Functional evaluation of a novel fibreglass-reinforced polyamide custom dynamic AFO for foot drop patients: A pilot study.

BACKGROUND: Ankle-foot orthoses (AFOs) are orthopaedic devices often prescribed to treat foot drop. For patients who are not satisfied with off-the-shelf solutions, custom AFOs personalized to the patient's lower limb anatomy are required. Dynamic AFOs provide stability while allowing for physiological ankle mobility in the stance phase of walking. RESEARCH QUESTION: Can a morphology-based dynamic custom AFO made of fiberglass-reinforced polyamide restore a quasi-normal gait pattern and improve comfort in patients with foot drop? METHODS: In this pilot study, the legs and feet of ten foot drop patients (age=64.9 ± 11.4 years; BMI=26.2 ± 2.1 kg/m2) were scanned using a Kinect-based 3D scanner. A custom AFO was designed and produced for each patient using a fiberglass-reinforced polyamide through selective laser sintering. To assess kinematics, skin markers were placed on relevant bony landmarks according to a validated protocol. Each patient was instructed to walk at a self-selected comfortable speed under three conditions: wearing the custom AFO, wearing an off-the-shelf orthosis (Codivilla spring), and without any AFO (shod condition). Muscle activation in the tibialis anterior, gastrocnemius, rectus femoris and biceps femoris muscles in both legs was recorded using wireless sEMG sensors. The comfort and of each AFO was evaluated using a Visual Analogue Scale. RESULTS: The custom AFO resulted in significant increase of stride length and walking speed compared to the shod condition. Except for the hip joint, which exhibited greater maximum flexion and reduced range of motion, the kinematic parameters of all other joints were similar to those observed in a healthy control population. Furthermore, the custom AFO received significantly higher comfort scores compared to the Codivilla spring. SIGNIFICANCE: This study has provided evidence supporting the effectiveness of custom orthotic solutions in restoring lower limb kinematics and improving the perceived comfort in foot drop patients compared to off-the-shelf solutions.

Postural stability and plantar pressure parameters in healthy subjects: variability, correlation analysis and differences under open and closed eye conditions.

Introduction: The "postural control system" acts through biomechanical strategies and functional neuromuscular adaptations to maintain body balance under static and dynamic conditions. Postural stability and body weight distribution can be affected by external sensory inputs, such as different visual stimuli. Little information is available about the influence of visual receptors on stabilometric and plantar pressure parameters. The aim of this study was to analyze variability, correlations, and changes in these parameters under open- (OE) and closed-eye (CE) conditions. Methods: A total of 31 stabilometric and plantar pressure parameters were acquired in 20 young and healthy adults during baropodometric examination performed in bipedal standing under both visual conditions. Variability of parameters was evaluated via the coefficient of variation, correlation analysis via Pearson's R2, and statistical differences via the Wilcoxon test. Results: High intra-subject repeatability was found for all plantar pressure parameters and CoP-speed (CV < 40%) under OE and CE conditions, while CoP-sway area (CoPsa) and length surface function (LSF) showed larger variability (CV > 50%). Mean and peak pressures at midfoot and total foot loads showed the least number of significant correlations with other parameters under both visual conditions, whereas the arch-index and rearfoot loads showed the largest number of significant correlations. The limb side significantly affected most plantar pressure parameters. A trend of larger LSF and lower CoPsa and mean and peak pressures at the right forefoot was found under the CE condition. Discussion: The present study provides a deeper insight into the associations between postural stability and foot load. Interesting postural adaptations, particularly with respect to different visual stimuli, the effect of the dominant side, and the specific role of the midfoot in balance control were highlighted.

A novel apparatus to assess the mechanical properties of Ankle-Foot Orthoses: Stiffness analysis of the Codivilla spring.

Ankle-Foot Orthoses (AFOs) are the most common devices prescribed to support the ankle and restore a quasi-normal gait pattern in drop-foot patients. AFO stiffness is possibly the main mechanical property affecting foot and ankle biomechanics. A variety of methods to evaluate this property have been reported, however no standard procedure has been validated and widely used. This study is reporting the repeatability of a novel apparatus to measure AFO stiffness in ideal frictionless conditions. The apparatus is based on a servo-hydraulic testing machine and allows to apply a displacement-controlled rotation of the AFO shell, simulating the physiological ankle dorsi/plantarflexion movement. The repeatability of the apparatus in measuring AFO stiffness in dorsiflexion and plantarflexion was assessed intra- and inter-session in a sample of standard polypropylene AFOs of different sizes (Codivilla spring). The repeatability of the apparatus in measuring the AFO stiffness was high. The Intra- and Inter-session Coefficient of Variation ranged between 0.02 ÷ 1.3 % and 1.3 ÷ 5 %, respectively. The Intra Class Correlation Coefficient ranged between 0.999 ÷ 1 intra- and 0.993 ÷ 0.997 inter-session. AFOs stiffness was observed to increase with the AFO size. The setup is easy to replicate and can be implemented with any torsion-controlled servo-hydraulic testing machine and has resulted simple to use and flexible enough to adapt to AFOs with different sizes. The frictionless contacts characterizing the apparatus make it possible to measure the ideal AFO stiffness by excluding the effect of the fixation methods to the leg and help to improve the repeatability of measurements.

A new ligament-compatible patient-specific 3D-printed implant and instrumentation for total ankle arthroplasty: from biomechanical studies to clinical cases.

BACKGROUND: Computer navigation and patient-specific instrumentation for total ankle arthroplasty have still to demonstrate their theoretical ability to improve implant positioning and functional outcomes. The purpose of this paper is to present a new and complete total ankle arthroplasty customization process for severe posttraumatic ankle joint arthritis, consisting of patient-specific 3D-printed implant and instrumentation, starting from a ligament-compatible design. CASE PRESENTATION: The new customization process was proposed in a 57-year-old male patient and involved image analysis, joint modeling, prosthesis design, patient-specific implant and instrumentation development, relevant prototyping, manufacturing, and implantation. Images obtained from a CT scan were processed for a 3D model of the ankle, and the BOX ankle prosthesis (MatOrtho, UK) geometries were customized to best fit the model. Virtual in silico, i.e., at the computer, implantation was performed to optimize positioning of these components. Corresponding patient-specific cutting guides for bone preparation were designed. The obtained models were printed in ABS by additive manufacturing for a final check. Once the planning procedure was approved, the models were sent to final state-of-the-art additive manufacturing (the metal components using cobalt-chromium-molybdenum powders, and the guides using polyamide). The custom-made prosthesis was then implanted using the cutting guides. The design, manufacturing, and implantation procedures were completed successfully and consistently, and final dimensions and location for the implant corresponded with the preoperative plan. Immediate post-op X-rays showed good implant positioning and alignment. After 4 months, clinical scores and functional abilities were excellent. Gait analysis showed satisfactory joint moment at the ankle complex and muscle activation timing within normality. CONCLUSIONS: The complete customization process for total ankle arthroplasty provided accurate and reliable implant positioning, with satisfactory short-term clinical outcomes. However, further studies are needed to confirm the potential benefits of this complete customization process. LEVEL OF EVIDENCE: 5.

Three-dimensional displacement after a medializing calcaneal osteotomy in relation to the osteotomy angle and hindfoot alignment.

BACKGROUND: A medializing calcaneal osteotomy is frequently performed to correct adult-acquired flatfoot deformities, but there is lack of data on the associated three-dimensional variables defining the final correction. The aim of this study was to assess the correlation between the pre-operative hindfoot valgus deformity and calcaneal osteotomy angles and the post-operative calcaneal displacement. METHODS: Weight-bearing CT scans obtained pre- and post-operatively were retrospectively analyzed for sixteen patients. Corresponding three-dimensional bone models were used to measure valgus deformity pre- and post-operatively, inclination of the osteotomy and displacement of the calcaneus. Linear regression was conducted to assess the relationship between these measurements. RESULTS: On average, the hindfoot valgus changed from 13.1° (±4.6) pre-operatively to 5.7° (±4.3) post-operatively. A mean inferior displacement of 3.2mm (±1.3) was observed along the osteotomy with a mean inclination of 54.6° (±5.6), 80.5° (±10.7), -13.7° (±15.7) in the axial, sagittal and coronal planes, respectively. A statistically significant positive relationship (p<.05, R2=0.6) was found between the pre-operative valgus, the axial osteotomy inclination, and the inferior displacement. CONCLUSIONS: This study shows that the degree of pre-operative hindfoot valgus and the axial osteotomy angle are predictive factors for the amount of post-operative inferior displacement of the calcaneus. These findings demonstrate the added value of a computer-based pre-operative planning in clinical practice. Level of evidence II Prospective comparative study.

Three-dimensional patellar tendon fibre kinematics in navigated TKA with and without patellar resurfacing.

PURPOSE: Physiological elongation and orientation of patellar tendon fibres are among the scopes of total knee arthroplasty, but little is known in the three dimensions. The study aims to assess in vitro these variations at the intact and replaced knee, with and without patellar resurfacing. It was hypothesised that fibre patterns differ before and after prosthesis implantation, and between specific prosthesis designs. It was also expected that patellar resurfacing would affect relevant results. METHODS: Measurements from 16 intact cadaver knees free from anatomical defects are here reported using a surgical navigation system. Data were collected at the intact joint and after implantation with cruciate-retaining or posterior-stabilised prosthesis designs, with and without patellar resurfacing. Relevant anatomical landmarks and patellar tendon attachments were digitised. Anatomical reference frames in the femur, tibia and patella were defined to measure component implantation parameters. Representative tendon fibres were defined as the straight line segments joining the two extremities. Changes in length and orientation of these fibres were calculated and reported versus flexion at the intact knee and after prosthesis implantation, both with and without patellar resurfacing. RESULTS: A good intra- and inter-specimen repeatability was found at the intact and replaced knees. In both prosthesis designs, the patterns of fibre lengthening were similar to those in the intact knee, though significant differences were observed before and after patellar resurfacing. Corresponding fibre orientations in the frontal and sagittal planes showed significantly smaller ranges than those in the corresponding intact joints. More natural patterns were observed in the knees implanted with the posterior-stabilised design. Significant correlations were identified between patellar component implantation parameters and both patellar tendon fibre elongation and orientation. CONCLUSIONS: Differences, however small, in patellar tendon fibre elongation and orientation were observed after total knee arthroplasty. The posterior-stabilised design provided better results, whereas patellar resurfacing affected significantly normal patellar function. In the clinical practice, the present findings can contribute to the understanding of current prosthesis designs and patellar resurfacing, recommending also enhanced care during this surgery.

Functional and clinical evaluation at 5-year follow-up of a three-component prosthesis and osteochondral allograft transplantation for total ankle replacement.

BACKGROUND: Severe ankle arthritis is a life-limiting condition which often requires surgery. Ankle arthroplasty via artificial or "biological" reconstruction is a viable option in those patients who are not comfortable with arthrodesis. More functional studies are needed to compare the performance and outcomes of the two function-preserving arthroplasties. METHODS: In this study two groups of 10 patients affected by severe ankle arthritis were treated either with a 3-component ankle prosthesis or with bipolar fresh osteochondral allograft transplantation. Patients were evaluated pre-operatively and at 5-year follow-up. The American Orthopaedic Foot and Ankle Society score was used for clinical evaluation, and gait analysis for functional assessment. Activation pattern of lower limb muscles was obtained by surface electromyography (EMG). In each group, kinematic, kinetic, and EMG data were compared between pre-op and follow-up assessments, and also versus corresponding data from a 20 healthy subject control group. The median clinical score significantly increased between pre-op and follow-up from 53 to 74.5 in the transplantation and from 28.5 to 80 in the prosthesis group. Spatio-temporal parameters showed a statistically significant improvement in cadence and cycle time. Improvement of gait speed was also observed only in the prosthesis group. EMG patterns at follow-up were strongly correlated with the corresponding control data for both groups. Although no significant amelioration in the joints' range of motion was detected in either surgical procedure, preservation of the functional conditions at medium-term, along with significant improvement of the clinical score, may be considered a positive outcome for both techniques.

Tibial component alignment and risk of loosening in unicompartmental knee arthroplasty: a radiographic and radiostereometric study.

PURPOSE: Unicompartmental knee arthroplasty (UKA) has shown a higher rate of revision compared with total knee arthroplasty. The success of UKA depends on prosthesis component alignment, fixation and soft tissue integrity. The tibial cut is the crucial surgical step. The hypothesis of the present study is that tibial component malalignment is correlated with its risk of loosening in UKA. METHODS: This study was performed in twenty-three patients undergoing primary cemented unicompartmental knee arthroplasties. Translations and rotations of the tibial component and the maximum total point motion (MTPM) were measured using radiostereometric analysis at 3, 6, 12 and 24 months. Standard radiological evaluations were also performed immediately before and after surgery. Varus/valgus and posterior slope of the tibial component and tibial-femoral axes were correlated with radiostereometric micro-motion. A survival analysis was also performed at an average of 5.9 years by contacting patients by phone. RESULTS: Varus alignment of the tibial component was significantly correlated with MTPM, anterior tibial sinking, varus rotation and anterior and medial translations from radiostereometry. The posterior slope of the tibial component was correlated with external rotation. The survival rate at an average of 5.9 years was 89%. The two patients who underwent revision presented a tibial component varus angle of 10° for both. CONCLUSIONS: There is correlation between varus orientation of the tibial component and MTPM from radiostereometry in unicompartmental knee arthroplasties. Particularly, a misalignment in varus larger than 5° could lead to risk of loosening the tibial component. LEVEL OF EVIDENCE: Prognostic studies-retrospective study, Level II.

Multi-segment foot mobility in a hinged ankle-foot orthosis: the effect of rotation axis position.

Hinged ankle-foot orthoses are prescribed routinely for the treatment of ankle joint deficits, despite the conflicting outcomes and the little evidence on their functional efficacy. In particular, the axis of rotation of the hinge is positioned disregarding the physiological position and orientation. A multi-segment model was utilized to assess in vivo the effect of different positions for this axis on the kinematics of foot joints. A special custom-made hinged orthosis was manufactured via standard procedures for a young healthy volunteer. Four locations for the mechanical axis were obtained by a number of holes where two nuts and bolts were inserted to form the hinge: a standard position well above the malleoli, at the level of the medial malleolus, at the level of the lateral malleolus, and the physiological between the two malleoli. The shank and foot were instrumented with 15 reflective markers according to a standard protocol, and level walking was collected barefoot and with the orthosis in the four mechanical conditions. The spatio-temporal parameters observed in the physiological axis condition were the closest to normal barefoot walking. As expected, ankle joint rotation was limited to the sagittal plane. When the physiological axis was in place, rotations of the ankle out-of-sagittal planes, and of all other foot joints in the three anatomical planes, were found to be those most similar to the natural barefoot condition. These preliminary measures of intersegmental kinematics in a foot within an ankle-foot orthosis showed that only a physiological location for the ankle mechanical hinge can result in natural motion at the remaining joints and planes.

Load along the tibial shaft during activities of daily living.

External load at the tibia during activities of daily living provides baseline measures for the improvement of the design of the bone-implant interface for relevant internal and external prostheses. A motion analysis system was used together with an established protocol with skin markers to estimate three-dimensional forces and moments acting on ten equidistant points along the tibial shaft. Twenty young and able-bodied volunteers were analysed while performing three repetitions of the following tasks: level walking at three different speeds, in a straight-line and with sudden changes of direction to the right and to the left, stair ascending and descending, squatting, rising from a chair and sitting down. Moment and force patterns were normalised to the percentage of body weight per height and body weight, respectively, and then averaged over all subjects for each point, about the three tibial anatomical axes, and for each task. Load patterns were found to be consistent over subjects, but different among the anatomical axes, tasks and points. Generally, moments were higher in the medio/lateral axis and influenced by walking speed. In all five walking tasks and in ascending stairs with alternating feet, the more proximal the point was the smaller the mean moment was. For the remaining tasks the opposite trend was observed. The overall largest value was observed in the medio/lateral direction at the ankle centre in level walking at high speed (9.1% body weight * height on average), nearly three times larger than that of the anterior/posterior axis (2.9) during level walking with a sidestep turn. The present results should be of value also for in-vitro mechanical tests and finite element models.

Tibio-femoral and patello-femoral joint kinematics during navigated total knee arthroplasty with patellar resurfacing.

PURPOSE: In total knee arthroplasty, surgical navigation systems provide tibio-femoral joint (TFJ) tracking for relevant bone preparation, disregarding the patello-femoral joint (PFJ). Therefore, the important intra-operative assessment of the effect of component positioning, including the patella, on the kinematics of these two joints is not available. The objective of this study is to explore in vivo whether accurate tracking of the patella can result in a more physiological TFJ and PFJ kinematics during surgery. METHODS: Ten patients underwent navigated knee replacement with patellar resurfacing. A secondary system was used to track patellar motion and PFJ kinematics using a special tracker. Patellar resection plane position and orientation were recorded using an instrumented probe. During all surgical steps, PFJ kinematics was measured in addition to TFJ kinematics. RESULTS: Abnormal PFJ motion patterns were observed pre-operatively at the impaired knee. Patellar resection plane orientation on sagittal and transverse planes of 3.9° ± 9.0° and 0.4° ± 4.1° was found. A good restoration of both TFJ and PFJ kinematics was observed in all replaced knees after resurfacing, in particular the rotations in the three anatomical planes and medio-lateral patellar translation. CONCLUSIONS: Patella tracking results in nearly physiological TFJ and PFJ kinematics in navigated knee arthroplasty with resurfacing. The intra-operative availability also of PFJ kinematics can support the positioning not only of the patellar component in case of resurfacing, but also of femoral and tibial components.

Load along the femur shaft during activities of daily living.

A comprehensive knowledge of the loads applied during activities of daily living to the femur shaft is necessary to the design of direct attachments of relevant prostheses. A motion analysis system was used together with an established protocol with skin markers to estimate the three components of the forces and moments acting on ten equidistant points along the full femur shaft. Twenty healthy young volunteers were analyzed while performing three repetitions of the following tasks: level walking at three different speeds, straight-line and with sudden changes of direction to the right and to the left, stairs ascending and descending, squat, rising from a chair and sitting down. Average load patterns, after normalisation for body weight and height, were calculated over subjects for each point, about the three anatomical axes, and for each motor task. These patterns were found consistent over subjects, but different among the anatomical axes and tasks. In general, the moments were observed limitedly influenced by the progression speed, and higher for more proximal points. The moments were also higher in abd/adduction (8.1% body weight*height on average), nearly three times larger than those in flex/extension (2.6) during stair descending. The largest value over all moments was 164.8 N m, abd/adduction in level walking at high speed. The present results should be of value also for a most suitable level for amputation in transfemoral amputation, for in-vitro mechanical tests and for finite element models of the femur.

Inter-laboratory consistency of gait analysis measurements.

The dissemination of gait analysis as a clinical assessment tool requires the results to be consistent, irrespective of the laboratory. In this work a baseline assessment of between site consistency of one healthy subject examined at 7 different laboratories is presented. Anthropometric and spatio-temporal parameters, pelvis and lower limb joint rotations, joint sagittal moments and powers, and ground reaction forces were compared. The consistency between laboratories for single parameters was assessed by the median absolute deviation and maximum difference, for curves by linear regression. Twenty-one lab-to-lab comparisons were performed and averaged. Large differences were found between the characteristics of the laboratories (i.e. motion capture systems and protocols). Different values for the anthropometric parameters were found, with the largest variability for a pelvis measurement. The spatio-temporal parameters were in general consistent. Segment and joint kinematics consistency was in general high (R2>0.90), except for hip and knee joint rotations. The main difference among curves was a vertical shift associated to the corresponding value in the static position. The consistency between joint sagittal moments ranged form R2=0.90 at the ankle to R2=0.66 at the hip, the latter was increasing when comparing separately laboratories using the same protocol. Pattern similarity was good for ankle power but not satisfactory for knee and hip power. The force was found the most consistent, as expected. The differences found were in general lower than the established minimum detectable changes for gait kinematics and kinetics for healthy adults.

Functional evaluation of patients treated with osteochondral allograft transplantation for post-traumatic ankle arthritis: one year follow-up.

Severe post-traumatic ankle arthritis poses a reconstructive challenge in active patients. Whereas traditional surgical treatments, i.e. arthrodesis and arthroplasty, provide good pain relief, arthrodesis is associated to functional and psychological limitations, and arthroplasty is prone to failure in the active patient. More recently the use of bipolar fresh osteochondral allografts transplantation has been proposed as a promising alternative to the traditional treatments. Preliminary short- and long-term clinical outcomes for this procedure have been reported, but no functional evaluations have been performed to date. The clinical and functional outcomes of a series of 10 patients who underwent allograft transplantation at a mean follow-up of 14 months are reported. Clinical evaluation was performed with the AOFAS score, functional assessment by state-of-the-art gait analysis. The clinical score significantly improved from a median of 54 (range 12-65) pre-op to 76.5 (range 61-86) post-op (p=0.002). No significant changes were observed for the spatial-temporal parameters, but motion at the hip and knee joints during early stance, and the range of motion of the ankle joint in the frontal plane (control: 13.8°±2.9°; pre-op: 10.4°±3.1°, post-op: 12.9°±4.2°; p=0.02) showed significant improvements. EMG signals revealed a good recovery in activation of the biceps femoris. This study showed that osteochondral allograft transplantation improves gait patterns. Although re-evaluation at longer follow-ups is required, this technique may represent the right choice for patients who want to delay the need for more invasive joint reconstruction procedures.

Three-dimensional motion analysis of the human knee joint: comparison between intra- and post-operative measurements.

PURPOSE: To compare intra-operative knee joint kinematic measurements immediately after total knee replacement with those of the same patients post-operatively at 6-month follow-up. METHODS: Fifteen patients who underwent total knee arthroplasty were analysed retrospectively. Eight were implanted with one prosthesis design and seven with another. The intra-operative measurements were performed by using a standard knee navigation system. This provided accurate three-dimensional positions and orientations for the femur and tibia by corresponding trackers pinned into the bones. At 6-month follow-up, the patients were analysed by standard three-dimensional video-fluoroscopy of the replaced knee during stair climbing, chair rising and step-up. Relevant three-dimensional positions and orientations were obtained by an iterative shape-matching procedure between the silhouette contours and the CAD-model projections. A number of traditional kinematic parameters were calculated from both measurements to represent the joint motion. RESULTS: Good post-operative replication of the intra-operative measurements was observed for most of the variables analysed. The statistical analysis also supported the good consistency between the intra- and post-operative measurements. CONCLUSIONS: Intra-operative kinematic measurements, accessible by a surgical navigation system, are predictive of the following motion performance of the replaced knees as experienced in typical activities of daily living. LEVEL OF EVIDENCE: Prognostic studies--investigating natural history and evaluating the effect of a patient characteristic, Level II.

Functional performance of a total ankle replacement: thorough assessment by combining gait and fluoroscopic analyses.

BACKGROUND: A thorough assessment of patients after total ankle replacement during activity of daily living can provide complete evidence of restored function in the overall lower limbs and replaced ankle. This study analyzes how far a possible restoration of physiological mobility in the replaced ankle can also improve the function of the whole locomotor apparatus. METHODS: Twenty patients implanted with an original three-part ankle prosthesis were analyzed 12 months after surgery during stair climbing and descending. Standard gait analysis and motion tracking of the components by three-dimensional fluoroscopic analysis were performed on the same day using an established protocol and technique, respectively. FINDINGS: Nearly physiological ankle kinematic, kinetic and electromyography patterns were observed in the contralateral side in both motor activities, whereas these patterns were observed only during stair climbing in the operated side. Particularly, the mean ranges of flexion at the replaced ankle were 13° and 17° during stair climbing and descending, respectively. Corresponding 2.1 and 3.1mm antero/posterior meniscal-to-tibial translations were correlated with flexion between the two metal components (p<0.05). In addition, a larger tibiotalar flexion revealed by fluoroscopic analysis resulted in a physiological hip and knee moment. INTERPRETATION: The local and global functional performances of these patients were satisfactory, especially during stair climbing. These might be associated to the recovery of physiological kinematics at the replaced ankle, as also shown by the consistent antero/posterior motion of the meniscal bearing, according to the original concepts of this ankle replacement design.

Geometrical changes of knee ligaments and patellar tendon during passive flexion.

Patterns of fibre elongation and orientation for the cruciate and collateral ligaments of the human knee joint and for the patellar tendon have not yet been established in three-dimensions. These patterns are essential for understanding thoroughly the contribution of these soft tissues to joint function and of value in surgical treatments for a more conscious assessment of the knee status. Measurements from 10 normal cadaver knees are here reported using an accurate surgical navigation system and consistent anatomical references, over a large flexion arc, and according to current recommended conventions. The contours of relevant sub-bundles were digitised over the corresponding origins and insertions on the bones. Representative fibres were calculated as the straight line segments joining the centroids of these attachment areas. The most isometric fibre was also taken as that whose attachment points were at the minimum change in length over the flexion arc. Changes in length and orientation of these fibres were reported versus the flexion angle. A good general repeatability of intra- and inter-specimens was found. Isometric fibres were found in the locations reported in the literature. During knee flexion, ligament sub-bundles slacken in the anterior cruciate ligament, and in the medial and lateral collateral ligaments, whereas they tighten in the posterior cruciate ligament. In each cruciate ligament the two compounding sub-bundles have different extents for the change in fibre length, and also bend differently from each other on both tibial planes. In the collateral ligaments and patellar tendon all fibres bend posteriorly. Patellar tendon underwent complex changes in length and orientation, on both the tibial sagittal and frontal planes. For the first time thorough and consistent patterns of geometrical changes are provided for the main knee ligaments and tendons after careful fibre mapping.

Estimation of spatial-temporal gait parameters in level walking based on a single accelerometer: validation on normal subjects by standard gait analysis.

This paper investigates the ability of a single wireless inertial sensing device stuck on the lower trunk to provide spatial-temporal parameters during level walking. The 3-axial acceleration signals were filtered and the timing of the main gait events identified. Twenty-two healthy subjects were analyzed with this system for validation, and the estimated parameters were compared with those obtained with state-of-the-art gait analysis, i.e. stereophotogrammetry and dynamometry. For each side, from four to six gait cycles were measured with the device, of which two were validated by gait analysis. The new acquisition system is easy to use and does not interfere with regular walking. No statistically significant differences were found between the acceleration-based measurements and the corresponding ones from gait analysis for most of the spatial-temporal parameters, i.e. stride length, stride duration, cadence and speed, etc.; significant differences were found for the gait cycle phases, i.e. single and double support duration, etc. The system therefore shows promise also for a future routine clinical use.

Joint line is well restored when navigation surgery is performed for total knee arthroplasty.

PURPOSE: The incorrect restoration of the joint line during TKA can result in joint instability, anterior knee pain, limited range of motion, and joint stiffness. The joint line level is usually measured only on pre- and post-operative radiographs. Current knee navigation systems can now potentially support intra-operatively joint line restoration by controlling the exact amount of the bone-cartilage removed and the corresponding overall thickness of the components implanted. The aim of this study was to assess how well the joint line level is restored and the tibiofemoral overstuffing prevented when standard knee surgical navigation is used carefully also with these purposes. Intra-operative measurements during navigated TKA were taken. METHODS: Sixty-seven primary TKAs were followed prospectively. The variation before and after prosthesis component implantation of the joint line level, both in the femoral and tibial reference, was measured intra-operatively by an instrumented probe. Overstuffing was measured as the difference between the overall craniocaudal thickness of the femoral and tibial prosthesis components inserted and the thickness of the bone-cartilage removed. RESULTS: A significant elevation in the joint line level after prosthesis implantation was found with respect to the tibial reference (1.9 ± 2.4 mm, mean ± SD), very little to the femoral reference (0.3 ± 2.1 mm), perhaps accounted for the femur-first operative technique utilized. Overstuffing was on the average of 2.2 ± 3.0 mm. CONCLUSIONS: These results suggest that a knee navigation system can also support well a proper restoration of the joint line level and limit the risk of overstuffing when relevant measurements are taken carefully during operation. LEVEL OF EVIDENCE: III.

A one-degree-of-freedom spherical mechanism for human knee joint modelling.

In-depth comprehension of human knee kinematics is necessary in prosthesis and orthosis design and in surgical planning but requires complex mathematical models. Models based on one-degree-of-freedom equivalent mechanisms have replicated well the passive relative motion between the femur and tibia, i.e. the knee joint motion in virtually unloaded conditions. In these mechanisms, fibres within the anterior and posterior cruciate and medial collateral ligaments were taken as isometric and anatomical articulating surfaces as rigid. A new one-degree-of-freedom mechanism is analysed in the present study, which includes isometric fibres within the two cruciates and a spherical pair at the pivot point of the nearly spherical motion as measured for this joint. Bounded optimization was applied to the mechanism to refine parameter first estimates from experimental measurements on four lower-limb specimens and to best-fit the experimental motion of these knees. Relevant results from computer simulations were compared with those from one previous equivalent mechanism, which proved to be very accurate in a former investigation. The spherical mechanism represented knee motion with good accuracy, despite its simple structure. With respect to the previous more complex mechanism, the less satisfactory results in terms of replication of natural motion were counterbalanced by a reduction of computational costs, by an improvement in numerical stability of the mathematical model, and by a reduction of the overall mechanical complexity of the mechanism. These advantages can make the new mechanism preferable to the previous ones in certain applications, such as the design of prostheses, orthoses, and exoskeletons, and musculoskeletal modelling of the lower limb.