Sreesha Rao

Shoulder joint kinetics during the push phase of wheelchair propulsion.

The purpose of this investigation was to quantify the forces and moments at the shoulder joint during free, level wheelchair propulsion and to document changes imposed by increased speed, inclined terrain, and 15 minutes of continuous propulsion. Data were collected using a six-camera VICON motion analysis system, a strain gauge instrumented wheel, and a wheelchair ergometer. Seventeen men with low level paraplegia participated in this study. Shoulder joint forces and moments were calculated using a three-dimensional model applying the inverse dynamics approach. During free propulsion, peak shoulder joint forces were in the posterior (46 N) and superior directions (14 N), producing a peak resultant force of 51 N at an angle of 185° (180° = posterior). Peak shoulder joint moments were greatest in extension (14 Newton-meters [Nm]), followed by abduction (10 Nm), and internal rotation (6 Nm). With fast and inclined propulsion, peak vertical force increased by greater than 360%, and the increase in posterior force and shoulder moments ranged from 107% to 167%. At the end of 15 minutes of continuous free propulsion, there were no significant changes compared with short duration free propulsion. The increased joint loads documented during fast and inclined propulsion could lead to compression of subacromial structures against the overlying acromion.

The influence of patellofemoral pain on lower limb loading during gait

OBJECTIVE To determine if subjects with patellofemoral pain demonstrate excessive lower limb loading during gait. DESIGN Prospective study utilizing a group of patients with patellofemoral pain and a control group. BACKGROUND Increased rate of lower limb loading has been hypothesized as being contributory to knee osteoarthritis and may be the result of decreased knee flexion during weight acceptance. Since patients with patellofemoral pain have been reported to limit knee flexion during gait, these individuals may be at risk for the adverse effects of impulse loading. METHODS Force plate parameters, lower extremity kinematics and stride characteristics were recorded in 15 females with patellofemoral pain and 10 pain-free controls during self-selected free and fast walking velocities. RESULTS Individuals in the patellofemoral pain group demonstrated a significantly slower gait velocity during the free and fast trials as well as decreased stance phase knee flexion during fast walking. The average peak loading rate for the patellofemoral pain group was significantly less than the control group during both free (P=0.004) and fast walking (P=0. 03). CONCLUSIONS Despite diminished stance phase knee flexion during fast walking, subjects with patellofemoral pain did not demonstrate increased lower limb loading. During gait, the ground reaction forces appeared to be minimized by adopting a slower walking velocity. RELEVANCE These results indicate that altered knee kinematics as a result of patellofemoral pain do not place these individuals at risk for the adverse effects of impulse loading.

Knee kinetics in trans-tibial amputee gait

This study evaluated the mechanics of the knee during gait in persons with trans-tibial amputations. Spatiotemporal, kinematic, kinetic, and electromyographic data (EMG) were collected from ten individuals with trans-tibial amputations and ten control subjects during level walking. Results found that the trans-tibial amputee (TTA) group had significantly greater EMG activity of the knee extensors and knee flexors compared to normal. The muscle action of the TTA group was inconsistent with the knee kinetic data as demonstrated by a minimal external knee flexion moment and negligible knee power. The discrepancy between the mechanical and physiological measures of knee demand in this population illustrates the need for an integrated approach for the study of joint function during gait (i.e. EMG in combination with kinetic measures). Copyright 1998 Elsevier Science B.V.

Three-dimensional kinematics of wheelchair propulsion

A three-dimensional (3-D) biomechanical model was used to determine upper extremity kinematics of 16 male subjects with low-level paraplegia while performing wheelchair propulsion (WCP). A six-camera VICON motion analysis system was used to acquire the coordinate data of ten anatomic markers. Joint axes for the wrist and elbow were defined along with the planes of motion for the upper arm (humerus) and trunk. The groups mean and standard deviation profiles were graphed for eight of the nine rotations measured during WCP. Variability in the intercycle and intersubject movement patterns were calculated using the root mean square standard deviation (RMS sigma) and the coefficient of variation (CV). Motion pattern similarities were quantified using the coefficient of multiple correlation (CMC). The intercycle (Nc > or = 6) motion patterns of individual subjects were highly consistent, similar, and repeatable during WCP. This was confirmed by low CVc values (3-31%), high CMCc values (0.724-0.996) and RMS sigma c values below 3.2 degrees. For the group, mean values of the propulsion velocity, cadence, and propulsion cycle duration were 89.7 m/min, 66.1 pushes/min, and 0.96 s, respectively. Humeral plane and rotation showed large excursions (76.1-81.6 degrees), while trunk lean and forearm carrying angle displayed relatively small ranges of motion (5.5-10.9 degrees). The intersubject (N3 = 16) motion patterns were less similar compared to individual intercycle patterns. This was evidenced by higher CVc values (12-128%) and lower CMC3 values (0.418-0.935). Intersubject humeral patterns were the most consistent while trunk lean was the least consistent. Intersubject root mean square standard deviations (RMS sigma c) were more than three times the corresponding intercycle values for all nine rotations.

The effect of level of spinal cord injury on shoulder joint kinetics during manual wheelchair propulsion

OBJECTIVE The effects of spinal cord injury level on shoulder kinetics during manual wheelchair propulsion were studied. DESIGN Single session data collection in a laboratory environment. METHODS Male subjects were divided into four groups: low level paraplegia (n=17), high level paraplegia (n=19), C7 tetraplegia (C7, n=16) and C6 tetraplegia (C6, n=17). Measurements were recorded using a six-camera VICON motion analysis system, a strain gauge instrumented wheel, and wheelchair ergometer. Shoulder joint forces and moments were calculated using the inverse dynamics approach. RESULTS Mean self-selected propulsion velocity was higher in the paraplegic (low paraplegia=90.7 m/min; high paraplegia=83.4 m/min) than tetraplegic (C7=66.5 m/min; C6=47.0 m/min) groups. After covarying for velocity, no significant differences in shoulder joint moments were identified. However, superior push force in subjects with tetraplegia (C7=21.4 N; C6=9.3 N) was significantly higher than in those with high paraplegia (7.3 N), after covarying velocity. CONCLUSIONS The superior push force in the tetraplegic groups coupled with weakness of thoraco-humeral depressors increases susceptibility of the subacromial structures to compression. RELEVANCE Increased vertical force at the shoulder joint, coupled with reduced shoulder depressor strength, may contribute to shoulder problems in subjects with tetraplegia. Wheelchair design modifications, combined with strength and endurance retention, should be considered to prevent shoulder pain development.

Three dimensional upper extremity motion during manual wheelchair propulsion in men with different levels of spinal cord injury

This investigation compared three dimensional upper extremity motion during wheelchair propulsion in persons with 4 levels of spinal cord injury: low paraplegia (n=17), high paraplegia (n=19), C7 tetraplegia (n=16), and C6 tetraplegia (n=17). Upper extremity motion was recorded as subjects manually propelled a wheelchair mounted on a stationary ergometer. For all motions measured, subjects with paraplegia had similar patterns suggesting that the wheelchair backrest adequately stabilizes the trunk in the absence of abdominal musculature. Compared with paraplegic subjects, those with tetraplegia differed primarily in the strategy used to contact the wheel. This was most evident among subjects with C6 tetraplegia who had greater wrist extension and less forearm pronation.

Relationship between foot pronation and rotation of the tibia and femur during walking.

The purpose of this study was to test the hypothesis that the magnitude and timing of peak foot pronation would be predictive of the magnitude and timing of peak rotation of tibia and femur. Thirty subjects who demonstrated a wide range of pronation participated. Three-dimensional kinematics of the foot, tibia, and femur segments were recorded during self-selected free walking trials using a six-camera VICON motion analysis system. Regression analysis demonstrated that the magnitude and timing of peak pronation was not predictive of the magnitude and timing of tibial and femoral rotation. The lack of a relationship between peak foot pronation and the rotation of the tibia and femur is contrary to the clinical hypothesis that increased pronation results in greater lower extremity rotation. It would seem, therefore, that the relationship between foot pronation and rotation of the lower extremity segments should be assessed on a patient-by-patient basis.

Prosthetic weight acceptance mechanics in transtibial amputees wearing the Single Axis, Seattle Lite, and Flex Foot

Loading response challenges the limb with the dual demands of accepting rapidly moving body weight to both absorb the shock of floor contact and create a stable limb over which the body can advance. Delay in achieving foot flat contact with the floor causes a prolonged period of heel only support and results in an unstable base of support for those persons with transtibial amputations. The purpose of this study was to identify mechanical causes of instability during weight acceptance with three different prosthetic foot designs, Single Axis, Seattle Lightfoot, and Flex Foot. Ten male individuals with transtibial amputations were tested on three separate occasions wearing each prosthetic foot. A comparison group of ten individuals without transtibial amputations was also examined. Mean free walking speed was significantly slower for those with transtibial amputations regardless of the prosthetic foot worn (p < 0.05). Contralateral toe off times were significantly later for each prosthetic foot (p < 0.01). The timing of peak knee flexion was found to be significantly later than normal for each prosthetic foot (p < 0.01). To minimize the impact of initial floor contact, persons with an intact limb used rapid plantar flexion, followed by a slower lowering of the foot to the floor. Dorsiflexion then stimulated knee flexion and foot flat. Two altered functions were found for all three prosthetic feet, reduced knee flexion and prolonged heel only support. Diminished knee flexion reflected delayed dorsiflexion and tibial advancement as a result of the cushioned heel. Lateness in reaching foot flat was also found. To improve the walking abilities of those persons with transtibial amputations, prosthetic foot designs need to incorporate mechanisms which promote early foot flat while preserving limb stability.

Segment velocities in normal and transtibial amputees: prosthetic design implications

Dynamic elastic response foot and ankle prostheses (Seattle-Lite, Flex Foot, etc.) used by transtibial amputees feature substantial design improvements over conventional designs (SACH, Single Axis, etc.). Despite this progress, transtibial amputees continue to expend greater energy than normals. Increased residual limb EMG data and altered gait patterns suggest that impaired mobility may be the cause of overactive muscles in early stance. Prosthetic mobility was therefore quantified by measuring foot, shank and thigh velocities in nine transtibial amputees, wearing three different foot designs: Single Axis (SA), Seattle Lite (SL) and Flex Foot (FF). The magnitude, timing and rate of segment velocities for each prosthetic design, characterizing early stance mobility, were compared with corresponding measures in normal, nonamputee (NA) controls using Dunnetts test. Regardless of foot type, transtibial (TT) amputees walked slower than non amputee controls (63.3-65.8 m/min versus 78.5 m/min, p < 0.05) and their stride length was shorter (1.21-1.26 m versus 1.41 m, p < 0.01). In early stance, peak foot and shank velocities were lower (p < 0.01) for both the SL and FF while only shank velocity was lower (p < 0.01) with the SA compared to NA controls. Significant delays in the timing of early stance events such as peak shank velocity, peak ankle plantarflexion and peak knee flexion compromised shank and knee stability in TT amputees. Foot and shank mobility was uncontrolled with the SA design while ankle mobility was restricted by the FF and SL feet. In NA controls on the other hand, appropriate timing and rate of segment velocity changes preserved dynamic stability and forward progression in early stance. This was evidenced by rapid decreases in foot and shank velocity as the thigh velocity increased during weight acceptance. Future prosthetic designs should provide TT amputees with improved ankle mobility that attempt to capture the dynamic characteristics of a normal articulation between the foot and shank segments during the early stance weight acceptance period.