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Biomedical subjects

P R Cavanagh

Publications and source records attributed to P R Cavanagh.

At least 37 records · Page 2Linked to original sources
PubMed1998

The role of muscle spindles in ankle movement perception in human subjects with diabetic neuropathy.

The objective of this study was to develop a quantitative method to assess muscle spindle function. Three groups of subjects were studied: ten young and healthy subjects, 15 older subjects with diabetic neuropathy, and 15 age-matched controls. All subjects performed an ankle-movement matching task with and without muscle vibration. Input from the plantar cutaneous mechanoreceptors was minimized by using a foot-clamping device. The younger subjects tracked the movement very well, but vibration had a significant effect on their performance (P < 0.001). Similar results were seen in the older control subjects, but they were less successful in tracking movement and slightly less affected by vibration. The neuropathic subjects had the most difficulty tracking, and vibration had only a small but still significant effect on their performance. The interaction between the group and the vibration effect was highly significant (P < 0.001), indicating that the performance of the control subjects changed to a greater degree in the presence of vibration than the performance of the subjects with diabetic neuropathy. Muscle spindles are the primary receptors that are involved in the change in tracking performance when vibration is added during an ankle-movement matching task, and we therefore conclude that the procedure described provides a quantitative evaluation of muscle spindle function. The results demonstrate that diabetic neuropathy degrades muscle sensory function, which may contribute to the impaired balance and unsteadiness of gait that has been observed in diabetic neuropathy.

Achilles Tendon↗
PubMed1998

The Penn State Safety Floor: Part I--Design parameters associated with walking deflections.

A new flooring system has been developed to reduce peak impact forces to the hips when humans fall. The new safety floor is designed to remain relatively rigid under normal walking conditions, but to deform elastically when impacted during a fall. Design objectives included minimizing peak force experienced by the femur during a fall-induced impact, while maintaining a maximum of 2 mm of floor deflection during walking. Finite Element Models (FEMs) were developed to capture the complex dynamics of impact response between two deformable bodies. Validation of the finite element models included analytical calculations of theoretical buckling column response, experimental quasi-static loading of full-scale flooring prototypes, and flooring response during walking trials. Finite Element Method results compared well with theoretical and experimental data. Both finite element and experimental data suggest that the proposed safety floor can effectively meet the design goal of 2 mm maximum deflection during walking, while effectively reducing impact forces during a fall.

Accidental Falls↗
PubMed1998

The Penn State Safety Floor: Part II--Reduction of fall-related peak impact forces on the femur.

The goal of this study was to develop and validate a finite element model (FEM) for use in the design of a flooring system that would provide a stable walking surface during normal locomotion but would also deform elastically under higher loads, such as those resulting from falls. The new flooring system is designed to reduce the peak force on the femoral neck during a lateral fall onto the hip. The new flooring system is passive in nature and exhibits two distinct stiffnesses. During normal activities, the floor remains essentially rigid. Upon impact, the floor collapses and becomes significantly softer. The flooring system consists of a multitude of columns supporting a continuous walking surface. The columns were designed to remain stiff up to a specific load and, after exceeding this load, to deform elastically. The flooring returns to its original shape after impact. Part I of this study presented finite element and experimental results demonstrating that the floor deflection during normal walking remained less than 2 mm. To facilitate the floor's development further, a nonlinear finite element model simulating the transient-impact response of a human hip against various floor configurations was developed. Nonlinearities included in the finite element models were: changing topology of deformable-body-to-deformable-body contact, snap-through buckling, soft tissue stiffness and damping, and large deformations. Experimental models developed for validating the finite element model included an anthropomorphic hip, an impact delivery mechanism, a data collection system, and four hand-fabricated floor tiles. The finite element model discussed in this study is shown to capture experimentally observed trends in peak femoral neck force reduction as a function of flooring design parameters. This study also indicates that a floor can be designed that deflects minimally during walking and reduces the peak force on the femoral neck during a fall-related impact by 15.2 percent.

Accidental Falls↗
PubMed1998

The non-healing diabetic foot wound: fact or fiction?

Wounds on the feet of diabetic patients are often labeled as "non-healing." This article discusses the basis for and the dangers of such a classification. The evidence suggests that if the foot has an adequate vascular supply and no significant infection, a plantar wound that does not heal is the result of poor treatment and/or poor compliance. Wounds that do not heal despite optimal treatment and compliance are extremely rare and need to be referred to the appropriate specialist for care.

Diabetic Foot↗
PubMed1998

The Charcot foot in diabetes: six key points.

The Charcot foot commonly goes unrecognized, particularly in the acute phase, until severe complications occur. Early recognition and diagnosis, immediate immobilization and a lifelong program of preventive care can minimize the morbidity associated with this potentially devastating complication of diabetic neuropathy. If unrecognized or improperly managed, the Charcot foot can have disastrous consequences, including amputation. The acute Charcot foot is usually painless and may mimic cellulitis or deep venous thrombosis. Although the initial radiograph may be normal, making diagnosis difficult, immediate detection and immobilization of the foot are essential in the management of the Charcot foot. A lifelong program of patient education, protective footwear and routine foot care is required to prevent complications such as foot ulceration.

Acute Disease↗
PubMed1997

The total contact cast: a method for treating neuropathic diabetic ulcers.

Plantar ulcers that do not heal in patients with diabetes and peripheral sensory neuropathy have been shown to be precursors of lower extremity amputation. The total contact cast is considered by many authorities to be the most effective technique for healing of wounds in the neuropathic extremity, yet it still is not widely used in clinical practice. Use of the total contact cast allows mobilization and results in diminished edema and decreased pressure over the ulcerated area. Complete healing usually occurs in eight weeks or less. Total contact casting with careful follow-up should be considered as a useful modality for healing plantar ulcers in diabetic patients with neuropathy of the extremities.

Adult↗
PubMed1997

The relationship of static foot structure to dynamic foot function.

Many theories have been advanced concerning the relationship between structure and function in the human foot, yet few of these theories have been subjected to quantitative examination. In this study, foot structure was characterized by 27 measurements taken from standardized lateral and dorsi-plantar weight-bearing plain radiographs of 50 healthy adult subjects. Regional plantar pressure distribution data collected from the same feet were chosen as the functional measures. A stepwise regression analysis was performed to (1) explore what portion of the variance in peak plantar pressure during walking can be explained by the radiographic measurements, and (2) identify structural characteristics of the foot which are significant predictors of peak plantar pressure under the heel and the first metatarsal head (MTH1). Most of the radiographic measurements were highly reliable. However, only 31 and 38% of the variance in peak plantar pressure at the heel and MTH1, respectively, could be explained using multiple regression analyses with the radiographic measurements as independent variables. Among the structural predictors that were identified, soft tissue thickness (e.g. calcaneus or sesamoid heights), and arch-related measurements were the strongest predictors of plantar pressure under both the heel and the first metatarsal head. We conclude that, in normal subjects, only about 35% of the variance in dynamic plantar pressure can be explained by the measurements of foot structure derived from radiographs. This implies that the dynamics of gait are likely to exert the major influences on plantar pressure during walking.

Adult↗
PubMed1997

The effect of insoles in therapeutic footwear--a finite element approach.

Current practice in the prevention of recurrence of neuropathic foot ulcers is to prescribe accommodative in-shoe orthoses or insoles which reduce plantar pressure levels at locations of bony prominences, particularly under the metatarsal heads. To date, design of these orthoses has largely been a trial and error process. There is little quantitative information available regarding the effects of thickness and the influence of soft tissue characteristics on the cushioning effect of such interventions. The current paper investigated alterations in pressure under the second metatarsal head as a function of insole thickness and tissue thickness. Both experimental and quasi-static plane strain finite element approaches were employed. The orthoses chosen reduced plantar pressure by a maximum of approximately 30% and were more effective (on a percentage basis) in the setting of reduced sub-metatarsal tissue thickness. Peak normal stresses predicted by the FE models were, on average, within 5.9% of experimentally measured values for the normal tissue case and 8.1% for the reduced tissue case. The techniques presented represent a promising approach to understanding plantar cushioning and the principles involved in the design of therapeutic footwear for insensate feet.

Equipment Design↗
PubMed1997

Plantar pressure reduction in an incremental weight-bearing system.

BACKGROUND AND PURPOSE: Harness-supported treadmill ambulation has been advocated for patients to provide reduction in weight bearing to healing tissues and to reduce the energy cost of treadmill ambulation. The purposes of this technical report are to analyze the ability of one of these devices (Zuni Exercise System) to support a specific percentage of a subject's body weight during walking and running and to explore the relationship of unloading to pressure reduction in selected plantar surface regions of the foot. SUBJECTS: Ten male volunteers with no known foot pathology participated. METHODS: In-shoe plantar pressure and vertical ground reaction forces (GRFs) were measured during walking and running at full body weight and at 20% of body weight supported. RESULTS: Walking at a setting of 20% of body weight supported resulted in a reduction of the first and second vertical force peaks of 23.8% (SD = 7.3%) and 27.2% (SD = 4.1%), respectively. The total force-time integral during walking unloaded was 22.8% (SD = 3.3%). During running, the active vertical force peak and total force-time integral were reduced by 19.9% (SD = 6.0%) and 20.0% (SD = 3.3%), respectively, in the unloaded condition. Plantar pressures were reduced from 6.8% to 27.8% in the body weight-supported conditions. The reduction was variable across different regions of the foot. CONCLUSION AND DISCUSSION: The Zuni Exercise System appears to reduce the vertical component of the GRF during walking and running with 20% of body weight supported. Plantar pressures were reduced during body weight-supported conditions, but the reduction varied at different regions of the foot.

Adult↗
PubMed1997

The mechanism of plantar unloading in total contact casts: implications for design and clinical use.

Although the total contact cast (TCC) has been shown to be an extremely effective treatment for the healing of plantar ulcers in diabetic patients, little is known about the biomechanics of its action. In this study, plantar pressure and ground reaction force measurements were obtained from over 750 foot contacts as five subjects with known elevated plantar forefoot pressures walked barefoot, in a padded cast shoe, and a TCC. Peak plantar pressures in the forefoot were markedly reduced in the cast compared with both barefoot and shoe walking (reductions of 75% and 86% respectively, P < 0.05). Peak plantar pressures in the heel were not, however, significantly different between the shoe and the TCC, and the longer duration of heel loading resulted in an impulse that was more than twice as great in the cast compared with the shoe (P < 0.05). An analysis of load distribution indicated that the mechanisms by which the TCC achieves forefoot unloading are (1) transfer of approximately 30% of the load from the leg directly to the cast wall, (2) greater proportionate load sharing by the heel, and (3) removal of a load-bearing surface from the metatarsal heads because of the "cavity" created by the soft foam covering the forefoot. These results point out some of the "essential design features" of the TCC (which are different from what had been previously supposed), support the use of the TCC for healing plantar ulcers in the forefoot, but raise questions about its utility in the healing of plantar ulcers on the heel.

Adult↗
PubMed1997

How do the elderly negotiate stairs?

Stair navigation, particularly stair descent, is an extremely challenging and dangerous locomotor task, yet studies suggest that most elderly are unlikely to move to new residences in order to avoid this challenge. The knee and ankle are the key joints where adequate strength and power are required for safe stair descent, and it is not yet clear if sarcopenia in the elderly is likely to result in residual strength below that which is required for successful stair performance. Sensory cues are also critical, and the lack of literature on the specific roles of the various intrinsic and extrinsic factors that affect stair navigation is a clear indication of the need for such research in order to define safer strategies and optimal conditions for elderly individuals to transit between living areas of differing levels.

Aged↗
PubMed1996

Diabetic sensory neuropathy effect on ankle joint movement perception.

OBJECTIVE: To determine if diabetic subjects with lower extremity cutaneous sensory neuropathy also have a loss of ankle joint movement perception. The strength of association between measurements of ankle joint movement perception and measures of cutaneous sensory function was also investigated. DESIGN: Diabetic subjects with and without sensory neuropathy and individuals without diabetes participated in this study. SETTING: All subjects were community-living individuals. PARTICIPANTS: Fifty-one subjects, ages 40 to 68. Seventeen of the 34 subjects with diabetes had significant distal sensory neuropathy as determined by cutaneous perception of mechanical vibration. All individuals without diabetes were volunteers from the community. Most subjects with diabetes were recruited through direct referral from their physicians. INTERVENTIONS: Ankle joint movement perception threshold (JMPT) was assessed using a device designed for this study. Cutaneous sensory function under both halluces was measured for vibration perception using a vibrometer and for touch-pressure perception using Semmes-Weinstein monofilaments. MAIN OUTCOME MEASURES: Ankle JMPTs (degrees) were compared to measurements of cutaneous vibration perception (volts) and touch-pressure perception (monofilaments force ratings). RESULTS: Diabetic subjects with cutaneous sensory neuropathy demonstrated a significant loss of ankle movement perception (p < .01). Correlation between JMPT and cutaneous sensory tests ranged from Spearman's rank r = .43 to .67. CONCLUSIONS: Although individuals with cutaneous sensory loss secondary to diabetic neuropathy also demonstrated loss of movement perception at the ankle, the relatively low explained variance between the two types of assessment (18% to 45%) indicates that the severity of ankle joint movement perception deficits cannot be directly implied from cutaneous sensory tests.

Adult↗
PubMed1996

Six weeks of training does not change running mechanics or improve running economy.

Running technique and economy (VO2submax) were examined before and after a 6-wk period of running training. Fifteen males were filmed and performed 10-min economy runs at 3.36 m.s-1 on a treadmill. An incremental treadmill test was used to record running performance and maximal oxygen consumption (VO2max). Subjects were randomly assigned to a training group and a control group that did not participate in any running program. There were no significant changes in kinematic variables between pre- and post-training tests for either group. Neither were there any significant physiological changes over the 6 wk in the control group. However, the training group demonstrated a significantly (P < 0.01) increased VO2max (57.7 +/- 6.2 vs 61.3 +/- 6.3 ml.kg-1.min-1) and running performance. VO2submax in the training group was significantly (P < 0.05) worse (41.0 +/- 4.5 vs 42.4 +/- 4.3 ml.kg-1.min-1) post-training, although the percent utilization of VO2max (71.6 +/- 7.9 vs 69.3 +/- 6.9%) and submaximal heart rate (169 +/- 15 vs 161 +/- 15 beats.min-1) were significantly lower (P < 0.05). The training-induced improvements in running performance could be attributed to physiological rather than biomechanical modifications. There were no changes in biomechanical descriptors of running style that signaled changes in running economy.

Adolescent↗
PubMed1996

Foot function in diabetic patients after partial amputation.

The function of partially amputated feet in 10 patients with diabetes mellitus was studied. First-step bilateral barefoot plantar pressure distribution and three-dimensional kinematic data were collected using a Novel EMED platform and three video cameras. Analysis of the plantar pressure data revealed a significantly greater mean peak plantar pressure in the feet with transmetatarsal amputation (TMA) than in the intact feet of the same patients. The heels of the amputated feet had significantly lower mean peak plantar pressures than all the forefoot regions. A significantly greater maximum dynamic dorsiflexion range of motion was seen in the intact compared with the TMA feet. However, no difference was noted in the static dorsiflexion range of motion between the two feet and there was, therefore, a trend for the TMA feet to use less of the available range of motion. Given the altered kinematics and elevated plantar pressures noted in this study, careful postsurgical footwear management of feet with TMA would appear to be essential if ulceration is to be prevented.

Aged↗
PubMed1996

In-shoe plantar pressures during activities of daily living: implications for therapeutic footwear design.

Pressures on the plantar surface of the foot during activities of daily living were measured in 12 young, healthy subjects using an in-shoe pressure-measuring device. The tasks chosen were standing, slow and fast walking, slow running, walking up and down stairs, rising from and sitting in a chair, and walking in a circle. All except the sitting tasks showed significantly higher pressures in all regions of the foot compared with standing, with the exception of walking up stairs and walking down stairs in the heel region. Both running and walking in a circle led to higher pressures (up to 1.42 times greater) in the total foot compared with "normal" walking. Furthermore, pressures during other activities were not always well predicted by walking pressures (r2 = 0.10-0.77). Therefore, measurement during level walking alone cannot be considered to fully define the plantar pressure affecting a foot in a particular shoe during activities of daily life.

Activities of Daily Living↗
PubMed1996

A method for the investigation of the effects of outsole modifications in therapeutic footwear.

Experiments to determine the effects of therapeutic shoe outsole modifications frequently require the examination of many different configurations and typically use in-shoe pressure measurement to determine the optimal design. A method is presented here to allow the foot-shoe interface to remain undisturbed as different outsole designs are used in the same patient. A standard extra-depth (or super extra-depth) shoe is modified to house three receptacles for quarter-turn fasteners in a carbon fiber plate. The fasteners pass through the outsole unit and secure it firmly to the plate. Results from a typical experiment are presented to illustrate the effectiveness of the approach. It is possible that a large clinic could use this approach in complex cases to assist with optimal footwear prescription.

Humans↗