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Polymer‐based dielectric composites with simultaneously improved dielectric constant and breakdown strength have great potential applications in energy storage. In this paper, polyaniline@BaTiO3 (PANI@BT) nanoparticles with core‐shell structure are first fabricated by in‐situ chemical oxidative polymerization, and deposited on the surface of two‐dimensional nanoplatelets (graphene oxide [GO] and hexagonal boron nitride nanosheets [BNNS]), which are then utilized to prepare poly(vinylidene fluoride) (PVDF)‐based composites. The presence of 2D nanoplatelets is found to significantly ameliorate the dispersion of PANI@BT particles in the PVDF matrix, and thus endowing the resultant PVDF composites with improved comprehensive performance. The dielectric constant of PANI@BT‐GO/PVDF and PANI@BT‐BNNS/PVDF composites with 50 wt% fillers increase to 124.9 and 169.5 at 100 Hz, accompanied with relatively low dielectric loss. When the filler content is 10 wt%, the breakdown strength of PANI@BT‐BNNS/PVDF achieves 133.5 kV/mm, which is 9.7% and 71.8% higher than that of the pristine PVDF and PANI@BT/PVDF composites. Meanwhile, the tensile stress also reaches the highest value of 43.38 MPa. In addition, the PANI@BT‐GO/PVDF and PANI@BT‐BNNS/PVDF composites present higher thermal decomposition temperature in comparison with PANI@BT/PVDF composites. [ABSTRACT FROM AUTHOR]

Obesity increases the risk of knee osteoarthritis (OA). Knee joint contact characteristics have been thought to provide insights into the pathogenesis of knee OA; however, the cartilage contact characteristics in individuals with obesity have not been fully described. We conducted cartilage‐to‐cartilage contact analyses through high‐precision fluoroscopy imaging with subject‐specific magnetic resonance cartilage models. Twenty‐five individuals with obesity were recruited for this study, and previously published data consisted of eight nonobese individuals who were used as the comparator group. In both groups, knees were imaged by a dual fluoroscopic imaging system during treadmill walking, and the tibiofemoral cartilage contact locations were analyzed and described on the tibial plateau in the medial−lateral (ML) and anterior−posterior (AP) directions and on femoral condyle surfaces using contact angles in the sagittal plane and deviation angles in a plane perpendicular to the sagittal plane. On the medial tibial plateau, the ML contact locations in the individuals with obesity were located more medially than in the nonobese group throughout the stance phase. The medial plateau AP contact locations in individuals with obesity showed a different pattern compared with the nonobese group. The ML contact excursions on the medial plateau in the individuals with obesity were larger than in the nonobese group. These findings suggest that obesity affects the contact location mainly in the medial compartment, which explains, in part, the high prevalence of medial knee OA in the obese population. [ABSTRACT FROM AUTHOR]

Objective: To determine the three‐dimensional (3D) changes of the spinal canal length (SCL) after corrective surgeries and their association with the radiographic and clinical outcomes of idiopathic scoliosis patients. The length of the spinal cord has been demonstrated to be strongly correlated with the SCL. Understanding the changes in SCL could help determine the morphologic changes in the spinal cord to prevent spinal cord injury. Methods: Twenty‐seven scoliotic patients' 3D spinal canal were investigated using computed tomography images. The SCL between the upper and lower end vertebrae (U/L‐EV) was measured at five locations. The radiographic parameters of each patient and the patient‐reported outcomes (PROs) scores were also collected. The correlations of the changes of the SCLs with the other factors were analyzed. Results: The SCL between the U/L‐EV changed non‐uniformly at different locations. The post‐operative SCLs were significantly elongated by 7.5 ± 3.5 mm (6.0 ± 2.5%, P <.001) at the concave side and compressed by −2.6 ± 2.6 mm (−1.9 ± 1.9%, P <.001) at the convex side. The elongations of the SCL at the concave and posterior locations were correlated with the radiographic parameters including the pre‐operative main Cobb angles (r =.511, P =.006; r =.613, P =.001) and apical vertebral translation (AVT) (r =.481, P =.011; r =.684, P =.000). No PRO scores were found to correlate with the SCL changes. Conclusion: The corrective surgeries elongated the spinal canal mainly at the concave side and compressed at the convex side. The main thoracic Cobb angle, the changes of AVT, and Cobb angles were moderately associated with the changes of the SCLs, but no PRO score was found to associate with the changes of the SCLs. The data could be instrumental for the improvement of corrective surgeries that are aimed to maximize the correction of scoliosis and minimize the negative effect on the spinal cord to prevent neurological complications. [ABSTRACT FROM AUTHOR]

Using large femoral heads in total hip arthroplasty (THA) has been widely advocated to improve the function and longevity of the components. However, increasing the head size has been shown to accelerate polyethylene liner wear. Few studies have investigated the effect of other important structural parameters (such as polyethylene liner thickness, metal cup size, head‐liner conformity, loading conditions, etc.) on the biomechanical functions of the THAs. In this study, an analytical model was used to evaluate the polyethylene liner wear characteristics of the THAs (defined using a biomechanical wear factor) with various structural parameters of the THAs and loading conditions. For all the THA systems examined in this study, under the same loading conditions, a larger head leads to increasing contact areas, lower contact stresses, and higher biomechanical wear factors. When the head size is fixed, a decrease in the polyethylene liner thickness or a decrease in the head‐liner conformity leads to higher peak contact stresses and smaller contact areas and consequently, lower biomechanical wear factors. This study provides a parametric analysis tool for the optimal design/selection of the THA systems and for prediction of early effects of various structural parameters on the biomechanical function (such as contact stresses) and longevity (such as polyethylene liner wear) of the THA systems. [ABSTRACT FROM AUTHOR]

Bi‐cruciate retaining (BCR) total knee arthroplasty (TKA) design preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. Abnormal knee kinematics and "paradoxical" anterior femoral translation in conventional TKA designs have been suggested as potential causes of patient dissatisfaction. However, there is a paucity of data on the in vivo kinematics and articular contact behavior of BCR‐TKA. This study aimed to investigate in vivo kinematics, articular contact position, and pivot point location of the BCR‐TKA during gait. In vivo kinematics of 30 patients with unilateral BCR‐TKA during treadmill walking was determined using validated dual fluoroscopic imaging tracking technique. The BCR‐TKA exhibited less extension than the normal healthy knee between heel strike and 48% of gait cycle. Although the average external rotation trend observed for BCR TKA was similar to the normal healthy knee, the range of motion was not fully comparable. The lowest point of the medial condyle showed longer anteroposterior translation excursion than the lateral condyle, leading to a lateral‐pivoting pattern in 60% of BCR TKA patients during stance phase. BCR‐TKA demonstrated no statistical significant differences in anterior–posterior translation as well as varus rotation, when compared to normal healthy knees during the stance phase. However, sagittal plane motion and tibiofemoral articular contact characteristics including pivoting patterns were not fully restored in BCR TKA patients during gait, suggesting that BCR TKA does not restore native tibiofemoral articular contact kinematics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1929–1937, 2019 [ABSTRACT FROM AUTHOR]

Anterior and posterior cruciate ligament (ACL and PCL) sacrifice in contemporary total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal knee kinematics. Bi‐cruciate retaining (BCR) TKA design allows retention of both ACL and PCL. However, there is a limited data on the ACL/PCL in‐vivo elongation characteristics of BCR TKA. The study aimed to evaluate and compare the in‐vivo elongation patterns of ACL/PCL between BCR TKA and contralateral non‐implanted knee and to explore potential factors leading to the changed elongation patterns between limbs. ACL/PCL elongations of both knees during sit‐to‐stand were measured in 29 unilateral BCR TKA patients using a validated dual fluoroscopic tracking technique. Joint gap changes of the BCR TKA knees relative to the contralateral knee were quantified. BCR TKA and the contralateral non‐implanted knee exhibited similar ACL elongation at extension and clinical anterior knee laxity. However, BCR TKA showed significantly greater PCL elongation during flexion than the non‐implanted knee. Variation of changed elongation was observed for both ACL and PCL, suggesting a heterogeneous restoration of normal ACL/PCL functions. A significant correlation was found between extension joint gap change and the change of ACL elongation, highlighting the importance of precise joint line restoration and soft tissue balancing during BCR TKA surgery. Our findings suggest that BCR TKA did not fully restore "near‐normal" cruciate ligament elongation patterns and anteroposterior stability. Considerable heterogeneity remains in the retained ligament elongation patterns and warrants further investigations of multifactorial factors to optimize ACL/PCL functions in BCR TKA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3239–3246, 2018. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

ABSTRACT Accurate knowledge of tibiofemoral articular contact kinematics of the knee after total knee arthroplasty (TKA) is important for understanding the intrinsic knee biomechanics and improving the longevity of the components. The objective of this study was to compare the in vivo articular contact kinematics of the knees with end-stage medial osteoarthritis (OA) during a weight-bearing, single leg lunge activity before and after a posterior cruciate retaining TKA (CR-TKA) using a dual fluoroscopic imaging technique. We found that the CR-TKA resulted in more posterior contact positions on the tibial surface and a reduced range of motion in the medial and lateral compartments. The distances between medial and lateral contact locations in the CR-TKA knees were statistically larger than the OA knees. The articular contact centers have shifted from medial side of the tibial plateau pre-operatively to the lateral side after operation. This study indicated that the CR-TKA resulted in significant changes in contact kinematics of the knees in both anteroposterior and mediolateral directions. Further studies are needed to determine the influence of the altered in vivo contact kinematics on the longevity of polyethylene liner and long term clinical outcomes of the TKA. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:???-???, 2015. [ABSTRACT FROM AUTHOR]

We investigated the in vivo cartilage contact biomechanics of the tibiofemoral joint in patients after reconstruction of a ruptured anterior cruciate ligament (ACL). A dual fluoroscopic and MR imaging technique was used to investigate the cartilage contact biomechanics of the tibiofemoral joint during in vivo weight-bearing flexion of the knee in eight patients 6 months following clinically successful reconstruction of an acute isolated ACL rupture. The location of tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation of the ACL-reconstructed knees were compared with those previously measured in intact (contralateral) knees and ACL-deficient knees of the same subjects. Contact biomechanics of the tibiofemoral cartilage after ACL reconstruction were similar to those measured in intact knees. However, at lower flexion, the abnormal posterior and lateral shift of cartilage contact location to smaller regions of thinner tibial cartilage that has been described in ACL-deficient knees persisted in ACL-reconstructed knees, resulting in an increase of the magnitude of cartilage contact deformation at those flexion angles. Reconstruction of the ACL restored some of the in vivo cartilage contact biomechanics of the tibiofemoral joint to normal. Clinically, recovering anterior knee stability might be insufficient to prevent post-operative cartilage degeneration due to lack of restoration of in vivo cartilage contact biomechanics. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1781-1788, 2012 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Knowledge of patellofemoral joint biomechanics is important for understanding sex-related dimorphism in patellofemoral pathologies and advancement of related treatments. We evaluated the hypotheses that sex differences exist in patellar tendon (PT) orientation and patellar tracking during weight-bearing knee flexion and that they relate to differences in tibiofemoral rotation. The PT orientation and patellar tracking were measured in healthy subjects (18 male, 13 female) during weight-bearing knee flexion, using magnetic resonance and dual fluoroscopic imaging. These data were analyzed for sex differences and correlation with previously reported tibiofemoral rotation data. The results indicated a significant effect of sex on PT orientation, particularly at low flexion angles. In females, the PT was oriented more anteriorly in the sagittal plane, more medially in the coronal plane, and showed greater external tilt in the transverse plane of the tibia ( p < 0.05). Significant correlations between tibiofemoral rotation and PT orientation ( p < 0.01) indicated that sex differences in coronal and transverse plane orientation of the PT relate to differences in tibiofemoral rotation. Patellar tracking did not show significant sex differences or correlation to tibiofemoral rotation. Further studies are warranted to determine implications for patellofemoral pathologies and treatments like total knee arthroplasty. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:322-328, 2010 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Quantitative data on in vivo deformation of articular cartilage is important for understanding the articular joint function and the etiology of degenerative joint diseases such as osteoarthritis. This study experimentally determined the in vivo cartilage thickness distribution and articular cartilage contact strain distribution in human ankle joints under full body weight loading conditions using a combined dual fluoroscopic and magnetic resonance imaging technique. The average cartilage thickness with the joint non-weight bearing was found to be 1.43 mm ± 0.15 mm and 1.42 mm ± 0.18 mm in the distal tibial and proximal talar cartilage layers, respectively. During weight bearing on a single leg, the strain distribution data revealed that 42.4% ± 15.7% of the contact area had contact strain higher than 15% in the ankle joint. Peak cartilage contact strain reached 34.5% ± 7.3%. This quantitative data on in vivo human cartilage morphology and deformation demonstrated that the cartilage may undergo large deformations under the loading conditions experienced in human ankle joints during daily activities. The in vivo cartilage contact deformation can be used as displacement boundary conditions in three-dimensional (3D) finite element models of the joint to calculate in vivo 3D articular cartilage contact stress/strain distributions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1081-1089, 2008 [ABSTRACT FROM AUTHOR]

Patellar tracking during in vivo weightbearing knee function is not well understood. This study investigated patellar tracking of eight subjects during a full range of weightbearing flexion using magnetic resonance imaging and dual orthogonal fluoroscopy. The data were reported using a clinical description based on patellar and femoral joint coordinate systems and using patellar indices based on geometrical features of the femur and patella. The mean patellar shift was within 3 mm over the entire range of flexion. The patella tilted laterally from 0° to 75°, and then tilted medially beyond 75° of flexion. The mean tilt was within 6°. Similarly, the mean patellar rotation was small at early flexion, and the mean total excursion of patellar rotation was about 8°. The patellofemoral indices showed that the mean sulcus angle and congruence angle varied within 8° over the entire flexion range. The mean lateral patellar displacement was within 6 mm. A consistent decrease in lateral patellar tilt and an increase in lateral patellofemoral angle were observed with knee flexion. In conclusion, patellar motion is relatively small with respect to the femur during in vivo weightbearing knee flexion. These data may provide baseline knowledge for understanding normal patellar tracking. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1067-1074, 2008 [ABSTRACT FROM AUTHOR]

Anterior polyethylene post failure in posterior stabilizing total knee arthroplasty (TKA) has been reported in recent patient follow-up studies. However, no data have been reported on the biomechanic interaction between the anterior tibial post and femoral component in posterior stabilizing TKA patients under physiological conditions. The objective of this study was to measure the in vivo anterior tibial post contact area at full knee extension using a dual-orthogonal fluoroscopic imaging technique. Eleven osteoarthritic patients were investigated after posterior stabilizing TKA to measure the contact between the femoral component box and anterior aspect of the tibial post. Anterior tibial post contact, ranging between 0.5 and 80.9 mm2, was detected in 63% of the healthy patients (seven out of the eleven patients) at weight-bearing full extension of the knee. The patients with anterior tibial post contact had significantly higher hyperextension angles (−8.4 ± 4.3°) than those without contact (1.4 ± 7.2°). A statistically significant difference was also detected in the femoral component flexion with respect to the femoral shaft between the patients with anterior post contact (2.7 ± 2.7°) and without anterior post contact (−1.3 ± 2.2°). These data indicated that anterior post contact did occur in hyperextension within posterior stabilizing TKA patients. While excessive anterior tibial post contact may cause polyethylene wear and potentially lead to post failure, the tibial post may also act as a substitute for the ACL at low flexion, thus providing stability to the joint after posterior stabilizing TKA. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1447-1453, 2007 [ABSTRACT FROM AUTHOR]

Accurate knowledge of in vivo ankle joint complex (AJC) biomechanics is critical for understanding AJC disease states and for improvement of surgical treatments. This study investigated 6 degrees-of-freedom (DOF) in vivo kinematics of the human AJC using a combined dual-orthogonal fluoroscopic and magnetic resonance imaging (MRI) technique. Five healthy ankles of living subjects were studied during three in vivo activities of the foot, including maximum plantarflexion and dorsiflexion, maximum supination and pronation, and three weight-bearing positions in simulated stance phases of walking. A three-dimensional (3D) computer model of the AJC (including tibia, fibula, talus, and calcaneus) was constructed using 3D MR images of the foot. The in vivo AJC position at each selected position of the foot was captured using two orthogonally positioned fluoroscopes. In vivo AJC motion could then be reproduced by coupling the orthogonal images with the 3D AJC model in a virtual dual-orthogonal fluoroscopic system. From maximum dorsiflexion to plantarflexion, the arc of motion of the talocrural joint (47.5 ± 2.2°) was significantly larger than that of the subtalar joint (3.1 ± 6.8°). Both joints showed similar degrees of internal-external and inversion-eversion rotation. From maximum supination to pronation, all rotations and translations of the subtalar joint were significantly larger than those of the talocrural joint. From heel strike to midstance, the plantarflexion contribution from the talocrural joint (9.1 ± 5.3°) was significantly larger than that of the subtalar joint (−0.9 ± 1.2°). From midstance to toe off, internal rotation and inversion of the subtalar joint (12.3 ± 8.3° and −10.7 ± 3.8°, respectively) were significantly larger than those of the talocrural joint (−1.6 ± 5.9° and −1.7 ± 2.7°). Strong kinematic coupling between the talocrural and subtalar joints was observed during in vivo AJC activities. The contribution of the talocrural joint to active dorsi-plantarflexion was higher than that of the subtalar joint, whereas the contribution of the subtalar joint to active supination-pronation was higher than that of the talocrural joint. In addition, the talocrural joint demonstrated larger motion during the early part of stance phase while the subtalar joint contributes more motion during the later part of stance phase. The results add quantitative data to an in vivo database of normals that can be used in clinical diagnosis, treatment, and evaluation of the AJC after injuries. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

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° 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°, with SD within 0.11 mm and 0.48°, 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° 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°. Varus rotation was also measured with flexion but had a mean magnitude less than 2.0°. 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. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

Unicompartmental knee arthroplasty (UKA) has regained popularity in recent years. However, limited data exist on how UKA affects knee biomechanics. The role of the anterior cruciate ligament (ACL) after fixed bearing UKA remains controversial. In this study, a robotic testing system was used to apply a quadriceps/hamstrings load to cadaveric knee specimens in the intact state, after medial UKA, and after transection of the ACL in UKA. The load was applied to the knee from full extension to 120° of flexion in 30° increments. UKA generally did not affect anterior-posterior (AP) femoral position, but did cause external tibial rotation and variations in varus-valgus rotation compared to the intact knee. ACL transection after UKA shifted the femur posteriorly compared to the intact and UKA knees and increased internal tibial rotation compared to the UKA knee at low flexion. The AP motion of the articular contact position in the implant was increased after ACL transection. These data might help explain the mechanism of tibial component loosening and provide insight into further investigations of polyethylene wear in UKA. Based on the kinematic data, the ACL should be functional to provide patients the greatest opportunity for long-term success after medial UKA. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

Abstract: Despite the numerous long-term success reports of posterior stabilized (PS) total knee arthroplasty (TKA), recent retrieval studies of various PS TKA designs revealed wear and deformation on the anterior side of the tibial post. This study investigated the mechanisms of anterior impingement of the post with the femoral component. Seven cadaveric knees were tested to study kinematics and tibial post biomechanics during simulated heel strike using an in vitro robotic testing system. Intact knee kinematics and in situ anterior cruciate ligament (ACL) forces were determined at hyperextension (0° to −9°) and low flexion angles (0° to 30°) under the applied loads. The same knee was reconstructed using a PS TKA. The kinematics and the tibial post contact forces of the TKA were measured under the same loading condition. The ACL in the intact knee carried load and contributed to knee stability at low flexion angles and hyperextension. After TKA, substantial in situ contact forces (252.4±173N at 9° of hyperextension) occurred in the tibial post, indicating anterior impingement with the femoral component. Consequently, the TKA showed less posterior femoral translation compared to the intact knee after the impingement. At 9° of hyperextension, the medial condyle of the intact knee translated 0.1±1.1mm whereas the medial condyle of the TKA knee translated 5.6±6.9mm anteriorly. The lateral condyle of the intact knee translated 1.5±1.0mm anteriorly whereas the lateral condyle of the TKA knee translated 2.1±5.8mm anteriorly. The data demonstrated that anterior tibial post impingement functions as a substitute for the ACL during hyperextension, contributing to anterior stability. However, anterior post impingement may result in additional polyethylene wear and tibial post failure. Transmitted impingement forces might cause backside wear and component loosening. Understanding the advantages and disadvantages of the tibial post function at low flexion angles may help to further improve component design and surgical techniques and thus enhance knee stability and component longevity after TKA. [Copyright &y& Elsevier]

Abstract: No study has investigated the three-dimensional morphological changes of the anterior cruciate ligament (ACL) during functional activities in vivo. The purpose of this study was to analyze the elongation, rotation (twist), and orientation of the ACL during weight-bearing flexion in five human subjects using dual-orthogonal fluoroscopic images and MR image-based computer models. The ACL consistently decreased in length with flexion. At 90°, the length decreased by 10% compared to its length at full extension. The ACL twisted internally by only 20° at 30° of flexion. The ACL was oriented more vertically (approximately 60°) and slightly laterally (approximately 10°) at low flexion angles. These data on in vivo ligament elongation demonstrate that the ACL plays a more important role in lower flexion angles than at higher flexion angles during weight-bearing flexion. These data also suggest that successful ACL reconstruction should not only restore the ligament’s elongation behavior, but also its rotational and orientation characteristics, so that normal ACL biomechanics are restored. [Copyright &y& Elsevier]

The function of the anterior and posterior cruciate ligaments (ACL and PCL) in the first 120° of flexion has been reported extensively, but little is known of their behavior at higher flexion angles. The aim of this investigation was to study the effects of muscle loads on the in situ forces in both ligaments at high knee flexion (>120°). Eighteen fresh-frozen human knee specimens were tested on a robotic testing system from full extension to 150° of flexion in response to quadriceps (400 N), hamstrings (200 N), and combined quadriceps and hamstrings (400 N/200 N) loads. The in situ forces in the ACL and PCL were measured using the principle of superposition. The force in the ACL peaked at 30° of flexion (71.7 ± 27.9 N in response to the quadriceps load, 52.3 ± 24.4 N in response to the combined muscle load, 32.3 ± 20.9 N in response to the hamstrings load). At 150°, the ACL force was approximately 30 N in response to the quadriceps load and 20 N in response to the combined muscle load and isolated hamstring load. The PCL force peaked at 90° (34.0 ± 15.3 N in response to the quadriceps load, 88.6 ± 23.7 N in response to the combined muscle load, 99.8 ± 24.0 N in response to the hamstrings load) and decreased to around 35 N at 150° in response to each of the loads.These results demonstrate that the ACL and PCL carried significantly less load at high flexion in response to the simulated muscle loads compared to the peak loads they carried in response to the same muscle loads at other flexion angles. The data could provide a reference point for the investigation of non-weight bearing flexion and extension knee exercises in high flexion. Furthermore, these data could be useful in designing total knee implants to achieve high flexion. [Copyright &y& Elsevier]

Restoration of knee function after total knee, meniscus, or cruciate ligament surgery requires an understanding of knee behavior throughout the entire range of knee motion. However, little data are available regarding knee kinematics and kinetics at flexion angles greater than 120° (high flexion). In this study, 13 cadaveric human knee specimens were tested using an in vitro robotic experimental setup. Tibial anteroposterior translation and internal–external rotation were measured along the passive path and under simulated muscle loading from full extension to 150° of flexion. Anterior tibial translation was observed in the unloaded passive path throughout, with a peak of 31.2 ± 13.2 mm at 150°. Internal tibial rotation increased with flexion to 150° on the passive path to a maximum of 11.1 ± 6.7°. The simulated muscle loads affected tibial translation and rotation between full extension and 120° of knee flexion. Interestingly, at high flexion, the application of muscle loads had little effect on tibial translation and rotation when compared to values at 120°. The kinematic behavior of the knee at 150° was markedly different from that measured at other flexion angles. Muscle loads appear to play a minimal role in influencing tibial translation and rotation at maximal flexion. The results imply that the knee is highly constrained at high flexion, which could be due in part to compression of the posterior soft tissues (posterior capsule, menisci, muscle, fat, and skin) between the tibia and the femur. [Copyright &y& Elsevier]

The mechanism of chronic degeneration of the knee after posterior cruciate ligament (PCL) injury is still not clearly understood. While numerous biomechanical studies have been conducted to investigate the function of the PCL with regard to antero-posterior stability of the knee, little has been reported on its effect on the rotational stability of the knee. In this study, eight cadaveric human knee specimens were tested on a robotic testing system from full extension to 120° of flexion with the PCL intact and with the PCL resected. The antero-posterior tibial translation and the internal–external tibial rotation were measured when the knee was subjected to various simulated muscle loads. Under a quadriceps load (400 N) and a combined quadriceps/hamstring load (400/200 N), the tibia moved anteriorly at low flexion angles (below 60°). Resection of the PCL did not significantly alter anterior tibial translation. At high flexion angles (beyond 60°), the tibia moved posteriorly and rotated externally under the muscle loads. PCL deficiency significantly increased the posterior tibial translation and external tibial rotation. The results of this study indicate that PCL deficiency not only changed tibial translation, but also tibial rotation. Therefore, only evaluating the tibial translation in the antero-posterior direction may not completely describe the effect of PCL deficiency on knee joint function. Furthermore, the increased external tibial rotations were further hypothesized to cause elevated patello-femoral joint contact pressures. These data may help explain the biomechanical factors causing long-term degenerative changes of the knee after PCL injury. By fully understanding the etiology of these changes, it may be possible to develop an optimal surgical treatment for PCL injury that is aimed at minimizing the long-term arthritic changes in the knee joint. [Copyright &y& Elsevier]

Objective: To investigate the in vivo cartilage contact biomechanics of the tibiofemoral joint following anterior cruciate ligament (ACL) injury., Methods: Eight patients with an isolated ACL injury in 1 knee, with the contralateral side intact, participated in the study. Both knees were imaged using a specific magnetic resonance sequence to create 3-dimensional models of knee bone and cartilage. Next, each patient performed a lunge motion from 0 degrees to 90 degrees of flexion as images were recorded with a dual fluoroscopic system. The three-dimensional knee models and fluoroscopic images were used to reproduce the in vivo knee position at each flexion angle. With this series of knee models, the location of the tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation were compared between intact and ACL-deficient knees., Results: Rupture of the ACL changed the cartilage contact biomechanics between 0 degrees and 60 degrees of flexion in the medial compartment of the knee. Compared with the contralateral knee, the location of peak cartilage contact deformation on the tibial plateaus was more posterior and lateral, the contact area was smaller, the average cartilage thickness at the tibial cartilage contact area was thinner, and the resultant magnitude of cartilage contact deformation was increased. Similar changes were observed in the lateral compartment, with increased cartilage contact deformation from 0 degrees to 30 degrees of knee flexion in the presence of ACL deficiency., Conclusion: ACL deficiency alters the in vivo cartilage contact biomechanics by shifting the contact location to smaller regions of thinner cartilage and by increasing the magnitude of the cartilage contact deformation.