Foot Ultrasound Introduction
Ultrasound (US) has emerged as a valuable imaging modality for addressing many foot disorders and allows a more precise approach to intra-articular and soft tissue injections. US-guided injection techniques involving the plantar fascia, medial and inferior calcaneal nerves, the intersection of flexor hallucis longus (FHL) and flexor digitorum longus (FDL), midfoot joints, metatarsophalangeal (MTP) joints, sesamoids, plantar plate, and Morton’s neuromas are reviewed in this chapter. This chapter does not contain an exhaustive list of all foot injections, but rather, serves as an outline for the different approaches to common foot injections.
Plantar Fascia
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Disorders of the central cord of the plantar fascia are the most common cause of heel pain in the adult population. Enthesopathy of the lateral cord of the plantar fascia is an often overlooked cause of lateral foot pain and can coexist with plantar fasciopathy.
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Corticosteroid injections are controversial in the setting of degenerative plantar fasciopathy, particularly when used repetitively. However, they are occasionally utilized for pain control during the rehabilitative process and while addressing underlying biomechanical factors.
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There is no strong evidence for a preference of placing a corticosteroid injection deep, superficial, or directly within the central cord of the plantar fascia. In theory, a corticosteroid injection superficial to the central cord may cause fat pad atrophy. Alternatively, an injection within the central cord may propagate undersurface partial-thickness tears, which are common with plantar fasciopathy.
Pertinent Anatomy ( Fig. 23.1 )
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The plantar fascia is composed of three components: the central, medial, and lateral cords. The central and lateral cords are the most clinically relevant.
Fig. 23.1
Anatomy of The Medial Ankle Ligaments and Plantar Fascia.
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The central cord originates from the plantar aspect of the medial tubercle of the calcaneus and has a complex insertion distally onto the MTP joint and plantar fat pad. The lateral cord originates on the lateral aspect of the medial tubercle of the calcaneus and inserts onto the base of the fifth metatarsal lateral to the insertion of the peroneus brevis.
Pathology
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Undersurface partial-thickness tears are often present adjacent to a calcaneal enthesophyte.
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Enthesopathy of the lateral cord of the plantar fascia (LCPF) at its insertion onto the base of the fifth metatarsal can occur in isolation or coexist with plantar fasciopathy.
Equipment
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27–22 gauge, 1.5–2 inch needle for fascia injection
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25–18 gauge, 1.5–2 inch needle for tenotomy
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High- or medium-frequency linear array transducer
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Prolotherapy
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Orthobiologics
Injectate Volume
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1–3 mL
TECHNIQUE: Approach for injection of the central cord of the plantar fascia
Patient Position
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Prone with knee fully extended and ankle resting on a towel or over the edge of the table.
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Alternatively, patient lying supine, knee fully extended with the ankle on a towel and/or hanging over edge of table.
Clinician Position
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Seated at end of table
Transducer Position
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Short axis (SAX) to plantar fascia near its origin on the calcaneus (in-plane approach) ( Fig. 23.2A and B )
Fig 23.2
Sax In-Plane Approach for Injection of The Proximal Central Cord of The Plantar Fascia.
(A) Patient and needle position for medial to lateral SAX in-plane approach (patient supine). (B) Patient and needle position for medial to lateral SAX in-plane approach (patient prone). (C) Ultrasound image and needle position ( arrow ) for medial to lateral SAX in-plane approach, corresponding to the images shown in A and B. MT , Medial tubercle of the calcaneus.
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Long axis (LAX) to the plantar fascia (in-plane approach) ( Fig. 23.3A )
Fig. 23.3
LAX in-Plane Approach for Injection of the Proximal Central Cord of the Plantar Fascia.
(A) Patient and needle position for distal to proximal LAX in-plane approach. (B) Ultrasound image and needle position ( arrow ) for distal to proximal LAX in-plane approach corresponding to image A. MT , Medial tubercle of the calcaneus.
Needle Position
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SAX in-plane approach directed medial to lateral (see Fig. 23.2C )
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LAX in-plane approach directed either proximal to distal or distal to proximal (see Fig. 23.3B )
Target
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Pathogenic areas of the tendon if using orthobiologics or needle tenotomy
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Peritendinous if using corticosteroids
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Avoid placing injectate directly into the plantar fat pad when utilizing a corticosteroid.
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A tibial nerve block may minimize the need for local anesthetic when using an orthobiologic or needle tenotomy.
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The principle of needle fenestration is to pass the needle repeatedly through the tendinopathic areas of the central cord. The number of fenestrations can vary widely, depending on the severity and extent of the central cord involvement.
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Alternating SAX and LAX imaging during the fenestration assures that the full extent of the tendinopathic portion of the tendon is addressed.
Technique: Approach for injection or fenestration of the lateral cord of the plantar fascia
Patient Position
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Side-lying with the lateral aspect of the affected foot facing up. Towel under the ankle for comfort ( Fig. 23.4A )
Fig 23.4
LAx In-Plane Approach for Injection of The LCPF.
(A) Patient and transducer position for distal to proximal LAX in-plane approach. (B) Corresponding US image and needle position ( arrow ) for distal to proximal LAX in-plane approach. May also approach this injection from proximal to distal. LCPF , Lateral cord of the plantar fascia; MT 5 , fifth metatarsal.
Clinician Position
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Seated at end of table
Transducer Position
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LAX to the LCPF (in-plane approach) (see Fig. 23.4A )
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SAX to the LCPF (in-plane approach) ( Fig. 23.5A )
Fig 23.5
SAX in-plane approach for injection of the LCPF.
(A) Patient and transducer position for dorsal to plantar SAX in-plane approach. (B) Corresponding US image and needle position ( arrow ) for a dorsal to plantar SAX in-plane approach. LCPF , Lateral cord of the plantar fascia; MT 5 , fifth metatarsal; PB , peroneus brevis. The top of the image is dorsal. To the left is medial.
Needle Position
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LAX in-plane approach directed proximal to distal or distal to proximal (see Fig. 23.4B )
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SAX in-plane approach directed dorsal to plantar (see Fig. 23.5B )
Target
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Pathogenic areas of the lateral cord if using orthobiologics or needle tenotomy
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Peritendinous if using corticosteroids
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If utilizing a corticosteroid, consider placing the injectate along the superficial border of the LCPF to minimize the risk of tearing.
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Fenestration and/or orthobiologic injection may take months for full recovery.
Medial Calcaneal Nerve and Inferior Calcaneal Nerve (Baxter’s Nerve)
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Neuropathic pain is not an uncommon cause of heel pain.
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Selectively blocking the medial calcaneal nerve (MCN) or inferior calcaneal nerve (ICN) can help decipher heel pain arising from nerve entrapment versus plantar fasciopathy. However, pain from an entrapment neuropathy can coexist with symptomatic proximal plantar fasciopathy.
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Both the ICN and MCN are approached similarly with a posterior to anterior SAX in-plane approach.
Pertinent Anatomy (see Fig. 23.6 )
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The MCN most commonly comes directly off the tibial nerve and remains in the superficial subcutaneous tissue as it traverses towards the posteromedial calcaneal region.
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The ICN is typically the first branch of the lateral plantar nerve (LPN). It travels posteriorly from its take-off point before turning inferiorly between the abductor hallucis (AH) and the quadratus plantae (QP) muscles. It then courses between the flexor digitorum brevis (FDB) and the QP, deep to the calcaneal osteophyte (if present), before terminating at the abductor digiti minimi (ADM) muscle.
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There is some variability in the take-off of the ICN and may divide above the tarsal tunnel in 12% of cases.
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The ICN is motor to the ADM muscle.
Common Pathology
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Neuropathies involving both the MCN and ICN can lead to heel pain and mimic plantar fasciopathy. An entrapment neuropathy of the ICN can occur in isolation or in conjunction with plantar fasciopathy. Up to 20% of cases of heel pain have been attributed to ICN entrapment. Entrapment of the ICN typically occurs as it traverses between the QP and AH muscles, or more distally between the FDB and QP muscles adjacent to the calcaneal osteophyte.
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Atrophy and fatty replacement of the ADM muscle is a clue to entrapment of the ICN.
Equipment
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High-frequency linear or hockeystick ultrasound transducer
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27–22 gauge, 1.25–1.5 inch needle for perineural injection
Common Injectates
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Local anesthetics, corticosteroids
Injectate Volume
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Local anesthetic 0.5–2mL
Technique
Patient Position
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Supine
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Affected leg is externally rotated to expose the medial ankle. The lateral ankle rests comfortably on a towel or over the side of the examination table ( Fig. 23.6 ).
Fig 23.6
MCN and ICN.
The MCN typically branches off the tibial nerve before the bifurcation of the medial plantar nerve ( MPN ) and lateral plantar nerve ( LPN ). Note that the MCN travels posterior to the ICN. ICN, Inferior calcaneal nerve; MCN, medial calcaneal nerve; TN , tibial nerve.
Fig 23.7
Approach to Injection of the Medial Calcaneal Nerve (MCN) and Inferior Calcaneal Nerve (ICN).
(A) Patient and transducer position for a posterior to anterior SAX in-plane approach for injection of either the MCN or ICN. (B) Corresponding image and needle position ( arrow ) for injection of the MCN ( open white arrowhead ), which appears as a single hypoechoic fascicle traversing posteriorly into the subcutaneous tissue superficial to the calcaneus ( CALC ). Black arrowhead = lateral plantar nerve; open black arrowhead = medial plantar nerve. (C) Corresponding image and needle position ( arrow ) for injection of the ICN ( white arrowhead ), which appears as a single hypoechoic fascicle branching posteriorly from the lateral plantar nerve ( black arrowhead ) and is located adjacent to the quadratus plantae ( QP ) muscle before it enters the interval between the QP and AH muscles.
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Alternatively, patient is prone with ankle over the side of the examination table.
Clinician Position
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Seated directly distal to the foot being injected.
Transducer Position
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SAX to the targeted nerve (see Fig. 23.7A )
Needle Position
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SAX in-plane approach from posterior to anterior (see Fig. 23.7B and C ).
Target
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Perineural
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Identify the MCN by tracing in SAX as it separates from the tibial nerve and traverses inferiorly and posteriorly. It remains fairly superficial, which helps distinguish it from the ICN, which will dive between the AH and QP muscles.
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An isolated local block of the MCN will often differentiate it from ICN entrapment. In such a case, an MCN block will anesthetize the medial calcaneal region but should not affect plantar heel pain if the pain arises from ICN entrapment.
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The ICN is identified by tracing the LPN until a small single fascicle branches posteriorly toward the AH and QP interval. Occasionally, the ICN branches from the tibial nerve proximal to its bifurcation into the medial and lateral plantar nerves.
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Lighten the probe pressure to assure that adjacent venous structures are not compressed and properly identified in planning the needle approach.
Intersection Syndrome
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This represents a friction syndrome between the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) tendons as they cross distal to the medial tarsal tunnel (master knot of Henry).
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The differential diagnosis of medial ankle and/or midfoot pain is broad, and an injection into the knot of Henry can be both diagnostic and potentially therapeutic.
Pertinent Anatomy
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The FHL and the FDL are viewed in proximity to each other at the sustentaculum tali (ST) in short axis. The FDL is visualized just superficial to the ST while the FHL is located slightly distal and posterior. Scanning distal to the ST in short axis, the two tendons will intersect. The point of intersection, or the knot of Henry, is the common location of pathology.
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The medial plantar neurovascular bundle is most often medial to the tendons at their intersection point.
Common Pathology
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Tendinosis or tenosynovitis
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Adhesions between the two tendons
Equipment
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High- or medium-frequency linear array ultrasound transducer
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30–25 gauge. 1.25–1.5 inch needle
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Saline for hydrodissection
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Orthobiologics
Injectate Volume
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1-2 mL
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5-10 mL for hydrodissection
Technique
Patient Position
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Supine or seated
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Affected leg externally rotated to expose the medial ankle. Lateral ankle resting comfortably on a towel or over the side of the examination table ( Figs. 23.8A and 23.9A )
Fig 23.8
Intersection Syndrome Injection.
SAX in-plane approach to injection of the intersection of the FDP and flexor halluceis longus (FHL) at the knot of Henry: (A) Patient and transducer position for a dorsal to plantar SAX in-plane approach. (B) Corresponding US image and needle position ( arrow ) for the dorsal to plantar SAX in-plane approach. The MPN ( white arrowhead ) and medial plantar artery and vein ( open white arrowhead ) are typically adjacent to the fexor digitorum profundus (FDP) and flexor hallucis longus (FHL) tendons. Black arrowhead , FDP; open black arrowhead , FHL; AH , abductor hallucis.
Fig 23.9
Intersection Syndrome Injection.
LAX in-plane approach to injection of the intersection of the FDP and FHL at the knot of Henry: (A) Patient and transducer position for a distal to proximal long-axis (LAX) in-plane approach. (B) Corresponding US image and needle position ( arrow ) for the distal to proximal LAX in-plane approach. AH, Abductor hallucis; FDL , flexor digitorum longus; FHL, flexor hallucis longus.
Clinician Position
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Seated directly distal to the foot being injected
Transducer Position
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SAX to the crossover of the FDL and FHL (in-plane approach) (see Fig. 23.8A )
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LAX to the crossover of the FDL and FHL (in-plane approach) (see Fig. 23.9A )
Needle Position
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SAX in-plane approach directed dorsal to plantar (see Fig. 23.8B )
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LAX in-plane approach from distal to proximal (see Fig. 23.9B )
Target
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Between the FDL and FHL at the knot of Henry
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Identify and carefully map the medial plantar neurovascular bundle as they traverse adjacent to the knot of Henry.
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Lighten the probe pressure to avoid compression of the medial plantar vein during pre-injection planning.
Midfoot Joints
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US-guided midfoot injections can provide both diagnostic and therapeutic benefits.
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Osteoarthrosis (OA) is the most common midfoot joint disorder in the adult population.
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View radiographs as part of injection planning to become familiar with the bony anatomy.
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Patients often have multiple joints involved with midfoot OA. Careful scanning with correlative sono-palpatory pain can help guide providers with information regarding which joint(s) to inject.
Pertinent Anatomy
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The midfoot joints include the talonavicular, calcaneocuboid, naviculo-cuneiform, and tarsometatarsal joints.
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Synovial compartments of the midfoot involve joint complexes rather than separate compartments for each individual joint ( Fig. 23.10 ).
Fig 23.10
Anteroposterior (AP) and Oblique Radiographs of The Foot Demonstrating The Midfoot Joint Complexes ( red lines ).
(A) AP radiograph of the foot showing the medial column joint complexes. Note that the medial tarsometatarsal joints communicate with the naviculocuneiform joints. (B) Oblique radiograph of the foot showing the lateral midfoot joint complexes.
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Abnormal communication between joint compartments is likely to occur in the setting of osteoarthrosis or inflammatory arthropathy.
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At-risk structures include the dorsalis pedis artery and vein, branches of the superficial and deep fibular nerves, and extensor tendons.
Common Pathology
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Osteoarthrosis
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Inflammatory arthropathy
Equipment
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High-frequency linear or hockeystick ultrasound transducer
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30–27 gauge, 1.0–1.25 inch if using local anesthetic before injection; 27–22 gauge, 1.0–1.5 inch for injectate
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Prolotherapy
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Orthobiologics
Injectate Volume
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0.5–1.5 mL
Technique
Patient Position
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Supine with posterior ankle on towel or hanging over the edge of the table
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Alternatively, knee flexed with foot on table ( Figs. 23.11A and 23.12A )
Fig 23.11
Midfoot Joint Injection. Long-Axis (Lax) out-of-Plane Approach.
(A) Transducer and needle position for a lateral to medial LAX out-of-plane approach for an injection into the talonavicular joint. The approach may be medial to lateral or lateral to medial, depending on the location of at-risk structures. A similar approach is applied for injections involving the naviculocuneiform and tarsometatarsal joints. (B) Corresponding ultrasound image and needle position ( white dot ) for the LAX out-of-plane approach. NAV , Navicular bone.
Fig 23.12
Midfoot Joint Injection. SAX in-Plane Approach.
(A) Transducer and needle position for a lateral to medial SAX in-plane approach for an injection into the talonavicular joint. The approach may be medial to lateral or lateral to medial, depending on the location of at-risk structures. A similar approach is applied for injections involving the naviculocuneiform and tarsometatarsal joints. (B) Corresponding ultrasound image and needle position ( arrow ) for the SAX in-plane approach.
Clinician Position
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Seated at the end of the table
Transducer Position
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LAX to the joint (out-of-plane approach) (see Fig. 23.11A )
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SAX to the joint (in-plane approach) (see Fig. 23.12A )
Needle Position
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Dorsal medial to lateral or lateral to medial (depending on location of at-risk structures) LAX out-of- plane approach (see Fig. 23.11B )
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Dorsal medial to lateral or lateral to medial (depending on location of at-risk structures) SAX in-plane approach (see Fig. 23.12B )
Target
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Directly between the bones into the joint.
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Can also inject the overlying joint capsule with prolotherapy or orthobiologics.
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In advanced talonavicular joint arthrosis, dorsal overhanging of bony hypertrophic changes may obscure the joint line. In this case, scan distal to proximal to definitively identify the metatarsals, cuneiforms, and navicular bones. A more medial or lateral approach may also allow better visualization of the joint space and access to the intra-articular joint space.
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Apply light transducer pressure in pre-injection images to avoid compression of vascular structures.
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Assess overlying extensor tendons for attritional changes. In the setting of OA, the joint space may communicate with the overlying tendons due to capsular attrition. Thus, the injectate that contains a corticosteroid may leak into the tendon sheath and predispose to rupture.
Approach to Injection of the Lisfranc Joint
Injections Key Points
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The Lisfranc joint complex often remains symptomatic after injury due to instability or post-traumatic osteoarthrosis.
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An injection into the joint complex may provide diagnostic value for surgical planning or for management of pain.
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View radiographs as part of injection planning to become familiar with bony anatomy. Normal bony articulations may be altered after injury.
Pertinent Anatomy
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The Lisfranc joint is the articulation between the medial cuneiform and medial base of the second metatarsal.
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The Lisfranc ligament complex lies in an oblique plane between the medial cuneiform and second metatarsal base. It is composed of a dorsal, interosseous, and plantar component. The dorsal component is visible on ultrasound.
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At-risk structures include the medial branch of the deep fibular nerve, which most commonly travels directly over the Lisfranc joint.
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Scan SAX on the first and second metatarsals from distal to proximal until the first metatarsal disappears and the medial cuneiform appears ( Fig. 23.13A and B ).
Fig 23.13
Sonographic Localization of Lisfranc Joint.
(A) AP radiograph of the foot showing the transducer position for localizing the Lisfranc joint. Beginning anatomic coronal at the mid-metatarsal level between the first and second metatarsals (more distal probe position), translate the probe proximally until the first metatarsal disappears and the medial cuneiform ( Med Cun ) is visualized adjacent to the second metatarsal (proximal probe position). (B) Ultrasound transducer position to visualize Lisfranc joint corresponding to the more proximal transducer position in A. (C) Corresponding ultrasound image of Lisfranc joint. Note the overlying dorsal Lisfranc ligament ( arrowheads ). Med Cun , Medial metatarsal; MT 2 , second metatarsal.
Common Pathology
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Ligamentous injury with or without associated fracture
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Post-traumatic osteoarthrosis
Equipment
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High-frequency linear or hockeystick ultrasound transducer
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30–27 gauge, 1.0–1.25 inch if using local anesthetic before injection; 30–22 gauge, 1.0–1.5 inch for injectate
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Prolotherapy
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Orthobiologics
Injectate Volume
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1–2 mL
Technique
Patient Position
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Supine with posterior ankle on towel or hanging over the edge of the table ( Fig. 23.14A and B ; see also Fig. 23.13A and B )
