Ultrasonic heel pad thickness measurements: a preliminary study

Ultrasonic Evaluation of the Heel Fat Pad under Weight-Bearing Conditions Using a Polymethylpentene Resin Plate: Part 1

To evaluate the two-layer structure of the heel fat pad (HFP) from non-weight-bearing to full-weight-bearing conditions, we developed an instrument that assesses these changes from the sole through a polymethylpentene resin plate (PMP) with ultrasonography. For actual use, we investigated the influence on measured values and ultrasonogram appearance by interposing the PMP. Additionally, as the PMP may be bent under weight-bearing conditions, its influence on the measured values was investigated. First, two examiners measured the distances inside the phantom with and without a PMP. Second, ultrasonograms were obtained from 40 healthy adults with and without a PMP, and the thicknesses of the whole layer and the two layers of the HFP were measured using the same ultrasonogram. For each experiment, reproducibility was investigated. Third, the distances inside the phantom were measured and compared through the bent PMP, which models the weight-bearing condition, and the flat PMP. The reproducibility of the measurements was equivalent with and without the PMP interposed. Potential bias in measured values arising from deformation of PMP under weight-bearing conditions was not detected. Overall, the PMP's interposition and the bending of the PMP might not influence the measured values and reproducibility of the measurements.

Sonographic Assessment of Heel Pad Thickness in Patients With Poorly Controlled Diabetes

The aim was to compare the heel pad thickness (HPT) in diabetic patients with high biochemical parameters (fasting blood sugar [FBS], hemoglobin A1c [HbA1c], and lipid profile) with nondiabetic counterparts. A total of 438 subjects made up of 216 diabetics with high biochemical parameters (poorly controlled) and 222 apparently healthy subjects were recruited. The HPT, FBS level, HbA1c values and lipid profile, and duration of diabetes mellitus were assessed. Results showed that the mean HPT was 13.33 ± 1.29 mm in the control subjects and 16.79 ± 1.84 mm in diabetics. The HPT among diabetics differed significantly from the control group ( P < .05). The mean value of HbA1c in the control group was 5.4 ± 1.3 compared to diabetics with values of 8.53 ± 2.1. The values of HbA1c among diabetics were significantly higher than that of the control group ( P < .05). HPT had a significant linear relationship with HbA1c among the diabetic subjects ( r = 0.42, P < .05).

Dynamic material characterization of the human heel pad based on in vivo experimental tests and numerical analysis

A numerical-experimental, proof-of-concept approach is described to characterize the mechanical material behavior of the human heel pad under impact conditions similar to a heel strike while running. A 3D finite-element model of the right foot of a healthy female subject was generated using magnetic resonance imaging. Based on quasi-static experimental testing of the subject's heel pad, force-displacement data was obtained. Using this experimental data as well as a numerical optimization algorithm, an inverse finite-element analysis and the 3D model, heel pad hyperelastic (long-term) material parameters were determined. Applying the same methodology, based on the dynamic experimental data from the impact test and obtained long-term parameters, linear viscoelastic parameters were established with a Prony series. Model validation was performed employing quasi-static and dynamic force-displacement data. Coefficients of determination when comparing model to experimental data during quasi-static and dynamic (initial velocity: 1480mm/s) procedure were R(2) = 0.999 and R(2) = 0.990, respectively. Knowledge of these heel pad material parameters enables realistic numerical analysis to evaluate internal stress and strain in the heel pad during different quasi-static or dynamic load conditions.

A device for characterising the mechanical properties of the plantar soft tissue of the foot

The plantar soft tissue is a highly functional viscoelastic structure involved in transferring load to the human body during walking. A Soft Tissue Response Imaging Device was developed to apply a vertical compression to the plantar soft tissue whilst measuring the mechanical response via a combined load cell and ultrasound imaging arrangement. Accuracy of motion compared to input profiles; validation of the response measured for standard materials in compression; variability of force and displacement measures for consecutive compressive cycles; and implementation in vivo with five healthy participants. Static displacement displayed average error of 0.04 mm (range of 15 mm), and static load displayed average error of 0.15 N (range of 250 N). Validation tests showed acceptable agreement compared to a Houndsfield tensometer for both displacement (CMC > 0.99 RMSE > 0.18 mm) and load (CMC > 0.95 RMSE < 4.86 N). Device motion was highly repeatable for bench-top tests (ICC = 0.99) and participant trials (CMC = 1.00). Soft tissue response was found repeatable for intra (CMC > 0.98) and inter trials (CMC > 0.70). The device has been shown to be capable of implementing complex loading patterns similar to gait, and of capturing the compressive response of the plantar soft tissue for a range of loading conditions in vivo.

The relationship between the mechanical properties of heel-pad and common clinical measures associated with foot ulcers in patients with diabetes

AIM

The present study aims at investigating the correlation between the mechanical properties of the heel-pad of people with type-2 diabetes and the clinical parameters used to monitor their health and ulceration risk.

METHODS

A new device for the in-vivo testing of plantar soft tissues was built and pilot-tested. This device consists of an ultrasound probe connected in series with a dynamometer. Loading is applied manually using a ball-screw actuator. A total of 35 volunteers with type-2 diabetes were recruited and the thickness, stiffness of their heel-pads as well as the energy absorbed during loading were assessed. The participants with diabetes also underwent blood tests and measurements of Ankle Brachial Index and Vibration Perception Threshold.

RESULTS

Pearson correlation analysis revealed strong correlations between triglycerides and heel-pad stiffness (r=0.675, N=27, p<0.001) and between triglycerides and energy (r=-0.598, N=27, p=0.002). A correlation of medium strength was found between Fasting Blood Sugar (FBS) and stiffness (r=0.408, N=29, p=0.043).

CONCLUSIONS

People with type-2 diabetes and high levels of triglycerides and FBS are more likely to have stiffer heel-pads. Increased stiffness could limit the tissues' ability to evenly distribute loads making them more vulnerable to trauma and ulceration.

Heel fat pad involvement in rheumatoid arthritis and in spondyloarthropathies: an ultrasonographic study

BACKGROUND

Heel fat pad inflammation and degeneration have been frequently proved to cause talalgia. Painful heel fat pad is often confused with plantar fasciitis, and only magnetic resonance imaging (MRI) or ultrasonography (US) can differentiate these conditions. Scanty data are available about heel fat pad involvement in the course of chronic polyarthritis.

OBJECTIVE

To investigate with US the heel fat pad involvement in patients with rheumatoid arthritis (RA) and spondyloarthropathies (SpA); to describe and compare the clinical and sonographic features of this lesion in the two groups.

METHODS

The heels of 181 consecutive outpatients with RA and 160 with SpA were studied by US and radiography. A control group of 60 healthy subjects was examined by US.

RESULTS

Two different patterns of involvement of the heel fat pad were observed. The inflammatory-oedematous pattern was more frequent in patients with RA (6.6%) than in those with SpA (1.8%), and was associated with talalgia--even if it was not associated with plantar fasciitis or enthesophyte (bony spur). The degenerative-atrophic pattern was less frequent (1.1% in RA, 1.9% in SpA), and was associated with plantar fasciitis and subcalcaneal enthesophyte.

CONCLUSIONS

The inflammatory-oedematous lesion of the heel fat-pad is relatively frequent in RA and causes subcalcaneal pain. Degenerative-atrophic changes of the heel fat pad can be observed in RA and SpA, and seem to be associated with chronic abnormalities of the plantar fascia and of its enthesis.

Skin to calcaneus distance in the neonate

BACKGROUND

Current recommendations for obtaining blood from neonates advise avoidance of the midline area of the heel and are based on postmortem studies.

OBJECTIVE

Because of the potential pain and tissue damage from repeated heel pricking in the same area, to investigate using ultrasonography whether the distance from skin to calcaneus is less at the midline than at the borders.

METHODS

One hundred consecutive healthy preterm and 105 consecutive healthy term neonates were studied 48-72 hours after delivery. The skin to perichondrium distance (SPD) was measured on two occasions by ultrasound at the external, midline, and internal areas of the heel.

FINDINGS

Mean SPD was 0.2 mm less at the midline than at the other sites. The proportion of measurements <3 mm at any of the three sites was the same. Depth was <3 mm in less than 3% of the term and approximately 20% of the preterm infants. The SPD correlated only with gestational age. Of children <33 weeks gestational age, 38% had an SPD <3 mm compared with 8% of older preterm infants. The proportions of preterm infants of > or = 33 weeks gestation and term infants with an SPD <3 mm were similar (8% v 3%).

INTERPRETATION

With the use of automated lancets of 2.2 mm length or less, the whole heel plantar surface is safe for obtaining blood in term and preterm infants of > or = 33 weeks gestation. This means that soft tissue damage and pain from repeated pricking in the same area can be reduced.

Sonographic study of calcaneal entheses in erosive osteoarthritis, nodal osteoarthritis, rheumatoid arthritis and psoriatic arthritis

OBJECTIVE

To establish by ultrasonography (US) the frequency of calcaneal entheses involvement in erosive osteoarthritis (EOA), nodal osteoarthritis (NOA), RA and PsA, and to compare these results in order to aid clinicians in the differential diagnosis among these diseases. A comparison between US results and radiography was also made.

METHODS

The heels of 56 consecutive outpatients with EOA, 209 with NOA, 158 with RA and 125 with PsA were studied by US and radiography. A control group of 50 subjects was examined by US.

RESULTS

US showed no significant difference in inferior calcaneal enthesophytosis among the four diseases. The frequency of posterioinferior enthesophytosis was lower in RA (34%) in comparison with the other diseases (57% in EOA, 47% in NOA, 49% in PsA). Achilles enthesitis was found in 8% of PsA and in 2% of RA. Retrocalcaneal bursitis was found in 18% of RA and in 6% of PsA. Posterior erosions were present in 12% of RA and 5% of PsA. Inferior erosions were present in 6% of RA and in 1% of PsA. Plantar fasciitis was found in 26% of RA, in 37% of PsA, and in 15% of NOA and 12% of EOA. Subcalcaneal panniculitis was observed in 10% of RA and in 1% of PsA. In the control group, only posterioinferior and inferior enthesophytosis (22% and 18% respectively) were found. Kappa statistics show excellent agreement between US and radiography in detecting posterioinferior (kappa = 0.89) and inferior enthesophytosis (kappa = 0.83), and entheseal erosions (kappa = 0.86).

CONCLUSIONS

The calcaneal lesions that could be found in EOA are similar to those observed in NOA. The frequency of calcaneal enthesophytosis is similar in EOA, NOA, and PsA, but inflammatory lesions of calcaneal entheses and of the adjacent bursae are more frequent in RA and in PsA. In terms of heel involvement, EOA seems to be similar to NOA. US shows an excellent concordance with radiography in detecting entheseal cortical bone abnormalities.