tibiofemoral kinematics. Forces in the anteromedial and posterolateral bundles of both the anterior cruciate ligament (aACL and pACL) and the anterolateral and posteromedial bundles of the posterior cruciate ligament (aPCL and pPCL) during knee flexion were analyzed pre- and post-UKA. Correlations between changes in kinematics and ligament forces post-UKA were also analyzed. Preoperatively, the aACL forces were highly correlated with anteroposterior (AP) translation of the lateral condyles (Correlation coefficient [r] = 0.59). The pPCL forces were highly correlated with the varus–valgus angulation (r =  − 0.57). However, postoperatively, the PCL forces in both bundles were highly correlated with the AP translation of the medial femoral condyle (aPCL: r = 0.62, pPCL: r = 0.60). The ACL and PCL forces of the knees post-UKA were larger than those of the knees pre-UKA. Kinematic changes were significantly correlated with the cruciate ligament force changes.

The Association Between Cement Viscosity and Revision Risk After Primary Total Knee Arthroplasty

BACKGROUND

Recent case series have reported early failure with the use of high-viscosity cement (HVC) in total knee arthroplasty (TKA). We evaluated revision risk after TKA with HVC compared with medium-viscosity cement (MVC) in a large cohort.

METHODS

We conducted a cohort study using data from Kaiser Permanente's Total Joint Replacement Registry. Patients who underwent fully cemented primary TKA for osteoarthritis were identified (2001-2018). Only posterior-stabilized, fixed-mobility designs of the 3 highest-volume implant systems (DePuy PFC, Zimmer NexGen, and Zimmer Persona) were included to mitigate confounding from implant characteristics. Palacos (Zimmer/Heraeus) and Simplex (Stryker) cements comprised the HVC and MVC exposure groups, respectively. Propensity score-weighted Cox proportional hazards regression was used to evaluate risk for any revision during follow-up and risk for revision from aseptic loosening specifically.

RESULTS

The final cohort comprised 76,052 TKAs, 41.1% using MVC. The crude 14-year cumulative revision probability was 4.55% and 5.12% for TKA with MVC and HVC, respectively. In propensity score-weighted Cox models, MVC compared with HVC had a lower risk of any revision (hazard ratio = 0.82, 95% confidence interval = 0.70-0.95) while no difference was observed for revision from aseptic loosening (hazard ratio = 0.80, 95% confidence interval = 0.56-1.13).

CONCLUSION

While we observed a lower risk for any revision with the use of Simplex MVC compared with Palacos HVC, we did not observe a difference in revision for aseptic loosening specifically. Given the widespread use of HVC, additional research to investigate other HVC and potential mechanisms for failure outside of loosening is warranted.

LEVEL OF EVIDENCE

Level III.

In Vivo Knee Kinematics: How Important Are the Roles of Femoral Geometry and the Cruciate Ligaments?

BACKGROUND

While posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component.

METHODS

Tibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant.

RESULTS

In early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar.

CONCLUSION

Subjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.

In vivo kinematics and cruciate ligament forces in bicruciate-retaining total knee arthroplasty

We analyzed the effects of bicruciate-retaining total knee arthroplasty (BCR-TKA) on knee kinematics and cruciate ligament forces. Patients (N = 15) with osteoarthritis (OA) and an intact anterior cruciate ligament (ACL) underwent magnetic resonance imaging and single-plane fluoroscopy to measure tibiofemoral kinematics during two deep knee bend activities before and after BCR-TKA: (1) weight-bearing squat; (2) non-weight-bearing cross-legged sitting. Forces in ligament bundles were calculated using VivoSim. The dynamic range of varus-valgus angulation decreased from 3.9 ± 4.4° preoperatively to 2.2 ± 2.7° postoperatively. Preoperatively, the medial femoral condyle translated anteriorly from 10° to 50° of flexion, and posteriorly beyond 50° of flexion. Postoperatively, the medial and lateral femoral condyles translated posteriorly throughout flexion in a medial pivot pattern. ACL forces were high in extension and decreased with flexion pre- and postoperatively. PCL forces increased with flexion preoperatively and did not change significantly postoperatively. Preoperatively, ACL forces correlated with anteroposterior translation of the femoral condyles. Postoperatively, PCL forces correlated with anteroposterior translation of the lateral femoral condyle. BCR-TKA altered knee kinematics during high flexion activity which correlated significantly with changes in cruciate ligament forces.

Bi-cruciate retaining total knee arthroplasty: a systematic literature review of clinical outcomes

Total knee arthroplasty (TKA) has been shown to have good long-term outcomes and survivorship. Nonetheless, dissatisfied patients are frequently reported in the literature. Bi-cruciate retaining total knee prostheses (BCR TKA) were designed to address the demand for more kinematically functional implants that better reconstruct natural knee kinematics. In BCR TKA, the anterior cruciate ligament (ACL) is preserved. Improved patient-reported outcomes and satisfaction levels are expected. This review aimed to summarize indications for and clinical outcomes of BCR TKA. A systematic literature review on BCR TKA was performed. 24 articles were included for data analysis. Indications covered osteoarthritis, inflammatory arthritis and others. The degree of deformity was often but not always limited to minor axial deformity and contractures: maximum acceptable varus/valgus deformity reached 10°-30° and flexion contractures of 15°-65°. ACL intactness was macroscopically examined intraoperatively in nine studies and clinically tested in ten studies (e.g., Lachmann Test, drawer-test). Objective and patient-reported outcome scores were reported for follow-up periods of up to 22 years. Survival rates varied significantly. For first generation implants, 22-year survival reached 82% while a second generation design was associated with 13.5% revision rate at 18 months. Reasons for varying outcomes were not clear and may be attributed to the implant itself, surgical techniques and patient specific variables including changed expectations and functional demand. The literature has not shown clear indications and guidelines for the use of BCR implants. The promising results of first generation BCR TKA designs may be optimized through improved implant designs in the future. Further studies are advocated to provide the necessary evidence of second generation BCR TKA designs.

Insufficient lateral joint laxity after bicruciate-retaining total knee arthroplasty potentially influences kinematics during flexion: A biomechanical cadaveric study

BACKGROUND

Soft tissue balancing in bicruciate-retaining (BCR) total knee arthroplasty (TKA) is a challenge that must be overcome to achieve excellent clinical outcomes. However, the optimal degree of joint laxity has yet to be clarified. This cadaveric study sought to examine joint laxity after BCR TKA using a navigation system.

METHODS

Knee joint laxity was quantified using an image-free navigation system in 8 intact fresh frozen cadavers under three conditions: the native knee, BCR TKA knee, and BCR TKA knee after anterior cruciate ligament resection. Rotational kinematics in the BCR TKA knee during flexion were compared according to whether joint laxity was increased or decreased.

RESULTS

Knee joint laxity after BCR TKA under varus-valgus movement, anterior translation, and internal-external rotation loadings was similar to that of the native knee. However, lateral joint laxity was decreased during flexion in some cases. BCR TKA-treated knees with decreased lateral joint laxity at 90° of flexion demonstrated more limited tibial internal rotation in deep flexion than the native knee (p < 0.05). The loss of internal rotation in deep flexion was partly recovered by using a lateral insert with a posterior slope of +3°.

CONCLUSIONS

Restoring optimal joint laxity was not always straightforward in BCR TKA if the 4 ligaments were preserved. Lateral joint laxity was potentially decreased in BCR TKA and may result in kinematic conflict during flexion. Surgeons should be aware of the need to achieve sufficient lateral joint laxity in this type of BCR TKA.

Functional assessment of the anterior cruciate ligament in knee osteoarthritis

The purpose of this study was to evaluate anterior cruciate ligament (ACL) function in knee osteoarthritis (OA) and clarify the relationship of MRI and arthroscopic findings with ACL function. Eighty patients with knee OA were evaluated for anterior knee joint laxity, Kellgren-Lawrence grade, MRI ACL grade, arthroscopic ACL grade, osteophytes, and meniscus tears. ACL function was significantly correlated with osteophyte scores and medial and lateral meniscus tears. The MRI ACL grade was strongly correlated with the arthroscopic ACL grade, and anterior knee joint laxity decreased as the grades increased, suggesting a decrease in the elasticity of degenerated ACLs.

Early results with a bicruciate-retaining total knee arthroplasty: a match-paired study

BACKGROUND

The aim of this study is to compare 2 groups of total knee arthroplasties (TKAs): the bicruciate-retaining (BCR-group) and cruciate-retaining total knee arthroplasty (CR-group), evaluating the functional results in the short-term follow-up.

METHODS

24 BCR were included in the study and were compared with a group of 24 TKAs performed with the same implant, but with sacrifice of the ACL and retention of the posterior cruciate ligament. For preoperative and postoperative clinical evaluation, the visual analogue score (VAS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were used. Radiological evaluation included weight-bearing long-leg view, a Rosemberg view, lateral view of the knee and tangential view of the patella. Hip-knee-ankle angle (HKA) was recorded pre and postoperatively. Radiolucent lines (RLLs) were evaluated according the Knee Society Roentgenographic Evaluation System (KSRES).

RESULTS

At last follow-up the mean VAS score was 1.81 for BCR group and 1.43 for CR group (p = 0.61). The mean WOMAC score was 8.68 for BCR group and 12.81 for CR group (p = 0.33). As for the radiological evaluation, preoperative HKA angle was 0.53° varus for BCR group and 3.14° varus for CR group (p = 0.24); postoperative HKA was 0.72° valgus for BCR group and 0.38° valgus for CR group (p = 0.75). The percentage of RLLs was similar between the two groups (12% versus 15%).

CONCLUSIONS

BCR-TKA has showed to give similar functional and radiographic outcomes compared to conventional CR-TKA in a similar cohort of patients. An higher operative times and higher number of complications respect were found in BCR group. These results can be explained by the early learning curve experiences. Future randomized controlled trials should be performed to support new implant designs such as BCR.

LEVEL OF EVIDENCE

Level of evidence Case-control study, level III.

Greater postoperative relatively medial loose gap at 90° of flexion for varus knees improves patient-reported outcome measurements in anatomical bi-cruciate retaining total knee arthroplasty

BACKGROUND

The purpose of the present study was to measure the intraoperative joint gap using tensor device and pre- and, postoperative joint stability at 0, 30 and 90° of flexion using stress radiography and to identify whether these factors influence patient-reported outcome measurement (PROM) in anatomical bi-cruciate retaining (BCR) knee arthroplasty (TKA).

METHODS

Fifty-three knees with preoperative varus osteoarthritis of the knee underwent anatomical BCR TKA with oblique three-degree angle femorotibial joint line. The intraoperative medial and lateral joint gap using a tensor device and gap difference (lateral minus medial; varus laxity) were also calculated. Postoperative joint stability was measured using stress radiographs. PROM was also evaluated at 1.5 years postoperatively. The effect of intraoperative and postoperative joint stabilities on PROMs were analyzed using Spearman's rank correlation analysis.

RESULTS

Intraoperative greater difference between medial joint gap at 140° and 0° of flexion showed significant positive correlation with postoperative function of patellofemoral joint. Intraoperative varus laxity at extension improved postoperative symptoms in 2011 Knee Society Score (2011 KSS); greater postoperative lateral stability at 30 and 90° of flexion with the varus stress test was associated with the better patient expectation in 2011 KSS. Postoperative medial laxity at 90° of flexion with the valgus stress test positively correlated with the patient expectation and satisfaction in 2011 KSS.

CONCLUSIONS

Surgeons should notice that the postoperative lateral stability and medial laxity at 90° of flexion improved PROM in anatomical BCR TKA.

Erratum to "Greater postoperative relatively medial loose gap at 90° of flexion for varus knees improves patient-reported outcome measurements in anatomical bi-cruciate retaining total knee arthroplasty" [The Knee 27(5) (2020) 1534-1541]"

BACKGROUND

The purpose of the present study was to measure the intraoperative joint gap using tensor device and pre- and, postoperative joint stability at 0, 30 and 90° of flexion using stress radiography and to identify whether these factors influence patient-reported outcome measurement (PROM) in anatomical bi-cruciate retaining (BCR) knee arthroplasty (TKA).

METHODS

Fifty-three knees with preoperative varus osteoarthritis of the knee underwent anatomical BCR TKA with oblique 3° angle femorotibial joint line. The intraoperative medial and lateral joint gap using a tensor device and gap difference (lateral minus medial; varus laxity) were also calculated. Postoperative joint stability was measured using stress radiographs. PROM was also evaluated at 1.5 years postoperatively. The effect of intraoperative and postoperative joint stabilities on PROMs were analyzed using Spearman's rank correlation analysis.

RESULTS

Intraoperative greater difference between medial joint gap at 140° and 0° of flexion showed significant positive correlation with postoperative function of patellofemoral joint. Intraoperative varus laxity at extension improved postoperative symptoms in 2011 Knee Society Score (2011 KSS); greater postoperative lateral stability at 30 and 90° of flexion with the varus stress test was associated with the better patient expectation in 2011 KSS. Postoperative medial laxity at 90° of flexion with the valgus stress test positively correlated with the patient expectation and satisfaction in 2011 KSS.

CONCLUSION

Surgeons should notice that the postoperative lateral stability and medial laxity at 90° of flexion improved PROM in anatomical BCR TKA.

Abnormal knee kinematics caused by mechanical alignment in symmetric bicruciate-retaining total knee arthroplasty are alleviated by kinematic alignment

BACKGROUND

Bicruciate-retaining total knee arthroplasty (BCR-TKA) was developed to maintain anterior cruciate ligament function and thus reproduce natural knee kinematics postoperatively. Traditional surgical techniques, however, may cause several complications secondary to kinematic conflict and ligament overtension. The objective of this study was to use a computer simulation of symmetric BCR-TKA to evaluate the effects of alternative surgical techniques on knee kinematics and ligaments.

METHODS

A musculoskeletal computer model of a healthy knee was constructed and was used to simulate a BCR model with mechanical alignment (MA). Five adjusted models were investigated, characterized, respectively, by kinematic alignment (KA), two degrees increased tibial slope, two-millimeter distal setting of the tibial component, and an undersized femoral component with either MA or KA.

RESULTS

All models exhibited a normal femoral position against the tibia at knee extension, with no anterior paradoxical motion during mid-flexion. The healthy knee model showed medial pivot motion and rollback. In contrast, the BCR MA model demonstrated abnormal bi-condylar rollback with excessive tensions of the lateral collateral ligament and posterior cruciate ligament during knee flexion, whereas the undersized femoral model with MA partly reduced both tensions. The BCR KA model retained relatively physiological kinematics and suppressed excessive ligament tensions. However, no adjusted model completely reproduced healthy knee conditions.

CONCLUSIONS

The BCR MA model showed abnormal biomechanics due to kinematic conflict between the retained ligaments and the replaced joint surface. Surgeons using symmetric BCR-TKA should consider using the KA method to achieve sufficient ligament laxity throughout knee flexion.

Knee joint laxity is restored in a bi-cruciate retaining TKA-design

PURPOSE

The goal is to evaluate the passive stability of a bicruciate retaining, cruciate retaining and bicruciate substituting TKA design in relation to the native knee stability in terms of the laxity envelope. A bicruciate retaining knee prosthesis was hypothesized to offer a closer to normal knee stability in vitro.

METHODS

Fourteen cadaveric knee specimens have been tested under passive conditions with and without external loads, involving a varus/valgus and an external/internal rotational torque, distraction/compression force and an anteroposterior shear force. Subsequently, the native knee, bicruciate retaining, cruciate retaining and finally a bicruciate substituting total knee arthroplasty were tested.

RESULTS

Through the range of motion, the width of the varus/valgus and internal/external laxity envelope for the native knee and the bicruciate retaining knee were almost equivalent, whereas the cruciate retaining and the bicruciate substituting knee displayed less laxity and more joint distraction. In all prosthetic knees, an equal anteroposterior laxity was seen for the lateral and medial side whereas in the native knee, a difference in laxity was seen between the stable medial side and the more mobile lateral side.

CONCLUSION

Bicruciate retaining knee prostheses can restore normal laxity and thus have the potential to offer more normal knee function. Restoration of natural peri-articular soft-tissue tension is clinically important because of its obvious effects on joint stability and range of motion. Furthermore, the results of this study could help to establish the ideal ligament tension and laxity in more conventional implants by approaching the normal values for passive knee evaluation as presented here.

Bicruciate-retaining total knee arthroplasty reproduces in vivo kinematics of normal knees to a lower extent than unicompartmental knee arthroplasty

PURPOSE

This study aimed to clarify the natural knee kinematics provided by bicruciate-retaining total knee arthroplasty (BCR-TKA) compared with those of unicompartmental knee arthroplasty (UKA) and normal knees.

METHODS

Volunteers and patients who had undergone UKA and BCR-TKA with anatomical articular surface performed squatting motion under fluoroscopy. To estimate the knee's spatial position and orientation, a two-dimensional/three-dimensional registration technique was used. The rotation angle and anteroposterior translation of the medial and lateral sides of the femur relative to the tibia in each flexion angle were directly evaluated using the same local coordinate system and their differences amongst the three groups were analysed using two-way analysis of variance and Bonferroni post hoc pairwise comparison.

RESULTS

From 0° to 10° of flexion, the femoral external rotation angle of BCR-TKA knees was significantly greater than that of normal and UKA knees and the medial side of BCR-TKA knees was significantly more anteriorly located than that of normal and UKA knees. From 40° to 50° of flexion, the medial side of UKA knees was significantly more posteriorly located than that of normal and BCR-TKA knees. From 30° to 120° of flexion, the lateral side of BCR-TKA knees was significantly more anteriorly located than that of normal and UKA knees.

CONCLUSION

The in vivo kinematics of BCR-TKA knees reproduces those of normal knees to a lower extent than those of UKA knees. Thus, BCR-TKA with anatomical articular surface reproduces in vivo kinematics of normal knees to a lower extent than UKA.

LEVEL OF EVIDENCE

III.

In vivo kinematics of deep lunges and sit-to-stand activities in patients with bicruciate-retaining total knee arthroplasty

AIMS

The removal of the cruciate ligaments in total knee arthroplasty (TKA) has been suggested as a potential contributing factor to patient dissatisfaction, due to alteration of the in vivo biomechanics of the knee. Bicruciate retaining (BCR) TKA allows the preservation of the cruciate ligaments, thus offering the potential to reproduce healthy kinematics. The aim of this study was to compare in vivo kinematics between the operated and contralateral knee in patients who have undergone TKA with a contemporary BCR design.

METHODS

A total of 29 patients who underwent unilateral BCR TKA were evaluated during single-leg deep lunges and sit-to-stand tests using a validated computer tomography and fluoroscopic imaging system. In vivo six-degrees of freedom (6DOF) kinematics were compared between the BCR TKA and the contralateral knee.

RESULTS

During single-leg deep lunge, BCR TKAs showed significantly less mean posterior femoral translation (13 mm; standard deviation (SD) 4) during terminal flexion, compared with the contralateral knee (16.6 mm, SD 3.7; p = 0.001). Similarly, BCR TKAs showed significantly less mean femoral rollback (11.6 mm (SD 4.5) vs 14.4 mm (SD 4.6); p < 0.043) during sit-to-stand. BCR TKAs showed significantly reduced internal rotation during many parts of the strenuous flexion activities particularly during high-flexion lunge (4° (SD 5.6°) vs 6.5° (SD 6.1°); p = 0.051) and during sit-to-stand (4.5° (SD 6°) vs 6.9° (SD 6.3°); p = 0.048).

CONCLUSION

The contemporary design of BCR TKA showed asymmetrical flexion-extension and internal-external rotation, suggesting that the kinematics are not entirely reproduced during strenuous activities. Future studies are required to establish the importance of patient factors, component orientation and design, in optimizing kinematics in patients who undergo BCR TKA. Cite this article: Bone Joint J 2020;102-B(6 Supple A):59-65.

Indications for bi-cruciate retaining total knee replacement: An international survey of 346 knee surgeons

There is limited evidence on total knee arthroplasty (TKA) that retains the anterior and the posterior cruciate ligaments. Bi-cruciate retaining (BCR) TKA is considered to show improved clinical function and kinematics. This survey aimed to (1) identify interest in and acceptance of BCR TKA surgery and (2) to capture the range of indications for BCR in the opinion of practicing knee surgeons. 346 surgeons with experience in TKA surgery completed a bi-lingual online survey. Demographics, arthroplasty experience as well as acceptance of and indications for BCR TKA were collected. 53 surgeons were experienced in BCR TKA and 225 would consider implanting it. A mean of 19.5% of TKA patients were considered eligible for BCR TKA. 56.3% were thought to have intact ACL at the time of TKA surgery. Surgeons were not likely to perform BCR TKA in patients with inflammatory arthritis, aged over 80, BMI above 34.9 kg/m², a varus or valgus deformity of more than 10° and flexion contractures of more than 10°. There is strong interest among orthopedic surgeons to perform BCR TKA and the percentage of potentially eligible patients is high. Significant joint deformity is a limitation of BCR TKA, while age and high BMI are less relevant. BCR TKA experienced surgeons are less restrictive.

A Narrative Review: The Use of the Topical NSAID Ibuprofen for the Treatment of Knee Osteoarthritis. Supporting Clinician Decision-Making in the First-Line Treatment of Osteoarthritis

A Narrative Review

The use of the topical nonsteroidal anti-inflammatory drugs (NSAID) ibuprofen for the treatment of knee osteoarthritis. Supporting clinician decision-making in the first-line treatment of osteoarthritis.

Objective

To open discussion at a clinical level on the guidelines for the pharmacological management of osteoarthritis of the knee, this narrative review looks into the use of topical NSAID being a clinically effective, safe, and cost-efficient treatment compared to an oral alternative.

Background

With the over prescription of NSAIDs in the age of above 65 years, there has been a call for increased restrictions of the sale of oral preparations of NSAIDs. It is our view that there is still a lack of awareness in the benefit of topical NSAIDs to the patient (no evidence of adverse reactions recorded by the Joint Formulary Committee [JFC] to date) as well as provider (topical application is cheaper as a National Health Service [NHS] prescription).

Methods

Key online resources included PubMed, Athens, Cochrane Library, Google Scholar, MEDLINE, and relevant clinical and commissioning guidelines with the final date of data collection in March 2017. We also contacted the manufacturer and license holder directly for further clarification. Randomized, double-blind control studies, commissioned reports, International Guidelines, MEHA Guidelines, and license holder data were included. Where possible studies included had to have fair randomization and adhere to key treatment pathways as highlighted by National Institute for Health and Clinical Excellence (NICE) and other guidelines.

Discussion

Current guidelines advise that patients who seek initial treatment of osteoarthritis of the knee should consider a combination of treatment modalities, including pharmacological therapies, particularly the use of NSAIDs. At a clinical level, a reoccurring issue identified with this advice is the inappropriate use of oral NSAIDs, and the concern that the risks associated with ease of access ("over the counter"), and overuse, may result in systemic adverse events in this cohort of patients. Multiple studies have examined the negative effect of oral NSAIDs and the associated risks of use. We were unable to source studies that showed any adverse systemic events from the use of topical NSAIDs; however, there are good quality trials comparing oral to topical NSAIDs, showing similar levels of efficacy at 6 and 12 weeks.

Conclusion

Topical NSAIDs provide good levels of pain relief in subjects with mild to moderate knee osteoarthritis. There is also evidence for the use of the topical application being a clinically effective, safe, and cost-efficient treatment.

Comparable level of joint awareness between the bi-cruciate and cruciate retaining total knee arthroplasty with patient-specific instruments: a case-controlled study

PURPOSE

Bi-cruciate-retaining total knee arthroplasty (BCR-TKA) is recognized as an alternative to the cruciate-retaining total knee arthroplasty (CR-TKA) within the pursuit of retrieving the "forgotten artificial knee joint". The aim of this study was to provide a short-term comparison in functional and clinical outcomes between BCR- and CR-TKA.

METHODS

The cohort consisted of 61 BCR-TKA patients, matched with 61 suitable CR-TKA patients, and operated between 2014 and 2016 due to osteoarthritis. Patient-reported outcome measurements were assessed preoperatively and at 3, 12, 24 and 36 months postoperatively. In addition, perioperative conditions were observed and radiological images were analysed pre- and 1 year postoperatively. Effect size for the FJS-12 was calculated at 3-year follow-up to quantify the difference between BCR- and CR-TKA.

RESULTS

Patients reported a significant improved health-related quality of life (p = 0.017) and a non-significant difference in joint awareness at 3-year-follow-up with a moderate effect size (0.4). Operating time in BCR-TKA (1:16, ± 0:16) is significantly longer (p < 0.000) than in CR-TKA (0:50, ± 0:12). Blood loss significantly increased (p = 0.005) in BCR-TKA (246.4 cc, 79.8) compared to CR-TKA (195.5 cc, ± 106.2). Comparable length of hospital stay (n.s.) was observed in BCR-TKA (1.1 days, ± 1.1) and CR-TKA (1.3 days, ± 1.3). Outliers of the hip-knee-ankle axis occurred significantly more frequent (P = 0.015) in the BCR group (37.7%) compared to CR-TKA (18.0%).

CONCLUSION

Joint awareness of the BCR-TKA was not significantly reduced compared to the CR-TKA. However, this study illustrates that bi-cruciate-retaining surgical technique for TKA is a promising step further in the pursuit of reducing joint awareness and retrieving the artificial forgotten total knee. Since a functional ACL increases rotational stability and proprioception, future research should focus on knee kinematics in modern BCR-TKA measured with gait analyses.

LEVEL OF EVIDENCE

IV therapeutic, retrospective, cohort study.

Mean Three-Year Survivorship of a New Bicruciate-Retaining Total Knee Arthroplasty: Are Revisions Still Higher Than Expected?

BACKGROUND

Given the need for continued post-market surveillance, especially on novel implants, the present study attempts to determine the 3-year survivorship and patient-reported outcomes of a contemporary bicruciate-retaining total knee arthroplasty design, and to determine if a learning curve existed which could explain previously reported revision rates.

METHODS

We performed a retrospective review on a consecutive series of 141 bicruciate-retaining total knee arthroplasties performed at our institution between May 2013 and October 2015. Thirty-four knees (19%) missing 2-year follow-up were excluded. Mean follow-up was 3 years (range 0.34-4.9). Patients who died (n = 5) or were revised prior to 2 years (n = 6) were included. A Kaplan-Meier analysis was used to evaluate revision-free survival.

RESULTS

Survivorship at 3 years was 88% (82%-93%). Revisions were for isolated tibial loosening (5/19), anterior cruciate ligament (ACL) impingement (3/19), pain (4/19), unknown reasons (3/19), femoral and tibial loosening (2/19), ACL deficiency (1/19), and arthrofibrosis (1/19). The mean physical function computerized adaptive test T-score was 45 units (range 23-63). The mean T-scores for Patient-Reported Outcomes Measurement Information System Global measures were 49 (range 27-68) for physical health, 50 (range 28-68) for mental health, and a median 3 (interquartile range 1-8) on the numeric pain scale.

CONCLUSION

Revision-free survival of 88% at 3 years was lower than existing traditional TKA designs. The primary failure mechanisms were tibial loosening, ACL impingement, and pain. In the setting of higher than anticipated revision rates, despite patient-reported outcomes that are not different than seen in the general population, it is possible that further refinement in implant design or surgical technique may be needed prior to widespread use of this, or similar implant designs.

In-vivo elongation of anterior and posterior cruciate ligament in bi-cruciate retaining total knee arthroplasty

Anterior and posterior cruciate ligament (ACL and PCL) sacrifice in contemporary total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal knee kinematics. Bi-cruciate retaining (BCR) TKA design allows retention of both ACL and PCL. However, there is a limited data on the ACL/PCL in-vivo elongation characteristics of BCR TKA. The study aimed to evaluate and compare the in-vivo elongation patterns of ACL/PCL between BCR TKA and contralateral non-implanted knee and to explore potential factors leading to the changed elongation patterns between limbs. ACL/PCL elongations of both knees during sit-to-stand were measured in 29 unilateral BCR TKA patients using a validated dual fluoroscopic tracking technique. Joint gap changes of the BCR TKA knees relative to the contralateral knee were quantified. BCR TKA and the contralateral non-implanted knee exhibited similar ACL elongation at extension and clinical anterior knee laxity. However, BCR TKA showed significantly greater PCL elongation during flexion than the non-implanted knee. Variation of changed elongation was observed for both ACL and PCL, suggesting a heterogeneous restoration of normal ACL/PCL functions. A significant correlation was found between extension joint gap change and the change of ACL elongation, highlighting the importance of precise joint line restoration and soft tissue balancing during BCR TKA surgery. Our findings suggest that BCR TKA did not fully restore "near-normal" cruciate ligament elongation patterns and anteroposterior stability. Considerable heterogeneity remains in the retained ligament elongation patterns and warrants further investigations of multifactorial factors to optimize ACL/PCL functions in BCR TKA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3239-3246, 2018.

Native rotational knee kinematics are lost in bicruciate-retaining total knee arthroplasty when the tibial component is replaced

PURPOSE

To compare the kinematics between native knees and knees that have undergone bicruciate-retaining (BCR) total knee arthroplasty (TKA) with cruciate-retaining (CR) TKA converted from BCR TKA in the same whole-body cadaveric specimen using a navigation system and, if differences exist, to investigate the point at which normal kinematics are lost during the procedure.

METHODS

The rotational kinematics throughout passive flexion of the native knee and of knees after meniscectomy, femoral replacement, BCR TKA, or CR TKA were assessed in nine fresh frozen cadavers using an image-free navigation system.

RESULTS

The rotational kinematic pattern of a knee after BCR TKA was different from that of a native knee, especially in the early flexion phase, and was similar to that after CR TKA. Screw-home movement was not observed after BCR TKA, but still occurred after meniscectomy or femoral replacement with intact cruciate ligaments and an intact tibial articular surface.

CONCLUSION

The rotational kinematics of the native knee are not always preserved after BCR TKA. Native rotational kinematics are preserved after meniscectomy and femoral replacement, but are lost after tibial replacement in BCR TKA. Surgeons should pay close attention to maintain the anteroposterior stabilizing function of the ACL in BCR TKA, rather than to restore the native rotational kinematics.

ACL Function in Bicruciate-Retaining Total Knee Arthroplasty

BACKGROUND

Bicruciate-retaining total knee arthroplasty (BCR-TKA) is attracting attention because of the functional and satisfaction outcomes associated with keeping the anterior cruciate ligament (ACL) intact. However, knowledge of the functional importance of the ACL after BCR-TKA is limited. We performed a biomechanical investigation of ACL function following BCR-TKA compared with that in the intact knee.

METHODS

We investigated 8 fresh-frozen human cadaveric knees using a 6-degrees-of-freedom robotic system that allowed natural joint motion. Three knee states-intact knee, BCR-TKA, and BCR-TKA with ACL transection (BCR-TKA + ACLT)-were evaluated. For each knee state, the kinematics during passive flexion-extension motion (from 0° to 120°) and anteroposterior laxity at 0°, 15°, 30°, 60°, and 90° of flexion in response to a 100-N load were investigated. The recorded knee motions of the intact and BCR-TKA knees during each test were repeated after ACLT to calculate the ACL in situ force.

RESULTS

The femur in the BCR-TKA group translated posteriorly and rotated externally during passive knee flexion and was in an anterior position compared with the femur in the intact-knee state. After ACLT, the femur translated posteriorly, compared with the BCR-TKA group, at 0° and 10° (p < 0.05). The anteroposterior laxities of the BCR-TKA and intact knees were comparable at all flexion angles and increased 2-fold or more after ACLT (p < 0.01). The ACL in situ force in the BCR-TKA knees was 2-fold to 6-fold higher than that in the intact knees at 0°, 15°, 90°, and 120° during a passive path (p < 0.05) and equivalent to that in the intact knees under anterior loading.

CONCLUSIONS

The preserved ACL in the BCR-TKA knees was functional, like the ACL in the intact knees, under anterior tibial loading and contributed to good anteroposterior stability. However, the kinematics and ACL in situ force differed between the intact and BCR-TKA knees during passive flexion-extension movements.

CLINICAL RELEVANCE

Surgeons may not be able to prevent overtensioning of the ACL during a standardized BCR-TKA procedure, which could potentially limit range of motion.

Level and Downhill Walking to Assess Implant Functionality in Bicruciate- and Posterior Cruciate-Retaining Total Knee Arthroplasty

BACKGROUND

The goal of this study is to set up a functional motion analysis test to examine effects of the anterior cruciate ligament in total knee arthroplasty (TKA) patients by comparing knee kinematics, kinetics, and muscle activation patterns during level and downhill walking for patients with posterior cruciate-retaining (PCR) and bicruciate-retaining (BiCR) TKAs.

METHODS

Motion and electromyography (EMG) data were collected for 12 subjects (4/8 male/female, 64 ± 11 years, 31.3 ± 7.3 body mass index, 6/6 right/left) with BiCR TKAs and 15 subjects (6/9 male/female, 67 ± 7 years, 30.5 ± 5.1 body mass index, 4/11 right/left) with PCR TKAs during level and downhill walking using the point cluster marker set and surface electrodes placed on the vastus medialis obliquus, rectus femoris, biceps femoris, and semitendinosus muscles.

RESULTS

Level walking exhibited no significant differences in knee kinematics, kinetics, or EMG patterns. During downhill walking, BiCR subjects had significantly lower peak muscle activity in the vastus medialis obliquus and rectus femoris (P = .045 and .018, respectively), a trending higher peak knee flexion moment (2.0 ± 0.6% BW*HT vs 1.5 ± 0.6% BW*HT, P = .076), and significantly more knee flexion at heel strike (5.1° ± 4.7° vs 1.8° ± 2.8°, P = .044) compared with PCR subjects.

CONCLUSION

Anterior cruciate ligament retention led to altered muscle recruitment during downhill walking in BiCR subjects compared with PCR subjects; thus, BiCR TKAs may offer some neuromuscular benefits for stabilizing the knee joint. In conclusion, level and downhill walking knee kinematics and kinetics combined with corresponding quadriceps and hamstrings EMG signals begin to build an overall picture of implant functionality.

Modern Day Bicruciate-Retaining Total Knee Arthroplasty: A Short-Term Review of 146 Knees

BACKGROUND

Bicruciate retaining (BCR) implants were first proposed in the 1960s with the polycentric knee. Given the technical difficulty of implanting these devices, and the mixed results at the time, the BCR concept had stalled, until recently. This study seeks to provide a short-term review of the BCR implant design, describe patient-reported outcomes, and discuss key aspects to ensure successful implantation of the modern-day BCR implant design.

METHODS

Between October 2014 and December 2016, the senior author performed 146 primary total knee arthroplasties using BCR implants. Arthritic knees, with minimal soft tissue damage and an intact anterior cruciate ligament, were the general indications used for this cohort. All patients implanted with the BCR device were included in this analysis. One hundred forty-six (100%) BCR knees were available for follow-up at an average of 12 months (range, 1-33 months) postoperatively.

RESULTS

Ninety-one percent of respondents reported their knee always or sometime feels normal, with only 9% of respondents reporting their knee never feels normal. Our study reports 94% of patients reported neutral satisfaction or higher, with only 6% of patients reporting dissatisfaction and 1% reported being very dissatisfied. Of all 146 BCR devices implanted, there were 2 (1.4%) revisions and 1 (0.7%) reoperation, a manipulation under anesthesia.

CONCLUSION

This is the largest consecutive series of BCR total knee arthroplasties using the modern-day implant design with 1-year follow-up in the United States. The results of our study show great patient-reported satisfaction, function, and short-term outcomes for patients implanted with the new BCR design.

Reduced joint-awareness in bicruciate-retaining total knee arthroplasty compared to cruciate-sacrificing total knee arthroplasty

PURPOSE

There is rising impact of patient-reported outcome (PRO) measurement in joint arthroplasty over the past years. Bicruciate-retaining implants have shown more physiologic knee kinematics and provide superior proprioceptive capacities. The aim of this study was to evaluate if the functional properties of this new implant design lead to improved PRO results after total knee arthroplasty (TKA).

METHODS

This prospective, controlled trial compares PRO of bicruciate-retaining total knee arthroplasty (BCR-TKA) to unicondylar knee arthroplasty (UKA) and standard posterior-stabilized total knee arthroplasty (PS-TKA). We evaluated 102 patients (34 patients in each group) 18 months postoperatively after knee arthroplasty. Primary outcome measure was the Forgotten Joint Score (FJS).

RESULTS

The BCR-group showed the same level of joint awareness as the UKA-group (p = 0.999). The second control group of PS-TKA patients had a lower mean score value in the FJS compared to the BCR-group (p = 0.035) and UKA-group (p = 0.031). There was no correlation of age, gender, body mass index (BMI) and the FJS. No relevant floor- or ceiling effects occurred.

CONCLUSIONS

This study found reduced joint awareness for BCR-TKA compared to a standard total knee arthroplasty. The score values of the BCR-group were equal to the UKA-group. Further prospective, randomized studies to investigate long-term survivorship of bicruciate-retaining implants are needed.

LEVEL OF EVIDENCE

Level II.

The minimal clinically important difference for Knee Society Clinical Rating System after total knee arthroplasty for primary osteoarthritis

PURPOSE

The Knee Society Clinical Rating System (KS) is one of the most popular tools used to assess patient outcome after total knee arthroplasty (TKA), but its minimal clinically important difference (MCID) has not been identified. This study aims to identify the MCID of KS function score (KS-FS) and knee score (KS-KS) after TKA in patients with primary knee osteoarthritis.

METHODS

The authors retrospectively analysed patients who underwent TKA for primary knee osteoarthritis between 2005 and 2015 in a single institution. KS-FS, KS-KS, and Oxford Knee Score (OKS) were collected pre-operatively and 2 years post-operatively. Patient satisfaction with TKA at 2 years was also collected. Anchor-based approach with 2 external indicators was used. The MCID for KS-FS and KS-KS was determined using simple linear regression according to patient satisfaction with TKA and the MCID of OKS.

RESULTS

The mean age of the 550 subjects studied was 66 ± 8 years. There were 373 (67.8 %) female subjects. The KS-FS improved by 22.8 (95 % CI 20.9-24.6) points, and the KS-KS improved by 44.4 (95 % CI 42.6-46.3) points. The MCID identified for KS-FS is between 6.1 (95 % CI 5.1-7.1) and 6.4 (95 % CI 4.4-8.4) and between 5.3 (95 % CI 4.3-6.3) and 5.9 (95 % CI 3.9-7.8) for KS-KS.

CONCLUSIONS

This is the first study, to the knowledge of the authors, to identify the MCID of KS. This will allow future trials to have an accurate prediction of sample size. Clinically, physicians will be able to better interpret outcomes of TKA studies to guide a treatment option.

LEVEL OF EVIDENCE

IV.

Proprioception after bicruciate-retaining total knee arthroplasty is comparable to unicompartmental knee arthroplasty

PURPOSE

Rising expectations in functional performance of total knee joints are inciting further improvement of knee arthroplasty implants. From a patient-centred view, bicruciate-retaining models provide a more natural feeling knee. However, there is no evidence of functional advantage for these implants. The aim of this study was to evaluate balance ability as a measure of proprioception in patients with a bicruciate-retaining total knee arthroplasty.

METHODS

A prospective, controlled trial was conducted to compare balance ability in 60 patients after arthroplasty of the knee for osteoarthritis. We compared patients with a bicruciate-retaining knee arthroplasty (BCR group) to a control group of patients with a medial unicompartmental knee arthroplasty (UKA group) and another control group of patients with a posterior stabilized total knee arthroplasty (PS group). The patient population comprised 30 women (50.0 %) and 30 men in three cohorts of 20 each. The mean age was 62.1 ± 8.0 years (range 43-78). Patients were evaluated preoperatively and 9 months post-operatively. The evaluation included clinical, radiological, and balance testing-a single-leg stance with eyes closed compared to eyes open. The difference in area of sway between eyes closed and eyes open represents static balance ability after knee arthroplasty.

RESULTS

Perioperative data showed that there was no intra-operative fracture of the intercondylar eminence. There was a decreased post-operative knee extension 9 months post-operative in the BCR group, which was not clinically relevant in any case. We recorded a lower difference in the area of sway between eyes closed and eyes open (ΔA _(ec-eo)) for the BCR group (p = 0.01) and the UKA group (p = 0.04) compared to the PS group.

CONCLUSIONS

This study found superior static balance ability after preservation of both cruciate ligaments in arthroplasty of the knee, indicating superior proprioceptive function. Hence, BCR implants could provide improved functional properties. Superior proprioceptive function of bicruciate-retaining implants can be an important factor in implant selection. Further prospective, randomized studies to investigate kinematics and long-term survivorship of bicruciate-retaining implants are needed.

LEVEL OF EVIDENCE

II.

Clinical, radiological and survivorship results after ten years comparing navigated and conventional total knee arthroplasty: a matched-pair analysis

PURPOSE

Our aim was to compare the long-term outcome between navigated and conventional total knee arthroplasty (TKA), which is currently not known.

METHODS

Long-term survivorship, clinical scores and radiographic results of a matched-pair group of 350 patients (350 knees) treated with navigated (n = 157) or conventional (n = 188) TKA for osteoarthritis over a period of 11 years were reviewed retrospectively.

RESULTS

The mean clinical follow-up was ten years. There were no clinically relevant differences with respect to any clinical outcome, patient satisfaction or pain between the two groups. Coronal leg alignment was closer (1.7-3.1°) to the neutral mechanical axis in the navigated group compared with the conventional group (2.6-4.7°). A total of 12 knees (6.4%) in the conventional group and three (1.9%) in the navigated group underwent revision surgery (p = 0.04), resulting in an absolute risk reduction of 4.5% for revision surgery by using navigation. Using any revision as an end point, the ten-year Kaplan-Meier survivorship was 98.1% in the navigated and 92.5% in the conventional group.

CONCLUSIONS

Navigated TKA improves implant survivorship compared with conventional TKA.

Higher Frequency of Reoperation With a New Bicruciate-retaining Total Knee Arthroplasty

BACKGROUND

With as many as 25% of patients reporting residual knee symptoms after primary total knee arthroplasty (TKA), alternative implant designs and surgical techniques have been proposed to further reduce these symptoms. There is growing evidence that retention of the anterior cruciate ligament (ACL) results in more natural knee kinematics; thus, implants with more normal joint mechanics could provide improved physical function postoperatively and reduce the amount of residual symptoms. Advancements in the bicruciate-retaining (BCR) TKA implant design have been made, and based on these, we wished to compare the BCR with a more traditional cruciate-retaining (CR) implant.

QUESTIONS/PURPOSES

(1) Was there a difference in the risk of reoperation after primary TKA between BCR and CR implant designs? (2) Was there a difference in the radiographic findings of radiolucent lines (RLLs) between the implant designs? (3) Was there a difference in patient-reported and clinical outcomes between the two implant designs?

METHODS

Between January 2013 and May 2014, two surgeons performed 475 primary TKAs. During this time, 78 (16%) of these were performed with BCR implants and 294 (62%) with CR implants; the remainder were performed with anterior-stabilized or more constrained designs as a result of increased deformity and/or ligamentous deficiencies. During this period, the general indications for BCR TKA were arthritic knees with only slight to moderate deformity and sufficient ligamentous integrity of both the ACL and posterior cruciate ligament. The indications for CR TKA were similar other than these patients presented with a deficient ACL. A total of 66 (85%) of the BCR and 237 (81%) of the CR TKAs were available for followup at a minimum of 12 months or when reoperation occurred before 12 months (mean, 18 months; range, 2-32 months). With the numbers available, there were no differences between the groups in terms of age and sex, but the patients undergoing CR TKA had a greater mean body mass index (33 ± 7 versus 31 ± 5 kg/m², p = 0.032). The frequency of early reoperation was compared between the groups as were radiographic evidence of RLL, patient-reported outcomes, and knee range of motion (ROM).

RESULTS

Knees in the BCR group had a higher frequency of all-cause revision (5% [three of 66] versus 1.3% [three of 237]; hazard ratio (HR), 7.44; 95% confidence interval [CI], 1.24-44.80; p = 0.028). Knees in the BCR group had a higher frequency of irrigation and débridement with component retention (HR, 0.07; 95% CI, 0.02-0.28; p < 0.001). No differences were found between groups for subsequent manipulation (HR, 0.34; 95% CI, 0.08-1.42; p = 0.137). The proportion of RLLs was greater in the BCR group (HR, 2.93; 95% CI, 1.62-5.32; p < 0.001) compared with the CR group. There were no differences between the groups in terms of the Physical Function Computerized Adaptive Test scores, Global10 scores or knee ROM outcomes.

CONCLUSIONS

Preliminary short-term findings suggest the BCR implant has inferior survivorship and concerning radiographic findings when compared with a conventional CR implant with respect to complications after primary TKA. These findings raise concerns about the new BCR design; however, further randomized trials are necessary to determine superiority between alternative implant designs.

LEVEL OF EVIDENCE

Level III, therapeutic study.

The utility of bicruciate-retaining total knee arthroplasty

Background

We describe the features of modern and historical bicruciate-retaining (BCR) total knee arthroplasty (TKA) implants compared with other TKA implant designs, reviewing kinematics, proprioception, operative technique, and clinical results.

Methods

We performed a review based on PubMed, Embase, CINAHL Plus, and Cochrane databases from January 1990 to April 2016 using combinations of the following keywords: “bicruciate-retaining arthroplasty,” “bicruciate-retaining total knee arthroplasty,” “bicruciate-retaining TKA,” “kinematics,” “knee kinematics,” and “TKA kinematics.”

Results

Four studies have supported the notion that preservation of both cruciate ligaments in TKA preserves more “normal” knee kinematics. BCR implants provide greater proprioceptive performance when compared with posterior cruciate-retaining (CR) TKA implants. However, the operative implantation is more challenging with BCR TKAs, requiring the surgeon to take additional precautions. Overall, there did not seem to be a significant difference in short-term clinical outcomes between the BCR and CR implants.

Conclusions

The utility of BCR TKA is still debatable. The literature has not shown clear indications and guidelines for the value and use of this implant. Although kinematics have been shown to mirror the native knee more closely, the clinical outcomes of BCR vs CR TKAs do not differ significantly. Moreover, additional care must be taken when inserting a BCR implant. The anterior cruciate ligament exploration and preservation is more challenging and certain preparation and precautions must take place. Overall, we have not found that BCR implants are significantly superior to CR implants with regards to short term clinical outcomes despite the BCR TKA having improved kinematics and proprioception.

Tibial component considerations in bicruciate-retaining total knee arthroplasty: A 3D MRI evaluation of proximal tibial anatomy

BACKGROUND

Restoration of normal anatomy and proper ligament balance are theoretical prerequisites for reproducing physiological kinematics with bicruciate-retaining total knee arthroplasty (TKA). The purpose of this study was to use a 3D MRI technique to evaluate the topography of the proximal tibia and outline considerations in tibial component design for bicruciate-retaining TKA.

METHODS

We identified 100 consecutive patients (50 males and 50 females) between ages 20 and 40 years with knee MRIs without arthritis, dysplasia, ACL tears, or prior knee surgery. A novel 3D MRI protocol coordinating axial, coronal, and sagittal images was used to measure: 1) medial and lateral posterior tibial slopes; 2) medial and lateral coronal slopes; and 3) distance from the anterior tibia to the ACL footprint.

RESULTS

There was no overall difference in medial and lateral posterior tibial slopes (5.5° (95% CI 5.0 to 6.0°) vs. 5.4° (95% CI 4.8 to 6.0°), respectively (p=0.80)), but 41 patients had side-to-side differences greater than 3°. The medial coronal slope was greater than the lateral coronal slope (4.6° (95% CI 4.0 to 5.1°) vs. 3.3° (95% CI 2.9 to 3.7°), respectively (p<0.0001)). Females had less clearance between the anterior tibia and ACL footprint than males (10.8mm (95% CI 10.4 to 11.2mm) vs. 13.0mm (95% CI 12.5 to 13.5mm), respectively (p<0.0001)).

CONCLUSIONS

Due to highly variable proximal tibial topography, a monoblock bicruciate-retaining tibial baseplate may not reproduce normal anatomy in all patients.

LEVEL OF EVIDENCE

Level IV - Anatomic research study.

Bicruciate retaining

Total knee replacement (TKR) is a procedure used to treat knee arthropathy. Patients' dissatisfaction is still relevant (literature reports dissatisfaction rates as high as 40%). The anterior cruciate ligament is usually removed while performing a total knee arthroplasty, thus changing knee biomechanics. As patients' mean age to surgery is decreasing, bicruciate retaining models, which preserve normal biomechanics, may be useful in increasing patients' outcomes. Limited data concerning bicruciate retaining arthroplasty is available; although clinical results are encouraging, there are concerns regarding surgical exposure, anterior cruciate integrity evaluation, and implant fixation.

Proprioception and Knee Arthroplasty: A Literature Review

Proprioceptive mechanoreceptors provide neural feedback for position in space and are critical for three-dimensional interaction. Proprioception is decreased with osteoarthritis of the knees, which leads to increased risk of falling. As the prevalence of osteoarthritis increases so does the need for total knee arthroplasty (TKA), and knowing the effect of TKA on proprioception is essential. This article reviews the literature regarding proprioception and its relationship to balance, aging, osteoarthritis, and the effect of TKA on proprioception. Knee arthroplasty involving retention of the cruciate ligaments is also reviewed, as well the evidence of proprioception in the posterior cruciate ligament after TKA.

Histopathological Evaluation of the Anterior Cruciate Ligament in Patients Undergoing Primary Total Knee Arthroplasty

This study assessed gross and histopathological ACL changes in arthritic knees (n=174) undergoing total knee arthroplasty. Histopathological changes were assessed and graded as absent (0), mild (1), moderate (2), or marked (3). These were correlated to demographic and clinical factors, and radiographic evaluations. The ACL was intact in 43, frayed in 85, torn in 15, and absent in 31 knees. Eighty-five percent had histological changes. Overall, there were significant associations between greater age and BMI, and histological changes. Grade IV knees had significantly greater calcium pyrophosphate deposits, microcyst formation, and number of pathologic changes. These correlations may aid decision-making when determining suitability for unicompartmental or bicruciate-retaining arthroplasties, though further studies should correlate these histological findings to mechanical and functional knee status.

Macroscopic evaluation of the anterior cruciate ligament in osteoarthritic patients undergoing total knee arthroplasty

BACKGROUND

Sacrifice of the anterior cruciate ligament (ACL) is currently common practice during total knee arthroplasty (TKA). However, patients who receive an ACL-retaining TKA maintain more normal knee kinematic patterns than those without an ACL. Additionally, satisfactory survival and function more than 20 years after bicruciate-retaining TKA has recently been reported. The purpose of this study was to compare the percentage of knees with a visually intact ACL prior to TKA surgery with previously reported values.

METHODS

A total of 247 knees (216 consecutive patients) that underwent TKA were retrospectively evaluated. The preoperative diagnosis for all patients was primary OA. The macroscopic appearance of the ACL at the time of surgery was retrospectively assessed using routinely recorded digital photographs and classified as normal, moderately damaged (fissured), or completely ruptured. Both normal and moderately damaged ACLs were defined as intact.

RESULTS

Ninety-four percent (233/247) of the knees had an intact ACL (normal or moderately damaged). This value is higher than that found in previous reports.

CONCLUSIONS

Our results show more candidates for bicruciate ligament-retaining TKA surgery than reported previously. This suggests that improved techniques for bicruciate-retaining TKA would be clinically useful and could benefit a large number of patients.

Regaining Native Knee Kinematics Following Joint Arthroplasty: A Novel Biomimetic Design with ACL and PCL Preservation

Lack of ACL and non-anatomic articular surfaces in contemporary total knee implants result in kinematic abnormalities. We hypothesized that such abnormalities may be addressed with a biomimetic bi-cruciate retaining (BCR) design having anatomical articular surfaces. We used dynamic computer simulations to compare kinematics among the biomimetic BCR, a contemporary BCR and cruciate-retaining implant for activities of daily living. During simulated deep knee bend, chair-sit and walking, the biomimetic BCR implant showed activity dependent kinematics similar to healthy knees in vivo. Restoring native knee geometry together with ACL preservation provided these kinematic improvements over contemporary ACL-preserving and ACL-sacrificing implants. Further clinical studies are required to determine if such biomimetic implants can result in more normal feeling knees and improve quality of life for active patients.

Is Local Viscosupplementation Injection Clinically Superior to Other Therapies in the Treatment of Osteoarthritis of the Knee: A Systematic Review of Overlapping Meta-analyses

PURPOSE

To conduct a systematic review of overlapping meta-analyses comparing treatment of knee osteoarthritis (OA) with intra-articular viscosupplementation (intra-articular hyaluronic acid [IA-HA]) versus oral nonsteroidal anti-inflammatory drugs (NSAIDs), intra-articular corticosteroids (IA-corticosteroids), intra-articular platelet-rich plasma (IA-PRP), or intra-articular placebo (IA-placebo) to determine which meta-analyses provide the best current evidence and identify potential causes of discordance.

METHODS

Literature searches were performed for meta-analyses examining use of IA-HA versus NSAIDs, IA-corticosteroids, IA-PRP, or IA-placebo. Clinical data were extracted, and meta-analysis quality was assessed. The Jadad algorithm was applied to determine which meta-analyses provided the highest level of evidence.

RESULTS

Fourteen meta-analyses met the eligibility criteria and ranged in quality from Level I to IV evidence. In studies reporting patient numbers, there were a total of 20,049 patients: 13,698 receiving IA-HA, 355 receiving NSAIDs, 294 receiving IA-corticosteroids, and 5,702 receiving IA-placebo. Ten studies examined the effects of IA-HA versus IA-placebo; of these, 5 found that IA-HA improved pain and 4 found that IA-HA improved function. No clinically relevant differences in the efficacy of IA-HA versus NSAIDs regarding pain and function were found. Regarding IA-HA versus IA-PRP, IA-HA improved knee function at 2 and 6 months after injection but the effects were less robust than those of IA-PRP. Regarding IA-HA versus IA-corticosteroids, the positive effects of IA-HA were greater at 5 to 13 weeks and persisted for up to 26 weeks. After application of the Jadad algorithm, 2 concordant high-quality meta-analyses were selected and both showed that IA-HA provided clinically relevant improvements in pain and function compared with IA-placebo.

CONCLUSIONS

This systematic review of overlapping meta-analyses comparing IA-HA with other nonoperative treatment modalities for knee OA shows that the current highest level of evidence suggests that IA-HA is a viable option for knee OA. Its use results in improvements in knee pain and function that can persist for up to 26 weeks. IA-HA has a good safety profile, and its use should be considered in patients with early knee OA.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I to IV studies.

Bicruciate-retaining Total Knee Replacement Provides Satisfactory Function and Implant Survivorship at 23 Years

BACKGROUND

One of the goals of a TKA is to approximate the function of a normal knee. Preserving the natural ligaments might provide a method of restoring close to normal function. Sacrifice of the ACL is common and practical during a TKA. However, this ligament is functional in more than 60% of patients undergoing a TKA and kinematic studies support the concept of bicruciate-retaining (that is, ACL-preserving) TKA; however, relatively few studies have evaluated patients treated with bicruciate-retaining TKA implants.

QUESTIONS/PURPOSES

I asked: (1) what is the long-term (minimum 20-year) survivorship, (2) what are the functional results, and (3) what are the reasons for revision of bicruciate-retaining knee arthroplasty prostheses?

METHODS

From January 1989 to September 1992, I performed 639 total knee replacements in 537 patients. Of these, 489 were performed in 390 patients using a bicruciate-retaining, minimally constrained device. During the period in question, this knee prosthesis was used for all patients observed intraoperatively to have an intact, functional ACL with between 15° varus and 15° valgus joint deformity. There were 234 women and 156 men with a mean age at surgery of 65 years (range, 42-84 years) and a primary diagnosis of osteoarthritis in 89%. The patella was resurfaced in all knees. The mean followup was 23 years (range, 20-24 years). At the time of this review, 199 (51%) patients had died and 31 (8%) patients were lost to followup, leaving 160 (41%) patients (214 knees) available for review. Component survivorship was determined by competing-risks analysis and Kaplan Meier survivorship analysis with revision for any reason as the primary endpoint. Patients were evaluated every 2 years to assess ROM, joint laxity, knee stability, and to determine American Knee Society scores.

RESULTS

The Kaplan-Meier survivorship was 89% (95% CI, 82%-93%) at 23 years with revision for any reason as the endpoint. Competing-risks survivorship was 94% (95% CI, 91%%-96 %) at 23 years. At followup, the mean age of the patients was 84 years (range, 63-101 years), the mean flexion was 117° (range, 90°-130°), the mean American Knee Society score improved from a preoperative mean of 42 (range, 26-49) to 91 (range, 61-100; p < .001). Twenty-two knees in 21 patients (5.6%) were revised, most commonly because of polyethylene wear.

CONCLUSIONS

ACL sacrifice may be an unnecessary concession during TKA. This study found satisfactory survivorship and function after more than 20 years of use for patients receiving a bicruciate-retaining TKA implant. A TKA that preserves cruciate ligaments provides a stable, well-functioning knee with a low likelihood of revision at long-term followup. Retaining both cruciate ligaments during knee arthroplasty is an attractive concept that is worth considering.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

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.