Introducing a new staircase design to quantify healthy knee function during stair ascent and descent

The design, manufacture and validation of a new free standing staircase for motion analysis measurements are described in this paper. The errors in vertical force measurements introduced when the stairs interface with a force plate (FP) are less than 0.6%. The centre of pressure error introduced is less than 0.7 mm compared to the error from the FP. The challenges of introducing stair gait into a clinical trial with a limited number of FPs and time limitations for assessment sessions are addressed by introducing this cost effective solution.

The staircase was used in a study to measure non-pathological knee function of 10 subjects performing stair ascent and descent. The resulting knee kinematics and knee joint moments are in agreement with previous studies. The kinematic and joint moment profiles provide a normative range, which will be useful in future studies for identifying alterations in joint function associated with pathology and intervention.     

The Energy Expenditure of Stair Climbing One Step and Two Steps at a Time: Estimations from Measures of Heart Rate

Stairway climbing provides a ubiquitous and inconspicuous method of burning calories. While typically two strategies are employed for climbing stairs, climbing one stair step per stride or two steps per stride, research to date has not clarified if there are any differences in energy expenditure between them. Fourteen participants took part in two stair climbing trials whereby measures of heart rate were used to estimate energy expenditure during stairway ascent at speeds chosen by the participants. The relationship between rate of oxygen consumption () and heart rate was calibrated for each participant using an inclined treadmill. The trials involved climbing up and down a 14.05 m high stairway, either ascending one step per stride or ascending two stair steps per stride. Single-step climbing used 8.5±0.1 kcal min⁻¹, whereas double step climbing used 9.2±0.1 kcal min⁻¹. These estimations are similar to equivalent measures in all previous studies, which have all directly measured The present study findings indicate that (1) treadmill-calibrated heart rate recordings can be used as a valid alternative to respirometry to ascertain rate of energy expenditure during stair climbing; (2) two step climbing invokes a higher rate of energy expenditure; however, one step climbing is energetically more expensive in total over the entirety of a stairway. Therefore to expend the maximum number of calories when climbing a set of stairs the single-step strategy is better.     

A novel design for an instrumented stairway

Kinetics during stair ambulation is currently studied via either the use of sensing elements embedded in the steps of the stairway or simple rigid blocks of different height positioned on top of existing force platforms, typically embedded in a walkway for gait analysis. Neither of these approaches is truly satisfactory for gait analysis laboratories. The first one is expensive and requires setting up a dedicated space. The second approach is limited by the number of platforms utilized in the laboratory for evaluating level walking. This communication proposes a novel design, referred to as "interlaced stairway", that allows one to measure ground reaction force and position of the center of pressure (CoP) for four foot contacts during stair ambulation using only two force platforms embedded in a walkway. Accuracy and precision of the CoP estimates and natural frequency of the stairway structure were derived from experimental data. Test results indicate that the interlaced stairway structure does not appreciably reduce the quality of the measures gathered by the existing force platforms. Specifically, the estimated CoP coordinates show good agreement with the horizontal coordinates of the geometric center of the calibration object utilized to assess accuracy and precision of the CoP estimates (max difference < 6 mm). The natural frequency of the stairway structure is lower than the one for the unloaded force platform but higher than the frequency components of interest in stair ambulation analysis.     

A dynamic force analysis system for climbing of large primates

Registering substrate reaction forces from primates during climbing requires the design and construction of customized recording devices. The technical difficulties in constructing a reliable apparatus hinder research on the kinetics of primate locomotion. This is unfortunate since arboreal locomotion, especially vertical climbing, is an important component of the hominoid locomotor repertoire. In this technical paper, we describe a custom-built climbing pole that allows recordings of dynamic 3-dimensional forces during locomotion on horizontal and sloping substrates and during vertical climbing. The pole contains an instrumented section that can readily be modified and enables us to register forces of a single limb or multiple limbs in a broad range of primates. For verification, we constructed a similar set-up (which would not be usable for primates) using a conventional force plate. Data for a human subject walking on both set-ups were compared. The experimental set-up records accurate and reliable substrate reaction forces in three orthogonal directions. Because of its adjustability, this type of modular set-up can be used for a great variety of primate studies. When combining such kinetic measurements together with kinematic information, data of great biomechanical value can be generated. These data will hopefully allow biological anthropologists to answer current questions about primate behaviours on vertical substrates.     

Influence of step-height and body mass on gastrocnemius muscle fascicle behavior during stair ascent

To better understand the role of the ankle plantar flexor muscles in stair negotiation, we examined the effects of manipulation of kinematic and kinetic constraints on the behavior of the gastrocnemius medialis (GM) muscle during stair ascent. Ten subjects ascended a four-step staircase at four different step-heights (changing the kinematic constraints): standard (17 cm), 50% decreased, 50% increased and 75% increased. At the standard height, subjects also ascended the stairs wearing a weighted jacket, adding 20% of their body mass (changing the kinetic constraints). During stair ascent, kinematics and kinetics of the lower legs were determined using motion capture and ground reaction force measurements. The GM muscle fascicle length was measured during the task with ultrasonography. The amount of GM muscle fascicle shortening increased with step-height, coinciding with an increase in ankle joint moment. The increase in body mass resulted in an increased ankle joint moment, but the amount of GM muscle fascicle shortening during the lift-off phase did not increase, instead, the fascicles were shorter over the whole stride cycle. Increasing demands of stair ascent, by increasing step-height or body mass, requires higher joint moments. The increased ankle joint moment with increasing demands is, at least in part, produced by the increase in GM muscle fascicle shortening.     

Forces and moments telemetered from two distal femoral replacements during various activities.

Two distal femoral replacements were instrumented to measure axial force, torque and bending moments in the prosthesis shaft. Data are reported up to 2.5 years for the following activities: uni- and bi-lateral standing, walking, stair climbing and descending, treadmill walking, jogging and jumping. In the first subject the greatest averaged peak shaft forces found were: jogging 3.6Bodyweight (BW), stair descending 3.1BW, walking 2.8BW, treadmill walking 2.75BW, and stair ascending 2.8BW. Bending moments about the antero-posterior axis (varus-valgus) and medio-lateral axis (flexion-extension) peaked in the range 8.5-9.8 and 4.7-7.6BWcm respectively, over the follow-up period. Axial torques peaked in the range 0.2-1.3BWcm, outwardly directed. At most follow-up sessions, forces and moments during jogging were generally greater than those for other gait activities. In the second subject forces and moments were generally only 45-70% of those in the first subject, due to inadequate musculature around the knee. The data can be applied to the design and testing of distal femoral replacements and even to total knee replacements, and contributes to the knowledge of forces acting in the distal femur during activity.     

The demands of stair descent relative to maximum capacities in elderly and young adults.

In this study, we aimed to establish the joint moment and joint range of motion requirements of stair descent and the demands relative to maximal capacities in elderly and young adults. Participants descended a custom-built standard dimension four-step staircase, at their self-selected speed in a step-over manner. Kinetic data were acquired from force platforms embedded into each of the steps and into the floor at the base of the stairs. A motion analysis system was used to acquire kinematic data and joint moments were calculated using the kinematic and kinetic data. Maximum capacities (joint moment and joint range of motion) were assessed using a dynamometer. During stair descent the elderly generated lower absolute ankle joint moments than the young, which enabled them to operate at a similar relative proportion of their maximal capacity compared to young adults (75%). The knee joint moments during stair descent were similar between groups, but the elderly operated at a higher proportion of their maximal capacity (elderly: 42%; young: 30%). Ankle plantarflexion-dorsiflexion angle changes were similar between groups, which meant that the elderly operated at a higher proportion of their maximal assisted dorsiflexion angle. These results indicate that the elderly redistribute the joint moments in order to maintain the task demands within 'safe' limits.     

In vivo knee moments and shear after total knee arthroplasty

Tibiofemoral loading is very important in cartilage degeneration as well as in component survivorship after total knee arthroplasty. We have previously reported the axial knee forces in vivo. In this study, a second-generation force-sensing device that measured all six components of tibial forces was implanted in a 74-kg, 83-year-old male. Video motion analysis, ground reaction forces, and knee forces were measured during walking, stair climbing, chair-rise, and squat activities. Peak total force was 2.3 times body weight (BW) during walking, 2.5 x BW during chair rise, 3.0 x BW during stair climbing, and 2.1 x BW during squatting. Peak anterior shear force at the tibial tray was 0.30 x BW during walking, 0.17 x BW during chair rise, 0.26 x BW during stair climbing, and 0.15 x BW during squatting. Peak flexion moment at the tray was 1.9% BW x Ht (percentage of body weight multiplied by height) for chair-rise activity and 1.7% BW x Ht for squat activity. Peak adduction moment at the tray was -1.1% BW x Ht during chair-rise, -1.3% BW x Ht during squatting. External knee flexion and adduction moments were substantially greater than flexion and adduction moments at the tray. The axial component of forces predominated especially during the stance phase of walking. Shear forces and moments at the tray were very modest compared to total knee forces. These findings indicate that the soft tissues around the knee absorbed most of the external shear forces. Our results highlight the importance of direct measurements of knee forces.     

Analysis of bone–prosthesis interface micromotion for cementless tibial prosthesis fixation and the influence of loading conditions

A lack of initial stability of the fixation is associated with aseptic loosening of the tibial components of cementless knee prostheses. With sufficient stability after surgery, minimal relative motion between the prosthesis and bone interfaces allows osseointegation to occur thereby providing a strong prosthesis-to-bone biological attachment. Finite element modelling was used to investigate the bone–prosthesis interface micromotion and the relative risk of aseptic loosening. It was anticipated that by prescribing different joint loads representing gait and other activities, and the consideration of varying tibial–femoral contact points during knee flexion, it would influence the computational prediction of the interface micromotion. In this study, three-dimensional finite element models were set up with applied loads representing walking and stair climbing, and the relative micromotions were predicted. These results were correlated to in-vitro measurements and to the results of prior retrieval studies. Two load conditions, (i) a generic vertical joint load of 3×body weight with 70%/30% M/L load share and antero-posterior/medial-lateral shear forces, acted at the centres of the medial and lateral compartments of the tibial tray, and (ii) a peak vertical joint load at 25% of the stair climbing cycle with corresponding antero-posterior shear force applied at the tibial–femoral contact points of the specific knee flexion angle, were found to generate interface micromotion responses which corresponded to in-vivo observations. The study also found that different loads altered the interface micromotion predicted, so caution is needed when comparing the fixation performance of various reported cementless tibial prosthetic designs if each design was evaluated with a different loading condition.     

Hip contact forces and gait patterns from routine activities.

In vivo loads acting at the hip joint have so far only been measured in few patients and without detailed documentation of gait data. Such information is required to test and improve wear, strength and fixation stability of hip implants. Measurements of hip contact forces with instrumented implants and synchronous analyses of gait patterns and ground reaction forces were performed in four patients during the most frequent activities of daily living. From the individual data sets an average was calculated. The paper focuses on the loading of the femoral implant component but complete data are additionally stored on an associated compact disc. It contains complete gait and hip contact force data as well as calculated muscle activities during walking and stair climbing and the frequencies of daily activities observed in hip patients. The mechanical loading and function of the hip joint and proximal femur is thereby completely documented. The average patient loaded his hip joint with 238% BW (percent of body weight) when walking at about 4 km/h and with slightly less when standing on one leg. This is below the levels previously reported for two other patients (Bergmann et al., Clinical Biomechanics 26 (1993) 969-990). When climbing upstairs the joint contact force is 251% BW which is less than 260% BW when going downstairs. Inwards torsion of the implant is probably critical for the stem fixation. On average it is 23% larger when going upstairs than during normal level walking. The inter- and intra-individual variations during stair climbing are large and the highest torque values are 83% larger than during normal walking. Because the hip joint loading during all other common activities of most hip patients are comparably small (except during stumbling), implants should mainly be tested with loading conditions that mimic walking and stair climbing.     

Frontal joint dynamics when initiating stair ascent from a walk versus a stand

Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair treads were recorded simultaneously as ten healthy young adults ascended a custom-built staircase. Data were collected from two starting conditions of stair ascent, from a walk (speed: 1.42 ± 0.21 m/s) and from a stand. Results showed that subjects generated greater peak knee abductor moment and greater peak hip abductor moment when initiating stair ascent from a walk. Greater peak joint moments and powers at all joints were also seen while ascending the second ipsilateral step. Particularly, greater peak hip abductor moment was needed to avoid contact of the contralateral limb with the intermediate step by counteracting the pelvic drop on the contralateral side. This could be important for therapists using stair climbing as a testing/training tool to evaluate hip strength in individuals with documented frontal plane abnormalities (i.e. knee and hip osteoarthritis, ACL injury).     

Experimental verification of a computational technique for determining ground reactions in human bipedal stance

We have developed a three-dimensional (3D) biomechanical model of human standing that enables us to study the mechanisms of posture and balance simultaneously in various directions in space. Since the two feet are on the ground, the system defines a kinematically closed-chain which has redundancy problems that cannot be resolved using the laws of mechanics alone. We have developed a computational (optimization) technique that avoids the problems with the closed-chain formulation thus giving users of such models the ability to make predictions of joint moments, and potentially, muscle activations using more sophisticated musculoskeletal models. This paper describes the experimental verification of the computational technique that is used to estimate the ground reaction vector acting on an unconstrained foot while the other foot is attached to the ground, thus allowing human bipedal standing to be analyzed as an open-chain system. The computational approach was verified in terms of its ability to predict lower extremity joint moments derived from inverse dynamic simulations performed on data acquired from four able-bodied volunteers standing in various postures on force platforms. Sensitivity analyses performed with model simulations indicated which ground reaction force (GRF) and center of pressure (COP) components were most critical for providing better estimates of the joint moments. Overall, the joint moments predicted by the optimization approach are strongly correlated with the joint moments computed using the experimentally measured GRF and COP (0.78 < or = r(2) < or = 0.99,median,0.96) with a best-fit that was not statistically different from a straight line with unity slope (experimental=computational results) for postures of the four subjects examined. These results indicate that this model-based technique can be relied upon to predict reasonable and consistent estimates of the joint moments using the predicted GRF and COP for most standing postures.     

Ground reaction force estimation using an insole-type pressure mat and joint kinematics during walking

Kinetic analysis of walking requires joint kinematics and ground reaction force (GRF) measurement, which are typically obtained from a force plate. GRF is difficult to measure in certain cases such as slope walking, stair climbing, and track running. Nevertheless, estimating GRF continues to be of great interest for simulating human walking. The purpose of the study was to develop reaction force models placed on the sole of the foot to estimate full GRF when only joint kinematics are provided (Type-I), and to estimate ground contact shear forces when both joint kinematics and foot pressure are provided (Type-II and Type-II-val). The GRF estimation models were attached to a commercial full body skeletal model using the AnyBody Modeling System, which has an inverse dynamics-based optimization solver. The anterior–posterior shear force and medial–lateral shear force could be estimated with approximate accuracies of 6% BW and 2% BW in all three methods, respectively. Vertical force could be estimated in the Type-I model with an accuracy of 13.75% BW. The accuracy of the force estimation was the highest during the mid-single-stance period with an average RMS for errors of 3.10% BW, 1.48% BW, and 7.48% BW for anterior–posterior force, medial–lateral force, and vertical force, respectively. The proposed GRF estimation models could predict full and partial GRF with high accuracy. The design of the contact elements of the proposed model should make it applicable to various activities where installation of a force measurement system is difficult, including track running and treadmill walking.     

The effect of stride length on the dynamics of barefoot and shod running

A number of interventions and technique changes have been proposed to attempt to improve performance and reduce the number of running related injuries. Running shoes, barefoot running and alterations in spatio-temporal parameters (stride frequency and stride length) have been associated with significant kinematic and kinetic changes, which may have implications for performance and injury prevention. However, because footwear interventions have been shown to also affect spatio-temporal parameters, there is uncertainty regarding the origin of the kinematic and kinetic alterations. Therefore, the purpose of this study was to independently evaluate the effects of shoes and changes in stride length on lower extremity kinetics. Eleven individuals ran over-ground at stride lengths ±5 and 10% of their preferred stride length, in both the barefoot and shod condition. Three-dimensional motion capture and force plate data were captured synchronously and used to compute lower extremity joint moments. We found a significant main effect of stride length on anterior–posterior and vertical GRFs, and sagittal plane knee and ankle moments in both barefoot and shod running. When subjects ran at identical stride lengths in the barefoot and shod conditions we did not observe differences for any of the kinetic variables that were measured. These findings suggest that barefoot running triggers a decrease in stride length, which could lead to a decrease in GRFs and sagittal plane joint moments. When evaluating barefoot running as a potential option to reduce injury, it is important to consider the associated change in stride length.     

Determination of muscle loading at the hip joint for use in pre-clinical testing

The stability of joint endoprostheses depends on the loading conditions to which the implant-bone complex is exposed. Due to a lack of appropriate muscle force data, less complex loading conditions tend to be considered in vitro. The goal of this study was to develop a load profile that better simulates the in vivo loading conditions of a "typical" total hip replacement patient and considers the interdependence of muscle and joint forces. The development of the load profile was based on a computer model of the lower extremities that has been validated against in vivo data. This model was simplified by grouping functionally similar hip muscles. Muscle and joint contact forces were computed for an average data set of up to four patients throughout walking and stair climbing. The calculated hip contact forces were compared to the average of the in vivo measured forces. The final derived load profile included the forces of up to four muscles at the instances of maximum in vivo hip joint loading during both walking and stair climbing. The hip contact forces differed by less than 10% from the peak in vivo value for a "typical" patient. The derived load profile presented here is the first that is based on validated musculoskeletal analyses and seems achievable in an in vitro test set-up. It should therefore form the basis for further standardisation of pre-clinical testing by providing a more realistic approximation of physiological loading conditions.     

Stair climbing is more critical than walking in pre-clinical assessment of primary stability in cementless THA in vitro

Pre-clinical testing of hip endoprostheses is a mandatory requirement before clinical release. Inadequate loading conditions may lead to lower elastic and plastic interface movements than those occurring post-operatively in vivo. This study investigated the influence of patient activity on the primary stability of cementless prostheses with a special emphasis on active simulation of muscle forces. A loading setup, based on validated musculo-skeletal analyses, was used to generate the hip contact force during walking and stair climbing by transmitting muscle forces through the femur. In addition, a loading configuration which only generated the hip contact force occurring during stair climbing at the prosthesis head was simulated. CLS prostheses were implanted in 18 composite femora and subjected to cyclical loading. The relative micro-movements at the bone-prosthesis interface were determined and appeared to be extremely sensitive to the specific patient activity. Compared to walking, stair climbing generated higher micro-movements, with pronounced axial and rotational components. Stair climbing with the femur loaded by the resultant hip contact force only exhibited a characteristic valgus tilt of the stem with significantly lower interface micro-movements than under active simulation of muscle forces. The analyses suggest that stair climbing induced the highest mechanical instability at the bone-prosthesis interface, a level which may compromise the necessary osseointegration process. Active simulation of muscle forces considerably affects the primary stability of cementless hip endoprostheses. Pre-clinical in vitro tests should therefore simulate stair climbing and include muscle activity in the assessment of initial implant stability, otherwise micro-movements may be underestimated and the primary stability overestimated.     

Kinematics and kinetics of the lower extremities of young and elder women during stairs ascent while wearing low and high-heeled shoes

The effect of the heel height on the temporal, kinematic and kinetic parameters was investigated in 16 young and 11 elderly females. Kinematic and kinetic data were collected when the subjects ascended stairs with their preferred speed in two conditions: wearing low-heeled shoes (LHS), and high-heeled shoes (HHS). The younger adults showed more adjustments in forces and moments at the knee and hip in frontal and transverse planes. Besides a few significantly changes in joint forces and moments, the elder group demonstrated longer cycle duration and double stance phase, larger trunk sideflexion and hip internal rotation, less hip adduction while wearing HHS. Most differences in joint motions between two groups were found at the hip and knee either in LHS or HHS condition. Instead, the differences in moment occurred at the hip joint and only in HHS. The interaction of the heel height and age showed the influences of heel height on trunk rotation, hip abduction/adduction, and knee and hip force and moment at the frontal plane depended on age. These phenomena suggest that younger and elderly women adapt their gait and postural control differently during stair ascent (SA) while wearing HHS.     

Estimation of foot joint kinetics in three and four segment foot models using an existing proportionality scheme: Application in paediatric barefoot walking

Recent studies which estimated foot segment kinetic patterns were found to have inconclusive data on one hand, and did not dissociate the kinetics of the chopart and lisfranc joint. The current study aimed therefore at reproducing independent, recently published three-segment foot kinetic data (Study 1) and in a second stage expand the estimation towards a four-segment model (Study 2).Concerning the reproducibility study, two recently published three segment foot models (Bruening et al., 2014; Saraswat et al., 2014) were reproduced and kinetic parameters were incorporated in order to calculate joint moments and powers of paediatric cohorts during gait. Ground reaction forces were measured with an integrated force/pressure plate measurement set-up and a recently published proportionality scheme was applied to determine subarea total ground reaction forces. Regarding Study 2, moments and powers were estimated with respect to the Instituto Ortopedico Rizzoli four-segment model. The proportionality scheme was expanded in this study and the impact of joint centre location on kinetic data was evaluated.Findings related to Study 1 showed in general good agreement with the kinetic data published by Bruening et al. (2014). Contrarily, the peak ankle, midfoot and hallux powers published by Saraswat et al. (2014) are disputed. Findings of Study 2 revealed that the chopart joint encompasses both power absorption and generation, whereas the Lisfranc joint mainly contributes to power generation.The results highlights the necessity for further studies in the field of foot kinetic models and provides a first estimation of the kinetic behaviour of the Lisfranc joint.     

Posturographic analysis through markerless motion capture without ground reaction forces measurement

The ability of the central nervous system to control posture and balance has been used with increasing frequency for the diagnosis and/or treatment evaluation of various neuromuscular diseases. Typically this analysis (Posturographic Analysis) is based on tracking the motion of the center of mass (COM) during quiet standing, however direct measurement of the COM has been commonly approximated using the movement of the center of pressure (COP). The purpose of this study was to apply and validate a new method to track the COM (center of mass) and COP (center of pressure) from a visual hull measured using a markerless motion capture (MMC) method. The method was tested by comparing the calculation of the COP from direct measurements of the COP. The deviations between the methods, below 2 mm, were small relative to the average range of movement guaranteeing a satisfactory signal to noise ratio. This new method requires only kinematic data through MMC method and without the need of a force plate can identify the influence of individual body segments to motion of the COM.     

Effects of soft tissue artifacts on the calculated kinematics and kinetics of the knee during stair-ascent

Biomechanics of the knee during stair-ascent has mostly been studied using skin-marker-based motion analysis techniques, but no study has reported a complete assessment of the soft tissue artifacts (STA) and their effects on the calculated joint center translation, angles and moments at the knee in normal subjects during this activity. This study aimed to bridge the gap. Twelve young adults walked up a three-step stair while data were acquired simultaneously from a three-dimensional motion capture system, a force plate and a dynamic fluoroscopy system. The "gold standards" of poses of the knee were obtained using a 3D fluoroscopy method. The STA of the markers on the thigh and shank were then calculated, together with their effects on the calculated joint center translations, angles and moments at the knee. The STA of the thigh markers were greater than those on the shank, leading to significantly underestimated flexion and extensor moments, but overestimated joint center translations during the first half of the stance phase. The results will be useful for a better understanding of the normal biomechanics of the knee during stair-ascent, as a baseline for future clinical applications and for developing a compensation method to correct for the effects of STA.