The relatively superficial location and high innervation of the mid- and forefoot allows good clinical location of most pathologies, but the exact nature and severity of the pathology is often unclear. The superficial location of most mid- and forefoot structures also facilitates assessment by ultrasound (US). The only areas limited to assessment by US are the internal joint areas, the subcortical parts of bones, and the deeper soft tissues on the plantar aspect of the midfoot.
Radiographs, as a first-line investigation, are usually sufficient to fully evaluate most traumatic fractures or dislocations of the mid- and forefoot. Weight-bearing radiographs, while helpful, are not always achievable in some painful, post-traumatic conditions. Coned oblique radiographs may be useful in evaluating sesamoid pathology. For most other conditions, US is the next best imaging investigation. In general, the more precise the symptom location, the greater the benefit of US examination. In most cases, US allows determination of both (a) the exact anatomical site of pathology and (b) the precise nature and severity of this pathology.
Advanced US techniques (e.g. elastography, contrast enhancement) are usually not necessary. US also facilitates diagnostic maneuvers such as fluid aspiration for culture and sensitivity and crystal analysis, percutaneous biopsy, or therapeutic maneuvers such as corticosteroid injection of a joint, tendon sheath, or around Morton’s neuromas. When US fails to adequately identify or fully assess the underlying pathology, magnetic resonance imaging (MRI) with or without computed tomography (CT) are helpful ancillary investigations. Table 1 and Tab. 2 outline practical tips to optimize US and MRI examinations of the mid- and forefoot.
Ultrasound technique tips for examination of the mid- and forefoot
Ensure both you and the patient are in a comfortable position to adequately examine the mid- and hindfoot. Examination of the dorsum or plantar aspect of the foot is normally performed with the foot resting on the examination table, as shown in Fig. 1. Review any radiographs. Take a history and palpate any lump, if present. Use a linear high resolution (7–18 MHz) linear transducer. Higher resolution transducers such as a ‘hockey stick’ (18 MHz) or 25 MHz transducer can be used to improve the resolution of smaller structures. Use of copious acoustic gel to minimalize air gap interference. Start by examining the corresponding area on the contralateral unaffected foot. This enables one to assess normal anatomy for that part and set up the transducer optimally. Ensure optimization of transducer depth, focal zone, and time-gain curve settings. Use compressibility and dynamic assessment for tendon, ligament, or plantar plate assessment Applied specific maneuvers such as Mulder’s maneuver, when appropriate. Use minimal transducer pressure when assessing vascularity of superficial structures with color Doppler imaging. Ensure that the abnormality found on US examination concurs with the clinical symptoms. If the pathology does not fully explain the clinical symptoms or if the lesion has not been fully evaluated, arrange an alternative imaging examination, which will usually be MRI. Use a full aseptic technique, including a sterile transducer cover, for any interventional procedures. |
MRI technique tips for examination of the mid- and forefoot
Use a dedicated coil, such as an ‘ankle and foot ‘coil or a flexible surface coil. The larger dedicated foot and ankle coil enables the examination to be extended to the ankle region, if necessary, and also helps minimize movement artifacts. Small field-of-view coils are helpful for localized pathology e.g. subungual glomus tumor. Due to the small structures involved and the need for high-resolution imaging, 3T imaging is preferable to 1.5 T imaging, if available. A combination of coronal and sagittal with or without oblique axial sequences are used. T1W and T2W FS sequences are most commonly used. Dixon technique is useful to acquire homogeneous imaging as well as the simultaneous acquisition of water and fat images. Oblique axial imaging parallel to the metatarsal shafts is especially helpful if mid-foot bone pathology, such as osteomyelitis or stress fracture, is suspected. Intravenous contrast may be helpful to assess the presence of collections within an inflammatory mass, to assess synovitis and vascular tumor. Most MRI examinations can be adequately performed without intravenous contrast. T1W FS or subtraction images may be helpful before and after contrast administration. Dynamic contrast-enhanced MRI imaging or other functional imaging techniques are generally not necessary for MRI assessment of the mid- and forefoot. |
Stress fractures typically occur in young to middle-aged individuals undertaking unaccustomed high levels of exercise over an extended period. The 2nd and, less frequently, the 3rd metatarsal mid-shafts are commonly affected sites(1) (Fig. 1). The base of the 2nd metatarsal is splinted between the distal end of the medial cuneiform and the 3rd metatarsal bone. It is also a key weight-bearing bone, making it more susceptible to injury. The 1st, 2nd and 5th metatarsal bases, the navicular, cuneiform, cuboid, and medial sesamoid bones are additional common sites of stress fractures in the mid- and forefoot(1,2) (Fig. 2). Radiographs are normal in the earliest stages of stress fracture. US at this juncture may reveal a cuff of echogenic thickening due to thickened periosteum (‘periostitis’) around the cortex of the affected bone area. The cortex may be less distinct than usual, together with juxtacortical soft tissue edema and hyperemia (Fig. 1). While such findings are non-specific, they are usually diagnostic in the appropriate clinical setting without the need for additional imaging other than radiographic follow-up. MRI will provide even earlier detection of stress fracture than US, revealing focal bone marrow edema (BME) at the affected site, often with a thin hypointense fracture line(1) (Fig. 2). In the appropriate clinical setting, BME on fat-suppressed, fluid-sensitive sequences without a visible fracture line is termed a ‘stress reaction’ rather than a ‘stress fracture’(1). Radiographs and US will typically be normal in stress reaction. It is important to correlate any BME with clinical symptoms, as BME may occur due to physiological bone remodeling without necessarily being reflective of an injurious stress reaction(3).
Sesamoid pathology is quite common and includes osteoarthritis of the sesamoid-first metatarsophalangeal (MTP) articulation, traumatic sesamoid bone fracture, and sesamoid bone stress fracture and sesamoid bone inflammation, known as sesamoiditis, which may be secondary to either stress reaction or osteonecrosis(4). Osteoarthritis between the sesamoid and the undersurface of the first metatarsal head articulation is usually assessed radiographically. Sesamoid fracture is also evaluated by radiography and should be distinguished from a bipartite sesamoid bone (Fig. 3). In bipartite sesamoid, the summated size of both sesamoid components is greater than the expected size of the sesamoid bone. Also, the opposing bone edges are smooth and corticated, with a transversely orientated partition, as opposed to the often irregular, obliquely orientated margins of a sesamoid fracture (Fig. 4). Sesamoiditis is seen on MRI examination as diffuse edema of the affected sesamoid bone.
Although clinical symptoms are often severe, ligamentous injury of Chopart’s and Lisfranc joints is often associated with only minor bony avulsions or subtle bony malalignment. Hence, both injuries tend to be overlooked if not specifically considered.
Injury to the 1st MTP joint, which is broadly termed ‘turf toe’, is common among athletes(4). As the anatomy of the first MTP joint differs from that of the lesser MTP joints, the injury spectrum also differs. The first MTP joint contains the paired sesamoid bones which are held in place by a framework of ligament, tendon, capsule, and fibrocartilaginous plantar plate attachments (Fig. 10, Fig. 11). The plantar plate is a trapezoidal-shaped thickening on the plantar aspect of the MTP joint (Fig. 10, Fig. 11). Distally, it is attached to the proximal phalanx and proximally to the inter-sesamoid ligament (Fig. 10, Fig. 11). As the 1st MTP joint anatomy is rather complex, plantar plate and ligament injury is usually best assessed with MRI rather than with US.
The plantar plate is the most frequently injured component of the 1st MTP joint though other supporting structures can also be torn either in isolation or in conjunction with a plantar plate tear. Plantar plate injury may be acute from traumatic hyperextension or chronic. The relative prevalence of acute or chronic tears seen is largely dependent on the referral population. Chronic tears occur in degenerative attenuated plantar plates from repetitive overload (Fig. 12). On MRI, degenerated plantar plates will tend to have intermediate rather than low signal intensity on all pulse sequences(11). Partial tears are more common than complete tears. If complete tears are accompanied by tearing of the supporting sesamoid ligaments, proximal migration of one or both sesamoid bones may occur. Unlike plantar plate tears of the lesser MTP joints, 1st MTP joint plantar plate tears tend not to induce exuberant reactive capsular/pericapsular fibrosis.
Even more so than the 1st MTP joint, the plantar plates of the lesser MTP joints resist joint hyperextension and provide sagittal stability(11). Distally, the plantar plates are firmly attached to the proximal phalangeal bases while proximally, they are loosely attached to the metacarpal necks by fibro-synovial tissue(12). On either side, the plantar plates are firmly attached to the medial and lateral accessory collateral ligaments (Fig. 13) and, as such, co-existent injury of the plantar plate and accessory ligaments commonly occurs(12). Plantar plate tear can lead to MTP joint medial or lateral deviation, dorsal subluxation, and hammer toe(13). The normal plantar plate and plate tears are shown on US and MRI in Fig. 14 and Fig. 15. As with the 1st MTP joint, a midline hyperintense zone, measuring up to 2.5 mm long, at the phalangeal base is a normal anatomic recess(11) (Fig. 10). This is less frequently appreciated on US as a hyperechoic zone.
The 2nd, followed by the 3rd, MTP joint plantar plates are the most frequently injured(12). Plantar plate tears typically occur at the junction between the plantar plate and the accessory collateral ligament close to the phalangeal attachment, most commonly at the inferolateral aspect of the joint (Fig. 13). On US, most plantar plate tears are seen as discrete partial or full thickness hypoechoic defects in the plate substance(13,14). Flattening or attenuation may occur with plantar plate degeneration. When the plantar plate is completely torn, the flexor digitorum tendon may directly contact the metatarsal head(13,14). In the chronic setting, reactive pericapsular fibrosis can be seen as a non-compressible hypoechoic cuff of tissue abutting the plantar and inferolateral (or inferomedial) aspects of the MTP joint(13,14). US should be performed in both longitudinal and transverse planes, scanning the plantar aspect of the MTP joint slowly from lateral to medial and from distal to proximal, with angling of the transducer to avoid anisotropy. Most injuries occur at the distal attachment of the plate. Longitudinal US is best to detect and characterize tears while transverse US is useful to delineate the eccentric location of pericapsular fibrosis and to exclude subluxation of the flexor digitorum tendon. Longitudinal US during toe dorsiflexion can improve tear detection and appreciation of MTP joint subluxation(14).
For MR imaging, T1-weighted (T1W) coronal images are usually the most helpful as routine sagittal forefoot images do not always image the plantar plate in a true sagittal plane(12) (Fig. 15). Performing MRI in the prone position, with the foot in plantarflexion, results in less magic angle artifact and less movement artefact potentially facilitating assessment of the plantar plate(11). Prone positioning also leads to slight plantar shift of the interdigital soft tissues improving assessment of Morton’s neuroma(15). Dynamic US assessment during MTP joint dorsiflexion or during dorsal drawer (Lachman) testing can help assessment of plantar plate integrity and MTP joint stability. Compared with surgical findings, the pooled sensitivity (93%) of US for detecting plantar plate tears is comparable to that of MRI (89–95%), though MRI has a higher specificity (54–83%) than US (33–52%)(16). A negative US examination makes plantar plate injury very unlikely. If US is positive or equivocal, MRI can provide more specificity as to the nature of the injury and yield a more global assessment of the MTP joint(17).
Additional indirect MRI signs of plantar plate tear are joint effusion, subarticular BME, flexor tenosynovitis, an elongated 2nd metatarsal bone, and reparative pericapsular fibrosis while intermetatarsal bursitis and Morton’s neuroma are quite common accompaniments. Pericapsular fibrosis is a useful indirect sign of chronic plantar plate tear which often mimics Morton’s neuroma (i.e. ‘pseudoneuroma’)(11) (Fig. 16). Helpful features to distinguish between pericapsular fibrosis and Morton’s neuroma are listed in Tab. 3. It is likely that as pericapsular fibrosis/plantar plate tear becomes more widely recognized, less Morton’s neuromas and more chronic plantar plate tears will be diagnosed.
Features helpful in distinguishing the pericapsular fibrosis of lesser metatarsophalangeal (MTP) plantar plate injury from the perineural fibrosis of Morton’s neuroma
Pericapsular fibrosis | Morton’s neuromas | |
---|---|---|
2nd > 3rd MTP | 3rd > 2nd intermetatarsal space | |
Crescent-shaped | Roundish or ovoid ± ginkgo leaf shape on side-to side compression | |
Abuts inferolateral (or inferomedial) aspect of affected MTP joint over a broad area | Located centrally in intermetatarsal space ± contacts but does not envelope MTP joint capsule | |
No continuity | Continuity may be visible | |
Maximum over MTP joint region | Maximum over intermetatarsal area | |
Negative (no displacement of fibrotic mass) | ± Positive (fibrotic mass displaces inferiorly) | |
Additional 10 or 20 features of plantar plate degeneration / tear usually present | MTP joint usually normal | |
± Unstable | Stable |
The intermetatarsal bursae have a synovial lining and are located in the superior intermetatarsal space, dorsal to the intermetatarsal ligament(18). Bursal enlargement of >3 mm in the axial plane is considered significant. Intermetatarsal bursitis may be seen on MRI in early RA before clinical joint swelling in patients with clinically suspected arthralgia(19) (Fig. 17).
Soft tissue masses in the mid- and forefoot region are nearly always benign. The most frequently encountered masses are ganglion cyst, Morton’s neuroma, gouty tophus, plantar fibroma, leiomyoma, nerve sheath tumor, lipoma, vascular malformation, tenosynovial giant cell tumor (Ts-GCT), and foreign body granuloma(20). In most instances, US enables an accurate assessment and characterization based on imaging findings alone, without the need for percutaneous biopsy or additional imaging. If histological confirmation is required prior to definitive treatment as, for example, in most cases of Ts-GCT, percutaneous biopsy is undertaken. Additional imaging with MRI is usually very helpful if the mass is large or deep extension cannot be fully defined on US examination.
Rather than being a true neuroma, Morton’s neuroma is a reactivetype fibrous mass in and around a plantar common digital nerve, usually occurring where the common interdigital nerve divides into its medial and lateral digital branches and leading to a focal increase in nerve size. These nerves are located plantar to the intermetatarsal ligament (Fig. 13), which is helpful when distinguishing Morton’s neuroma from intermetatarsal bursitis(18).
Morton’s neuroma is mostly seen in middle-aged women, and is possibly related to mechanical loading from high-heeled shoes. Patients typically have intermetatarsal head pain or numbness radiating to the adjacent toes. US, which can be performed from either the dorsal or plantar side, allows close clinical correlation and dynamic assessment(13). Pressure with the thumb from the dorsal aspect of the forefoot as well as the squeeze test (Mulder’s maneuver) help move the hypoechoic neuroma towards the plantar placed transducer(13) (Fig. 20). This displacement of the neuroma may be accompanied by a palpable, or even audible, click. On longitudinal US, Morton’s neuroma is seen as a normal fibrillar echogenic common interdigital nerve coursing into a focal heterogeneous hypoechoic mass about 14 mm in length (range, 9.0–24.0 mm) containing a more central echogenic area, about 7.5 mm in length(21). The central echogenic area more closely approximates the size of the actual neuroma histologically with the surrounding hypoechoic area representing scar tissue(21). On histology, the resected neuroma will comprise a “neuroma-bursal complex” consisting of the thickened degenerated nerve, fibrotic perineurium, tangled vessels, and scarred/ thickened bursa(21). A neuroma >5 mm in transverse dimension is more likely to be symptomatic(13).
On MRI, Morton’s neuroma is seen as a rounded to spindle-shaped T1-intermediate signal, T2-hypointense mass in the inferior intermetatarsal space, either with or without contrast enhancement. Visible continuity with the plantar digital nerve (‘rat’s tail sign’) also improves diagnostic confidence. In contrast, intermetatarsal bursitis is more cyst-like, with rim enhancement in the superior intermetatarsal space (Fig. 17)(22). Both US and MRI have comparable high sensitivity for diagnosing Morton’s neuroma, with US being more cost-effective(23).
A ganglion cyst is connected to a joint or, less commonly, a tendon sheath. It contains synovial fluid, though the cyst itself has no synovial lining. Visualizing a deep connection, which may be thin and serpiginous, enables a more definitive diagnosis and is helpful for surgical excision (Fig. 21). Occasionally, only a suggestion of a tract pointing towards the joint of origin is apparent. On MRI, a ganglion cyst is seen as a demarcated mass with a high signal intensity on fluid-sensitive sequences, which may be multilobular with septae, and display peripheral enhancement after intravenous gadolinium administration.
US is the method of choice for examining suspected ganglion cysts and shows a well-defined anechoic lesion, occasionally multilocular, and usually non-compressible (Fig. 21). Occasionally, echogenic colloid aggregates suspended within the myxoid cyst fluid may be visible. Emptying or reducing the size of the cyst by US-guided aspiration with a large bore needle and intra-cystic corticosteroid injection is sometimes helpful. Some cysts may be too viscous to aspirate. In the absence of intracystic suspensions, it is not possible to gauge cyst content viscosity. A smaller, and usually less symptomatic, cyst remnant often persists following aspiration(24).
Plantar fibromatosis is a benign condition with focal nodular fibrous enlargement of the plantar aponeurosis (i.e. plantar fibroma). Classically, a nodule is felt by the patient at the medial side of the middle one-third of the sole. US shows a typical uniform hypoechoic fusiform thickening in continuity with the plantar fascia, which may be multifocal in the same foot in one-quarter and bilateral in one-third of patients(25,26) (Fig. 22). It can be differentiated from the much less common plantar fascial tears, which show focal reparative fibrosis with or without plantar fascial discontinuity at a site of previous injury, or the more common plantar fasciitis, which is located at the calcaneal insertion. Plantar fibromas can also be seen on MRI (Fig. 23), though US examination alone is generally satisfactory. On MRI, plantar fibromas are seen as small to medium-sized fusiform-shaped nodule or clustered nodules attached to and extending along the plantar aponeurosis (‘fascial tail sign’), usually the medial cord. T2 hyperintense (relative to muscle) lesions with avid contrast enhancement tend to be actively growing lesions, containing proliferative fibroblastic tissue, that are more responsive to electron beam irradiation therapy, while T2 isointense or hypointense lesions with poor enhancement tend to be quiescent lesions, containing mature collagenous tissue(27).
This entity usually occurs in the subcutaneous fat on the plantar aspect of the foot. The patient often recalls a history of penetrating trauma. Radiopaque foreign bodies, such as metal and large pieces of glass, can be detected on radiographs. US is the preferred investigation to detect radiolucent foreign bodies, such as wood, plastic, or small glass splinters. US also allows the location of the foreign body to be precisely defined, and detects injury to structures such as tendons, nerves, and vessels(28). All foreign bodies are echogenic(28). Smooth, flat surfaces will lead to a hypoechoic, ‘dirty’ acoustic shadowing, while irregular, curved surfaces will lead to echogenic, ‘clean’ shadowing(28). Often, the US is performed weeks or months following initial penetrating injury. In such instances, US reveals a hypoechoic halo of granulation tissue on greyscale imaging, either with or without hyperemia, close to or encasing the hyperechoic foreign body on Doppler imaging (Fig. 24). The size of the hypoechoic halo will vary depending on the intensity of foreign body reaction induced. Such reactions may occasionally be seen after 24 hours(28). Abscess is infrequently present.
Two-thirds of leiomyomas (or angioleiomyomas) occur in the lower leg, ankle, or foot region. This is a benign solitary smooth muscle tumor that mostly occurs in the subcutaneous tissues. Most are <2 cm in diameter and occur close to neurovascular bundles(29). On US, they are well-defined, homogenously hypoechoic, or ovoid, with a smooth margin, even though no discernible capsule is seen. About half of leiomyomas will have small hypoechoic protrusions at one or both ends of the mass, most likely due to extension along the vessel of origin(29). Mild to moderate posterior enhancement is usually seen(29). Most tend to be moderately hypervascular, occasionally with peripheral vascular convergence (Fig. 25). Many of these features can also be seen in small subcutaneous peripheral nerve sheath tumors arising from small subcutaneous nerves and, as such, do not have a visible neural tail. Consequently, the distinction between leiomyoma and nerve sheath tumor is often difficult.
Osteoarthritis may affect any joint in the mid- to forefoot, but it most commonly involves the joints of the medial longitudinal arch. The medial column, which is composed of the 1st MTP joint, or middle column, which comprises the 2nd and 3rd MTP joints, are usually affected more than the lateral column, which includes the 4th and 5th MTP joints(30). Patients present with pain aggravated by prolonged weight-bearing. Radiography is the first line of investigation. US is usually undertaken to establish osteoarthritis as the likely cause of dorsal midfoot pain and swelling. Dorsal foot swelling in such instances is typically caused by hypertrophic dorsal osteophytes and capsular/soft tissue swelling, though paraarticular ganglia are also common. US reveals joint space narrowing with marginal osteophytosis, capsular thickening, and mild surrounding soft tissue swelling, possibly with hyperemia on Doppler imaging (Fig. 26)(30). As the curvature of the articular surfaces and marginal osteophytosis limits accurate US assessment of joint space narrowing, radiographic correlation is useful in this regard. If surgery is considered, CT optimizes delineation of osseous anatomy, disease extent, and severity, as well as alignment. Cone beam CT is a small footprint, self-shielded device, producing high-quality localized CT images of the mid- and forefoot, and is a useful emerging imaging modality for foot osteoarthritis, not least that the examination can be obtained in the weightbearing position(30). MRI is advantageous in showing subchondral BME, which is moderately associated with pain with or without focal articular cartilage defects. MRI, however, is usually not required to investigate suspected mid- and forefoot osteoarthritis.
Gravity and the relatively colder temperatures of the mid- and forefoot encourage uric acid crystal deposition. This deposition mainly occurs in periarticular tissues and ligamentous insertions. Intratendinous or peritendinous deposition is also common (Fig. 27). The first MTP joint is the most affected. Patients may present acutely with a painful joint similar to septic arthritis, or chronically with an intermittently painful mass or an enlarged joint due to gouty tophi. A diagnosis of gouty arthritis/gouty tophi can usually be adequately established with radiographs and US. There is usually little benefit to performing MRI examination. Dual energy CT is helpful to establish the presence of uric acid accumulations, though it is falsely negative in gouty arthritis without uric acid accumulation.
Calcium pyrophosphate deposition (CPPD) can also occur in the foot. The presentation is similar to gout, though tophi tend to be less prevalent, and crystal deposition occurs in the mid-zone articular cartilage layer, as opposed to the cartilage surface, though such delineation is generally not feasible in the thin articular cartilage of the foot.
Hallux valgus is excessive adduction at the first MTP joint. This diagnosis is made clinically, with supportive radiographs(31). US is usually not necessary, though it may reveal osteoarthritis of the first MTP joint. MRI is usually not indicated. The normal hallux angle is 8–12°(31). Adventitial bursitis is a relatively uncommon complication of hallux valgus that can be assessed by US.
Pes planus, or flatfoot, results from variable collapse of the medial longitudinal arch. This can be associated with posterior tibialis tendinosis either at its insertion or along the course of the posterior tibialis tendon (Fig. 28). Tendinosis and tendon tears can be evaluated well with US, as can the presence of an often accompanying accessory navicular bone or cornuate configuration to the medial pole of the navicular bone. MRI allows a more comprehensive assessment of navicular configuration, medial longitudinal arch flattening, talar head support, heel valgus, sub-talar and sub-fibular impingement, as well as reactive ligamentous thickening and tears.
RA, which is primarily a disease of the synovium, usually affects the small joints of the wrists, hands, and feet. Over the last two decades, with more effective medication, emphasis has shifted towards early disease detection, early treatment, and minimization of joint damage. Both US and MRI can detect subclinical synovitis and tenosynovitis, while MRI can, in addition, detect BME (‘osteitis’) (Fig. 29, Fig. 30). In patients with undifferentiated arthritis (UA), MRI-detected inflammation predicts RA development. The European League Against Rheumatism (EULAR) advocates using MRI in the diagnostic process(32,33). MR parameters used in the RA-MRI scoring method (RAMRIS) include BME, synovitis, tenosynovitis, and erosions(34). To reduce costs and optimize image resolution, only the most symptomatic joint area, rather than MRI of both wrists, hands, ankles, and feet, is undertaken(35). MRI of early RA is facilitated by using a short, modified Dixon protocol instead of gadolinium-enhanced T1W FS MRI-sequences(36).
US is less sensitive than MRI in the detection of early synovitis and tenosynovitis(37). Tenosynovitis close to the MTP joints is probably a primary synovitis feature rather secondary to MTP synovitis, as anatomic study of the synovial sheaths shows the presence of synovial cells in both the extensor and flexor tendons at the MTP joint level(38).
Clinical disease activity score (DAS28) is one of the best measures to determine RA disease activity, with a persistently high score associated with an increased likelihood of progressive joint damage, even in clinically well patients(39). There is a discordance between clinical and US scores for assessing disease activity, and no consensus on how many joints to count during US assessment, limiting the use of US for assessing disease activity in RA(40,41). US-guided injection is used to treat joints not responding to systemic therapy.
Very early changes of tenosynovitis are difficult to detect. However, tenosynovitis with synovial hypertrophy and tendon sheath fluid can be readily detected with US. The flexor and extensor tendons at the MTP joint level are often involved in RA. Overuse and mechanical loading may cause tenosynovitis in non-RA patients at typical locations.
Tendinous, ligamentous, or fascial insertion into bone can show thickening and hyperemia secondary to mechanical overloading or a systemic disease (e.g. spondyloarthritis, such as psoriatic arthritis). More common examples are the peroneus brevis tendon insertion and lateral band plantar fascial insertion to the 5th metatarsal base (Fig. 31) as well as the posterior tibialis tendon insertion into the medial pole of the navicular bone. When evaluating such structures, the examiner should use minimal transducer pressure during color Doppler assessment to optimize the detection of tissue hyperemia (Fig. 28, Fig. 31).
This review outlines the imaging appearances of the most common mid- and forefoot pathologies. Following radiography, high-resolution US is the examination of choice to evaluate the mid- and forefoot. In most instances, an adequate explanation for symptoms can be found. MRI or CT may be helpful when symptoms cannot be fully explained, or the pathology cannot be fully assessed, by US examination.