Comparison of the mechanical properties of the heel pad between young and elderly adults

The effect of aging on the biomechanical properties of plantar soft tissues

BACKGROUND

Foot problems are common in elderly people and stiffened plantar soft tissues may lead to ulceration in people with Diabetes Mellitus. It is unclear how the biomechanical properties of plantar soft tissues change with advancing age. Therefore, this study examined the age-related differences in the biomechanical properties of plantar soft tissues.

METHODS

Sixty healthy volunteers without foot problems, aged from 41 to 83 years, were examined using tissue ultrasound palpation system. The thickness and stiffness of the plantar soft tissues under the big toe, first metatarsal head, third metatarsal head, fifth metatarsal head, and heel were measured. The load-deformation curve of the plantar soft tissues was plotted. The correlation between age and biomechanical properties was examined and comparisons were made between four age groups.

FINDINGS

The mean stiffness of the plantar soft tissues at big toe, first metatarsal head, third metatarsal head, fifth metatarsal head, and the heel significantly increased with age (P<0.001). The plantar soft tissues at the heel were the thickest (P<0.001), with the plantar soft tissue tending to be increasingly thicker with age, although there was no statistical significance. Strong positive correlations between age and stiffness of the plantar soft tissues were found at the big toe (r=0.608), first metatarsal head (r=0.549), third metatarsal head (r=0.657), fifth metatarsal head (r=0.633), and heel (r=0.584) (all P<0.001).

INTERPRETATION

The loss of compliance in the plantar soft tissues may be one of the factors responsible for the higher incidence of foot problems in elderly individuals.

Biomechanical properties of the forefoot plantar soft tissue as measured by an optical coherence tomography-based air-jet indentation system and tissue ultrasound palpation system

BACKGROUND

The forefoot medial plantar area withstand high plantar pressure during locomotion, and is a common site that develops foot lesion problems among elderly people. The aims of the present study were to (1) determine the correlation between the biomechanical properties of forefoot medial plantar soft tissue measured by a newly developed optical coherence tomography-based air-jet indentation system and by tissue ultrasound palpation system, and (2) to compare the biomechanical properties of plantar soft tissues of medial forefoot between a young and old adult group.

METHODS

Thirty healthy subjects were classified as the young or older group. The biomechanical properties of plantar soft tissues measured at the forefoot by the air-jet indentation system and tissue ultrasound palpation system were performed, and the correlation of the findings obtained in the two systems were compared.

FINDINGS

A strong positive correlation was obtained from the findings in the two systems (r=0.88, P<0.001). The forefoot plantar soft tissue of the older group was significantly stiffer at the second metatarsal head and thinner at both metatarsal heads than that of the young group (all P<0.05). The stiffness coefficient at the second metatarsal head was 28% greater than that at the first metatarsal head in both study groups.

INTERPRETATION

Older subjects showed a loss of elasticity and reduced thickness in their forefoot plantar soft tissue, with the second metatarsal head displaying stiffer and thicker plantar tissue than the first metatarsal head. The air-jet indentation system is a useful instrument for characterizing the biomechanical properties of soft tissue.

A musculoskeletal ultrasound course for physical medicine and rehabilitation residents

Musculoskeletal ultrasound is an imaging modality that can be used to evaluate nerve, tendon, muscle, ligament, and joint disorders and to guide therapeutic procedures. A growing proportion of physiatrists are interested in musculoskeletal ultrasound as demonstrated by the increasing number of musculoskeletal ultrasound articles published in physical medicine and rehabilitation journals and quantity of musculoskeletal ultrasound courses and workshops at physical medicine and rehabilitation conferences. The Mayo Clinic (Rochester, MN) Physical Medicine and Rehabilitation residency program developed a musculoskeletal ultrasound course for their physical medicine and rehabilitation residents, which was implemented in 2008. A detailed description of the course is provided in this article. In addition, results from a premusculoskeletal ultrasound course and postmusculoskeletal ultrasound course practical and written test are presented, and the results of a postmusculoskeletal ultrasound course resident survey are discussed. This information can be used by other physical medicine and rehabilitation residency programs to assist in the creation of their own musculoskeletal ultrasound course.

Evaluation of bone-tendon junction healing using water jet ultrasound indentation method

The re-establishment of bone-tendon junction (BTJ) tissues with the junction, characterized as a unique transitional fibrocartilage zone, is involved in many trauma and reconstructive surgeries. Experimental and clinical findings have shown that a direct BTJ repair requires a long period of immobilization, which may be associated with a postoperative weak knee. Therefore, it is necessary to evaluate the morphologic and mechanical properties of BTJ tissues in situ to better understand the healing process for the purpose of reducing the adverse effects of immobilization. We previously reported a noncontact ultrasound water jet indentation system for measuring and mapping tissue mechanical properties. The key idea was to utilize a water jet as an indenter as well as the coupling medium for high-frequency ultrasound. In this article, we used ultrasound water jet indentation to evaluate the BTJ healing process. The system's capability of measuring the material elastic modulus was first validated using tissue-mimicking phantoms. Then it was employed to assess the healing of the BTJ tissues after partial patellectomy over time on twelve 18-week-old female New Zealand White rabbits. It was found that in comparison with the normal control samples, the elastic modulus of the fibrocartilage of the postoperative samples was significantly smaller, while its thickness increased significantly. Among the postoperative sample groups, the elastic modulus of the fibrocartilage of the samples harvested at week 18 was significantly higher than those harvested at week 6 and week 12, which was even comparable with the value of the control samples at the same sacrifice time. The results suggested that the noncontact ultrasound water jet indentation system provided a nondestructive way to evaluate the material properties of small animal tissues in situ and thus had the ability to evaluate the healing process of BTJ.

Augmentation of atrophic plantar soft tissue with an acellular dermal allograft: a series review

Treatment of plantar fat pad migration and atrophy has caused concern for decades. Patients can present with pain, callus formation, or ulceration. The purpose of this article is to review the results of a consecutive series of patients treated for fat pad atrophy of the plantar foot, using a minimally invasive implantation of an acellular human dermal allograft as a tissue augmentation. This material was chosen for the fat pad supplementation because of previous reports of success in tendon and ligament augmentation, wound healing, and interpositional arthroplasty.

Diabetic effects on microchambers and macrochambers tissue properties in human heel pads

BACKGROUND

The study attempted to highlight the differences of mechanical properties in microchambers and macrochambers between patients with type 2 diabetes mellitus and age-matched healthy volunteers.

METHODS

A total of 29 heels in 18 diabetic patients and 28 heels in 16 age-matched healthy participants were examined by a loading device consisting of a 10-MHz compact linear-array ultrasound transducer, a Plexiglas cylinder, and a load cell. Subjects in both groups were on average about 55 years old with a body mass index of approximately 25 kg/m(2). A stepping motor was used to progressively load the transducer on the tested heels at a velocity of 6mm/s from zero to the maximum stress of 78 kPa. Unloaded thickness, strain, and elastic modulus in microchambers, macrochambers and heel pads were measured.

FINDINGS

Microchambers strain in diabetic patients was significantly greater than that in healthy subjects (0.291 (SD 0.14) vs. 0.104 (SD 0.057); P<0.001). Macrochambers strain in diabetic patients was significantly less than that in healthy subjects (0.355 (SD 0.098) vs. 0.450 (SD 0.092); P=0.001). Microchambers stiffness in diabetic patients was significantly less than that in healthy persons (393 (SD 371)kPa vs. 1140 (SD 931)kPa; P<0.001). Macrochambers stiffness in diabetic patients was significantly greater than that in healthy persons (239 (SD 77)kPa vs. 181 (SD 42)kPa; P=0.001).

INTERPRETATION

Heel pad tissue properties are altered heterogeneously in people with diabetes. Increased macrochambers but decreased microchambers stiffness may cause diminished cushioning capacities in diabetic heels.

Bulk compressive properties of the heel fat pad during walking: a pilot investigation in plantar heel pain

BACKGROUND

Altered mechanical properties of the heel pad have been implicated in the development of plantar heel pain. However, the in vivo properties of the heel pad during gait remain largely unexplored in this cohort. The aim of the current study was to characterise the bulk compressive properties of the heel pad in individuals with and without plantar heel pain while walking.

METHODS

The sagittal thickness and axial compressive strain of the heel pad were estimated in vivo from dynamic lateral foot radiographs acquired from nine subjects with unilateral plantar heel pain and an equivalent number of matched controls, while walking at their preferred speed. Compressive stress was derived from simultaneously acquired plantar pressure data. Principal viscoelastic parameters of the heel pad, including peak strain, secant modulus and energy dissipation (hysteresis), were estimated from subsequent stress-strain curves.

FINDINGS

There was no significant difference in loaded and unloaded heel pad thickness, peak stress, peak strain, or secant and tangent modulus in subjects with and without heel pain. However, the fat pad of symptomatic feet had a significantly lower energy dissipation ratio (0.55+/-0.17 vs. 0.69+/-0.08) when compared to asymptomatic feet (P<.05).

INTERPRETATION

Plantar heel pain is characterised by reduced energy dissipation ratio of the heel pad when measured in vivo and under physiologically relevant strain rates.

Utilization of the foot load monitor for evaluating deep plantar tissue stresses in patients with diabetes: proof-of-concept studies

The purposes of the present study were to (1) determine the internal plantar mechanical stresses in diabetic and healthy subjects during everyday activities, and (2) identify stress parameters potentially capable of distinguishing between diabetic and healthy subjects. A self-designed, portable, real-time and subject-specific foot load monitor which employs the Hertz contact theory was utilized to determine the internal dynamic plantar tissue stresses in 10 diabetic patients and 6 healthy subjects during free walking and outdoors stair climbing. Internal stress parameters and average stress-doses were evaluated, and the results obtained from the two groups were compared. Internal plantar stresses and averaged stress-doses during free walking and outdoors stairs climbing in the diabetic group were 2.5-5.5-fold higher than in the healthy group (p<0.001; stair climbing comparisons incorporated data from five diabetic patients). The interfacial pressures measured during free walking were slightly higher ( approximately 1.5-fold) in the diabetic group (p<0.05), but there was no significant difference between the two groups during stairs climbing. We conclude that during walking and stair climbing, internal plantar tissue stresses are considerably higher than foot-shoe interface pressures, and in diabetic patients, internal stresses substantially exceed the levels in healthy. The proposed method can be used for rating performances or design of footwear for protecting sub-dermal plantar tissues in patients who are at risk for developing foot ulcers. It may also be helpful in providing biofeedback to neuropathic diabetic patients.

Plantar calcaneal spurs in older people: longitudinal traction or vertical compression?

BACKGROUND

Plantar calcaneal spurs are common, however their pathophysiology is poorly understood. This study aimed to evaluate the prevalence and correlates of plantar calcaneal spurs in a large sample of older people.

METHODS

Weightbearing lateral foot radiographs of 216 people (140 women and 76 men) aged 62 to 94 years (mean age 75.9, SD 6.6) were examined for plantar calcaneal and Achilles tendon spurs. Associations between the presence of spurs and sex, body mass index, radiographic measures of foot posture, self-reported co-morbidities and current or previous heel pain were then explored.

RESULTS

Of the 216 participants, 119 (55%) had at least one plantar calcaneal spur and 103 (48%) had at least one Achilles tendon spur. Those with plantar calcaneal spurs were more likely to have Achilles tendon spurs (odds ratio [OR] = 2.0, 95% confidence interval [CI] 1.2 to 3.5). Prevalence of spurs did not differ according to sex. Participants with plantar calcaneal spurs were more likely to be obese (OR = 7.9, 95% CI 3.6 to 17.0), report osteoarthritis (OR = 2.6, 95% CI 1.6 to 4.8) and have current or previous heel pain (OR = 4.6, 95% CI 2.3 to 9.4). No relationship was found between the presence of calcaneal spurs and radiographic measures of foot posture.

CONCLUSION

Calcaneal spurs are common in older men and women and are related to obesity, osteoarthritis and current or previous heel pain, but are unrelated to radiographic measurements of foot posture. These findings support the theory that plantar calcaneal spurs may be an adaptive response to vertical compression of the heel rather than longitudinal traction at the calcaneal enthesis.

Análise cinemática comparativa da fase de apoio da corrida em adultos e idosos

A preocupação com a qualidade de vida tem levado ao aumento do interesse por atividades físicas pelos idosos. A corrida de rua é uma das atividades que obteve maior número de adeptos dessa faixa etária. Os movimentos excessivos da região do tornozelo têm sido associados às lesões musculoesqueléticas em corredores. Os achados da literatura sugerem que idosos são mais susceptíveis às lesões relacionadas à corrida do que adultos. Contudo, ainda é desconhecido se as alterações teciduais trazidas pelo envelhecimento realmente contribuem para esses resultados. O objetivo do presente estudo foi comparar a cinemática da fase de apoio da corrida em adultos e idosos. Foram analisados 17 adultos (31±5 anos) e 17 idosos (69±2 anos) recrutados voluntariamente. Os sujeitos correram em uma esteira ergométrica a 11 km/h, enquanto eram filmados por quatro câmeras de vídeo com freqüência de 120 Hz. Os ângulos do retropé e do joelho durante a fase de apoio da corrida foram mensurados. Os idosos apresentaram menor excursão de movimentos de flexão do joelho e de rotação medial da tíbia. Aparentemente os idosos apresentaram maior assincronia entre os movimentos do retropé e do joelho em relação aos adultos. Esses resultados sugerem que os idosos adotam padrões de movimentos diferentes dos adultos durante a fase de apoio da corrida. A prescrição de exercícios e as estratégias de prevenção de lesões em idosos corredores devem considerar essas diferenças.

Revision of the Fully technique for estimating statures

The "anatomical" method of Fully (1956 Ann. Legale Med. 35:266-273) for reconstructing stature, involving the addition of skeletal elements from the calcaneus to the skull, has been increasingly used in anthropological and forensic contexts, but has undergone little systematic testing on samples other than the original sample used to develop the technique. The original description by Fully of the method also does not provide completely explicit directions for taking all of the necessary measurements. This study tested the accuracy and applicability of his method, and clarified measurement procedures. The study sample consisted of 119 adult black and white males and females of known cadaveric statures from the Terry Collection. Cadaveric statures were adjusted to living statures, following the recommendations of Trotter and Gleser (1952 Am. J. Phys. Anthropol. 10:469-514). We obtained the best results using maximum vertebral body heights (anterior to the pedicles) and measurement of the articulated talus and calcaneus height in anatomical position. Statures derived using the original Fully technique are strongly correlated with living statures in our sample (r = 0.96), but underestimate living stature by an average of about 2.4 cm. Anatomical considerations also suggest that the correction factors applied by Fully to convert summed skeletal height to living stature are too small. New formulae are derived to calculate living stature from skeletal height. There is no effect of sex or ancestry on stature prediction. Resulting stature estimates are accurate to within 4.5 cm in 95% of the individuals in our sample, with no directional bias.

Effects of varying material properties on the load deformation characteristics of heel cushions

Various insole materials were used in attenuation of heel-strike impact. This study presented a compression test to investigate the deformation characteristics of common heel cushions. There were two materials (thermoplastic elastomer "TPE" and silicone) with three hardness and six thickness being analyzed. They underwent consecutive loading-unloading cycles with a load control mode. The displacement of material thickness was recorded during cyclic compression being applied and released from 0 to 1050 N. The energy input, return and dissipation were evaluated based on the load deformation curves when new and after repeated compression. The TPE recovered more deformed energy and thickness than the silicone after the first loading cycle. The silicone would preserve more strain energy with increasing its hardness for the elastic recovery in the unloading process. The deformed energy was decreased as the original thickness did not completely recover under cyclic tests. The reduction in hysteresis area was gradually converged within 20 cycles. The silicone attenuated more impact energy in the initial cycles, but its energy dissipation was reduced after repeated loading. To increase hardness or thickness should be considered to improve resilience or accommodate persistent compression without flattening. The careful selection of cushion materials is imperative to meet individual functional demands.

Microchambers and macrochambers in heel pads: are they functionally different?

The heel pad consists of a superficial microchamber layer and a deep macrochamber layer. This study highlights the different biomechanical behaviors between the microchamber and macrochamber layers using ultrasonography. The heel pad in each left foot of six healthy volunteers aged ∼25 yr old was measured with a device consisting of a 10-MHz linear-array ultrasound transducer and a load cell. The testing heels were loaded on the ultrasound transducer with a loading velocity of ∼0.5 cm/s and were withdrawn when the specified maximum stress (158 kPa) was reached. Unloaded tissue thickness, end-loaded thickness, deformation proportion, average deformation, and rebound rates and elastic modulus of the microchamber and macrochamber layers were assessed. The unloaded thickness of the microchamber layer was ∼30% of the macrochamber layer. The microchamber layer also had significantly less unloaded thickness, end-loaded thickness, mean deformation rate, mean rebound rate, and deformation proportion than the macrochamber layer. A significant difference between the unloaded and end-loaded thickness in the macrochamber layer was observed. The average soft tissue deformation rate was significantly different from the rebound rate in the microchamber layer. A similar trend was detected in the macrochamber layer. The elastic modulus of the microchamber layer was 450 kPa (SD 240), which was nearly 10 times of that in the macrochamber layer. In conclusion, ultrasound can identify the heterogeneous tissue properties of the heel pad. The macrochamber layer responds to loading with large deformation, and the microchamber layer has a high degree of tissue stiffness.

Effect of footwear and orthotic devices on stress reduction and soft tissue strain of the neuropathic foot

BACKGROUND

Ground reaction forces from walking result in stress (pressure) and soft tissue strain at the plantar aspect of the foot. Excessive plantar pressure and tissue strain on the insensate foot may lead to ulceration. Our study investigated the effect of therapeutic footwear and custom-made orthotic inserts on pressure and tissue strain along the second ray of the plantar foot, and how these two variables are associated.

METHODS

Twenty subjects (mean age 57.3 [SD 9.3] years, 12 male, 8 female, body mass index 32.5 [SD 7.4] kg/m2) with diabetes mellitus, peripheral neuropathy, and a history of a plantar ulcer participated. Plantar pressure data were recorded during computed tomography scans for four conditions (barefoot, shoe, shoe+total contact insert, and shoe+total contact insert+metatarsal pad). For each condition tested, tissue strain and plantar pressure were determined at the second metatarsal head and at 15 other points along the second ray.

FINDINGS

Differences were noted between the 4 conditions for pressure (P<0.004) and soft tissue strain (P<0.042) at the second metatarsal head. Correlation coefficients demonstrated an association between pressure and strain (Barefoot r=0.81, Shoe r=0.75, Shoe+total contact insert r=0.73, and Shoe+total contact insert+metatarsal pad r=0.44).

INTERPRETATION

Footwear and orthotic devices tested in this study decreased pressure and soft tissue strain at the second ray of the foot, and these two variables were strongly related. A better understanding of the role tissue strain plays in distributing plantar forces may lead to improvements in the design of orthotic devices.

A novel method to obtain modulus image of soft tissues using ultrasound water jet indentation: a phantom study

The alteration of tissue stiffness is generally known to be associated with pathological changes. Ultrasound indentation is one of the methods that can be used to assess the mechanical properties of the soft tissues. It uses a flat-ended ultrasound transducer to directly contact the tissue to sense tissue deformation under an applied load. This paper introduced a novel noncontact ultrasound indentation system using water jet compression. The key idea was to utilize a water jet as the indenter as well as the coupling medium for propagation of the ultrasound beam. High frequency focused ultrasound (20 MHz) was used to measure the indentation deformation at a microscopic level. It has been demonstrated that the system could effectively assess the tissue-mimic phantoms with different stiffness. Water jet coupling allows the system to conduct C-scan on soft tissues rapidly and conveniently. By applying different pressures while taking C-scan sequences, the modulus images of the phantoms could be obtained based on the applied pressure and the phantom deformation and thickness. This paper presented the preliminary results on gel phantoms. The spatial resolution, the contrast resolution of the measurements and the reproducibility of the results were also discussed.

Altered energy dissipation ratio of the plantar soft tissues under the metatarsal heads in patients with type 2 diabetes mellitus: a pilot study

BACKGROUND

Foot ulceration occurs frequently on the plantar aspect of the metatarsal head region, in which the altered foot biomechanics has been mentioned as a contributor. This study attempted to compare the energy dissipation in the plantar soft tissue under the metatarsal head between type 2 diabetic patients and age-matched healthy subjects in vivo.

METHODS

The plantar soft tissues under the metatarsal heads in each left foot of 13 patients with type 2 diabetes mellitus and eight age-matched healthy subjects were measured with a loading-unloading device. The system comprised a 5-12 MHz linear-array ultrasound transducer and a load cell that operated at an impact velocity of about 5 cm/s. The stress-strain plot was derived by simultaneously recording the stress response and tissue deformation during a loading-unloading cycle. The energy dissipation ratio in all subjects could then be analyzed.

FINDINGS

Although only the plantar soft tissue under the fourth metatarsal head in the diabetic patients endured significantly greater energy (P=0.035) than the healthy subjects, a trend of an increased energy dissipation ratio for the metatarsals in the diabetic patients was observed.

INTERPRETATION

The plantar soft tissue under the metatarsal head in the diabetic patients endures high dissipated energy during a simulating walking status in the study. The increased dissipated energy in the tissue may be responsible for the tissue breakdown in the diabetic patients.

Plantar pressure and sole thickness of the forefoot

BACKGROUND

Based on earlier observations that the forefoot bears the highest plantar pressure at its center, the existence of a functional distal transverse arch in normal feet was denied, and plantar pressure was defined as merely the outcome of loading, surface area, and soft tissue. Although plantar pressure drives the changes in the foot, neither the position nor the behavior of the metatarsals during loading can be derived from plantar pressure alone. In light of this, our goal was to describe the changes in thickness in the sole and the corresponding plantar pressure during loading of the foot.

METHODS

We used CT to image the foot of 10 subjects in four postures that were chosen to imitate four phases in the walking cycle. Before imaging we also recorded the plantar pressure with a pressure measuring insole on which the subjects were standing. From the data, the minimal thickness of the sole and the corresponding plantar pressure were derived.

RESULTS

With the exception of the sesamoids, the thickness of the sole under the bones of the forefoot increased from lateral to medial. This persisted in all postures. Our pressure readings matched previously reported distributions.

CONCLUSIONS

Depending on the point of view concerning the sesamoids, the bony prominences were placed in a geometrical arch; but they did not form a functional arch. The soft tissue underneath the heads kept the metatarsals in place; the soft-tissue thickness reflected the principle of adequate cushioning.

Effects of aging on the plantar soft tissue properties under the metatarsal heads at different impact velocities

The plantar soft tissue properties under the metatarsal heads at different impact velocities in different age groups were measured. Each metatarsus of the left foot in healthy young adults (n = 9, 19 to 35 years old) and in healthy older persons (n = 10, 42 to 72 years old) was examined in vivo using a self-constructed loading-unloading device at low, medium and high impact status; the impact velocities of the device were about 2.5, 5 and 10 cm/s, respectively. The device comprised a 5- to 12-MHz linear-array ultrasound transducer, a miniature load cell and a fixation frame. From low to high impact status, the elastic modulus (E) in young adults significantly increased from about 300 kPa to about 500 kPa. However, the E in the older group did not show this trend. From low to high impact status, the energy dissipation ratio (EDR) of the metatarsus significantly increased from about 30% to about 60% in the young group and significantly increased from about 40% to about 70% in the older group. Most of the metatarsus in the older subjects had significantly greater E and EDR than those in the younger persons.

A novel noncontact ultrasound indentation system for measurement of tissue material properties using water jet compression

This study is aimed to develop a novel noncontact ultrasonic indentation system for measuring quantitative mechanical properties of soft tissues, which are increasingly important for tissue assessment and characterization. The key idea of this method is to use a water jet as an indenter to compress the soft tissue while at the same time as a medium for an ultrasound beam to propagate through. The use of water jet indentation does not require a rigid compressor in front of the focused high frequency ultrasound transducer to compress the tissue, so that the additional attenuation caused by the rigid compressor and the strong echoes reflected from its surfaces can be avoided. The indentation deformation was estimated from the ultrasound echoes using a cross-correlation algorithm and the indentation force was calculated from the water pressure measured inside the water pipe. Experiments were performed on uniform tissue-mimicking phantoms with different stiffness. The Young's moduli and Poisson's ratios of these phantoms were measured using a uniaxial ultrasound compression system. The ratio of the indentation pressure to the tissue relative deformation was obtained from the water indentation. This ratio was well correlated with the Young's modulus (r = 0.87). The results also demonstrated that the water indentation approach could differentiate materials with different stiffness in a combined phantom (288 kPa and 433 kPa). This novel noncontact water indentation approach could be potentially used for the measurement of the elasticity of small samples and with a fast scanning speed.

Is Epidural Fat Associated With Body Habitus?

OBJECTIVE

To evaluate, in the spine, the relationship between the amount of epidural fat to body weight, height, body mass index (BMI), presence of obesity, depth of posterior subcutaneous fat, as well as gender and age.

METHODS

At 1.5 T, 101 random patients were analyzed. In the lumbar spine, we calculated the depth of the anterior and posterior epidural fat, as well as posterior subcutaneous fat, separately at the L3-4, L4-5, and L5-S1 levels. Obtained via questionnaire was patient's age, gender, body weight, height, with a calculated BMI (body weight/height, kg/m). Statistical analysis was performed to assess the correlation between epidural and subcutaneous fat with age and gender, weight, height, BMI, and presence of obesity (BMI > 27.5 kg/m).

RESULTS

There were 66 men and 45 women, age ranged 14-83 years old (mean 43). The weight range was 47.6-135.4 (mean 79.5 kg); height range was 124.5-208.3 (mean 169.7 cm); BMI range was 16.9-42.8 (mean 27.8). Female gender correlated only with subcutaneous fat depth (sum, r=-0.31, P=0.002). Younger patients had more anterior epidural fat (sum, r=-0.22, P=0.024) but not posterior epidural fat (sum, r=0.01, P=0.954) or subcutaneous fat (sum, r=0.09, P=0.0357). Weight correlated with posterior epidural fat (sum, r=0.21, P=0.037) and subcutaneous fat (sum, r=0.51, P <0.0001). Height showed correlation negatively with posterior subcutaneous fat thickness (sum, r=-0.25, P=0.014), but had no significant correlation with epidural fat. BMI showed a correlation with posterior subcutaneous fat (r=0.71, P <0.0001 for sum). Somewhat unexpectedly, BMI had no correlation with either posterior (r=0.12, P=0.221 for sum) or anterior epidural fat (r=0.11, P=0.271 for sum), and most importantly the presence of obesity was associated only with subcutaneous fat (P <0.0001), but not with any specific or summated epidural fat measurement (P=0.0801-0.7692).

CONCLUSION

Weight but not body habitus is associated with specific, usually posterior, patterns of epidural fat deposition. Overall obesity is unrelated to epidural fat.

The effect of localized leg muscle fatigue on tibial impact acceleration

OBJECTIVE

The objective of this study was to assess the effect of localized leg muscle fatigue on tibial acceleration following impact.

BACKGROUND

Peak tibial accelerations measured just distal to the knee joint during running have been shown to increase with general body fatigue. However, the role that local leg muscle fatigue plays in shock attenuation is not clear.

METHODS

The unshod, dominant foot of 24 healthy women in two different age groups was impacted into a vertical force plate, using a human pendulum method. Impact velocity and force approximated that found in running. EMG activity of the gastrocnemius and tibialis anterior muscles was monitored during fatiguing isometric exercise to assess fatigue, and quantified at impact as a measure of muscle activation level. A skin-mounted uni-axial accelerometer, was located at the tibial tubercle under pre-load, to measure tibial acceleration at impact.

RESULTS

There was a significant decrease in peak tibial acceleration (P = 0.008) and acceleration slope (P = 0.033) following fatigue. There were no significant main effects or interactions for age group or muscle group for all tibial response variables.

CONCLUSION

The reduction in peak tibial acceleration following fatigue (for the test performed) is contrary to the response documented following whole-body fatigue.

Ground reaction forces and kinematics in distance running in older-aged men

PURPOSE

The biomechanics of distance running has not been studied before in older-aged runners but may be different than in younger-aged runners because of musculoskeletal degeneration at older age. This study aimed at determining whether the stance phase kinematics and ground reaction forces in running are different between younger- and older-aged men.

METHOD

Lower-extremity kinematics using three-dimensional motion analysis and ground reaction forces (GRF) using a force plate were assessed in 16 older-aged (55-65 yr) and 13 younger-aged (20-35 yr) well-trained male distance runners running at a self-selected (SRS) and a controlled (CRS) speed of 3.3 m.s-1.

RESULTS

The older subjects ran at significantly lower self-selected speeds than the younger subjects (mean 3.34 vs 3.77 m.s-1). In both speed conditions, the older runners exhibited significantly more knee flexion at heel strike and significantly less knee flexion and extension range of motion. No age group differences were present in subtalar joint motion. Impact peak force (1.91 vs 1.70 BW) and maximal initial loading rate (107.5 vs 85.5 BW.s-1) were significantly higher in the older runners at the CRS. Maximal peak vertical and anteroposterior forces and impulses were significantly lower in the older runners at the SRS.

CONCLUSION

The biomechanics of running is different between older- and younger-aged runners on several relevant parameters. The larger impact peak force and initial loading rate indicate a loss of shock-absorbing capacity in the older runners. This may increase their susceptibility to lower-extremity overuse injuries. Moreover, it emphasizes the focus on optimizing cushioning properties in the design and prescription of running shoes and suggests that older-aged runners should be cautious with running under conditions of high impact.

Material properties of the human calcaneal fat pad in compression: experiment and theory

The structural behaviour of the human heel pad has been studied extensively due to its ability to absorb shock, protect against excessive local stress, and reduce plantar pressures. However, the material properties of the tissue have not been adequately measured. These must be known in order to perform a finite element analysis of the effect of factors such as foot geometry and shoe/surface construction on heel pad function. Therefore, the purposes of this study were to (a). measure the viscoelastic behaviour of the fat pad in compression, and (b). to determine an appropriate constitutive equation to model the tissue. A series of unconfined compression tests were performed on 8mm diameter cylinders of fat pad tissue, consisting of quasi-static, 175, 350 mm/s and stress-relaxation tests to approximately 50% deformation. The tissue exhibited nonlinear, viscoelastic behaviour. No significant difference was found in the quasi-static behaviour between samples from different locations and orientations in the heel. The stress-relaxation tests were used to determine the time constant (tau(1)=0.5s), the 175 mm/s test to determine the relaxation coefficient (g(1)=28), and the 350 mm/s compression test to determine the material constants (C(100)=C(010)=0.01, C(200)=C(020)=0.1 Pa) of a single-phase, hyperelastic, linear viscoelastic strain energy function (r(2)=0.98).

Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy

OBJECTIVE

To determine if a difference exists in the plantar soft tissue of patients with diabetes mellitus (DM) and peripheral neuropathy (PN) compared with age-matched controls.

DESIGN

Case-control study with a parallel 3-element 1-dimensional viscoelastic model developed to characterize indentation data.

SETTING

Data collection performed in an academic physical therapy laboratory.

PARTICIPANTS

Forty subjects were recruited into 2 groups (20 subjects with DM, PN, and history of plantar ulcers; 20 control subjects), matched for age (DM: 55.22+/-9.39 y; control: 55.91+/-10.97 y), gender (DM: 14 men, 6 women; control: 14 men, 6 women), and body mass index (DM: 32.96+/-8.39 kg/m(2); control: 32.58+/-7.69 kg/m(2)).

INTERVENTIONS

The plantar soft tissue stiffness was measured over the first, third, and fifth metatarsals, and heel of each subject using an indentor system that accurately measures force/displacement (F/D) data. A parallel 3-element viscoelastic mechanical model was then used to transform the F/D data into values that were used to make stiffness assessments.

MAIN OUTCOME MEASURE

The element coefficients of our model indicated the stiffness of the plantar tissue.

RESULTS

The plantar tissue of the subjects with DM over the metatarsal heads was stiffer than the control population as indicated by one of the spring constants in the parallel 3-element model (first: 1.13+/-0.55 N/mm vs.72+/-.32 N/mm; third:.96+/-.32 N/mm vs.79+/-.17 N/mm; fifth:.90+/-.31 N/mm vs.69+/-.28 N/mm; P<.05).

CONCLUSIONS

The plantar tissue of subjects with DM, PN, and a history of ulcers was stiffer than control subjects. However, additional research is needed to determine the relationship among increased soft tissue stiffness, plantar pressures, and skin breakdown.

Biomechanics of the heel pad for type 2 diabetic patients

OBJECTIVES

To quantify the dynamic behavior of the heel pad in type 2 diabetic patients and age-matched healthy individuals using mathematical modeling.

BACKGROUND

No single parameter can fully describe the heel-pad biomechanical properties during the loading-unloading process.

DESIGN

A descriptive study using pseudoelastic modeling was conducted to simulate the heel-pad stress-strain relationship in the loaded and unloaded states. Transmission electron microscope was used to examine six heel specimens taken from amputated legs in diabetic and non-diabetic patients.

METHODS

Energy dissipation ratio, loading curvature, and unloading curvature were calculated from the stress-strain curve-fits. Differences in ultrastructure between the heel pad of healthy subjects and those with diabetes were described.

RESULTS

The diabetic patients had a significantly higher mean energy dissipation ratio (mean 36.1% (SD, 8.7%) vs mean 27.9% (SD, 6.1%); P<0.001) and mean unloaded curvatures (mean 11.8 (SD, 5.1) vs mean 8.46 (SD, 2.6); P<0.001) than those of the control group. The collagen fibrils in diabetic heel samples were ruptured with unclear striation and uneven distribution.

CONCLUSIONS

The curvature parameters may explain the poor rebound phenomenon resulting in the high impact energy in diabetic heel pads. Breakdown in collagen fibrils may be responsible for this observation.

RELEVANCE

These findings can be integrated into the fabrication of orthotics that dissipate excessive heel impact energy and protect against injury.

Heel pad stiffness in runners with plantar heel pain

OBJECTIVE

To evaluate significant differences in heel pad stiffness within a cohort of runners with diagnosed plantar heel pain and to explore the clinical importance of maximum heel pad stiffness values.

DESIGN

A cross-sectional design was used to quantify the heel pad stiffness of 166 runners with 33 diagnosed with plantar heel pain.

BACKGROUND

Palpation is still widely used to evaluate heel pad stiffness subjectively in everyday clinical practice. However, there is limited quantifiable data pertaining to heel pad stiffness measurements in runners and those with heel pain.

METHODS

A portable hand-held device measured force applied by a metal probe, and its displacement into the plantar surface of the heel pad. Non-linear modelling allowed curve coefficients b0 and b1 to be evaluated and was described by an exponential function using a non-linear regression equation. Exploratory analysis was used to describe a single-point approximation for clinical use.

RESULTS

An independent t-test demonstrated a statistically significant difference between the curve coefficient b1 (p<0.05). No significant difference was found for coefficient b0 between the plantar heel pain group and the non-plantar heel pain group (p>0.05). Exploratory analysis demonstrated maximum mean stiffness of 3.22 N/mm for the non-plantar heel pain group and 2.87 N/mm for the plantar heel pain-group, an 11% mean difference.

CONCLUSION

The results suggested that heel pad stiffness may be associated with plantar heel pain subjects.

RELEVANCE

Heel pad stiffness measurements may give a better insight into the mechanical properties of the heel pad in subjects with plantar heel pain.

Altered heel-pad mechanical properties in patients with Type 2 diabetes mellitus

AIMS

To compare the heel-pad mechanical properties in patients with Type 2 diabetes mellitus with forefoot ulceration, without forefoot ulceration and age-matched healthy subjects.

METHODS

Heel-pad mechanical properties in 40 heels of 20 healthy subjects (group I) age-matched with the other groups, 42 heels of 21 diabetic patients without forefoot ulceration (group II), and 14 heels of 12 diabetic patients with active forefoot ulceration (group III) were assessed using a self-constructed loading-unloading device and a 10-MHz linear-array ultrasound transducer.

RESULTS

There were no differences in the unloaded heel-pad thickness, compressibility index and elastic modulus between the three groups. When compared with group I subjects (mean +/- SD, 27.9 +/- 6.1%), a significant increase (P < 0.001) was found in both group II (36.1 +/- 8.7%) and group III patients (43.2 +/- 6.6%) for the energy dissipation ratio. This ratio was also significantly different (P = 0.003) between groups II and III.

CONCLUSIONS

The higher impact energy dissipated in the heel-pad may put patients with Type 2 diabetes at higher risk for developing foot ulceration.

Treatment of proximal plantar fasciitis with ultrasound-guided steroid injection

OBJECTIVE

To investigate the efficacy of ultrasound-guided steroid injection for the treatment of proximal plantar fasciitis and to evaluate mechanical properties of the heel pad after steroid injection.

DESIGN

Proximal plantar fascia and heel pad were assessed with a 10-MHz linear array ultrasound transducer. Pain intensity was quantified with a tenderness threshold (TT) and visual analog scale (VAS). The transducer was incorporated into a specially designed device to measure mechanical properties of the heel pad. Evaluations were performed before injection and at 2 weeks and 3 months after injection.

SETTING

An outpatient clinic of a tertiary care center.

PATIENTS

Fourteen consecutive patients with unilateral proximal plantar fasciitis.

INTERVENTION

Ultrasound-guided injection of 7 mg betamethasone and 0.5 mL of 1% lidocaine into the inflamed proximal plantar fascia.

MAIN OUTCOME MEASURES

VAS, TT, heel pad and plantar fascia thickness, and echogenicity of the proximal plantar fascia on sonogram were assessed. Mechanical properties included unloaded heel pad thickness, compressibility index, and energy dissipation ratio.

RESULTS

Both VAS score +/- standard deviation (SD; 5.43 +/- 2.03, 1.39 +/- 2.19, 0.57 +/- 1.40 at the 3 measurements, respectively) and TT +/- SD (5.05 +/- 1.42, 9.34 +/- 1.84, 9.93 +/- 1.98 kg/cm2 at the 3 measurements, respectively) improved significantly (p < .001) after steroid injection. The mean thickness of the plantar fascia was greater in the symptomatic side than in the asymptomatic side before treatment (0.58 +/- 0.13 cm vs 0.40 +/- 0.11 cm, p < .001). The thickness had decreased significantly 3 months after injection (0.46 +/- 0.12 cm at 2 weeks, 0.42 +/- 0.10 cm at 3 months, p < .001). The hypoechogenicity at the proximal plantar fascia disappeared after steroid injection (p < .001). Mechanical properties of the heel pad did not change 3 months after steroid injection (p > .05).

CONCLUSION

Ultrasound offers an objective measurement of the therapeutic effect on proximal plantar fasciitis. Accurate steroid injection under ultrasound guidance can effectively treat proximal plantar fasciitis without significant deterioration of the mechanical properties of the heel pads.

Development of a clinical instrument to measure heel pad indentation

OBJECTIVE

To provide an accurate, reliable, non-invasive, portable instrument to measure heel pad indentation in a clinical setting.

DESIGN

A novel instrument was applied to assess heel pad indentation.

BACKGROUND

For the lack of quantitative biomechanical tools for in vivo assessment, palpation is used to evaluate heel pad stiffness subjectively in everyday clinical practice. Furthermore, previous studies have evaluated heel pad stiffness using non-portable instrumentation.

METHODS

Cylindrical probe was attached to an electronic force gauge unit that passed through a Perspex plate for placement on heel pad. Displacement of the plate was connected to a linear variable differential transformer. A laptop PC allowed for portability and storage of data. An exponential curve described the force-displacement data. Ten healthy subjects (mean 21. 7; SD, 1.7 years) were assessed on ten separate occasions. The procedure was standardised for subject position and placement.

RESULTS

Accuracy and reliability of each device component was established. An intraclass correlation (2,1) of 0.90 and 0.88 demonstrated curve coefficients b1 and b0 respectively. A paired t-test demonstrated no significant difference between the left and right foot coefficients.

CONCLUSION

The results demonstrated that each system component could be measured accurately and reliable. Reproducible results were obtained over separate occasions. The study has described a method to analyse the force-displacement curve. RelevanceThe development of a hand-held device may help the clinician to assess heel pad stiffness in the clinical setting. Heel pad stiffness may be associated in the development of plantar heel pain in athletes.

The mechanical properties of the heel pad in unilateral plantar heel pain syndrome

Plantar heel pain syndrome has been attributed to entrapment neuropathy, plantar fasciitis, calcaneal spurs, and stress fractures of the calcaneus. Although deteriorated mechanical properties of the heel pads may play an important role in the pathogenesis of heel pain syndrome, this has received little notice. In this study, a specially designed compression relaxation device with a push-pull scale and a 10-MHz linear array transducer was used to determine thickness of the heel pad under different loading conditions. Twenty consecutive patients aged 29 to 77 years with unilateral plantar heel pain syndrome were enrolled. Thickness of heel pad bilaterally was measured when the heel pad was compressed by serial increments of 0.5 kg to a maximum of 3 kg and then relaxed sequentially. The load-displacement curve during a loading-unloading cycle was plotted, and the compressibility index and energy dissipation ratio of the heel pad were calculated accordingly. Phase I displacement of the heel pad (from 0 to 1 kg load) on the painless side was greater than that on the painful side (P < 0.01), but there was no statistically significant difference between painless and painful sides in thickness of unloaded heel pads, compressibility index, or energy dissipation ratio (P > 0.05). In conclusion, the affected heel pad in plantar heel pain syndrome was stiffer under light pressure than the heel pad on the painless side. The changed nature of chambered adipose tissue in a painful heel pad may be responsible for its increased stiffness under light pressure.

Ultrasonographic measurement of the mechanical properties of the sole under the metatarsal heads

The sole under the metatarsal heads functions as a shock absorber during walking and running. The mechanical properties of the sole provide the primary defense against the development of metatarsalgia and foot ulceration. However, limited information about these properties has been documented. In this study, we used ultrasonography to evaluate the mechanical properties, including unloaded thickness, compressibility index, elastic modulus, and energy dissipation ratio, of the sole in 20 healthy subjects. The unloaded thickness decreased progressively from the first to the fifth metatarsal heads, with values of 1.50, 1.36, 1.25, 1.14, and 1.04 cm. The sole under the first metatarsal head had the greatest values for the compressibility index and elastic modulus (55.9% and 1.39 kg/cm2), and the sole under the third metatarsal head had the smallest values (50.8% and 1.23 kg/cm2). The sole under the fifth metatarsal head had the greatest energy dissipation ratio (33.7%), followed by that under the third, second, first, and fourth metatarsal heads. Multivariate adjusted linear regression showed that the unloaded thickness, compressibility index, and elastic modulus values increased significantly with age and body weight (p < 0.05) and that the energy dissipation ratio increased significantly with body weight (p < 0.05)