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Biomedical subjects

C M Powers

Publications and source records attributed to C M Powers.

30 records · Page 2Linked to original sources
PubMed1997

Stair ambulation in persons with transtibial amputation: an analysis of the Seattle LightFoot.

The purpose of this study was to document gait patterns in a group of individuals with transtibial amputations (TTA) during stair ambulation, and to identify the functional limitations associated with this task. Ten persons with TTA fitted with a Seattle LightFoot prosthetic component, and 14 nondisabled subjects participated in this study. Electromyographic activity (EMG) of the vastus lateralis (VL), rectus femoris (RF), gluteus maximus (GMAX), semimembranosus (SMEMB), biceps femoris long head (BFLH), and biceps femoris short head (BFSH) was assessed using indwelling wire electrodes during ascending and descending stairs. Lower limb kinematics (VICON) and stride characteristics (Footswitch Stride Analyzer System) also were collected. Stride characteristics revealed that those with TTA had a significantly slower rate of stair ambulation and demonstrated stance phase asymmetry between limbs compared to the nondisabled. Kinematic analysis determined significant limitations in prosthetic ankle motion, which necessitated compensatory functions at the hip and knee to accomplish stair ascent and descent and resulted in significantly greater muscular effort (increased EMG intensity and duration) compared to nondisabled.

Adult↗
PubMed1996

The influence of lower-extremity muscle force on gait characteristics in individuals with below-knee amputations secondary to vascular disease.

BACKGROUND AND PURPOSE: The purpose of this study was to establish the relationship between isometric muscle force and temporal-spatial gait characteristics for individuals who have had a below-knee amputation secondary to vascular disease. SUBJECTS: Twenty-two individuals (15 male, 7 female) with dysvascular below-knee amputations participated. The male subjects were aged 35 to 72 years (x=59.6, SD=11.1), and the female subjects were aged 54 to 68 years (x=60.5, SD=5.1). Methods. The subjects underwent stride analysis during free-speed and fast walking, as well as bilateral isometric force testing of their remaining hip, knee, and ankle muscles. RESULTS: Stepwise regression analysis revealed that hip extensor force on the amputated side was the only predictor of both free speed (gamma=.50) and fast speed (gamma=.72). Hip abduction force of the sound++ limb was correlated with cadence for both free-speed trials (gamma=.57) and fast-speed trials (gamma=.57). Sound-side knee extensor force was related to free-speed stride length (gamma=.44), whereas residual-limb knee extensor force predicted stride length during fast walking (gamma=.67). CONCLUSION AND DISCUSSION: These results indicate that adequate force is necessary in both residual and sound limbs to improve functional gait ability and that ther hip extensors and abductors and the knee extensors should be emphasized in the rehabilitation of individuals with below-knee amputations.

Adult↗
PubMed1996

Timing and intensity of vastus muscle activity during functional activities in subjects with and without patellofemoral pain.

BACKGROUND AND PURPOSE: Differences in intensity and timing of muscle activity between the vastus medialis and vastus lateralis muscles have been hypothesized as contributing to lateral patellar tracking and patellofemoral pain (PFP). The purpose of this study was to ascertain whether there were differences in the activity of the vastus muscles that would be suggestive of patellar instability in subjects with PFP. SUBJECTS: Twenty-six subjects with PFP and 19 subjects without PFP participated in the study. METHODS: Fine-wire electromyography was used to record activity of the vastus medialis oblique, vastus medialis longus, vastus lateralis, and vastus intermedius muscles during level walking, stair climbing, and walking on ramps. Knee motion was assessed using a six-camera motion analysis system. RESULTS: No differences in onset or cessation of muscle activity was found among the vastus muscles for either group, regardless of condition. Subjects with PFP demonstrated less activity of all vastus muscles for level walking and ramp walking than did subjects without PFP. CONCLUSIONS AND DISCUSSION: These results do not support the hypothesis that timing or intensity differences between the vastus medialis and vastus lateralis muscles are associated with PFP.

Adolescent↗
PubMed1995

Rearfoot posture in subjects with patellofemoral pain.

The relationship between structural foot deformities and excessive subtalar joint pronation as being contributory to patellofemoral pain has not been well documented. It was the purpose of this study to assess the rearfoot posture in patients diagnosed with patellofemoral pain compared with a normal population. In addition, the intratester reliability in obtaining rearfoot measurements was assessed for right and left sides in 21 normal subjects. A goniometer was used to measure rearfoot posture in 30 female subjects (15 with patellofemoral pain and 15 controls). Measurements were taken with the subjects prone and the subtalar joint in neutral. Intraclass correlation coefficients were good for both the right and left measurements (.87 and .86, respectively). A small but significant increase in rearfoot varus was found in the patellofemoral pain group compared with the control group (8.9 vs. 6.8 degrees; p = .0002). These results suggest that increased rearfoot varus may be a contributing factor in patellofemoral pain and should be assessed when evaluating the events at the subtalar joint and the lower extremity. In addition, it has been demonstrated that consistent rearfoot measurements can be obtained by an individual clinician.

Adult↗
PubMed1995

Energy expenditure during ambulation in dysvascular and traumatic below-knee amputees: a comparison of five prosthetic feet.

Recent advancement in prosthetic technology has led to the development of dynamic elastic response feet (DER), which are reported to store and release energy to facilitate gait. To date, there has been no objective evidence to suggest energy conservation while using these foot designs. The purpose of this study was to compare the energy expenditure of five commercially available prosthetic feet (SACH and four DER feet) in both the traumatic and dysvascular populations during level walking. Seventeen male subjects with below-knee amputation (nine traumatic and seven dysvascular) were tested for energy expenditure (Douglas Bag technique) during a 20-min walk while wearing each of the prosthetic feet. The DER prosthetic foot designs were not shown to reduce the energy cost (ml O2/kg-m) or rate of energy expenditure (ml O2/kg-min) compared to the SACH foot. Overall, the traumatic amputees had a similar oxygen consumption per meter traveled compared to the dysvascular amputees; however, the rate of energy consumption was much higher in the traumatic group. This increased rate was a function of the greater walking velocity employed by the traumatic subjects, made possible by their better physical fitness.

Amputation, Traumatic↗
PubMed1995

The effect of five prosthetic feet on the gait and loading of the sound limb in dysvascular below-knee amputees.

The purpose of this study was to determine the effects of prosthetic foot design on the vertical ground reaction forces experienced by the sound and amputated limbs in a group of persons with dysvascular below-knee amputations. Stride characteristics, joint motion, and ground reaction forces were recorded simultaneously during a self-selected free walking velocity in seven subjects wearing five different prosthetic feet (SACH, Flex-Foot, Carbon Copy II, Seattle, Quantum). Subjects used each foot for one month prior to testing. Results indicated that the sound limb was exposed to higher vertical ground reaction forces than normal despite a reduced walking velocity. Use of the Flex-Foot resulted in the lowest sound limb vertical forces, which appears to be related to its large arc of dorsiflexion motion. In addition, there was increased loading response knee flexion of the sound limb indicating an attempt by these subjects to modulate floor impact. These results suggest that the intact lower extremity is susceptible to excessive floor impact, and that prosthetic foot design can have an effect on the magnitude of the vertical forces experienced by the limb.

Aged↗
PubMed1994

Single mRNAs visualized by ultrastructural in situ hybridization are principally localized at actin filament intersections in fibroblasts.

Considerable evidence indicates that mRNA associates with structural filaments in the cell (cytoskeleton). This relationship would be an important mechanism to effect mRNA sorting since specific mRNAs could be sequestered at sites within the cell. In addition, it can provide a mechanism for spatial regulation of mRNA expression. However, the precise structural interactions between mRNA and the cytoskeleton have yet to be defined. An objective of this work was to visualize "individual" poly(A) mRNA molecules in situ by electron microscopy to identify their relationship to individual filaments. Poly(A) RNA and filaments were identified simultaneously using antibodies to detect hybridized probe and filaments or actin-binding proteins. In human fibroblasts, most of the poly(A) mRNA (72%) was localized within 5 nm of orthogonal networks of F-actin filaments. Poly(A) mRNA also colocalized with vimentin filaments (29%) and microtubules (< 10%). The sites of mRNA localization were predominantly at filament intersections. The majority of poly(A) mRNA and polysomes colocalized with the actin crosslinking proteins, filamin, and alpha-actinin, and the elongation factor, EF-1 alpha (actin-binding protein; ABP-50). Evidence that intersections contained single mRNA molecules was provided by using a labeled oligo dT probe to prime the synthesis of cDNA in situ using reverse transcriptase. Both the poly(A) and cis sequences of the same mRNA molecule could then be visualized independently. We propose that the cytoskeletal intersection is a mRNA receptor and serves as a "microdomain" where mRNA is attached and functionally expressed.

Actins↗
PubMed1994

Isometric shoulder torque in subjects with spinal cord injury.

The etiology of shoulder pain in spinal cord injured (SCI) patients has been attributed to overuse, with dysfunction being more prevalent as the time since injury increases. Impingement syndrome, the most common diagnosis in this population, may be related to weakness of the rotator cuff and shoulder girdle musculature. Shoulder dysfunction is greater in subjects with SCI than in able-bodied patients; consequently, this study compares isometric strength of quadriplegic and paraplegic subjects to able-bodied controls. Peak isometric torque for internal rotation, external rotation, and scapular elevation was assessed using a Lido isokinetic dynamometer. The strength (torque) values of the quadriplegic group were significantly lower than the control group and paraplegic group for all motions tested (p < .0005). The only significant difference between the paraplegic and able-bodied groups was found with internal rotation (p < .0001). These results indicate that quadriplegic patients may be at greater risk for shoulder pathology because of both muscular limitation and increased functional demand.

Adult↗
PubMed1994

Influence of prosthetic foot design on sound limb loading in adults with unilateral below-knee amputations.

Altered gait patterns resulting from amputation has been implicated as a possible mechanism for early degenerative changes in the sound limb of unilateral amputees. The purpose of this study was to examine the ground reaction force characteristics and joint motion in this population. Ground reaction forces, joint motion, and stride characteristics of 10 traumatic below-knee amputees were analyzed while wearing five different prosthetic feet (SACH, Flex-foot, Carbon Copy II, Seattle, and Quantum). Subjects used each foot for 1 month prior to testing. Results indicated that the Flex-foot significantly reduced the initial peak of the vertical ground reaction force on the sound limb compared to all other feet tested (p < .0001). The SACH foot consistently produced the greatest ground reaction forces on the sound limb; however, this was not statistically significant. The effective factor of the Flex-foot appears to be minimization of the center of gravity elevation, which was accomplished through a significant increase in terminal stance dorsiflexion compared to the other feet tested (p < .0001).

Adult↗
PubMed1994

Below-knee amputee gait in stair ambulation. A comparison of stride characteristics using five different prosthetic feet.

The purpose of this study was to compare the stride characteristics provided by four of the new dynamic elastic response prosthetic feet and the SACH foot to determine if any of them provided an increased performance during stair ambulation. Ten traumatic below-knee amputees were studied; each of them tested all five prosthetic feet (Flex-Foot, Carbon Copy II, Seattle, Quantum, and SACH). Compression closing footswitches were used to calculate stride characteristics while ascending and descending a four-step staircase. The only significant difference between feet was found during the initial double-limb support (IDLS) phase of stair ascent, with the Flex-Foot providing a more symmetrical amputated:sound limb IDLS ratio compared with the SACH foot (1.03 versus 1.30). The increased IDLS time seen with the SACH foot reflects the inability to adequately advance the tibia and body weight over the prosthetic foot to achieve progression. This lack of progression and symmetrical gait pattern between limbs may be a function of the limited dorsiflexion range inherent with the SACH foot.

Amputation, Traumatic↗
PubMedDate not supplied

Quantification of patellar tracking using kinematic MRI.

The purpose of this study was to describe a method to quantify dynamic patellar tracking using kinematic MRI (KMRI). Twelve normal females and three patients with patellofemoral pain participated. Imaging was performed with a 1.5-T/64-MHz MR system using a fast spoiled gradient-recalled acquisition in the steady state (GRASS) pulse sequence. A nonferromagnetic positioning device permitted active, bilateral knee extension against resistance (15% bwt) from 45 degrees knee flexion to full extension. Subjects were instructed to extend their knees at a rate of 9 degrees per second, which allowed images to be obtained at 45 degrees, 36 degrees, 27 degrees, 18 degrees, 9 degrees, and 0 degrees. All images were assessed for medial/lateral patellar displacement, patellar tilt, and sulcus angle using a computer-aided system. Normal patellar motion was characterized by medial movement from 45 degrees to 18 degrees, followed by a reversal toward lateral displacement from 18 degrees to full extension. The results for patellar tilt revealed a tendency toward decreasing lateral tilt as the knee extended. Sulcus angle measurements indicated that the patella was moving to a more shallow portion of the trochlear groove (superiorly) during extension.

Adult↗