Moderate-Heeled Shoes and Knee Joint Torques Relevant to the Development and Progression of Knee Osteoarthritis

Gender differences in foot and ankle sporting injuries: A systematic literature review

BACKGROUND

In response to the all-time high of female sports participation, there has been increasing scientific discourse and media interest in women's sporting injuries in recent years. In gender comparable sports the rate of foot and ankle injury for women is higher than for men. There are intrinsic and extrinsic factors which may explain this difference.

METHODS

A systematic literature search was performed according to the PRISMA guidelines of PubMed, Ovid EMBASE and OVID MEDLINE. Relevant key terms were used to narrow the scope of the search prior to screening. Case reports, review articles, paediatric patients, non foot and ankle injuries and combat sports were excluded. We used dual author, two pass screening to arrive at final included studies.

RESULTS

2510 articles were screened after duplicate exclusion. 104 were included in this literature review. We identified lack of reporting gender difference in the literature.We identified that females have higher frequency and severity of injury. We provide an overview of our current understanding of ankle ligament complex injuries, stress fractures, ostochondral lesions of the talus and Achilles tendon rupture. We expand on the evidence of two codes of football, soccer and Australian rules, as a "case study" of how injury patterns differ between genders in the same sport. We identify gender specific characteristics including severity, types of injury, predisposing risk factors, anatomy, endocrinology and biomechanics associated with injuries. Finally, we examine the effect of level of competition on female injury patterns.

CONCLUSIONS

There is a lack of scientific reporting of gender differences of foot and ankle injuries. Female athletes suffer foot and ankle injuries at higher rates and with greater severity compared to males. This is an under-reported, yet important area of orthopaedics and sports medicine to understand, and hence reduce the injury burden for female athletes.

Impact of biomechanics on therapeutic interventions and rehabilitation for major chronic musculoskeletal conditions: A 50-year perspective

The pivotal role of biomechanics in the past 50 years in consolidating the basic knowledge that underpins prevention and rehabilitation measures has made this area a great spotlight for health practitioners. In clinical practice, biomechanics analysis of spatiotemporal, kinematic, kinetic, and electromyographic data in various chronic conditions serves to directly enhance deeper understanding of locomotion and the consequences of musculoskeletal dysfunctions in terms of motion and motor control. It also serves to propose straightforward and tailored interventions. The importance of this approach is supported by myriad biomechanical outcomes in clinical trials and by the development of new interventions clearly grounded on biomechanical principles. Over the past five decades, therapeutic interventions have been transformed from fundamentally passive in essence, such as orthoses and footwear, to emphasizing active prevention, including exercise approaches, such as bottom-up and top-down strengthening programs for runners and people with osteoarthritis. These approaches may be far more effective inreducing pain, dysfunction, and, ideally, incidence if they are based on the biomechanical status of the affected person. In this review, we demonstrate evidence of the impact of biomechanics and motion analysis as a foundation for physical therapy/rehabilitation and preventive strategies for three chronic conditions of high worldwide prevalence: diabetes and peripheral neuropathy, knee osteoarthritis, and running-related injuries. We conclude with a summary of recommendations for future studies needed to address current research gaps.

Effects of high-heeled shoes on lower extremity biomechanics and balance in females: a systematic review and meta-analysis

BACKGROUND

High-heeled shoes (HHS) are widely worn by women in daily life. Limited quantitative studies have been conducted to investigate the biomechanical performance between wearing HHS and wearing flat shoes or barefoot. This study aimed to compare spatiotemporal parameters, kinematics, kinetics and muscle function during walking and balance between wearing HHS and flat shoes or barefoot.

METHODS

According to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement, PubMed Medline, Cochrane, EMBASE, CINAHL Complete and Web of Science databases were searched from the earliest record to December 2021. A modified quality index was applied to evaluate the risk of bias, and effect sizes with 95% confidence intervals were calculated as the standardized mean differences (SMD). Potential publication bias was evaluated graphically using funnel plot and the robustness of the overall results was assessed using sensitivity analyses.

RESULTS

Eighty-one studies (n = 1501 participants) were included in this study. The reduced area of support requires the body to establish a safer and more stable gait pattern by changing gait characteristics when walking in HHS compared with walking in flats shoes or barefoot. Walking in HHS has a slight effect on hip kinematics, with biomechanical changes and adaptations concentrated in the knee and foot-ankle complex. Females wearing HHS performed greater ground reaction forces earlier, accompanied by an anterior shift in plantar pressure compared with those wearing flat shoes/barefoot. Furthermore, large effect sizes indicate that wearing HHS resulted in poor static and dynamic balance.

CONCLUSION

Spatiotemporal, kinematic, kinetic and balance variables are affected by wearing HHS. The effect of specific heel heights on women's biomechanics would benefit from further research.

Effects of Occasional and Habitual Wearing of High-Heeled Shoes on Static Balance in Young Women

The purpose of this study was to examine the effects of occasional and habitual wearing of high-heeled shoes on static balance in young women. Groups of habitual high-heel wearers and non-wearers (n = 7 in both groups) were asked to stand quietly on a force platform without shoes (WS condition) or with high heels (heel area 1 cm², heel height 7 cm) (HH condition). During the trials, the center-of-pressure (CoP) position in the anterior-posterior direction was measured, and its root mean square (as a measure of postural sway magnitude, CoP_RMS) and mean velocity (as a measure of regulatory activity, CoP_MV) were calculated. To further examine the effect of high-heel wearing on the temporal aspects of slow and fast processes in static balance, the CoP sway was decomposed into low- (below 0.5 Hz) and high- (above 0.5 Hz) frequency components, and then spectral analysis was performed. Results showed that the CoP_RMS was not significantly different between the groups or between the shoe conditions, indicating that wearing high heels with a heel height of 7 cm did not increase the magnitude of postural sway, irrespective of high-heel experience. The CoP_MV was significantly larger in the HH condition than in the WS condition, whereas it was not significantly different between the groups. This result indicates that wearing high heels increased the amount of regulatory activity in both habitual wearers and non-wearers. The spectral analysis further showed that habitual high-heel wearers showed significantly decreased rate of regulatory activity than non-wearers, both while standing with and without high heels. These results suggest that use-dependent changes in static balance control are evident in both high-heeled and without shoes conditions.

Effect of Heeled Shoes on Joint Symptoms and Knee Osteoarthritis in Older Adults: A 5-Year Follow-Up Study

OBJECTIVE

Our aims were to examine the effects of heeled shoes on incident knee osteoarthritis (OA) and joint pain.

METHODS

We used longitudinal data from the Chingford 1000 Women Study (Chingford Study), a prospective cohort of women aged 50 years or older. Participants with musculoskeletal disorders and/or a history of knee-related injury/surgery were excluded. Participants were followed for up to 5 years for incident outcomes including 1) radiographic knee OA (RKOA) and 2) joint pain (feet, knees, hips, and back). Footwear data, including ever worn heels of 2 inches or more and daytime/evening hours (per week) spent wearing heeled shoes over five decades (ages <20 years, 20-30 years, 30-40 years, and >50 years), were available at Year 10 whereas knee radiographs and joint symptom data were also collected at Year 15. Cumulative time spent wearing heeled shoes was calculated for women reporting ever-use of heeled shoes (≥2 inches). Multiple logistic regression was used to examine the relationship between exposures and outcomes (from Year 10 to Year 15).

RESULTS

A total of 356 women were eligible at Year 10 with a median (interquartile range) age of 60 (56-65) years. Compared with non-use, ever-use of heeled shoes (≥2 inches) was not associated with incident RKOA (1.35; 95% confidence interval: 0.56-3.27). No associations were observed between increasing cumulative time spent wearing heels and incident outcomes.

CONCLUSION

Compared with the non-use of heeled shoes, ever-use of heels (≥2 inches) was not associated with incident RKOA and incident joint symptoms. Further, increasing cumulative time spent wearing heels was not associated with any of our outcomes.

Increased knee flexion and varus moments during gait with high-heeled shoes: A systematic review and meta-analysis

BACKGROUND

High-heeled shoes have been thought to alter lower extremity joint mechanics during gait, however its effects on the knee remain unclear.

RESEARCH QUESTION

This systematic review and meta-analysis aimed to determine the effects of high-heeled shoes on the sagittal- and frontal-plane knee kinetics/kinematics during gait.

METHODS

1449 studies from 6 databases were screened for the following criteria: 1) healthy adult females, 2) knee joint kinematics/kinetics reported for the early stance phase during gait under varying shoe heel heights (including barefoot). Excluded studies included those mixing different shoe styles in addition to altering the heel heights. A total of 14 studies (203 subjects) met the selection criteria, resulting in 51 and 21 Cohen's d effect sizes (ESs) comparing the differences in knee sagittal- (flexion) and frontal-plane (varus) moment/angle, respectively, between shoes with higher heels and shoes with lower heels/barefoot.

RESULTS

Meta-analyses yielded a significant medium-to-large effect of higher heels compared to lower heels on increasing knee flexion moment (overall ES = 0.83; P < 0.01), flexion angle (overall ES=0.46; P < 0.01), and varus moment (overall ES=0.52; P < 0.01) during the early stance phase of gait. The results of meta-regressions used to explore factors explaining the heterogeneity among study ESs revealed that a greater ES in the knee flexion moment was associated with an elevated heel height of the high-heeled shoes (P = 0.02) and greater body mass of the individuals (P = 0.012). A greater ES in the knee varus moment during high-heeled gait was associated with a greater body height (P = 0.003) and mass (P = 0.006).

SIGNIFICANCE

Given the association between increased knee flexion/varus moments and risk of developing knee osteoarthritis (OA), women who wear high-heel shoes frequently and for a long period may be more susceptible to knee OA. Preventive treatments, such as lower extremity muscle strengthening, may help improve shock absorption to decrease knee loading in high-heel users.

Focusing research efforts on the unique needs of women prosthesis users

Introduction

Women with lower limb loss represent a relevant and growing patient cohort with unique rehabilitation needs. These needs are emphasized in a growing body of literature and the most recent Veteran Affairs/Department of Defense clinical practice guidelines.

Prosthetics Challenges

Women with limb loss experience greater dissatisfaction with prosthetic fit, appearance, and types of footwear they can use. There is a lack of prosthetics solutions to accommodate the desire of women to wear different footwear varieties, including high heels. The choice to wear a variety of footwear is important to attire and hence community participation. Despite these recognized challenges, women are still underserved in prosthetics research, which limits available information to guide the rehabilitation process.

Research Initiatives

This narrative review describes considerations of lower limb prosthesis prescription and use by women, and examples of current research to address these topics. Research efforts are beginning to explore factors that contribute to prosthetics prescription for women, and design creative prosthetics solutions to expand the range of available footwear options. Research is still needed to characterize the types of footwear women with limb loss prefer to use, and the effects of prosthesis designs, footwear, and lower limb loss on women mobility outcomes and community participation.

Conclusions

Through targeted research initiatives, scientists and clinicians can be responsive to the specific needs of women to provide evidence-based guidelines for prosthetics prescription and improve the patient-centered care after limb loss.

Is being barefoot, wearing shoes and physical activity associated with knee osteoarthritis pain flares? Data from a usually barefoot Sri Lankan cohort

AIM

To identify the association between hours of being barefoot/wearing footwear, physical activity (PA) and knee osteoarthritis pain flares (KOAF).

METHODS

Persons with a diagnosis of knee osteoarthritis, who reported previous KOAF, were followed up in a 3 months long telephone-based case-crossover study. Exposures to risk factors were assessed every 10 days and whenever the participants experienced a KOAF. Conditional logistic regression examined associations of KOAF with following: hours of being barefoot/using footwear and PA performed (P < .05).

RESULTS

There were 260 persons recruited, of whom 183 continued longitudinal follow up. Of them, 120 persons had at least one valid KOAF and control period. Participants were female (90%) with mean (SD) age and body mass index of 59.9 (7.0) years, 28.0 (5.0) kg/m² respectively. Participants were barefoot for a mean duration of 12.7 hours (SD 4.6) and used footwear for 5.1 (SD 4.7) hours daily; 99% wore heel heights <2.5 cm. Duration of being barefoot, 1 and 2 days before, demonstrated reduced multivariate odds of KOAF (odds ratio [OR] = 0.85; 95% CI 0.80-0.90). Moderate PA performed 1, 2 days prior was associated with a significantly increased risk of KOAF (multivariate OR 4.29; 2.52-7.30 and OR 3.36; 2.01-5.61). Similarly, hours of using footwear 1 and 2 days before flare demonstrated increased odds of KOAF (OR 1.15; 1.07-1.23 and 1.10; 1.03-1.18).

CONCLUSIONS

Increased duration of being barefoot 1 to 2 days before is associated with reduced risk of KOAF. Performing moderate PA 1 to 2 days before was associated with an increased risk of KOAF.

Experimental and numerical investigation of a polypropylene orthotic device for assistance in level ground walking

This study investigates the use of an orthotic device for improving pathologic gait lacking a heel-strike and its effect on the joint loads. The orthosis is fabricated from 10-mm thick polypropylene sheets joined together using a bolted joint. The gait trials are recorded using a Qualisys motion capture system and Kistler's force platform. The data recorded in this study comprise five male and five female participants, executing level ground gait under barefoot, shod and orthotic conditions. Computed tomography reconstructed foot bone-tissue model and computer-aided design model of the orthosis are used to predict the mechanical behaviour with and without orthosis under static loading. A one-way analysis of variance is conducted to compare the peak gait parameters in the early and late stance phase between the three walking conditions. The experimental results show that the orthosis reduces the peak joint forces and the rate of change of moment at the hip, knee and ankle joints. The finite element analysis results present a decrease in foot plantar pressure from 0.74 to 0.32 MPa with orthotic usage. The results of this study indicate that the orthosis can eliminate the heel-ground gap while retaining sufficient ankle motion and providing peak joint force reduction.

Effect of high heel gait on hip and knee-ankle-foot rollover characteristics while walking over inclined surfaces - A pilot study

Given the massive number of individuals wearing high-heeled shoes, understanding the gait biomechanics associated with their use could provide insight into clinically preventable abnormalities. The effects of inclined surfaces on the high-heeled gait have been investigated in the present pilot study, as most walking surfaces encountered in routine life are rarely perfectly level grounded. The rollover shapes of the high-heel shod gait are calculated to obtain the desired results. An adjustable inclined walkway setup was fabricated and comprising fixed slots permitting discrete and variable angle of inclinations (≤30°). The gait trials were recorded for the heel shod walking of ten healthy female volunteers using the three-dimensional motion analysis system by varying the inclination of the fabricated walkway. From the calculated rollover shapes, the necessary radii of the hip and the knee-ankle- foot rollover shapes were obtained and a repeated measures analysis of variance was carried out to establish the existence of correlation between the angle of inclination and rollover radii. The results of the present pilot study show that for high heel-shod walking there exist variable radii of curvature for early and late stance phases and that the same may vary depending upon the inclination. The same information can be used to modify the design of high-heel shoes to improve the stability while retaining their aesthetics.

Shoe design for older adults: Evidence from a systematic review on the elements of optimal footwear

Due to changes in foot morphology and the occurrence of foot deformities and foot pain with ageing, older people frequently wear ill-fitting shoes. This can lead to discomfort and reduced mobility. A review of the literature was performed in Medline, Scopus and Embase with three aims: (a) to evaluate the effects of shoes or shoe elements on the comfort and mobility of older adults, (b) to summarise the evidence-based elements of a safe and comfortable shoe for older adults, and (c) from that, to compile those elements into design recommendations for a safe and comfortable shoe for older adults. Safe elements of footwear include proper anatomical fit, a well-fitting toe box, limited heel height, a broad enough heel, a firm insole and midsole, an outsole with sufficient tread, bevelled heel, firm heel counter with snug fit, and an easy and effective closing mechanism. We conclude that there is a need for shoe design specifically aimed at the foot morphology and demands of older people. The shoe market should increase the availability of well-fitting shoes designed for the older foot and person.

Everyday footwear: An overview of what we know and what we should know on ill-fitting footwear and associated pain and pathology

Footwear has been used to protect feet for millennia with socially exclusive population adopting stylish and fashionable shoes with expensive materials. In terms of historic timeline, only more recently footwear has been worn by all classes in the western world as an integral part of their apparel. Traditionally, footwear has been constructed from natural materials, mainly leather, but has recently benefitted from the flexibility that technology has provided with a plethora materials and new design innovations. Although it has expanded the availability for a variety of consumers, the choice and fit continue to be problematic with many individuals wearing shoes that are ill-fitting. Provision of specific footwear advice for problem feet is poorly evidenced and is heavily practitioner dependant limiting its efficacy. There is limited understanding as to the changes that can occur from regularly wearing footwear that is unsuitable in shape, style and construction which is referred to as ill-fitting. Current research on the effect that everyday footwear has on foot function and pain focuses mainly on women's shoes, particularly high heels. Defining what is a good fitting shoe, that does not damage the foot or mechanics of walking, may need to be individualised, but best fit is based on loose historical parameters rather than research evidence. The aim of this overview is to highlight aspects of current research, establishing what is known about the effect's shoes have on the feet as well as exploring the mythology around footwear fit and advice that is often historical in nature.

Ultrasonographic Evaluation of the Femoral Cartilage, Achilles Tendon, and Plantar Fascia in Young Women Wearing High-Heeled Shoes

BACKGROUND

Specific attention on the musculoskeletal impact of wearing high-heeled shoes (HHS) has mainly focused on knee osteoarthritis and the literature is limited to biomechanical changes. The distal femoral cartilage has not been morphologically studied. Additionally, although heel elevation is coupled with a shear stress at the heel and overloaded calf muscles, Achilles tendon (AT) and plantar fascia (PF) thicknesses have not been assessed either.

OBJECTIVE

To investigate whether the distal femoral cartilage, AT, and PF were different in women wearing HHS and flat-heeled shoes (FHS) and specifically, different in terms of AT/PF and distal femoral cartilage thicknesses.

DESIGN

Cross-sectional observational study.

SETTING

Tertiary care center.

PARTICIPANTS

There were 34 women (mean age; 31.1 ± 6.4, body mass index [BMI]; 21.6 ± 2.4 kg/m² ) in the HHS group and 54 women (mean age; 29.5 ± 7.2 years, BMI 22.5 ± 2.9 kg/m² ) in the FHS group (P = .271, P = .102, respectively). Women wearing shoes with a heel height of >5 cm were enrolled in the HHS group, and those wearing shoes with a heel height of <1.4 cm were included in the FHS group.

MAIN OUTCOME MEASUREMENTS

Distal femoral cartilage from the lateral condyle, intercondylar area and medial condyle (MFC), AT and PF thicknesses, and any abnormalities were evaluated bilaterally by ultrasound.

RESULTS

Within-group comparisons yielded thicker right MFC (P = .022) and left AT (P = .028) only in the HHS group. Between-group comparisons yielded thicker left AT in the HHS group (P = .040). PF thicknesses were similar both within and between group comparisons (all P > .05). Right AT thickness was positively correlated with right (r = .469, P = .005) and left (r = .402, P = .018) PF thicknesses only within the HHS group. Only calcaneal irregularity/spur was found to be common in the HHS group (P = .038).

CONCLUSIONS

We found thickening of the right MFC and left AT in those wearing HHS, whereas PF thickness was not significantly different between those wearing HHS and those wearing FHS.

LEVEL OF EVIDENCE

III.

The influence of heel height related on quality of life on the foot in a sample of women

Many women have worn high-heel shoes (HHS) at some point in their lives and many wear them on a daily basis, with higher prevalence between 39% and 78% observed in institutional and clinical settings. The purpose of this study was to describe and compare the scores obtained with regard to foot health and health in general in a sample of women that use HHS as opposed to a sample of women without HHS with normalized reference values. A sample of 120 participants with a mean age of 41.94 ± 13.912 came to a health center where self-reported data were registered. The subjects with and without HHS were determined and the scores obtained were compared in the Foot Health Status Questionnaire (FHSQ). This questionnaire is made of 13 questions that assess 4 health domains of the feet, namely pain, function, general health and footwear. The women in the HHS group showed a worse quality of life related to health in general and to foot health specifically. Differences between the two groups were evaluated by means of a t-test for independent samples, showing statistical significance (P<0.01). Women with HHS present a negative impact on the quality of life related to foot health.

Creative prosthetic foot selection enables successful ambulation in stiletto high heels

BACKGROUND

Walking in high heels presents biomechanical challenges, yet they remain part of many women's attire. However, women with a lower limb amputation are limited in available footwear options. Case description and methods: This case study is in response to one patient's assertion that she walked better and more symmetrically in heels than flat shoes with her below-knee prosthesis. She underwent gait analysis in athletic shoes and 10-cm stiletto high heels worn with a pediatric running foot to determine if these claims could be substantiated through biomechanical measures. Global gait asymmetry indices were calculated. Findings and outcomes: Asymmetry indices were nearly identical between athletic shoes and heels but joint-level findings differed substantially. Ankle mechanics were more symmetrical in heels but hip mechanics were less.

CONCLUSION

The maintenance of symmetry in stiletto high heels does not imply maintenance of gait quality, as high heels are known to adversely affect some components walking mechanics. Clinical relevance Returning to high-heel wear is achievable for prosthesis users. Accommodations can be made using creativity in prosthetic foot selection to enable successful ambulation; however, attention to gait mechanics may be important for patient safety.

Walking variations in healthy women wearing high-heeled shoes: Shoe size and heel height effects

BACKGROUND

The use of high heels is widespread in modern society in professional and social contests. Literature showed that wearing high heels can produce injurious effects on several structures from the toes to the pelvis. No studies considered shoe length as an impacting factor on walking with high heels.

RESEARCH QUESTION

The aim of this study is to evaluate walking parameters in young healthy women wearing high heels, considering not only the heel height but also the foot/shoe size.

METHODS

We evaluate spatio-temporal, kinematic and kinetic data, collected using a 8-camera motion capture system, in a sample of 21 healthy women in three different walking conditions: 1) barefoot, 2) wearing 12 cm high heel shoes independently from shoe size, and 3) wearing shoes with heel height based on shoe size, keeping the ankles' plantar flexion angle constant. The main outcome measures were: spatio-temporal parameters, gait harmony measurement, range of motion, flexion and extension maximal values, power and moment of lower limb joints.

RESULTS

Comparing the three walking conditions, the Mixed Anova test, showed significant differences between both high heeled conditions (variable and constant height) and barefoot in spatio-temporal, kinematic and kinetic parameters.

SIGNIFICANCE

Regardless of the shoe size, both heeled conditions presented a similar gait pattern and were responsible for negative effects on walking parameters. Considering our results and the relevance of the heel height, further studies are needed to identify a threshold, over which it is possible to observe that wearing high heels could cause harmful effects, independently from the foot/shoe size.

Using Gold-standard Gait Analysis Methods to Assess Experience Effects on Lower-limb Mechanics During Moderate High-heeled Jogging and Running

A limited number of studies have explored lower-limb biomechanics during high-heeled jogging and running, and most studies have failed to clarify the wearing experience of subjects. This protocol describes the differences in lower-limb kinematics and ground reaction force (GRF) between experienced wearers (EW) and inexperienced wearers (IEW) during moderate high-heeled jogging and running. A three-dimensional (3D) motion analysis system with a configured force platform was used to synchronously capture lower-limb joint movements and GRF. 36 young females volunteered to participate in this study and were asked about high-heeled shoe-wearing experience, including frequency, duration, heel types, and heel heights. Eleven who had the experience of 3 to 6 cm heels for a minimum of three days per week (6 h per day) for at least two years and eleven who wore high heels less than twice per month participated. Subjects performed jogging and running at comfortable low and high speeds, respectively, with the right foot completely stepping onto a force platform when passing by along a 10 m walkway. EW and IEW adopted different biomechanical adaptations while jogging and running. IEW exhibited a generally larger range of joint movement, while EW showed a dramatically larger loading rate of GRF during running. Hence, further studies on the lower-limb biomechanics of high-heeled gait should strictly control the wearing experience of the subjects.

Does Heel Height Cause Imbalance during Sit-to-Stand Task: Surface EMG Perspective

The purpose of this study was to determine whether electromyography (EMG) muscle activities around the knee differ during sit-to-stand (STS) and returning task for females wearing shoes with different heel heights. Sixteen healthy young women (age = 25.2 ± 3.9 years, body mass index = 20.8 ± 2.7 kg/m²) participated in this study. Electromyography signals were recorded from the two muscles, vastus medialis (VM) and vastus lateralis (VL) that involve in the extension of knee. The participants wore shoes with five different heights, including 4, 6, 8, 10, and 12 cm. Surface electromyography (sEMG) data were acquired during STS and stand-to-sit-returning (STSR) tasks. The data was filtered using a fourth order Butterworth (band pass) filter of 20–450 Hz frequency range. For each heel height, we extracted median frequency (MDF) and root mean square (RMS) features to measure sEMG activities between VM and VL muscles. The experimental results (based on MDF and RMS-values) indicated that there is imbalance between vasti muscles for more elevated heels. The results are also quantified with statistical measures. The study findings suggest that there would be an increased likelihood of knee imbalance and fatigue with regular usage of high heel shoes (HHS) in women.

Differences in lower limb muscle activation patterns during Sit to Stand Task for different heel heights

The purpose of this study was to investigate differences in lower limb muscle activation patterns for females wearing shoes with different heel heights during Sit to Stand Task (STS). Ten female participants with no prior history of neurological disorders participated in this study. Surface electromyography (sEMG) characteristics were recorded for four different heel heights (ranging from 4cm to 10cm) while performing the STS task. Signal processing analysis suggests that muscle activities increases on elevated heel heights, which may induce muscle imbalance for frequent STS tasks. In addition, results of muscle utilisation (percentage) for different heel heights suggest that lower limb muscles tend to compensate in order to maintain postural balance.

The Effects of Heel Height on Head Position, Long-Term Average Spectra, and Perceptions of Female Singers

Female singers often wear high heels for auditions and performances. Heel height research in non-singing contexts indicates that wearing heels can affect body alignment and head position. Studies in orthodontics, sleep apnea, and voice science suggest that head and neck positioning can alter the vocal tract. The purpose of this study was to assess the effects, if any, of heel height (barefoot, 10.16-cm stilettos) on three angles of singer head position (calculated from C7-tragus-nasion), long-term average spectra data, and perceptual data (questionnaire) acquired from female (N = 30) soloists during alternating periods of silence and singing. Results indicated that all participants (100%) significantly decreased head position angle measurements (inferior and posterior head and neck movement) when singing in high heels compared with singing barefoot. Participants, on average, significantly increased head position angle measurements (superior and anterior head and neck movement) when singing compared with standing silently, and did so to a greater degree when transitioning from silent heels to singing heels compared with transitioning from silent barefoot to singing barefoot. Long-term average spectra data indicated significant spectral energy differences between barefoot and high heel singing conditions across participants. Most participants (n= 21, 70.00%) indicated they felt comfortable and sang their best while barefoot. Results of this study, the second in a series of experiments addressing the effects of shoe heel height on female singers' vocal production, were discussed in terms of application to vocal pedagogy and directions for future research.

Effects of duration of wearing high-heeled shoes on plantar pressure

In the present study we investigated the effects of different durations of using high-heeled shoes on plantar pressure and gait. A questionnaire survey and dynamic plantar pressure measurements were performed in 20 control females and 117 females who had worn high-heeled shoes for a long time. According to the duration of using high-heeled shoes (as specified in the questionnaire), subjects were divided into a control group and five groups with different durations of use (i.e. <2years, 2-5years, 6-10years, 11-20years and >20years). Parameters, including peak pressure, impulse and pressure duration, in different plantar regions were measured with the Footscan pressure plate. The 2-5years group had smaller midfoot contact areas for both feet and higher subtalar joint mobility, while the 6-10years group had larger midfoot contact areas for both feet and prolonged foot flat phase during gait. The peak pressure and impulse under the second and fourth metatarsus were increased with the prolonged wearing of high-heeled shoes, and the pressure and impulse under the midfoot were substantially reduced in the 2-5years group. The findings suggest that long-term use of high-heeled shoes can induce changes in arch morphology: the longitudinal arch tends to be elevated within 2-5years; the longitudinal arch tends to be flattened within 6-10years; and the forefoot latitudinal arch tends to collapse in more than 20years.

Lower limb mechanics during moderate high-heel jogging and running in different experienced wearers

The aim of this study is to investigate the differences in lower limb kinematics and kinetics between experienced (EW) and inexperienced (IEW) moderate high-heel wearers during jogging and running. Eleven experienced female wearers of moderate high-heel shoes and eleven matched controls participated in jogging and running tests. A Vicon motion analysis system was used to capture kinematic data and a Kistler force platform was used to collect ground reaction force (GRF). There were no significant differences in jogging and running speed respectively. Compared with IEW, EW adopted larger stride length (SL) with lower stride frequency (SF) at each corresponding speed. During running, EW enlarged SL significantly while IEW increased both SL and SF significantly. Kinematic data showed that IEW had generally larger joint range of motion (ROM) and peak angles during stance phase. Speed effect was not obvious within IEW. EW exhibited a significantly increased maximal vertical GRF (Fz2) and vertical average loading rate (VALR) during running, which was potentially caused by overlong stride. These suggest that both EW and IEW are at high risk of joint injuries when running on moderate high heels. For wearers who have to do some running on moderate high heels, it is crucial to control joint stability and balance SL and SF consciously.

Long-term use of minimal footwear on pain, self-reported function, analgesic intake, and joint loading in elderly women with knee osteoarthritis: A randomized controlled trial

BACKGROUND

Efforts have been made to retard the progressive debilitating pain and joint dysfunction in patients with knee osteoarthritis. We aimed to evaluate the therapeutic effect of a low-cost minimalist footwear on pain, function, clinical and gait-biomechanical aspects of elderly women with knee osteoarthritis.

METHODS

Throughout a randomized, parallel and controlled clinical trial, fifty-six patients with medial knee osteoarthritis were randomly allocated to an intervention (n=28) or control group (n=28), and assessed at baseline and after three and six months. The intervention involved wearing Moleca(®) footwear for at least 6h/day, 7 days/week, over 6 months. The pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index was the primary outcome. The secondary outcomes were the other subscales, Lequesne score, distance walked in 6 min, knee oedema and effusion, knee adduction moment and paracetamol intake. Intention-to-treat analysis was performed using two-way casewise ANOVA (< .05) and Cohen's d coefficient.

FINDINGS

Intervention group showed improvement in pain (effect size: 1.41, p<.001), function (effect size: 1.22, p=.001), stiffness (effect size: 0.76, p=.001), Lequesne score (effect size: 1.07, p<.001), and reduction by 21.8% in the knee adduction moment impulse (p=.017) during gait wearing Moleca(®). The analgesic intake was lower in the intervention group.

INTERPRETATION

The long-term use of Moleca(®) footwear relieves pain, improves self-reported function, reduces the knee loading while wearing Moleca(®), refrains the increase of analgesic intake in elderly women with knee osteoarthritis and can be considered as a conservative mechanical treatment option. ClinicalTrials.gov (NCT01342458).

Barefoot vs common footwear: A systematic review of the kinematic, kinetic and muscle activity differences during walking

Habitual footwear use has been reported to influence foot structure with an acute exposure being shown to alter foot position and mechanics. The foot is highly specialised thus these changes in structure/position could influence functionality. This review aims to investigate the effect of footwear on gait, specifically focussing on studies that have assessed kinematics, kinetics and muscle activity between walking barefoot and in common footwear. In line with PRISMA and published guidelines, a literature search was completed across six databases comprising Medline, EMBASE, Scopus, AMED, Cochrane Library and Web of Science. Fifteen of 466 articles met the predetermined inclusion criteria and were included in the review. All articles were assessed for methodological quality using a modified assessment tool based on the STROBE statement for reporting observational studies and the CASP appraisal tool. Walking barefoot enables increased forefoot spreading under load and habitual barefoot walkers have anatomically wider feet. Spatial-temporal differences including, reduced step/stride length and increased cadence, are observed when barefoot. Flatter foot placement, increased knee flexion and a reduced peak vertical ground reaction force at initial contact are also reported. Habitual barefoot walkers exhibit lower peak plantar pressures and pressure impulses, whereas peak plantar pressures are increased in the habitually shod wearer walking barefoot. Footwear particularly affects the kinematics and kinetics of gait acutely and chronically. Little research has been completed in older age populations (50+ years) and thus further research is required to better understand the effect of footwear on walking across the lifespan.

Development of inexpensive prosthetic feet for high-heeled shoes using simple shoe insole model

The large majority of prosthetic feet are aimed at low-heeled shoes, with a few models allowing a heel height of up to 5 cm. However, a survey by the American Podiatric Medical Association indicates that most women wear heels over 5 cm; thus, current prosthetic feet limit most female prosthesis users in their choice. Some prosthetic foot components are heel-height adjustable; however, their plantar surface shapes do not change to match the insole shapes of the shoes with different heel heights. The aims of the study were therefore (1) to develop a model that allows prediction of insole shape for various heel height shoes in combination with different shoe sizes and (2) to develop and field-test low-cost prototypes of prosthetic feet whose insole shapes were based on the new model. An equation was developed to calculate insole shapes independent of shoe size. Field testing of prototype prosthetic feet fabricated based on the equation was successful and demonstrated the utility of the equation.

Effects of high heel wear and increased weight on the knee during walking

Knee osteoarthritis (OA), a leading cause of disability, is more prevalent in women than men. Wearing high heeled shoes has been implicated as a potential contributing factor for the higher lifetime risk of osteoarthritis in women. This study tests the hypotheses that changes to knee kinematics and kinetics observed during high heeled walking increase in magnitude with increasing heel height and are accentuated by a 20% increase in weight. Fourteen healthy females were tested using marker-based gait analysis in combinations of footwear (flat athletic shoe, 3.8 cm and 8.3 cm heeled shoes) and weight (with and without 20% bodyweight vest). At preferred walking speed, knee flexion angle at heel-strike and midstance increased with increasing heel height and weight. Maximum knee extension moment during loading response decreased with added weight; maximum knee extension moment during terminal stance decreased with heel height; maximum adduction moments increased with heel height. Many of the changes observed with increasing heel height and weight were similar to those seen with aging and OA progression. This suggests that high heel use, especially in combination with additional weight, may contribute to increased OA risk in women.

A survey of footwear advice, beliefs and wear habits in people with knee osteoarthritis

Background

Expert opinion recommends cushioned and supportive footwear for people with knee osteoarthritis (OA). However, little is known about the footwear advice people receive from healthcare professionals, or the beliefs and footwear habits of people with knee OA. This study aimed to determine i) what types of shoes people are advised to wear for their knee OA and by whom; ii) establish which types of shoes people with knee OA believe are best for managing their knee OA symptoms and (iii) which shoes they wear most often.

Methods

204 people with symptomatic knee OA completed an online survey. The survey comprised 14 questions asking what footwear advice people had received for their knee OA and who they received it from, individual beliefs about optimal footwear styles for their knee OA symptoms and the types of footwear usually worn.

Results

Only one third (n = 69, 34%) of participants reported receiving footwear advice for their knee OA, and this was most frequently received from a podiatrist (n = 47, 68%). The most common advice was to wear sturdy/supportive shoes (n = 96, 47%) or shoes with arch supports (n = 84, 41%). These were also amongst the shoe styles that participants believed were best for their knee OA (n = 157 (77%) and n = 138 (68%) respectively). The type of shoes most frequently worn were athletic (n = 131, 64%) and sturdy/supportive shoes (n = 116, 57%).

Conclusions

Most people with knee OA who completed our survey had not received advice about footwear for their knee OA symptoms. Our participants typically believed that sturdy/supportive shoes were best for their knee OA and this shoe style was most frequently worn, which is reflective of expert opinion. Future research is needed to confirm whether sturdy/supportive shoes are indeed optimal for managing symptoms of knee OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13047-014-0043-8) contains supplementary material, which is available to authorized users.

Effect of rocker-soled shoes on parameters of knee joint load in knee osteoarthritis

PURPOSE

This study evaluated the immediate effects of rocker-soled shoes on parameters of the knee adduction moment (KAM) and pain in individuals with knee osteoarthritis (OA).

METHODS

Three-dimensional gait analysis was performed on 30 individuals (mean (SD): age, 61 (7) yr; 15 (50%) male) with radiographic and symptomatic knee OA under three walking conditions in a randomized order: i) wearing rocker-soled shoes (Skechers Shape-ups), ii) wearing non-rocker-soled shoes (ASICS walking shoes), and iii) barefoot. Peak KAM and KAM angular impulse were measured as primary indicators of knee load distribution. Secondary measures included the knee flexion moment (KFM) and knee pain during walking.

RESULTS

Peak KAM was significantly lower when wearing the rocker-soled shoes compared with that when wearing the non-rocker-soled shoes (mean difference (95% confidence interval), -0.27 (-0.42 to -0.12) N·m/BW × Ht%; P < 0.001). Post hoc tests revealed no significant difference in KAM impulse between rocker-soled and non-rocker-soled shoe conditions (P = 0.13). Both peak KAM and KAM impulse were significantly higher during both shoe conditions compared with those during the barefoot condition (P < 0.001). There were no significant differences in KFM (P = 0.36) or knee pain (P = 0.89) between conditions.

CONCLUSIONS

Rocker-soled shoes significantly reduced peak KAM when compared with non-rocker-soled shoes, without a concomitant change in KFM, and thus may potentially reduce medial knee joint loading. However, KAM parameters in the rocker-soled shoes remained significantly higher than those during barefoot walking. Wearing rocker-soled shoes did not have a significant immediate effect on walking pain. Further research is required to evaluate whether rocker-soled shoes can influence symptoms and progression of knee OA with prolonged wear.

The effects of high heeled shoes on female gait: a review

Walking is the most common form of human locomotion. From a motor control perspective, human bipedalism makes the task of walking extremely complex. For parts of the step cycle, there is only one foot on the ground, so both balance and propulsion are required in order for the movement to proceed smoothly. One condition known to compound the difficulty of walking is the use of high heeled shoes, which alter the natural position of the foot-ankle complex, and thereby produce a chain reaction of (mostly negative) effects that travels up the lower limb at least as far as the spine. This review summarises recent studies that have examined acute and chronic effects of high heels on balance and locomotion in young, otherwise healthy women. Controversial issues, common study limitations and directions for future research are also addressed in detail.

A comparison of gait biomechanics of flip-flops, sandals, barefoot and shoes

BACKGROUND

Flip-flops and sandals are popular choices of footwear due to their convenience. However, the effects of these types of footwear on lower extremity biomechanics are still poorly understood. Therefore, the objective of this study was to investigate differences in ground reaction force (GRF), center of pressure (COP) and lower extremity joint kinematic and kinetic variables during level-walking in flip-flops, sandals and barefoot compared to running shoes.

METHODS

Ten healthy males performed five walking trials in the four footwear conditions at 1.3 m/s. Three-dimensional GRF and kinematic data were simultaneously collected.

RESULTS

A smaller loading rate of the 1st peak vertical GRF and peak propulsive GRF and greater peak dorsiflexion moment in early stance were found in shoes compared to barefoot, flip-flops and sandals. Barefoot walking yielded greater mediolateral COP displacement, flatter foot contact angle, increased ankle plantarflexion contact angle, and smaller knee flexion contact angle and range of motion compared to all other footwear.

CONCLUSIONS

The results from this study indicate that barefoot, flip-flops and sandals produced different peak GRF variables and ankle moment compared to shoes while all footwear yield different COP and ankle and knee kinematics compared to barefoot. The findings may be helpful to researchers and clinicians in understanding lower extremity mechanics of open-toe footwear.

Influência de diferentes tipos de calçado na atividade eletromiográfica do músculo quadríceps de mulheres ao subir e descer degrau

INTRODUÇÃO: A síndrome da dor femoropatelar (SDFP) é caracterizada por dor difusa na região retropatelar, aumentada durante realização de tarefas diárias, tais como subir e descer escadas e ajoelhar. A SDFP tem maior prevalência em mulheres jovens e sua etiologia não é totalmente conhecida. OBJETIVO: Avaliar a influência do uso de diferentes tipos de calçados na atividade dos músculos estabilizadores da patela durante as tarefas de subir e descer degrau. MATERIAIS E MÉTODOS: Participaram do estudo dez mulheres saudáveis e dez mulheres com SDFP. As voluntárias realizaram as tarefas de subir e descer um degrau em três situações: descalças, usando tênis e salto alto de 10 cm. Durante a realização das tarefas, foi registrada com eletrodos superficiais a atividade eletromiográfica dos músculos vasto medial oblíquo (VMO), vasto lateral (VL) e reto femoral (RF). A comparação intergrupos foi realizada com o teste t não pareado; para a análise intragrupo, utilizou-se ANOVA com medidas repetidas e post hoc Tukey, todos com um nível de significância de 5%. RESULTADOS: Os resultados demonstraram, no grupo controle, aumento da atividade do VMO nas tarefas concêntrica e excêntrica realizadas com salto alto. No entanto, no grupo SDFP, a atividade do VMO não foi influenciada em nenhuma das condições testadas. Não foram observadas diferenças estatísticas na razão VMO/VL e no tempo de ativação dos músculos. CONCLUSÃO: Os resultados sugerem que em mulheres assintomáticas uso do calçado de salto alto modificou a atividade de todos os músculos. Entretanto, mulheres com SDFP não apresentaram alterações no VMO.

Gait deviations in individuals with inflammatory joint diseases and osteoarthritis and the usage of three-dimensional gait analysis

This chapter describes three-dimensional gait analysis and common gait deviations in adults with rheumatoid arthritis (RA) and osteoarthritis (OA). Furthermore, we describe changes in gait deviations following surgical and non-surgical interventions. Gait analysis is used to define gait deviations and to evaluate varying surgical approaches, types of surgeries and non-pharmacologic interventions. Most studies examine gait in adults with knee OA. Limitations of existing studies include small samples, poor selection of controls, sample heterogenecity, lack of baseline gait assessments and inconsistency in measurement. Across studies, time and distance parameters are generally used to provide a global measure of gait deviations. Individuals with RA and OA in the lower extremities exhibit reduced walking speed/cadence and decreased motion and moments in relation to healthy subjects. Future research should include larger sample sizes, the use of proper controls, pre- and post-assessments and identify gait abnormalities early in the disease process to minimise long-term consequences.

Medial arch supports do not significantly alter the knee adduction moment in people with knee osteoarthritis

OBJECTIVE

This study aimed to evaluate the immediate effects of medial arch supports on indices of medial knee joint load (the peak external knee adduction moment (KAM) and knee adduction angular (KAA) impulse) and knee pain during walking in people with medial knee osteoarthritis (OA).

DESIGN

Twenty-one people with medial compartment OA underwent gait analysis in standardised athletic shoes wearing (1) no medial arch supports and (2) prefabricated medial arch supports, in random order. Outcomes were the first and second peaks in the external KAM, the KAA impulse and severity of knee pain during testing. Outcomes were compared across conditions using paired t tests (gait data) and Wilcoxon Signed Ranks test (pain data).

RESULTS

There were no significant changes in either first or second peak KAM, or in the KAA impulse, with the addition of medial arch supports (all P > 0.05). Considerable individual variation in response to the arch supports was observed across participants. There was no immediate change in knee pain during walking when medial arch supports were worn (P = 0.56).

CONCLUSIONS

This study showed no mean change in any of the measured indices of medial knee load with medial arch supports. No immediate changes in knee pain were evident.

The pathophysiology of osteoarthritis: a mechanical perspective on the knee joint

Osteoarthritis (OA) is the most frequent cause of disability in the United States, with the medial compartment of the knee being most commonly affected. The initiation and progression of knee OA is influenced by many factors, including kinematics. In response to loading during weight-bearing activity, cartilage in healthy knees demonstrates spatial adaptations in morphology and mechanical properties. These adaptations allow certain regions of the cartilage to respond to loading; other regions are less well suited to accommodate loading. Alterations in normal knee kinematics shift loading from cartilage regions adapted for loading to regions less well suited for loading, which leads to the initiation and progression of degenerative processes consistent with knee OA. Kinematic variables that are associated with the development, progression, and severity of knee OA are the adduction moment and tibiofemoral rotation. Because of its strong correlation with disease progression and pain, the peak adduction moment during gait has been identified as a target for treatment design. Gait modification offers a noninvasive option for seeking significant reductions. Gait modification has the potential to reduce pain and slow the progression of medial compartment knee OA.

Joint loading decreased by inexpensive and minimalist footwear in elderly women with knee osteoarthritis during stair descent

OBJECTIVE

Previous studies indicate that flexible footwear, which mimics the biomechanics of walking barefoot, results in decreased knee loads in patients with knee osteoarthritis (OA) during walking. However, the effect of flexible footwear on other activities of daily living, such as descending stairs, remains unclear. Our objective was to evaluate the influence of inexpensive and minimalist footwear (Moleca) on knee adduction moment (KAM) during stair descent of elderly women with and without knee OA.

METHODS

Thirty-four elderly women were equally divided into an OA group and a control group (CG). Stair descent was evaluated in barefoot condition, while wearing the Moleca, and while wearing heeled shoes. Kinematics and ground reaction forces were measured to calculate KAM by using inverse dynamics.

RESULTS

The OA group experienced a higher KAM during midstance under the barefoot condition (233.3%; P = 0.028), the Moleca (379.2%; P = 0.004), and heeled shoes (217.6%; P = 0.007). The OA group had a similar knee load during early, mid, and late stance with the Moleca compared with the barefoot condition. Heeled shoes increased the knee loads during the early-stance (versus barefoot [16.7%; P < 0.001] and versus the Moleca [15.5%; P < 0.001]), midstance (versus barefoot [8.6%; P = 0.014] and versus the Moleca [9.5%; P = 0.010]), and late-stance phase (versus barefoot [10.6%; P = 0.003] and versus the Moleca [9.2%; P < 0.001]). In the CG, the Moleca produced a knee load similar to the barefoot condition only during the early-stance phase.

CONCLUSION

Besides the general foot protection, the inexpensive and minimalist footwear contributes to decreasing knee loads in elderly women with OA during stair descent. The loads are similar to the barefoot condition and effectively decreased when compared with heeled shoes.

Effect of footwear on the external knee adduction moment - A systematic review

CONTEXT

Footwear modifications have been investigated as conservative interventions to decrease peak external knee adduction moment (EKAM) and pain associated with knee osteoarthritis (OA).

OBJECTIVE

To evaluate the literature on the effect of different footwear and orthotics on the peak EKAM during walking and/or running.

METHODS

A systematic search of databases resulted in 348 articles of which 33 studies were included.

RESULTS

Seventeen studies included healthy individuals and 19 studies included subjects with medial knee OA. Quality assessment (modified Downs and Black quality index) showed an (average±SD) of 73.1±10.1%. The most commonly used orthotic was the lateral wedge, with three studies on the medial wedge. Lateral wedging was associated with decreased peak EKAM in healthy participants and participants with medial knee OA while there is evidence for increased peak EKAM with the use of medial wedges. Modern footwear (subjects' own shoe, "stability" and "mobility" shoes, clogs) were likely to increase the EKAM compared to barefoot walking in individuals with medial knee OA. Walking in innovative shoes ("variable stiffness") decreased the EKAM compared to control shoes. Similarly, shoes with higher heels, sneakers and dress shoes increased EKAM in healthy individuals compared to barefoot walking.

CONCLUSIONS

Further development may be needed toward optimal footwear for patients with medial knee OA with the aim of obtaining similar knee moments to barefoot walking.

The influence of heel height on patellofemoral joint kinetics during walking

Although wearing high-heeled shoes has long been considered a risk factor for the development for patellofemoral pain (PFP) in women, patellofemoral joint kinetics during high-heeled gait has not been examined. The purpose of this study was to determine if heel height increases patellofemoral joint loading during walking. Eleven healthy women (mean age 25.0±3.1 yrs) participated. Lower extremity kinematics and kinetics were obtained under 3 different shoe conditions: low heel (1.27 cm), medium heel (6.35 cm), and high heel (9.53 cm). Patellofemoral joint stress was estimated using a previously described biomechanical model. Model outputs included patellofemoral joint reaction force, patellofemoral joint stress and utilized contact area as a function of the gait cycle. One-way ANOVAs with repeated measures were used to compare the model outputs and knee joint angles among the 3 shoe conditions. Peak patellofemoral joint stress was found to increase significantly (p=0.002) with increasing heel height (low heel: 1.9±0.7 MPa, medium heel: 2.6±1.2 MPa, and high heel: 3.6±1.5 MPa). The increased patellofemoral joint stress was mainly driven by an increase in joint reaction force owing to higher knee extensor moments and knee flexion angles. Our findings support the premise that wearing high-heeled shoes may be a contributing factor with respect to the development of PFP.

The influence of heel height on lower extremity kinematics and leg muscle activity during gait in young and middle-aged women

The aim of this study was to evaluate the changes in electromyographic (EMG) activity of the lower limb muscles, and hip, knee and ankle kinematics during gait while wearing low- (4-cm) and high-heeled (10-cm) shoes in 31 young and 15 middle-aged adult women. We observed an increase in knee flexion and decrease in ankle eversion associated with elevated heel heights suggesting that compensatory mechanisms attenuating ground reaction forces may be compromised during gait with higher-heeled shoes. Additionally, we observed increased muscle activity during high-heeled gait that may exacerbate muscle fatigue. Collectively, these findings suggest that permanent wearing of heeled footwear could contribute to muscle overuse and repetitive strain injuries.