Lower material stiffness in rupture-repaired Achilles tendon during walking: transmission-mode ultrasound for post-surgical tendon evaluation.

PURPOSE: This cross-sectional study used transmission-mode ultrasound to evaluate dynamic tendon properties during walking in surgically repaired and contralateral Achilles tendon (AT), with a median (range) post-operative period of 22 (4-58) months. It was hypothesised that the axial transmission speed of ultrasound (TSOU) during walking would be slower, indicating lower material stiffness in repaired compared with contralateral AT. METHODS: Ten patients [median (range) age 47 (37-69) years; height 180 (170-189) cm; weight 93 (62-119) kg], who had undergone open surgical repair of the AT and were clinically recovered according to their treating clinicians, walked barefoot on a treadmill at self-selected speed (1.0 ± 0.2 m/s). Synchronous measures of TSOU, sagittal ankle motion, vertical ground reaction force (GRF), and spatiotemporal gait parameters were recorded during 20 s of steady-state walking. Paired t tests were used to evaluate potential between-limb differences in TSOU, GRF, ankle motion, and spatiotemporal gait parameters. RESULTS: TSOU was significantly lower (≈175 m/s) in the repaired than in the contralateral AT over the entire gait cycle (P < 0.05). Sagittal ankle motion was significantly greater (≈3°) in the repaired than in the contralateral limb (P = 0.036). There were no significant differences in GRF or spatiotemporal parameters between limbs. CONCLUSIONS: Repaired AT was characterised by a lower TSOU, reflecting a lower material stiffness in the repaired tendon than in the contralateral tendon. A lower material stiffness may underpin greater ankle joint motion of the repaired limb during walking and long-term deficits in the muscle-tendon unit reported with AT repair. Treatment and rehabilitation approaches that focus on increasing the material stiffness of the repaired AT may be clinically beneficial. Transmission-mode ultrasound would seem useful for quantifying tendon properties post AT rupture repair and may have the potential to individually guide rehabilitation programmes, thereby aiding safer return to physical activity. LEVEL OF EVIDENCE: II.

The time course of in vivo recovery of transverse strain in high-stress tendons following exercise.

OBJECTIVE: To evaluate the time course of the recovery of transverse strain in the Achilles and patellar tendon following a bout of resistance exercise. METHODS: Seventeen healthy adults underwent sonographic examination of the right patellar (n=9) and Achilles (n=8) tendons immediately prior to and following 90 repetitions of weight-bearing quadriceps and gastrocnemius-resistance exercise performed against an effective resistance of 175% and 250% body weight, respectively. Sagittal tendon thickness was determined 20 mm from the enthesis and transverse strain, as defined by the stretch ratio, was repeatedly monitored over a 24 h recovery period. RESULTS: Resistance exercise resulted in an immediate decrease in Achilles (t7=10.6, p<0.01) and patellar (t8=8.9, p<0.01) tendon thickness, resulting in an average transverse stretch ratio of 0.86±0.04 and 0.82±0.05, which was not significantly different between tendons. The magnitude of the immediate transverse strain response, however, was reduced with advancing age (r=0.63, p<0.01). Recovery in transverse strain was prolonged compared with the duration of loading and exponential in nature. The average primary recovery time was not significantly different between the Achilles (6.5±3.2 h) and patellar (7.1±3.2 h) tendons. Body weight accounted for 62% and 64% of the variation in recovery time, respectively. CONCLUSIONS: Despite structural and biochemical differences between the Achilles and patellar tendon, the mechanisms underlying transverse creep recovery in vivo appear similar and are highly time dependent. These novel findings have important implications concerning the time required for the mechanical recovery of high-stress tendons following an acute bout of exercise.

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.

The pathomechanics of plantar fasciitis.

Plantar fasciitis is a musculoskeletal disorder primarily affecting the fascial enthesis. Although poorly understood, the development of plantar fasciitis is thought to have a mechanical origin. In particular, pes planus foot types and lower-limb biomechanics that result in a lowered medial longitudinal arch are thought to create excessive tensile strain within the fascia, producing microscopic tears and chronic inflammation. However, contrary to clinical doctrine, histological evidence does not support this concept, with inflammation rarely observed in chronic plantar fasciitis. Similarly, scientific support for the role of arch mechanics in the development of plantar fasciitis is equivocal, despite an abundance of anecdotal evidence indicating a causal link between arch function and heel pain. This may, in part, reflect the difficulty in measuring arch mechanics in vivo. However, it may also indicate that tensile failure is not a predominant feature in the pathomechanics of plantar fasciitis. Alternative mechanisms including 'stress-shielding', vascular and metabolic disturbances, the formation of free radicals, hyperthermia and genetic factors have also been linked to degenerative change in connective tissues. Further research is needed to ascertain the importance of such factors in the development of plantar fasciitis.

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.

Tendinopathy alters cumulative transverse strain in the patellar tendon after exercise.

INTRODUCTION: This research evaluated the effect of tendinopathy on the cumulative transverse strain response of the patellar tendon to a bout of resistive quadriceps exercise. METHODS: Nine adults with unilateral patellar tendinopathy (age, 18.2 ± 0.7 yr; height, 1.92 ± 0.06 m; weight, 76.8 ± 6.8 kg) and 10 healthy adults free of knee pain (age, 17.8 ± 0.8 yr; height, 1.83 ± 0.05 m; weight, 73.2 ± 7.6 kg) underwent standardized sagittal sonograms (7.2-14 MHz linear array transducer) of both patellar tendons immediately before and after 45 repetitions of a double-leg decline squat exercise performed against a resistance of 145% body weight. Tendon thickness was determined 5 and 25 mm distal to the patellar pole. Transverse Hencky strain was calculated as the natural log of the ratio of post- to preexercise tendon thickness and expressed as percentage. Measures of tendon echogenicity were calculated within the superficial and deep aspects of each tendon site from grayscale profiles. Intratendinous microvessels were evaluated using power Doppler ultrasound. RESULTS: The cumulative transverse strain response to exercise in symptomatic tendinopathy was significantly lower than that in asymptomatic and healthy tendons (P < 0.05). There was also significant reduction (57%) in the area of microvascularity immediately after exercise (P = 0.05), which was positively correlated (r = 0.93, P < 0.05) with a Victorian Institute of Sport Assessment for patellar tendinopathy score. CONCLUSIONS: This study is the first to show that patellar tendinopathy is associated with altered morphological and mechanical response of the tendon to exercise, which is manifest by reduction in cumulative transverse strain and microvascularity, when present. Research directed toward identifying factors that influence the acute microvascular and transverse strain response of the patellar tendon to exercise in the various stages of tendinopathy is warranted.

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.

A comparison of two analytical techniques for detecting differences in regional vertical impulses due to plantar fasciitis.

The vertical impulse distribution beneath the foot has been shown to be a useful objective method for evaluating gait and the efficacy of treatment programs. However, recent studies employing similar methods, but different analytical techniques, have reached divergent conclusions regarding the effect of plantar fasciitis on hindfoot, midfoot and forefoot impulses. The aim of the current study was to determine whether the impulse distribution beneath the hindfoot, midfoot and forefoot in subjects with, and without, plantar fasciitis was dependent on the analytic technique employed. A pressure platform was used to collect impulse estimates from 16 subjects with plantar fasciitis, and 16 control subjects, while walking at their preferred speed. The findings indicate that an impulse calculation incorporating the position of the center of pressure is more effective in detecting alterations in gait than the conventional method of estimating the impulse distribution beneath the foot. This study also demonstrates that subjects with plantar fasciitis possess modified gait patterns that are primarily manifest by a reduced hindfoot and an increased midfoot impulse, as defined by the pathway of the center of pressure.

The effect of exercise repetition on the frequency characteristics of motor output force: implications for Achilles tendinopathy rehabilitation.

OBJECTIVES: To investigate the frequency characteristics of the ground reaction force (GRF) recorded throughout the eccentric Achilles tendon rehabilitation programme described by Alfredson. DESIGN: Controlled laboratory study, longitudinal. METHODS: Nine healthy adult males performed six sets (15 repetitions per set) of eccentric ankle exercise. Ground reaction force was recorded throughout the exercise protocol. For each exercise repetition the frequency power spectrum of the resultant ground reaction force was calculated and normalised to total power. The magnitude of peak relative power within the 8-12 Hz bandwidth and the frequency at which this peak occurred was determined. RESULTS: The magnitude of peak relative power within the 8-12 Hz bandwidth increased with each successive exercise set and following the 4th set (60 repetitions) of exercise the frequency at which peak relative power occurred shifted from 9 to 10 Hz. CONCLUSIONS: The increase in magnitude and frequency of ground reaction force vibrations with an increasing number of exercise repetitions is likely connected to changes in muscle activation with fatigue and tendon conditioning. This research illustrates the potential for the number of exercise repetitions performed to influence the tendons' mechanical environment, with implications for tendon remodelling and the clinical efficacy of eccentric rehabilitation programmes for Achilles tendinopathy.

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.

Running shoes increase achilles tendon load in walking: an acoustic propagation study.

BACKGROUND: Footwear remains a prime candidate for the prevention and rehabilitation of Achilles tendinopathy because it is thought to decrease tension in the tendon through elevation of the heel. However, evidence for this effect is equivocal. PURPOSE: This study used an acoustic transmission technique to investigate the effect of running shoes on Achilles tendon loading during barefoot and shod walking. METHODS: Acoustic velocity was measured in the Achilles tendon of 12 recreationally active males (age, 31 ± 9 yr; height, 1.78 ± 0.06 m; weight, 81.0 ± 16.9 kg) during barefoot and shod walking at matched self-selected speed (3.4 ± 0.7 km·h). Standard running shoes incorporating a 10-mm heel offset were used. Vertical ground reaction force and spatiotemporal parameters were determined with an instrumented treadmill. Axial acoustic velocity in the Achilles tendon was measured using a custom-built ultrasonic device. All data were acquired at a rate of 100 Hz during 10 s of steady-state walking. Statistical comparisons between barefoot and shod conditions were made using paired t-tests and repeated-measure ANOVA. RESULTS: Acoustic velocity in the Achilles tendon was highly reproducible and was typified by two maxima (P1, P2) and minima (M1, M2) during walking. Footwear resulted in a significant increase in step length, stance duration, and peak vertical ground reaction force compared with barefoot walking. Peak acoustic velocity in the Achilles tendon (P1, P2) was significantly higher with running shoes. CONCLUSIONS: Peak acoustic velocity in the Achilles tendon was higher with footwear, suggesting that standard running shoes with a 10-mm heel offset increase tensile load in the Achilles tendon. Although further research is required, these findings question the therapeutic role of standard running shoes in Achilles tendinopathy.

Concurrent validity of accelerations measured using a tri-axial inertial measurement unit while walking on firm, compliant and uneven surfaces.

Although accelerometers are extensively used for assessing gait, limited research has evaluated the concurrent validity of these devices on less predictable walking surfaces or the comparability of different methods used for gravitational acceleration compensation. This study evaluated the concurrent validity of trunk accelerations derived from a tri-axial inertial measurement unit while walking on firm, compliant and uneven surfaces and contrasted two methods used to remove gravitational accelerations; i) subtraction of the best linear fit from the data (detrending); and ii) use of orientation information (quaternions) from the inertial measurement unit. Twelve older and twelve younger adults walked at their preferred speed along firm, compliant and uneven walkways. Accelerations were evaluated for the thoracic spine (T12) using a tri-axial inertial measurement unit and an eleven-camera Vicon system. The findings demonstrated excellent agreement between accelerations derived from the inertial measurement unit and motion analysis system, including while walking on uneven surfaces that better approximate a real-world setting (all differences <0.16 m.s(-2)). Detrending produced slightly better agreement between the inertial measurement unit and Vicon system on firm surfaces (delta range: -0.05 to 0.06 vs. 0.00 to 0.14 m.s(-2)), whereas the quaternion method performed better when walking on compliant and uneven walkways (delta range: -0.16 to -0.02 vs. -0.07 to 0.07 m.s(-2)). The technique used to compensate for gravitational accelerations requires consideration in future research, particularly when walking on compliant and uneven surfaces. These findings demonstrate trunk accelerations can be accurately measured using a wireless inertial measurement unit and are appropriate for research that evaluates healthy populations in complex environments.

Achilles tendinopathy modulates force frequency characteristics of eccentric exercise.

INTRODUCTION: Previous research has demonstrated that ground reaction force (GRF) recorded during eccentric ankle exercise is characterized by greater power in the 8- to 12-Hz bandwidth when compared with that recorded during concentric ankle exercise. Subsequently, it was suggested that vibrations in this bandwidth may underpin the beneficial effect of eccentric loading in tendon repair. However, this observation has been made only in individuals without Achilles tendinopathy. This research compared the force frequency characteristics of eccentric and concentric exercises in individuals with and without Achilles tendinopathy. METHODS: Eleven male adults with unilateral midportion Achilles tendinopathy and nine control male adults without tendinopathy participated in the research. Kinematics and GRF were recorded while the participants performed a common eccentric rehabilitation exercise protocol and a concentric equivalent. Ankle joint kinematics and the frequency power spectrum of the resultant GRF were calculated. RESULTS: Eccentric exercise was characterized by a significantly greater proportion of spectral power between 4.5 and 11.5 Hz when compared with concentric exercise. There were no significant differences between limbs in the force frequency characteristics of concentric exercise. Eccentric exercise, in contrast, was defined by a shift in the power spectrum of the symptomatic limb, resulting in a second spectral peak at 9 Hz, rather than 10 Hz in the control limb. CONCLUSIONS: Compared with healthy tendon, Achilles tendinopathy was characterized by lower frequency vibrations during eccentric rehabilitation exercises. This finding may be associated with changes in neuromuscular activation and tendon stiffness that have been shown to occur with tendinopathy and provides a possible rationale for the previous observation of a different biochemical response to eccentric exercise in healthy and injured Achilles tendons.

Overweight and obesity alters the cumulative transverse strain in the Achilles tendon immediately following exercise.

This research evaluated the effect of obesity on the acute cumulative transverse strain of the Achilles tendon in response to exercise. Twenty healthy adult males were categorized into 'low normal-weight' (BMI <23 kg m(-2)) and 'overweight' (BMI >27.5 kg m(-2)) groups based on intermediate cut-off points recommended by the World Health Organization. Longitudinal sonograms of the right Achilles tendon were acquired immediately prior and following weight-bearing ankle exercises. Achilles tendon thickness was measured 20-mm proximal to the calcaneal insertion and transverse tendon strain was calculated as the natural log of the ratio of post- to pre-exercise tendon thickness. The Achilles tendon was thicker in the overweight group both prior to (t18 = -2.91, P = 0.009) and following (t18 = -4.87, P < 0.001) exercise. The acute transverse strain response of the Achilles tendon in the overweight group (-10.7 ± 2.5%), however, was almost half that of the 'low normal-weight' (-19.5 ± 7.4%) group (t18 = -3.56, P = 0.004). These findings suggest that obesity is associated with structural changes in tendon that impairs intra-tendinous fluid movement in response to load and provides new insights into the link between tendon pathology and overweight and obesity.

The acute transverse strain response of the patellar tendon to quadriceps exercise.

INTRODUCTION: The human patellar tendon is highly adaptive to changes in habitual loading, but little is known about its acute mechanical response to exercise. This research evaluated the immediate transverse strain response of the patellar tendon to a bout of resistive quadriceps exercise. METHODS: Twelve healthy adult males (mean age, 34.0 ± 12.1 yr; height, 1.75 ± 0.09 m; and weight, 76.7 ± 12.3 kg) free of knee pain participated in the research. A 10- to 5-MHz linear array transducer was used to acquire standardized sagittal sonograms of the right patellar tendon immediately before and after 90 repetitions of a double-leg parallel-squat exercise performed against a resistance of 175% bodyweight. Tendon thickness was determined 20-mm distal to the pole of the patellar, and transverse Hencky strain was calculated as the natural log of the ratio of post- to preexercise tendon thickness and expressed as a percentage. Measures of tendon echotexture (echogenicity and entropy) were also calculated from subsequent grayscale profiles. RESULTS: Quadriceps exercise resulted in an immediate decrease in patellar tendon thickness (P < 0.05), equating to a transverse strain of -22.5% ± 3.4% and was accompanied by increased tendon echogenicity (P < 0.05) and decreased entropy (P < 0.05). The transverse strain response of the patellar tendon was significantly correlated with both tendon echogenicity (r = -0.58, P < 0.05) and entropy after exercise (r = 0.73, P < 0.05), whereas older age was associated with greater entropy of the patellar tendon before exercise (r = 0.79, P < 0.05) and a reduced transverse strain response (r = 0.61, P < 0.05) after exercise. CONCLUSIONS: This study is the first to show that quadriceps exercise invokes structural alignment and fluid movement within the matrix that are manifested by changes in echotexture and transverse strain in the patellar tendon.

Achilles tendinopathy has an aberrant strain response to eccentric exercise.

PURPOSE: Eccentric exercise has become the treatment of choice for Achilles tendinopathy. However, little is known about the acute response of tendons to eccentric exercise or the mechanisms underlying its clinical benefit. This research evaluated the sonographic characteristics and acute anteroposterior (AP) strain response of control (healthy), asymptomatic, and symptomatic Achilles tendons to eccentric exercise. METHODS: Eleven male adults with unilateral midportion Achilles tendinopathy and nine control male adults without tendinopathy participated in the research. Sagittal sonograms of the Achilles tendon were acquired immediately before and after completion of a common eccentric rehabilitation exercise protocol and again 24 h later. Tendon thickness, echogenicity, and AP strain were determined 40 mm proximal to the calcaneal insertion. RESULTS: Compared with the control tendon, both the asymptomatic and symptomatic tendons were thicker (P < 0.05) and hypoechoic (P < 0.05) at baseline. All tendons decreased in thickness immediately after eccentric exercise (P < 0.05). The symptomatic tendon was characterized by a significantly lower AP strain response to eccentric exercise compared with both the asymptomatic and control tendons (P < 0.05). AP strains did not differ in the control and asymptomatic tendons. For all tendons, preexercise thickness was restored 24 h after exercise completion. CONCLUSIONS: These observations support the concept that Achilles tendinopathy is a bilateral or systemic process and structural changes associated with symptomatic tendinopathy alter fluid movement within the tendon matrix. Altered fluid movement may disrupt remodeling and homeostatic processes and represents a plausible mechanism underlying the progression of tendinopathy.

Footprint-based estimates of arch structure are confounded by body composition in adults.

Previous research employing indirect measures of arch structure, such as those derived from footprints, have indicated that obesity results in a "flatter" foot type. In the absence of radiographic measures, however, definitive conclusions regarding the osseous alignment of the foot cannot be made. We determined the effect of body mass index (BMI) on radiographic and footprint-based measures of arch structure. The research was a cross-sectional study in which radiographic and footprint-based measures of foot structure were made in 30 subjects (10 males, 20 female) in addition to standard anthropometric measures of height, weight, and BMI. Multiple (univariate) regression analysis demonstrated that both BMI (ß = 0.39, t(26) = 2.12, p = 0.04) and radiographic arch alignment (ß = 0.51, t(26) = 3.32, p < 0.01) were significant predictors of footprint-based measures of arch height after controlling for all variables in the model (R(2) = 0.59, F(3,26) = 12.3, p < 0.01). In contrast, radiographic arch alignment was not significantly associated with BMI (ß = -0.03, t(26) = -0.13, p = 0.89) when Arch Index and age were held constant (R(2) = 0.52, F(3,26) = 9.3, p < 0.01). Adult obesity does not influence osseous alignment of the medial longitudinal arch, but selectively distorts footprint-based measures of arch structure. Footprint-based measures of arch structure should be interpreted with caution when comparing groups of varying body composition.

Conditioning of the Achilles tendon via ankle exercise improves correlations between sonographic measures of tendon thickness and body anthropometry.

Although conditioning is routinely used in mechanical tests of tendon in vitro, previous in vivo research evaluating the influence of body anthropometry on Achilles tendon thickness has not considered its potential effects on tendon structure. This study evaluated the relationship between Achilles tendon thickness and body anthropometry in healthy adults both before and after resistive ankle plantarflexion exercise. A convenience sample of 30 healthy male adults underwent sonographic examination of the Achilles tendon in addition to standard anthropometric measures of stature and body weight. A 10-5 MHz linear array transducer was used to acquire longitudinal sonograms of the Achilles tendon, 20 mm proximal to the tendon insertion. Participants then completed a series (90-100 repetitions) of conditioning exercises against an effective resistance between 100% and 150% body weight. Longitudinal sonograms were repeated immediately on completion of the exercise intervention, and anteroposterior Achilles tendon thickness was determined. Achilles tendon thickness was significantly reduced immediately following conditioning exercise (t = 9.71, P < 0.001), resulting in an average transverse strain of -18.8%. In contrast to preexercise measures, Achilles tendon thickness was significantly correlated with body weight (r = 0.72, P < 0.001) and to a lesser extent height (r = 0.45, P = 0.01) and body mass index (r = 0.63, P < 0.001) after exercise. Conditioning of the Achilles tendon via resistive ankle exercises induces alterations in tendon structure that substantially improve correlations between Achilles tendon thickness and body anthropometry. It is recommended that conditioning exercises, which standardize the load history of tendon, are employed before measurements of sonographic tendon thickness in vivo.

Incidental walking activity is sufficient to induce time-dependent conditioning of the Achilles tendon.

The Achilles tendon has been seen to exhibit time-dependent conditioning when isometric muscle actions were of a prolonged duration, compared to those involved in dynamic activities, such as walking. Since, the effect of short duration muscle activation associated with dynamic activities is yet to be established, the present study aimed to investigate the effect of incidental walking activity on Achilles tendon diametral strain. Eleven healthy male participants refrained from physical activity in excess of the walking required to carry out necessary daily tasks and wore an activity monitor during the 24 h study period. Achilles tendon diametral strain, 2 cm proximal to the calcaneal insertion, was determined from sagittal sonograms. Baseline sonographic examinations were conducted at approximately 08:00 h followed by replicate examinations at 12 and 24 h. Walking activity was measured as either present (1) or absent (0) and a linear weighting function was applied to account for the proximity of walking activity to tendon examination time. Over the course of the day the median (min, max) Achilles tendon diametral strain was -11.4 (4.5, -25.4)%. A statistically significant relationship was evident between walking activity and diametral strain (P<0.01) and this relationship improved when walking activity was temporally weighted (AIC 131 to 126). The results demonstrate that the short yet repetitive loads generated during activities of daily living, such as walking, are sufficient to induce appreciable time-dependant conditioning of the Achilles tendon. Implications arise for the in vivo measurement of Achilles tendon properties and the rehabilitation of tendinopathy.

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.