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 in rotationally unconstrained total knee arthroplasty

Total knee replacement designs claim characteristic kinematic performance that is rarely assessed in patients. In the present study, in vivo kinematics of a new prosthesis design was measured during activities of daily living. This design is posterior stabilized for which spine–cam interaction coordinates free axial rotation throughout the flexion–extension arc by means of a single radius of curvature for the femoral condyles in the sagittal and frontal planes. Fifteen knees were implanted with this prosthesis, and 3D video‐fluoroscopic analysis was performed at 6‐month follow‐up for three motor tasks. The average range of flexion was 70.1° (range: 60.1–80.2°) during stair‐climbing, 74.7° (64.6–84.8°) during chair‐rising, and 64.1° (52.9–74.3°) during step‐up. The corresponding average rotation on the tibial base‐plate of the lines between the medial and lateral contact points was 9.4° (4.0–22.4°), 11.4° (4.6–22.7°), and 11.3° (5.1–18.0°), respectively. The pivot point for these lines was found mostly in the central area of the base‐plate. Nearly physiological range of axial rotation can be achieved at the replaced knee during activities of daily living. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29: 1484–1490, 2011     

Intraoperative passive kinematics of osteoarthritic knees before and after total knee arthroplasty.

Total knee arthroplasty is a successful procedure to treat pain and functional disability due to osteoarthritis. However, precisely how a total knee arthroplasty changes the kinematics of an osteoarthritic knee is unknown. We used a surgical navigation system to measure normal passive kinematics from 7 embalmed cadaver lower extremities and in vivo intraoperative passive kinematics on 17 patients undergoing primary total knee arthroplasty to address two questions: How do the kinematics of knees with advanced osteoarthritis differ from normal knees?; and, Does posterior substituting total knee arthroplasty restore kinematics towards normal? Osteoarthritic knees displayed a decreased screw‐home motion and abnormal varus/valgus rotations between 10° and 90° of knee flexion when compared to normal knees. The anterior–posterior motion of the femur in osteoarthritic knees was not different than in normal knees. Following total knee arthroplasty, we found abnormal varus/valgus rotations in early flexion, a reduced screw‐home motion when compared to the osteoarthritic knees, and an abnormal anterior translation of the femur during the first 60° of flexion. Posterior substituting total knee arthroplasty does not appear to restore normal passive varus/valgus rotations or the screw motion and introduces an abnormal anterior translation of the femur during intraoperative evaluation. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1607–1614, 2006     

MRI analysis of in vivo meniscal and tibiofemoral kinematics in ACL-deficient and normal knees.

The objectives of this study were to analyze simultaneously meniscal and tibiofemoral kinematics in healthy volunteers and anterior cruciate ligament (ACL)-deficient patients under axial load-bearing conditions using magnetic resonance imaging (MRI). Ten healthy volunteers and eight ACL-deficient patients were examined with a high-field, closed MRI system. For each group, both knees were imaged at full extension and partial flexion ( approximately 45 degrees ) with a 125N compressive load applied to the foot. Anteroposterior and medial/lateral femoral and meniscal translations were analyzed following three-dimensional, landmark-matching registration. Interobserver and intraobserver reproducibilities were less than 0.8 mm for femoral translation for image processing and data analysis. The position of the femur relative to the tibia in the ACL-deficient knee was 2.6 mm posterior to that of the contralateral, normal knee at extension. During flexion from 0 degrees to 45 degrees , the femur in ACL-deficient knees translated 4.3 mm anteriorly, whereas no significant translation occurred in uninjured knees. The contact area centroid on the tibia in ACL-deficient knees at extension was posterior to that of uninjured knees. Consequently, significantly less posterior translation of the contact centroid occurred in the medial tibial condyle in ACL-deficient knees during flexion. Meniscal translation, however, was nearly the same in both groups. Axial load-bearing MRI is a noninvasive and reproducible method for evaluating tibiofemoral and meniscal kinematics. The results demonstrated that ACL deficiency led to significant changes in bone kinematics, but negligible changes in the movement of the menisci. These results help explain the increased risk of meniscal tears and osteoarthritis in chronic ACL deficient knees.     

Preclinical Evaluation Method for Total Knees Designed to Restore Normal Knee Mechanics

The objective was to develop a simple, rapid, and low-cost method for evaluating proposed new total knee arthroplasty (TKA) models and then to evaluate 3 different TKA models with different kinematic characteristics. A “desktop” knee testing rig was used to apply forces and moments over a full flexion range, representing a spectrum of positions and activities; and the positions of the femur on the tibia were measured. The average neutral path of motion (for compressive force only) and the laxities about the neutral path (for superimposed shear and torque) were determined from 8 knee specimens to be used as a benchmark for the TKA evaluations. A typical posterior-stabilized TKA did not display the normal external femoral rotation with flexion and also showed abnormal anterior sliding on the medial side. A medial-pivot type of guided-motion design showed medial stability comparable to anatomical but still did not produce external femoral rotation and posterior lateral displacement with flexion. The addition of a central cam-post produced the rotation and displacement but only after 75° of flexion. It was concluded that the test method satisfied the objective and could be used as a design tool for evaluating new and existing designs, as well as for formulating a TKA with anatomical characteristics.     

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     

Analysis of weight-bearing kinematics of posterior-stabilized total knee arthroplasty with novel helical post-cam design

We developed a new posterior-stabilized total knee arthroplasty (TKA) with a unique post-cam design that induces and accommodates internal tibial rotation with deep knee flexion. To validate the design concept of this system, we conducted an image analysis study employing a computer-aided diagnosis system for 24 TKA-implanted knees. In the analysis, the tibiofemoral relationship in the following 3 postures was evaluated: standing at extension, forward lunge, and kneeling with maximum knee flexion. The results of the image analysis showed achievement of consistent internal rotation of the tibia in deep flexion with a broad contact area at the post-cam interface as intended by the original design concept of this TKA system.     

The kinematics and stability of single‐radius versus multi‐radius femoral components related to Mid‐range instability after TKA

There continues to be some dissatisfaction with the function of total knee arthroplasties (TKA). “Mid‐range instability” has been linked to multi‐radius femoral components allowing transient ligament slackness and instability during knee flexion. Single‐radius designs have been introduced to avoid this. We compared the kinematics and stability of eight natural knees versus multi‐radius and single‐radius TKAs in vitro. The loading conditions imposed across the range of active knee extension were anterior–posterior drawer forces, internal–external rotation torques, and varus–valgus moments. Significant differences were not found between the biomechanical behavior of the two TKAs. Both were significantly different from the natural knee in allowing greater anterior drawer laxity near extension, probably caused by excision of the anterior cruciate ligament, but no difference occurred beyond 30° flexion. No differences were found for any of the other degrees‐of‐freedom of movement. A geometric analysis suggested that the multi‐radius design may tense the MCL more than the single‐radius in mid‐flexion, contrary to expectation. These kinematic and stability tests did not find mid‐range instability of the knees, and so they could not demonstrate enhanced mid‐range stability of the single‐radius TKA over the older multi‐radius implant. This suggests that mid‐range instability may relate to unrecognized ligament laxity during surgery, rather than being inherent to a specific feature of implant design. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:53–58, 2012     

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.     

Gender differences in trochlear groove orientation and rotational kinematics of human knees

Knowledge of the morphology and kinematics of the male and female knees is important for understanding gender‐related dimorphism in knee pathology and improvement of related surgical treatments. Twelve male and 12 female subjects with healthy knees were recruited, and each subject performed a single leg lunge while images of the knee were recorded by two fluoroscopes. Tibiofemoral joint motion was then reproduced using bony models matched to the fluoroscopic images. Femoral trochlear groove orientation was also measured in each knee. While many of the measured parameters were found to be similar between the genders, a few interesting differences were also noted. Females showed greater external tibial rotation at 0° flexion (?5.4° vs. ?1.3 °, p = 0.03), smaller internal rotation at 30° flexion (1.7° vs. 6.4°, p = 0.04) and greater range of tibial rotation (18.2° vs. 12.4°, p = 0.01) compared to males. Female knees also had a more medially oriented proximal trochlear groove (10.0° vs. 4.5°, p = 0.04). These gender differences in rotational kinematics and trochlear groove orientation may warrant further studies to determine implications for surgical treatments such as total knee arthroplasty, and gender‐related dimorphism in certain knee injuries and pathologies, like anterior cruciate ligament injury and patellofemoral problems. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 871–878, 2009     

Total knee arthroplasty in patients with stiff knees

The purpose of this study was to evaluate the clinical outcome of total knee arthroplasty and analyze the prognostic factors in patients with stiff knees. Thirty-two patients (39 knees) with severe knee arthritis and an arc of motion of 50° or less were treated by total knee arthroplasty. The mean follow-up period was 58 months (range, 24-123 months). The mean arc of motion improved from 35° before the operation to 94° at the time of the latest follow-up (P<.05). Improvement in knee motion after postoperative 3 months was insignificant. The most important factor related to the final arc of knee motion was preoperative arc of knee motion. The V-Y quadricepsplasty was associated with an inferior clinical outcome. Total knee arthroplasty in patients with stiff knees has substantially improved in the clinical outcome and the arc of motion.     

In‐vivo patellar tendon kinematics during weight‐bearing deep knee flexion

This study quantified in‐vivo 3D patellar tendon kinematics during weight‐bearing deep knee bend beyond 150°. Each knee was MRI scanned to create 3D bony models of the patella, tibia, femur, and the attachment sites of the patellar tendon on the distal patella and the tibial tubercle. Each attachment site was divided into lateral, central, and medial thirds. The subjects were then imaged using a dual fluoroscopic image system while performing a deep knee bend. The knee positions were determined using the bony models and the fluoroscopic images. The patellar tendon kinematics was analyzed using the relative positions of its patellar and tibial attachment sites. The relative elongations of all three portions of the patellar tendon increased similarly up to 60°. Beyond 60°, the relative elongation of the medial portion of the patellar tendon decreased as the knee flexed from 60° to 150° while those of the lateral and central portions showed continuous increases from 120° to 150°. At 150°, the relative elongation of the medial portion was significantly lower than that of the central portion. In four of seven knees, the patellar tendon impinged on the tibial bony surface at 120° and 150° of knee flexion. These data may provide useful insight into the intrinsic patellar tendon biomechanics during a weight‐bearing deep knee bend and could provide biomechanical guidelines for future development of total knee arthroplasties that are intended to restore normal knee function. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1596–1603, 2012     

Influence of Total Knee Arthroplasty on Patellar Kinematics and Patellofemoral Pressure

Background

Patellofemoral complications are one of the main problems after total knee arthroplasty (TKA). The design of the TKA component may affect the patellar biomechanics, which may be associated with this postoperative complication. The purpose of this study was to assess the influence of TKA and prosthesis designs on the patellar kinematics and patellofemoral pressure.

Variations in medial‐lateral hamstring force and force ratio influence tibiofemoral kinematics

A change in hamstring strength and activation is typically seen after injuries or invasive surgeries such as anterior cruciate reconstruction or total knee replacement. While many studies have investigated the influence of isometric increases in hamstring load on knee joint kinematics, few have quantified the change in kinematics due to a variation in medial to lateral hamstring force ratio. This study examined the changes in knee joint kinematics on eight cadaveric knees during an open‐chain deep knee bend for six different loading configurations: five loaded hamstring configurations that varied the ratio of a total load of 175 N between the semimembranosus and biceps femoris and one with no loads on the hamstring. The anterior–posterior translation of the medial and lateral femoral condyles’ lowest points along proximal‐distal axis of the tibia, the axial rotation of the tibia, and the quadriceps load were measured at each flexion angle. Unloading the hamstring shifted the medial and lateral lowest points posteriorly and increased tibial internal rotation. The influence of unloading hamstrings on quadriceps load was small in early flexion and increased with knee flexion. The loading configuration with the highest lateral hamstrings force resulted in the most posterior translation of the medial lowest point, most anterior translation of the lateral lowest point, and the highest tibial external rotation of the five loading configurations. As the medial hamstring force ratio increased, the medial lowest point shifted anteriorly, the lateral lowest point shifted posteriorly, and the tibia rotated more internally. The results of this study, demonstrate that variation in medial‐lateral hamstrings force and force ratio influence tibiofemoral transverse kinematics and quadriceps loads required to extend the knee. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1707–1715, 2016.     

Shape is only a weak predictor of deep knee flexion kinematics in healthy and osteoarthritic knees

Tibiofemoral shape influences knee kinematics but little is known about the effect of shape on deep knee flexion kinematics. The aim of this study was to examine the association between tibiofemoral joint shape and kinematics during deep kneeling in patients with and without osteoarthritis (OA). Sixty-one healthy participants and 58 patients with end-stage knee OA received a computed tomography (CT) of their knee. Participants completed full flexion kneeling while being imaged using single-plane fluoroscopy. Six-degree-of-freedom kinematics were measured by registering a three-dimensional (3D)-static CT onto 2D-dynamic fluoroscopic images. Statistical shape modeling and bivariate functional principal component analysis (bfPCA) were used to describe variability in knee shape and kinematics, respectively. Random-forest-regression models were created to test the ability of shape to predict kinematics controlling for body mass index, sex, and group. The first seven modes of the shape model up to three modes of the bfPCAs captured more than 90% of the variation. The ability of the random forest models to predict kinematics from shape was low, with no more than 50% of the variation being explained in any model. Furthermore, prediction errors were high, ranging between 24.2% and 29.4% of the data. Variations in the bony morphology of the tibiofemoral joint were weakly associated with the kinematics of deep knee flexion. The models only explained a small amount of variation in the data with high error rates indicating that additional predictors need to be identified. These results contribute to the clinical understanding of knee kinematics and potentially the expectations placed on high-flexion total knee replacement design.     

The effect of an augmentation patella prosthesis versus patelloplasty on revision patellar kinematics and quadriceps tendon force: an ex vivo study

The purpose of this study was to assess the effect of 2 revision reconstructive interventions on patellofemoral joint mechanics in comparison to control. We flexed 8 cadaver knee specimens from 0 degrees to 60 degrees of flexion in a test rig designed to simulate weight-bearing flexion and extension (Oxford rig). Quadriceps tendon extensor force and patellar kinematics were recorded for control total knee arthroplasty (TKA) (normal primary TKA with patella resurfaced) and then for each of the 2 revision patellar interventions (after patelloplasty of typical revision knee patellar bone defect to leave a simple bony shell, and after TKA with augmentation patella resurfacing). Our results demonstrate that patellar kinematics and quadriceps extensor force are optimized when the patella is reconstructed to normal anteroposterior thickness.     

Analysis of the kinematics of total knee prostheses with a medial pivot design

Analysis of the kinematics of the FINE Total Knee System (Nakashima Medical, Okayama, Japan) revealed that the medial condyle is fixed and the lateral condyle shows lateral posterior movement and tibial internal rotation. Analysis of the kinematics of the ADVANCE Total Knee System (Wright Medical Technology, Arlington, Tenn) revealed that the medial condyle is fixed and the lateral condyle shows anterior movement in the early stage, changing thereafter to posterior movement. With regard to rotation, initial external rotation subsequently changes to internal rotation. Analysis of the kinematics of the ADVANTIM Total Knee System (Wright Medical Technology) revealed that the bicondyle shows posterior movement, subsequently changing to anterior and posterior movements. Thus, unlike the FINE or ADVANCE Total Knee Systems, the ADVANTIM Total Knee System shows internal rotation.     

In Vivo Knee Kinematics in Patients With Bilateral Total Knee Arthroplasty of 2 Designs

Many younger and highly active patients desire to achieve high flexion after total knee arthroplasty. This study's purpose was to determine if a contemporary total knee arthroplasty design improved functional knee flexion compared with a traditional total knee arthroplasty in patients living a Western lifestyle. Ten patients with bilateral total knee arthroplasty of 2 types were studied during weight-bearing lunge, kneeling, and stair activities using fluoroscopic imaging. There were no differences in maximum knee flexion during lunging or kneeling. Statistically significant differences in tibial rotation and condylar translation were observed during the 3 activities. Although several joint kinematic differences were observed, no important functional differences were observed in clinically excellent, high performing subjects with bilateral total knee arthroplasty of 2 types.     

Total knee arthroplasty in valgus knees using minimally invasive medial-subvastus approach

Background:

An ideal approach for valgus knees must provide adequate exposure with minimal complications due to approach per se. Median parapatellar approach is most commonly used approach in TKA including valgus knees. A medial subvastus approach is seldom used for valgus knees and has definite advantages of maintaining extensor mechanism integrity and minimal effect on patellar tracking. The present study was conducted to evaluate outcomes of total knee arthroplasty (TKA) and efficacy of subvastus approach in valgus knees in terms of early functional recovery, limb alignment and complications.

Materials and Methods:

We retrospectively reviewed 112 knees with valgus deformity between January 2006 and December 2011. All patients were assessed postoperatively for pain using Visual Analog Scale (VAS) and quadriceps recovery in form of time to active straight leg raising (SLR) and staircase competency and clinical outcomes using American Knee Society (AKS) score and radiographic evaluation with average followup of 40 months (range 24–84 months).

Results:

The mean VAS on postoperative day (POD) 1 and POD2 at rest was 2.73 and 2.39, respectively and after mobilization was 3.28 and 3.08, respectively (P < 0.001). The quadriceps recovery was very early and 92 (86.7%) patients were able to do active SLR by POD1 with mean time of 21.98 h while reciprocal gait and staircase competency was possible at 43.05 h. The AKS and function score showed significant improvement from preoperative mean score of 39 and 36 to 91 and 79 (P < 0.001), respectively, and the mean range of motion increased from 102° preoperatively to 119° at recent followup (P < 0.001). The mean tibiofemoral valgus was corrected from preoperative 16° (range 10°–35°) to 5° (range 3°–9°) valgus (P < 0.001).

Conclusions:

Mini-subvastus quadriceps approach provides adequate exposure and excellent early recovery for TKA in valgus knees, without increase in incidence of complications.     

Oxford medial unicompartmental knees display contact‐loss during step‐cycle motion and bicycle motion: A dynamic radiostereometric study

The Oxford medial unicompartmental knee is designed fully congruent, with the purpose of maintaining a large contact‐area throughout motion and minimize wear. No other study has investigated this design feature in‐vivo. We aimed to evaluate if contact‐loss was introduced between the articulating surfaces of the Oxford medial unicompartmental knee during bicycle‐ and step‐cycle motion, and whether this correlated with essential implant parameters, such as polyethylene (PE) wear, knee‐loadings, and clinical outcome. To study contact‐loss, 15 patients (12 males, mean age 69 years) with an Oxford medial unicompartmental knee (7 cemented, mean follow‐up 4.4 years) were examined with use of dynamic radiostereometry (RSA) (10 frames/s). PE wear was measured from static RSA and clinical outcome was evaluated with American Knee Society Score (AKSS) and Oxford Knee Score (OKS). Data on knee‐loadings were acquired from the literature. Contact‐loss was deteced in all patients during both exercises, and the trend of contact‐loss correlated with the knee‐loadings. Median contact‐loss was 0.8 mm (95%PI: 0.3; 1.5) for bicycle motion and 0.3 mm (95%PI: 0.24; 0.35) for step‐cycle motion, and did not correlate with the PE wear rate of mean 0.06 mm/year. Possible in‐congruency was seen in three patients. Clinical outcome scores correlated with contact‐loss during step‐cycle motion. In conclusion, contact‐loss was seen in all patients indicating a clinical tolerance during load. Contact‐loss followed the knee‐loadings, which could explain why no correlation was seen with PE wear, as an increase in load was acommadated by an increase in contact‐area (contact‐loss reduction). The size of contact‐loss may reflect clinical outcome. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:357–364, 2018.