Can Asymmetry in Total Knee Arthroplasty Design Lead to More Normal-Like Postoperative Kinematics? A Multi-Implant Evaluation.

BACKGROUND: Few studies have evaluated the effects of symmetrical versus asymmetrical implant designs, more specifically the femoral condyles, trochlear groove, joint line, and bearing surfaces. The objective of this study was to investigate multiple posterior cruciate-retaining (PCR) total knee arthroplasty (TKA) designs influencing factors related to TKA asymmetry, and to investigate whether asymmetry can improve postoperative knee kinematics. METHODS: In vivo tibio-femoral kinematics for 99 subjects was evaluated in this retrospective study. Overall, 10 subjects had a nonimplanted, normal knee, and 89 subjects had 1 of 3 PCR TKAs with varying degrees of asymmetry within their femoral and tibial components (PCR #1 = 30, PCR #2 = 29, PCR #3 = 30). All TKAs were implanted by the same surgeon and were analyzed using fluoroscopy during a deep knee bend. RESULTS: At full extension, all 3 PCR TKAs experienced a more posteriorized position of the femoral condyles compared to the normal knee, with the 2 asymmetrical PCR TKAs experiencing more anteriorization compared to the third, symmetrical PCR TKA. Both the normal knee and the PCR TKA with greatest amount of asymmetry experienced statistically more posterior femoral rollback of the lateral condyle than the other 2 PCR TKAs. The PCR TKA with greater asymmetry also experienced statistically greater range of motion than the other 2 PCR TKAs. CONCLUSIONS: With increasing flexion, the design with the most asymmetry also experienced the most posterior femoral rollback, axial rotation, and greatest range of motion. The results in this study seem to suggest that the inclusion of asymmetry in a TKA could be beneficial for achieving more normal-like kinematics and greater weight-bearing knee flexion.

In Vivo Weight-Bearing Kinematics for Constrained Versus Traditional Bicruciate Stabilized Total Knee Arthroplasty Cohorts Compared to the Normal Knee.

BACKGROUND: Constrained inserts in total knee arthroplasty (TKA) may offer additional stability, but can this insert type allow unrestricted movements or will the extra conformity cause kinematic conflict with the cam-post mechanism in deeper flexion? The objective of this study was to evaluate the weight-bearing kinematics of both traditional and constrained bicruciate stabilized (BCS) TKA inserts to determine if the rollback induced by the cam-post mechanism will work in unison with the constrained polyethylene insert. METHODS: This study used previously published 3-dimensional model fitting techniques to compare weight-bearing flexion and femoro-tibial condylar motion patterns for 20 patients who had a traditional insert, 20 patients who had a constrained insert, and 10 previously published nonimplanted knees, all performing a deep knee bend activity while under fluoroscopic surveillance. RESULTS: The results from this study indicate that subjects having a bicruciate stabilized TKA experienced similar postoperative kinematics for both constrained and unconstrained insert options, comparable to normal knees. CONCLUSIONS: Subjects in this study having either a constrained or traditional insert experienced progressive rollback of both condyles, with the lateral condyle rolling more posterior than the medial condyle, leading to axial rotation. Although less in magnitude, these results were comparable to the normal knee in pattern, indicating that kinematic conflict did not occur for subjects having a constrained insert.

Improved accuracy of implant placement with an imageless handheld robotic system compared to conventional instrumentation in patients undergoing total knee arthroplasty: a prospective randomized controlled trial using CT-based assessment of radiological outcomes.

PURPOSE: Image-free handheld robotic-assisted total knee arthroplasty (RATKA) has shown to achieve desired limb alignment compared to conventional jig-based instrumented total knee arthroplasty (CTKA). The aim of this prospective randomized controlled trial (RCT) was to evaluate the accuracy of a semi-autonomous imageless handheld RATKA compared to CTKA in order to achieve the perioperative planned target alignment of the knee postoperatively. METHODS: Fifty-two patients with knee osteoarthritis were randomized in 1:1 ratio to undergo unilateral CTKA or an imageless handheld RATKA. A full-length lower limb CT-scan was obtained pre- and 6-week postoperative. The primary outcomes were radiologic measurements of achieved target hip-knee-ankle axis (HKA-axis) and implant component position including varus and external rotation and flexion of the femur component, and posterior tibial slope. The proportion of outliers in above radiographic outcomes, defined as > 3° deviation in postoperative CT measurements as compared to perioperative planned target, were also noted. Knee phenotypes were compared with use of the Coronal Plane Alignment of the Knee (CPAK) classification. RESULTS: Baseline conditions were comparable between both groups. The overall proportion and percentage of outliers (n = 38, 24.4% vs n = 9, 5.8%) was statistically significant (p < 0.001) in favor of RATKA. The achieved varus-valgus of the femoral component (varus 1.3° ± 1.7° vs valgus - 0.1° ± 1.9°, p < 0.05) with statistically significant less outliers (0% vs 88.5%, p < 0.01), the achieved HKA-axis (varus 0.4° ± 2.1° vs valgus - 1.2° ± 2.1°, p < 0.05) and the posterior tibial slope (1.4° ± 1.1° vs 3.2° ± 1.8°, p < 0.05) were more accurate with RATKA. The most common postoperative CPAK categories were type II (50% CTKA vs 61.5% RATKA), type I (3.8% CTKA vs 23.1% RATKA) and type V (26.9% CTKA vs 15.4% RATKA). CPAK classification III was only found in CTKA (19.2%). Type VI, VII, VIII, and IX were rare in both populations. CONCLUSIONS: The present trial demonstrates that an imageless handheld RATKA system can be used to accurately perioperatively plan the desired individual component implant positions with less alignment outliers whilst aiming for a constitutional alignment. LEVEL OF EVIDENCE: I.

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

BACKGROUND: 3D-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. METHODS: The 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. FINDINGS: The 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. INTERPRETATION: A 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.

Anatomic vs Dome Patella: Is There a Difference Between Fixed- vs Mobile-Bearing Posterior-Stabilized Total Knee Arthroplasties?

BACKGROUND: It has been hypothesized that the patella, working in conjunction with both medial and lateral femoral condyles, can influence kinematic parameters such as posterior femoral rollback and axial rotation. The objective of this study is to determine the in vivo kinematics of subjects implanted with a fixed-bearing (FB) or mobile-bearing (MB) posterior-stabilized (PS) total knee arthroplasty (TKA), with a specific focus on evaluating the impact that Anatomic and Medialized Dome patellar components have on tibiofemoral kinematic patterns. METHODS: Tibiofemoral kinematics were assessed for 40 subjects; 20 with an anatomic patella and 20 with a dome patella. Within these groups, 10 subjects received an FB PS TKA and 10 subjects received an MB PS TKA. All subjects were analyzed using fluoroscopy while performing a deep knee bend activity. Kinematics were collected during specific intervals to determine similarities and differences in regard to patella and bearing type. RESULTS: The greatest variation in kinematics was detected between the 2 Anatomic patellar groups. Specifically, the MB-Anatomic subjects experienced greater translation of the lateral condyle, the highest magnitude of axial rotation, and the highest range of motion compared to the FB-Anatomic subjects. Subjects with a Dome Patella displayed much variability among the average kinematics, with all parameters between FB and MB cohorts being similar. CONCLUSION: The findings in this study suggest that subjects with an Anatomic patellar component could have more normal kinematic patterns with an MB PS TKA as opposed to an FB PS TKA, while subjects with a Dome patella could achieve similar kinematics regardless of TKA type.

Effects of the Medial Plateau Bearing Insert Conformity on Mid-Flexion Paradoxical Motion in a Posterior-Stabilized Total Knee Arthroplasty Design.

BACKGROUND: One of the most common kinematic abnormalities reported for posterior-stabilized (PS) total knee arthroplasty (TKA) design is paradoxical anterior sliding during early and mid-flexion. PS TKAs have been designed such that the cam-post mechanism does not engage until later in flexion, making these implants vulnerable to anterior sliding during early and mid-flexion. The objective of this study is to investigate the biomechanical effect of increasing bearing conformity on a PS TKA. METHODS: Using a validated computational model of the knee joint, the sagittal conformity of the medial plateau of a PS TKA design was altered. Three scenarios were created and evaluated for mechanics: (1) baseline conformity, (2) increased conformity, and (3) decreased conformity. RESULTS: From full extension to approximately 70° of knee flexion, the medial condyle demonstrated minimal anterior sliding for the increased medial conformity design but revealed anterior sliding of 2 and 4 mm for the baseline and decreased conformity designs, respectively. After cam-post engagement, the medial condyle consistently rolled back for all 3 designs. The lateral condyle experienced consistent rollback throughout the entire flexion range for all 3 designs. However, femorotibial contact force was higher for the increased conformity design, peaking at 3.13 times body weight (×BW) compared to 3.0 × BW contact force for other 2 designs. CONCLUSION: Increasing medial conformity of the bearing insert appears to reduce mid-flexion sliding for PS TKA designs, although this comes at the expense of increased femorotibial forces. This could be due to kinematic conflicts that may be introduced with highly constraining designs.

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

BACKGROUND: It 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. METHODS: A 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. RESULTS: Increasing 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. CONCLUSION: The 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.

Can an OA Knee Brace Effectively Offload the Medial Condyle? An In Vivo Fluoroscopic Study.

BACKGROUND: Previous studies evaluating the effectiveness of OA offloading knee braces focused on qualitative results. The objective of this study was to analyze the effectiveness of an off-loading knee brace with respect to in vivo three-dimensional knee kinematics to quantitatively measure the changes in medial joint space and relative bone alignment when wearing the brace. METHODS: Twenty subjects diagnosed with medial compartmental joint space narrowing and varus deformity due to OA were recruited. During fluoroscopic surveillance, subjects performed normal gait on a treadmill with and without the brace. Images were sequenced at heel-strike and mid-stance during the weight-bearing portion of gait. 3D-to-2D image registration was performed on each subject using 3D bone models derived from CT segmentation and 3D ultrasound scans. RESULTS: Medial joint space was to increase when the brace was applied in all subjects (1.6 ± 0.7 mm at heel-strike, 1.6 ± 0.8 mm at mid-stance) and was statistically significant (P < .001). It was also found that sixteen of the twenty subjects experienced a medial joint space increase of more than 1.0 mm during heel-strike while thirteen of twenty experienced this change at mid-stance. While wearing the brace, over half of the subjects experienced a valgus correction to their alignment. CONCLUSIONS: All subjects in this study experienced a positive change in the medial joint space when wearing the offloading knee brace. In addition, many subjects also saw joint space values representative of previously documented, nonosteoarthritic subjects and valgus changes in bone alignment more akin to the normal knee.

Development of a hip joint mathematical model to assess implanted and non-implanted hips under various conditions.

While total hip arthroplasty does generally improve patient quality of life, current systems can still yield atypical forces, premature component wear, and abnormal kinematics compared to native joints. Specifically, common complications include instability, separation, sliding, and edge loading within the hip joint. Unfortunately, evaluating potential solutions to these issues can be costly and time-consuming. Fortunately, mathematical modeling is an accurate and efficient tool that can be used to evaluate potential solutions. A forward dynamics mathematical model of the hip allows users to virtually insert a hip implant into a theoretical patient and observe the predicted postoperative mechanics. The objective of this study is therefore to develop, validate, and use a fully functional forward solution mathematical model that allows for a comparison between various hip implant designs and a determination of factors leading to in vivo hip separation, instability, and edge loading. The model presented herein has been validated kinetically against telemetric data and kinematically against fluoroscopic data. It was determined through this research that shifting of the joint rotation center during total hip arthroplasty has the potential to yield postoperative instability, and surgical errors can exacerbate these outcomes. However, the relationships between subject-specific joint shifting and hip instability are extremely complex, and therefore it becomes essential for surgeons to focus on implanting components as accurately as possible to minimize these risks.

A Validated Forward Solution Dynamics Mathematical Model of the Knee Joint: Can It Be an Effective Alternative for Implant Evaluation?

BACKGROUND: Mathematical modeling is among the most common computational tools for assessing total knee arthroplasty (TKA) mechanics of different implant designs and surgical alignments. The main objective of this study is to describe and validate a forward solution mathematical of the knee joint to investigate the effects of TKA design and surgical conditions on TKA outcomes. METHODS: A 12-degree of freedom mathematical model of the human knee was developed. This model includes the whole lower extremity of the human body and comprises major muscles and ligaments at the knee joint. The muscle forces are computed using a proportional-integral-derivative controller, and the joint forces are calculated using a contact detection algorithm. The model was validated using telemetric implants and fluoroscopy, and the sensitivity analyses were performed to determine how sensitive the model is to both implant design, which was analyzed by varying medial conformity of the polyethylene, and surgical alignment, which was analyzed by varying the posterior tibial tilt. RESULTS: The model predicted the tibiofemoral joint forces with an average accuracy of 0.14× body weight (BW), 0.13× BW, and 0.17× BW root-mean-square errors for lateral, medial, and total tibiofemoral contact forces. With fluoroscopy, the kinematics were validated with an average accuracy of 0.44 mm, 0.62 mm, and 0.77 root-mean-square errors for lateral anteroposterior position, medial anteroposterior position, and axial rotation, respectively. Increasing medial conformity resulted in reducing the paradoxical anterior sliding midflexion. Furthermore, increasing posterior tibial slopes shifted the femoral contact point more posterior on the bearing and reduced the tension in the posterior cruciate ligament. CONCLUSION: A forward solution dynamics model of the knee joint was developed and validated using telemetry devices and fluoroscopy data. The results of this study suggest that a validated mathematical model can be used to predict the effects of component design and surgical conditions on TKA outcomes.

In Vivo Knee Kinematics for a Cruciate Sacrificing Total Knee Arthroplasty Having Both a Symmetrical Femoral and Tibial Component.

BACKGROUND: Early total knee arthroplasty (TKA) designs were symmetrical, but lead to complications due to over-constraint leading to loosening and poor flexion. Next-generation TKAs have been designed to include asymmetry, pertaining to the trochlear groove, femoral condylar shapes, and/or the tibial component. More recently, an advanced posterior cruciate sacrificing (PCS) TKA was designed to include both a symmetrical femoral component with a patented V-shaped trochlear groove and a symmetrical tibial component with an ultracongruent insert, in an attempt to reduce inventory costs. Because previous PCS TKA designs produced variable results, the objective of this study is to determine and evaluate the in vivo kinematics for subjects implanted with this symmetrical TKA. METHODS: Twenty-one subjects, implanted with symmetrical PCS fixed-bearing TKA, were asked to perform a weight-bearing deep knee bend (DKB) while under fluoroscopic surveillance. A 3-dimensional to 2-dimensional registration technique was used to determine each subject's anteroposterior translation of lateral and medial femoral condyles as well as tibiofemoral axial rotation and their weight-bearing knee flexion. RESULTS: During the DKB, the average active maximum weight-bearing flexion was 111.7° ± 13.3°. On average, from full extension to maximum knee flexion, subjects experienced -2.5 ± 2.0 mm of posterior femoral rollback of the lateral condyle and 2.5 ± 2.2 mm of medial condyle motion in the anterior direction. This medial condyle motion was consistent for the majority of the subjects, with the lateral condyle exhibiting rollback from 0° to 60° of flexion and then experienced an average anterior motion of 0.3 mm from 60° to 90° of knee flexion. On average, the subjects in this study experienced 6.6°± 3.3° of axial rotation, with most of the rotation occurring in early flexion, averaging 4.9°. CONCLUSION: Although subjects in this study were implanted with a symmetrical PCS TKA, they did experience femoral rollback of the lateral condyle and a normal-like pattern of axial rotation, although less in magnitude than the normal knee. The normal axial rotation pattern occurred because the lateral condyle rolled in the posterior direction, while the medial condyle moved in the anterior direction. Interestingly, the magnitude of posterior femoral rollback and axial rotation for subjects in this study was similar in magnitude reported in previous studies pertaining to asymmetrical TKA designs. It is proposed that more patients be analyzed having this TKA implanted by other surgeons.

In Vivo Determination and Comparison of Total Hip Arthroplasty Kinematics for Normal, Preoperative Degenerative, and Postoperative Implanted Hips.

BACKGROUND: The study objective is to analyze subjects having a normal hip and compare in vivo kinematics to subjects before and after receiving a total hip arthroplasty. METHODS: Twenty subjects, 10 with a normal hip and 10 with a preoperative, degenerative hip were analyzed performing normal walking on level ground while under fluoroscopic surveillance. Seven preoperative subjects returned after receiving a total hip arthroplasty using the anterior surgical approach by a single surgeon. Using 3-dimensional to 2-dimensional registration techniques, joint models were overlayed on fluoroscopic images to obtain transformation matrices in the image space. From these images, displacements of the femoral head and acetabulum centers were computed, as well as changes in contact patches between the 2 surfaces throughout the gait cycle. RESULTS: Implanted hips experienced the least amount of separation, compression, and overall sliding throughout the entire gait cycle, but they did show signs of edge loading contact patterns. Conversely, the degenerative hips experienced the most compression, sliding, and separation, with the maximum amount of sliding being 6.9 mm. The normal group ranged in the middle, with the maximum amount of sliding being 1.75 mm. CONCLUSION: Current analysis revealed trends that degenerative hips experience more abnormal hip kinematics that leads to higher articulating surface forces and stresses within the acetabulum. None of the implanted hips experienced hip separation.

Confirmation of long-term in vivo bearing mobility in eight rotating-platform TKAs.

BACKGROUND: Posterior-stabilized rotating-platform prostheses for TKAs were designed to improve contact mechanics at the femoral-polyethylene (PE) interface. Short-term followup studies have shown that the PE bearings rotate with respect to the tibia but might not necessarily track with the femur. It is important to know how kinematics in these designs change owing to long-term in vivo use. QUESTIONS/PURPOSES: We asked whether there is a significant change in the in vivo kinematic performance of a posterior-stabilized rotating-platform prosthesis at as much as 10 years postoperative. We specifically examined (1) relative femoral component-PE bearing and relative PE bearing-tibial tray motion; (2) relative AP motion of the femoral condyles with respect to the tibial tray; and (3) relative femorotibial condylar translations. METHODS: In vivo three-dimensional kinematics were evaluated for eight patients at 3 months, 15 months, 5 years, and 10 years after TKA with primary implantation of a posterior-stabilized rotating-platform prosthesis. Each patient performed deep knee bend activity, and three-dimensional kinematics were reconstructed from multiple fluoroscopic images using a three-dimensional to two-dimensional registration technique. Once complete, relative component axial rotation patterns, medial and lateral condyle motions throughout flexion, and the presence of femoral condylar lift-off were analyzed. RESULTS: Overall, tibial bearing rotation was maintained at 10 years postoperatively. There was no statistical difference between postoperative periods for any kinematic parameter except for femoral component-PE bearing axial rotation, which was reduced at the 10-year evaluation versus other assessment periods (p = 0.0006). The lack of statistical difference between postoperative evaluation periods indicates sustained overall implant kinematic performance. CONCLUSIONS: Our study showed that PE bearing-tibial tray mobility was maintained and that femoral component-PE bearing rotation was reduced at the 10-year followup. This suggests that the overall kinematic performance of this mobile-bearing implant is not negatively affected 10 years postoperatively. LEVEL OF EVIDENCE: Level III, retrospective study. See the Instructions for Authors for a complete description of levels of evidence.