How does TKA kinematics vary with transverse plane alignment changes in a contemporary implant?

Gradual-radius femoral component with s-curve post-cam provides stable kinematics at mid-flexion after total knee arthroplasty

BACKGROUND

Mid-flexion instability is the one of the reasons for patient dissatisfaction after total knee arthroplasty (TKA). The purposes of this study were to evaluate in vivo knee kinematics and clinical outcomes using a novel TKA design with a gradual femoral radius component and s-curve post-cam, which are intended to prevent the instability initiated by sudden reductions in the femoral radius observed with conventional components.

METHODS

We used radiographic-based, image-matching techniques to analyze femorotibial anteroposterior translation, axial rotation, and anterior/posterior cam-post contact during two dynamic movements, squatting and stair climbing, in 20 knees that had undergone posterior-stabilized fixed-bearing TKA with an improved sagittal profiles of the femoral component and post-cam mechanism. We also evaluated patient-reported outcomes assessed by the 2011 Knee Society Score (KSS 2011).

RESULTS

Squatting and stair climbing produced a similar trend in anteroposterior translation and a relatively small standard deviation at mid-flexion. Although the rotation angles varied widely during squatting and stair climbing, the femoral component was consistently externally rotated. Anterior/posterior cam-post contact during squatting and stair climbing were observed in 0/17 knees and 0/0 knees, respectively. The "Symptoms", "Satisfaction", and "Functional activities" subscales of the KSS 2011 were significantly (P < 0.05) improved postoperatively compared to preoperatively ("Symptoms", 10 to 21; "Satisfaction", 15 to 26; "Functional activities", 25 to 71).

CONCLUSION

A gradual femoral radius component with an s-curve post-cam provided stable kinematics and favorable clinical results during squatting and stair climbing at 1 year after surgery.

Can TKA outcomes be predicted with computational simulation? Generation of a patient specific planning tool

BACKGROUND

Computer simulations of knee movement allow Total Knee Arthroplasty (TKA) dynamic outcomes to be studied. This study aims to build a model predicting patient reported outcome from a simulation of post-operative TKA joint dynamics.

METHODS

Landmark localisation was performed on 239 segmented pre-operative computerized tomography (CT) scans to capture patient specific soft tissue attachments. The pre-operative bones and 3D implant files were registered to post-operative CT scans following TKA. Each post-operative knee was simulated undergoing a deep knee bend with assumed ligament balancing of the extension space. The kinematic results from this simulation were used in a Multivariate Adaptive Regression Spline algorithm, predicting attainment of a Patient Acceptable Symptom State (PASS) score in captured 12 month post-operative Knee Injury and Osteoarthritis Outcome Scores (KOOS). An independent series of 250 patients was evaluated by the predictive model to assess how the predictive model behaved in a pre-operative planning context.

RESULTS

The generated predictive algorithm, called the Dynamic Knee Score (DKS) contained features, in order of significance, related to tibio-femoral force, patello-femoral motion and tibio-femoral motion. Area Under the Curve for predicting attainment of the PASS KOOS Score was 0.64. The predictive model produced a bimodal spread of predictions, reflecting a tendency to either strongly prefer one alignment plan over another or be ambivalent.

CONCLUSION

A predictive algorithm relating patient reported outcome to the outputs of a computational simulation of a deep knee bend has been derived (the DKS). Simulation outcomes related to tibio-femoral balance had the highest correlation with patient reported outcome.

Knee kinematics after cruciate retaining highly congruent mobile bearing total knee arthroplasty: An in vivo dynamic RSA study

PURPOSE

This work presents a kinematic evaluation of a cruciate retaining highly congruent mobile bearing total knee arthroplasty design using dynamic Roentgen sterephotogrammetric analysis. The aim was to understand the effect of this implant design on the kinematics of prosthetic knees during dynamic activities.

METHODS

A cohort of 15 patients was evaluated at nine month follow-up after surgery. The mean age was 74.8 (range 66-85) years. The kinematics was evaluated using the Grood and Suntay decomposition and the Low-Point (LP) methods.

RESULTS

?tlsb=-0.15pt?>From sitting to standing up position, the femoral component internally rotated (from -11.3 ± 0.2° to -7.0 ± 0.2°). Varus-valgus rotations were very close to 0° during the whole motor task. LP of medial condyle moved from an anterior position of 12.0 ± 0.2 mm to a posterior position of -12.4 ± 0.2 mm; LP of the lateral condyle moved from an anterior position of 8.1 ± 0.2 mm to a posterior position of -12.4 ± 0.2 mm, showing a bi-condylar rollback where both condyles moved parallel backward. Moreover, the femoral component showed anterior translation with respect to the tibia from 80° to 20° (from -4.9 ± 0.2 mm to 3.3 ± 0.2 mm), then a posterior translation from 20° to full extension was identified (from 3.3 ± 0.2 mm to 0.5 ± 0.2 mm).

CONCLUSIONS

Paradoxical anterior femoral translation and absence of medial-pivoting motion were recorded, highlighting the role of the symmetric deep dishes insert as main driver of the kinematic of this TKA design.

Stair Climbing and High Knee Flexion Activities in Bi-Cruciate Retaining Total Knee Arthroplasty: In Vivo Kinematics and Articular Contact Analysis

BACKGROUND

Bi-cruciate retaining (BCR) total knee arthroplasty (TKA) preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. However, there is limited information regarding articular contact behavior in the contemporary BCR TKA design during high knee flexion activities. This study aimed to investigate the articular knee contact performance in unilateral BCR TKA patients during strenuous flexion activities.

METHODS

Twenty-nine unilateral BCR TKA patients were evaluated for both knees during single deep lunges, step-ups, and sit-to-stand (STS) using a validated combined computer tomography and dual fluoroscopic imaging system. Medial and lateral condylar contact positions were quantified during weight-bearing flexion.

RESULTS

Contact excursions of the lateral condyle in BCR TKAs were significantly more anteriorly located than the contralateral non-operated knees during STS (-4.9 ± 3.1 vs -9.7 ± 4.6 mm, P < .05), single deep lunge (-5.7 ± 3.2 vs -10.0 ± 4.5 mm, P < .05), and step-ups (-4.8 ± 3.6 vs -9.1 ± 3.9 mm, P < .05). Contact points of BCR TKAs indicated reduced femoral external rotation during STS (2.1 ± 4.8° vs 7.7 ± 5.4°, P < .05), single deep lunges (1.8 ± 4.8° vs 7.0 ± 7.1°, P < .05), and step-ups (0.1 ± 4.1° vs 6.2 ± 4.9°, P < .05). Medial pivoting patterns were observed in only 59%, 56%, and 48% of the BCR TKA knees for step-ups, STS, and single deep lunge, respectively.

CONCLUSION

The contemporary BCR TKA design demonstrated asymmetric femoral rollback, medial translation, as well as lateral pivoting in about half of the patient cohort, suggesting that in vivo tibiofemoral kinematic parameters were not fully restored in BCR patients during strenuous flexion activities.

Bi-cruciate stabilized total knee arthroplasty can reduce the risk of knee instability associated with posterior tibial slope

PURPOSE

The purpose of this study was to evaluate the relationship between posterior tibial slope and knee kinematics in bi-cruciate stabilized (BCS) total knee arthroplasty (TKA), which has not been previously reported.

METHODS

This computer simulation study evaluated Journey 2 BCS components (Smith & Nephew, Inc., Memphis, TN, USA) implanted in a female patient to simulate weight-bearing stair climbing. Knee kinematics, patellofemoral contact forces, and quadriceps forces during stair climbing (from 86° to 6° of flexion) were computed in the simulation. Six different posterior tibial slope angles (0°-10°) were simulated to evaluate the effect of posterior tibial slope on knee kinematics and forces.

RESULTS

At 65° of knee flexion, no anterior sliding of the tibial component occurred if the posterior tibial slope was less than 10°. Anterior contact between the anterior aspect of the tibial post- and the femoral component was observed if the posterior tibial slope was 6° or more. An increase of 10° in posterior tibial slope (relative to 0°) led to a 4.8% decrease in maximum patellofemoral contact force and a 1.2% decrease in maximum quadriceps force.

CONCLUSION

BCS TKA has a wide acceptable range of posterior tibial slope for avoiding knee instability if the posterior tibial slope is less than 10°. Surgeons should prioritize avoiding adverse effects over trying to achieve positive effects such as decreasing patellofemoral contact force and quadriceps force by increasing posterior tibial slope. Our study helps surgeons determine the optimal posterior tibial slope during surgery with BCS TKA; posterior tibial slope should not exceed 10° in routine clinical practice.

Variability in static alignment and kinematics for kinematically aligned TKA

BACKGROUND

Total knee arthroplasty (TKA) significantly improves pain and restores a considerable degree of function. However, improvements are needed to increase patient satisfaction and restore kinematics to allow more physically demanding activities that active patients consider important. The aim of our study was to compare the alignment and motion of kinematically and mechanically aligned TKAs.

METHODS

A patient specific musculoskeletal computer simulation was used to compare the tibio-femoral and patello-femoral kinematics between mechanically aligned and kinematically aligned TKA in 20 patients.

RESULTS

When kinematically aligned, femoral components on average resulted in more valgus alignment to the mechanical axis and internally rotated to surgical transepicondylar axis whereas tibia component on average resulted in more varus alignment to the mechanical axis and internally rotated to tibial AP rotational axis. With kinematic alignment, tibio-femoral motion displayed greater tibial external rotation and lateral femoral flexion facet centre (FFC) translation with knee flexion than mechanical aligned TKA. At the patellofemoral joint, patella lateral shift of kinematically aligned TKA plateaued after 20 to 30° flexion while in mechanically aligned TKA it decreased continuously through the whole range of motion.

CONCLUSIONS

Kinematic alignment resulted in greater variation than mechanical alignment for all tibio-femoral and patello-femoral motion. Kinematic alignment places TKA components patient specific alignment which depends on the preoperative state of the knee resulting in greater variation in kinematics. The use of computational models has the potential to predict which alignment based on native alignment, kinematic or mechanical, could improve knee function for patient's undergoing TKA.

No condylar lift-off occurs because of excessive lateral soft tissue laxity in neutrally aligned total knee arthroplasty: a computer simulation study

PURPOSE

Condylar lift-off can induce excessive polyethylene wear after total knee arthroplasty (TKA). A computer simulation was used to evaluate the influence of femoral varus alignment and lateral collateral ligament (LCL) laxity on lift-off after single-design TKA. It was hypothesised that proper ligament balancing and coronal alignment would prevent lift-off.

METHODS

The computer model in this study is a dynamic musculoskeletal program that simulates gait up to 60° of knee flexion. The lift-off phenomenon was defined as positive with an intercomponent distance of >2 mm. In neutrally aligned components in the coronal plane, the femoral and tibial components were set perpendicular to the femoral and tibial mechanical axis, respectively. The femoral coronal alignment was changed from neutral to 5° varus in 1° increments. Simultaneously, the LCL length was elongated from 0 to 5 mm in 1-mm increments to provide a model of pathological slack.

RESULTS

Within 2° of femoral varus alignment, lift-off did not occur even if the LCL was elongated by up to 5 mm. However, lift-off occurred easily in the stance phase in femoral varus alignments of >3° with slight LCL slack. The contact forces of the tibiofemoral joint were influenced more by femoral varus alignment than by LCL laxity.

CONCLUSIONS

Aiming for neutral alignment in severely varus knees makes it difficult to achieve appropriate ligament balance. Our study suggests that no lift-off occurs with excessive LCL laxity alone in a neutrally aligned TKA and therefore that varus alignment should be avoided to decrease lift-off after TKA.

LEVEL OF EVIDENCE

Case series, Level IV.

Tibiofemoral Rotation During Sit-to-Stand Activity After TKA

The objective of this study was to describe how tibiofemoral internal/external rotation varies in patients after total knee arthroplasty (TKA) when compared with control participants during a sit-to-stand (STS) maneuver. Motion analysis was used to measure internal/external knee rotation during STS in the control and TKA groups. Fourteen participants were included in the study. Six patients with 7 TKA knees (6 posterior stabilized and 1 cruciate-retaining TKA) were compared with 8 control participants with 8 knees from the current authors' laboratory database. Participants performed 3 STS maneuvers, and the average internal/external rotation of the femur with respect to the tibia was compared. All control participants and 2 TKA participants had internal rotation of the femur with respect to the tibia, whereas 4 TKA participants had external rotation, and 1 had no rotation during STS. Further investigation into the surgical and patient- and implant-related factors that affect this resulting reverse kinematic profile seems to be warranted. [Orthopedics. 2016; 39(3):S41-S44.].

Total Knee Post-Cam Design Variations and Their Effects on Kinematics and Wear Patterns

Post-cam designs for posterior-stabilized total knee arthroplasy (TKA) implants have evolved over the last 2 decades. These designs have evolved from symmetric post and cam to asymmetric designs that include anterior post interactions to affect a kinematic change in full extension. All design changes have consequences on the resulting femorotibial contact kinematics and, depending on the amount of constraint built into the design, these changes may have significant consequences on the wear patterns on the tibial polyethylene insert. The current authors review the kinematic effects of symmetric and asymmetric cam designs and use a retrieval database of TKA implants obtained at the time of necropsy to show how different design variables may affect polyethylene wear patterns after 10 or more years of implantation or from modeled wear in simulators. More modern designs seem to have moved the post posteriorly and sloped the anterior aspect to avoid impingement of the anterior post in terminal flexion on the inferior aspect of the patella button. [Orthopedics. 2016; 39(3):S45-S49.].

Cruciate Retaining Implant With Biomimetic Articular Surface to Reproduce Activity Dependent Kinematics of the Normal Knee

Alterations in normal knee kinematics following total knee arthroplasty (TKA) arise in part from the non-anatomic articular geometry of contemporary implants. In this study, the kinematics of a novel posterior cruciate-retaining (CR) implant with anatomic (biomimetic) articular surface, were compared to that of contemporary CR implants during various simulated activities. Across different simulated activities the biomimetic-CR mimicked normal kinematic patterns more closely than contemporary CR implants. In particular, during deep knee bend and chair-sit, the biomimetic-CR showed medial pivot motion, while other CR implants showed abnormal motion including lateral pivot or no pivot, and paradoxical anterior sliding. Further in vivo and clinical studies are needed to determine whether such biomimetic implants can truly help to achieve a more normal feeling knee and improved patient satisfaction.

Posterior tibial slope and femoral sizing affect posterior cruciate ligament tension in posterior cruciate-retaining total knee arthroplasty

BACKGROUND

During cruciate-retaining total knee arthroplasty, surgeons sometimes encounter increased tension of the posterior cruciate ligament. This study investigated the effects of femoral size, posterior tibial slope, and rotational alignment of the femoral and tibial components on forces at the posterior cruciate ligament in cruciate-retaining total knee arthroplasty using a musculoskeletal computer simulation.

METHODS

Forces at the posterior cruciate ligament were assessed with the standard femoral component, as well as with 2-mm upsizing and 2-mm downsizing in the anterior-posterior dimension. These forces were also determined with posterior tibial slope angles of 5°, 7°, and 9°, and lastly, were measured in 5° increments when the femoral (tibial) components were positioned from 5° (15°) of internal rotation to 5° (15°) of external rotation.

FINDINGS

Forces at the posterior cruciate ligament increased by up to 718N with the standard procedure during squatting. The 2-mm downsizing of the femoral component decreased the force at the posterior cruciate ligament by up to 47%. The 2° increment in posterior tibial slope decreased the force at the posterior cruciate ligament by up to 41%. In addition, posterior cruciate ligament tension increased by 11% during internal rotation of the femoral component, and increased by 18% during external rotation of the tibial component.

INTERPRETATION

These findings suggest that accurate sizing and bone preparation are very important to maintain posterior cruciate ligament forces in cruciate-retaining total knee arthroplasty. Care should also be taken regarding malrotation of the femoral and tibial components because this increases posterior cruciate ligament tension.

Effect of Tibial Posterior Slope on Knee Kinematics, Quadriceps Force, and Patellofemoral Contact Force After Posterior-Stabilized Total Knee Arthroplasty

We used a musculoskeletal model validated with in vivo data to evaluate the effect of tibial posterior slope on knee kinematics, quadriceps force, and patellofemoral contact force after posterior-stabilized total knee arthroplasty. The maximum quadriceps force and patellofemoral contact force decreased with increasing posterior slope. Anterior sliding of the tibial component and anterior impingement of the anterior aspect of the tibial post were observed with tibial posterior slopes of at least 5° and 10°, respectively. Increased tibial posterior slope contributes to improved exercise efficiency during knee extension, however excessive tibial posterior slope should be avoided to prevent knee instability. Based on our computer simulation we recommend tibial posterior slopes of less than 5° in posterior-stabilized total knee arthroplasty.

Kinematic alignment produces near-normal knee motion but increases contact stress after total knee arthroplasty: A case study on a single implant design

BACKGROUND

Kinematically aligned total knee arthroplasty (TKA) is of increasing interest because this method might improve postoperative patient satisfaction. In kinematic alignment the femoral component is implanted in a slightly more valgus and internally rotated position, and the tibial component is implanted in a slightly more varus and internally rotated position, than in mechanical alignment. However, the biomechanics of kinematically aligned TKA remain largely unknown. The aim of this study was to compare the kinematics and contact stresses of mechanically and kinematically aligned TKAs.

METHODS

A musculoskeletal computer simulation was used to determine the effects of mechanically or kinematically aligned TKA. Knee kinematics were examined for mechanically aligned, kinematically aligned, and kinematically aligned outlier models. Patellofemoral and tibiofemoral contact forces were measured using finite element analysis.

RESULTS

Greater femoral rollback and more external rotation of the femoral component were observed with kinematically aligned TKA than mechanically aligned TKA. However, patellofemoral and tibiofemoral contact stresses were increased in kinematically aligned TKA.

CONCLUSIONS

These findings suggest that kinematically aligned TKA produces near-normal knee kinematics, but that concerns for long-term outcome might arise because of high contact stresses.

Clinical alignment variations in total knee arthroplasty with different navigation methods

BACKGROUND

We compared the resulting alignment in 90° of flexion and in full extension after total knee arthroplasty (TKA) with two navigation systems using different techniques: a measured resection (MR) system and a gap - balancing (GB) system.

METHODS

Varus and valgus alignment in extension and flexion was compared in 100 consecutive patients who had TKA with an MR distal-femoral-cut-first technique at one institution and 100 consecutive patients in whom a GB tibial-cut-first technique was used at another institution. Alignment deviation of three degrees or more from neutral was considered an outlier.

RESULTS

No significant difference between the groups in coronal alignment in extension or flexion was found, but there were three times the number of outliers for clinical alignment in flexion for the MR group compared to the GB group.

CONCLUSIONS

The use of the GB tibial-cut-first computer-assisted TKA navigation may provide a more consistent clinical alignment in flexion than systems using an MR technique.

LEVEL OF EVIDENCE

Therapeutic study. Level 2.

The effect of geometric variations in posterior-stabilized knee designs on motion characteristics measured in a knee loading machine

BACKGROUND

In different posterior-stabilized (PS) total knees, there are considerable variations in condylar surface radii and cam-post geometry. To what extent these variations affect kinematics is not known. Furthermore, there are no clearly defined ideal kinematics for a total knee.

QUESTIONS/PURPOSES

The purposes of this study were to determine (1) what the kinematic differences are caused by geometrical variations between PS total knee designs in use today; and (2) what design characteristics will produce kinematics that closely resemble that of the normal anatomic knee.

METHODS

Four current PS designs with different geometries and one experimental asymmetric PS design, with a relatively conforming medial side, were tested in a purpose-built machine. The machine applied combinations of compressive, shear, and torque forces at a sequence of flexion angles to represent a range of everyday activities, consistent with the ASTM standard test for measuring constraint. The femorotibial contact points, the neutral path of motion, and the AP and internal-external laxities were used as the kinematic indicators.

RESULTS

The PS designs showed major differences in motion characteristics among themselves and with motion data from anatomic knees determined in a previous study. Abnormalities in the current designs included symmetric mediolateral motion, susceptibility to excessive AP medial laxity, and reduced laxity in high flexion. The asymmetric-guided motion design alleviated some but not all of the abnormalities.

CONCLUSIONS

Current PS designs showed kinematic abnormalities to a greater or lesser extent. An asymmetric design may provide a path to achieving a closer match to anatomic kinematics.

CLINICAL RELEVANCE

One criterion for the evaluation of PS total knees is how closely the kinematics of the prosthesis resemble that of the anatomic knee, because this is likely to affect the quality of function.

Is there a gold standard for TKA tibial component rotational alignment?

BACKGROUND

Joint function and durability after TKA depends on many factors, but component alignment is particularly important. Although the transepicondylar axis is regarded as the gold standard for rotationally aligning the femoral component, various techniques exist for tibial component rotational alignment. The impact of this variability on joint kinematics and stability is unknown.

QUESTIONS/PURPOSES

We determined how rotationally aligning the tibial component to four different axes changes knee stability and passive tibiofemoral kinematics in a knee after TKA.

METHODS

Using a custom surgical navigation system and stability device to measure stability and passive tibiofemoral motion, we tested 10 cadaveric knees from five hemicorpses before TKA and then with the tibial component aligned to four axes using a modified tibial tray.

RESULTS

No changes in knee stability or passive kinematics occurred as a result of the four techniques of tibial rotational alignment. TKA produces a 'looser' knee over the native condition by increasing mean laxity by 5.2°, decreasing mean maximum stiffness by 4.5 N·m/°, increasing mean anterior femoral translation during passive flexion by 5.4 mm, and increasing mean internal-external tibial rotation during passive flexion by 4.8°. However, no statistically or clinically important differences occurred between the four TKA conditions.

CONCLUSIONS

For all tibial rotations, TKA increased laxity, decreased stiffness, and increased tibiofemoral motion during passive flexion but showed little change based on the tibial alignment.

CLINICAL RELEVANCE

Our observations suggest surgeons who align the tibial component to any of the axes we examined are expected to have results consistent with those who may use a different axis.

Total knee arthroplasty kinematics may be assessed using computer modeling: a feasibility study

The next generational leap in computer navigation will hopefully aid surgeons in personalizing surgical techniques to patients' individual anatomical variables to optimize outcomes. To effectively use the information obtained in the operating room, a multitude of kinematic variables must be conveyed to the orthopedic surgeon in a usable and coherent manner. This study used an intraoperative navigation system to record passive knee kinematics after a total knee arthroplastyperformed. The clinical measures were taken via research software with the ability to record kinematic data in 10-second intervals. The data from 10 consecutive clinical cases were averaged, and the translation (anterior/posterior) and rotation (internal/external) were recorded and compared from 0° to 100° of flexion to allow for comparison with the previously recorded computer model. Model and clinical curves compared favorably, with less than 1° rotational and 1.5-mm differences, on average. The comparison of information and analyses were reviewed to indicate how they might be interpreted in the operating room for future use during surgery to allow a more personalized approach to improving functional outcomes after total knee arthroplasty.