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ABSTRACT Soft-tissue impingement with dual mobility liners can cause anterior hip pain and intra-prosthetic dislocation. The hypothesis of this study was that reducing liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and hip joint stability. The interaction of conventional and contoured liners with anterior soft tissues was evaluated in cadaver specimens via visual observation and fluoroscopic imaging. Resistance to inner-head pull-out was evaluated via finite element analyses, and hip joint stability was evaluated by rigid-body mechanics simulation of dislocation in two modes (A, B). Cadaveric experiments showed that distal portion of conventional liners impinge on anterior hip capsule and cause iliopsoas tenting at low flexion angles (≤30°). During hip extension, the rotation imparted to the liner from posterior engagement with femoral neck was impeded by anterior soft-tissue impingement. The iliopsoas tenting was significantly reduced with contoured liners ( p ≤ 0.04). Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901 N vs. 909 N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Thus, soft-tissue impingement with conventional dual mobility liners may be mitigated by reducing liner profile below the equator, without affecting mechanical performance. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:889-897, 2016. [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]

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]

Aseptic loosening of total joint replacements is believed to be initiated by a macrophage response to prosthetic wear debris. To better characterize the early response to clinically relevant wear debris, we challenged primary human macrophages from four donors with ultra high molecular weight polyethylene (UHMWPE), TiAlV, CoCr, and alumina particles. After a 24‐h culture, protein arrays were used to quantify the secretion of 30 different cytokines and chemokines. Macrophages secreted detectable levels of nine mediators in culture: Interleukin‐1α (IL‐1α), tumor necrosis factor‐α (TNF‐α), IL‐1β, MCP‐1, IL‐8, IL‐6, GM‐CSF, IL‐10, and IL‐12p40. TiAlV particles were the most stimulatory, causing 5‐ to 900‐fold higher cytokine expression compared with nonstimulated cells and uniquely eliciting high levels of IL‐1α, IL‐6, IL‐10, and GM‐CSF. CoCr and alumina were mildly stimulatory and typically elicited two‐ to fivefold greater levels than nonstimulated cells. Surprisingly, UHMWPE did not elicit a significant increase in cytokine release. Our data suggests that IL‐1α, TNF‐α, IL‐1β, and MCP‐1 are the primary initiators of osteolysis and implicates metallic debris as an important trigger for their release. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008 [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]

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]