Andrew Gitter

Joint moment and muscle power output characteristics of below knee amputees during running: The influence of energy storing prosthetic feet

Stance phase joint moments, muscle power outputs and mechanical energy characteristics were determined in five normal and five below knee amputee subjects running at 2.8 m s-1. The amputees were studied sequentially on three different prosthetic feet: the SACH foot (solid ankle cushion heel), and two energy storing feet, Seattle and Flex. While wearing the SACH foot, the amputees exhibited major alterations in the distribution and magnitude of muscle power output and muscle work: (1) the total work done by the lower extremity was reduced; (2) the hip extensors became the main source of energy absorption and generation, while in normal subjects the ankle plantarflexors were the major energy generators and the knee extensors the major energy absorbers; (3) the eccentric and concentric knee extensor power outputs were reduced and an abnormal concentric knee flexor power output was noted immediately after heel contact. In four of the amputees, energy storing feet resulted in improvements in the power output and mechanical work characteristics of the lower extremity: (1) the energy storing prosthetic feet generated 2-3 times greater energy than the SACH foot; (2) with the Flex foot the amputees exhibited a more normal pattern and magnitude of hip and knee extensor muscle work. One of the subjects, however, exhibited increased abnormalities with the energy storing prosthetic feet. The amount of energy restored relative to the amount of energy absorbed by each of the prosthetic feet was greater with the energy storing feet than the SACH foot (Flex 84%, Seattle 52%, SACH 31%).

Biomechanical Analysis Of The Influence Of Prosthetic Feet On Below-knee Amputee Walking

Although energy storing prosthetic feet have achieved widespread clinical acceptance, the effect of these components on the biomechanics of below-knee amputee gait is poorly understood. The purpose of this study was to determine the biomechanical adaptations used by the below-knee amputee while wearing a conventional prosthetic foot and to assess the influence of energy storing prosthetic feet on these adaptations. Mechanical power outputs of the lower extremity in five normal and five below-knee amputee subjects using the SACH, Seattle and Flex feet were studied. Ground reaction forces and kinematic data were collected at a walking speed of 1.5 m/s and were used to determine the muscular power outputs of the lower extremity during stance. Consistent patterns of muscular power output at the hip and knee of the residual limb occur. While wearing the SACH foot, negligible energy generation occurs at the prosthetic foot during pushoff. A decrease in energy absorption at the knee during the first half of stance and an increase in energy generation by the hip extensors were the major adaptations noted in the proximal muscle groups. Compared to the SACH foot, the energy storing feet demonstrated increased energy generation during pushoff. Despite the improvements in the performance of the energy storing prosthetic feet, no significant differences were found in the pattern or magnitude of knee and hip power outputs compared to the SACH foot.

Ulnar nerve entrapment at the elbow: Correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings

The diagnosis of ulnar nerve entrapment at the elbow has relied primarily on clinical and electrodiagnostic findings. Recently, magnetic resonance imaging (MRI) has been used in the evaluation of peripheral nerve entrapment disorders to document signal and configuration changes in nerves. We performed a prospective study on a population of 31 elbows in 27 patients with ulnar nerve entrapment at the elbow. The study correlated MRI findings with clinical, electrodiagnostic, and operative findings. A control population consisting of 10 asymptomatic subjects also was studied by MRI. Electrodiagnostic evaluation confirmed ulnar neuropathy in 24 (77%) elbows of the 31, with localization to the elbow region in 21 (68%). MRI, using a short tau inversion recovery sequence, demonstrated increased signal of the ulnar nerve in 30 (97%) elbows of the 31 and enlargement of the ulnar nerve in 23 (74%). No MRI abnormalities were found in the control population. MRI signal increase of the ulnar nerve occurred an average of 27 mm proximal to the distal humerus and extended distally an average of 4 mm below the distal humerus. The mean total length of increased ulnar nerve signal was 34 mm. Ulnar nerve enlargement occurred an average of 19 mm proximal to the distal humerus and extended distally an average of 8 mm above the distal humerus. The mean total length of ulnar nerve enlargement was 12 mm. The 12 patients who underwent a surgical procedure for ulnar nerve entrapment were found to have ulnar nerve compression, with 9 (75%) having excellent and 3 (25%) having good postoperative results. In this study, MRI was both sensitive and specific in diagnosing ulnar nerve entrapment at the elbow as defined by clinical, electrodiagnostic, and operative findings.

THE ROLE OF ANKLE PLANTAR FLEXOR MUSCLE WORK DURING WALKING

Impaired ankle plantar flexor (APF) function is a frequent cause of gait limitations, but the role of the APF in the forward propulsion of the body remains controversial. To better understand both the direct and indirect effects of the APF during push-off and through advancement of the leg, mechanical work and inverse dynamic analyses were performed on 8 normal subjects during level walking. During push-off, 23.1 joules (J) of energy were generated, primarily by the APF, but only 4.2 J of this energy is transferred into the trunk. Ankle plantar flexor work is primarily used to accelerate the leg into swing. Most of the energy, 18.6 J, is recovered by transfer into the trunk at the end of swing. The timing of the energy transfers relative to the trunk motion imply that the APF contributes to the forward kinetic energy of the trunk but that other mechanisms likely account for the work used to raise the trunk against gravity.

Carpal tunnel syndrome: Correlation of magnetic resonance imaging, clinical, electrodiagnostic, and intraoperative findings

We undertook a prospective study of 43 wrists in 32 patients who had been clinically diagnosed as having carpal tunnel syndrome (study group) and 5 wrists in people who had no symptoms (control group), correlating the clinical, electrodiagnostic, intraoperative, and magnetic resonance imaging (MRI) findings. MRI of the carpal tunnel and thenar eminence was performed, using coronal and axial T1- and T2-weighted, proton density, and short tau inversion recovery sequences. Abnormalities of the median nerve, as revealed by MRI, were found in 43 of 43 (100%) wrists in the study group and in 0 of 5 (0%) wrists in the control group. Increased signal of the median nerve was seen in 41 of 43 (95%) wrists, increased signal of the flexor tendon sheath in 41 of 43 (95%), volar bowing of the flexor retinaculum in 39 of 43 (91%), increased distance between the flexor tendons in 37 of 43 (86%), and abnormal nerve configuration in 28 of 43 (65%). Increased short tau inversion recovery signal of the thenar muscles was found in 5 of 43 (12%) wrists, all of which had undergone severe denervation changes, as revealed by electromyography. Operative release was performed for 27 of 43 (63%) wrists, and follow-up was obtained for 42 of 43 (98%). A good or excellent postoperative outcome resulted for 20 of 27 (74%) patients, a fair outcome for 2 of 27 (7%), and a poor outcome for 4 of 27 (15%), and 1 of 27 (4%) patients was lost to follow-up. For patients undergoing carpal tunnel release whose MRI revealed an abnormal nerve configuration, the outcome was improved, with good or excellent results in 15 of 18 (83%) patients. No association with outcome was seen with median nerve or flexor tendon signal changes, increased interspace between the flexor tendons, or flexor retinaculum bowing. Our results indicate that MRI is a sensitive diagnostic modality that can demonstrate signal and configurational abnormalities of the median nerve in patients diagnosed with carpal tunnel syndrome. Increased signal of the thenar muscles, as revealed by MRI, using short tau inversion recovery sequences, occurs only in muscles that have undergone severe denervation changes, as revealed by electromyography.

A reassessment of center-of-mass dynamics as a determinate of the metabolic inefficiency of above-knee amputee ambulation

Above-knee (AK) amputation substantially increases the metabolic cost of ambulation. Although the biomechanical mechanisms contributing to the increase have not been well studied, it has been assumed that altered center-of-mass (COM) kinematics and increased mechanical work account for the adverse effect on oxygen consumption. To understand better the relationship between mechanical work and the metabolic cost, 8 normal subjects and 8 traumatic AK amputees were studied during overground ambulation. Using segmental energy and inverse dynamics analyses, trunk COM excursion, the mechanical work associated with movement of the COM, and the work done by the major lower limb sagittal plane muscle groups were determined. Oxygen consumption was measured using the Douglas bag technique. The metabolic cost was 27% higher in amputees compared with normal subjects (P > 0.01), but no significant differences were noted in the excursion of or the work done on the trunk COM. The muscle work needed to complete a stride was significantly greater in normal subjects compared with amputees. These results indicate that the role of abnormal kinematics and their effect on the mechanical work of walking are complex and incompletely understood, but may be overemphasized as a cause of the increased metabolic cost. Alternative mechanisms for the metabolic inefficiency must be considered.

Energy transfer mechanisms as a compensatory strategy in below knee amputee runners

Below knee amputee runners exhibit abnormalities in the mechanical work characteristics of the lower extremity musculature during stance phase. The most significant abnormality is a marked reduction in the mechanical work done in the stance phase prosthetic limb. Energy transfer across the hip joint to the trunk during deceleration of the swing phase leg may be an important energy distribution mechanism to compensate for the reduced work done during prosthetic stance phase. Five unilateral below knee amputee runners wearing the SACH prosthetic foot and 5 normal subjects were studied. All subjects ran at a controlled velocity of 2.8 ms(-1) while kinematic and ground reaction force data were collected. Using a four segment linked segment model and an inverse dynamics approach joint moments, muscle power outputs, mechanical work values and energy transfers across the hip were calculated. The total amount of energy transferred during swing phase and the energy transferred out of the swing phase leg into the trunk were both significantly greater than normal. Energy transfer mechanisms are important in influencing the lower extremity energetics during swing phase. In addition, the 74 percent increase in energy transfer out of the intact swing phase limb combined with the temporal characteristics of this energy flow suggests that energy transfer may be an adaptive mechanism that allows energy redistribution to the trunk which may partially compensate for the reduced power output of the stance phase prosthetic limb.

EFFECT OF ALTERATIONS IN PROSTHETIC SHANK MASS ON THE METABOLIC COSTS OF AMBULATION IN ABOVE-KNEE AMPUTEES

ABSTRACTThe metabolic costs of above-knee amputee ambulation are significantly greater than normal. The role of prosthetic mass and mass distribution on the metabolic costs of walking has received limited study. The metabolic costs of eight unilateral traumatic above-knee amputees were therefore studied under varying mass conditions. All of the subjects were active young amputees with a common prosthetic prescription, which included a total contact ischial containment, suction suspension socket with a graphlite knee assembly and a hydraulic unit, with a Seattle Light Foot (Model and Instrument Development, Seattle, WA). Expired gases were collected during over-ground ambulation at their self-selected walking speed and at three control speeds (.6, 1.0 and 1.5 m/s). The expired volumes and gas concentrations were measured, and the metabolic cost (ml/kg/m) at each ambulation speed was calculated. Data were collected on two further sessions with the addition of 0.68 and 1.34 kg to the center of mass of the shank, after a 1 wk acclimatization period. Results show that in the unweighted condition, the self-selected walking speed had the lowest metabolic energy expenditure and that the addition of weight to the shank did not significantly alter the metabolic costs of ambulation at any of the speeds studied. The common request for lighter weight prostheses does not appear to be based on the metabolic costs of ambulation.

Effect of prosthetic mass on swing phase work during above-knee amputee ambulation.

Recent advances in prosthetic technology have resulted in prosthetic limbs that weigh substantially less than those previously used by amputees. Although one of the clinical expectations associated with lighter limbs was that they would reduce the abnormally high metabolic cost of amputee ambulation, this has not be shown in oxygen consumption studies. This expectation was based on previous studies of normal walking, which showed that the greatest changes in mechanical work occurs in the leg during swing phase acceleration and deceleration. To better understand the relationship between limb mass and mechanical work, this study assessed the effect of varying prosthetic limb masses on the sources and magnitude of the mechanical work required for limb movement during swing. Eight above-knee amputees were studied during over ground walking at their self-selected speeds while wearing identical prosthetic limbs under three weight conditions: unweighted; 0.68 kg of added mass; 1.34 kg of added mass. Using inverse dynamics, the mechanical work from muscle sources and joint transfer sources that was used to accelerate the limb forward during late stance and early swing was determined and compared with the recovery of energy from the limb by hip joint transfer to the trunk during terminal swing deceleration. With the addition of 1.34 kg of mass, there was a combined increase in hip flexor muscle concentric work and mechanical energy transfer across the hip joint of 5.4 J, which was needed to accelerate the heavier prosthetic limb into the swing phase. The increase in acceleration work was balanced by a comparable increase (5.6 J) in the recovery of leg energy during terminal swing deceleration. By effectively conserving the additional mechanical work needed to propel a heavier limb, amputees appear to minimize any adverse effect of prosthetic mass on the mechanical work of walking. This may explain the absence of differences in metabolic cost between limbs of different masses.

Insights into amputee running. A muscle work analysis.

Czerniecki JM, Gitter A: Insights into amputee running: a muscle work analysis. Am/Phys Med Rehabil 1992;71:209-218. Five young, active, unilateral below knee amputees wearing the SACH prosthetic foot, and six normal subjects participated in the study. Subjects ran at a controlled velocity of 2.8 m/s ± 10% over a ground reaction force plate while being filmed with a video camera. Joint moments, power outputs and mechanical work characteristics were then calculated. During stance phase the amputee prosthetic limb exhibited a marked reduction in total work. There was a reduction in the mechanical work at the knee and the prosthetic foot/ankle with a compensatory increase in mechanical work by the hip musculature. The intact stance phase limb mechanical work characteristics were not significantly different from normal. The hip flexors were the only muscle group in the swing phase prosthetic limb with a significant increase in muscle work compared with normal subjects. The intact swing phase limb in contrast exhibited a marked increase in concentric muscle work by the hip flexors and eccentric muscle work by the knee flexors in early swing phase, and an increase in concentric hip extensor and eccentric knee flexor muscle work in late swing phase. The major compensatory patterns, therefore, that allow below knee amputees to run appear to be an increase in stance phase hip muscle work on the prosthetic limb and increased hip and knee muscle work on the intact limb during swing phase.