Accelerometry as a measure of subject compliance in unilateral lower limb suspension

INTRODUCTION: Human unilateral lower limb suspension (ULLS) is a commonly used model to study the effects of disuse and unweighting of human skeletal muscle. ULLS requires subjects to ambulate on crutches with an elevated shoe on the weight-bearing limb or a strap on the unloaded limb for prolonged periods of time (i.e., 4-5 wk). Ensuring compliance during ULLS participation is critical to the integrity of the study. PURPOSE: The purpose of this study was to determine the accuracy of an accelerometer to detect steps taken while walking and to measure the effectiveness of an accelerometer to monitor compliance during ULLS. METHODS: There were 10 subjects (26.2 +/- 3.6 yr; 170.9 +/- 6.9 cm; 68.0 +/- 9.6 kg) who participated in two conditions: normal walking and ULLS (left leg was unweighted via an elevated shoe on the contralateral limb) at various speeds. Additionally, subjects completed an obstacle course to simulate daily activities. During these activities, subjects wore a planar accelerometer on their left ankle to measure acceleration. The mean peak axial acceleration (MPAA) of the leg in the swing phase of walking was determined by the accelerometer and a step was detected during ULLS if the MPAA was greater than or equal to the minimum MPAA observed during walking. From this, the sensitivity of the accelerometer was determined. During ULLS, the number of steps detected by the accelerometer with an MPAA--the minimum MPAA during walking was computed and the specificity of the accelerometer was determined. RESULTS: The sensitivity of the accelerometer during walking was 96% and the specificity during ULLS was 97%. CONCLUSION: An accelerometer is an accurate tool to quantify the number of steps taken during walking and it may be used to measure subject compliance during ULLS.     

Lower limb joint-specific contributions to standing postural sway in persons with unilateral lower limb loss

BackgroundIndividuals with lower limb loss are at an increased risk for falls, likely due to impaired balance control. Standing balance is typically explained by double- or single-inverted pendulum models of the hip and/or ankle, neglecting the knee joint. However, recent work suggests knee joint motion contributes toward stabilizing center-of-mass kinematics during standing balance.Research QuestionTo what extent do hip, knee, and ankle joint motions contribute to postural sway in standing among individuals with lower limb loss?MethodsForty-two individuals (25 m/17f) with unilateral lower limb loss (30 transtibial, 12 transfemoral) stood quietly with eyes open and eyes closed, for 30 s each, while wearing accelerometers on the pelvis, thigh, shank, and foot. Triaxial inertial measurement units were transformed to inertial anterior-posterior components and sway parameters were computed: ellipse area, root-mean-square, and jerk. A state-space model with a Kalman filter calculated hip, knee, and ankle joint flexion-extension angles and ranges of motion. Multiple linear regression predicted postural sway parameters from intact limb joint ranges of motion, with BMI as a covariate (p < 0.05).ResultsWith eyes open, intact limb hip flexion predicted larger sway ellipse area, whereas hip flexion and knee extension predicted larger sway root-mean-square, and hip flexion, knee extension, and ankle plantarflexion predicted larger sway jerk. With eyes closed, intact limb hip flexion remained the predictor of sway ellipse area; no other joint motions influenced sway parameters in this condition.SignificanceHip, knee, and ankle motions influence postural sway during standing balance among individuals with lower limb loss. Specifically, increasing intact-side hip flexion, knee extension, and ankle plantarflexion motion increased postural sway. With vision removed, a re-weighting of lower limb joint sensory mechanisms may control postural sway, such that increasing sway may be regulated by proximal coordination strategies and vestibular responses, with implications for fall risk.     

Uphill and downhill walking in unilateral lower limb amputees

OBJECTIVE: To study adjustment strategies in unilateral amputees in uphill and downhill walking. DESIGN: Observational cohort study. SUBJECTS: Seven transfemoral, 12 transtibial unilateral amputees and 10 able-bodied subjects. METHODS: In a motion analysis laboratory the subjects walked over a level surface and an uphill and downhill slope. Gait velocity and lower limb joint angles were measured. RESULTS: In uphill walking hip and knee flexion at initial contact and hip flexion in swing were increased in the prosthetic limb of transtibial amputees. In downhill walking transtibial amputees showed more knee flexion on the prosthetic side in late stance and swing. Transfemoral amputees were not able to increase prosthetic knee flexion in uphill and downhill walking. An important adjustment strategy in both amputee groups was a smaller hip extension in late stance in uphill and downhill walking, probably related with a shorter step length. In addition, amputees increased knee flexion in early stance in the non-affected limb in uphill walking to compensate for the shorter prosthetic limb length. In downhill walking fewer adjustments were necessary, since the shorter prosthetic limb already resulted in lowering of the body. CONCLUSION: Uphill and downhill walking can be trained in rehabilitation, which may improve safety and confidence of amputees. Prosthetic design should focus on better control of prosthetic knee flexion abilities without reducing stability.     

Balance control on a moving platform in unilateral lower limb amputees

OBJECTIVE: To study balance control on a moving platform in lower limb amputees. DESIGN: Observational cohort study. PARTICIPANTS: Unilateral transfemoral and transtibial amputees and able-bodied control subjects. INTERVENTIONS: Balance control on a platform that moved in the anteroposterior direction was tested with eyes open, blindfolded and while performing a dual task. MAIN OUTCOME MEASURES: Weight bearing symmetry, anteroposterior ground reaction force and centre of pressure shift. RESULTS: Compared to able-bodied subjects, in amputees the anteroposterior ground reaction force was larger in the prosthetic and non-affected limb, and the centre of pressure displacement was increased in the non-affected limb and decreased in the prosthetic limb. In amputees body weight was loaded more on the non-affected limb. Blindfolding or adding a dual task did not influence the outcome measures importantly. CONCLUSION: The results of this study indicate that experienced unilateral amputees with a high activity level compensate for the loss of ankle strategy by increasing movements and loading in the non-affected limb. The ability to cope with balance perturbations is limited in the prosthetic limb. To enable amputees to manage all possible balance disturbances in real life in a safe manner, we recommend to improve muscle strength and control in the non-affected limb and to train complex balance tasks in challenging environments during rehabilitation.     

Functional outcomes of unilateral lower limb amputee soldiers in two districts of Sri Lanka

The purpose of this study was to describe functional outcomes of unilateral lower limb amputee soldiers, in comparison to nonamputee male subjects, and to identify factors affecting functional outcomes. Selected lower limb amputee soldiers of the Sri Lanka Army (n = 461) and matched nonamputee male subjects (n = 461) were evaluated with the prevalidated self-administered version of Short-Form Health Survey-36. A majority were below-knee amputees (n = 413; 89.6%), and the mean age was 30.2 +/- 4.6 years. Short-Form Health Survey-36 health profile scores of amputees were significantly lower than those of nonamputees (p < 0.001). The differences in profiles were largest in scales sensitive to physical health. Higher levels of amputation and problems with the stump and sound leg were significantly associated with poor physical and mental health scores. Amputee soldiers' assessment of changes in health over the past year was significantly worse than that of nonamputees (p < 0.001). The study concluded that amputees have comparatively poor functional outcomes, which could be improved by modifying some associated factors.     

EMG analysis of lower limb muscles in humans during quick change in running directions

Open and cross maneuvers for changing running direction were studied to characterize selective EMG activity between the maneuvers. Eleven subjects turned towards the right or the left during running. The gluteus medius modified foot trajectory of the leading leg during the open maneuver, whereas the sartorius worked modestly during the cross maneuver. Compared with the cross maneuver the open maneuver exhibited greater vastus medialis and gastrocnemius activity during the ground support phase, faster running speed and wider turning angle. These results suggest that the open maneuver is more effective than the cross maneuver for quickly changing running direction.     

Measurement of regional lower limb blood flow in normal humans by inhalation of 133Xe

A non-invasive method of measuring regional calf blood flow after inhalation of 133Xe has been investigated. The mean blood flow at rest was 3.3 ml X min-1 X 100 g tissue-1 by the 133Xe method and 3.5 ml X min-1 X 100 g tissue-1 by plethysmography. There was a significant correlation r = 0.88, P less than 0.001. During exercise the mean blood flow in the anterior tibial compartment increased from 3.4 to 10.9 ml X min-1 X 100 g tissue-1 in ten cases and in the posterior compartment from 3.3 to 7.1 ml X min-1 X 100 g tissue-1 in seven cases as measured by the 133Xe technique. The inhalation method seems to be an accurate, reliable and non-invasive method for measuring tissue blood flow in the human calf at rest and during exercise.     

Measurement of regional lower limb blood flow in normal humans by inhalation of 133Xe

A non-invasive method of measuring regional calf blood flow after inhalation of ¹³³Xe has been investigated. The mean blood flow at rest was 3.3 ml·min^-1·100 g tissue^-1 by the ¹³³Xe method and 3.5 ml·min^-1·100 g tissue^-1 by plethysmography. There was a significant correlation r=0.88, P<0.001. During exercise the mean blood flow in the anterior tibial compartment increased from 3.4 to 10.9 ml·min^-1·100 g tissue^-1 in ten cases and in the posterior compartment from 3.3 to 7.1 ml·min^-1·100 g tissue^-1 in seven cases as measured by the ¹³³Xe technique. The inhalation method seems to be an accurate, reliable and non-invasive method for measuring tissue blood flow in the human calf at rest and during exercise.     

Observer variation in the interpretation of lower limb venograms.

After agreeing on diagnostic criteria and after a pilot study, two experienced radiologists twice independently reviewed 40 lower limb venograms performed by a standard technique in patients suspected or known to have venous thrombosis. The observers reviewed 20 examinations at a time, their analysis requiring separate identification of 11 major veins. At each site observers stated whether thrombus was "absent," "doubtful," "presumed," or "definite," or declared "no opinion possible." They then rediscussed criteria of diagnosis and, using the same experimental design, examined another 40 venograms. To correct for agreement expected by chance, data were analyzed by using the kappa statistic. In general, levels of agreement were higher than those reported for many other clinical and radiologic investigations, probably because of refinement of criteria after the pilot study. Nonetheless, observers disagreed about the probable presence or absence of thrombus at some site in the limb in about 10% of examinations. Observer variation should be considered when venography is used as a reference standard to evaluate other methods of diagnosing thrombi.     

Limb specific training magnitude and asymmetry measurement to discriminate between athletes with and without unilateral or bilateral lower limb injury history

ObjectivesThis study investigates the use of tibia-mounted inertial measurement units (IMUs) as an alternative to upper trunk-mounted IMUs for assessing lower limb training magnitudes and asymmetries in Badminton players.DesignCross-Sectional Study.SettingYouth athlete training environment.ParticipantsThirty-three adolescent Badminton players, grouped based on injury history (non-injured = 19, bilateral = 6, unilateral = 8).Main outcome measuresPlayers wore 1 upper trunk-mounted and 2 tibia-mounted IMUs during simulated match-play. Modified vector magnitudes were assessed to identify if the IMUs can discriminate between injury history groups to assess the device location sensitivity, determine to what extent players exhibit movement asymmetry within the sport, and explore if asymmetries exist within groups with injury history.ResultsUpper trunk-mounted IMUs could not distinguish between injury history groups. Statistically significant asymmetries were observed in the non-injured group, however these were below the 10% threshold for clinical asymmetry. No significant asymmetries were observed in the bilaterally injured group, while statistically significant asymmetries were observed in the unilaterally injured group, which were above the 10% threshold for clinical asymmetry.ConclusionThese results suggest that direct limb specific IMU measurement offers a method to suitably assess training magnitudes and asymmetry within a sporting performance, rather than isolated non-sport specific testing.     

Gait initiation in lower limb amputees

OBJECTIVE: To study limitations in function and adjustment strategies in lower limb amputees during gait initiation. DESIGN: Observational cohort study. SETTING: University Medical Center. PARTICIPANTS: Amputees with a unilateral transfemoral or transtibial amputation, and able-bodied subjects. MAIN OUTCOME MEASURES: Leading limb preference, temporal variables, ground reaction forces, and centre of pressure shift. RESULTS: Amputees demonstrated a decrease in peak anterior ground reaction force, a smaller or absent posterior centre of pressure shift, and a lower gait initiation velocity. The main adjustments strategies in amputees were more limb-loading on the non-affected limb, prolonging the period of propulsive force production in the non-affected limb and initiating gait preferably with the prosthetic limb. CONCLUSION: Since an intact ankle joint and musculature is of major importance in gait initiation, functional limitations and adjustment strategies in transfemoral and transtibial amputees were similar. Improving prosthetic ankle properties and initiating gait with the prosthetic limb may facilitate the gait initiation process in amputees.     

Obstacle crossing in lower limb amputees

OBJECTIVE: To study limitations in function and adjustment strategies in lower limb amputees during obstacle crossing. DESIGN: Observational cohort study. SUBJECTS: Transfemoral and transtibial amputees and able-bodied control subjects. METHODS: In a motion analysis laboratory unimpeded and obstacle crossing runs were performed. The subjects stepped over an obstacle of 0.1m height and thickness and 1m width. Outcome measures were gait velocity, hip, knee and ankle joint angles and leading limb preference. RESULTS: Whereas able-bodied and transtibial subjects demonstrated an increase in knee flexion during obstacle crossing compared to unimpeded walking, in transfemoral amputees the opposite was seen, namely a decrease in knee flexion. The lack of knee strategy in transfemoral amputees was compensated by circumduction at the hip on the prosthetic side and plantar flexion of the non-affected ankle. Transtibial amputees preferred to cross the obstacle with the prosthetic limb first, while transfemoral amputees preferred the non-affected limb. CONCLUSION: The different leading limb strategy in transfemoral and transtibial amputees could be explained by the restricted flexion and propulsion properties of the prosthetic knee. Training of obstacle crossing tasks during rehabilitation and improvement of prosthetic design may contribute to safe obstacle crossing.     

Gait termination in lower limb amputees

OBJECTIVE: To study the limitations in function and adjustment strategies of lower limb amputees in gait termination. DESIGN: Observational cohort study. SETTING: University Medical Centre. PARTICIPANTS: Unilateral transfemoral and transtibial amputees, and able-bodied control subjects. MAIN OUTCOME MEASURES: Leading limb preference, temporal variables, lower limb joint angles, ground reaction forces, and centre of pressure shift. RESULTS: Compared to able-bodied subjects, amputees showed a decreased peak braking ground reaction force in the prosthetic limb, no anterior centre of pressure shift during leading with the prosthetic limb and an increased mediolateral centre of pressure shift. Amputees used several adjustment strategies to compensate for the limitations in function; leading limb preference for the non-affected limb, longer production of braking force in the non-affected limb, decreased gait termination velocity and more weight-bearing on the non-affected limb. CONCLUSION: Limitations in function and adjustment strategies were mainly similar in transfemoral and transtibial amputees. Due to the lack of active ankle function, amputees were not able to increase the braking force and to shift the centre of pressure anteriorly. Leading with the non-affected limb is favourable for adequate deceleration and balance control, but in daily life not always applicable. It is important that amputees are trained in gait termination during rehabilitation and prosthetic design should focus on a more active role of the prosthetic foot and knee.     

The appearances of artefacts on lower limb phlebograms.

The various artefacts that may be encountered in phlebograms and which may be confused with thrombus are described. Methods of avoiding these pitfalls are discussed. the conclusions are based on over 2500 phlebograms carried out for suspected deep vein thrombosis.