Technical report: dynamic assessment of plantar fasciitis and plantar fascia tears utilising dorsiflexion of the great toe

Abstract

Discrimination between plantar fasciitis and partial tears of the plantar fascia can be difficult on ultrasound given laxity of the plantar fascia in the region of its calcaneal insertion and anisotropy. Dynamic assessment with great toe dorsiflexion can improve visualisation of the proximal portion of the plantar fascia on ultrasound, by straightening the plantar fascia due to the windlass mechanism. This article describes the technique and its anatomical basis.

Background

Both plantar fasciitis and plantar fascia tears commonly occur in the proximal aspect of the central band of the plantar fascia close to the calcaneal insertion [1–4]. Discrimination between plantar fasciitis and partial tears of the plantar fascia can be difficult on ultrasound given the laxity of the plantar fascia in the region of its calcaneal insertion and the presence of anisotropy. Direct visualisation of disruption of the plantar fascia fibres is important in the sonographic evaluation for plantar fascia tears as indirect signs such as plantar fascia oedema can occur in plantar fasciitis with or without associated tears [2–4]. Dynamic assessment with dorsiflexion of the great toe can improve visualisation of the proximal portion of the plantar fascia. This imaging technique is reported with a review of the anatomical basis of its use.

Dynamic ultrasound technique

The patient may be imaged in the supine or prone position depending on patient and ultrasound operator preferences. Where the prone position is used, the patient’s feet should be hanging over the end of the examination couch.

With the ankle in neutral, a high-frequency linear US probe is placed onto the heel, aligned along a slightly oblique sagittal plane with the ends of the probe pointing towards the heel proximally and the great toe distally. The probe is moved along this plane until the proximal aspect of the central band of the plantar fascia including its calcaneal insertion is visualised longitudinally (Fig. 1).

Fig. 1.

Longitudinal image of the proximal aspect of the central band of the plantar fascia including its calcaneal insertion. The thickness of the normal plantar fascia should be under 4 mm

With the US probe held longitudinal to the plantar fascia and toes in neutral position, the central band of the plantar fascia is evaluated for thickening (> 4 mm thickness) and hypoechogenicity that signify plantar fasciitis [2–7]. In this same position, gentle passive dorsiflexion of the great toe is then performed to straighten the proximal aspect of the plantar fascia and help the visualisation of tears. The entire width of the central band of the plantar fascia in this manner is evaluated by sweeping the probe medially and laterally. Figure 2 demonstrates the improved visualisation of a tear when using dynamic assessment, with MRI correlation in Fig. 3.

Fig. 2.

a A mildly hypoechoic region is noted in the plantar fascia, with the great toe in neutral. This is nonspecific for a tear, and could also represent fasciitis fascia, or anisotropy. Note the concavity in the contour of the plantar fascia. b Dorsiflexion of the great results in straightening of plantar fascia in the same patient. A tear is readily identified in the plantar fascia as a discrete hypoechoic cleft interrupting the continuity of the plantar fascia

Fig. 3.

Focal tear in the plantar fascia just distal to the calcaneal insertion is demonstrated as a high signal cleft on sagittal PDFS images (arrow), in the same patient as Fig. 2. Thickening and increased signal in the plantar fascia on T1 (a) and PDFS images (b) in proximity of the tear demonstrates co-existent plantar fasciitis

The plantar fascia can then be followed distally up to the insertions on the metatarsophalangeal joints in short axis and longitudinally to exclude plantar fibromas [2–4]. Finally, evaluation of the tarsal tunnel is performed to exclude tibial nerve compression, or neuromas that can mimic symptoms of plantar fascia pathology [8, 9].

Discussion

The plantar fascia comprises three distinct bands (medial, central, and lateral) that extend from plantar aspect of the calcaneum into the forefoot. Amongst these, the central band is the thickest component. Distally, the central band of the plantar fascia divides unequally into five separate components that insert into the 1st–5th MTPJs, including onto the plantar plate and sesamoids [10, 11]. Further fibres from the plantar fascia blend into the fascia of the intrinsic muscles of the feet, as well as attach onto the skin of the sole of the foot [10, 11].

Tears of the plantar fascia, also known as plantar fascia rupture, may present as acute or chronic heel pain [12] and can mimic plantar fasciitis when chronic. Previous steroid injections for plantar fasciitis are a reported risk factor [12–14].

The rationale for dorsiflexion of the great toe is the ‘windlass’ mechanism which was first described by Hicks [15]. During the propulsive phase of gait, dorsiflexion of the toes, including the great toe, draws the plantar fascia over the MTP joints and results in tightening and straightening of the plantar fascia [15, 16]. Conversely, with the great toe in neutral, the plantar fascia is lax proximally and concave relative to the skin surface, resulting in anisotropy and non-uniform echogenicity in the fascia when scanned in the longitudinal plane (Fig. 4).

Fig. 4.

Schematic diagram demonstrating straightening of the plantar fascia during dorsiflexion of the big toe (upper image). With the big toe in neutral position (lower image), the contour of the plantar fascia is concave relative to the probe just distal to the calcaneal origin with resulting hypoechogenicity

Dorsiflexion of the toes has been utilised in studies assessing plantar fascia thickness measurements on US [17]. Some authors in previous articles on US evaluation of hindfoot pain have opined that that dorsiflexion of the great toe or toes can increase conspicuity of tears of the plantar fascia and/or help discrimination from fasciitis on ultrasound [3, 4]. However, as far as the authors are aware, there has been no previous published literature detailing the technique of dynamic ultrasound evaluation or previous case examples where dorsiflexion of the great toe has aided the assessment of the plantar fascia for tears on US.

The thickness of the plantar fascia has been shown to be similar in supine or prone position [18]. Plantar fascia thickness is measured with the toes in neutral prior to great toe dorsiflexion as this dorsiflexion results in thinning of the plantar fascia [19].

Demonstration of plantar fascia tears on ultrasound is important, because treatment differs from plantar fasciitis. For example, shockwave therapy is contraindicated, as the safety of this procedure has not been evaluated in the presence of plantar fascia tears [20, 21].

Conclusion

Dynamic evaluation of the plantar fascia utilises dorsiflexion of the great toe to aid in visualisation of plantar fascia tears on ultrasound. The rationale for this is the straightening of the plantar fascia during great toe dorsiflexion due to the windlass mechanism.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.