Design features of total knees for achieving normal knee motion characteristics

The goal of the study was to achieve a normal neutral anatomical path of motion with a total knee arthroplasty (TKA) using specific motion-guiding design features. Two reference TKA models were used, consisting of a partially conforming double-dished geometry and the same with a central cam-post for femoral rollback. Four experimental TKA models included features to produce femoral rollback with and without guidance for tibial rotation, and a feature to prevent paradoxical anterior femoral sliding. The femur was loaded down the tibial axis, and the femoral-tibial positions were recorded at a sequence of flexion angles. Subsequently, the positions were recorded with an anterior shear force superimposed. Software was used to reconstruct the paths of the transverse femoral axis on the tibia, during a full flexion range. The reference knees did not reproduce a normal neutral path of motion. However, this was achieved with an experimental design incorporating all of the motion-guiding features.     

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

BackgroundEarly 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.MethodsTwenty-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.ResultsDuring 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°.ConclusionAlthough 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.     

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Kinematic Performance of Gradually Variable Radius Posterior-Stabilized Primary TKA During Various Activities: An In Vivo Study Using Fluoroscopy

BackgroundPosterior-stabilized total knee arthroplasty (TKA) with gradually variable radii (G-curve) femoral condylar geometry is now available. It is believed that a G-curve design would lead to more mid-flexion stability leading to reduced incidence of paradoxical anterior slide. The objective of this study was to assess the in vivo kinematics for subjects implanted with this type of TKA under various conditions of daily living.MethodsTibiofemoral kinematics of 35 patients having posterior-stabilized TKA with G-curve design were analyzed using fluoroscopy while performing three activities: weight-bearing deep knee bend, gait, and walking down a ramp. The subjects were assessed for range of motion, condylar translation, axial rotation, cam-spine engagement, and condylar lift-off.ResultsThe average weight-bearing flexion during deep knee bend was 111.4°. On average, the subjects exhibited 5.4 mm of posterior rollback of the lateral condyle and 2.0 mm of the medial condyle from full extension to maximum knee flexion. The femur consistently rotated externally with flexion, and the average axial rotation was 5.2°. Overall movement of the condyles during gait and ramp-down activity was small. No incidence of condylar lift-off was observed.ConclusionSubjects in this study experienced consistent magnitudes of posterior femoral rollback and external rotation of the femur with weight-bearing flexion. The variation is similar to that previously reported for normal knee where the lateral condyle moves consistently posterior compared to the medial condyle. Subjects experienced low overall mid-flexion paradoxical anterior sliding and no incidence of condylar lift-off leading to mid-flexion stability.     

Total knees designed for normal kinematics evaluated in an up‐and‐down crouching machine

We constructed a crouching machine to study the motion of the knee joint, in which a motor was used to wind the quadriceps tendon so as to move the knee from high flexion to extension and back into flexion, while springs simulated hamstrings forces. Seven human cadaveric knees were tested intact and then after anterior cruciate ligament (ACL) resection. Motions of the femur, tibia, and patella were recorded by an optical tracking system. We then inserted plastic models representing commonly used total condylar and posterior stabilized knee replacement designs. Femoral motion was described by successive positions of the transverse axis of the femur projected onto the tibial surface. In the knee replacements, motions were similar to that of an ACL‐deficient knee. We then tested two new designs with features intended to prevent anterior paradoxical sliding and to promote a medial pivot motion with femoral rollback primarily on the lateral side. The motion path more closely followed that of the normal intact knee. We concluded that motion guiding features in a total knee replacement could reproduce a normal neutral path that might result in functional improvements for the patient. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 1022–1027, 2009     

Robotic testing of proximal tibio‐fibular joint kinematics for measuring instability following total knee arthroplasty

Pain secondary to instability in total knee arthroplasty (TKA) has been shown to be major cause of early failure. In this study, we focused on the effect of instability in TKA on the proximal tibio‐fibular joint (PTFJ). We used a robotics model to compare the biomechanics of the PTFJ in the native knee, an appropriately balanced TKA, and an unbalanced TKA. The tibia (n = 5) was mounted to a six‐degree‐of‐freedom force/torque sensor and the femur was moved by a robotic manipulator. Motion at the PTFJ was recorded with a high‐resolution digital camera system. After establishing a neutral position, loading conditions were applied at varying flexion angles (0°, 30°, and 60°). These included: internal/external rotation (0 Nm, ±5 Nm), varus/valgus (0 Nm, ±10 Nm), compression (100 N, 700 N), and posterior drawer (0 N, 100 N). With respect to anterior displacement, external rotation had the largest effect (coefficient = 0.650; p < 0.0001). Polyethylene size as well as the interaction between polyethylene size and flexion consistently showed substantial anterior motion. Flexion and mid‐flexion instability in TKA have been difficult to quantify. While tibio‐femoral kinematics is the main aspect of TKA performance, the effects on adjacent tissues should not be overlooked. Our data show that PTFJ kinematics are affected by the balancing of the TKA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:47–52, 2011     

Investigation of in vivo 6DOF total knee arthoplasty kinematics using a dual orthogonal fluoroscopic system.

Fluoroscopic techniques have been recently used to detect in vivo knee joint kinematics. This article presents a technique that uses two fluoroscopes to form a dual orthogonal fluoroscopic system for accurately measuring in vivo 6DOF total knee arthoplasty (TKA) kinematics. The system was rigorously validated and used to investigate in vivo kinematics of 12 patients after cruciate-retaining TKA. In a repeatability study, the pose of two different TKA components was reproduced with standard deviations (SD) of 0.17 mm and 0.57 degrees about all three axes. In an accuracy study, the reproduced component positions were compared to the known component positions. Position and rotation mean errors were all within 0.11 mm and 0.24 degrees, with SD within 0.11 mm and 0.48 degrees, respectively. The results of this study show that the matching process of the imaging system is able to accurately reproduce the spatial positions and orientations of both the femoral and tibial components. For CR TKA patients, a consistent anterior femoral translation was observed with flexion through 45 degrees of flexion, and thereafter, the femur translated posteriorly with further flexion. The medial-lateral translation was measured to be less than 2 mm throughout the entire flexion range. Internal tibial rotation steadily increased through maximum flexion by approximately 6 degrees. Varus rotation was also measured with flexion but had a mean magnitude less than 2.0 degrees. In conclusion, the dual orthogonal fluoroscopic system accurately detects TKA kinematics and is applicable towards other joints of the musculoskeletal system, including the wrist, elbow, shoulder, ankle, and spine.     

In Vivo Kinematic Analysis of a High-Flexion, Posterior-Stabilized, Mobile-Bearing Knee Prosthesis in Deep Knee Bending Motion

The objective of this study was to evaluate the kinematics of a high-flexion, posterior-stabilized, mobile-bearing total knee arthroplasty (TKA) in weight-bearing, deep knee bending motion. Thirteen patients implanted with the Legacy Posterior Stabilized Flex (Zimmer, Warsaw, IN) mobile-bearing TKA were examined during a deep knee bending motion using fluoroscopy. Femorotibial motion was determined using a 2-dimensional to 3-dimensional registration technique, which used computer-assisted design models to reproduce the position of metallic implants from single-view fluoroscopic images. The average flexion range of motion between the metallic implants was 116°. The average rotation of the femoral component was 9.3° external rotation. The mean kinematic pathway was early rollback, lateral pivot with external rotation, and bicondylar rollback. We found that the kinematic pattern of the Legacy Posterior Stabilized Flex mobile-bearing TKA was different than normal knee kinematics.     

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

BackgroundWhile posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component.MethodsTibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant.ResultsIn early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar.ConclusionSubjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.     

Kinematic analysis of kneeling in cruciate‐retaining and posterior‐stabilized total knee arthroplasties

Kneeling is an important function of the knee for many activities of daily living. In this study, we evaluated the in vivo kinematics of kneeling after total knee arthroplasty (TKA) using radiographic based image‐matching techniques. Kneeling from 90 to 120° of knee flexion produced a posterior femoral rollback after both cruciate‐retaining and posterior‐stabilized TKA. It could be assumed that the posterior cruciate ligament and the post‐cam mechanism were functioning. The posterior‐stabilized TKA design had contact regions located far posterior on the tibial insert in comparison to the cruciate‐retaining TKA. Specifically, the lateral femoral condyle in posterior‐stabilized TKA translated to the posterior edge of the tibial surface, although there was no finding of subluxation. After posterior‐stabilized TKA, the contact position of the post‐cam translated to the posterior medial corner of the post with external rotation of the femoral component. Because edge loading can induce accelerated polyethylene wear, the configuration of the post‐cam mechanism should be designed to provide a larger contact area when the femoral component rotates. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:435–442, 2008     

Knee kinematics of high-flexion activities of daily living performed by male Muslims in the Middle East

Full flexion is critical for total knee arthroplasty (TKA) patients in the Middle East, where daily activities require a high range of motion in the lower limb. This study aimed to increase understanding of the knee kinematics of normal Muslim subjects during high-flexion activities of daily living, such as kneeling, Muslim prayer, sitting cross-legged, and squatting. The early postoperative kinematics for a select group of Muslim, high-flexion TKA patients are also reported. Mean curves were compared between the normal group and the TKA group. During kneeling, the average maximum flexion was 141.6° for the normal group and 140.2° for the TKA group. The normal group's maximum and minimum knee angles (flexion, abduction, external rotation) were reported and, with the exception of maximum extension, were not significantly different from the TKA group, despite short postoperative times.     

Motion of the femoral condyles in flexion and extension during a continuous lunge

Numerous studies have reported on in‐vivo posterior femoral condyle translations during various activities of the knee. However, no data has been reported on the knee motion during a continuous flexion‐extension cycle. Further, few studies have investigated the gender variations on the knee kinematics. This study quantitatively determined femoral condylar motion of 10 male and 10 female knees during a continuous weightbearing flexion‐extension cycle using two‐dimensional to three‐dimensional fluoroscopic tracking technique. The knees were CT‐scanned to create three‐dimensional models of the tibia and femur. Continuous images of each subject were taken using a single‐fluoroscopic imaging system. The knee kinematics were measured along the motion path using geometric center axis of the femur. The results indicated that statistical differences between the flexion and extension motions were only found in internal‐external tibial rotation and lateral femoral condylar motion at the middle range of flexion angles. At low flexion angles, male knees have greater external tibial rotation and more posteriorly positioned medial femoral condyle than females. The knee did not show a specific pivoting type of rotation with flexion. Axial rotation center varied from lateral to medial compartments of the knee. These data could provide useful information for understanding physiological motion of normal knees. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:591–597, 2015.     

In vivo comparison of knee kinematics for subjects having either a posterior stabilized or cruciate retaining high-flexion total knee arthroplasty

The objective of this study was to determine the in vivo kinematics for subjects having either a fixed posterior stabilized (PS) or cruciate retaining (CR) high-flexion total knee arthroplasty (TKA). Three-dimensional kinematics from full extension to maximum flexion were determined for 30 subjects (15 PS, 15 CR) using fluoroscopy. On average, the PS subjects demonstrated 112 degrees of weight-bearing (WB) flexion, -6.4 mm of posterior femoral rollback, and 2.9 degrees of axial rotation. The CR subjects averaged 117 degrees of WB flexion, -4.9 mm of posterior femoral rollback, and 4.8 degrees of axial rotation. Posterior femoral rollback of the lateral condyle occurred for all PS TKAs and in 93% of the CR TKAs. Only 2 subjects in each group experienced greater than 1.0 mm of condylar lift-off. Subjects in both TKA groups demonstrated excellent WB ranges of motion and kinematic patterns similar to the normal knee, but less in magnitude.     

In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy

Background

The bicruciate stabilized (BCS) total knee arthroplasty (TKA) features asymmetrical bearing geometry and dual substitution for the anterior cruciate ligament and posterior cruciate ligament (PCL). Previous TKA designs have not fully replicated normal knee motion, and they are characterized by lower magnitudes of overall rollback and axial rotation than the normal knee.

In Vivo Kinematic Comparison Between Mobile-Bearing and Fixed-Bearing Total Knee Arthroplasty During Step-Up Activity

Mobile-bearing total knee arthroplasty (TKA) expects high conformity and low contact stress. It is designed to correct the rotational mismatch between femoral and tibial components. We examined the difference in weight-bearing knee kinematics in patients with mobile-bearing and fixed-bearing TKA performing step-up activities. We randomly assigned 40 knees (37 patients) to mobile-bearing TKA (n = 20) or fixed-bearing TKA (n = 20). Using fluoroscopic imaging we evaluated knee kinematics during step-up activity one year after surgery. The total extent of rotation was not different for the two TKAs. Due to the axial rotation of the polyethylene insert, patients with mobile-bearing TKA had a wider range of absolute axial rotation. The position of the medial and the lateral condyles was significantly more posterior in the fixed-bearing TKA. There were only minor kinematic differences between the two TKAs. The polyethylene insert in the mobile-bearing TKA moved as designed especially with respect to the self-alignment feature.     

In Vivo Movement of Femoral Flexion Axis of a Single-Radius Total Knee Arthroplasty

The objective of this study was to investigate in vivo femoro-tibial motion using the movement of femoral flexion axis of a single-radius TKA. We examined 20 clinically successful knees with a single-radius posterior stabilized TKA to evaluate the kinematics of deep knee flexion using 2–3-dimensional registration techniques. The mean knee flexion range of motion was 117.8°. The mean rotation of the femoral component was 7.6° external rotation. The mean knee flexion angle at initial post-cam engagement was 55.2°. No paradoxical movement of femoral component was shown until 70° flexion, afterward the femoral component rolled back with flexion. The data showed that the design of this prosthesis might contribute to reduce the paradoxical anterior femoral movement and provide stability in mid-flexion ranges.     

Distal femoral cut perpendicular to the mechanical axis may induce varus instability in flexion in medial osteoarthritic knees with varus deformity in total knee arthroplasty: a pitfall of the navigation system

Two factors that influence the external rotation angle of the femoral rotational axis in total knee arthroplasty (TKA) were assessed in 40 medial osteoarthritic knees with varus deformity. First, the anatomic configuration of the femur was assessed using standardized radiographs of the patients lower extremities before TKA. Second, the degree of medial soft tissue release was assessed during TKA. The radiographs showed that the characteristics of the femur were lateral bowing of the shaft and external rotation of the condyle in the coronal plane. Therefore, when the distal femur is cut perpendicular to the mechanical axis, the cut surface may be in too much of a valgus position. Furthermore, some degree of medial soft tissue release was necessary in all knees. Medial soft tissue release rotates the femur externally in extension in the coronal plane, and it rotates the femur externally around the femoral axis in flexion relative to the tibia. A distal femoral cut in too much of a valgus position and medial soft tissue release induces varus instability in flexion in knees with lateral bowing of the femoral shaft. Anatomic variation such as femoral bowing should be considered when a navigation system is used for TKA because the navigation system shows only the mechanical axis.     

In vivo kinematic analysis of a high-flexion posterior stabilized fixed-bearing knee prosthesis in deep knee-bending motion

The objective of this study was to evaluate in vivo kinematics of a high-flexion, posterior-stabilized fixed-bearing, total knee arthroplasty in weight-bearing deep knee-bending motion. A total of 20 knees implanted with the Scorpio Non-Restrictive Geometry knee system in 17 patients were assessed in this study. The Scorpio Non-Restrictive Geometry is a recent implant design with modifications made to accommodate a higher flexion range of motion and greater axial rotation, particularly during more functionally demanding activities. Patients were examined during a deep knee-bending motion using fluoroscopy, and femorotibial motion was determined using a 2-dimensional to 3-dimensional registration technique. The average flexion angle was 126.5° (110°-149°). The femoral component demonstrated a mean of 13.5° (5.2°-21°) external rotation. The external rotation increased up to maximum flexion. The pivot pattern was a medial pivot pattern similar to that reported in normal knee kinematics.     

Effect of component mal‐rotation on knee loading in total knee arthroplasty using multi‐body dynamics modeling under a simulated walking gait

Mal‐rotation of the components in total knee arthorplasty (TKA) is a major cause of postoperative complications, with an increased propensity for implant loosening or wear leading to revision. A musculoskeletal multi‐body dynamics model was used to perform a parametric study of the effects of the rotational mal‐alignments in TKA on the knee loading under a simulated walking gait. The knee contact forces were found to be more sensitive to variations in the varus–valgus rotation of both the tibial and the femoral components and the internal–external rotation of the femoral component in TKA. The varus–valgus mal‐rotation of the tibial or femoral component and the internal–external mal‐rotation of the femoral component with a 5° variation were found to affect the peak medial contact force by 17.8–53.1%, the peak lateral contact force by 35.0–88.4% and the peak total contact force by 5.2–18.7%. Our findings support the clinical observations that a greater than 3° internal mal‐rotation of the femoral component may lead to unsatisfactory pain levels and a greater than 3° varus mal‐rotation of the tibial component may lead to medial bone collapse. These findings determined the quantitative effects of the mal‐rotation of the components in TKA on the contact load. The effect of such mal‐rotation of the components of TKA on the kinematics would be further addressed in future studies. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1287–1296, 2015.     

Influence of Component Rotation in Total Knee Arthroplasty on Tibiofemoral Kinematics—A Cadaveric Investigation

Background

Physiological tibiofemoral kinematics have been shown to be important for good knee function after total knee arthroplasty (TKA). The purpose of the present study was to investigate the influence of component rotation on tibiofemoral kinematics during knee flexion. We asked which axial component alignment best reconstructs physiological tibiofemoral kinematics and which combinations should be avoided.