Ultrasound guided injections in ankle and foot

Abstract

Ultrasound guidance is particularly useful for percutaneous injections in the diagnosis and management of painful conditions of the ankle and foot. The injectates used include steroids and local anesthetics, such as lidocaine, mepivacaine, bupivacaine, ropivacaine, and platelet-rich plasma. Osteoarthritis is the main indication for joint injections. Joints amenable to being injected include the tibiotalar, subtalar, midtarsal, and metatarsophalangeal joints. Tendon injections mainly involve the Achilles, peroneus, extensors, and tibialis tendons, while plantar fascia injections are useful for treating plantar fasciitis and plantar fibromatosis. Forefoot injections include joint arthritis, intermetatarsal bursitis, and Morton neuroma. The standardized approaches and doses reviewed in this paper are based on the authors' experience and can lead to high success in symptomatic relief for various conditions. These injections can be curative or serve as a guide to identify the source of pain when surgery or other therapeutic options are planned.

Introduction

Ankle/foot pain is prevalent, affecting 15–24% of the adult population older than 45 years. It has been shown to have a detrimental impact on health-related quality of life due to its association with difficulty performing activities of daily living, problems with balance and gait, and an increased risk of falls [1]. Ultrasound is an extremely useful method for quickly and accurately localizing and characterizing foot pathology. The wide availability of ultrasound, combined with its low cost, lack of ionizing radiation, high spatial resolution, multiplanar capability, and excellent patient tolerance, makes it an ideal technique for assessing the superficial structures of the ankle and foot. Ultrasound can also be used to guide interventional procedures, making it easy to avoid intervening neurovascular and tendinous structures during the procedures and increasing accuracy to around 90–100% [2].

This work aims to present techniques for diagnosing and treating musculoskeletal sources of pain in the ankle and foot under ultrasound guidance, based on our experience.

Methods and background

Percutaneous injections in the diagnosis and management of painful conditions of the ankle and foot involve several targets that are better approached by ultrasound. Steroids and local anesthetics (LA) are among the most frequent injectates used, mainly particulate steroids such as triamcinolone acetonide and methylprednisolone acetate. LA is usually short-acting, such as lidocaine or mepivacaine, but long-lasting anesthetics such as bupivacaine or ropivacaine can be used for longer foot blocking. Platelet-rich plasma (PRP) is increasingly used to treat tendon partial tears and osteoarthritis [3]. Hyaluronic acid can be used in combination with steroids in ankle osteoarthritis or, more rarely, in other smaller joints. Other products such as ozone or botulinum toxin are not routinely used in the ankle and foot [4]. Regarding needles, 23–25 G needles are usually recommended for small joints and tendons, and a 21 G needle for larger joints and the plantar fascia.

Joints

Ultrasound can be used to inject any joint in the foot and ankle. It is particularly useful for guiding injections in patients who have large osteophytes and extremely narrowed joints. The joints amenable to injection include the tibiotalar, subtalar, midtarsal, and metatarsophalangeal joints, with osteoarthritis being the main indication.

For the tibiotalar joint, an anterior long-axis approach is easiest, directing the tip of the needle over the anterior aspect of the talar dome (Fig. 1). The patient can be placed supine with the leg straight and toes pointing to the ceiling, or with the knee bent and the foot flat on the examination table. An in-plane anteromedial or anterolateral approach can be used, although some authors prefer an in-plane short-axis approach. In both cases, the goal is to touch or slide over the hyaline cartilage of the talar dome. The probe is positioned medially to the tibialis anterior tendon in the anteromedial long-axis approach, with the probe placed in long-axis with respect to the tendon. Real-time imaging of the needle helps avoid traversing sensitive structures such as arteries, tendons, and nerves. In the preprocedural scan, it is important to document the location of the dorsalis pedis artery, which usually courses laterally to the tibialis anterior tendon. The injection of anesthetic confirms the intra-articular needle position, and once confirmed, the mixture of corticosteroid and local anesthetic can be injected. Approximately 6 ml of injectate is used for steroid + LA, and 3–5 ml is used for PRP. Joint fluid aspiration for analysis can be performed prior to injection in case of joint effusion.

Fig. 1.

Ankle joint injection. A Radiography with an arrow pointing to the entrance point. B Long-axis view of the joint and C ultrasound guided injection with the needle positioned over the talar cartilage (*)

Ultrasound guidance can also be used for injecting radionuclides such as Yttrium 90 or Rhenium 186 in chronic synovitis for radioisotope synovectomy [5].

The subtalar joint can be approached through the sinus tarsi. The cause of sinus tarsi pain is not well understood and may be related to the pathology of the subtalar joint, tears of the ligaments within the sinus tarsi, or trauma [6]. Relief of pain with sinus tarsi corticosteroid injections has been reported in the literature [7]. Under ultrasound guidance, a lateral approach is used over the superolateral aspect of the calcaneus. The needle is aimed at the lateral aspect of the talar neck-head junction (Fig. 2). Up to 6 ml of injectate can be introduced.

Fig. 2.

Subtalar injection. A Radiography with an arrow pointing to the entrance point. B Ultrasound-guided injection at the sinus tarsi. C Severe subtalar osteoarthritis. D Lateral approach to the subtalar joint

The subtalar joint can also be approached posteriorly, either medially or laterally, although this is more technically demanding due to the deepness and the interposition of the tibialis posterior or peroneal tendons, respectively [8].

Midtarsal joints can also be approached under ultrasound guidance. The approach must be customized to the anatomy of the osteoarthritic joint, avoiding spurring to reach the joint space. Osteoarthritic joints have a large capacity, and one sign that the joint space has been reached is the lack of resistance to introducing the injectate. One of the most frequently affected joints is the talonavicular joint (Fig. 3), although any of the other joints may be affected, including the calcaneocuboid, naviculocuneiform, and tarsometatarsal joints [9]. Checking the needle on its long and short axis may help in entering the joint at the correct place (Fig. 4). Between 2 and 5 ml of injectate is used. Normal or pathological communication between the midtarsal joints allows more room for injectate to enter [10].

Fig. 3.

Talonavicular joint injection. A Radiography of talonavicular joint osteoarthritis. Long-axis (B) and short-axis (C) view during ultrasound-guided injection

Fig. 4.

Tarsometatarsal joint injection. A Lateral and anteroposterior B views of osteoarthritis between the 2nd cuneiform and metatarsal (arrows). Ultrasound long-axis view of the osteoarthritis before (C) and during ultrasound-guided injection (D)

Metatarsophalangeal joints are approached from the dorsal aspect. An in-plane approach is used, tracking the length of the needle entering the joint. However, some authors prefer an out-of-plane approach from the medial or lateral aspect of the joint. Between 1–2 ml of injectate is used. Sometimes, bending the needle may be necessary to ease entrance into the joint (Fig. 5). Ultrasound-guided injections increase accuracy compared to blind injections based on anatomical landmarks, due to its ability to identify the synovial cavity and avoid bone osteophytes that may hamper access to the joint [11, 12].

Fig. 5.

Metatarsophalangeal joint (MTPJ) injection. A Radiography with an arrow pointing to the entrance point in the long and short axis. B Bent needle accessing the MTPJ. C Injection under US guidance using a long axis in-plane entrance

The joints between the sesamoid bones and the first metatarsal head can also be injected. 1–2 ml of injectate is sufficient. A medial approach is recommended (Fig. 6). Injection deep (over the 1st metatarsal head) and superficial (under the flexor hallucis longus tendon) to the sesamoid bones is performed to cover any source of pain in this area. Nevertheless, some authors have reported that communication between the 1st metatarsophalangeal joint and the metatarsosesamoid articulations does exist, and therefore, injecting the 1st metatarsophalangeal joint may be an alternative way to reach those joints [13].

Fig. 6.

Injection around sesamoid bones. A, B Medial approach to the sesamoid joint. Injection over (C) and under (D) the sesamoid bones. FHL flexor hallucis longus tendon

The short-term benefit of injections of the ankle and foot joints in our patients is over 80%, similar to previous reports [14].

Tendons

Tendon injections mainly involve the Achilles, peroneus, extensors, and tibialis tendons. The volume of injectate in small tendons is around 1–2 ml, while for the Achilles tendon and retrocalcaneal bursa, up to 6 ml can be used.

For the Achilles tendon, local anesthetics (LA) and steroids are injected into the superficial and deep parts of the paratenon. In partial tears, platelet-rich plasma (PRP) can be used. Depending on the clinical evolution, injections can be performed up to three times, with 15–20 days between each injection, using approximately 3–5 ml of volume, around and inside the tendon. However, PRP injections and dry needling have shown similar short-term results at 3–6 months [4, 15]. Prolotherapy is another technique that has been used to treat chronic tendinosis. This technique involves intratendinous injection of glucose to treat the hypoechoic areas of tendinosis, achieving a reduction of pain in treated patients by more than 70% [16] (Fig. 7).

Fig. 7.

Injections in the Achilles tendon. A Tendinosis of the Achilles tendon with moderate neovascularity. Steroid injection in the deep (B) and superficial part (C) of the paratenon. D Platelet-rich plasma injected at the tendon tear

Image-guided anesthetic-corticosteroid injections into other tendons of the ankle and foot have shown good results in providing symptomatic relief in patients with tenosynovitis [4, 17] (Fig. 8). In the case of tendinosis and partial rupture of tendons, PRP can also be used intra and peritendinous instead of steroids [18].

Fig. 8.

Tendinous injections. A Intratendinous PRP injection in the peroneus longus tendon. B Injection of steroids in the peroneal tendon sheath. C Intratendinous cyst in an accessory peroneus tertius tendon. D Ultrasound-guided drainage of the cyst

Ganglion cysts

Ganglion cysts are the most frequent benign soft tissue masses in the foot, and they are often related to a joint or a tendon sheath. However, they can also be present as intratendinous mucinous cysts. Before peritendinous injection, they can be drained (Fig. 8). They may manifest as a painless or painful lump or may cause paresthesia secondary to compression of neural structures, such as tarsal tunnel syndrome. Intra and extra-neural ganglion cysts have been described to cause nerve impairment, and ultrasound can be used for therapeutic drainage in both cases (Fig. 9) [19].

Fig. 9.

Ganglion cyst of the foot. A 14 G Abbocath needle used for drainage of the ganglion cyst. B Entrance of the needle into the cyst. C Ganglion cyst compressing the tibial posterior nerve branches (arrows) in the tarsal tunnel. D Drainage under ultrasound guidance

Drainage of the cyst usually requires thicker needles (14–19 G) due to the gelatinous texture of the content. Several punctures of the cyst wall in different places, followed by steroid injection after drainage, are recommended to avoid recurrence [20] (Fig. 9).

Plantar fascia

A posterior tibial nerve block is recommended before injecting the plantar fascia for plantar fasciitis because it is often very painful (Fig. 10). A 4-5 ml injection of 1% mepivacaine or lidocaine is sufficient to provide an appropriate block of the area. We generally approach the tibial nerve with a 23 G needle just medial to the Achilles tendon, ensuring that the posterior tibial arteries and veins do not interpose between the needle trajectory and the nerve. The needle may be approached to the deep and/or superficial part of the nerve to ensure that the anesthetic surrounds most of the nerve. The injection is performed slowly to avoid puncturing the nerve. Repeated aspiration during injection is recommended to detect and avoid intravascular injection. The patient should be informed that the heel skin can still be sensitive despite the nerve block.

Fig. 10.

Posterior tibial nerve block. A Injection procedure. B The needle located at the deepest part of the nerve. C The needle located at the superficial part of the nerve. D The nerve surrounded by anesthetic

Alternatively, topical anesthesia using cryo-anesthetic spray can be used in less painful cases. We usually perform a longitudinal access to the fascia, from proximal to distal, traversing the fascia 3 or 4 times. When only LA + steroids are used, the injection is performed superficially and deeply to the fascia. In the case of injecting PRP, it is injected peri- and intra-fascially. Other approaches, such as longitudinal distal to proximal or transverse, can also be used (Fig. 11). A recent meta-analysis found that PRP injection showed better outcomes than steroid injection in 3–6 months of follow-up [22].

Fig. 11.

Plantar fascia injections. A Longitudinal approach. B Injection over the fascia. C Injection under the fascia. D Transverse approach to the fascia. E Deep injection of corticoids in the transverse plane. F Intrafascial and perifascial injection of PRP in the transverse plane

Plantar fibromatosis can also be injected. In this case, steroid injection is performed inside and around the fibromatosis nodule (Fig. 12). Usually, 3–4 ml of injectate is used. Currently, recommendations for intralesional injections of triamcinolone or methylprednisolone include a total of 3–5 injections given 4–6 weeks apart [23].

Fig. 12.

Plantar fibromatosis. A Coronal T1-weighted image showing nodular thickening of the plantar fascia consistent with plantar fibromatosis. B Doppler ultrasound. C Injection under the fibromatosis nodule

Forefoot

Forefoot injections can be used to treat various conditions, primarily joint arthritis, intermetatarsal bursitis, and Morton's neuroma. The dorsal approach is recommended in all cases because it is less painful (Fig. 13). Usually, 0.5–1 ml of local anesthetic and 40 mg of triamcinolone are used to inject Morton's neuroma [24]. Ultrasound-guided injections have reported higher success rates (69–89%) compared to blind injections (48–59%) based on anatomical landmarks, both in short and long-term follow-ups [24, 25]. Other techniques, such as radiofrequency ablation, can also be used with success rates around 80%, leaving surgery as an option only for non-responsive cases [26]. Approximately 15–50% of patients may require surgery, but for those treated with ultrasound-guided injections, this rate may be around 20%, which is in the lower range of the values reported in the literature [25].

Fig. 13.

Injection in Morton's neuroma. A Dorsal approach with the probe in the plantar aspect of the foot. B Sagittal view of the Morton's neuroma and bursa. C Injection. D Dorsal approach with the probe in the dorsal aspect of the foot. E Morton's neuroma. F Injection. MN Morton's neuroma complex, B Bursa, IOM interosseous muscles

Intermetatarsal bursitis may be associated with Morton's neuroma or present in isolation without nerve pathology. The bursa can be distinguished from Morton's neuroma as it is not connected to the proximal nerve. It is usually more anechoic than neuroma tissue, collapses more when pressing the skin with fingers, and distends during injection [25, 27]. When the bursa is symptomatic and large enough, drainage can be attempted, followed by steroid injections (Fig. 14).

Fig. 14.

Intermetatarsal bursitis in the first web space. A External swelling of the first web space. B Bursitis without Morton's neuroma in the 3rd web space. Normal nerve (arrows). C Injection of the bursa under ultrasound guidance

Conclusions

Ultrasound is a safe method for diagnosing and treating sources of pain in the ankle and foot. Standardized approaches and doses for treating painful conditions of the ankle and foot are reviewed based on our experience. High success in providing symptomatic relief can be achieved for many painful conditions, such as joint osteoarthritis or inflammatory arthritis, tendinosis and tenosynovitis, ganglion compression, or Morton's neuroma. These injections may be curative or serve as a guide to identify the source of pain when surgery or other therapeutic options are planned.

Funding

The authors have not disclosed any funding.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest to disclose.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national 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.