Is 2D SWE sufficient as clinical diagnosis in patients with plantar fasciitis?

Abstract

Background

The use of shear wave elastography (SWE) seems to be an important imaging method in the diagnosis of plantar fasciitis (PF).

Purpose

To compare patients diagnosed with PF with similar and young healthy control groups in terms of B-mode ultrasound (US) and SWE results and to evaluate the elasticity of the plantar fascia.

Material and Methods

A total of 140 feet of 70 participants were evaluated, including 30 patients and 40 healthy individuals as the control. Clinical, B-mode US, and SWE evaluations were performed for each patient. In addition, American Orthopedic Foot and Ankle Score (AOFAS) was calculated to evaluate pain and foot function in both groups.

Results

Of the patients in the PF group, 40 (88%) were women and the healthy control groups had similar sex distributions (P = 0.23). The AOFAS score was lower in feet with PF compared to the other groups (P < 0.001). Of 30 patients with PF, 15 (50%) had bilateral PF and 15 (50%) unilateral PF. In addition, ≥4 mm thickness measurement, which was used as a diagnostic criterion for PF as a US finding, could be shown in 11 (73.3%) patients with unilateral PF and 6 (40%) patients with bilateral PF.

Conclusion

In conclusion, the evaluation of the diagnosis of PF with clinical findings and regular follow-up of measurements with SWE can provide measurement results with higher sensitivity in the diagnosis of PF.

Keywords

Plantar fasciitis elastography shear wave elastography sonoelastography ultrasound plantar fasciitis

Introduction

Plantar fasciitis (PF) is the most common cause of non-traumatic heel pain, which can be reduced by treatments such as steroid injections (1,2). The lifetime prevalence of PF in the general population is approximately 10% (3,4). It is thought that PF is caused by repetitive load-bearing stress and degenerative changes in the fascia (4,5). There are many different causes of the development of PF. Inappropriate shoes, obesity, or standing for long periods are risk factors for PF (6,7). The typical symptom in patients with PF is pain when taking the first steps in the morning or during the steps taken after a period of inactivity (8). While standing or during other routine activities, patients experience a progressive worsening of symptoms, often with complaints of increasing pain towards the end of the day. Pain in the plantar fascia normally begins at the plantar medial tubercle of the calcaneus, at the site of the PF (9). In approximately 80% of cases of PF, the pain is self-limiting and resolves within a year. However, the effect of heel pain during routine activities causes patients, especially athletes, to seek treatment earlier.

Diagnostic criteria for PF are heel pain that worsens on awakening in the morning or after a rest period, and tenderness in the medial tubercle of the calcaneus (10,11). So far, the diagnosis of PF has been based on clinical history and examination. Although ultrasound (US) is not required for the diagnosis of PF, it can confirm the diagnosis or be used as an imaging guide for injection procedures. Typical US findings of PF include thickening of the plantar fascia, loss of normal striation, a hypoechoic area within the fascia, and perifascial effusion (11). However, these morphological changes are not always observed on US in patients with PF (11,12).

Shear wave elastography (SWE) is a non-invasive US imaging technique that provides information about tissue elasticity and stiffness using a wave generated by the probe (13,14). In particular, SWE is thought to provide user-independent quantitative measures of tissue elasticity expressed in kPa or m/s, and its clinical applications have been widely validated (14).

Based on this information, it was aimed to compare patients diagnosed with PF with similar and young healthy control groups in terms of B-mode ultrasound and SWE results and to evaluate the elasticity of the plantar fascia.

Material and Methods

Study design and patients

The present study was performed to evaluate the diagnostic role of elastography in the evaluation of PF characteristics between patients with PF and a healthy control group. The data of the patients and healthy controls were randomly obtained as cross-sectional and retrospective. The study was based on the results of orthopedic examination and plantar fascia SWE measurements performed over a three-month period. A total of 140 feet of 30 patients and 40 (20 of them at similar ages and 20 of them aged 18–25 years) healthy controls were evaluated with US. Horizonal B-mode and longitudinal elastography imaging of the feet is included in the routine US protocol for healthy controls and patients with unilateral or bilateral heel pain in our clinic. Patients aged >18 years with foot complaints for a minimum of three months or longer, among the patients who were evaluated as PF by the evaluation of the orthopedic specialist, were included in our study.

Diagnostic evaluation

The diagnostic evaluation of the patients in the study in terms of PF was performed by an experienced orthopedic specialist (AY).

The exclusion criteria were as follows:

A systemic inflammatory disease or connective tissue disease

Past local trauma

Presence of plantar fibroma

History of previous surgery and treatment with PF corticosteroids, hyaluronic acid, or PRP injections in the three months before diagnosis, or oral cortisone therapy in the previous month

In addition, patients diagnosed with PF were administered local steroid injection for therapeutic purposes after US-SWE elastography examination.

Age, weight, and height distributions of the two groups were similar. All eligible patients whose clinical data were completed were included in the study. Clinical, B-mode US, and SWE assessment were performed for each patient. In addition, American Orthopedic Foot and Ankle Score (AOFAS) was calculated to evaluate pain and foot function in both groups. The study protocol was approved by the Van Training and Research Hospital Ethics Review Committee, and the study was carried out in accordance with the principles of the Declaration of Helsinki (Date: 2016, Issue No: 39). Informed consent form was signed by all patients.

Individuals participating in the study were divided into four groups: Group 1 = feet of patients diagnosed with PF by an orthopedic specialist (15 patients unilateral and 15 patients bilateral); Group 2 = feet of asymptomatic volunteers with similar age and sex distribution as Group 1 (n = 40); Group 3 = feet of asymptomatic healthy volunteers aged 18–24 years (n = 40); Group 4 = the other feet of the patients in group 1 with one symptomatic foot (n = 15).

Radiological evaluation

All examinations were performed by a musculoskeletal radiologist (EB) with >20 years of experience in B-mode US imaging and >36 months in US elastography. Radiologists performed the examination without knowing which group the cases belonged to. Sonographic evaluation was performed with TOSHIBA APLIO 500 (software version 6.0; Toshiba Medical Systems, Tokyo, Japan) US device and 6-MHz probe. The examinations were performed with the patients lying on their back on the examination stretcher, with the knee at 90° of flexion and the foot in the neutral position. In the B-mode US examination, the thickness and echogenicity of the plantar fascia and possible differences were evaluated. Differences in echogenicity were noted. Longitudinal and short axis B-mode imaging of the feet and longitudinal elastography imaging were performed. PF thickness was measured from the anterior border of the medial inferior calcaneal border perpendicular to the inferior border of the PF, and the overall symptomatic PF thickness was measured. Immediately afterwards, SWE examination was performed. In the elastography examination, three measurements were made from the calcaneus insertion point of the fascia and 1.5-cm area, and the average of the measurements was taken.

Statistical analysis

SPSS version 27.0 (IBM Corp., Armonk, NY, USA) was used in the analysis of the variables. The Mann–Whitney U-test was used together with the Monte Carlo results to compare two independent groups with each other according to quantitative data. The one-way ANOVA (Robust Test: Brown-Forsythe) and the Kruskal–Wallis H tests were used to compare more than two groups with each other according to quantitative data. Dunn’s, Tukey, and Games-Howell tests were used for post hoc analyses. While quantitative variables were expressed as mean ± standard deviation (SD) and median (interquartile range [IQR]) in the tables, categorical variables were shown as n (%). Variables were analyzed at 95% confidence level and were considered significant when the P value was <0.05.

Results

In this study, a total of 140 feet of 70 participants, including 30 patients (15 unilateral and 15 bilateral) and 40 healthy controls (20 of them at similar ages and 20 aged 18–25 years), were evaluated. Of the patients in the PF group, 40 (88%) were women, and the sex distribution of the healthy controls was similar (P = 0.23). It was determined that the thickness of the plantar fascia of the patients with PF increased more than the asymptomatic opposite feet and the feet in the control group. In the SWE measurements of the feet with PF, m/s and kPA levels were lower than the other groups (P < 0.001). The AOFAS score was found to be lower in feet with PF compared to the other groups. In addition, while plantar fascia echogenicity was found to be homogeneous in all individuals in the healthy control group aged 18–25 years, decreased echogenicity was observed in 60% of the feet with PF. A decrease in echogenicity was found in 25% of individuals in the healthy control group at a similar age to those with a diagnosis of PF (Table 1).

Table 1.

Evaluation of PF diagnosed and healthy control groups.

	Total (n = 140)	Group I (PF) (A) (n = 45)	Group II (Healthy controls) (B)* (n = 40)	Group III (Healthy controls aged 18–25 years) (C)^† (n = 40)	Group IV (D)^‡ (n = 15)	P
Sex						0.237
Female	116 (82.5)	40 (88.8)	34 (85.0)	32 (80.0)	10 (66.7)
Male	24 (17.5)	5 (11.2)	6 (15.0)	8 (20.0)	5 (33.3)
Echogenicity						<0.001
Homogeneous	96 (68.6)	18 (40.0)	30 (75.0)	40 (100.0)	8 (53.3)
Decreased	44 (32.4)	27 (60.0)	10 (25.0)	0 (0.0)	7 (46.7)
Age (years)	37 (24–44)	41 (35–52)	40.5 (37–49.5)	24 (22.5–24)	40 (35–47)	<0.001
PF thickness	3.35 (3–4)	4 (3.4–5)^BCD	3.5 (3.1–3.95)^AC	3 (2.7–3.2)^AB	3.3 (3–3.8)^A	<0.001
m/s	4.265 (2.78–5.97)	2.4 (2.16–2.78)^BCD	4.94 (4.38–5.465)^ACD	6.405 (5.97–7.22)^ABD	3.68 (3.5–4.07)^ABC	<0.001
kPa	58.4 (24.3–94.2)	18.7 (14.9–24.5)^BCD	77.9 (59.6–93.75)^ACD	108.3 (92.15–118.4)^ABD	43.4 (26.2–53.6)^ABC	<0.001
AOFAS	80 (50–90)	45 (40–50)^BC	82.5 (80–87.5)^A	90 (90–95)^A	–	<0.001

Values are given as n (%) or median (IQR).

Pearson chi-square test (Monte Carlo, Exact); Post hoc test: Benjamini–Hochberg correction, Kruskal–Wallis test (Monte Carlo), Post hoc test, Dunn’s test. A, PF group; B, healthy controls; C, healthy controls aged 18–25 years; D, feets of patients with one healthy side of PF.

*Healthy controls of similar age.

^†

Healthy controls aged 15–25 years.

^‡

Feet of patients with one healthy side.

AOFAS, American Orthopaedic Foot & Ankle Society Ankle-Hindfoot Score; PF, plantar fascia.

Of the 30 patients with PF, 15 (50%) had bilateral PF and 15 (50%) unilateral PF. The table comparing the mean SWE findings of patients with bilateral PF and symptomatic foot findings of patients with unilateral PF is summarized. All patients (100%) with bilateral PF and 10 (66%) with unilateral PF were women. When the mean values of unilateral and bilateral PF were compared, no significant difference was found in terms of echogenicity, fascia thickness, patient age, m/sn, kPa, and AOFAS scores. In addition, ≥4 mm thickness measurement, which is used as a diagnostic criterion for PF as a US finding, was shown in 11 (73.3%) patients with unilateral PF and 6 (40%) patients with bilateral PF (Table 2).

Table 2.

Comparison of patients with unilateral and bilateral PF.

	Total (n = 30)	Unilateral (n = 15)	Bilateral (n = 15)	P
Sex				0.042
Female	25 (83.3)	10 (66.7)	15 (100.0)
Male	5 (16.7)	5 (33.3)	0 (0.0)
Echogenicity				0.264
Homogeneous	13 (43.3)	8 (53.3)	5 (33.3)
Decreased	17 (56.7)	7 (46.7)	10 (66.7)
PF thickness				0.139
≥4	17 (56.7)	11 (73.3)	6 (40.0)
<4	13 (43.3)	4 (26.7)	9 (60.0)
Age (years)	43.66 ± 8.95	42.87 ± 7.88	44.46 ± 10.12	0.633
PF thickness	4.19 ± 1.20	4.24 ± 1.15	4.14 ± 1.29	0.818
m/s	2.56 ± 0.56	2.57 ± 0.54	2.54 ± 0.60	0.883
kPa	22.05 ± 10.35	22.03 ± 8.97	22.06 ± 11.89	0.993
AOFAS	46.33 ± 4.72	48.0 ± 4.14	44.66 ± 4.81	0.052

Values are given as n (%) or mean ± SD.

Pearson chi-square test (Monte Carlo, Exact); Post hoc test: Benjamini–Hochberg correction; Kruskal–Wallis test (Monte Carlo).

AOFAS, American Orthopaedic Foot & Ankle Society Ankle-Hindfoot Score; PF, plantar fascia.

Discussion

Today, the diagnosis of PF is made in the light of clinical findings and supported by different imaging methods. In the present study, patients diagnosed and treated for PF by the orthopedic clinic were compared with similar and different asymptomatic control groups. In the study, it was determined that clinical findings were related to US and SWE findings, but increase in plantar fascia thickness and elasticity findings did not have a sufficiently sensitive predictive value for the diagnosis of PF.

Plantar heel pain is a symptom commonly encountered by clinicians and may be due to conditions such as PF, calcaneal fracture, heel fat pad atrophy, and tarsal tunnel syndrome. Muscle and tendon stiffness have been extensively investigated using different methods (15,16). US can help differentiate between causes of heel pain, for example, by detecting external compression of the nerve tarsal tunnel by a ganglion cyst or neurogenic tumor. If US findings are not helpful in the diagnosis, further investigations such as MRI or electrodiagnostic tests may be required. It is known that elastography is an appropriate diagnostic tool in case of insufficient US findings to show early changes in the elasticity of the PF in symptomatic patients (12,17).

In patients with PF, US may show plantar fascia thickening and perifascial effusion (11). Diagnosis of PF with US and sonoelastography can reduce unnecessary examinations (10,18). Sonoelastography is an alternative imaging method used to identify changes in connective tissues and is recommended in EFSUMB guidelines (19). Different sonoelastography techniques (strain elastography and SWE) have been developed and evaluated in different applications (20 –23). Because of the complex rigid textural distribution of the plantar fascia, differentiating PF is also highly dependent on the area of view (24 –27). It has been reported that the proximal PF regions around the calcaneal insertion are significantly thicker and stiffer than the middle and distal regions (25). In the present study, the elasticity of the plantar fascia was evaluated from three different locations of the calcaneus and averaged over a relatively standard and narrow region (ROI) (26).

Micro-tears in collagen fibers in the plantar fascia are related to the histological changes of PF, such as fibroblastic hypertrophy and chronic degeneration caused by repetitive overstrain (7). However, these morphological changes are not always seen with conventional US in patients with PF (28,29). For example, in one study, hypoechoic areas in the plantar fascia were reported in 16 (84%) of 19 patients with PF, and plantar fascia thicknesses >4 mm in 15 (79%) (11). US and magnetic resonance imaging (MRI) are used to distinguish PF from other causes of heel pain, to determine the extent of the disease and to stage it (30). Some authors have evaluated the plantar fascia thickness values of >4 mm, measured by US, as pathognomonic for PF (13). In addition, in a recent systematic review and meta-analysis on the use of US in PF, it was revealed that a thickening of >4 mm in the plantar fascia was associated with a 100-fold increased risk for the diagnosis of PF (29). Broholm et al. stated that a threshold value could not be defined for the diagnosis of PF due to insufficient in-group calibration (31). In the present study, fascia thickness was ≥4 mm in 17 (56.7%) patients with PF, while this rate was 73.3% in patients with unilateral PF and 40% in patients with bilateral PF. As a result, it was thought that the measurement of the plantar fascia thickness of 4 mm in patients with clinically defined PF did not have sufficient diagnostic sensitivity.

SWE is an effective method for assessing tissue stiffness. US elastography has been used to characterize breast, prostate, and thyroid tumors by distinguishing between benign and malignant tumors (32 –34). In SWE, the acoustic radiation force is generated by the ultrasound probe to disrupt the tissue in the focal area by inducing shear waves that propagate transversely within the tissue. Current elastography methods (strain or SWE imaging) use color channel image information to evaluate PF where hardness is quantified in various color grades (35 –37). However, these methods depend on the visual diagnosis of the musculoskeletal radiologist and are not sufficient to characterize PFs. Although US elastography shows softening of the plantar fascia and enthesitis in the common extensor tendon of the elbow and the Achilles tendon, few studies have used elastography to view musculoskeletal structures (10,12,36,38,39). It has recently been shown that SWE is applicable in the evaluation of PF and the plantar fascia softens in these patients (10).

A few studies report sonoelastography results of PFs showing softening of the PF on the affected side, while conventional US reports normal PF echogenicity and thickness. In other studies, it has been reported that the plantar fascia is softer in patients with PF compared to the healthy controls (10,35). Quantitative color histogram analyzes of sonoelastography showed that 72.7% of the fascia was moderately elastic and had no significant association with PF (40). Another study reported that PF softens with age in patients with PF (10). From this point of view, increase in plantar fascia thickness, decrease in echogenicity and softening are expected in elderly people compared to younger people. In addition, a strong correlation between Young's modulus and clinical scores (FFI-pain, FFI function, AOFAS) in symptomatic PFs was previously demonstrated by SWE, confirming the findings of this study (26). In the present study, while a strong positive correlation was found between AOFAS and m/sn and kPA, there was a negative correlation between fascia thickness and age. In this case, it can be thought that fascia thickness and aging cause symptoms of PF to become more pronounced, although it shows that fascia softness increases and elasticity decreases with increasing age.

This study has several limitations. Inter- and intra-observer compatibility was not evaluated in elastography performance since it was not included in the study plan. Second, the radiologist was unaware of the symptomatic and asymptomatic aspects while performing US. For this reason, we think that the results of the study can be compared more objectively in the light of the literature. In the present study, the diagnosis method based on the opinion of an orthopedic specialist was used in contrast to the use of the increase in plantar fascia thickness as a diagnostic criterion in other similar studies. This is important in detecting symptomatic (probably PF) patients without increased fascia thickness.

In conclusion, SWE US and SWE measurement results of patients who were evaluated as PF with clinical findings and whose diagnosis was confirmed according to treatment response were found to have increased PF thickness and softness compared to those of similar age and younger age. In addition, an important finding was that the asymptomatic side of plantar fascia measurements were similar to the symptomatic side in patients with unilateral PF. In conclusion, evaluation of the diagnosis of PF with clinical findings and regular follow-up of measurements with SWE can provide measurement results with higher sensitivity in the diagnosis of PF.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Engin Beydoğan

References

Rompe

. Plantar fasciopathy. Sports Med Arthrosc 2009;17:100–104.

Kamel

. Ultrasonographic diagnosis of de Quervain’s tenosynovitis. Ann Rheum Dis 2002;61:1034–1035.

Hautmann

Rechner

Hipp

, et al. Re-irradiation for osteoarthritis—retrospective analysis of 217 joints. Strahlentherapie und Onkol 2019;195:1060–1067.

Schepsis

Leach

Gorzyca

. Plantar fasciitis. Etiology, treatment, surgical results, and review of the literature. Clin Orthop Relat Res 1991;266:185–196.

Fazal

Tsekes

Baloch

. Is there a role for MRI in plantar heel pain. Foot Ankle Spec 2018;11:242–245.

Niewald

Holtmann

Prokein

, et al. Randomized multicenter follow-up trial on the effect of radiotherapy on painful heel spur (plantar fasciitis) comparing two fractionation schedules with uniform total dose: first results after three months’ follow-up. Radiat Oncol 2015;10:174.

Wearing

Smeathers

Urry

, et al. The pathomechanics of plantar fasciitis. Sport Med 2006;36:585–611.

Rosenbaum

DiPreta

Misener

. Plantar heel pain. Med Clin North Am 2014;98:339–352.

Schneider

Baca

Carpenter

, et al. American College of Foot and Ankle Surgeons Clinical Consensus Statement: diagnosis and treatment of adult acquired infracalcaneal heel pain. J Foot Ankle Surg 2018;57:370–381.

10.

C-H

Chang

K-V

Mio

, et al. Sonoelastography of the plantar fascia. Radiology 2011;259:502–527.

11.

Cardinal

Chhem

Beauregard

, et al. Plantar fasciitis: sonographic evaluation. Radiology. 1996;201:257–259.

12.

C-H

Chen

W-S

Wang

T-G

, et al. Can sonoelastography detect plantar fasciitis earlier than traditional B-mode ultrasonography? Am J Phys Med Rehabil 2012;91:185.

13.

Piskin

Yavuz

Kose

, et al. A comparative study of the pancreas in pediatric patients with cystic fibrosis and healthy children using two-dimensional shear wave elastography. J Ultrasound 2020;23:535–542.

14.

Săftoiu

Gilja

Sidhu

, et al. The EFSUMB Guidelines and Recommendations for the Clinical Practice of Elastography in Non-Hepatic Applications: Update 2018. Ultraschall Med 2019;40:425–453.

15.

Alviti

Gurzì

Santilli

, et al. Achilles tendon open surgical treatment with platelet-rich fibrin matrix augmentation: biomechanical evaluation. J Foot Ankle Surg 2017;56:581–585.

16.

Walshe

Wilson

Murphy

. The validity and reliability of a test of lower body musculotendinous stiffness. Eur J Appl Physiol Occup Physiol 1996;73:332–339.

17.

Prado-Costa

Rebelo

Monteiro-Barroso

, et al. Ultrasound elastography: compression elastography and shear-wave elastography in the assessment of tendon injury. Insights Imaging 2018;9:791–814.

18.

Irving

Cook

Menz

. Factors associated with chronic plantar heel pain: a systematic review. J Sci Med Sport 2006;9:11–22.

19.

Bamber

Cosgrove

Dietrich

, et al. EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography. Part 1: Basic Principles and Technology. Ultraschall Med 2013;34:169–184.

20.

Jung

Kubale

Jungius

K-P

, et al. Digitale Ultraschalldiagnostik der Unterschenkelvenenthrombose mit Harmonic Imaging und Cross-Beam-Technik. RöFo 2006;178:55–63.

21.

Marcon

Trottmann

Rübenthaler

, et al. Shear wave elastography of the testes in a healthy study collective – differences in standard values between ARFI and VTIQ techniques. Clin Hemorheol Microcirc 2017;64:721–728.

22.

Hollerieth

Gaßmann

Wagenpfeil

, et al. Preclinical evaluation of acoustic radiation force impulse measurements in regions of heterogeneous elasticity. Ultrasonography 2016;35:345–352.

23.

Cosgrove

Piscaglia

Bamber

, et al. EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography. Part 2: Clinical Applications. Ultraschall Med 2013;34:238–253.

24.

Wang

Liu

, et al. Noninvasive in vivo study of the morphology and mechanical properties of plantar fascia based on ultrasound. IEEE Access. 2019;7:53641–53649.

25.

Shiotani

Yamashita

Mizokuchi

, et al. Site- and sex-differences in morphological and mechanical properties of the plantar fascia: a supersonic shear imaging study. J Biomech 2019;85:198–203.

26.

Gatz

Bejder

Quack

, et al. Shear wave elastography (SWE) for the evaluation of patients with plantar fasciitis. Acad Radiol 2020;27:363–370.

27.

Sconfienza

Orlandi

Cimmino

, et al. A few considerations on “sonoelastography of the plantar fascia.” Radiology 2011;261:995–996.

28.

Tsai

W-C

Ming-Fa Chiu

. Ultrasound evaluation of plantar fasciitis. Scand J Rheumatol 2000;29:255–259.

29.

McMillan

Landorf

Barrett

, et al. Diagnostic imaging for chronic plantar heel pain: a systematic review and meta-analysis. J Foot Ankle Res 2009;2:32.

30.

Gibbon

Long

. Ultrasound of the plantar aponeurosis (fascia). Skeletal Radiol 1999;28:21–26.

31.

Broholm

Pingel

Simonsen

, et al. Applicability of contrast-enhanced ultrasound in the diagnosis of plantar fasciitis. Scand J Med Sci Sports 2017;27:2048–2058.

32.

Satake

Nishio

Ikeda

, et al. Predictive value for malignancy of suspicious breast masses of BI-RADS categories 4 and 5 using ultrasound elastography and MR diffusion-weighted imaging. AJR Am J Roentgenol 2011;196:202–209.

33.

Burnside

Hall

Sommer

, et al. Differentiating benign from malignant solid breast masses with US strain imaging. Radiology 2007;245:401–410.

34.

Taljanovic

Gimber

Becker

, et al. Shear-wave elastography: basic physics and musculoskeletal applications. RadioGraphics 2017;37:855–870.

35.

C-H

Chen

W-S

Wang

T-G

. Plantar fascia softening in plantar fasciitis with normal B-mode sonography. Skeletal Radiol 2015;44:1603–1607.

36.

De Zordo

Chhem

Smekal

, et al. Real-time sonoelastography: findings in patients with symptomatic achilles tendons and comparison to healthy volunteers. Ultraschall Med 2009;31:394–400.

37.

Lee

S-Y

Park

Kwag

, et al. Ultrasound elastography in the early diagnosis of plantar fasciitis. Clin Imaging 2014;38:715–718.

38.

Yanagisawa

Niitsu

Kurihara

, et al. Evaluation of human muscle hardness after dynamic exercise with ultrasound real-time tissue elastography: A feasibility study. Clin Radiol 2011;66:815–819.

39.

Lalitha

Reddy

MCB

Reddy

. Musculoskeletal applications of elastography: a pictorial essay of our initial experience. Korean J Radiol 2011;12:365.

40.

Ríos-Díaz

Martínez-Payá

del Baño-Aledo

, et al. Sonoelastography of plantar fascia: reproducibility and pattern description in healthy subjects and symptomatic subjects. Ultrasound Med Biol 2015;41:2605–2613.

41.

Chang

Moon

Cho

, et al. Breast mass evaluation: factors influencing the quality of US elastography. Radiology 2011;259:59–64.

42.

Ball

EMA

McKeeman

HMA

Patterson

, et al. Steroid injection for inferior heel pain: a randomised controlled trial. Ann Rheum Dis 2013;72:996–1002.