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Ultrasound of the plantar foot: a guide for the assessment of plantar intrinsic muscles

Federico Zaottini
Federico Zaottini
, 
Riccardo Picasso
Riccardo Picasso
, 
Federico Pistoia
Federico Pistoia
, 
Maribel Miguel Perez
Maribel Miguel Perez
, 
Deborah Bianco
Deborah Bianco
, 
Rinaldi Simone
Rinaldi Simone
, 
Gabriele Rossi
Gabriele Rossi
, 
Marta Macciò
Marta Macciò
, 
Michelle Pansecchi
Michelle Pansecchi
, 
Luca Tovt
Luca Tovt
 y 
Carlo Martinoli
Carlo Martinoli
   | 11 sept 2023
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Article Category: Review paper
Publicado en línea: 11 sept 2023
Páginas: e151 - e160
Recibido: 01 abr 2023
Aceptado: 29 may 2023
DOI: https://doi.org/10.15557/jou.2023.0024
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© 2023 Federico Zaottini et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1.

In A and B, the schematic drawings show, respectively, the first and the third layers of the plantar intrinsic muscles (PIM). In C and D, two 18MHZ ultrasound images demonstrate two axial views at different levels of the medial group of the PIM. In C, the AbdH is seen immediately inferior to the navicular tuberosity (N). Note the medial plantar neurovascular bundle (a2 and empty arrowhead) and lateral plantar neurovascular bundles (al and white arrowhead) crossing the undersurface of the AbdH. In D, a more distal scan shows the two heads of the flexor hallucis brevis (FHB1; FHB2) underneath the FHL tendon. The FHL is a good landmark to identify the FHB, since it runs in between the two heads of the FHB and, more distally, in between the two sesamoids bones. AbdH – abductor hallucis; AbdV – abductor digiti minimi; AddHl – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; N – navicular bone; * calcaneal tuberosity; black arrowhead – flexor hallucis brevis
In A and B, the schematic drawings show, respectively, the first and the third layers of the plantar intrinsic muscles (PIM). In C and D, two 18MHZ ultrasound images demonstrate two axial views at different levels of the medial group of the PIM. In C, the AbdH is seen immediately inferior to the navicular tuberosity (N). Note the medial plantar neurovascular bundle (a2 and empty arrowhead) and lateral plantar neurovascular bundles (al and white arrowhead) crossing the undersurface of the AbdH. In D, a more distal scan shows the two heads of the flexor hallucis brevis (FHB1; FHB2) underneath the FHL tendon. The FHL is a good landmark to identify the FHB, since it runs in between the two heads of the FHB and, more distally, in between the two sesamoids bones. AbdH – abductor hallucis; AbdV – abductor digiti minimi; AddHl – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; N – navicular bone; * calcaneal tuberosity; black arrowhead – flexor hallucis brevis

Fig. 2.

The schematic drawing in A depicts the second layer of the plantar intrinsic muscle (PIM) and the crossing point of the FHL tendon and the FDL tendon (black dashed circle), also known as the master knot of Henry. It represents a valuable landmark to identify the FHL deep and lateral to the AdbH, at the level of the navicular bone undersurface. In B , an anatomic specimen of the foot is shown: note the spatial relation of the medial plantar neurovascular bundle respect to the master knot of Henry. In C, a 18 MHZ ultrasound axial view shows the knot of Henry in between the AbdH on the medial side and the QP on the lateral side. The medial plantar nerve (white arrow) can be identified on the plantar aspect of the FHL. AbdH – abductor hallucis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; L – lumbrical muscle; N – navicular bone; QP – quadratus plantae; S – sesamoid bone; TP – tibialis posterior; * flexor digitorum longus tendon slips; black arrowhead – flexor hallucis brevis
The schematic drawing in A depicts the second layer of the plantar intrinsic muscle (PIM) and the crossing point of the FHL tendon and the FDL tendon (black dashed circle), also known as the master knot of Henry. It represents a valuable landmark to identify the FHL deep and lateral to the AdbH, at the level of the navicular bone undersurface. In B , an anatomic specimen of the foot is shown: note the spatial relation of the medial plantar neurovascular bundle respect to the master knot of Henry. In C, a 18 MHZ ultrasound axial view shows the knot of Henry in between the AbdH on the medial side and the QP on the lateral side. The medial plantar nerve (white arrow) can be identified on the plantar aspect of the FHL. AbdH – abductor hallucis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; L – lumbrical muscle; N – navicular bone; QP – quadratus plantae; S – sesamoid bone; TP – tibialis posterior; * flexor digitorum longus tendon slips; black arrowhead – flexor hallucis brevis

Fig. 3.

In A and B, two 18 MHZ ultrasound axial views of the central compartment of the plantar intrinsic muscles are shown. The image A is obtained at the level of the calcaneocuboid joint. The flattened FDL tendon (white arrowheads) is seen to separate the first layer of muscle (FDB) from the second layer (QP). The image in B was acquired more proximal than A; the lateral plantar nerve (white arrow) can be seen running between the FDB and the QP. Note the hyperechoic long plantar ligament (dashed line) that separates the medial and lateral bellies of the QP (in the image, only the medial belly of QP is visible). AbdH– abductor hallucis; FDB – flexor digitorum brevis; QP – quadratus plantae
In A and B, two 18 MHZ ultrasound axial views of the central compartment of the plantar intrinsic muscles are shown. The image A is obtained at the level of the calcaneocuboid joint. The flattened FDL tendon (white arrowheads) is seen to separate the first layer of muscle (FDB) from the second layer (QP). The image in B was acquired more proximal than A; the lateral plantar nerve (white arrow) can be seen running between the FDB and the QP. Note the hyperechoic long plantar ligament (dashed line) that separates the medial and lateral bellies of the QP (in the image, only the medial belly of QP is visible). AbdH– abductor hallucis; FDB – flexor digitorum brevis; QP – quadratus plantae

Fig. 4.

The schematic drawings in A and B represent the second and third layers of the plantar intrinsic muscles. The QP muscle and the AddH2 overlap for a short tract. In order to accurately distinguish the two muscles, the peroneus longus (PL) tendon can be used as a landmark. It crosses obliquely the plantar aspect of the foot from lateral to medial, and it inserts onto the base of the first metatarsal bone. The oblique head of the AddH appears distally to the PL tendon. The 18 MHZ axial/oblique ultrasound image in C shows the long axis of the PL (white arrowheads). The muscle tissue overlying the PL is the distal portion of the QP inserting in the lateral margin of FDL tendon (white arrow). The image in D is acquired distal to the PL, and the oblique head of the adductor (AddH2) is visualized. At the same level, the FDL has already divided into four tendinous bands for the lesser toes (2, 3, 4, 5). Superficial to FDL, the intramuscular aponeurosis of the four tendon slips of the FDB are shown (II, III, IV, V). The surface of the FDB is strictly adherent to the central band of the plantar fascia (white arrowheads). AddH1 – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; L – lumbrical muscle; PB – peroneus brevis tendon; PL – peroneus longus tendon; QP – quadratus plantae; S – sesamoid bone; TP – tibialis posterior; black arrowhead – plantaris longus ligament
The schematic drawings in A and B represent the second and third layers of the plantar intrinsic muscles. The QP muscle and the AddH2 overlap for a short tract. In order to accurately distinguish the two muscles, the peroneus longus (PL) tendon can be used as a landmark. It crosses obliquely the plantar aspect of the foot from lateral to medial, and it inserts onto the base of the first metatarsal bone. The oblique head of the AddH appears distally to the PL tendon. The 18 MHZ axial/oblique ultrasound image in C shows the long axis of the PL (white arrowheads). The muscle tissue overlying the PL is the distal portion of the QP inserting in the lateral margin of FDL tendon (white arrow). The image in D is acquired distal to the PL, and the oblique head of the adductor (AddH2) is visualized. At the same level, the FDL has already divided into four tendinous bands for the lesser toes (2, 3, 4, 5). Superficial to FDL, the intramuscular aponeurosis of the four tendon slips of the FDB are shown (II, III, IV, V). The surface of the FDB is strictly adherent to the central band of the plantar fascia (white arrowheads). AddH1 – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; L – lumbrical muscle; PB – peroneus brevis tendon; PL – peroneus longus tendon; QP – quadratus plantae; S – sesamoid bone; TP – tibialis posterior; black arrowhead – plantaris longus ligament

Fig. 5.

The schematic drawing in A depicts the axial section of the forefoot at the level of the distal metatarsal diaphysis (I, II, III, IV, V). The fourth layer of the plantar intrinsic muscles is represented. It includes four bipennate dorsal interossei (black arrowhead) and three unipennate ventral interossei (white asterisk). The axial 18 MHZ ultrasound image in B shows, from the superficial to deep layers: the FDB tendons (white circular line), the FDL tendons (dashed circular line) with the lumbrical muscles (white arrow), the transverse head (dashed withe line, Addh1) and distal portion of the oblique head (AddH2) of the adductorpollicis, the ventral interossei (white asterisk) and the metatarsal bones (I, II, III, IV). AbdH – abductor hallucis brevis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHB – flexor hallucis brevis; FHL – flexor hallucis longus; black arrow – lumbrical muscle
The schematic drawing in A depicts the axial section of the forefoot at the level of the distal metatarsal diaphysis (I, II, III, IV, V). The fourth layer of the plantar intrinsic muscles is represented. It includes four bipennate dorsal interossei (black arrowhead) and three unipennate ventral interossei (white asterisk). The axial 18 MHZ ultrasound image in B shows, from the superficial to deep layers: the FDB tendons (white circular line), the FDL tendons (dashed circular line) with the lumbrical muscles (white arrow), the transverse head (dashed withe line, Addh1) and distal portion of the oblique head (AddH2) of the adductorpollicis, the ventral interossei (white asterisk) and the metatarsal bones (I, II, III, IV). AbdH – abductor hallucis brevis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHB – flexor hallucis brevis; FHL – flexor hallucis longus; black arrow – lumbrical muscle

Fig. 6.

The image in A shows an anatomic specimen of the plantar fascia. In particular, the origins and the proximal tracts of the central and lateral bands of the plantar fascia can be seen. The two bands represent landmarks to identify with ultrasound the FDB (central band) and the AbdV (lateral band). The 18MHZ axial ultrasound image inBshows the thin hyperechoic structure overlying the AbdV (white arrowheads) corresponding to the lateral band of plantar fascia, and the FDB (empty arrowhead) corresponding to the central band of the fascia. Underneath the AbdV, the peroneus longus tendon (PL) is seen curving in the cuboid groove
The image in A shows an anatomic specimen of the plantar fascia. In particular, the origins and the proximal tracts of the central and lateral bands of the plantar fascia can be seen. The two bands represent landmarks to identify with ultrasound the FDB (central band) and the AbdV (lateral band). The 18MHZ axial ultrasound image inBshows the thin hyperechoic structure overlying the AbdV (white arrowheads) corresponding to the lateral band of plantar fascia, and the FDB (empty arrowhead) corresponding to the central band of the fascia. Underneath the AbdV, the peroneus longus tendon (PL) is seen curving in the cuboid groove

Fig. 7.

The schematic drawings in A and B depict the first and third layers of the plantar intrinsic muscles (PIM). The 18 MHZ ultrasound image C is acquired just distal to the calcaneal tuberosity and shows a panoramic axial view of the PIM at this level. The AbdV is the most superficial muscle of the lateral group and is located on the lateral side of the FDB and the QP. In D, the US axial view at the proximal third of the fifth metatarsal diaphysis (white asterisk) shows the flexor digiti minimi brevis (FDVB) belly located medial and deeper respect to the AbdV. Along the medial surface of the FDV, the lateral branch of the lateral plantar nerve can be spotted (white arrow). AbdH – abductor hallucis; AbdV – abductor digiti minimi; AddH1 – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; PB – peroneus brevis tendon; PL – peroneus longus tendon; * fifth metatarsal head; black arrowhead – flexor digiti minimi brevis
The schematic drawings in A and B depict the first and third layers of the plantar intrinsic muscles (PIM). The 18 MHZ ultrasound image C is acquired just distal to the calcaneal tuberosity and shows a panoramic axial view of the PIM at this level. The AbdV is the most superficial muscle of the lateral group and is located on the lateral side of the FDB and the QP. In D, the US axial view at the proximal third of the fifth metatarsal diaphysis (white asterisk) shows the flexor digiti minimi brevis (FDVB) belly located medial and deeper respect to the AbdV. Along the medial surface of the FDV, the lateral branch of the lateral plantar nerve can be spotted (white arrow). AbdH – abductor hallucis; AbdV – abductor digiti minimi; AddH1 – transverse head of the adductor hallucis; AddH2 – oblique head of the adductor hallucis; FDB – flexor digitorum brevis; FDL – flexor digitorum longus; FHL – flexor hallucis longus; PB – peroneus brevis tendon; PL – peroneus longus tendon; * fifth metatarsal head; black arrowhead – flexor digiti minimi brevis

Fig. 8.

The schematic drawing in A illustrates the anatomy of the inferior plantar calcaneal nerve (black arrow) running anterior to the calcaneal tuberosity, deep to the central band of the plantar fascia and the FDB. The 18 MHZ ultrasound images B and C show a case of Baxter’s neuropathy. In B, a longitudinal view of the plantar fascia demonstrates an insertional thickening (white arrowheads) of the central band at the level of the medial tubercle of the calcaneal tuberosity. Some fibrotic changes in the underlying FDB muscle (empty arrow) can be seen. An enlarged hypoechoic inferior calcaneal nerve (white arrow) is spotted between the FDB and the calcaneal tuberosity (calc). The compressive neuropathy attributable to the plantar fasciitis has caused atrophy of the AbdV, which appears smaller and more hyperechogenic than the AbdH, FDB and QP. AbdH – abductor hallucis; AbdV – abductor digiti minimi; FDB – flexor digitorum brevis; QP– quadratus plantae; * calcaneal tuberosity; black arrowheads – short axis view of the thickened central band of the plantar fascia
The schematic drawing in A illustrates the anatomy of the inferior plantar calcaneal nerve (black arrow) running anterior to the calcaneal tuberosity, deep to the central band of the plantar fascia and the FDB. The 18 MHZ ultrasound images B and C show a case of Baxter’s neuropathy. In B, a longitudinal view of the plantar fascia demonstrates an insertional thickening (white arrowheads) of the central band at the level of the medial tubercle of the calcaneal tuberosity. Some fibrotic changes in the underlying FDB muscle (empty arrow) can be seen. An enlarged hypoechoic inferior calcaneal nerve (white arrow) is spotted between the FDB and the calcaneal tuberosity (calc). The compressive neuropathy attributable to the plantar fasciitis has caused atrophy of the AbdV, which appears smaller and more hyperechogenic than the AbdH, FDB and QP. AbdH – abductor hallucis; AbdV – abductor digiti minimi; FDB – flexor digitorum brevis; QP– quadratus plantae; * calcaneal tuberosity; black arrowheads – short axis view of the thickened central band of the plantar fascia

Fig. 9.

The 18 MHZ ultrasound image A demonstrates an intermuscular inhomogeneous solid mass (white asterisk) between the FDB and the QP. The matched T2-weighted axial magnetic resonance image confirms the presence of a solid expansive mass between the FDB and the QP. The lateral plantar veins (white circular line in A , white arrowhead in B is enlarged, probably as a consequence of the mass effect. Note the diffuse muscle atrophy, with the muscles of the three compartments reduced of volume and hyperechogenic in A: the patient reported not being able to walk properly for months because of the painful mass. Surgery was proposed. At the histology, the mass came out as a benign nerve sheath tumor. AbdH – abductor hallucis; AbdV – abductor digiti minimi; FDB – flexor digitorum brevis; QP – quadratus plantae; black asterisk – solid expansive mass
The 18 MHZ ultrasound image A demonstrates an intermuscular inhomogeneous solid mass (white asterisk) between the FDB and the QP. The matched T2-weighted axial magnetic resonance image confirms the presence of a solid expansive mass between the FDB and the QP. The lateral plantar veins (white circular line in A , white arrowhead in B is enlarged, probably as a consequence of the mass effect. Note the diffuse muscle atrophy, with the muscles of the three compartments reduced of volume and hyperechogenic in A: the patient reported not being able to walk properly for months because of the painful mass. Surgery was proposed. At the histology, the mass came out as a benign nerve sheath tumor. AbdH – abductor hallucis; AbdV – abductor digiti minimi; FDB – flexor digitorum brevis; QP – quadratus plantae; black asterisk – solid expansive mass

Fig. 10.

The picture in A shows advanced flatfoot deformity with hindfoot valgus. The 18 MHZ ultrasound axial image in B depicts severe muscle atrophy of the AbdH (curved white line), while the FDB (curved dashed line) and the QP (white arrowhead) show a lower grade of fat infiltration. These findings are consistent with the pattern of muscle alterations reported in the literature for the flatfoot deformity. The strict functional relation existing between the plantar intrinsic muscle function and plantar fascia pathologies is confirmed in the image C. The image in C displays a 18 MHZ ultrasound long axis view of the central band of the plantar fascia: the fascia is abnormally thickened (white arrows) distal to the origin from the medial tubercle, likely as a result of mechanical overuse. AbdH – abductor hallucis; FDB – flexor digitorum brevis; QP – quadratus plantae; calc – calcaneus
The picture in A shows advanced flatfoot deformity with hindfoot valgus. The 18 MHZ ultrasound axial image in B depicts severe muscle atrophy of the AbdH (curved white line), while the FDB (curved dashed line) and the QP (white arrowhead) show a lower grade of fat infiltration. These findings are consistent with the pattern of muscle alterations reported in the literature for the flatfoot deformity. The strict functional relation existing between the plantar intrinsic muscle function and plantar fascia pathologies is confirmed in the image C. The image in C displays a 18 MHZ ultrasound long axis view of the central band of the plantar fascia: the fascia is abnormally thickened (white arrows) distal to the origin from the medial tubercle, likely as a result of mechanical overuse. AbdH – abductor hallucis; FDB – flexor digitorum brevis; QP – quadratus plantae; calc – calcaneus
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