Introduction

Plantar fascia (PF) is the fibrous layer of connective tissue across the plantar surface of foot that has been an important role in ankle and foot biomechanics [1]. It consists of 3 main bands which are lateral, central and medial. The lateral band extends beneath the plantar surface of the abductor digiti quinti muscle and passes laterally with the posterior fascia and distally with the 5th metatarsophalangeal joint capsule. The central band is thickest and strongest one of the fascia, arising from the medial calcaneal tubercle and extending anteriorly to cover the plantar surface of the flexor digitorum brevis muscle. The medial band is the thinnest section, situated under the plantar surface of the abductor hallucis muscle, passing distally to the 1st metatarsophalangeal joint capsule and proximally to the flexor retinaculum of the foot [2, 3]. PF provides a static and dynamic support of the longitudinal arch foot, being as a dynamic shock absorber [4, 5].

Plantar fasciitis is commonly used to describe a plantar heel pain with inflammation of the PF at its origin, not to pain arising along the course of the fascia. In contrary, a substantial evidence of plantar fasciosis is associated with degenerative changes without inflammation [6]. Ledderhose disease, also known plantar fibromatosis, is a benign condition characterized by proliferation of fibrous tissue in form of nodules or cords in the PF, occasionally located on the medial and central bands of the fascia [7].

Nevertheless, there is a controversy regarding the appropriate term of plantar fasciitis, whether the disease should be referred to as “plantar fasciitis”, “plantar fasciosis” or “plantar heel pain”. Although the nature of plantar fasciitis can be either inflammatory or degenerative, imaging and histological findings confirm the hypothesis that “plantar fasciitis” is actually a degenerative disorder rather than inflammatory [4, 8]. Several studies; therefore, have used “plantar heel pain” as a general term [9,10,11,12]. In contrast, the recent trials and reviews [13] have regained to the most common clinical phrase of “plantar fasciitis”. Thus, we will use the term “plantar fasciitis (PFS)” in this review.

PFS is the most common cause of plantar heel pain in adults with the prevalence estimated 10% of the general population [14, 15]. Despite the pathogenesis of PFS is still ambiguous, the intrinsic muscle weakness, prolong standing, longtime walking and running, decreased elasticity of the plantar fascia, increased body mass index, reduced strength of gastrosoleus muscles, reduced dorsiflexion of ankle, leg length discrepancy and longitudinal arch deformity such as pes planus may increase the risk of PFS [16,17,18].

PFS is characterized by intense pain over the medial plantar aspect of the heel, sharpened with first step in the morning or after rest and increased during weightbearing activity [19,20,21,22,23,24].

The Cochrane review showed that an efficacy for any type of PFS treatments is not studied well [25]. Furthermore, treatment modalities and options for PFS remain inconsistent as well as the recommended methods of intervention are very limited [11, 13, 18, 26, 27]. There is a little evidence for using conservative treatment such as custom orthoses or prefabricated for long-term improvements in heel pain or disability [13, 28, 29] in spite of a recent trial revealed that short-term improvements in heel pain using full-length silicone insoles is considered as an initial line for PFS treatment [30]. In the light of that, a recent systematic review concluded that manual physiotherapy such as PF stretching and joint mobilization could reduce pain and stiffness, improve function and impairments. However, the optimum dosage of manual physiotherapy is still controversial [31]. In the same context, stretching of intrinsic foot muscle has been shown to be effective for improving heel pain and disability of PFS [32, 33].

As ultrasound is available, low-cost and comfortable for patients, it is superior to MRI in imaging the PF and diagnosis the PFS in many studies and as a guide therapeutic tool in patients with PFS [14]. This study was conducted to systematically review the previous studies using ultrasound as assessment tool in patient with PFS underwent different interventions.

Methodology

A searching was included the original articles published over the last 5 years from 2017 to 2022. The following electronic databases were depended: Science Direct, Scopus, Web of Science, Springer and PubMed. This systematic review was conducted according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [34].

Search strategy

The following keywords: “ultrasound”, “sonography”, “ultrasonography”, “plantar fasciitis”, “imaging of plantar fascia”, “physiotherapy of plantar fasciitis”, “interventional treatment of plantar fasciitis”, “randomized controlled trial of plantar fasciitis” and “interventional ultrasound” were used in the searching.

Inclusion criteria

The papers that have met the following criteria: (1) patients aged over 18 years. (2) patients with PFS, controlled (positive control) or healthy (negative control) groups for comparison. (3) randomized control trial or case–control design. (4) treatment of PFS with ultrasound assessment. (5) ultrasound was used in evaluation PF and surrounding tissues in patients with PFS. (6) the papers were written in English language. (7) original researches.

Data extraction

The articles were first checked based on titles and abstracts. If the title and abstracts were unclear, the full-length article was screened. The articles were chosen according to Critical Appraisal Skills Program (CASP, CASP UK, Oxford, UK) checklist. CASP results were summarized in Table 1. Two reviewers separately extracted the data from the final selected articles. If there was no agreement, the final decision was sought from the third reviewer.

Table 1 Critical appraisal skills programme results
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Data collection process

During the search process, 4569 articles were found using proper keywords in which 1661 articles were found over the last five years. Of these, 666 articles were identified after removing the review and duplicated articles. Thirty- three of the 666 articles were relevant of this review. Two articles out of 33 articles are required subscribing to be able to download. One article was written in Chinese language except the abstract was written in English-language. Thus, thirty articles were analyzed and included in this search. Twenty-six of the 30 articles have assessed the effect of different treatments on PF in patients with PFS using both clinical examination and ultrasound imaging. Eight of 26 articles used ultrasound as both an assessment tool of PF and guide therapeutic in patients with PFS. Eighteen of the 26 articles used ultrasound as only assessment technique in diagnosis of PFS. The remaining 4 articles have compared PF thickness as well as intrafascial changes using different ultrasound modes between PFS patients and healthy subjects (Fig. 1). Twenty-nine of 30 articles have evaluated the PF thickness and its changes whereas only one article has only assessed the hypoechoic area within PF using B-mode ultrasound. In addition to measuring the thickness of the PF, there were 4 of the 30 articles have assessed the stiffness of PF using sonoelastography. In 3 of the 30 articles, the vascularity of PF was monitored using color Doppler ultrasound. In 7 articles, the echogenicity of PF was separately assessed on real-time B-mode. In one of the 30 articles, the fat pad thickness combined with PF thickness were measured.

Fig. 1
figure 1

Flow diagram of the study. PF plantar fascia, PFS plantar fascitiis, US ultrasound

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Results

Six hundred sixty-six articles were found by the search process. Of these, thirty original articles [35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64] were closely related and included in this review. The articles have assessed the PF in patients with PFS under different conditions using different ultrasound modes from 2017 to 2022 (Table 2).

Table 2 Overview of studies conducted on the evaluation of PF under different conditions using US
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Twenty-six of the 30 articles [35, 36, 38, 41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58, 60,61,62,63,64] assessed the efficacy of different treatments on PF in patients with PFS using ultrasound (Table 3). As shown in Table 3, in 8 of the 26 articles, ultrasound was used as both an evaluating modality for assessment the PF thickness along with its alterations and a guided-treatment tool in patients with PFS who underwent the different interventions. In 5 of the 8 articles, the PF thickness was assessed alone using B-mode ultrasound. In 2 of the 8 articles, the combining PF thickness and echogenicity were monitored and recorded. In one article, the B-mode and color Doppler ultrasound evaluated the PF thickness, echogenicity and vascularity.

Table 3 Details of studies using US evaluating the PF in patients with PFS underwent different interventions
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In other 18 articles, ultrasound was used as only the assessment tool for imaging PF changes in patients with PFS before and after treatment. In 12 of the 18 articles have evaluated the PF thickness alone using B-mode ultrasound. In 4 more articles, the PF thickness along with its observation changes such as echogenicity, stiffness, vascularity or morphology were evaluated using B-mode, color Doppler or SWE. In another article, the heel fat pad thickness combined with PF thickness have been measured and recorded. The remaining one article has only investigated the hypoechoic area changes within and around PF and the size of area was recorded at pre and post intervention.

Four of the 30 articles [37, 39, 40, 59] were carried out to evaluate sonographically the PF thickness as well as fascial alterations between patients with PFS and healthy subjects that have no underwent therapeutic interventions (Table 4). One of the 4 articles has measured the PF thickness without evaluation of the fascial changes. In two more articles, combining the PF thickness and fascial stiffness were assessed using B-mode and SWE, respectively. The remaining one article was carried out to evaluate the PF thickness, stiffness and hyperemia using B-mode, SWE and color Doppler ultrasound, respectively.

Table 4 Details of studies conducted on the evaluation of PF changes between patients with PFS and healthy subjects using US
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Nine of the 30 articles [35, 37, 39, 40, 46, 48, 50, 59, 63] have included matched control groups. As outlined in Table 5, 7 of the 9 articles have included healthy subjects with no intervention (negative control). 4 of the 7 articles were carried out as case–control studies design having only two groups; PFS group with no intervention and healthy subjects. Other three were experimental studies as follows: one study included three groups; two of them with PFS received either treatment group or sham-treatment group (positive controls) and one group was healthy. Two studies had two groups in which one group with PFS was subjected to treatment whereas other had no PFS and had no exposure to treatment. The remaining two of the 9 studies were designed as experimental studies having two groups with PFS; one group underwent the treatment “study group” and other was subjected to sham-treatment.

Table 5 Matching control studies in evaluating the PF changes under different conditions using ultrasound
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Discussion

This study was carried out to systematically review published articles that assessed the PF in patients with PFS using ultrasound under different conditions from 2017 to 2022 (Table 2). Thirty studies conducted to evaluate the PF alterations and its thickness in patients with PFS underwent different intervention or compared to those with healthy subjects using different ultrasound modes such as B-mode, color Doppler or SWE. In these studies, ultrasound was used as assessment modality alone or combined with guide therapeutic for evaluation for evaluation the PFS. Based on the results of this systematic review, using ultrasound as assessment tool was available, low cost, safe and reliable in evaluating of PF changes.

In this review, all studies found that the PF thickness and/or fascial alterations was reliable in diagnosis of the PFS. In meanwhile, several differences of methods were observed among the previous studies during this review. The major differences were noted in sample size, study design, type of intervention, measurement tool and methods, sonographic features of PF (thickness, echogenicity, vascularity or stiffness) and follow-up period. In this review, majority of the reviewed articles showed that a monitoring of PF thickness and intrafascial changes are considered as a key role in the assessment of PFS using ultrasound particularly during follow-up treatment.

Assessment of PF thickness and fascial alterations after different interventions

As presented in Table 3, there 26 studies have sonographically assessed the different interventions such as injection, ESWT, manual physiotherapy, high-intensity laser therapy (HILT), low-level laser therapy (LLLT), Electroacupuncture (EA), Kinesiotaping (KT), Intense Therapeutic Ultrasound (ITU) and Monophasic Pulsed Current (MPC) in patients with PFS.

In 8 out of the 26 studies [36, 38, 42, 44, 57, 58, 62, 64], the ultrasound was used as assessment tool combined with guided treatment injection in PFS patients. These studies that were designed as randomized controlled trials showed that the use of ultrasound to guide injection and evaluate the PF changes was an effective modality. The trials assessed the efficacy of ultrasound-guided injection of different treatments in patients with PFS. All outcome measures were assessed at baseline and after treatments. The primary outcomes measured were as follows: pain by visual analog scale (VAS), daily life and exercise activities by Foot and Ankle Ability Measure (FAAM), and foot function by foot function index (FFI). The secondary outcomes measured by ultrasound were PF thickness alone or combined with PF echogenicity or vascularity or both. For example, five studies [36, 42, 44, 57, 58] assessed the PF thickness alone using B-mode ultrasound at baseline and at follow-ups interventions. Other two studies [38, 62] assessed both PF thickness and fascial echogenicity in order to evaluate the effects of treatments in patients with PFS. One study [64] investigated combining PF thickness, echogenicity and vascularity using B-mode and color Doppler ultrasound in patients with PFS at pre and post intervention. All these studies concluded that ultrasound was an effective, safe, tolerable and accurate to use as a guide-therapeutic and assessment tool in evaluation of patients with PFS.

The remaining 18 articles used the ultrasound with different modes as only assessment tool to evaluate the improvements of PF thickness alone or combined with intrafascial or perifascial changes in patients with PFS undergoing different interventions. In which four articles [35, 41, 43, 53] assessed the combining PF thickness and its fascial changes using different ultrasound modes. For example, a longitudinal follow-up study [43] evaluated the PF thickness and stiffness pre and post extracorporeal shockwave therapy (ESWT) in 22 patients with PFS. The PF thickness and stiffness were evaluated by B-mode and strain elastography, respectively. The PF changes was evaluated at baseline and at 1-week, 1-month, 3-month, 6-month, and 12-month e after ESWT. The study concluded that PF stiffness reduced at the first week and then increased at the 12-months after treatment. However, the PF thickness decreased gradually during 12-months follow-up intervention.

In single-center, non-randomized prospective study [53], forty patients with PFS received either platelet-rich plasma (PRP) injection (20 patients) or corticosteroid injection (CSI) (20 patients). The imaging assessment of the outcome measures were performed by ultrasound and magnetic resonance imaging (MRI). However, the ultrasound assessed the following outcome measures at baseline, 3 and 6 months; PF thickness and echogenicity by B-mode and neovascularization by color Doppler. The authors concluded that PF thickness has significantly reduced at 3-months after injection in both groups. The echogenicity and vascularity, however; have significantly reduced at 3- and 6-months after PRP injection only.

A double-blinded, randomized clinical trial [41] included 39 patients with PFS divided into two groups: 39 patients received polydeoxyribonucleotide (PDRN) versus 39 patients CSI. The outcomes measured by ultrasound included PF thickness and fascial echogenicity. The sonographic outcomes were evaluated at baseline and 6 months after injection. The studies concluded that PF echogenicity was significantly different within CSI group during follow-up injection whereas PF thickness did not differ intragroups. However, there were no significant different of PF thickness and echogenicity between both groups.

A prospective double-blinded randomized controlled [35] investigated the PF thickness and morphology of 22 patients divided into two groups: ESWT group and sham-ESWT group. The PF thickness and morphology of PF included (echogenicity, convexity and perifascial fluid) were assessed at baseline, 1, 4, 8 weeks after treatment. The trial revealed no changes in PF thickness pre and post intervention in both groups. However, the authors showed that alterations in the PF morphology such as decreased hypoechogenicity, increased convexity and presence perifascial fluid are considered as sonographic features of PFS.

A single-center, single-blinded, randomized clinical trial [51] conducted on 78 patients with PFS divided into two groups; 36 patients were subjected to Kinesiotaping (KT) and 42 patients were exposure to ESWT. The outcomes measured by ultrasound were PF thickness and heel fat pad thickness. The findings were monitored at baseline and 6-weeks after treatments. In both groups, the study concluded that PF thickness decreased after treatment whereas heel fat pad thickness increased.

A another single-blinded, pivotal clinical trial study [52] conducted on 33 patients with chronic PFS. The patients were exposure to intense therapeutic ultrasound (ITU) combined with standard conservative treatment at 0 (baseline), 4, 8, 12 and 26 weeks after treatments. The hypoechoic areas were only outcome measured by ultrasound. Perifascial and intrafascial hypoechoic areas/lesions were diagnosed in all patients and the size of area/lesion was measured at each follow-up visit. The study findings revealed that hypoechoic areas decreased gradually during follow-up period.

In the remaining 12 studies [45,46,47,48,49,50, 54,55,56, 60, 61, 63], different interventions were applied on different trials and different follow-up periods. In all these trials, the outcome measured by ultrasound was only PF thickness. The changes in PF thickness were different among the studies. For example, Naruseviciute and Kubilius [45], showed that the difference of PF thickness between groups after intervention was not significant. Mansiz-Kaplan et al. [46] concluded that there were improvements in PF thickness in intra – and intergroups after treatments. Xu et al. [49] found a significant improvement of PF thickness at 3- months in one group and 3- and 6- months in other group compared to the baseline values. Furthermore, a significant reduction in PF thickness was found between groups at 6-months follow-up. The remaining 8 articles stated that PF thickness was significantly improved between groups after treatments in PFS patients.

Evaluating of PF thickness and its alterations between PFS patients and healthy controls with no intervention

As shown in Table 4, Four studies [37, 39, 40, 59] compared the PF changes including thickness, stiffness and neovascularization between patients with and without PFS. Baur et al. [39] evaluated 108 unilateral PF including 87 with PFS and 21 healthy. The PF thickness, stiffness and vascularity were assessed in all subjects using B-mode, SWE and color Doppler, respectively. The study showed that shear wave velocity (SWV) and stiffness were significantly higher in healthy subjects than in patients. SWV and stiffness had sensitivity 79.31% and 80.46%, respectively; whereas had specificity 80.95% for both. The PF thickness was observed to be thicker in PFS patients than in healthy controls. There was no correlation between color Doppler and PF thickness with SWE measurements. Therefore, the study concluded that SWE represents an independent parameter in detecting PFS.

Two studies conducted by Schillizzi et al. [37] and Gatz et al. [40] compared the PF thickness and stiffness features between patients with PFS and healthy subjects and correlated the SWE values with clinical scores. The studies showed that SWE can be quantitatively assessed the stiffness of PF and can diagnose PFS changes. SWE was strongly correlated with clinical scores. The SWE measured the PF stiffness and SWV and B-mode measured the PF thickness can improve the diagnostic accuracy of ultrasound in diagnosis the PFS.

Granado et al. [59] investigated and compared the effectiveness of metatarsal phalangeal (MTP) joints extension on PF thickness in 40 subjects divided into two groups (20 unilateral PFS and 20 healthy subjects). The PF thickness was evaluated at rest, 30 degrees of extension from the plantar aspect, and maximal extension as much as possible. The study found that PF thickness reduced significantly with MTP joints extension in both PFS and healthy groups. Therefore, the study concluded that PF thickness could be influenced by MTP joints extension. Thus, the researchers recommended that PF thickness should be measured with toes at rest.

Comparing the PF changes between study group and matching control

As outlined in Table 5, 9 studies with different designs [35, 37, 39, 40, 46, 48, 50, 59, 63] evaluated PF changes in patients with PFS and control groups with or without interventions. Two randomized controlled trials [35, 46] conducted to evaluate the PF changes in patients with PFS underwent different interventions for different intervals. The PFS patients were divided into two groups: treatment group and placebo group. Caner et al. [35] observed no changes in PF thickness pre and post intervention in treatment group and placebo group. However, Mansiz-Kaplan et al. [46] stated that PF was significantly thicker in treatment group than in placebo group. Four case–control studies [37, 39, 40, 59] evaluated the PF thickness and its observation changes in patients with PFS and healthy subjects with no interventions using different ultrasound modes. Three more experimental studies [48, 50, 63] investigated PF thickness alone using ultrasound in patients with PFS received a treatment and healthy volunteers. In the latter three studies, PF thickness increased in patients with PFS as well as responded to the treatment as compared to healthy subjects.

Conclusion

This study was designed to systematically review published articles from 2017 to 2022 regarding the application of the ultrasound in evaluating the PF changes in patients with PFS. When the published articles have been reviewed, many differences were noted in methodology, sample size, study design, intervention and duration of follow-up. The findings revealed that ultrasound is reliable, accurate, safe, and non-invasive imaging tool in the assessment of PF changes, therapeutic guiding and observing different treatments in patients with PFS. The most suitable site to evaluate the PFS is at the point where PF is inserted into medial calcaneal tubercle and 1 cm distal to its insertion. The longitudinal scan is considered as the best scan for imaging the PF in which the probe is placed on the line between medial tuberosity of the calcaneus and the second finger over the PF. The thickness, echogenicity, vascularization and stiffness of the PF are the most sonographic outcome measures used in the evaluation of the PFS using B-mode, color doppler and SWE (Figs. 2, 3, 4, 5 and 6).

Fig. 2
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A longitudinal sonographic scan of a patient with PFS, showing the measurement of the PF thickness (arrowhead) at calcaneal insertion (orange line) and 1 cm distal to the insertion (white line). CB calcaneus bone, F fat pad, FDB flexor digitorum brevis muscle, PF plantar fascia (adopted from Ref. [36])

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Fig. 3
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Color Doppler ultrasound images of the PF, showing no neovascularization in PF (adopted from Ref. [65])

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Fig. 4
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Power Doppler ultrasound of PF showing one single vessel (adopted from Ref. [64])

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Fig. 5
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A longitudinal SWE and B-mode ultrasound images of normal PF shows stiffness of 98.8 kPa and SWV value of 5.7 m/s (adopted from Ref. [39])

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Fig. 6
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A longitudinal ultrasound images of PF. Normal appearance of asymptomatic plantar fascia (left) and chronic PFS with hypoechoic lesion (right) (adopted from Ref. [52])

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