Kinematics Of Total Knee Arthroplasty Research Articles

A novel post-processing technique for correcting symmetric implant ambiguity in measuring total knee arthroplasty kinematics from single-plane fluoroscopy

Recent advancements in computer vision and machine learning enable autonomous measurement of total knee arthroplasty kinematics through single-plane fluoroscopy. However, symmetric components present challenges in optimization routines, causing “symmetry traps” and ambiguous poses. Achieving clinically robust kinematics measurement requires addressing this issue. We devised an algorithm that converts a “true” pose to its corresponding “symmetry trap” orientation. From a dataset of nearly 13,000 human supervised kinematics, this algorithm constructs an augmented dataset of “true” and “symmetry trap” kinematics, used to train eight classification machine learning algorithms. The outputs from the highest-performing algorithm classify kinematics sequences as ’obviously true’ or ’potentially ambiguous.’ We construct a spline through ’obviously true’ poses, and ’ambiguous’ poses are compared to the spline to determine correct orientation. The machine learning algorithms achieved 88–94% accuracy on our internal test set and 91–93% on our external test set. Applying our spline algorithm to kinematics sequences yielded 91.1% accuracy, 94% specificity, but 67% sensitivity. The accuracy of standard ML algorithms for implants within 5 degrees of a pure-lateral view was 71%, rising to 88% beyond 5 degrees. This pioneering study systematizes addressing model-image registration issues with symmetric tibial implants. High accuracy suggests potential use of ML algorithms to mitigate shape-ambiguity errors in pose measurements from single-plane fluoroscopy. Our results also suggest an imaging protocol for measuring kinematics that favors more oblique viewing angles, which could further disambiguate “true” and “symmetry trap” poses.

Effect of Surgical Technique, Implant Design, and Time of Examination on Contact Kinematics: A Study of Bicruciate-Stabilized and Posterior-Stabilized Total Knee Arthroplasty

BackgroundBicruciate-stabilized (BCS) total knee arthroplasty (TKA) designs attempt to approximate natural knee mechanics. Multiple surgical techniques, including gap balancing (GB) and measured resection (MR), have been developed to provide optimal implant positioning and soft-tissue balance. The goal of this study was to determine the effect of surgical technique on BCS TKA contact kinematics. Secondary goals included investigating the change of kinematics over time and comparing BCS TKA kinematics to a posterior-stabilized (PS) design. MethodsThe study included the BCS-GB, BCS-MR, and PS-MR groups. The BCS-GB and BCS-MR groups underwent weight-bearing radiostereometric analysis for multiple knee flexion angles at 3 months and 1 year postoperatively, whereas the PS-MR group was imaged at 1 year postoperatively. The medial and lateral contact kinematics were determined from implant poses. ResultsThere were no differences in BCS TKA kinematics between the GB and MR techniques. There were differences in the mid-flexion ranges when comparing the 3-month and 1-year kinematics of the BCS design; however, they were less than 1.5 mm. Differences existed between the kinematics of the BCS and PS designs at all flexion angles for the medial condyle (P < .0006) and at 0° of flexion on the lateral condyle (P < .0001). ConclusionsContact kinematics for a BCS design were similar for both surgical techniques, suggesting both are appropriate for this design. Small, likely clinically insignificant differences were found between 3-month and 1-year kinematics. The BCS TKA kinematics differed from the PS design; however, it is unclear whether these differences improve clinical outcomes.

Total Knee Arthroplasty Kinematics Predict Patient-Reported Outcome Measures: Implications for Clinical Kinematic Examinations

BackgroundA core tenet of total knee arthroplasty (TKA) is that achieving more natural kinematics will lead to superior patient outcomes. Yet this relationship has not been proven for large representative cohorts of TKA patients because accurately measuring 3-dimensional TKA kinematics is time-consuming and expensive. But advanced imaging systems and machine learning–enhanced analysis software will soon make it practical to measure knee kinematics preoperatively and postoperatively in the clinic using radiographic methods. The purpose of this study was to assess the reported relationships between TKA kinematics and outcomes and distill those findings into a proposal for a clinically practical protocol for a clinical kinematic exam. MethodsThis study reviewed the recent literature relating TKA kinematics to patient outcomes. There were 10 studies that reported statistical associations between TKA kinematics and patient outcome scores utilizing a range of functional activities. We stratified these activities by the complexity of the radiographic examination to create a proposed examination protocol, and we generated a list of requirements and characteristics for a practical TKA clinical kinematic examination. ResultsGiven considerations for a clinically practical kinematic exam, including equipment, time and other resources, we propose 3 exam levels. With basic radiographs, we suggest studying single-leg stance in extension, lunge or squat, and kneeling. For fluoroscopic systems with X-ray pulses up to 20 ms, we propose chair-rise or stair ascent to provide additional dynamic information. For fluoroscopic systems with X-ray pulses of less than 10 ms, we propose rapid open-chain knee flexion-extension to simulate the highly dynamic swing phase of gait. ConclusionsIt is our hope that this proposed examination protocol spurs discussion and debate so that there can be a consensus approach to clinical examination of knee and TKA kinematics when the rapidly advancing hardware and software capabilities are in place to do so.

Intraoperative Kinematics in Posterior Cruciate Ligament Retaining Total Knee Arthroplasty Using Different Inserts.

We analyzed the intraoperative kinematics of total knee arthroplasty (TKA) using a navigation system to investigate the influence of different inserts on kinematics. This was a retrospective observational study. The Vanguard individualized design (33 patients, 33 knees) XP and anterior-stabilized (AS) inserts were used in TKA for osteoarthritis. Kinematic data were intraoperatively recorded. The range of motion, tibiofemoral rotational angle, anteroposterior translation of the femur, and varus-valgus laxity were compared between the two inserts (XP vs. AS). There was no significant difference in the range of motion (extension: XP, 3.7° ± 3.3° vs. AS, 3.8° ± 3.3°, p = 0.84; flexion: XP, 138.1° ± 10.2° vs. AS, 139.0° ± 13.3°, p = 0.73). With the AS insert, the tibia was gradually internally rotated as the knee was flexed. At maximum extension, the internal rotation was smallest with AS (XP 6.5° ± 4.0° vs. AS 5.1° ± 3.4°, p = 0.022), which was also associated with smaller anterior femoral translation (maximum extension: XP, 14.1 ± 4.8 mm vs. AS, 11.3 ± 4.7 mm, p = 0.00036; 30°: XP, 23.7 ± 5.6 mm vs. AS, 20.7 ± 5.1 mm, p = 0.000033; 45°: XP, 24.4 ± 4.9 mm vs. AS, 23.2 ± 4.5 mm, p = 0.0038). The AS was associated with a lower varus-valgus laxity (30° XP 4.1° ± 3.4 vs. AS 3.3° ± 2.7°, p = 0.036; 60°: XP, 3.2° ± 3.0° vs. AS, 2.4° ± 3.3°, p = 0.0089). The AS insert facilitated sequential tibiofemoral rotation with varus-valgus stability in mid-flexion without restricting the range of motion.

Preserving primary medial static stabilizer ligaments achieves physiological knee kinematics in total knee arthroplasty

PurposeAs postoperative knee instability has been reported to be one of the critical reasons for early failure in total knee arthroplasty (TKA), obtaining optimal knee stability—especially in medial—was indispensable for successful TKA. We hypothesized that preserving medial soft tissue structures was the key to maintain physiological medial knee stability. Thus, TKAs with preserving primary medial static stabilizer ligaments technique were performed, and the postoperative knee kinematics was evaluated. MethodsPrimary knee osteoarthritis patients with varus knee deformity and planed for primary TKA were enrolled. However, patients with severe varus knee deformities, valgus knee deformities, and rheumatoid arthritis were excluded. TKAs were performed by removing medial femoral and tibial osteophytes; however, the primary medial static stabilizer ligaments—the superficial medial collateral ligament (MCL), deep MCL, and posterior oblique ligament—were not released. The cruciate-retaining (CR), posterior-stabilized (PS), and medial-pivot (MP) inserts were implanted, and the knee kinematics was measured. These data were statistically analyzed using analysis of variance. The institutional review board approved the study. ResultsFrom full extension to maximum flexion, the lateral femoral condyle moved backward, greater than the medial femoral condyle, and consequently the femur external rotated on the tibia. These kinematics patterns were shown in CR, PS, and MP groups. ConclusionAs the knee kinematics of CR and PS are similar to that of MP, which has been reported to demonstrate physiological knee kinematics, preserving primary medial static stabilizer ligaments technique could potentially preserve physiological knee kinematics.

Advancements in total knee arthroplasty kinematics: 3D implant computer aided design model creation through X-ray or fluoroscopic images

Background3D-to-2D fluoroscopic registration is a popular and important step for analyzing total-knee-arthroplasty weight-bearing kinematics. Unfortunately, in vivo analyses using these techniques cannot be completed if the associated computer-aided design implant models are not available. This study introduces a novel method that enables the accessible computation of knee replacement patients' kinematics from fluoroscopy, achieved through the reconstruction of 3-dimensional knee component models using a limited set of 2-dimensional X-ray or fluoroscopic images. MethodsThe proposed non-rigid morphing algorithm, based on the coherent point drift algorithm, scales and transforms the shape of the template model to fit with the silhouette of the corresponding fluoroscopic images without changing the structure of the knee implant. While a greater number of fluoroscopic images can lead to higher accuracy, our study utilizes only 4 images. FindingsThe morphed models show excellent results in comparison with known models with a 0.52 mm average root-mean-square error and a 2.82 mm largest source error for 17 tested knee models of various implant types. The proposed algorithm also enables direct output of patient kinematics using fluoroscopy, with an average error of only 0.54 ± 0.42 mm for femorotibial contact and 0.86 ± 0.34 degrees for axial rotation. InterpretationA novel methodology was introduced to overcome common 3-dimentional to 2-dimensional registration limitations by recreating entire families of 3 dimensional models from a limited number of fluoroscopic images for both cruciate-retaining and posterior-stabilized knee replacement implants. Our algorithm has demonstrated high levels of accuracy with multiple potential extended applications.

Joint Track Machine Learning: An Autonomous Method of Measuring Total Knee Arthroplasty Kinematics From Single-Plane X-Ray Images

BackgroundDynamic radiographic measurements of 3-dimensional (3-D) total knee arthroplasty (TKA) kinematics have provided important information for implant design and surgical technique for over 30 years. However, current methods of measuring TKA kinematics are too cumbersome, inaccurate, or time-consuming for practical clinical application. Even state-of-the-art techniques require human-supervision to obtain clinically reliable kinematics. Eliminating human supervision could potentially make this technology practical for clinical use. MethodsWe demonstrate a fully autonomous pipeline for quantifying 3D-TKA kinematics from single-plane radiographic imaging. First, a convolutional neural network (CNN) segmented the femoral and tibial implants from the image. Second, those segmented images were compared to precomputed shape libraries for initial pose estimates. Lastly, a numerical optimization routine aligned 3D implant contours and fluoroscopic images to obtain the final implant poses. ResultsThe autonomous technique reliably produces kinematic measurements comparable to human-supervised measures, with root-mean-squared differences of less than 0.7 mm and 4° for our test data, and 0.8 mm and 1.7° for external validation studies. ConclusionA fully autonomous method to measure 3D-TKA kinematics from single-plane radiographic images produces results equivalent to a human-supervised method, and may soon make it practical to perform these measurements in a clinical setting.

Correlating Contact Kinematics to Tibial Component Migration Following Cemented Bicruciate Stabilized Total Knee Arthroplasty

BackgroundContact kinematics in total knee arthroplasty (TKA) has been shown to affect tibial component migration. However, previous studies correlating kinematic variables to implant migration were completed with older TKA designs. The goal of this study was to determine if there are associations between contact kinematics and tibial component migration for a cemented, bicruciate stabilized (BCS) TKA system. MethodsA total of 54 knees implanted with a BCS TKA system were analyzed using radiostereometric analysis (RSA). Patients underwent RSA exams at 2 weeks, 6 weeks, 3 months, 6 months, 1 year, and 2 years post operation to measure tibial component migration. At 1 year, contact kinematics was evaluated during a quasi-static deep knee bend. Linear regression analyses were performed between kinematic variables and migration values. ResultsSignificant correlations were found between contact kinematics and tibial component migration. Excursion on the lateral condyle was the most consistent variable correlating with implant migration. Six patients had > 0.2 mm migrations from 1 to 2 years post operation indicating continuously migrating tibial components, and most had atypical contact kinematics. ConclusionKinematics was shown to influence tibial component migration. Reduced lateral excursion, suggesting a more constrained lateral condyle, resulted in greater implant migration. The 6 patients who had continuously migrating tibial components had demographic factors that may limit the ability to endure unintended force transmissions caused by abnormal kinematics. These results highlight the importance of restoring knee kinematics with this BCS TKA design to minimize improper force transmissions and resultant increased implant migrations.

Posterior-stabilized total knee arthroplasty kinematics and joint laxity: A hybrid biomechanical study

BackgroundPosterior-stabilized (PS)-total knee arthroplasty (TKA) arose as an alternative to cruciate-retaining (CR)-TKA in the 1970s. Since then, it has become a popularly utilized TKA design with outcomes comparable to CR-TKA. The post-cam mechanism is unique to PS-TKA as it substitutes the function of the posterior cruciate ligament (PCL). The study aimed to understand the kinematic and laxity changes in PS-TKA with under- and overstuffing of the tibiofemoral joint space with the polyethylene (PE) insert.MethodsThis study employed a hybrid computational-experimental joint motion simulation on a VIVO 6 degrees of freedom (6-DoF) joint motion simulator (AMTI, Watertown, MA, USA). Physical prototypes of a virtually-performed TKA in mechanical alignment (MA) and kinematic alignment (KA) based on cadaveric CT scans and a virtual ligament model were utilized. The reference, understuffed (down 2 mm) and overstuffed (up 2 mm) joint spaces were simulated, neutral flexion and laxity testing loads and motions were performed for each configuration.ResultsThe PE insert thickness influenced post-cam engagement, which occurred after 60º in the overstuffed configurations, after 60º–75º in the reference configurations and after 75º in the understuffed configurations. The understuffed configurations, compared to the reference configurations, resulted in a mean 2.0º (28%) and 2.0º (31%) increase in the coronal laxity in MA and KA respectively. The overstuffed configurations, compared to the reference configuration, resulted in an increase in the mean joint compressive forces (JCFs) by 73 N (61%) and 77 N (62%) in MA and KA models, respectively.ConclusionsThe under- and overstuffing in PS-TKA alter the kinematics with variable effects. Understuffing decreases the stability, JCFs and inverse with overstuffing. Subtle changes in the PE insert thickness alter the post-cam mechanics.

Does Posterior Tibial Slope Influence Knee Kinematics in Medial Stabilized TKA?

During total knee arthroplasty (TKA), one of the key alignment factors to pay attention to is the posterior tibial slope (PTS). The PTS clearly influences the kinematics of the knee joint but must be adapted to the coupling degree of the specific TKA design. So far, there is hardly any literature including clear recommendations for how surgeons should choose the PTS in a medial stabilized (MS) TKA. The aim of the present study is to investigate the effects of different degrees of PTS on femorotibial kinematics in MS TKA. An MS TKA was performed in seven fresh-frozen human specimens successively with 0°, 3°, and 6° of PTS. After each modification, weight-bearing deep knee flexion (30-130°) was performed, and femorotibial kinematics were analyzed. A lateral femoral rollback was observed for all three PTS modifications. With an increasing PTS, the tibia was shifted more anteriorly on the lateral side (0° PTS anterior tibial translation -9.09 (±9.19) mm, 3° PTS anterior tibial translation -11.03 (±6.72) mm, 6° PTS anterior tibial translation 11.86 (±9.35) mm). No difference in the tibial rotation was found for the different PTS variants. All PTS variants resulted in internal rotation of the tibia during flexion. With a 3° PTS, the design-specific medial rotation point was achieved more accurately. According to our findings, we recommend a PTS of 3° when implanting the MS prosthesis used in this study.

Prospective sequential comparison of femoral roll-back between cruciate-retaining and posterior-stabilized total knee arthroplasty using an intra-operative sensor

BackgroundImplant design and surgical techniques affect postoperative knee kinematics in total knee arthroplasty (TKA). This study aimed to compare femoral roll-back between cruciate-retaining (CR) and posterior-stabilized (PS) TKA in the same knee by objectively quantifying the contact point kinematics of the tibiofemoral joint using a sensor. MethodsIn the present prospective study, we used an intraoperative sensor to compare medial and lateral roll-back during 0-120° knee flexion in 33 knees that underwent CR and PS TKA. We also examined the relationship between mediolateral balance and the lateral-to-medial roll-back ratio. We defined the contact percentage position as the vertical length to the contact point divided by the anteroposterior length of the tibial plate. ResultsThe roll-back percentage following PS TKA (19.8 ± 5.1%) was significantly higher than that after CR TKA in both the medial (19.8 ± 5.1% versus 7.1 ± 2.5%, P < 0.001) and lateral (26.8% ± 3.8% versus 18.7 ± 3.8%, P < 0.001) compartments. The medial contact pressure at 90° was significantly correlated with the increased lateral-to-medial roll-back ratio in both CR and PS TKA (both P < 0.001). ConclusionPS TKA resulted in a higher percentage of femoral roll-back in the medial and lateral compartments than CR TKA. CR TKA caused a higher lateral-to-medial roll-back ratio compared to PS TKA. To reproduce medial pivot knee motion similar to that of a normal knee, the medial soft tissue needed to be balanced more tightly than the lateral soft tissue during TKA. These findings provide some clinical evidence of TKA design selection and proper mediolateral balancing for successful TKA.

Intraoperative Load Sensing in Total Knee Arthroplasty Leads to a Functional but Not Clinical Difference: A Comparative, Gait Analysis Evaluation.

Introduction: Although Total Knee Arthroplasty (TKA) is a successful procedure, a significant number of patients are still unsatisfied, reporting instability at the mid-flexion range (Mid-Flexion Instability-MFI). To avoid this complication, many innovations, including load sensors (LS), have been introduced. The intraoperative use of LS may facilitate the balance of the knee during the entire range of motion to avoid MFI postoperatively. The objective of this study was to perform a Gait Analysis (GA) evaluation of a series of patients who underwent primary TKA using a single LS technology. Methods: The authors matched and compared two groups of patients treated with the same posterior stabilized TKA design. In Group A, 10 knees were intraoperatively balanced with LS technology, while 10 knees (Group B) underwent standard TKA. The correct TKA alignment was preoperatively determined aiming for a mechanical alignment. Clinical evaluation was performed according to the WOMAC, Knee Society Score (KSS) and Forgotten Joint Score, while functional evaluation was performed using a state-of-the-art GA platform. Results: We reported excellent clinical results in both groups without any statistical difference in patient reported outcome measurements (PROMs); from a functional standpoint, several GA space–time parameters were closer to normal in the sensor group when compared to the standard group, but a statistically significant difference was not reached. Conclusions: Gait Analysis represents a valid method to evaluate TKA kinematics. This study, with its limitations, showed that pressure sensitive technology represents a valid aid for surgeons aiming to improve the postoperative stability of TKA; however, other factors (i.e., level of intra-articular constraint and alignment) may play a major role in reproducing the normal knee biomechanics.

Comparison of in vivo kinematics of total knee arthroplasty between cruciate retaining and cruciate substituting insert

BackgroundThe decision to choose cruciate retaining (CR) insert or cruciate substituting (CS) insert during total knee arthroplasty (TKA) remains a controversial issue. We hypothesized that there are different knee kinematics between CR and CS inserts and that a raised anterior lip design would offer a potential minimization of the paradoxical movement and provide joint stability. The objective of this study was to evaluate and compare kinematics of a CR and CS TKA of the same single-radius design. MethodsWe investigated the in vivo knee kinematics of 20 knees with a CR TKA (10 knees in the CR insert and 10 knees in the CS insert). Patients were examined during deep knee flexion using fluoroscopy and femorotibial motion was determined using a 2- to 3-dimensional registration technique, which used computer-assisted design models to reproduce the spatial positions of the femoral and tibial components. We evaluated the knee range of motion (ROM), femoral axial rotation relative to the tibial component, anteroposterior translation, and kinematic pathway of the nearest point of the medial and lateral femoral condyles on the tibial tray. ResultsThe average ROM was 121.0 ± 17.3° in CR and 110.8 ± 12.4° in CS. The amount of femoral axial rotation was 7.2 ± 3.9° in CR, and 7.4 ± 2.7° in CS. No significant difference was observed in the amount of anterior translation between CR and CS. The CR and CS inserts had a similar kinematic pattern up to 100° flexion that was central pivot up to 70° flexion and then paradoxical anterior femoral movement until 100° flexion. ConclusionThe present study demonstrated that there was no significant difference between the inserts in knee kinematics. These kinematic results suggested that the increased anterior lip could not control anterior movement in the CS insert.

Outcomes of Kinematically Aligned Total Knee Arthroplasty in Indian Population-Case Series with Three Year Clinical Results.

Kinematic total knee arthroplasty (KA) is emerging as an alternative for conventional mechanically aligned (MA) total knee arthroplasty (TKA) for treating patients with osteoarthritis (OA) knee. Since its introduction, concerns remain about the reproducibility and outcomes in different ethnic groups. This study was undertaken to analyse patient-reported outcomes of kinematically aligned total knee arthroplasty using Oxford Knee Score (OKS) in Indian population. A total of 104 consecutive patients (75 females and 29 males) who underwent total knee arthroplasty between February 2016 and February 2018 were included in this prospective study. Only patients with primary OA knee were included, those with rheumatoid arthritis, previous knee surgery were excluded. All surgeries were done by a single surgeon using the same type of cruciate-retaining prosthesis (Vanguard, Zimmer Biomet, Indiana, United States) with the conventional instruments. The principles of kinematic knee alignment were followed. Preoperative and postoperative OKS were recorded. Secondary outcome variables such as Haemoglobin (Hb) drop and blood transfusion rate were noted. The mean age of this group of patients was 65.28years (range 54-83years). 96 patients (108 knees) were available for final review. The average preoperative OKS was 15.71 whereas the average OKS at 2years follow-up improved to 42.07. The mean Hb drop was 1.18g/dl and none of the patients required blood transfusion. This study demonstrates that kinematic alignment TKA provides excellent to good patient satisfaction in Indian population. There were no catastrophic failures in three years of follow-up in this series. The results of KA TKA were not compared to MA TKA in this study and our sample size is not big enough to make recommendations on routine use of this technique. Larger randomised trials in Indian patients are needed to propose solid recommendations. Our pilot data can be useful in calculating sample size for such studies.

Does contemporary bicruciate retaining total knee arthroplasty restore the native knee kinematics? A descriptive literature review.

There has been no consensus on the benefit of retaining the anterior cruciate ligament (ACL) in TKAs. This study aims to review recent evidences around the kinematics of bicruciate retaining (BCR) total knee arthroplasty (TKA). A search of the literature was conducted on PubMed and Web of Science. Reports that assessed the BCR TKA kinematics, including both in vitro cadaveric studies and in vivo clinical studies, were reviewed. A total number of 169 entries were obtained. By exclusion criteria, five in vitro studies using cadaveric knee specimens and six in vivo studies using patient cohorts were retained. In vitro studies showed a low internal rotation (< 10°) throughout the flexion path in all BCR TKAs. Compared to native knees, the difference in the internal rotation was maximal during early and late flexion; the femur in the BCR TKA was significantly more anteriorly positioned (1.7-3.6mm from 0° to 110°) and more externally rotated (3.6°-4.2° at 110° and 120°). In vivo studies revealed that the native knee kinematics, in general, were not fully restored after BCR TKA during various knee activates (squatting, level-walking, and downhill-walking). There are asymmetric kinematics during the stance phase of gait cycle and a smaller range of axial rotation (23% patients exhibiting external tibial rotation) throughout the gait cycle in BCR TKAs. Critical insights in the complex BCR TKA biomechanics have been reported from recent laboratory kinematics studies. However, whether contemporary BCR TKAs can fully restore native knee kinematics remains debatable, warranting further investigations.

Rotational Soft-Tissue Balance Is Highly Correlated with Rotational Kinematics in Total Knee Arthroplasty.

Recovery of normal knee kinematics is critical for improving functional outcomes and patient satisfaction after total knee arthroplasty (TKA). The kinematics pattern after TKA varies from case to case, and it remains unclear how to reproduce normal knee kinematics. The present study aimed to evaluate rotational knee kinematics and soft-tissue balance using a navigation system and to assess the influence of intraoperative soft-tissue balance on the rotational knee kinematics. We evaluated 81 osteoarthritic knees treated with TKA using a posterior stabilized (50 knees) or cruciate retaining (31 knees) prosthesis. Rotational kinematics were assessed at 0, 30, 45, 60, and 90 degrees flexion angles by using a computer-assisted navigation system. Correlation between femorotibial rotational position and measured soft tissue balance was assessed by using Spearman's rank correlation coefficient. Rotational soft-tissue balance (the median angle of rotational stress) was significantly correlated with rotational kinematics (rotational axis of the femur relative to the tibia throughout the range of motion) at all measured angles after TKA. The correlation coefficients between the median angle of rotational stress and rotational kinematics were 0.97, 0.80, 0.74, 0.71, and 0.70 at 0, 30, 45, 60, and 90 degrees of flexion, respectively (p-values <0.0001 in all measured angles). The correlation coefficient increased as the knee approached full extension. Our findings suggest that soft-tissue balance is a key factor for rotational kinematics, following both cruciate-retaining and posterior-stabilized TKA.

Measured Resection Techniques Do Not Align to the Cylindrical Axis in Kinematic Total Knee Arthroplasty.

BackgroundThere has been increasing interest with improved functional results in kinematically aligned total knee arthroplasty. Kinematic alignment seeks to replicate the rotational axes of the individual knee. The femoral component can either be aligned to the estimated prearthritic distal and posterior joint lines via a measured-resection technique or by aligning to the cylindrical axis (CA). The CA is calculated using three-dimensional imaging and defined as a line equidistant from the medial and lateral condylar surfaces from 15° to 115° flexion. This study investigates whether these 2 techniques lead to similar alignment angles in the coronal plane.Materials and MethodsOne hundred three knees undergoing total knee arthroplasty were assessed using a computed tomography-based protocol. The image-based cylindrical axis coronal angle (CAA) was calculated, and the distal condylar coronal angle (DCA) was calculated to simulate a caliper measured resection technique. A computed tomographic planning software program was used to measure the offset from the distal-most extent of the calculated cylinder to the distal-most aspect of the condyles.ResultsThe DCA measured 3.3° valgus (standard deviation 2.4°) and the CAA 1.8° valgus (standard deviation 2.1°). The mean difference in offset from CAA radius to DCA from the medial condyle and the lateral condyle was 2.85 mm and 1.51 mm, respectively, increasing valgus predilection.ConclusionsCaliper measured resection kinematically aligned techniques will position the femoral component in a significantly more valgus position than when aligning to the CA of the knee. This is due to an increased offset of the distal femoral articulation from the most distal aspect of the cylinder on the medial side of the knee.

Arthroplasty of the Knee: Current Techniques for Implant Alignment.

When a total knee arthroplasty (TKA) is implanted using the traditional mechanical alignment technique, this typically results in a straight leg, independently of pre-operative or even pre-arthrotic varus or valgus alignment. With mechanical alignment, we distinguish between 2 different alignment techniques: ligament balancing and bony referencing according to bony skeletal landmarks. In ligament balanced technique beside the straight mechanical axis, the prosthesis is implanted at 90° to the latter. The rotational alignment of the femur is set according to the ligament tension. In the skeletal referenced technique, the rotation of the femur is also set according to bony skeletal landmarks. As a variation of this technique, the prosthesis can be implanted with anatomical alignment. In this technique, the medial slope of the joint line of 3° in the frontal plane is respected during the implantation of TKA. Both techniques result in comparable long-term results with survival rates of almost 80% after 25 years. On the other hand, 15 – 20% of TKA patients report dissatisfaction with their clinical result. For more than 10 years now, the kinematic TKA alignment concept has been developed with the goal to achieve implantation that is adapted to the individual anatomy of the patient. The advocates of this technique expect better function of TKA. This strategy aims to reconstruct the pre-arthrotic anatomy of a given patient while preserving the existing joint line and the mechanical axis without performing ligamentary release. Studies have shown that the function of the prothesis is at least that good as in the conventional techniques. Long-term results are still sparse, but initial studies show that TKA implanted using the kinematic alignment technique exhibit comparable 10-year-survival rates to those implanted using the traditional mechanical alignment technique. Future studies need to show the limitations of this new technique and to identify patients who will or will not significantly benefit from this technique.

In vivo kinematics of cruciate-retaining total knee arthroplasty after a change of polyethylene insert configuration

BackgroundTo investigate in vivo kinematics of total knee arthroplasty (TKA) with the introduction of a mildly constrained (MC) type of polyethylene (PE). We compared the knee kinematics with a reported pattern after surgery using the same component with a conventionally constrained (CC) type of PE. MethodsFinite element analysis (FEA) was performed to examine different peak stress distribution of both types of PE. For in vivo study, patients who underwent cruciate-retaining TKA using a total knee system with MC-PE were included. Fluoroscopic surveillance was used to measure the weight-bearing deep knee bend (squatting) using a two-dimensional/three-dimensional (2-D/3-D) registration technique. ResultsFEA analysis revealed the edge loading of the femoral component on PE in CC but not in MC. During the study period, 42 patients underwent TKA with MC-PE. Among them, 13 agreed to participate in the present study. In vivo kinematics analysis found that starting from an average external rotation of femur being 7.1° at 0° of flexion, the rotation slightly decreased to 6.8° at 10° of flexion, then increased with increasing knee flexion until it reached 10.8° at 80° of flexion, and finally decreased to 9.8° at 100° of knee flexion. The results indicate a modest medial pivot pattern. Although the overall pattern was similar for both MC-PE and CC-PE, a slight difference was observed. MC-PE showed a slight internal rotation of 0.3° from 0 to 10° of knee flexion, whereas CC-PE showed a gradual increase of external rotation in this range. ConclusionsChange of configuration from CC to MC did not substantially affect in vivo kinematics of knees after TKA. Considering the theoretical wider range of allowance of rotation, MC-PE is easier for knee surgeons to use.

Effects of Posterior Tibial Slope on a Posterior Cruciate Retaining Total Knee Arthroplasty Kinematics and Kinetics

BackgroundIt has been hypothesized that increasing posterior tibial slope can influence condylar rollback and play a role in increasing knee flexion. However, the effects of tibial slope on knee kinematics are not well studied. The objective of this study is to assess the effects of tibial slope on femorotibial kinematics and kinetics for a posterior cruciate retaining total knee arthroplasty design. MethodsA validated forward solution model of the knee was implemented to predict the femorotibial biomechanics of a posterior cruciate retaining total knee arthroplasty with varied posterior slopes of 0°-8° at 2° intervals. All analyses were conducted on a weight-bearing deep knee bend activity. ResultsIncreasing the tibial slope shifted the femoral component posteriorly at full extension but decreased the overall femoral rollback throughout flexion. With no tibial slope, the lateral condyle contacted the polyethylene 6 mm posterior of the midline, but as the slope increased to 8°, the femur shifted an extra 5 mm, to 11 mm posterior of the tibial midline. Similar shifts were observed for the medial condyle, ranging from 7 mm posterior to 13 mm posterior, respectively. Increasing posterior slope decreased the posterior cruciate ligament tension and femorotibial contact force. ConclusionThe results of this study revealed that, although increasing the tibial slope shifted the femur posteriorly at full extension and maximum flexion, it reduced the amount of femoral rollback. Despite the lack of rollback, a more posterior location of condyles suggests lower chances of bearing impingement of the posterior femur and may explain why increasing slope may lead to higher knee flexion.