Biomedical subjects

A Leardini

Publications and source records attributed to A Leardini.

At least 19 recordsLinked to original sources

PubMed2007

Alignments and clinical results in conventional and navigated total knee arthroplasty.

In this prospective, randomized, controlled study, we compared the performance of conventional and navigated total knee arthroplasties. Component alignment was measured in 60 patients operated on using navigation and in 60 patients operated on using the conventional technique. The groups then were divided into a subpopulation to measure alignments of the distal femoral cuts in the three anatomic planes, the proximal tibial cut in the frontal and sagittal planes, and the resulting lower limb mechanical axis in the frontal plane. Postoperative weightbearing long-view radiographs were evaluated as were clinical results using three standard questionnaires at 28 months followup. The intraoperative measurements (mean +/- standard deviation) at the resection planes showed navigated surgeries result in more accurate alignments than conventional surgeries for the femur: in the frontal plane, 0.1 degrees +/- 0.9 degrees and 0.7 degrees +/- 1.6 degrees valgus, respectively; in the sagittal plane, 1.1 degrees +/- 1.8 degrees and 2.8 degrees +/- 2.0 degrees flexion; and in the transversal plane, 0.1 degrees +/- 1.2 degrees and 0.9 degrees +/- 1.7 degrees internal rotation. The navigated technique also reduced the number of cases with final mechanical axes greater than 3 degrees from 20.0% to 1.7%. Postoperative radiographs showed better component alignment using navigation, particularly at the femur. However, clinical scoring systems showed this radiographic improvement did not necessarily result in a better clinical outcome at short-term followup.

Aged↗

PubMed2006

Meniscal wear at a three-component total ankle prosthesis by a knee joint simulator.

Despite the fundamental value of wear simulation studies to assess wear resistance of total joint replacements, neither specialised simulators nor established external conditions are available for the human ankle joint. The aim of the present study was to verify the suitability of a knee wear simulator to assess wear rates in ankle prostheses, and to report preliminary this rate for a novel three-component total ankle replacement design. Four intact 'small' size specimens of the Box ankle were analysed in a four-station knee wear simulator. Special component-to-actuator holders were manufactured and starting spatial alignment of the three-components was sought. Consistent load and motion cycles representing conditions at the ankle joint replaced exactly with the prosthesis design under analysis were taken from a corresponding mechanical model of the stance phase of walking. The weight loss for the three specimens, after two million cycles, was 32.68, 14.78, and 62.28mg which correspond to a linear penetration of 0.018, 0.008, and 0.034mm per million-cycle, respectively for the specimens #1, #2, and #3. The knee wear simulator was able to reproduce load-motion patterns typical of a replaced ankle. Motion of the meniscal bearing in between the tibial and talar components was smooth, this component remaining in place and in complete congruence with the metal components throughout the test.

Ankle Joint↗

PubMed2006

Rear-foot, mid-foot and fore-foot motion during the stance phase of gait.

This paper proposes a new protocol designed to track a large number of foot segments during the stance phase of gait with the smallest possible number of markers, with particular clinical focus on coronal plane alignment of the rear-foot, transverse and sagittal plane alignment of the metatarsal bones, and changes at the medial longitudinal arch. The shank, calcaneus, mid-foot and metatarsus were assumed to be 3D rigid bodies. The longitudinal axis of the first, second and fifth metatarsal bones and the proximal phalanx of the hallux were also tracked independently. Skin markers were mounted on bony prominences or joint lines, avoiding the course of main tendons. Trajectories of the 14 markers were collected by an eight-camera motion capture system at 100 Hz on a population of 10 young volunteers. Three-dimensional joint rotations and planar angles were calculated according to anatomically based reference frames. The marker set was well visible throughout the stance phase of gait, even in a camera configuration typical of gait analysis of the full body. The time-histories of the joint rotations and planar angles were well repeatable among subjects and consistent with clinical and biomechanical knowledge. Several dynamic measurements were originally taken, such as elevation/drop of the medial longitudinal arch and of three metatarsal bones, rear-foot to fore-foot rotation and transverse plane deformation of the metatarsus. The information obtained from this protocol, consistent with previous clinical knowledge, enhanced our understanding of the dynamics of the human foot during stance.

Adult↗

PubMed2006

A new software tool for 3D motion analyses of the musculo-skeletal system.

BACKGROUND: Many clinical and biomechanical research studies, particularly in orthopaedics, nowadays involve forms of movement analysis. Gait analysis, video-fluoroscopy of joint replacement, pre-operative planning, surgical navigation, and standard radiostereometry would require tools for easy access to three-dimensional graphical representations of rigid segment motion. Relevant data from this variety of sources need to be organised in structured forms. Registration, integration, and synchronisation of segment position data are additional necessities. With this aim, the present work exploits the features of a software tool recently developed within a EU-funded project ('Multimod') in a series of different research studies. METHODS: Standard and advanced gait analysis on a normal subject, in vivo fluoroscopy-based three-dimensional motion of a replaced knee joint, patellar and ligament tracking on a knee specimen by a surgical navigation system, stem-to-femur migration pattern on a patient operated on total hip replacement, were analysed with standard techniques and all represented by this innovative software tool. Segment pose data were eventually obtained from these different techniques, and were successfully imported and organised in a hierarchical tree within the tool. FINDINGS: Skeletal bony segments, prosthesis component models and ligament links were registered successfully to corresponding marker position data for effective three-dimensional animations. These were shown in various combinations, in different views, from different perspectives, according to possible specific research interests. INTERPRETATION: Bioengineering and medical professionals would be much facilitated in the interpretation of the motion analysis measurements necessary in their research fields, and would benefit therefore from this software tool.

Aged↗

PubMed2006

Influence of tibial component posterior slope on in vivo knee kinematics in fixed-bearing total knee arthroplasty.

The relation between prosthesis component kinematics and posterior slope of the tibial component in total knee arthroplasty is much debated. Three-dimensional kinematics of the replaced knee was obtained by video fluoroscopy in 23 knees treated by cruciate-retaining or cruciate-substituting arthroplasty. Relative position and orientation of the metal components were calculated in stair ascending, getting up from and sitting down on a chair, and single step up-and-down. Significant correlations were found between tibial component posterior slope and anteroposterior position of tibiofemoral lateral contact and between this slope and maximum knee flexion. These correlations were task and design specific. However, the average of the tibiofemoral contact positions over all three motor tasks was slightly posterior to the midline of the tibial base plate, reaching at most 84% of its anteroposterior dimension. Performing a posterior slope of the tibial cut does not put total knee arthroplasty with high conforming designs at higher risk of failure, even when large posterior inclinations need to be achieved.

Aged↗

PubMed2005

Wear patterns on tibial plateau from varus osteoarthritic knees.

BACKGROUND: The knowledge of cartilage wear patterns at the medial tibial plateau is important to understand the main causes of arthritis in varus knees. The most important factors influencing knee arthritis in fact seem to be the severity of the degenerative changes determined by the lower limb mechanical axis and the abnormal knee joint kinematics which frequently results from dysfunction of the anterior cruciate ligament. METHODS: We studied the wear patterns of cartilage damage in 70 medial tibial plateaus resected at operation during total knee arthroplasty indicated for varus osteoarthritic knee. Anterior cruciate ligament and medial meniscus integrity was assessed intra-operatively. Calibrated digital images were used to measure the wear patterns with a standard software tool. The medial compartment of the tibial plateau was divided into six zones, and the amount of cartilage and bone destruction in each zone was classified into two grades. FINDINGS: The wear pattern was found to be highly dependent upon knee varus deformity (Mann Whitney P<0.001) and anterior cruciate ligament integrity (Friedman P<0.0005). Anterior cruciate ligament was found intact in 35.7% of the cases. Wear patterns on intact anterior cruciate ligament knees occurred in the central to medial aspect of the tibial plateau. Anterior cruciate ligament deficient knees had significantly larger wear patterns anteriorly and posteriorly in the most medial region of the medial plateau. INTERPRETATION: These observations suggest altered joint mechanics exist in anterior cruciate ligament deficient varus knees, which would worsen cartilage degeneration and osteoarthritis progression.

Adult↗

PubMed2005

Finite element analysis of a total ankle replacement during the stance phase of gait.

Total ankle replacement (TAR) designs have still several important issues to be addressed before the treatment becomes fully acceptable clinically. Very little is known about the performance, in terms of the contact pressures and kinematics of TAR when subjected to daily activities such as level gait. For this purpose, an explicit finite element model of a novel 3-component TAR was developed, which incorporated a previously validated mechanical model of the ankle ligament apparatus. The intermediate mobile polyethylene meniscal bearing was modelled as an elastic-plastic continuum while the articulating surfaces of the tibial and talar metal components as rigid bodies. Overall kinematics, contact pressures and ligament forces were analysed during passive, i.e. virtually unloaded, and active, i.e. stance phase of gait, conditions. Simulation of passive motion predicted similar kinematics as reported previously in an analytical four-bar linkage model. The meniscal bearing was observed to move 5.6 mm posteriorly during the simulated stance and the corresponding antero-posterior displacement of the talar component was 8.3 mm. The predicted pattern and the amount (10.6 degrees ) of internal-external rotation of the ankle complex were found to be in good agreement with corresponding in vivo measurements on normal ankles. A peak contact pressure of 16.8 MPa was observed, with majority of contact pressures below 10 MPa. For most ligaments, reaction forces remain within corresponding physiological ranges. A first realistic representation of the biomechanical behaviour of the human ankle when replaced by prosthetic joints is provided. The applied methodology can potentially be applied to other TAR designs.

Ankle Joint↗

PubMed2005

Advanced multimodal visualisation of clinical gait and fluoroscopy analyses in the assessment of total knee replacement.

Traditional gait and fluoroscopy analysis of human movement are largely utilised but are still limited in registration, integration, synchronisation and visualisation capabilities. The present work exploits the features of a recently developed software tool based on multimodal display (Data Manager developed within the EU-funded project 'Multimod') in an exemplary clinical case. Standard lower limb gait analysis, comprising segment position, ground reaction force and EMG data collection, and three-dimensional fluoroscopy analysis at the replaced joint were performed in a total knee replacement patient while ascending stairs. Clinical information such as X-rays and standard scores were also available. Data Manager was able to import all this variety of data and to structure these in an original hierarchical tree. Bone and prosthesis component models were registered to corresponding marker position data for effective three-dimensional animations. These were also synchronised with corresponding standard video sequences. Animations, video, time-histories of collected and also processed data were shown in various combinations, according to specific interests of the bioengineering and medical professionals expected to observe and to interpret this large amount of data. This software tool demonstrated to be a valuable means to enhance representation and interpretation of measurements coming from human motion analysis. In a single software, a thorough and effective clinical and biomechanical analysis of human motion was performed.

Arthroplasty, Replacement, Knee↗

PubMed2004

Mechanics of the anterior drawer test at the ankle: the effects of ligament viscoelasticity.

The anterior drawer test at the human ankle joint is a routine clinical examination. The relationship between the mechanical response of this joint and the flexion angle was elucidated by a recent mathematical model, using purely elastic mechanical characteristics for the ligament fibres. The objective of the present work was to assess the effect of ligament viscoelasticity on the force response of the ankle joint for anterior displacements of the foot relative to the tibia, at different ankle flexion positions. A viscoelastic model of the ligaments from the literature was included in the recently proposed mathematical model. Drawer tests were simulated at several flexion angles and for increasing velocities of the imposed anterior displacement. The stiffness of the model ankle joint increased only modestly with velocity. The response force found for a 6mm displacement at 20 degrees plantarflexion increased by only 13% for a one hundred-fold increase in velocity from 0.1 to 10 mm/s. The flexion angle was confirmed as the most influential parameter in the mechanical response of the ankle to anterior drawer test.

Ankle Joint↗

PubMed2004

Mathematical model for pre-operative planning of linear and closing-wedge metatarsal osteotomies for the correction of hallux valgus.

First-metatarsal osteotomy is performed for an abnormal intermetatarsal angle and severe hallux valgus deformity. The metatarsal head is slid along the osteotomy and fixed with a Kirschner wire to achieve angular and linear realignment with respect to the other metatarsals. When reduction of joint subluxation is also sought, a bone wedge is removed. A mathematical model and a corresponding computer-based tool were developed for pre-operative planning of the optimum surgical solution. Standard intermetatarsal angle correction, head-to-sesamoids re-alignment, joint subluxation reduction and metatarsal length adjustment were all pursued. A standard pre-surgical dorso-plantar radiograph of the patient, with an additional metal ball for calculation of X-ray magnification, was necessary to analyse the original and final geometrical configurations. For the first time, expected bone loss and wire diameter were also considered. The angles of bone cuts and the amount of sliding along these cuts were calculated by the model according to the surgical goal. All the resulting geometrical parameters, both in the pre- and planned post- operative configuration, were provided in graphical and tabular form. In a change from former qualitative analysis of radiograms, the surgeon can now enter the operating theatre with a detailed plan of the goal to be achieved.

Hallux Valgus↗

PubMed2003

Dynamic in-vivo tibio-femoral and bearing motions in mobile bearing knee arthroplasty.

To determine the tibio-femoral and bearing motions in well functioning mobile bearing total knee arthroplasties, a quantitative analysis by means of fluoroscopy was carried out during stair ascending, chair rising-sitting and step up-down motor tasks. Femoral and tibial component positions were obtained using a CAD-model-based shape matching technique. Direct measurement of mobile bearing motion was carried out by tracking previously inserted tantalum beads. A relatively small motion of the bearing was observed. The advantage of self-alignment claimed for the mobile bearing arthroplasty seems to be confirmed by subject-specific ranges of motion exhibited by these patients. It has also been demonstrated that these total knee arthroplasties, which are not fully conforming in flexion, provide little constraint to antero-posterior motion, leading to a kinematic pattern very similar to an ACL deficient knee.

Activities of Daily Living↗

PubMed2003

Ligament fibre recruitment and forces for the anterior drawer test at the human ankle joint.

Although the anterior drawer test at the ankle joint is commonly used in routine clinical practice, very little is known about the sharing of load between the individual passive structures and the joint response at different flexion angles.A mathematical model of the ankle joint was devised to calculate ligament fibre recruitment and load/displacement curves at different flexion angles. Ligaments were modelled as three-dimensional arrays of fibres, and their orientations at different flexion angles were taken from a previously validated four-bar-linkage model in the sagittal plane. A non-linear stress/strain relationship was assumed for ligament fibres and relevant mechanical parameters were taken from two reports in the literature. Talus and calcaneus were assumed to move as a single rigid body. Antero/distal motion of the talus relative to the tibia was analysed. The ankle joint was found to be stiffer at the two extremes of the flexion range, and the highest laxity was found around the neutral position, confirming previous experimental works. With a first dataset, a 20N anterior force produced 4.3, 5.5, and 4.4mm displacement respectively at 20 degrees plantarflexion, at neutral, and at 20 degrees dorsiflexion. At 10 degrees plantarflexion, for a 6mm displacement, 65% of the external force was supported by the anterior talofibular, 11% by the deep anterior tibiotalar and 5.5% by the tibionavicular ligament. Corresponding results from a second dataset were 1.4, 2.4 and 1.8mm at 40N force, and 80%, 0% and 2% for a 3mm displacement. A component of the contact force supported the remainder.

Ankle Joint↗

PubMed2003

Pre-operative planning and gait analysis of total hip replacement following hip fusion.

A computer-based pre- and post-operative analysis of total hip replacement (THR) is presented. The analysis was performed by using and innovative combination of X-ray measurements and gait analysis. The several important biomechanical factors that affect effective THR are analysed in a test clinical case of conversion of hip fusion into THR. Geometrical positioning of the artificial joint should restore correct motion and adequate leverage of the surrounding muscles in order to exert the appropriate functional joint moments. Hip joint centre positioning pre- and post-operation was evaluated using a computer-based X-ray measurement tool. This enabled the calculation of the medio-lateral and proximal-distal off-set of the joint centre, the lever arms of the abductor muscles and the limb length discrepancy. Pre- and post-operative function was also evaluated using gait analysis, including joint kinematics, kinetics and electromyography. The whole analysis suggests that a good restoration of joint motion, a regression of pelvic compensation and a phasic activity of gluteus medius occur only when a good positioning of the prosthetic hip joint is obtained. This study proved a fundamental role played by these two computer-based tools in the support of the clinical decision making process.

Arthroplasty, Replacement, Hip↗

PubMed2003

Femoral anatomical frame: assessment of various definitions.

The reliability of the estimate of joint kinematic variables and the relevant functional interpretation are affected by the uncertainty with which bony anatomical landmarks and underlying bony segment anatomical frames are determined. When a stereo-photogrammetric system is used for in vivo studies, minimising and compensating for this uncertainty is crucial. This paper deals with the propagation of the errors associated with the location of both internal and palpable femoral anatomical landmarks to the estimation of the orientation of the femoral anatomical frame and to the knee joint angles during movement. Given eight anatomical landmarks, and the precision with which they can be identified experimentally, 12 different rules were defined for the construction of the anatomical frame and submitted to comparative assessment. Results showed that using more than three landmarks allows for more repeatable anatomical frame orientation and knee joint kinematics estimation. Novel rules are proposed that use optimization algorithms. On the average, the femoral frame orientation dispersion had a standard deviation of 2, 2.5 and 1.5 degrees for the frontal, transverse, and sagittal plane, respectively. However, a proper choice of the relevant construction rule allowed for a reduction of these inaccuracies in selected planes to 1 degrees rms. The dispersion of the knee adduction-abduction and internal-external rotation angles could also be limited to 1 degrees rms irrespective of the flexion angle value.

Algorithms↗

PubMed2002

Dynamic simulation of the natural and replaced human ankle joint.

Disappointing results for total ankle replacement have been explained by poor knowledge of the mechanics of the intact and replaced joints. Dynamic simulation tools have the capacity to simulate dynamic conditions that occur in human joints. The Working Model 2D tool was used to simulate the mechanics of the intact and replaced ankle joints, based on previously validated mathematical models. Elementary objects were used to model ligaments, articular surfaces, retinacula and muscle-tendon units. The performance of several pairs of prosthetic articular surfaces was also analysed. According to the results of these simulations, rolling as well as sliding motion occurs in the natural ankle, governed by a ligamentous linkage. Elongation of the tibiocalcaneal and calcaneofibular ligaments was found to be 1.5% and 4.8%, respectively. A 13% change in lever arm length occurred for both the tibialis anterior and gastrocnemius muscles during ankle flexion. Unlike the currently available three-component designs, the newly proposed convex-tibial ligament-compatible prosthesis was found to be able to restore the original mobility and physiological function of the ligaments. This prosthesis combines freedom from restraint with congruity of the components throughout the range of flexion.

Ankle Joint↗

PubMed2001

Computer-assisted design of the sagittal shapes of a ligament-compatible total ankle replacement.

The poor results of total ankle replacement have been attributed to the inability of designers to restore adequately the critical mutual function of the ligaments and the articular surfaces. The purpose of this study was to design sagittal shapes of the articular surfaces for a new ankle prosthesis to be compatible with the geometry of the retained ligamentous structures. Several ligament-compatible pairs of articular surfaces were tested using a computerised version of a four-bar linkage model. The kinematics of the ankle when replaced by non-conforming two-component and by fully conforming three-component designs with either flat, concave or convex tibial surfaces were assessed by the model. A ligament-compatible convex-tibia fully-congruent three-component prosthesis showed the best features. The three-component prosthesis allows complete congruence over the entire range of flexion. A convex shape for the tibial arc was preferred because of the better degree of entrapment of the meniscal bearing. A 5 cm convex-tibia arc radius gave 2 mm entrapment together with 9.8 mm of tibial bone cut. Ligament elongation imposed by full congruence of the articular surfaces was less than 0.03% of the original length. The original patterns of joint kinematics and ligament tensioning are closely restored in the joint replaced by the proposed prosthesis.

Ankle Joint↗

PubMed2001

Mobility of the subtalar joint in the intact ankle complex.

A previous study by these authors showed that the calcaneus follows a unique path of unresisted coupled motion relative to the tibia during passive flexion and that most of this motion occurred at the ankle level. Subtalar motion in the intact ankle complex was observed only when perturbations from this path were induced by the application of force to the calcaneus. Relative motion of the bones of the ankle complex was tracked by stereophotogrammetry in seven specimens. Anatomical landmarks, reference frames and joint angles were defined by standard techniques. Sequential moments were applied to the calcaneus about the long axis of the tibia. Measured movements at subtalar level demonstrated plantarflexion coupled to supination and internal rotation (inversion) and dorsiflexion coupled to pronation and external rotation (eversion). These movements were resisted and were fully recovered when the external load was removed. Subtalar motion diminished as the ankle approached maximal dorsi- and plantarflexion. Two clearly distinguished mean axes of rotation were observed for inversion and eversion runs. The axes of inversion and eversion of the subtalar complex changed orientation along a preferred and repeatable path. The subtalar joint complex occupied only a single stable position in the unloaded state and with no range of unresisted motion. It is inferred that mobility was possible only by the stretching and lengthening of the ligaments and the indentation of the articular surfaces, requiring the application of loads. The subtalar joint complex behaves like a flexible structure.

Ankle Joint↗

PubMed2001

Geometry and mechanics of the human ankle complex and ankle prosthesis design.

The main objective of the study was to develop a model of the intact human ankle complex. It was also aimed at designing total ankle replacement which would better reproduce the physiological function of the joint. Passive flexion was analysed in seven lower-leg preparations with a stereophotogrammetric system. The articular surfaces and fibres within the calcaneofibular and tibiocalcaneal ligaments prescribed the changing positions of the axis of rotation. Joint motion included rolling as well as sliding. A computer-based model elucidated the observed kinematics at the intact joint. The experimental evidence and the geometrical model gave the basis for the design of models of replaced ankle in the sagittal plane. A three-component, convex-tibia prosthesis was eventually selected with articular surface shapes compatible with the geometry of the ligaments. It was demonstrated that in intact ankle joint, the geometry of the articular surfaces is strictly related to that of the ligaments and that current prosthesis designs do not restore physiological pattern of ligament tensioning. Careful reconstruction of the ligaments is recommended in any ankle surgery for maintenance of the normal kinematics and mechanics. A proposed novel design based on ligament/shape compatibility may improve total ankle replacement results.

Ankle Joint↗