The aim of the study was to evaluate changes in plantar pressure distribution in feet affected by hallux valgus compared with their contralateral non-affected feet and with the feet of healthy control subjects. Thirty-six patients with unilateral hallux valgus who were indicated for surgery and 30 healthy subjects were assessed on a pedobarographic instrumented treadmill for step length and width, mean stance phase, and plantar foot pressure distribution. Plantar pressure distribution was divided into eight regions. Significantly higher plantar pressures were observed in hallux valgus feet under the second and third metatarsal heads (p = .033) and the fourth and fifth toes (p < .001) than in the healthy control feet. Although decreased pressures were measured under the hallux in affected feet (197 [82–467] kPa) in contrast to the contralateral side (221 [89–514] kPa), this difference failed to reach statistical significance (p = .055). The gait parameters step width, step length, and single-limb support did not show any differences between hallux valgus and control feet. Although the literature on changes in plantar pressures in hallux valgus remains divided, our findings on transferring load from the painful medial to the central and lateral forefoot region are consistent with the development of transfer metatarsalgia in patients with hallux valgus.

Considering the discrepant results of the recent biomechanical studies, the purpose of this study was to simulate dynamic muscle-loaded knee flexion with a large number of specimens and to analyse the influence of total knee arthroplasty (TKA) without and with patellar resurfacing on the patellofemoral pressure distribution.

BACKGROUND:Posterior cruciate ligament (PCL) retaining (CR) and -sacrificing (PS) total knee arthroplasties (TKA) are widely-used to treat osteoarthritis of the knee joint. The PS design substitutes the function of the PCL with a cam-spine mechanism which may produce adverse changes to joint kinematics and kinetics.METHODS:CR- and PS-TKA were performed on 11 human knee specimens. Joint kinematics were measured with a dynamic knee simulator and motion tracking equipment. In-situ loads of the PCL and cam-spine were measured with a robotic force sensor system. Partial weight bearing flexions were simulated and external forces were applied.RESULTS:The PS-TKA rotated significantly less throughout the whole flexion range compared to the CR-TKA. Femoral roll back was greater in the PS-TKA; however, this was not correlated with lower quadriceps forces. Application of external loads produced significantly different in-situ force profiles between the TKA systems.CONCLUSIONS:Our data demonstrate that the PS-design significantly alters kinematics of the knee joint. Our data also suggest the cam-spine mechanism may have little influence on high flexion kinematics (such as femoral rollback) with most of the load burden shared by supporting implant and soft-tissue structures.

Several quantitative methods for the in vitro characterization of cartilage quality are available. However, only a few of these methods allow surgical cartilage manipulations and the subsequent analysis of the friction properties of complete joints. This study introduces an alternative approach to the characterization of the friction properties of entire joint surfaces using the dissipated energy during motion of the joint surfaces.Seven sheep wrist joints obtained post mortem were proximally and distally fixed to a material testing machine. With the exception of the carpometacarpal articulation surface, all joint articulations were fixed with 'Kirschner' wires. Three cartilage defects were simulated with a surgically introduced groove (16 mm(2), 32 mm(2), 300 mm(2)) and compared to intact cartilage without an artificial defect. The mean dissipated energy per cycle was calculated from the hysteresis curve during ten torsional motion cycles (+/- 10 degrees) under constant axial preload (100-900 N).A significant increase in dissipated energy was observed with increasing cartilage defect size and axial load (p<0.001). At lower load levels, the intact and 16 mm(2) defect showed a similar dissipated energy (p>0.073), while all other defect conditions were significantly different (p=0.015). All defect sizes were significantly different (p=0.049) at 900 N axial load.We conclude that the method introduced here could be an alternative for the study of cartilage damage, and further applications based on the principles of this method could be developed for the evaluation of different cartilage treatments. (C) 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

BACKGROUND: Osteoarthritis will change the frictional factor and performance of synovial joints. There is no perfect system to objectively measure and evaluate the fractional properties of synovial joints. OBJECTIVE: To observe the changes of fractional properties of synovial joints under different pressure conditions with biomechanical measurement system. METHODS: A sheep’s wrist joint was fixed in the biomechanical measurement system to measure the friction properties. Each sample was tested in four different axial loading conditions: 100 N, 200 N, 400 N and 800 N axial forces that vertical to the joint articular surface, in order to measure the torque and the coefficient by whirligig the joint for 5°. After measurement, 16 mm 2 cartilage defects were made in each specimen. Then the torque and the coefficient were measured under 100 N, 200 N, 400 N and 800 N axial forces. RESULTS AND CONCLUSION: The torque of sheep wrist joint was 0.021 7, 0.031 7, 0.063 0 and 0.145 0 N·m respectively, and the coefficient of fraction was 0.006 7, 0.007 3, 0.012 0 and 0.014 5 μ when it was loaded by four different axial forces without cartilage defect. The torque of sheep wrist joint was 0.027 0, 0.041 7, 0.080 6 and 0.172 4 N·m respectively, and the coefficient of fraction was 0.008 6, 0.009 7, 0.013 7 and 0.016 4 μ when it was loaded by four different axial forces with cartilage defect. The torque and the coefficient of fraction were gradually increased with the increasing of loading forces (P < 0.05), and the articular cartilage defects may lead to the increasing of joint torque and the coefficient of fraction (P < 0.05). The joint torque was positively correlated with coefficient of fraction.

The editor regrets that this paper was published erroneously as a case report.It is in fact an original article. The editor regrets that this paper was published erroneously as a case report. It is in fact an original article. Translational and rotational knee joint stability in anterior and posterior cruciate-retaining knee arthroplastyThe KneeVol. 18Issue 6PreviewThis study investigated passive translational and rotational stability properties of the intact knee joint, after bicruciate-retaining bi-compartmental knee arthroplasty (BKA) and after posterior cruciate retaining total knee arthroplasty (TKA). Fourteen human cadaveric knee specimens were used in this study, and a robotic manipulator with six-axis force/torque sensor was used to test the joint laxity in anterior–posterior translation, valgus–varus, and internal–external rotation. The results show the knee joint stability after bicruciate-retaining BKA is similar to that of the native knee. Full-Text PDF

In this study, we checked experimentally whether anterior–posterior accelerations of the head during quiet human stance are usually below or above known thresholds of the otolith sensor. Thereto, we measured head kinematics with high spatial resolution. Furthermore, we used both these experimental data and computer simulations of two double inverted pendulum (DIP) models in order to verify the validity of DIP models in general. The results are clear cut. First, not only are acceleration thresholds regularly exceeded about once a second but also are velocity thresholds exceeded, albeit probably less frequently. Second, COM and head movement predicted by interwoven DIP model dynamics can not reproduce the mean measured amplitudes at once. Thus, neither the formerly promoted single inverted pendulum nor any DIP model can causally explain the dynamics of quiet human stance. Instead, we suggest to factor in at least three mechanical degrees of freedom. Due to a couple of reasons discussed, the triple inverted pendulum (TIP) model seems to be a promising abstraction implying potential to better understand the dynamics of quiet human stance.

Cadaveric in vitro studies are essential to test hypotheses concerning surgical manipulations in the same individual. Robotic technologies as well as different knee-models have been developed to get an in-depth comprehension of knee joint kinematics. The purpose of this study was to compare utilization of these different established principles.Ten human cadaveric knee specimens were used to measure the kinematics during a weight-bearing flexion in a 6-degrees-of-freedom knee simulator. While flexing the knee, joint quadriceps muscle forces were dynamically simulated to reach a vertical ground reaction force of 100N. Fourteen knee specimens were mounted in 6-degrees-of-freedom robotic manipulator with a universal force sensor. The unloaded flexing motion of each specimen was measured by finding positions for each degree of flexion where all forces are minimal (passive path). The kinematic data of the knee-simulator and the robot concerning internal-external rotation, anterior-posterior translation, varus-valgus motion, and medial-lateral translation was examined.For all investigated degrees of freedom the kinematics of the robotic passive path differed from the loaded kinematics in the knee simulator.Simulated bodyweight as well as the examination method used has a substantial influence on joint kinematics during flexion which has to be considered when interpreting biomechanical studies as well as clinical tests.

Background: In patients with anterior knee pain and patellar instability, a specific training of the quadriceps muscle - especially the vastus medialis - is often recommended, although the practicability is discussed controversially and the proof of a measurable clinical effect is difficult. Therefore, this in vitro study investigates the influence of asymmetric muscle loading on the motion of the human patella.Methods: Seven human knee specimens were tested in a specially developed knee simulator. During simulated weight-bearing knee flexion, the kinematics of tibia, femur and patella were measured using an ultrasound motion capture system. The quadriceps forces were controlled to achieve a constant ankle force over the whole flexion range which is assumed to represent almost physiological loading. Three different force distributions of the quadriceps were tested - a central, equally distributed load as well as mainly lateral and medial loads.Results: A significant influence of different quadriceps force distributions was found for patellar tilt around a proximodistal axis (up to 1.7 degrees) and patellar rotation around an anteroposterior axis (up to 3.8) with respect to the femur. Interestingly, the patellar mediolateral shift was influenced only marginally (<1.5 mm).Conclusions: Specific muscle training might help patients with patellofemoral pain and cartilage damage by a slight modification of the kinematics, but we could show that even highly asymmetric quadriceps loads only led to a small alteration of the mediolateral shift in case of a physiologic anatomy of the trochlear groove. (C) 2012 Elsevier B.V. All rights reserved.

Females have a higher risk in terms of anterior cruciate ligament injuries during sports than males. Reasons for this fact may be different anatomy and muscle recruitment patterns leading to less protection for the cruciate- and collateral-ligaments. This in vitro study aims to evaluate gender differences in knee joint kinematics and muscle force during weight-bearing knee flexions.

Purpose The purpose of this in vitro study was to investigate the influence of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral pressure. Methods A dynamic muscle-loaded knee squat was simulated on eight knee specimens with an upright knee simulator while measuring tibiofemoral joint kinematics and patellofemoral pressure distribution. The quadriceps muscle was attached to three actuators simulating the three main extensor muscles, and five different quadriceps loading patterns were tested. Results Tibial axial and varus-valgus-rotation are affected most while changing quadriceps loading patterns from lateral to medial. Higher internal tibial rotation is associated with higher medial muscle load compared to the symmetrical loading condition. Contact force, contact area and maximum peak pressure rise with increasing flexion angles. Accentuating the vastus lateralis muscle induces a significant reduction in patellofemoral contact force and a 30% diminished contact area at 90° of flexion. Conclusion Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.

Background and Purpose: The gold standard for management of adult ureteropelvic junction obstruction is laparoscopic dismembered pyeloplasty (LPP), described by Anderson-Hynes, with reduced postoperative complications, early patient release, and favorable results. LPP, however, necessitates a high level of surgical expertise, especially with regard to reanastomosis. Knotless self-anchoring barbed sutures have also been introduced into aesthetic surgery and wound closure. We compared a self-retaining suture (SRS) Quill® (Angiotech, Canada) with a standard monofilament suture to further investigate their biomechanical and urodynamic aspects. Materials and Methods: We analyzed breaking strength and stiffness between SRS 4.0, 3.0, and polydioxanone suture (PDS®) 4.0 (Ethicon, Germany) using a biomechanical testing unit. Urodynamic evaluations were performed in the porcine upper urinary tract, closing a longitudinal incision either with SRS 4.0 (without knots) or with PDS 4.0 (five knots each end). Suture line shortening, suture time, tightness, and intrapelvic pressure were measured. Results: SRS 4.0 breaks at a mean of 11.57 N (standard deviation [SD]=1.25, stiffness 172.8 N/mm2, SD=10.84), SRS 3.0 at 16.01 N (1.81), and PDS 4.0 at 18.41 N (0.75, 128.9 N/mm2, 7.45). SRS 4.0 results in a suture line shortening from mean 3.08 to 2.26 mm (-26.6%) while PDS 4.0 shortens from 3.05 to 1.81 mm (-40.7%). The maximum intrapelvic pressure demonstrated no difference, and leakage was seen in 50% of the cases. Suture time was significantly decreased with SRS use (SRS 4.0 277 s and PDS 4.0 364 s). Conclusion: SRS offers immediate tissue adaption with reduced suture line shortening and equal tightness compared with nonbarbed material in vitro. Knotless suturing using SRS is time efficient and appears to be an excellent material for LPP.

Background: The cruciate ligaments are important stabilizers of the knee joint and determine joint kinematics in the natural knee and after cruciate retaining arthroplasty.No in vitro data is available to biomechanically evaluate the ability of the anterior cruciate ligament (ACL) to maintain knee joint kinematics after bicruciate-retaining bi-compartmental knee arthroplasty (BKA). Therefore, the objective of the current study was to investigate the kinematics of the natural knee joint, before and after installing bicruciate-retaining BKA and posterior cruciate retaining total knee arthroplasty. Specifically, we incorporated a dynamic knee simulator to simulate weight-bearing flexions on cadaveric knee specimen before and after surgical manipulations.Methods: In this cadaveric study we investigated rotational and translational tibiofemoral kinematics during simulated weight-bearing flexions of the intact knee, after bi-compartmental knee arthroplasty (BKA+), after resecting the ACL in BKA (BKA-), and after posterior cruciate retaining total knee arthroplasty (TKA).Results: Rotation of BKA+ is closest to the intact knee joint, whereas TKA shows significant differences from 30 to 90 degree of flexion. Within the tested flexion range (15 to 90 degree of flexion), there was no significant difference in the anterior-posterior translation among intact, BKA+, and TKA knees. Resecting the ACL in BKA leads to a significant anterior tibial translation.Conclusions: BKA with intact cruciate ligaments resembles rotation and translation of the natural knee during a simulated weight-bearing flexion. It is a suitable treatment option for medial and patellofemoral osteoarthritis with advantages in rotational characteristics compared to TKA.

Background: Reconstruction of the anterior cruciate ligament is a standard surgical procedure in sports traumatology. The widespread replacement method using hamstring tendons has an important shortcoming namely delayed or missing bony healing in contrast to patellar tendon grafts where implant-free fixation is established by using the adjacent bone blocks. The purpose of this study was to describe a new implant-free surgical procedure using hamstring tendon grafts and to analyse the influence on tibiofemoral kinematics in vitro.Methods: Nine human knee specimens with arthroscopically transected anterior cruciate ligaments were mounted on a dynamic knee simulator and weight-bearing muscle-loaded knee flexions were simulated while a robotic universal force sensor system was used to provide external tibial loads. Three different loading conditions were simulated including partial body weight only, an additional 50 N anterior tibial force or an additional Five Nm of internal rotational torque. After reconstruction of the anterior cruciate ligament using a tibial bone block hybrid technique these three trials were repeated. The kinematics was measured with an ultrasonic measuring system and different loading and ligament conditions were examined. Graft tunnel placement was verified by computed tomography.Findings: Our fixation method achieved stability to anterior tibial drawer force whereas internal tibial rotation did not change before and after the reconstruction. Computed tomography confirmed anatomical graft and tunnel placement.Interpretation: The presented operative procedure is technically feasible and leads to reproducible results concerning knee joint kinematics and graft placement. (C) 2011 Elsevier Ltd. All rights reserved.

This article describes a new measuring device to investigate balancing strategies of human stance: the totter-slab, i.e., a standing plate suspended with steel cables to hooks on a steel frame. First, we analysed the physical properties of the device by recording free oscillations under different conditions [varying amplitude, mass and centre of mass (COM) height]. This allowed LIS to determine the eigenfrequency (f) over cap and the damping coefficient D<1 Ns/m for each trial. The trials showed that the measured damped eigenfrequency of <(f)over cap>=0.63 Hz is barely dependent on the mass loaded. The ratio D/M approximate to 0.015 l/s is a constant almost independent of the different conditions. Furthermore, we determined the stiffnesses of the Suspending cables and their suspension points to check for potential energy storage capacity of the totter-slab. We found that the totter-slab is a useful, well-defined, reliable and developable measuring device for different non-rigid-ground stance conditions. In a second part of the investigation, we compared the frequency spectra of six subjects balancing on the totter-slab with their spectra while standing quietly on a force plate fixed to the ground. The totter-slab spectra showed two distinct, dominant peak regions at approximately 0.3 and 1.1 Hz. This finding enforces the double inverted pendulum to be an adequate model particularly for balancing on the totter-slab. Compared with the firm ground condition, these two peak regions were more pronounced when balancing on the totter-slab. However, there is a variety of frequencies in the region 0.2 ... 1.5 Hz specific for an individual Subject in both balancing conditions.

Ankle joint affections and injuries are common problems in sports traumatology and in the daily routine of arthroscopic surgeons. However, there is little knowledge regarding intraarticular loads. Pressures on the ankle were determined in a dynamic model on 8 cadaver specimens, applying forces to tendons of the foot over the stance phase under vertical loading. A characteristic course of loading in the tibiotalar joint with a rapid increase upon heel contact was observed. It increased gradually to reach a maximum after 70% of the stance phase, during the push-off phase. The major torque in the ankle joint is located anterolaterally. A dynamic loading curve of the ankle joint can be demonstrated. These observations explain phenomena such as the appearance of osteophytes on the anterior tibia in the case of ankle osteoarthritis and the relatively low incidence of posterior tibial edge fragments in the case of trimalleolar ankle fracture. Furthermore, the medial side of the talus is less loaded compared to the lateral side, which appears relevant to the treatment of osteochondrosis dissecans.

PURPOSE:We investigated knee kinematics during simulated weight-bearing flexion and determined the effect of 3 different parameters of external tibial loading on the kinematics of the anterior cruciate ligament (ACL)-intact and ACL-deficient knee.METHODS:Ten human knee specimens were mounted on a dynamic knee simulator, and weight-bearing muscle-loaded knee flexions were simulated while a robotic/universal force sensor system was used to provide external tibial loads during the motion. Three different loading conditions were simulated: partial body weight only, an additional 50 N of anterior tibial force (ATD), or an additional 5 Nm of internal rotational tibial torque (IRT). After arthroscopic transection of the ACL, these 3 trials were repeated. The kinematics were measured with an ultrasonic measuring system for 3-dimensional motion analysis, and different loading and knee conditions were examined.RESULTS:When the ACL was intact, ATD and IRT barely changed the anterior tibial translation. However, in the absence of the ACL, ATD significantly increased the anterior tibial translation by 5 mm whereas IRT did not. The application of IRT increased the internal tibial rotation of ACL-intact knees, but there was no difference in the internal rotation before and after transection of the ACL. Regardless of ACL status, the difference in the anterior tibial translation and the internal tibial rotation across different external tibial loadings was greater at lower flexion angles and gradually diminished with increasing flexion angles.CONCLUSIONS:We established an experimental protocol, incorporating a dynamic knee simulator and a robotic/universal force sensor system, to successfully measure the kinematics of the knee joint while applying external forces in weight-bearing flexion. Our findings suggest that, in muscle-loaded knee flexion, the ACL provides substantial resistance to externally applied ATD but not to IRT.CLINICAL RELEVANCE:Information from this study allows us to better understand the function of the ACL and, hence, treatment of injuries to this important stabilizing ligament.

OBJECTIVES:To assess changes in balance capacities after a 12-week sensory-motor training program for older adults with osteoarthritis or prosthesis of the hip.BACKGROUND:Sensory-motor training is recommended to help aging adults with osteoarthritis maintain activity, avoid injurious falls, and improve functioning. Up to now, however, there has been no standard training protocol for sensory-motor training.METHODS AND MEASURES:Thirty-five participants in a hip exercise group who had a mean age of 58 years (SD 12) were quasi-randomized into a training group (TG) and a control group (CG) by the month they applied for the Hip School program. The TG performed balance exercises using balance pads and received Hip School training once a week. The CG did not receive any training intervention. Balance was measured by recording center-of-pressure excursion while participants were in 1-legged stance on the oscillatory Posturomed platform. Outcome measures were the total path of center of pressure on the platform during balance recovery and the percentage of failed attempts.RESULTS:The TG had a lower percentage of failed attempts (TG 5%, CG 18%, P = .001) and required fewer balance recovery movements to maintain balance (TG: mean [SD] measurement is 59 [36] mm; CG: 96 [68] mm, P = .036] after completing the 12-week training program. After the training period, participants in the TG compensated better for perturbations in the nondisplaced medial-lateral (ML) direction (pretest [SD] measurement was 48 [18] mm; posttest, 36 [14] mm; P= .001].CONCLUSIONS:Participants could successfully cope with more disturbances and improved their reactions to sudden displacements after training intervention. This exercise setting improves balance abilities and should be included in Hip School programs for patients with osteoarthritis.

The single-inverted pendulum (SIP) model is still the paradigm describing dynamics and control of quiet human stance in the sagittal plane. We used two methods to verify this paradigm. First, in an experimental approach we acquired kinematic data of both legs of ten subjects at high spatial resolution while quietly standing on two force platforms. We calculated all leg joint angles, the belonging joint torques using inverse dynamics and estimates of joint stiffnesses. Some linear correlations and regressions of both local (joint) and global (COM, COP: centre of mass respectively pressure) variables predicted by the SIP model were investigated. All three verification criteria applied to mean values extracted from experimental data revealed that the SIP is not a valid model for quiet human stance. As a second method, we used computer synthesis to demonstrate that a double-inverted pendulum (DIP) model enters a stable attractor when just the "hip" joint torque is regulated, whereas no torque is applied to the "ankle" joint. Here, angle and torque fluctuations are necessary because such a DIP strategy is of inevitable dynamic character. The two predicted eigenfrequencies of this regulated DIP model approximate the upper and lower limits of the main part of measured power spectra of quiet human stance. We suggest this dynamic necessity to be representative of the biological constraints under which a mechanically unstable inverted multi-segment chain must be stabilised.