Purpose Patellofemoral pain syndrome is a common orthopedic trauma among runners. It is unclear whether patellofemoral joint stress (PFJS) is the highest (or lowest) when the knee joint flexion angle and extension moment are in combination under the condition that vastus medialis (VM) activation decreases. This study aimed to investigate the effects of changes in the PFJ contact area by decreasing the activation of the VM muscle on PFJS. Methods A PFJ sagittal model was used to quantify PFJ reaction force and PFJS. The PFJ model and mathematical modelling procedure were used to quantify PFJS based on previous studies. The simulation ranges were set to knee joint flexion angles of 10–45 degrees and extension moments of 0–240 Nm. PFJS was calculated for the normal condition (NC) and decrease condition (DC) in VM activation. Results When the knee joint angle and knee joint moment were at the maximum, the PFJS showed the maximum value under both conditions (NC; 14.9 N/cm2, DC; 16.4 N/cm2). PFJS was found to be higher in DC than that in NC for all simulation ranges. Conclusions Decreased VM activation may be involved in the mechanism of patellofemoral pain syndrome. In addition, the results of this study provide evidence that clinicians can enhance VM to relieve pain in patients with patellofemoral pain syndrome.

Purpose The objectives of the current study were to propose a calibration method for accurate augmented reality visualisation using an optical see-through head-mounted display, and to qualitatively evaluate visualisation accuracy for the application in computer assisted surgery. Methods An adaptation of stereo single-point active alignment method was proposed as the calibration procedure together with verification Three tests were performed: display of points in 3D space, on the plane, and on the surface of a skull phantom on inexperience users ( 5 participants) and experienced users ( 17 participants). Results The highest accuracy of visualization was obtained for skull phantom visualisation for an inexperienced user (3.00 mm, std 0.75 mm), while the lowest accuracy was obtained in a 3D visualisation test for an inexperienced user (22.95 mm, std 18.04 mm). The largest error was related to the depth component and amounted to 18.49 mm, std 18.10 mm for an inexperienced user. Conclusions It is possible to achieve relatively high visualisation accuracy (less than 5 mm for visualisation in space) for selected users but providing it for the group of inexperienced users seems to remain a major challenge. The accuracy of point indication can be substantially and statistically significantly increased by visualising objects on surfaces. The proposed methods and obtained results can serve as a basis for further implementation of augmented reality visualisation on an optical see-through head-mounted display in applications requiring high-quality augmented reality guidance of manual tasks.

Purpose Cutting maneuvers are important actions in multidirectional sports but associated with noncontact anterior cruciate ligament (ACL) injuries. This study aimed to investigate the effect of different foot strike patterns and cutting angles on knee kinematics and kinetics. Methods Twenty healthy male team sports athletes performed cuts with maximum speed at three angles (45°, 90°, and 135°) with different foot strike patterns (rearfoot strike [RFS] and forefoot strike [FFS]). A three-dimensional motion capture system combined with a force plate was used to collect makers trajectory and ground reaction force (GRF). Vertical GRF, and knee joint angles and moments were compared among these cutting tasks. Results Regardless of foot strike patterns, increased knee flexion angle, knee valgus moment, and knee internal rotation moment were observed during cutting to sharper angles (p < 0.001). At 90° and 135°, the FFS condition remained in a varus position and showed lower knee flexion moment than the RFS condition (p ≤ 0.004). However, no significant differences in knee kinematic and kinetic variables were found between foot strike patterns during cutting to 45°. Conclusions These findings suggest that sharper cutting angles potentially increase the risk of ACL injury. Compared with the RFS pattern, the FFS pattern induces a slight knee varus angle and a lower knee flexion moment at sharper angles, which might further reduce the load placed on the knee.

Purpose Rowing engages large muscle groups, and EMG analysis is used to assess athletes' condition and refine sports technique. The aim of the experiment was to evaluate the muscle activation level during different phases of the rowing cycle on an ergometer. Methods In a study involving one professional and five amateurs, the mean EMG amplitudes from the quadriceps, gastrocnemius, biceps, and triceps brachii were analyzed during different phases of rowing. A comparison was made between the degree of muscle engagement during the exercise between the professional and inexperienced individuals, as well as among the different individuals during recordings obtained at different rowing speeds. The correlation coefficient between the values recorded using a strain gauge and the EMG amplitude recorded from the surface of the biceps and triceps brachii muscles was evaluated. Results The muscle activation pattern during rowing has a predictable character. A difference in the muscle activation pattern during rowing between the professional and amateurs was observed. The EMG signal is correlated with the force recorded by the resistive strain gauge only in the experienced rower at a pace of 20 and 25 cycles per minute. Conclusions Electromyographic analysis can be useful for assessing the correctness of rowing techniques. The activation pattern of muscles during rowing has a predictable nature. The force generated by the participants increases with an increase in rowing frequency.

Purpose The study aimed to analyze the tarsus and knee setting in 3-year-old girls and boys, taking into account the six-month age ranges. Methods The study involved 800 children (400 girls, 400 boys) recruited from randomly selected preschools in the in the Podkarpackie region. Study group was divided into two age ranges: 1st group (children aged 3.00-3.49 years) and 2nd group (children aged 3.50-3.99 years). Baseline goniometer (Fei Fabrication Ltd., USA) was used as primary research tool. The data were analyzed based on Mann Whitney U test and Student’s t test for independent samples. Results Sex differences concern only the tibio-calcaneal angle in children in the 2nd age group (right: p<0.001) and left p<0.001). Statistically significant differences in both girls (right lower limb: p=0.003; left lower limb: p=0.002), and boys (right lower limb: p=0.001; left lower limb: p=0.001) were found. Conclusions Boys were characterized by greater valgus of the tarsus of the right and left foot than girls. Knees of girls and boys in the 1st age group were characterized by greater valgus, compared to children from the 2nd age group.

Purpose Experimental studies on comparing the ability of polyurethane cushions of three arbitrary selected thicknesses to minimize vibrations transmitted from the wheelchair to its user. Methods Measurements were made during passive motion on five different surfaces often found in public spaces. Two tests were carried out during the measurements. In the first test, the sensor was located directly on the surface of the wheelchair seat. In the second test, a polyurethane cushion was placed on the seat, on which the measuring sensor was then placed. Results The study showed that regardless of the surface on which the wheelchair user moves, the threshold defined in the ISO standard for frequencies in the range from 4 to 40 Hz is exceeded. However, thanks to the use of polyurethane cushions, vibration damping is visible for frequencies ranging from 10 to 40 Hz. The impact of the user’s weight on the magnitude of the perceived vibrations was also observed. Conclusions Studies show that wheelchair users are exposed to whole body vibration that can negatively affect their health. Cushions made of polyurethane seems to be a promising solution to reduce whole body vibration in the frequency range that is burdensome and harmful to human health.

Purpose Pedicle screw fixation has been considered a suitable surgical intervention for addressing a diverse range of indications involving the lumbar spinal segments, but the impact of bilateral pedicle screw internal fixation combinations on the stability and flexibility of vertebral body motion has been limited. This study aimed to the effect of pedicle screw internal fixation on the mechanical characterization of lumbar multi-segmental vertebra under various loading conditions. Methods Porcine lumbar multi-segmental vertebral samples were tested with three pedicle screw fixation groups including rigid fixation, mixed fixation and dynamic fixation under four loading conditions of flexion, posterior extension, left-side bend, and right-side bend at bending moments of 3 N⋅m, 4 N⋅m, 5 N⋅m and 6 N⋅m, respectively. The stability and flexibility of the segmental motion were statistically analysed. Results The flexibility of joint activities increased using one-way dynamic pedicle screws with the range of motion for mixed fixation and dynamic fixation increased by 30% and 47% in left side bend and by 25% and 73% in right side bend, respectively. The range of motion for lumbar vertebra increased with higher moments. Conclusions The flexibility of joint activities was improved using one-way dynamic pedicle screws and the mixed fixation was considered moderate providing larger flexibility in right and left side bend without compromising stabilization. The results of this study are useful for providing theoretical reference for clinical selection of surgical plans.

Purpose The main aim of the researches was the three-dimensional morphological assessment of the mandible in children. Methods The research group consisted of 34 infants from 21 to 417 days of age (0-13 months). Models of the mandibles were developed on the basis of tomographic images. Characteristic anatomical points were marked on the models, on the basis of which characteristic distances and angles were calculated, determining the length, width and height of the mandible as well as its proportion and symmetry. Based on the obtained database, models of mandibular growth in the first year of life in three directions were also developed. Results It was performed the statistical analysis to assess the jaw dimensions in children in the first year of life. The size, shape and proportions of the lower jaws were obtained and analyzed. Conclusions The analysis of the results revealed some significant objective information on the growth and development of the normal mandible.

Purpose Investigation of the relationship between changes in hip-joint center and hip loading pre- and post- total hip arthroplasty (THA) is important in evaluating the effect of surgery on motor function. However, few longitudinal studies comparing pre- and post-THA have been reported. The purpose of this study was to determine the effect of changes in hip-joint center pre- and post-THA on the magnitude and direction of hip-joint contact force during the gait cycle, using a patient-specific musculoskeletal model. Methods The simulation program AnyBody was used to create musculoskeletal models incorporating patient specific hip-joint shape and hip-joint center position for 17 patients. The relationship between the displacement distance of the hip-joint center and the amount of change in hip-joint contact force was examined by correlation analysis. Results A decrease in the medial force (p ≤ 0.049) and an increase in the anterior force (p ≤ 0.001) acting on the hip joint were observed during gait post-THA compared to pre-THA. Mediolateral displacement of the hip-joint center post-THA compared to pre-THA was significantly positively correlated with the difference in anterior hip-joint contact force, and negatively to hip-joint medial contact force. Conclusions Longitudinal observations revealed the effects of change in hip-joint center position induced by THA on the hip-joint contact force during gait. Therefore, the change of hip-joint center position during THA can be an important factor for estimating the improvement of motor function following THA.

Purpose The role of regional hemodynamics in intracranial aneurysms (IAs) hemodynamics and rupture risk has been widely discussed based on numerical models over the past decades. The aim of this paper is to investigate hemodynamics and rupture risk with a complicated IA model. Methods Fluid-structure interaction (FSI) simulations were performed to quantify the hemodynamic characteristics of the established IA models. Hemodynamic parameters, including wall shear stress (WSS), flow velocity, and flow pattern, were calculated and analyzed. Results In this paper, the risk assessment of intracranial aneurysms focuses on the mechanical properties of blood flow and blood vessel walls. Vortex flow and concentrated impact field during blood flow play a decisive role in the rupture and development of aneurysms. The uneven distribution of wall shear stress on the vessel wall has a great influence on growth and rupture. By observing the simulation results of rigid walls, risks can be predicted efficiently and accurately. Conclusions This paper focuses on the relationship between hemodynamics and ruptures risk with a double intracranial aneurysms disease mode and provides a new perspective on the treatment of intracranial aneurysms.