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Background Decreased strength and increased stiffness of the quadriceps have been associated with a higher risk of developing knee osteoarthritis (OA) in elders. Dynamic joint stiffness (DJS) represents collective resistance from active and passive knee structures for dynamic knee motions. Elevated sagittal knee DJS has been associated with worsening of cartilage loss in knee OA patients. Altered quadriceps properties may affect DJS, which could be a mediator for associations between quadriceps properties and knee OA. Hence, this study aimed to examine whether DJS and quadriceps properties would be associated with the development of clinical knee OA over 24 months, and to explore the mediation role of DJS in associations between quadriceps properties and knee OA. Methods This was a prospective cohort study with 162 healthy community-dwelling elders. Gait analysis was conducted to compute DJS during the loading response phase. Quadriceps strength and stiffness were evaluated using a Cybex dynamometer and shear-wave ultrasound elastography, respectively. Knee OA was defined based on clinical criteria 24 months later. Logistic regression with generalized estimating equations was used to examine the association between quadriceps properties and DJS and incident knee OA. Mediation analysis was performed to explore the mediation role of DJS in associations between quadriceps properties and the incidence of knee OA. Results A total of 125 participants (65.6 ± 4.0 years, 58.4% females) completed the 24-month follow-up, with 36 out of 250 knees identified as clinical knee OA. Higher DJS (OR = 1.86, 95%CI: 1.33–2.62), lower quadriceps strength (1.85, 1.05–3.23), and greater quadriceps stiffness (1.56, 1.10–2.21) were significantly associated with a higher risk of clinical knee OA. Mediation analysis showed that the DJS was not a significant mediator for the associations between quadriceps properties and knee OA. Conclusions Higher sagittal knee dynamic joint stiffness, lower quadriceps strength, and greater quadriceps stiffness are potential risk factors for developing clinical knee OA in asymptomatic elders. Associations between quadriceps properties and knee OA may not be mediated by dynamic joint stiffness. Interventions for reducing increased passive properties of the quadriceps and knee joint stiffness may be beneficial for maintaining healthy knees in the aging population.

First metatarsocuneiform arthrodesis is one of the surgical interventions to correct hallux valgus, especially those with hypermobile first ray. There is lacking of biomechanical investigations to assess this operation. The objective of this study was to explore the functional restoration and the risk of non-union after the surgery via finite element analysis. A three-dimensional foot model was constructed from a female aged 28 via magnetic resonance imaging. Thirty bones and encapsulated bulk tissue were modeled. Walking stance was simulated by the gait analysis data of the same participant. Parts of the first metatarsal and cuneiform were resected and the bone graft was assigned with the same stiffness as adjacent bones to resemble the surgery of first metatarsocuneiform arthrodesis. The third principal stress of the first metatarsal at midstance (25% stance) and push off (60% stance) was increased by 76% and 139% respectively after the operation, while that of the second metatarsal was decreased by 14% and 66%. The operation reduced the medial deviation of the first metatarsal head by about 3.5mm during initial push off (60% stance). Besides, the bone graft could experience tensile stress inferiorly (26.51MPa). In conclusion, the increase of stress on the first metatarsal and the reduced medial excursion of the first metatarsal head after the simulated operation reflected that metatarsocuneiform arthrodesis could restore the load-bearing function of the first ray. However, inter-fragmentary compression could not be guaranteed. The appropriate course of hardware and non-weight-bearing protocol should be noted and further investigated.

Patients with knee osteoarthritis walk with reduced speed and knee flexion excursion in the early stance phase. A slow walking speed is also associated with falls in older adults. A novel vision-based smartphone application could potentially facilitate the early detection of knee osteoarthritis and fall prevention. This study aimed to test the validity and reliability of the app-captured gait speed and peak knee flexion during the initial stance phase of gait. Twenty adults (aged 23–68 years) walked at self-selected comfortable walking speeds while the gait speed and knee flexion were simultaneously measured using retroreflective sensors and Xsens motion trackers and the app in two separate sessions for validity and reliability tests. Pearson’s r correlation and Bland–Altman plots were used to examine the correlations and agreements between the sensor- and app-measured outcomes. One-sample t-tests were performed to examine whether systematic bias existed. The intraclass correlation coefficient (ICC) was calculated to assess the test–retest reliability of the app. Very high correlations were found between the sensor and app measurements for gait speed (r = 0.98, p < 0.001) and knee flexion (r = 0.91–0.92, all p < 0.001). No significant bias was detected for the final app version. The app also showed a good to excellent test–retest reliability for measuring the gait speed and peak knee flexion (ICC = 0.86–0.94). This vision-based smartphone application is valid and reliable for capturing the walking speed and knee flexion during the initial stance of gait, potentially aiding in the early detection of knee osteoarthritis and fall prevention in community living locations.

Hallux valgus is a common foot problem affecting nearly one in every four adults. Generalized ligament laxity was proposed as the intrinsic cause or risk factor toward the development of the deformity which was difficult to be investigated by cohort clinical trials. Herein, we aimed to evaluate the isolated influence of generalized ligament laxity on the deterioration using computer simulation (finite element analysis). We reconstructed a computational foot model from a mild hallux valgus participant and conducted a gait analysis to drive the simulation of walking. Through parametric analysis, the stiffness of the ligaments was impoverished at different degrees to resemble different levels of generalized ligament laxity. Our simulation study reported that generalized ligament laxity deteriorated hallux valgus by impairing the load-bearing capacity of the first metatarsal, inducing higher deforming force, moment and malalignment at the first metatarsophalangeal joint. Besides, the deforming moment formed a deteriorating vicious cycle between hallux valgus and forefoot abduction and may result in secondary foot problems, such as flatfoot. However, the metatarsocuneiform joint did not show a worsening trend possibly due to the overriding forefoot abduction. Controlling the deforming load shall be prioritized over the correction of angles to mitigate deterioration or recurrence after surgery.

Three-dimensional (3D) ear morphology is critical for the design of in-the-ear hearing aids, earphones, transcutaneous auricular vagus nerve stimulation (taVNS) electrodes, and auricular reconstruction, yet most existing ear shape models still rely on manually placed landmarks. Here, a fully annotation-free pipeline is presented for constructing a 3D ear atlas and statistical shape model (SSM) of the auricular bowl from 50 surface meshes. Individual ears are iteratively registered to a current atlas using rigid the iterative closest point (ICP) algorithm followed by a bidirectional thin-plate spline (BiTPS) deformation, and dense surface correspondences are established by nearest-neighbour mapping. Registration quality is quantified using mean and maximum nearest-neighbour distance, symmetric Chamfer-L2 distance and coverage. Furthermore, SSM-derived bowl height and width are validated against manual 3D mesh measurements in Geomagic Design X. Across five atlas iterations, the BiTPS pipeline substantially reduces registration errors and increases coverage, and principal component analysis (PCA) derived dimensions show excellent agreement with manual measurements (Pearson r≥0.98, ICC ≥0.98). The proposed framework yields a stable, anatomically plausible ear atlas and an interpretable low-dimensional SSM without manual landmarks, providing a computational basis for the geometric optimization of ear-related medical and wearable devices.

Background Lower limb malalignment is associated with gait kinematics, but there is limited information on the relationship between gait kinematics and tibial torsion in individuals with knee osteoarthritis (OA). This study aimed to investigate possible associations between tibial torsion and early stance kinematics during gait in people with mild and moderate medial knee OA. Methods Forty-seven participants (age: 62.1 ± 6.0 years; female/male: 37/10) diagnosed with medial knee OA were recruited from a regional hospital. Thirty of them had mild and seventeen had moderate knee OA. Lower limb alignment including tibial torsion and valgus/varus alignment were assessed by an EOS biplaner X-ray system with participants in weight-bearing position. Lower limb kinematics during gait was captured using the Vicon motion analysis system. The associations were estimated by partial Pearson correlation coefficient test. Results Our results indicated that external tibial torsion was related to early stance knee flexion excursion in participants with moderate knee OA ( r  = -0.58, p  = 0.048), but not in participants with mild knee OA (r = 0.34, p  = 0.102). External tibial torsion was associated with external foot progression angle ( r  = 0.48, p  = 0.001), and knee varus/valgus alignment was associated with knee flexion excursion ( r  = -0.39, p  = 0.010) in all participants. Conclusions Both horizontal and frontal lower limb alignments were associated with knee flexion excursion at early stance of gait cycle in participants with medial knee OA. The distal rotational profile of lower limb would likely affect knee motion in sagittal plane. It implies that people with moderate knee OA could possibly benefit from correction of rotational alignment of lower limb.

Background In aging muscles, altered elastin and collagen type III and extracellular matrix may be responsible for the age-related increase in muscle stiffness, which may compromise muscle force production. Indeed, cross-sectional studies have compared quadriceps stiffness between older and younger adults, yet their findings are contradictory. We aim to longitudinally observe quadriceps stiffness/strength changes, and to examine how those changes are associated in elders. Methods This was a prospective longitudinal observation. Community-dwelling adults were recruited if they were aged 60–80 years and capable of walking 10 m independently. We excluded participants with knee injury/surgery, knee/hip joint replacement, cognitive impairment, or neurological conditions. Quadriceps stiffness and strength were assessed at baseline and the follow-up, using shear-wave ultrasound elastography and a Cybex dynamometer, respectively. Paired t-tests were used to examine changes in quadriceps stiffness and strength from baseline to the follow-up. Linear regression was performed to investigate the association between age-related changes in quadriceps stiffness and strength. Repeated measures ANOVA was used to assess differences in stiffness changes across rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM). Results A total of 172 eligible participants (age: 65.7 ± 4.0 years; 64.0% females) completed the baseline and 18-month follow-up assessments. Quadriceps stiffness increased by 0.76 (95% CI: 0.56, 0.97) kPa, while quadriceps strength decreased by -0.15 (-0.18, -0.12) Nm/kg. Estimated annual changes in quadriceps stiffness and strength were 9.14% (7.02, 11.26) and − 7.95% (-9.78, -6.12), respectively. Greater increase in quadriceps stiffness was significantly associated with larger strength reduction in females (R² adjusted = 0.106; P  = 0.021). RF stiffness underwent the most obvious increase, followed by VL and VM (1.41, 0.62, 0.26 kPa, P  < 0.001). However, only increased quadriceps stiffness (0.76 > 0.71 kPa), particularly the RF stiffness (1.41 > 1.24 kPa), exceeded minimum detectable changes over this 18-month observation. Conclusions Quadriceps stiffness is increased with aging, and it is associated with strength decrements in female older adults. Age-related increases in quadriceps stiffness are most prominent in RF, followed by VL and VM. Alongside muscle strengthening, interventions for reducing age-related increases in quadriceps stiffness may be important in geriatric rehabilitation.

While foot orthosis is suggested to improve rearfoot motion in running, little information is known about forefoot biomechanics. The objective of this study was to examine the effects of arch-support orthoses with various heel lift manipulation on the loading rate, spatiotemporal, and forefoot joint mechanics using a skin marker set model. Fifteen male habitual rearfoot strikers ran at their selected speeds on an instrumented treadmill in four foot orthoses conditions: flat-control, D2 (2 mm heel lift, arch-support), D6 (6 mm heel lift, arch-support), and D10 (10 mm heel lift, arch-support). A repeated measures ANOVA was performed to examine any significant difference in each of the tested variables, with α = 0.05. Wearing D10 led to smaller maximum loading rate than D2 (p < 0.001) and control (p = 0.002). For sagittal plane, D10 had larger rearfoot touchdown dorsiflexion than D2 (p = 0.027) and control (p = 0.007) and larger in D6 than control (p = 0.025). For frontal plane, wearing D10 demonstrated larger rearfoot frontal RoM than D2 (p = 0.018) and peak forefoot eversion than D6 (p = 0.047) and control (p = 0.048). Furthermore, the forefoot frontal range of motion was lowest when wearing D6. For joint moment, wearing control orthosis exhibited larger peak rearfoot eversion moment than D6 (p = 0.035), but smaller peak knee extension moment than D2 (p = 0.025) and D10 (p = 0.010). These findings indicate that the use of arch-support orthoses would alter the running mechanics that are related to injury potential. Lower heel lift orthoses led to alternations to most of the biomechanical variables than higher heel lift orthoses. Further longitudinal study seems necessary to optimize arch-support orthoses design in running.

Red is perceived as a “winning color”, which may influence actual and perceived performances in sports, but little effort has been done to assess the added value on colored foot insoles in basketball movements. This study examined if colored foot insole would influence perceived comfort and lower extremity biomechanics during drop landing. Nineteen male basketball players performed drop landing trials with different insoles (red arch-support, white arch-support, and white-flat) and landing heights (0.45 and 0.61 m). Two-way (Insole x Height) ANOVAs with repeated measures were performed on each of the knee and ankle angles and moments variables. Wearing red arch-support insoles induced better perception of forefoot and rearfoot cushioning and overall comfort but smaller plantarflexion moment than the white-flat insoles (p < 0.05). Increased landing height was related to higher ground reaction loading, sagittal flexion angles, range of motion, and joint moments but smaller ankle eversion (p < 0.05). Findings indicate that foot insoles might have influenced comfort perception and joint kinetics, but not joint kinematics. The use of red color in foot insoles could potentially maximize the effectiveness of foot insoles in a way that alters comfort perception and motor control during landing, with implications for risk of injury.

Information on the internal stresses/strains in the human foot and the pressure distribution at the plantar support interface under loading is useful in enhancing knowledge on the biomechanics of the ankle–foot complex. While techniques for plantar pressure measurements are well established, direct measurement of the internal stresses/strains is difficult. A three-dimensional (3D) finite element model of the human foot and ankle was developed using the actual geometry of the foot skeleton and soft tissues, which were obtained from 3D reconstruction of MR images. Except the phalanges that were fused, the interaction among the metatarsals, cuneiforms, cuboid, navicular, talus, calcaneus, tibia and fibula were defined as contact surfaces, which allow relative articulating movement. The plantar fascia and 72 major ligaments were simulated using tension-only truss elements by connecting the corresponding attachment points on the bone surfaces. The bony and ligamentous structures were embedded in a volume of soft tissues. The encapsulated soft tissue was defined as hyperelastic, while the bony and ligamentous structures were assumed to be linearly elastic. The effects of soft tissue stiffening on the stress distribution of the plantar surface and bony structures during balanced standing were investigated. Increases of soft tissue stiffness from 2 and up to 5 times the normal values were used to approximate the pathologically stiffened tissue behaviour with increasing stages of diabetic neuropathy. The results showed that a five-fold increase in soft tissue stiffness led to about 35% and 33% increase in the peak plantar pressure at the forefoot and rearfoot regions, respectively. This corresponded to about 47% decrease in the total contact area between the plantar foot and the horizontal support surface. Peak bone stress was found at the third metatarsal in all calculated cases with a minimal increase of about 7% with soft tissue stiffening.