Can post-cam function be replaced by addition of a third condyle in PS TKA?

Lateralized position of femoral and tibial components during posterior-stabilized total knee arthroplasty leads to better functional outcomes

BACKGROUND

The mediolateral position and postoperative translation of the femoral and tibial components relative to the respective bones after total knee arthroplasty (TKA) have not yet been investigated. The purpose of the current study was to investigate the effect of the mediolateral position of the femoral and tibial components on clinical outcomes including muscle strength and ambulatory function.

METHODS

A total of 86 consecutive knees were included. The mediolateral positions of the femoral and tibial components were measured on the postoperative long-leg radiographs. The mediolateral position of the femoral and tibial components was defined relative to the femoral distal anatomical axis and the tibial mechanical axis. The lateral position of the component was denoted as positive. The lateral translation of the femoral and tibial components was defined as the distance between the preoperative femoral and tibial centers and the postoperative center of the respective component. The Knee Society Score (KSS), New Knee Society Score (2011 KSS), and the Timed Up and Go (TUG) test results were evaluated 2 years postoperatively. Spearman's correlation coefficient was calculated.

RESULTS

The lateral position of the femoral component was significantly positively correlated with KSS function score (ρ = 0.250, p = 0.020), 2011 KSS functional activities (ρ = 0.258, p = 0.017), and TUG values (ρ = - 0.241, p = 0.027). The lateral translation of the tibial component was significantly correlated with knee extension strength (ρ = 0.259, p = 0.017).

CONCLUSIONS

The lateralized position of the femoral and tibial components positively influenced postoperative knee function. When the width of the component does not fit the resected surface, a lateralized position of the femoral and tibial components with respect to the respective bones can be recommended for better functional outcomes.

Total Knee Arthroplasty Design Without Cruciates to Achieve Anatomic Femoral-Tibial Motion and Laxity

BACKGROUND

A frequently stated goal of an artificial knee arthroplasties is to achieve normal kinematics. However, this is not easily defined based on variations in motions previously measured for a range of activities. For activities such as crouching up and down, a fan pattern has been measured, where the lateral femoral contact displaces progressively posteriorly with flexion, and the medial contact remains almost constant. In walking and other activities, femoral-tibial contacts vary considerably in position, and even lateral pivoting has been measured at the start of the motion cycle. Fluoroscopic studies of total knee arthroplasty (TKA) patients have shown that such kinematics is not usually achieved for most TKA designs. In recent years, there has been an increasing interest in noncruciate retaining knee arthroplasties, where both cruciate ligaments are resected. A challenge with such designs is to define the design criteria, taking account of the extensive kinematic data of normal knees, as well as clinical factors.

METHODS

A TKA design was formulated where the main bearing surfaces produced medial stability and lateral mobility, but where the addition of an offset cylindrical bearing surface in the center induced progressive axial rotation and lateral "rollback" with flexion. At the same time, anterior-posterior and rotational laxity were provided, as in the normal knee. The new design was compared experimentally with four types of contemporary noncruciate total knee arthroplasties. There were three-dimensional printed models fabricated. A test machine was constructed where shear and torque forces were applied at a range of flexion angles, and contact positions were determined.

RESULTS

It was found that the design with the intercondylar cylindrical surface satisfied the design criteria more closely compared with the other designs.

CONCLUSIONS

For noncruciate designs to produce more normal motion characteristics, some mechanical configuration acting in concert with the lateral and medial condyles is likely to be necessary.

Medial Laxity Leads to Inferior Postoperative Clinical Outcomes and Function in Total Knee Arthroplasty

BACKGROUND

Achieving proper soft-tissue balance is essential for improving total knee arthroplasty outcomes. This multicenter study aimed to analyze the effects of the gap angle and medial and lateral component gaps on clinical outcomes.

METHODS

This retrospective multicenter cohort study was conducted on 656 knees in 11 centers. A tensor device was used to measure the joint gap and varus-valgus angle of the joint gap, and medial and lateral component gaps were determined by subtracting the polyethylene thickness. Correlations between the gap angle, component gap, and clinical outcomes using the Knee Society Score (KSS) and the new Knee Society Score (2011 KSS) were analyzed.

RESULTS

The varus gap angle in flexion positively correlated with the KSS knee score (r = 0.118, P = 0.0183), KSS function score (r = 0.164, P = 0.0009), 2011 KSS symptoms (r = 0.148, P = 0.0030), and 2011 KSS functional activities (r = 0.129, P = 0.0099). The medial component gap in extension negatively correlated with the KSS function score (r = -0.113, P = 0.0241) and that in flexion negatively correlated with the 2011 KSS symptoms (r = -0.127, P = 0.0078) and the 2011 KSS patient satisfaction score (r = -0.119, P = 0.0126). The lateral component gap had no correlation with clinical outcomes. The valgus gap group in flexion showed poorer clinical outcomes than the severe varus, varus, and/or balanced gap groups. The slightly loose group of the medial component gap in extension showed lower 2011 KSS symptoms (P = 0.0352) and functional activities (P = 0.0085) than that in the tight group.

CONCLUSIONS

The valgus joint gap and medial looseness are negatively correlated with clinical outcomes, and residual varus joint gap and lateral laxity can be tolerated. Bone resection and soft-tissue release should be performed carefully to prevent medial looseness.

Medial-pivot total knee arthroplasty enhances tibiofemoral axial rotation stability in weight-bearing mid-range flexion compared to posterior-stabilised system

PURPOSE

Total knee arthroplasty (TKA) stands as a primary intervention for severe knee ailments, yet concerns remain regarding postoperative patient satisfaction and flexion instability. This study aims to evaluate the in-vivo kinematics of medial-pivot (MP) and posterior-stabilised (PS) designs during step-up activity, in comparison to the kinematics of the nonoperated contralateral knee.

METHODS

Sixteen patients with PS-TKA and 14 with MP-TKA were retrospectively examined. Clinical outcomes were assessed using patient-completed questionnaires. Motion during step-up was captured using a dual fluoroscopic system. Statistical analysis was applied to evaluate the in-vivo tibiofemoral six-degree-of-freedom kinematics and articular contact positions between the two groups.

RESULTS

Despite being older, patients in the MP group reported higher postoperative subjective scores for weight-bearing functional activities. The axial rotation centres of MP-TKA located on the medial tibial plateau exhibited less variance compared to PS-TKA and contralateral knees. Compared to the contralateral knee (contralateral to medial-pivot [C-MP] or contralateral to posterior-stabilised [C-PS]), the MP group exhibited limited range of motion in terms of anteroposterior translation (MP: 3.6 ± 1.3 mm vs. C-MP: 7.4 ± 2.5 mm, p < 0.01) and axial rotation (MP: 6.6 ± 1.9° vs. C-MP: 10.3 ± 4.9°, p = 0.02), as well as in the PS group for anteroposterior translation (PS: 3.9 ± 1.7 mm vs. C-PS: 7.2 ± 3.7 mm, p < 0.01).

CONCLUSION

The MP group with better postoperative ratings demonstrated a more stable MP axial rotation pattern during step-up activity compared to the PS group, underscoring the pivotal role of prosthetic design in optimising postoperative rehabilitation and functional recovery.

LEVEL OF EVIDENCE

Level III.

Larger Medial Contact Area and More Anterior Contact Position in Medial-Pivot than Posterior-Stabilized Total Knee Arthroplasty during In-Vivo Lunge Activity

This study aimed to compare the in-vivo kinematics and articular contact status between medial-pivot total knee arthroplasty (MP-TKA) and posterior stabilized (PS) TKA during weight-bearing single-leg lunge. 16 MP-TKA and 12 PS-TKA patients performed bilateral single-leg lunges under dual fluoroscopy surveillance to determine the in-vivo six degrees-of-freedom knee kinematics. The closest point between the surface models of the femoral condyle and the polyethylene insert was used to determine the contact position and area. The nonparametric statistics analysis was performed to test the symmetry of the kinematics between MP-TKA and PS-TKA. PS-TKA demonstrated a significantly greater range of AP translation than MP-TKA during high flexion (p = 0.0002). Both groups showed a significantly greater range of lateral compartment posterior translation with medial pivot rotation. The contact points of PS-TKA were located significantly more posterior than MP-TKA in both medial (10°–100°) and lateral (5°–40°, 55°–100°) compartments (p < 0.0500). MP-TKA had a significantly larger contact area in the medial compartment than in the lateral compartment. In contrast, no significant differences were observed in PS-TKA. The present study revealed no significant differences in clinical outcomes between the MP and PS groups. The PS-TKA demonstrated significantly more posterior translations than MP-TKA at high flexion. The contact points are located more posteriorly in PS-TKA compared with MP-TKA. A larger contact area and medial pivot pattern during high flexion in MP-TKA indicated that MP-TKA provides enhanced medial pivot rotation.

How does asymmetric tibial insert affect tibiofemoral kinematics and contact stresses in total knee Arthroplasty?

BACKGROUND

Asymmetric tibial insert design is expected to restore normal knee kinematics better than symmetric design. A tri-condylar implant has asymmetric and symmetric tibial inserts with a ball-and-socket joint to replace the post-cam mechanism. The purpose of this study was to compare the knee kinematics of the two designs and to measure tibiofemoral contact stresses, including that of the ball-and-socket joint.

METHODS

Using a computer simulation, the anteroposterior position and axial rotation of the femoral component were simulated during a weight-bearing deep knee bend for six validated models. Contact forces were simultaneously simulated in the medial, lateral, and ball-and-socket compartments. The relative position and the magnitude and direction of each contact force were applied to aforce/displacement control knee simulator. The contact stresses were measured individually using a pressure sensor.

RESULTS

The asymmetric tibial insert demonstrated a more posterior position of the femoral component in the lateral compartment during the entire range of motion and greater external rotation of the femoral component, compared to the symmetrical tibial insert. The mean peak contact stress of the medial and lateral compartments was < 9 Mpa, with no significant differences between the two designs except at 0°. The contact stress of the ball-and-socket joint was < 5 MPa.

CONCLUSIONS

Asymmetry of the tibial insert shows significant kinematic difference and has little influence on the peak contact stress, which is considerably lower than the yield strength of polyethylene. The asymmetric tibial insert can lead to clinical benefits owing to its kinematic and kinetic properties.

Kinematic comparison between asymmetrical and symmetrical polyethylene inserts during deep knee bend activity

BACKGROUND

The in vivo kinematic benefit of an asymmetrical polyethylene insert is still unknown in comparison with that of a symmetrical insert with the same femoral component design. The purpose of this study was to analyze the kinematic differences between symmetrical and asymmetrical polyethylene inserts and to detect the kinematic benefit in the asymmetrical polyethylene insert. The hypotheses are that greater axial rotation and more posterior rollback are observed in the asymmetrical polyethylene insert.

METHODS

The patients were randomly allocated to the following two groups: total knee arthroplasty with a symmetrical insert and with an asymmetrical insert. In vivo knee kinematics was analyzed in asymmetrical (17 knees) and symmetrical (16 knees) inserts using an image matching technique. The symmetrical polyethylene insert had the same geometry on both sides, whereas the asymmetrical polyethylene insert had a flat surface on the postero-lateral side. The anterior/posterior position and axial rotation were compared between the two polyethylene inserts.

RESULTS

The femoral component was significantly positioned posteriorly at 70° (p = 0.016) and 80° (p = 0.040) of knee flexion and externally rotated at 80° of knee flexion (p = 0.040) in the asymmetrical polyethylene insert as compared to the position of the symmetrical polyethylene insert. Femoral rollback and axial rotation from full extension to maximum flexion were greater in the asymmetrical polyethylene insert, although the difference was not significant.

CONCLUSIONS

In the asymmetrical polyethylene insert, slight kinematic benefit with greater axial rotation and more posterior rollback was observed in comparison with the symmetrical polyethylene insert. Further research should be required whether the kinematic benefit of an asymmetrical polyethylene insert will lead to better patient satisfaction and function.

Implant survival of 3rd-condyle and post-cam posterior-stabilised total knee arthroplasty are comparable at follow-up > 10 years: a systematic review

PURPOSE

To summarise the literature on 3rd-condyle total knee arthroplasty (TKA) designs and compare their survival rates to those of post-cam TKA designs. The null hypothesis was that 3rd-condyle TKAs would have equivalent survival rates compared to contemporary post-cam TKAs.

METHODS

An electronic literature search for Level I-V studies was independently conducted by two researchers using Medline^® and Web of Science for studies published between January 1984 and October 2020 that specifically reported on rates of implant survival and complications, joint kinematics, clinical outcomes, and radiographic outcomes of 3rd-condyle TKA. The methodological quality of clinical studies was assessed according to the Downs and Black Quality Checklist for Health Care Intervention Studies, and for in vitro and in silico studies according to the Joanna Briggs Institute (JBI) tool for assessing analytical cross-sectional studies. Findings extracted for each TKA design were presented as reported and synthesised narratively. Survival rates at 5, 10 and > 10 years of 3rd-condyle TKA designs were graphically compared to rates of post-cam TKA designs published in joint registries.

RESULTS

A total of 38 studies were identified that reported on kinematics, clinical outcomes, radiographic alignment, and rates of complications and survival. Mean survival rates ranged from 96 to 98% at 5 years, 78-100% at 5-10 years, and 86-99% at > 10 years for 3rd-condyle PS TKAs. Mean survival rates ranged from 93 to 98% at 5 years, 89-99% at 5-10 years, and 88-95% at > 10 years for post-cam PS TKAs.

CONCLUSION

Implant survival rates of 3rd-condyle TKAs are comparable to those of post-cam TKAs at follow-up > 10 years. When compared to post-cam PS TKA, 3rd-condyle designs offer an alternative for younger and more active patients when considering the added benefits of a lowered point-of-contact and larger congruent contact area at the intercondylar tibial sulcus, that reduce risks of loosening and component wear.

LEVEL OF EVIDENCE

V.

Static Mediolateral Tilt of the Joint Line after Total Knee Arthroplasty Does Not Reflect Dynamic Tilt during a Stair Ascent Activity

The correlation between static and dynamic mediolateral (ML) tilts of the joint line in the coronal plane remains unknown after total knee arthroplasty (TKA). The purpose was to evaluate the ML tilt as measured by two-dimensional to three-dimensional registration during stair ascent in TKA patients, and to examine the correlation between the dynamic ML tilt and radiographic measurements of static indices. Thirty-two knees that underwent TKA using the mechanical alignment method were included. Continuous sagittal fluoroscopy was taken from before initial contact (IC) until after the toe-off (TO) phase during the stair ascent. The ML tilt of the tibial component relative to the ground was analyzed in terms of dynamic alignment using image-matching techniques, whereas static alignment was measured using standing long-leg radiographs. The correlation between static and dynamic ML tilts was evaluated. In the fluoroscopic analysis, the joint line was neutral (0.0 degree, standard deviation [SD] = 3.4 degrees) around IC phases, then was tilted valgus (5.5° valgus, SD = 2.6 degrees) in the mid-stance (MS) phase. After the TO phase, the joint line became almost neutral (0.4 degrees valgus, SD = 3.1 degrees). The dynamic ML tilt was significantly more varus during the IC phase and significantly more valgus in MS and TO phases than the static ML tilt (1.4 degrees valgus, SD = 2.0 degrees). No correlation was found between static and dynamic ML tilts in weight-bearing phases. During stair ascent, the static tilt had no correlation with the dynamic tilt in weight-bearing phases despite being in the same range. Static lower limb alignment does not reflect coronal alignment during motion. Further research should be conducted to determine whether the horizontal dynamic ML tilt can improve long-term durability and clinical outcomes after TKA.

Varus alignment after total knee arthroplasty results in greater axial rotation during deep knee bend activity

BACKGROUNDS

The correlation between in vivo knee kinematics and alignment has not been fully elucidated. Recently, similar or better clinical outcomes have been reported by restoration of mild varus alignment after total knee arthroplasty for preoperative varus knees. The aim of this study was to evaluate the effect of postoperative alignment on knee kinematics during a deep knee bend activity.

METHODS

In vivo knee kinematics of 36 knees (25 patients) implanted with tri-condylar total knee arthroplasty were analyzed with a three dimensional model fitting approach using fluoroscopy. Under fluoroscopic surveillance, individual video frames were digitized at 30° increments from full extension to maximum flexion. Postoperative coronal and sagittal alignments were assessed using radiographs, and rotational alignment was assessed with computed tomography. Pearson correlation coefficients were calculated to determine the correlations between the alignment data and kinematic factors.

FINDINGS

Correlation analysis showed that coronal alignment was significantly correlated with knee kinematics. The varus alignment of the limb and tibial component led to a greater axial rotation from full extension to maximum flexion and more rotated position in the mid to deep flexion range. Neither the rotational alignment of the femoral nor tibial components showed significant correlation with axial rotation from full extension to maximum flexion.

INTERPRETATION

Varus alignment resulted in greater axial rotation, which could represent near-normal knee kinematics. The current study can be a kinematic rationale reporting similar or better clinical and functional outcomes for the total knee arthroplasty with residual varus alignment.

Tibial Tubercle-Trochlear Groove Distance Influences Patellar Tilt After Total Knee Arthroplasty

BACKGROUND

Tibial tubercle-trochlear groove (TT-TG) distance is associated with a greater risk of recurrent patellar dislocation in young, active patients. However, the effect of TT-TG distance after total knee arthroplasty (TKA) has not been investigated. The purpose is to analyze the effect of TT-TG distance and component rotation on patellar tilt and patellar shift after TKA.

METHODS

After TKA, axial computed tomography scans and axial radiograph were taken in 115 consecutive knees. TT-TG distance was measured between the most anterior point of the tibial tuberosity and the deepest point of the femoral component relative to a line connecting the anterior condyles. Femoral and tibial component rotation was measured relative to the femoral and tibial rotational axis, respectively. Pearson correlation coefficients were calculated.

RESULTS

TT-TG distance had a significant correlation with patellar tilt in extension (R = 0.220, P = .018), patellar tilt in flexion (R = 0.438, P < .001), and patellar shift (R = 0.330, P < .001). Tibial component rotation had a significant correlation with patellar tilt in flexion (R = -0.251, P = .007) and patellar shift (R = -0.360, P < .001). Femoral component rotation had no significant correlations. Tibial component rotation had a significant correlation with TT-TG distance (R = -0.573, P < .001), whereas femoral component rotation had no correlation (P = .192).

CONCLUSION

TT-TG distance had a significant correlation with patellar tilt and patellar shift. Surgeons need to understand the factors affecting TT-TG distance and to pay attention to avoiding excessive TT-TG distance after TKA.

New mobile-bearing TKA with unique ball and socket post-cam mechanism offers similar function and stability with better prosthesis fit and gap balancing compared to an established fixed-bearing prosthesis

PURPOSE

A mobile-bearing (MB) posterior-stabilized total knee arthroplasty (TKA) system with ball and socket post-cam mechanism has been developed with the aims of better prosthesis fit and enhanced stability. However, the data are limited to compare its clinical outcomes with an already established fixed-bearing (FB) implant design.

METHODS

This is a prospective randomized study comparing 260 patients in the MB group and 133 patients in FB group with a minimum 2 years of follow-up. Intraoperative variables, post-operative functional outcomes and incidence of adverse events were compared.

RESULTS

MB group showed better prosthesis fit as the incidence of over-hang of femoral component at junction (medial: 1% vs. 5% and lateral: 2% vs 4%, p < 0.001) and trochlea (medial: 2% vs 30%, p = 0.042 and lateral: 13% vs 21%, p = 0.015) was less than FB group. MB group also showed better gap balancing as the incidence of medio-lateral gap difference more than 2 mm was less in flexion (2.3% vs. 16%, p < 0.001) and extension (3.1% vs. 9.8%, p = 0.005). Post-operative functional outcomes and incidence of adverse events showed no difference between the two groups at 2 years.

CONCLUSIONS

New MB design offers similar functional outcomes and stability along with better intraoperative prosthesis fit and gap balancing compared to an established fixed-bearing design. Hence, this new MB design could be an alternative prosthesis of choice for posterior-stabilized TKA.

LEVEL OF EVIDENCE

I.

Patellofemoral design enhancements reduce long-term complications of postero-stabilized total knee arthroplasty

PURPOSE

Few studies investigated whether trochlear and patellar design enhancements improve long-term outcomes of total knee arthroplasty (TKA). This study aimed to compare the long-term survival and complication rates of two consecutive generations of the same TKA system with identical tibiofemoral geometry, but different patellofemoral designs.

METHODS

The authors retrieved the records of 93 patients (104 knees) operated with the HLS II system and 116 patients (122 knees) operated with HLS Evolution system. Patients were evaluated preoperatively and at a minimum of 10 years noting all complications. Kaplan-Meier (KM) survival was compared for two endpoints: (1) revision of all components and (2) revision of any component.

RESULTS

From the HLS II series, the incidence of revision of all components was 6.4%, and of any component was 9.8%. From the HLS Evolution series, the incidence of revision of all components was 4.1%, and of any component was 5.1%. Comparing the survival at equivalent follow-up of 14 years, considering revision of all components, the HLS II had higher survival than the HLS Evolution (98.9% vs 95.9%), while considering revision of any component, the HLS II had lower survival than the HLS Evolution (93.0% vs 94.9%). The differences in survival of the two implants were not significant, neither at equivalent follow-up of 14 years (n.s.), nor at maximum follow-up of each cohort (n.s.). The complication rate was higher for the HLS II series compared to the HLS Evolution (28% vs 12%, p = 0.009), but patellofemoral complications were not more frequent (8% vs 6%, n.s.).

CONCLUSIONS

Though the differences in survival of the two implants were not significant, conflicting findings are observed due to partial revisions for patellar fractures (5 in the HLS II series and 1 in the HLS Evolution series) which could be related to patellofemoral design enhancements. This study highlights the importance of patello-femoral geometry, which is often overlooked in TKA.

LEVEL OF EVIDENCE

Retrospective comparative study, Level III.

Correlation Between Intraoperative Anterior Stability and Flexion Gap in Total Knee Arthroplasty

BACKGROUND

Instability is a common failure mode after total knee arthroplasty. There have been only a few methods to quantify anterior translation with fixed forces applied during surgery. The purpose of the study was to measure the anterior translation with a new device and to analyze the relationships between the amount of anterior translation and the joint gaps.

METHODS

Fifty knees with medial osteoarthritis underwent surgery using a posterior-stabilized implant. During surgery, measurement of anterior translation was performed at 90° of knee flexion with a trial implant, applying a traction force of 70 N. The joint gap was measured using a tensor device, applying a distraction force of 178 N in flexion. The Pearson correlation coefficient was calculated between anterior translation and joint gaps and laxity.

RESULTS

On average, anterior translation during surgery was 8.5 mm (standard deviation [SD] = 3.6 mm). Medial gap (correlation coefficient [r] = 0.30), medial laxity (r = 0.33), and center laxity (r = 0.29) had a positive correlation with anterior translation, and anterior translation increased with larger joint gap or greater laxity.

CONCLUSION

Anterior translation was measured with a new device by applying the anterior force to the tibia, and the correlations between anterior translation and joint gap and laxity were analyzed. A larger medial gap and greater medial laxity were correlated with greater anterior translation, which could cause symptomatic feelings of instability. Surgeons should pay attention to the tension of medial structures in flexion and avoid excessive medial release during surgery.

Medial tilting of the joint line in posterior stabilized total knee arthroplasty increases contact force and stress

BACKGROUND

Kinematically aligned total knee arthroplasty is based on the concept to represent the premorbid joint alignment with cruciate-retaining implants, characterized by medial tilt and internal rotation. However, kinematic and kinetic effects of kinematically aligned total knee arthroplasty with posterior-stabilized implants is unknown. The purpose of this study was to examine the effect of medial tilting of the joint line with posterior-stabilized implants.

METHODS

A mechanical alignment model, and medial tilt 3° and 5° models were constructed. Knee kinematics and contact forces were simulated using a musculoskeletal computer simulation model. Contact stresses on the tibiofemoral joint and the post area were then calculated using finite element analysis.

FINDINGS

From 0° to 120° of knee flexion, greater external rotation of the femoral component was observed in medial tilt models (-0.6°, 1.8° and 4.2° in mechanical alignment, medial tilt 3° and medial tilt 5° models, respectively). The peak contact stresses on the tibiofemoral joint and the post area at 120° of knee flexion were higher in medial tilt models. The peak contact stresses on the post area in medial tilt 3° and 5° models were 2.2 and 3.8 times greater than that in mechanical alignment model, respectively.

INTERPRETATION

Medial tilting of the joint line causes greater axial rotation even with posterior-stabilized implants, which can represent near-normal kinematics. However, medial tilting of the joint line in total knee arthroplasty with posterior-stabilized implants may have a higher risk for polyethylene wear at the tibiofemoral joint and post area, leading to subsequent component loosening.

Replication and Substitution of Anatomic Stabilizing Mechanisms in a Total Knee Design

While the majority of the total knees used today are of the cruciate retaining (CR) and cruciate substituting (PS) types, the results are not ideal in terms of satisfaction, function, and biomechanical parameters. It is proposed that a design which specifically substituted for the structures which provided stability could produce normal laxity behavior, which may be a path forward to improved outcomes. Stabilizing structures of the anatomic knee were identified under conditions of low and high axial loading. The upward slope of the anterior medial tibial plateau and the anterior cruciate was particularly important under all loading conditions. A guided motion design was formulated based on this data, and then tested in a simulating machine which performed an enhanced ASTM constraint test to determine stability and laxity. The guided motion design showed much closer neutral path of motion and laxity in anterior–posterior (AP) and internal–external rotation, compared with the PS design. Particular features included absence of paradoxical anterior sliding in early flexion, and lateral rollback in higher flexion. A total knee design which replicated the stabilizing structures of the anatomical knee is likely to provide more anatomical motion and may result in improved clinical outcomes.

Long-Term Durability of Ceramic Tri-Condylar Knee Implants: A Minimum 15-Year Follow-Up

BACKGROUND

Ceramic bearings are not commonly used in total knee arthroplasty (TKA). So far, little information is available about whether long-term survivorship and good clinical outcomes can be ensured with ceramic knee implants. The purposes of the present study were to evaluate the clinical and radiological outcomes, and to assess the long-term durability of a ceramic tri-condylar implant.

METHODS

A total of 507 consecutive TKAs were carried out using a ceramic tri-condylar femoral implant. The posterior cruciate ligament was sacrificed, and all components were fixed with bone cement. Clinical outcomes were assessed retrospectively with the Knee Society scoring system. Kaplan-Meier survivorship was calculated to determine the cumulative survival rate.

RESULTS

One hundred sixty-seven knees (114 patients) were available for clinical outcomes. The average range of flexion improved from 118.1° preoperatively to 123.7° at a minimum 15-year follow-up (P < .001). The average Knee Society knee score improved from 39.1 to 92.8 (P < .001). The functional score also improved from 36.0 to 47.0 (P < .001). With revision for any surgery or radiographic failure as the end point, Kaplan-Meier survivorship at 15 years was 94.0%. With revision of any component as the end point, the corresponding survivorship was 96.2%.

CONCLUSION

Clinically, the postoperative knee flexion range and Knee Society scores were good after long-term follow-up. The survivorship of the ceramic knee implant was excellent over the 15-year follow-up, and long-term durability was achieved, making ceramic a promising alternative material for the femoral component in TKA.

In vitro biomechanical evaluation of tri-condylar total knee arthroplasty with posterior release for restoration of full extension

Background/Objective

The continuous improvement of knee function during deep flexion remains a challenge in total knee arthroplasty. Tri-condylar total knee arthroplasty has been designed to achieve this goal. However, the introduction of a third nonanatomic spherical condyle might prevent the joint from reaching full extension due to posterior soft tissue tightening. This study aimed to address these issues related to soft tissue tightening and full extension limitation.

Methods

Biomechanical tests were performed on six cadaveric specimens of the entire lower extremities. The tri-condylar design was compared with a posterior cruciate sacrificing design of the same shape without the ball structure. Knee joint kinematics was measured, including the extension and flexion angles, the extension balance, and the extension gap. The test was repeated after release of the medial and lateral posterior intercondylar soft tissues at a safe distance from the popliteal artery and nerves.

Results

Both designs resulted in a knee flexion angle up to ∼130°. The tri-condylar design showed an extension angle of -11.2 ± 5.4°, which was a significantly greater limitation than that obtained with the cruciate sacrificing design (-3.8 ± 4.7°; p = 0.047). Moreover, the extension angle of the tri-condylar design was significantly improved after the release of posterior intercondylar soft tissues (-0.1 ± 6.7°; p = 0.028).

Conclusion

The tri-condylar design efficiently allowed the full extension by the release of posterior intercondylar soft tissues at a safe distance from the popliteal artery and nerves.

Total knee implant posterior stabilised by a third condyle: Design evolution and post-operative complications

BACKGROUND

Despite excellent long-term outcomes, posterior stabilisation by a third condyle continues to receive unwarranted criticism regarding patellar complications and instability.

HYPOTHESIS

Complication rates with a tri-condylar posterior-stabilised implant are similar to those with other posterior-stabilised prostheses and have diminished over time due to improvements in prosthesis design.

MATERIAL AND METHODS

Post-operative complications and revision rates were assessed retrospectively in a prospective cohort of 4189 consecutive patients who had primary total knee arthroplasty (TKA) using a tri-condylar posterior-stabilised implant (Wright-Tornier) and were then followed-up for at least 24 months. The analysis included 2844 knees. The prosthesis generations were HLS1^®, n=20; HLS2^®, n=220; HLS Evolution^®, n=636; HLS Noetos^®, n=1373; and HLS KneeTec^®, n=595. Complications were compared across generations by applying Fisher's exact test, and survival was compared using the Kaplan-Meier method.

RESULTS

At last follow-up, there had been 341 (12%) post-operative complications in 306 (10.8%) knees, including 168 (5.9%) related to the implant, 41 (1.4%) infections, and 132 (4.6%) secondary complications unrelated to the implant. Re-operation was required for 200 complications (7%), including 87 (3.1%) consisting in revision of the prosthesis. Implant-related complications were stiffness (n=67, 2.4%), patellar fracture (n=34, 1.2%), patellar clunk syndrome (n=25, 0.9%), patellar loosening (n=3, 0.1%), tibial/femoral loosening (n=15, 0.5%), polyethylene wear (n=3, 0.1%), and implant rupture (n=1, 0.04%). Significant differences across generations were found for stiffness (P<0.0001), patellar fracture (P=0.03), clunk syndrome (P=0.03), and polyethylene wear (P=0.004), whose frequencies declined from one generation to the next. Overall 10-year survival was 92% with no significant difference across generations (P=0.1).

DISCUSSION

Outcomes of tri-condylar posterior-stabilised TKA are similar to those obtained using other posterior-stabilised implants. Neither patellar complications nor instability are more common, and improvements in implant design have contributed to correct early flaws.

LEVEL OF EVIDENCE

IV, historical cohort, retrospective assessment of prospectively collected data.

How exactly can computer simulation predict the kinematics and contact status after TKA? Examination in individualized models

BACKGROUND

It is unknown whether a computer simulation with simple models can estimate individual in vivo knee kinematics, although some complex models have predicted the knee kinematics. The purposes of this study are first, to validate the accuracy of the computer simulation with our developed model during a squatting activity in a weight-bearing deep knee bend and then, to analyze the contact area and the contact stress of the tri-condylar implants for individual patients.

METHODS

We compared the anteroposterior (AP) contact positions of medial and lateral condyles calculated by the computer simulation program with the positions measured from the fluoroscopic analysis for three implanted knees. Then the contact area and the stress including the third condyle were calculated individually using finite element (FE) analysis.

FINDINGS

The motion patterns were similar in the simulation program and the fluoroscopic surveillance. Our developed model could nearly estimate the individual in vivo knee kinematics. The mean and maximum differences of the AP contact positions were 1.0mm and 2.5mm, respectively. At 120° of knee flexion, the contact area at the third condyle was wider than the both condyles. The mean maximum contact stress at the third condyle was lower than the both condyles at 90° and 120° of knee flexion.

INTERPRETATION

Individual bone models are required to estimate in vivo knee kinematics in our simple model. The tri-condylar implant seems to be safe for deep flexion activities due to the wide contact area and low contact stress.

Analysis of the Flexion Gap on In Vivo Knee Kinematics Using Fluoroscopy

There is a paucity of information on the relationships between postoperative knee laxity and in vivo knee kinematics. The correlations were analyzed in 22 knees with axial radiographs and fluoroscopy based 3D model fitting approach after a tri-condylar total knee arthroplasty. During deep knee bend activities, the medial flexion gap had significant correlations with the medial contact point (r=0.529, P=0.011) and axial rotation at full extension. During kneeling activities, a greater medial flexion gap caused larger anterior translation at complete contact (r=0.568, P=0.011). Meanwhile, the lateral flexion gap had less effect. In conclusion, laxity of the medial collateral ligament should be avoided because the magnitude of medial flexion stability was crucial for postoperative knee kinematics.

In vivo kinematic effects of ball and socket third condyle as a post-cam mechanism in tri-condylar knee implants

BACKGROUND

Tri-condylar implants containing a ball and socket third condyle as a post-cam mechanism were developed to accommodate a lifestyle requiring frequent deep flexion activities. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during a deep knee bend activity, and to confirm the contact status of the ball and socket joint.

METHODS

Seventeen knees implanted with tri-condylar implants were analyzed using a 3D to 2D registration approach. A distance of less than 1mm denoted ball and socket contact. Medial and lateral contact positions and axial rotation were compared before and after contact. Moreover, the contact position at the third condyle and the center of the ball joint were analyzed.

RESULTS

After the third condyle contact, posterior translation of the medial and lateral contact positions increased considerably. Meanwhile, the angular rotation remained still. The center of the third condyle did not move after contact, and the contact position at the third condyle remained low.

CONCLUSIONS

The third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation, which was proved to work properly as a posterior stabilizing post-cam mechanism.