Force-deformation properties of the human heel pad during barefoot walking.

INTRODUCTION: The plantar heel pad is a specialized fibroadipose tissue that attenuates and, in part, dissipates the impact energy associated with heel strike. Although a near-maximal deformation of the heel pad has been shown during running, an in vivo measurement of the deformation and structural properties of the heel pad during walking remains largely unexplored. This study used a fluoroscope, synchronized with a pressure platform, to obtain force-deformation data for the heel pad during walking. METHODS: Dynamic lateral foot radiographs were acquired from 6 male and 10 female adults (mean ± SD; age = 45 ± 10 yr, height = 1.66 ± 0.10 m, and weight = 80.7 ± 10.8 kg) while walking barefoot at preferred speeds. The inferior aspect of the calcaneus was digitized, and the sagittal thickness and deformation of the heel pad relative to the support surface were calculated. A simultaneous measurement of the peak force beneath the heel was used to estimate the principal structural properties of the heel pad. RESULTS: Transient loading profiles associated with walking induced rapidly changing deformation rates in the heel pad and resulted in irregular load-deformation curves. The initial stiffness (32 ± 11 N·mm) of the heel pad was 10 times lower than its final stiffness (212 ± 125 N·mm), and on average, only 1.0 J of energy was dissipated by the heel pad with each step during walking. Peak deformation (10.3 mm) approached that predicted for the limit of pain tolerance (10.7 mm). CONCLUSION: These findings suggest that the heel pad operates close to its pain threshold even at speeds encountered during barefoot walking and provides insight as to why barefoot runners may adopt "forefoot" strike patterns that minimize heel loading.

Plantar enthesopathy: thickening of the enthesis is correlated with energy dissipation of the plantar fat pad during walking.

BACKGROUND: The enthesis of the plantar fascia is thought to play an important role in stress dissipation. However, the potential link between entheseal thickening characteristic of enthesopathy and the stress-dissipating properties of the intervening plantar fat pad have not been investigated. PURPOSE: This study was conducted to identify whether plantar fat pad mechanics explain variance in the thickness of the fascial enthesis in individuals with and without plantar enthesopathy. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: The study population consisted of 9 patients with unilateral plantar enthesopathy and 9 asymptomatic, individually matched controls. The thickness of the enthesis of the symptomatic, asymptomatic, and a matched control limb was acquired using high-resolution ultrasound. The compressive strain of the plantar fat pad during walking was estimated from dynamic lateral radiographs acquired with a multifunction fluoroscopy unit. Peak compressive stress was simultaneously acquired via a pressure platform. Principal viscoelastic parameters were estimated from subsequent stress-strain curves. RESULTS: The symptomatic fascial enthesis (6.7 ± 2.0 mm) was significantly thicker than the asymptomatic enthesis (4.2 ± 0.4 mm), which in turn was thicker than the enthesis (3.3 ± 0.4 mm) of control limbs (P < .05). There was no significant difference in the mean thickness, peak stress, peak strain, or secant modulus of the plantar fat pad between limbs. However, the energy dissipated by the fat pad during loading and unloading was significantly lower in the symptomatic limb (0.55 ± 0.17) when compared with asymptomatic (0.69 ± 0.13) and control (0.70 ± 0.09) limbs (P < .05). The sonographic thickness of the enthesis was correlated with the energy dissipation ratio of the plantar fat pad (r = .72, P < .05), but only in the symptomatic limb. CONCLUSION: The energy-dissipating properties of the plantar fat pad are associated with the sonograpic appearance of the enthesis in symptomatic limbs, providing a previously unidentified link between the mechanical behavior of the plantar fat pad and enthesopathy.

Tight orbit syndrome: a previously unrecognized cause of open-angle glaucoma.

PURPOSE: To describe a new syndrome of tight orbit and intractable glaucoma with a poor visual prognosis. METHODS: A retrospective observational case series of six patients seen at two centres between 2001 and 2007 assessing intraocular pressure (IOP), best-corrected visual acuity and visual field. RESULTS: Three men and three women, ranging in age at diagnosis from 14 to 53 years, demonstrated similar orbital features and progressive visual field loss despite intensive management with medication and laser and operative surgery. Highest IOPs ranged from 30 to 50 mmHg. Trabeculectomy and/or glaucoma drainage devices were attempted in five patients but all failed. One patient underwent orbital decompression with achievement of IOP control. Final IOP at last follow-up was variable; only two patients achieved IOP in the normal range, with the rest ranging from 25 to 40 mmHg. All patients had advanced visual field loss. CONCLUSION: Tight orbit syndrome presents a serious clinical challenge. Despite maximum medical therapy and surgical intervention IOP is difficult to control, resulting in progressive visual field loss.

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.

Plantar fasciitis: are pain and fascial thickness associated with arch shape and loading?

BACKGROUND AND PURPOSE: Although plantar fascial thickening is a sonographic criterion for the diagnosis of plantar fasciitis, the effect of local loading and structural factors on fascial morphology are unknown. The purposes of this study were to compare sonographic measures of fascial thickness and radiographic measures of arch shape and regional loading of the foot during gait in individuals with and without unilateral plantar fasciitis and to investigate potential relationships between these loading and structural factors and the morphology of the plantar fascia in individuals with and without heel pain. SUBJECTS: The participants were 10 subjects with unilateral plantar fasciitis and 10 matched asymptomatic controls. METHODS: Heel pain on weight bearing was measured by a visual analog scale. Fascial thickness and static arch angle were determined from bilateral sagittal sonograms and weight-bearing lateral foot roentgenograms. Regional plantar loading was estimated from a pressure plate. RESULTS: On average, the plantar fascia of the symptomatic limb was thicker than the plantar fascia of the asymptomatic limb (6.1+/-1.4 mm versus 4.2+/-0.5 mm), which, in turn, was thicker than the fascia of the matched control limbs (3.4+/-0.5 mm and 3.5+/-0.6 mm). Pain was correlated with fascial thickness, arch angle, and midfoot loading in the symptomatic foot. Fascial thickness, in turn, was positively correlated with arch angle in symptomatic and asymptomatic feet and with peak regional loading of the midfoot in the symptomatic limb. DISCUSSION AND CONCLUSION: The findings indicate that fascial thickness and pain in plantar fasciitis are associated with the regional loading and static shape of the arch.

Errors in measuring sagittal arch kinematics of the human foot with digital fluoroscopy.

Although fluoroscopy has been used to evaluate motion of the foot during gait, the accuracy and precision of fluoroscopic measures of osseous structures of the foot has not been reported in the literature. This study reports on a series of experiments that quantify the magnitude and sources of error involved in digital fluoroscopic measurements of the medial longitudinal arch. The findings indicate that with a global distortion correction procedure, errors arising from image distortion can be reduced threefold to 0.2 degrees for angular measurements and to 0.1 mm for linear measures. The limits of agreement for repeated angular measures of the calcaneus and first metatarsal were +/-0.5 degrees and +/-0.6 degrees , indicating that measurement error was primarily associated with the manual process of digitisation. While the magnitude of the residual error constitutes about +/-2.5% of the expected 20 degrees of movement of the calcaneus and first metatarsal, out-of-plane rotation may potentially contribute the greatest source of error in fluoroscopic measures of the foot. However, even at the extremes of angular displacement (15 degrees ) reported for the calcaneum during running gait, the root mean square (RMS) error was only about 1 degrees . Thus, errors associated with fluoroscopic imaging of the foot appear to be negligible when compared to those arising from skin movement artefact, which typically range between 1.5 and 4 mm (equating to errors of 2 degrees to 17 degrees for angular measures). Fluoroscopy, therefore, may be a useful technique for analysing the sagittal movement of the medial longitudinal arch during the contact phase of walking.

Sagittal movement of the medial longitudinal arch is unchanged in plantar fasciitis.

BACKGROUND: Although a lowered medial longitudinal arch has been cited as a causal factor in plantar fasciitis, there is little experimental evidence linking arch motion to the pathogenesis of the condition. This study investigated the sagittal movement of the arch in subjects with and without plantar fasciitis during gait. METHODS: Digital fluoroscopy was used to acquire dynamic lateral radiographs from 10 subjects with unilateral plantar fasciitis and 10 matched control subjects. The arch angle and the first metatarsophalangeal joint angle were digitized and their respective maxima recorded. Sagittal movement of the arch was defined as the angular change between heel strike and the maximum arch angle observed during the stance phase of gait. The thickness of the proximal plantar fascia was determined from sagittal sonograms of both feet. ANOVA models were used to identify differences between limbs with respect to each dependent variable. Relationships between arch movement and fascial thickness were investigated using correlations. RESULTS: There was no significant difference in either the movement or maximum arch angle between limbs. However, subjects with plantar fasciitis were found to have a larger metatarsophalangeal joint angle than controls (P < 0.05). Whereas the symptomatic and asymptomatic plantar fascia were thicker than those of control feet (P < 0.05), significant correlations were noted between fascial thickness and peak arch and metatarsophalangeal joint angles (P < 0.05) in the symptomatic limb only. CONCLUSIONS: Neither abnormal shape nor movement of the arch are associated with chronic plantar fasciitis. However, arch mechanics may influence the severity of plantar fasciitis, once the condition is present. Digital flexion, in contrast, has a protective role in what might be a bilateral disease process.