Individual Joint Contributions Research Articles

Joint contributions to sagittal plane total support moment in patients with knee osteoarthritis after anterior cruciate ligament reconstruction

BackgroundPatients with anterior cruciate ligament reconstruction (ACLR) demonstrate lower knee loading. This study aimed to determine whether sagittal plane TSM and joint contributions to total support moment (TSM) in the surgical limb are different between athletes who did and did not show radiological features of knee OA at 2 years after ACLR during triple hops (TH), single hop (TH), single-legged vertical jump (VJ), and walking. MethodsForty-one athletes with 2 years of unilateral ACLR surgery participated in this cross-sectional study. Athletes completed motion analysis testing of single-legged TH, SH, VJ, and walking tasks. Sagittal plane TSM and individual joint (ankle, knee, and hip) contributions to TSM were computed at peak knee flexion angle (TSM-PKF). Posterior-anterior radiographs were completed in standing and 30° knee flexion. Kellgren-Lawrence (KL) system was used to identify radiological features of knee OA in the medial compartment of the reconstructed knee (OA-group: KL ≥2; Non-OA group: KL<2). ResultsThere was a significant group-by-joint-by-task interaction for joint contributions to TSM-PKF (p = 0.012), with the OA-group (n = 13) had lower knee and higher hip contributions compared to the non-OA group during TH, SH, and VJ (p ≤ 0.049). There was a significant joint-by-group interaction for the joint contributions to TSM-PKF (p = 0.004), with the OA-group having lower knee (p = 0.003) and higher hip (p = 0.001) contributions compared to the Non-OA group. SignificanceThe OA-group exhibited lower knee and higher hip contributions to the sagittal plane TSM compared to the Non-OA group during the landing phase of single-limb high-demand activities. The OA-group exhibited decreased knee loading and compensated by shifting the mechanical load to the hip joint within the reconstructed knee. Decreased knee loading in the OA-group may have affected the required mechanical loading to maintain knee metabolism and integrity.

Complex motions embedded in a hand exercise regimen - effects on thumb function in participants with carpometacarpal osteoarthritis: A pilot study.

The goal of this pilot study was to identify changes associated with completion of a unique six-week hand exercise program in persons with carpometacarpal osteoarthritis. Twenty-four individuals, aged 55-80, with doctor-diagnosed carpometacarpal osteoarthritis participated in the study. Movement data from standard clinical motions and complex multi-planar motions were obtained using a motion capture system at three-time points: an initial visit, after two weeks of hand exercises, and after completion of the six-week exercise program. This exercise program produced trends of improvement in complex multi-planar motions. Specifically, joint angle changes were seen during opposition and the formation of an "okay sign" that was included as part of the exercise program. Through the use of motion capture, changes were identified in thumb joint function after exercise. Specifically, motions associated with the more complex multi-planar tasks showed changes in individual joint contributions following the six-week exercise intervention. The results suggest that further exploration of this exercise program, particularly the inclusion of complex multi-planar tasks during osteoarthritis treatment and associated evaluations, should be considered in future clinical studies.

Individuals with Bilateral Cerebral Palsy Rely On Excessive Hip Extension To Complete A Step-Up Task

<h3>Research Objectives</h3> To investigate the hip, knee, and ankle joint moments of individuals with bilateral cerebral palsy (CP) during a step-up task. Due to distal joint impairment, we hypothesized that individuals with bilateral CP would generate less knee and ankle moments and more hip moments when stepping up than individuals without CP. <h3>Design</h3> In this cross-sectional study, participants were instructed to step up onto a 10.2-cm platform 5-15 times with the same leading limb. <h3>Setting</h3> University gait laboratory. <h3>Participants</h3> We recruited from convenience samples of individuals with and without bilateral CP between 5-19 years of age. Individuals without bilateral CP (n=11, 6 females, mean age=12.8 years) were included if they had no known neurological conditions. Individuals with bilateral CP (n=5, 1 female, mean age=10.6 years) were included if they had some ambulatory function without assistive devices or orthotics, no botulinum toxin injections in the past 6 months, no lower limb surgeries in the past year, and no serious co-morbidities. <h3>Interventions</h3> N/A. <h3>Main Outcome Measures</h3> Extensor support moments were calculated by summing normalized hip, knee, and ankle sagittal plane moments. Peak support moments were identified in the push-off and pull-up stance phases, where typically the ankle and knee joints generate the highest moments, respectively. Individual joint contributions to peak support moments were averaged and compared between groups using a Welch's t-test. <h3>Results</h3> For the push-off phase, the difference in hip extension moments was significant between groups, where individuals with bilateral CP generated larger hip moments during peak support moments compared to individuals without bilateral CP (p< 0.001, CI: [0.445 0.798] Nm/kg). For the pull-up phase, differences in hip and knee extension moments were significant between groups. Individuals with bilateral CP generated larger hip moments (p< 0.001, CI: [0.364 0.911] Nm/kg) and smaller knee moments (p=0.007, CI: [-0.729 -0.161] Nm/kg) during peak support moments compared to individuals without bilateral CP. <h3>Conclusions</h3> Increased generation of hip extension moments during a step-up task is likely a neural and biomechanical compensation for distal joint impairment in individuals with bilateral CP. <h3>Author(s) Disclosures</h3> None.

What Makes an Online Review More Helpful: An Interpretation Framework Using XGBoost and SHAP Values

Online product reviews play important roles in the word-of-mouth marketing of e-commerce enterprises, but only helpful reviews actually influence customers’ purchase decisions. Current research focuses on how to predict the helpfulness of a review but lacks a thorough analysis of why it is helpful. In this paper, feature sets covering review text and context cues are firstly proposed to represent review helpfulness. Then, a set of gradient boosted trees (GBT) models is introduced, and the optimal one, which as implemented in eXtreme Gradient Boosting (XGBoost), is chosen to predict and explain review helpfulness. Specially, by including the SHAP (Shapley) values method to quantify feature contribution, this paper presents an integrated framework to better interpret why a review is helpful at both the macro and micro levels. Based on real data from Amazon.cn, this paper reveals that the number of words contributes the most to the helpfulness of reviews on headsets and is interactively influenced by features like the number of sentences or feature frequency, while feature frequency contributes the most to the helpfulness of facial cleanser reviews and is interactively influenced by the number of adjectives used in the review or the review’s entropy. Both datasets show that individual feature contributions vary from review to review, and individual joint contributions gradually decrease with the increase of feature values.

Lower extremity joints and their contributions to whole limb extension

ABSTRACT Lower extremity multi-joint strength curves tend not to evaluate individual joint contributions to endpoint force in maximum effort isometric whole limb extension. Therefore, the purpose of this study was to measure the contribution of the hip, knee, and ankle to vertical ground reaction force in maximum effort isometric whole limb extension at various postures. An effect of posture on the contributions of the hip, knee, and ankle to vertical ground reaction force was found (F(3,96) = 85.31, p < 0.0001; F(3,96) = 21.32, p < 0.0001; F(3,96) = 130.61, p < 0.0001 for the hip, knee, and ankle, respectively). The hip and knee contributed most to vertical endpoint force when the lower limb was in a flexed posture, and their contributions decreased when posture was extended. Conversely, the ankle contributed least when the limb was flexed, but its contribution increased as posture was changed from flexed to more extended. In comparison to recent research involving induced acceleration analysis, it appears that the hip, knee, and ankle utilize the same force allocation strategy in multi-joint maximum effort isometric leg extensions and activities of daily living.

Individual joint contributions to the total support moment during the sit-to-stand task differentiate mild and moderate knee osteoarthritis

BackgroundKnee osteoarthritis tends to modify the kinematics and kinetics of the sit-to-stand task. However, it is not clear whether the different degrees of knee osteoarthritis differentiate regarding these aspects. The objective was to identify if the trunk flexion, lower limb kinetics, total support moment, and individual joint contributions to the total support moment during the sit-to-stand task are different between patients with mild and moderate knee osteoarthritis. MethodsSixty-two participants were grouped as follows: moderate knee osteoarthritis (n = 16), mild knee osteoarthritis (n = 25), and controls (n = 21). The participants performed a sit-to-stand task, which was analyzed using a 3D-motion system and a force plate. FindingsThe three phases of the sit-to-stand task were analyzed. During Phase1, the moderate osteoarthritis group decreased the total support moment (P = 0.012). During Phase2, the moderate osteoarthritis group showed higher trunk flexion (P = 0.023) and lower internal hip and knee extension moments (P ≤ 0.001 and P ≤ 0.040, respectively) when compared to controls. Also in Phase2, both the mild and moderate groups used lower total support moment (P = 0.019, and P ≤ 0.001, respectively). When compared to the controls and mild osteoarthritis group, those with moderate osteoarthritis presented higher hip joint contribution to the total support moment (P ≤ 0.001 and P = 0.006, respectively) as well as lower knee joint contribution (P ≤ 0.003 and P = 0,013, respectively). InterpretationThose with moderate osteoarthritis showed modified sit-to-stand movement pattern. While in Phase3 a higher contribution of the hip joint to the total support moment was observed, during previous phases the individuals were able to decrease the load on the knee without influencing the lower limb load distribution.

Joint range of motion entropy changes in response to load carriage in military personnel

BackgroundOveruse accounts for 82% of injuries in military personnel, and these occur predominantly in the spine and lower limbs. While non-linear analyses have shown changes in overall stability of the movement during load carriage, individual joint contributions have not been studied. The concept of entropy compensation between task, organism and environmental constraints is studied at a joint level. Research questionThe aim of this study was to investigate whether using different methods of loading by military personnel would have an effect on the sample entropy of the joint ranges of motion. MethodsEleven male reserve infantry army soldiers (age: 22 ± 2 years; height: 1.80 ± 0.06 m; mass: 89.3 ± 14.4 kg) walked an outdoor, 800 m course under 5 load conditions: unloaded, 15 kg backpack, 25 kg backpack, 15 kg webbing and backpack and 25 kg webbing and backpack. Kinematic data was recorded at 240 Hz using the Xsens motion capture system. The ranges of motion (ROM) of the spine, hips and knee were calculated for each gait cycle. Mean ROM, coefficient of variation (CV) of the ROM and the sample entropy of the ROM were compared between conditions. ResultsSpine side flexion ROM decreased significantly from the control condition in all loaded conditions, while sample entropy of the spine side flexion ROM increased in some conditions with no significant change in CV. Conversely, the hip flexion ROM increased significantly from the control, while sample entropy of the hip flexion ROM decreased. SignificanceThese results suggest that entropy compensation may propagate at a joint level. Understanding that a decrease in certainty with which a joint angle is selected, may be accompanied by an increase at a neighbouring joint. This could be significant in monitoring injuries as a result of environmental or task constraints.

The Role of the Midfoot in Drop Landings.

The midfoot is instrumental to foot function; however, quantifying its roles in human movement has been difficult. A forceful dynamic activity like landing may help elucidate the midfoot's contribution to foot energetics and function. The main purpose of this study was to measure midtarsal joint kinematics and kinetics during a barefoot single-leg landing task. A secondary aim of this study was to explore the relationship between static foot posture and dynamic midfoot function. In a cross-sectional study design, 48 females (age = 20.4 ± 1.8 yr, body mass index = 21.6 ± 1.7 kg·m) performed drop landings from a height of 0.4 m onto split force platforms. Subjects hung from wooden rings and landed on their dominant leg. Midtarsal joint kinematic and kinetic data were recorded using a 14-camera optical motion capture system in conjunction with two in-ground force platforms and a custom kinetic three-segment foot model. Foot structure was measuring using the arch height index (AHI) and the static midtarsal joint angle from motion capture. Kinematic data revealed an average sagittal plane midtarsal joint range of motion of 27° through the landing phase. Kinetic data showed that between 7% and 22% of the total lower extremity joint, work during the landing was performed by the midtarsal joint. Both standing AHI and static midtarsal joint angle (static MA) were correlated with sagittal plane midtarsal joint range of motion (standing AHI: r = -0.320, P = 0.026; static MA: r = 0.483, P < 0.001) and with midtarsal joint work (standing AHI: r = 0.332, P = 0.021; static MA: r = -0.323, P = 0.025). The midfoot contributes substantially to landing mechanics during a barefoot single-leg landing task. Static foot posture measures have limited value in predicting midfoot kinematics and kinetics during sportlike landings.

Mechanisms contributing to reduced knee stiffness during movement.

The ability to modulate the mechanical properties of our limbs contributes to our ability to interact with the physical world in a consistent and predictable manner. An individual joint's contributions to whole limb mechanics can be quantified by its joint impedance, which characterizes the torque generated about a joint in response to external perturbations of position. A number of studies have estimated joint impedance during movement and have shown that it can be much lower than it is during posture. However, the mechanisms contributing to these differences remain unknown partly because conditions known to affect impedance, including muscle activation and joint angles, have not been carefully controlled across studies. The goal of this study was to contrast knee impedance during continuous volitional movements with that during maintained postures spanning a similar range of joint angles and muscle activations and to explore physiological mechanisms likely to contribute to the observed differences. We found that knee impedance was substantially lower during movement than during matched postural tasks, even for matched muscle activations. At times, the impedance during movement was even lower than that measured during isometric tasks with no volitional muscle activity. These decreases in impedance could be attributed in part to reduced stretch reflexes during movement and to an effect of movement itself on reducing knee impedance.

Multi-body dynamic coupling mechanism for generating throwing arm velocity during baseball pitching

The purpose of this study was to identify the detailed mechanism how the maximum throwing arm endpoint velocity is determined by the muscular torques and non-muscular interactive torques from the perspective of the dynamic coupling among the trunk, thorax and throwing and non-throwing arm segments. The pitching movements of ten male collegiate baseball pitchers were measured by a three-dimensional motion capture system. Using the induced-segmental velocity analysis (IVA) developed in this study, the maximum fingertip velocity of the throwing arm (MFV) was decomposed into each contribution of the muscular torques, passive motion-dependent torques due to gyroscopic moment, Coriolis force and centrifugal force, and other interactive torque components. The results showed that MFV (31.6±1.7m/s) was mainly attributed to two different mechanisms. The first is the passive motion-dependent effect on increasing the angular velocities of three joints (thorax rotation, elbow extension and wrist flexion). The second is the muscular torque effect of the shoulder internal rotation (IR) torque on generating IR angular velocity. In particular, the centrifugal force-induced elbow extension motion, which was the greatest contributor among individual joint contributions, was caused primarily by the angular velocity-dependent forces associated with the humerus, thorax, and trunk rotations. Our study also found that a compensatory mechanism was achieved by the negative and positive contributions of the muscular torque components. The current IVA is helpful to understand how the rapid throwing arm movement is determined by the dynamic coupling mechanism.

Reliability of 3D upper limb motion analysis in children with obstetric brachial plexus palsy

Kinematics, measured by 3D upper limb motion analysis (3D-ULMA), can potentially increase understanding of movement patterns by quantifying individual joint contributions. Reliability in children with obstetric brachial plexus palsy (OBPP) has not been established.Objective: This study aimed to determine between session reliability and measurement errors of 3D-ULMA using the acromion method (AM) in children with OBPP.Approach: Ten participants (mean 10 years, range 7–15 years, Narakas classification I–III) completed 3D-ULMA on two occasions, mean interval of 8.6 d (±2.8 d). Kinematic data were captured by a 4-CODA cx1 optoelectronic tracking system. Participants performed three trials of the modified Mallet scale tasks. Local coordinate systems, segment and joint rotations were defined as recommended by the International Society of Biomechanics. The intraclass correlation coefficient (ICC 2,K) and standard error of measurement (SEM) were calculated for task duration, range and joint angle at point of task achievement (PTA).Main Results: Results indicated poor reliability for spatiotemporal parameters and range. Moderate to excellent reliability at PTA was observed in 19/60 variables (ICC: 0.77–0.98; SEM: 3.5°–10.4°). The Abduction Task had the highest (ICC: 0.79–0.98; SEM: 3.5°–10.3°) with External Rotation the lowest reliability. Glenohumeral and thoracohumeral elevation had the most consistent reliability. Scapular protraction/retraction had consistently poor reliability (ICC: 0–0.72; SEM: 3.5°–10.2°) with axial rotation also poor (ICC: 0.00–0.91; SEM: 6.3°–32.8°).This study determined inconsistent test–retest reliability of 3D-ULMA, using AM, to track dynamic performance of functional tasks in children with OBPP. It is the first study to outline measurement error in this population. This information permits more reliable interpretation of future studies of kinematic patterns in children with OBPP.

A biomechanical evaluation of the combined elevation test

ObjectivesTo evaluate biomechanically the relationships between the outcome of the Combined Elevation Test, its component joint motions, and thoracic spine angles. DesignCross-sectional study. SettingLaboratory. Participants18 elite swimmers and triathletes (11 males and 7 females). Main outcome measuresCombined Elevation Test outcome in forehead and chin positions. Individual joint contributions to test outcome. ResultsNo sex differences were found in test components, or between head positions. Test outcome was greater in the forehead position than the chin position (34.3 cm vs 30.2 cm; p < 0.001). The variables most strongly associated with test outcome were glenohumeral joint flexion (r = 0.86–0.97; p < 0.001), and shoulder retraction (r = 0.75–0.82; p < 0.001). Total thoracic spine angle related strongly to test outcome in females (r = −0.77 to -0.88; p < 0.05), but not in males (r = −0.17 to -0.24; p > 0.05). ConclusionsThe Combined Elevation Test is an effective screening tool, measuring upper limb mobility into shoulder flexion and scapula retraction in both sexes, and thoracic extension in women. It is recommended that the test be performed in the forehead position. If a subject performs poorly on the test, follow up assessments are required to identify the impairment location.

Individual joint contribution to body weight support in the affected lower limb during walking in post-stroke hemiplegia

Objective: Patients with post-stroke hemiplegia have difficulty with body weight support during walking. However, it is unclear which intra-limb strategy for body weight support tends to predominate, and how the intra-limb strategy is related to gait function. Support moment and individual joint contribution to support moment are the parameters that reflect intra-limb strategy for body weight supporting. The aim of this study was to test whether support moment and individual joint contributions differed between post-stroke subjects with different gait function.Method: Laboratory gait analysis was performed for 14 non-hemiplegic elderly (NE) and 12 post-stroke hemiplegic elderly walking without cane (HNC) and 11 walking with a cane (HWC). Data were obtained for the vertical ground reaction force (vGRF) curve, 1st peak and 2nd peak of vGRF and corresponding temporal occurrences. Support moment (Ms) was numerical sum of hip extension, knee extension, and ankle plantar flexion moment. Individual joint contribution was calculated as the ratio of each joint moment to support moment. At temporal occurrences of vGRF peaks, Ms and individual joint contribution to Ms were calculated. Ms and individual joint contribution to Ms were compared among NE, HNC and HWC groups. Each subject’s characteristics of individual joint contribution to Ms were explored.Results: At the 1st peak of vGRF, support moments were similar among the three groups. However, the hip contributions were significantly greater in the NE group than in the other two groups, the ankle contributions were significantly greater in the HNC group than in the NE group. Notably, some of the subjects with post-stroke hemiplegia showed atypical characteristics that did not correspond to the group characteristics.Conclusion: Observing support moment and individual joint contribution is helpful to ascertain not only group characteristics, but also individual characteristics of intra-limb strategy for weight support in patients with post-stroke hemiplegia.

Absolute And Relative Joint Contributions To Landing In High- Compared To Low-Arched Athletes

Foot structure has been implicated in lower extremity injury. Research has shown that athletes with aberrant foot structure exhibit unique biomechanics during running and landing tasks. While foot function has been suggested to underlie distinct injury patterns in high- (HA) compared to low-arched (LA) athletes, no previous research has addressed the contribution of individual joints to load attenuation in a landing task. PURPOSE: Therefore, the purpose of this study was to quantify differences in individual joint contributions to total negative work during a landing task in high- compared to low-arched athletes. METHODS: Ten HA and 10 LA female athletes performed five landing trials from a height of 0.3 meters while three-dimensional kinematics and ground reaction forces were collected using an 8-camera motion capture system (240 Hz, ViconPEAK) and a force platform (960 Hz, AMTI), respectively. Lower extremity joint work values were calculated using Visual 3D (C-Motion, Inc.). Relative contributions of each joint to negative joint work was calculated as a percentage of the individual joint work relative to total joint work. Independent samples t-tests were used to compare relative joint work values for the lower extremity. RESULTS: HA athletes exhibited significantly smaller total negative joint work compared to LA athletes (p=0.016; HA: 1.79±0.43; LA: 2.16±0.26). HA athletes had significantly smaller knee (p=0.046; HA: 0.98±0.36; LA: 1.22±0.23) and hip joint work values (p=0.019; HA: 0.22±0.18; LA: 0.39±0.16). HA and LA athletes had similar ankle joint work values (p=0.252; HA: 0.59±0.16; LA: 0.55±0.12). When comparing relative joint work, HA athletes exhibited greater relative ankle contributions to total negative work than LA athletes (p = 0.032; HA: 35.1±25.7%; LA: 25.7±6.6%). No differences existed between HA and LA athletes at the knee (p=0.255; HA: 53.5±11.2%; LA: 56.3±6.3%). HA athletes had a smaller hip contribution to total negative work than the LA athletes during landing (p = 0.049; 11.4±8.8%; LA: 18.0±7.6%). CONCLUSIONS: These findings indicate that HA and LA athletes use unique biomechanical strategies to attenuate load during a landing task and may provide insight into the distinct injury patterns experienced by these two groups.

Inter-joint sharing of total support moments in the lower extremities during gait in narrow-heeled shoes of different heights

The study aimed to investigate the influence of the base and height of shoe heels on the total support moment (Ms) and individual joint contributions during gait. Fifteen healthy females walked barefoot and with narrow-heeled shoes (heel heights: 3.9, 6.3 and 7.3 cm) while kinematic and kinetic data were measured. Compared with the barefoot condition, the subjects maintained unaltered Ms in the sagittal plane in shod conditions. This was achieved by increasing the knee extensor moment to compensate for the diminished ankle plantarflexor moments in medium and high heel conditions. In the frontal plane, subjects in shod conditions had to sustain an increased Ms for balance control during late single-leg stance with increased knee abductor and ankle pronator moments as a result of the reduced base of the heels. The results will be helpful for future shoe designs to reduce fall risks and prevent relevant musculoskeletal problems

Influence of inclination angles on intra- and inter-limb load-sharing during uphill walking

Uphill walking is an inevitable part of daily living, placing more challenges on the locomotor system with greater risk of falls than level walking does. The current study aimed to investigate the effects of inclination angles on the inter-joint and inter-limb load-sharing during uphill walking in terms of total support moment and contributions of individual joint moments to the total support moment. Fifteen young adults walked up walkways with 0°, 5°, 10° and 15° of slope while kinematic and kinetic data were collected and analyzed. With increasing inclination angles, the first peak of the total support moment was increased with unaltered individual joint contributions, suggesting an unaltered inter-joint control pattern in the leading limb to meet the increased demands. The second peak of the total support moment remained unchanged with increasing inclination angles primarily through a compensatory redistribution of the hip and knee moments. During DLS, the leading limb shared the majority of the whole body support moments. The current results reveal basic intra- and inter-limb load-sharing patterns of uphill walking, which will be helpful for a better understanding of the control strategies adopted and for subsequent clinical applications.

Temporal Control and Hand Movement Efficiency in Skilled Music Performance

Skilled piano performance requires considerable movement control to accomplish the high levels of timing and force precision common among professional musicians, who acquire piano technique over decades of practice. Finger movement efficiency in particular is an important factor when pianists perform at very fast tempi. We document the finger movement kinematics of highly skilled pianists as they performed a five-finger melody at very fast tempi. A three-dimensional motion-capture system tracked the movements of finger joints, the hand, and the forearm of twelve pianists who performed on a digital piano at successively faster tempi (7–16 tones/s) until they decided to stop. Joint angle trajectories computed for all adjacent finger phalanges, the hand, and the forearm (wrist angle) indicated that the metacarpophalangeal joint contributed most to the vertical fingertip motion while the proximal and distal interphalangeal joints moved slightly opposite to the movement goal (finger extension). An efficiency measure of the combined finger joint angles corresponded to the temporal accuracy and precision of the pianists’ performances: Pianists with more efficient keystroke movements showed higher precision in timing and force measures. Keystroke efficiency and individual joint contributions remained stable across tempo conditions. Individual differences among pianists supported the view that keystroke efficiency is required for successful fast performance.

Stance leg frontal plane stability during lateral bounds

BackgroundLower limb stability is pivotal to successful dynamic sporting movements, with poor stability during single leg tasks commonly associated with lower limb non-contact injuries.ObjectiveThis study investigated stance leg frontal plane...

Knee osteoarthritis affects the distribution of joint moments during gait

Alterations in lower extremity kinetics have been shown to exist in persons with knee osteoarthritis (OA), however few investigations have examined how the intersegmental coordination of the lower extremity kinetic chain varies in the presence of knee joint pathology. The objective of this study was to evaluate how knee OA and walking speed affect total support moment and individual joint contributions to the total support moment. Fifteen healthy subjects and 30 persons with knee OA participated in 3D walking analysis at constrained (1.0 m/s), self-selected and fastest tolerable walking speeds. Individual joint contributions to total support moment were analyzed using separate ANOVAs with one repeated measure (walking speed). Linear regression analysis was used to evaluate the relationship between walking speed and joint contribution. Persons with knee OA reduced the contribution of the knee joint when walking at constrained ( p = 0.04) and self-selected walking speeds ( p = 0.009). There was a significant increase in the ankle contribution and a significant decrease in the hip contribution when walking speed was increased ( p < 0.004), however individual walking speeds were not significantly related to joint contributions. This suggests that the relationship between walking speed and joint contribution is dependent on the individual's control strategy and we cannot estimate the joint contribution solely based on walking speed. The slower gait speed observed in persons with knee OA is not responsible for the reduction in knee joint moments, rather this change is likely due to alterations in the neuromuscular strategy of the lower extremity kinetic chain in response to joint pain or muscle weakness.

A comparison of individual joint contributions to multijoint position reproduction acuity in overhead-throwing athletes

Measures of joint position sense often test single-axis motions isolating a single joint. Such methods hamper our ability to apply findings to functional multijoint activities. Using a functional, active, multijoint test, we measured upper-extremity position reproduction in overhead-throwers. We compared acuity among four joints and examined individual joint contributions or patterns of contribution among joints to overall task acuity. We used an electromagnetic tracking device to measure reproduction of two functional upper-extremity positions. We calculated absolute, constant and variable error at four upper-extremity joints around multiple axes of rotation: three axes at the scapulothoracic and glenohumeral joints and two axes at the elbow and wrist. To represent individual joint acuity, we calculated 3-dimensional variable error. Additional 3-dimensional variable error scores using deviation in hand position (with reference to the thorax) represented overall task acuity. We used principle component analyses to identify contributions of individual joints or patterns of contribution among joints to overall task acuity for absolute, constant and variable error. Scapulothoracic and glenohumeral joints displayed better acuity compared with elbow and wrist joints. When examined separately, absolute, constant and variable error scores did not indicate any individual joint contributed more to task acuity. When we examined the principle components of all error score measures together, a distinct proximal-to-distal pattern of joint contribution to overall task acuity emerged. Proximal joints display better reposition acuity compared with distal joints, however proximal joints contribute more to acuity of the overall task. Our results indicate that upper-extremity joints do not function independently in repositioning tasks and measures of absolute, constant and variable errors combined over multiple joints may better represent upper-extremity function.