Plantar compartmental infection in the diabetic foot. The role of computed tomography.

This review discusses the role of computed tomography (CT) in the evaluation of extent of plantar soft tissue infection in the diabetic foot. CT abnormalities are correlated with conventional radiography, results of preoperative aspiration cultures, intraoperative assessment, and bone, gallium, and 111In-leukocyte scan findings. Plantar soft tissue disease respects compartmental boundaries in general, with transcompartmental spread possible along musculotendinous units that normally transgress the intervening fascial septae. CT correlates well with the extent of infection as determined by other modalities, but cannot precisely predict its proximal boundary due to gradual transition between unequivocally abnormal and normal tissue. CT may be useful in establishing an appropriate level for contemplated amputation and can detect extension of superficial diabetic foot infections at an earlier stage than existing clinical methods, potentially resulting in less extensive surgical procedures.

Transcutaneous PO2 measurements in health and peripheral arterial occlusive disease.

Transcutaneous oxygen tensions (tcPO2) of the lower extremity were investigated in 24 control subjects and in 69 patients with various degrees of peripheral arterial occlusive disease. With a modified Clark-type oxygen electrode, tcPO2 was monitored from the right subclavicular region (position 1), upper calf (position 2), and dorsum of the foot (position 3). The tcPO2 was significantly lower in patients when compared to control subjects. The reproducibility of the method was determined from double determinations of the tcPO2 (position 2) in control subjects. The comparison of tcPO2 value between the right and left lower extremity showed no significant differences. The tcPO2 of the foot or leg showed an increase, when positioning the limb below the phlebostatic level. The response of the tcPO2 after transient arterial occlusion (4 minutes) was significantly delayed in patients compared to control subjects. Finally, preliminary results of 35 patients in whom amputations had been performed suggest that tcPO2 measurement may become a useful prognosticator for the determination of the optimal amputation level.

The role of non-invasive vascular studies in determining levels of amputation.

Various non-invasive vascular studies have been reported to provide valuable data for selection of the optimum level of amputation in limbs in patients who have vascular disease. We evaluated three such methods: (1) measurement of the change in the transcutaneous PO2 after inhalation of oxygen; (2) determination, by the Doppler method, of segmental blood pressure; and (3) measurement of the temperature of the skin. The records of eighty patients (ninety amputations) were retrospectively reviewed for correlations between the results of the vascular studies and the outcome of the amputation. Measurement of transcutaneous PO2 was found to be the most accurate predictor of successful healing of an amputation; the other two measurements were less reliable. The values for transcutaneous PO2 both at rest and after inhalation of oxygen were significantly different (p less than 0.001) for the patients who had a healed amputation compared with those who had a failed amputation. Regardless of the initial value, if, after inhalation of oxygen, the transcutaneous PO2 reached ten millimeters of mercury or more, it predicted healing of the amputation stump with a sensitivity of 98 per cent. When the level of amputation was selected on the basis of clinical judgment at the time of operation, the sensitivity was only 90 per cent.

Effect of velocity and SF/SL ratio on external work and gait movement waveforms.

Ten normal adult subjects were tested under a wide range of combinations of stride length and stride frequency. Both longitudinal and vertical accelerations of the body increased with velocity, while stride frequency to stride length ratio (SF/SL) had little effect. The peak-to-peak amplitude of the forward velocity (V) decreased with SF/SL, but at constant SF/SL remained essentially unchanged throughout the speed range from 0.4 to 1.4 m/s. The external work of locomotion related as a paraboloid of revolution to V and SF/SL with minimum work being 0.32 J/kg-m at V = 0.52 m/s and SF/SL = 0.76. The efficiency of transfer between potential and kinetic energies related as a paraboloid of revolution to V and SF/SL with maximum efficiency being 0.58 (58 percent at V = 0.98 m/s and SF/SL = 0.43). Latent work, herein defined as work divided by efficiency, related as a paraboloid of revolution to V and SF/SL being minimum at V = 0.7 m/s and SF/SL = 0.65. At any given velocity, latent work tended to be least in the SF/SL range of 0.6 to 0.7. The latter finding may suggest why people tend to walk at a nearly constant SF/SL ratio over a broad range of velocities.

Effect on gait using various prosthetic ankle-foot devices.

Five different commonly prescribed ankle-foot devices for below-knee prostheses were tested for effects on gait: SACH, SAFE, SEATTLE, SINGLE AXIS, and MULTIPLE AXIS. Subjective ratings by the amputees served to resolve which physical variables determined the preferred ankle-foot device. Ratings were related to age, body weight, length of residual limb, and ratio of stride frequency to stride length. Distinctions in performances were derived from analyses of anterior-posterior angular accelerations occurring in the prosthesis immediately following heel strike. The accelerations were characterized as a damped oscillatory waveform. These objective findings, when related to the subjective ratings, showed that the amputees preferred devices which developed the lesser shock and greater damping.

Load-bearing characteristics of polyethylene foam: an examination of structural and compression properties.

Cellular foams used in shoe insoles come in a variety of structural configurations differing with respect to cell geometry. The compression of a cellular foam depends on cell reticulation and size. Examination of the compression behavior of closed cell polyethylene foams revealed distinct time-and nontime-related properties that occur during static and cyclic loading. Physical parameters were developed and determined to exactly specify pressure profiles that occur at the plantar interface. Evaluation of an interface material can be made based on peak pressures which are dependent on depth of compression, foam thickness, and physical properties of the foam. Sustained loading damages the mechanical integrity of the cellular structure such that thickness does not completely recover. Therefore, issuing several pairs of thick insoles for daily rotation is recommended for a particular foam.

Analysis of below-knee suspension systems: effect on gait.

Seven different suspension systems for below-knee prostheses were tested on 20 adult, unilateral amputees. All subjects walked with a prosthesis. Gait was evaluated with regard to longitudinal and vertical accelerations of the body, forward velocity, axial (piston) movement of amputated limb in the socket, and knee movement. Harmonic analyses of variable waveforms provided the primary method to discriminate performances among the suspensions. The appropriateness of a given suspension system depended on both the length and the shape of the residual limb.

Volume changes occurring in postoperative below-knee residual limbs.

Comparative maturation rates of 36 below-knee postoperative, healed amputation residual limbs were observed. Measured were the limb volumes and circumferences. Three methods of residual limb stabilization were employed: 1) elastic wrap; 2) plaster cast and pylon; and, 3) plastic laminate socket and pylon. The limbs receiving the plastic laminate showed the most rapid stabilization, while the elastic wrap did not stabilize. Considerable variance existed in relations between variables. Correlation between limb circumference and volume was poor. However, in general, the rates of change, i.e., the relations between volume and time, and circumference and time, were statistically significant (p less than .05).

A technique for the display of joint movement deviations.

Detection of deviations in lower-limb joint movements derived during locomotion testing may be enhanced by displaying as a function of the gait cycle the algebraic difference between actual performance and a synthetic waveform. A synthetic waveform for a joint movement may be generated by applying Fourier series coefficients derived from a statistical treatment of test data characterizing the performance of normal healthy individuals walking at various velocities. Application of waveform specifics related to velocity yields a synthetic pattern serving as the criterion at the specific velocity demonstrated by a patient. The deviations, when plotted for the gait cycle, show the manner in which the actual waveform differs from the synthetic. At any increment of the gait cycle, the magnitude of the deviation and whether it is positive or negative can be determined. A positive deviation means that an expected angular position was exceeded, while a negative deviation means that an expected angular position was not reached. Individual signatures may be identified by the shape of the deviation pattern. Detection of the presence of oscillatory components in joint movements may be enhanced. Deviation patterns, developed from joint movements monitored bilaterally, often reveal compensatory activity with regard to the relative performances of the ipsilateral and contralateral limbs. Deviation amplitudes exceeding statistically determined boundaries for the synthetic waveform (e.g., two standard deviations) at specific zones of the support or wing phases facilitate identification of dysfunction. This paper describes the technique for deriving the deviation pattern, and touches upon its potential utility in evaluating locomotory performance of patients.

Oxygen inhalation--induced transcutaneous PO2 changes as a predictor of amputation level.

Noninvasive transcutaneous PO2 (TcpO2) determinations have been developed to study peripheral arterial occlusive disease. To evaluate this technique as a predictor of amputation outcome, a blind, prospective study of 101 patients undergoing 119 amputations (23 above-knee [AK], 57 below-knee [BK], and 39 forefoot) was performed. TcpO2 measurements were obtained from the dorsum of the foot and 10 cm distal to the patella, both prior to and 10 minutes after inhalation of 100% oxygen. On the basis of preliminary results, initial TcpO2 values greater than 10 mm Hg or an increase greater than 10 mm Hg after oxygen inhalation were considered to predict a successful outcome, whereas failure was predicted when the initial TcpO2 value was less than 10 mm Hg and the increase after oxygen inhalation did not exceed the 10 mm Hg level. In the BK amputation group the test was 95% sensitive, 100% specific, and 95% accurate. Retrospective utilization of the above criteria in patients who had undergone both oxygen inhalation testing and AK amputation suggested that 9 of 17 limbs (53%) might have undergone a more distal BK amputation successfully. These results document the effectiveness of an initial TcpO2 determination coupled with the response to 100% oxygen inhalation as an excellent predictor of the outcome of lower extremity amputations.

Multiple extremity amputations in hypotensive patients treated with dopamine.

Dopamine hydrochloride has been established as effective in the treatment of hypotension and shock in patients with adquate blood volume. The physiological response is dose related. Administration of more than 10 microgram/kg/min results in alpha-receptor stimulation and vasoconstriction, and peripheral extremity ischemia has been reported. Four patients treated with dopamine subsequently had the development of peripheral ischemia and gangrene, resulting in the need for multiple extremity amputations. These reactions represent a major complication of treatment.