Common foot and ankle disorders in pregnancy: the role of diagnostic ultrasound

Introduction

Foot and ankle disorders commonly occur during pregnancy as it induces profound physiological changes throughout the body, including alterations in weight distribution, hormonal levels, and fluid balance. Foot and ankle disorders in pregnancy present a multifaceted challenge for both patients and healthcare providers. As the body undergoes significant physiological changes to accommodate the growing fetus, the musculoskeletal system, particularly the feet and ankles, can be prone to a variety of ailments [1], [2], [3], [4], [5], [6], [7], [8]. Buchanan and Kung’s [9] analysis particularly highlights how shifts in posture and weight distribution can lead to increased discomfort and various musculoskeletal disorders, including those affecting the lower back, pelvis, and lower extremities. This paper provides and overview of the most common foot and ankle disorders in pregnancy and describes the value of ultrasound in the diagnostic work-up which may include vascular disorders such as thrombophlebitis and thrombosis and disorders of the muscle and tendons such as Achilles tendinopathy, plantar fasciitis, ankle sprains, ligament tears, and Morton’s neuroma, among others.

Though X-ray exposure to the fetus is minimized with proper shielding of the abdomen it is avoided in pregnant patients unless necessary. Consequently, there is a growing interest in exploring safer, non-invasive diagnostic alternatives such as ultrasound, and several authors have provided a thorough analysis of the current ultrasound techniques used for diagnosing foot and ankle disorders illustrating the versatility and precision of ultrasound imaging in identifying structural abnormalities and aiding in the differential diagnosis [10], [11], [12], [13].

Ultrasound imaging

Ultrasound imaging provides real-time imaging of soft tissue structures without the use of ionizing radiation, making it a safer choice for both the pregnant and fetal patients. Ultrasound technology has evolved greatly over recent years, enhancing its resolution and diagnostic capabilities. It allows for detailed visualization of the musculoskeletal system, including muscles, ligaments, tendons, and even small peripheral nerves. This advancement makes it a promising option for diagnosing foot and ankle disorders, which are common but often under-recognized complications of pregnancy.

Early and accurate diagnosis of foot and ankle conditions can prevent progression and facilitate effective management strategies. Ultrasound can aid in this by providing detailed images that help in the assessment of soft tissue integrity, fluid accumulation, and morphological changes in the foot and ankle. Furthermore, the non-invasive nature of ultrasound, combined with its widespread availability in a typical physician’s office, allows for repeated examinations without concerns about radiation exposure, making it ideal for monitoring the progression of conditions throughout pregnancy. This accessibility ensures that pregnant women can receive ongoing, comprehensive care conveniently, allowing for early detection and effective management of foot and ankle disorders. The practicality of integrating ultrasound equipment into a regular medical setting enhances its utility as a diagnostic tool, thereby improving patient outcomes by facilitating timely interventions. Ultrasonography also offers the advantage of being cost-effective and accessible in various healthcare settings, from advanced clinics to basic community medical centers. This accessibility is vital for the early detection and treatment of foot and ankle disorders, ensuring that pregnant women receive timely care.

Varicose veins of the ankle and foot in pregnancy

Pregnancy induces various circulatory changes, including increased blood volume and hormonal alterations, which predispose women to venous disorders like varicose veins [14], [15], [16]. Varicose veins of the ankle and foot are common complications in pregnancy, resulting from increased venous pressure and hormonal changes that affect venous wall and valve functioning. Approximately 40 % of pregnant women develop varicose veins, with the incidence rising with each subsequent pregnancy and among those with a family history of venous disorders.

Particularly the lower extremities are susceptible due to the additional pressure from the growing uterus on pelvic veins. Identifying varicose veins early in pregnancy allows for timely intervention, which can significantly alleviate symptoms such as pain and swelling and prevent complications such as venous ulcers or thrombosis. Management may include lifestyle modifications, compression therapy, and careful monitoring, with ultrasound guiding both initial assessment and ongoing treatment strategies.

Ultrasound, specifically Doppler ultrasound, is the gold standard for diagnosing venous insufficiency. It stands out as a critical diagnostic tool due to its non-invasive nature, providing real-time visualization of vein structure and function without exposure to ionizing radiation. It evaluates vein diameter, valve competence, blood flow direction, and the presence of any thrombosis. Common findings in pregnancy include vein dilation and reflux at valve sites, particularly in the superficial veins of the ankle and foot. The sensitivity and specificity of ultrasound in detecting venous insufficiency are exceptionally high, making it an invaluable tool in both diagnosis and subsequent monitoring of progression or treatment efficacy [17, 18].

Thrombophlebitis and deep vein thrombosis (DVT)

Venous thromboembolism (VTE) is a significant contributor to maternal mortality in the United States, responsible for 9.3 % of all maternal deaths. Pregnant and postpartum women face a four to five times higher risk of thromboembolism than women who are not pregnant. Venous events constitute approximately 80 % of all thromboembolic incidents during pregnancy, occurring at a rate of 0.5–2.0 cases per 1,000 pregnant women [19].

Superficial thrombophlebitis (ST) in pregnancy, which involves the inflammation of veins just under the skin’s surface, is generally considered a relatively benign condition compared to deep vein thrombosis (DVT). However, it can occasionally serve as a precursor to more serious conditions like DVT, particularly in pregnancy, where the risk of venous thromboembolism is heightened.

While ST and DVT are distinct conditions – ST affecting superficial veins and DVT affecting deeper veins – the presence of ST can increase the risk of developing DVT under certain circumstances. This risk is due to several factors specific to pregnancy, such as increased blood coagulability, venous stasis, and vein compression by the expanding uterus, all of which contribute to a hypercoagulable state. Symptoms of ST include tenderness, edema, erythema and warmth over a superficial vein. Risk factors overlap those of DVT, described above, with the notable addition of varicose veins.

Ultrasound plays a crucial role in the diagnosis of superficial thrombophlebitis (ST) in pregnancy (Figures 1 and 2), offering a safe, non-invasive, and highly effective method to assess the condition of superficial veins. It allows for real-time visualization of the venous structures, helping to confirm the presence of thrombi, evaluate the extent of vein involvement, and distinguish ST from deep vein thrombosis (DVT), which is critical given the increased thrombotic risks associated with pregnancy.

Figure 1:

Deep venous thrombosis (DVT) in the left common femoral vein (arrows). There is expansion of the luminal diameter and partial loss of color flow on color Doppler interrogation indicative of partial occlusion (A). Loss of compressibility with transducer pressure is also diagnostic (B).

Figure 2:

Grayscale images with power Doppler in transverse (A) and longitudinal (B) orientation to the cephalic vein shows a segmental thrombus (arrows) characterized by hypoechoic material expanding the vein with serpiginous flow through the clot indicative of early recanalization.

Ultrasound can detect changes in vein morphology, such as vein wall thickening and the presence of echogenic material within the vein, characteristic of thrombophlebitis. Additionally, the use of Doppler ultrasound enhances the diagnostic process by allowing the evaluation of blood flow and the functionality of venous valves, thus confirming the diagnosis of ST and assessing its severity [20, 21].

Ultrasound findings of superficial vein thrombosis (SVT) are a noncompressible hypoechoic material filling a superficial vein [22] (Figure 2). Significantly, SVT is associated with concomitant ipsilateral DVT in 23.5 % of patients and contralateral DVT in 1 % of patients. If SVT is diagnosed, a complete duplex ultrasound of both lower extremities should be considered [22].

Deep vein thrombosis (DVT) occurs in about 0.5–2 cases per 1,000 pregnancies [23]. This incidence rate is higher than in non-pregnant women of reproductive age, due to increased hypercoagulability during pregnancy which is a protective mechanism against hemorrhage at the time of delivery. However, it also raises the risk of thrombosis. The risk of developing DVT varies throughout pregnancy and is highest in the postpartum period. The left lower extremity is usually affected more commonly (82 %), possibly due to uterine compression of the right common iliac artery where it crosses over the subjacent left iliac vein. Symptoms of iliac or femoral venous thrombosis include abdominal and/or back pain, also common in pregnancy [23, 24].

Venous ultrasound is the standard imaging test for patients with suspected acute DVT and is highly accurate for the diagnosis of DVT, with a sensitivity and specificity of 97 % and 94 % for femoropopliteal DVT in the general population (4), however sensitivity decreases to 57 % in the calf [25, 26]. A complete duplex ultrasound of the lower extremity from the common femoral vein to the ankle, including the paired posterior tibial and peroneal veins of the calf, is the preferred diagnostic test. Ultrasound findings of acute thrombosis include an intraluminal clot which increases venous diameter, causes incomplete compressibility by the transducer, obscures color flow and decreases respiratory phasicity on spectral Doppler interrogation (Figure 1). Prominence of the superficial collateral veins is a secondary finding.

If symptoms persist in the setting of a negative study or the examination is technically limited, repeating the exam in 5–7 days is recommended [25]. The predictive value of a negative study is high, with a 3-month risk of venous thromboembolic disease of 0.57 % [27]. Of note, after 23 weeks gestation, the gravid uterus obscures more of the pelvic veins and is only 42 % sensitive for pelvic DVT [28]. If central thrombus is suspected after a negative US result in this population, magnetic resonance venography (MRV) should be obtained.

Edema of the lower limbs

Edema, characterized by the swelling of the feet and ankles, is a very common manifestation during pregnancy (“physiologic edema of pregnancy”), especially in the third trimester. The incidence of edema in pregnancy is quite high, with estimates suggesting that it affects up to 80 % of pregnant women [29, 30]. The hormonal changes during pregnancy, especially the increase in progesterone, lead to relaxation of the venous walls, contributing to the accumulation of fluid in physiologic edema of pregnancy. Additionally, the growing uterus can exert pressure on the veins in the pelvis, impeding blood flow from the legs back to the heart and causing fluid to pool in the lower limbs.

While physiologic edema of pregnancy is a common and generally benign condition, it is important to distinguish it from pathological conditions that also present with swelling and may pose risks to both the mother and the fetus. The differential diagnoses of leg edema in pregnancy include: physiologic pregnancy-related edema, venous insufficiency, lymphedema, deep vein thrombosis (DVT), cellulitis, gout, preeclampsia, heart failure, kidney disease, and pregnancy-induced hypertension (PIH). They need to be ruled out before making the diagnosis of “physiologic edema in pregnancy”.

The diagnosis of physiologic edema typically involves a clinical examination and patient history. However, to rule out these other conditions, additional tests such as blood pressure monitoring, urine tests (for protein), and ultrasound or Doppler studies (for DVT) might be conducted by assessing the venous flow and identifying any obstructions or clots to exclude other causes of leg swelling, especially when edema is severe, asymmetric, or associated with other symptoms. Recently, point of care ultrasound (POCUS) has been suggested in the management of high-risk obstetrics [31].

Overpronation (flat feet)

Overpronation, commonly referred to as flat feet, is a condition characterized by the collapse of the foot’s arch, resulting in the foot rolling inward excessively during walking. Pregnancy can exacerbate or unveil symptoms of overpronation due to the increased weight, altered center of gravity, and hormonal changes that relax connective tissue. While the exact incidence of overpronation in pregnancy is not well-defined, it is recognized as a common issue, with symptoms including foot pain, arch strain, and abnormal gait patterns [2, 32].

Diagnosis of overpronation is typically clinical but can be supported by ultrasound, which may reveal tendon abnormalities, particularly in the posterior tibial tendon, that contribute to the condition. Ultrasound can also assess the morphology of the foot’s arch and the integrity of the supporting structures. Although it is not the primary diagnostic tool for flat feet, ultrasound provides valuable insights, particularly when evaluating for complications or when considering orthotic or therapeutic interventions.

Ankle sprains

Ankle sprains are a prevalent concern during pregnancy, stemming from the increased joint laxity due to hormonal changes and the added stress from weight gain [6, 10]. The incidence of ankle sprains in pregnancy is not explicitly documented but is considered higher given the physiological changes that affect balance and proprioception. Symptoms typically include sudden onset of pain, swelling, bruising, and difficulty bearing weight on the affected limb.

Ultrasound serves as a valuable diagnostic tool for ankle sprains, providing a safe alternative to other imaging modalities [33, 34]. It allows for the dynamic assessment of the injured ligaments, revealing the degree of sprain through changes in ligament thickness, echotexture, and integrity. Ultrasound can also help identify associated pathologies such as ligamentous tears, avulsion fractures, and the presence of accompanying effusion.

Metatarsalgia

Metatarsalgia, a term denoting pain in the metatarsal area of the foot, often presents during pregnancy due to the increased body weight and altered weight distribution, which place excessive pressure on the forefoot. While the precise incidence of metatarsalgia in pregnancy is not widely reported, the condition is more frequently observed due to the anatomical and hormonal changes occurring during this period. Symptoms typically include localized pain and tenderness in the ball of the foot, which may be exacerbated by standing, walking, or wearing high heels [35, 36].

Ultrasound is an effective diagnostic tool for metatarsalgia [34, 37], allowing for the visualization of soft tissue abnormalities, such as thickening of the metatarsal heads, bursitis, or neuromas that may contribute to the condition. It can also detect joint effusion and inflammation that often accompany this pain syndrome. Ultrasound aids also in ruling out other causes of forefoot pain and guides appropriate management during pregnancy.

Stress fracture

Although stress fractures are rare in pregnancy, pregnancy related weight gain, postural changes and hormonal induced laxity leading to altered mechanics and hyperpronation may increase stress on the foot and ankle. Stress fractures during pregnancy are overuse injuries that occur when the bone is subjected to repetitive stress, often exacerbated by the increased weight and altered biomechanics of pregnancy [38, 39]. These fractures commonly present as persistent, localized pain and tenderness, frequently exacerbated by weight-bearing activities. The incidence of stress fractures in pregnancy is not well-documented; however, the risk may be increased due to changes in activity, calcium metabolism, and the mechanical load from weight gain. Diagnosis typically involves clinical evaluation and imaging, with magnetic resonance imaging (MRI) being the most sensitive method to detect early bone stress injuries without radiation exposure. Etiologically, the relaxed ligaments and altered gait during pregnancy contribute to abnormal stress distributions on bones, particularly in the lower extremities. Prevention and management strategies are crucial and include nutritional support, appropriate exercise modifications, and possibly orthotic support.

Distal fibular stress fractures in late term and early postpartum patients with underlying pes planus deformity or transient osteoporosis have been reported [40], [41], [42]. Radiographs are insensitive for the early diagnosis of stress fracture, positive in as few as 10 % of cases [43, 44]. When compared to MRI as the gold standard, ultrasound was 83 % sensitive and 76 % specific for the diagnosis of metatarsal stress fracture in symptomatic patients with negative radiographs [43]. It has also been used to diagnose fractures in other locations, such as the tibia [45]. Ultrasound findings of stress fracture are hypoechoic periosteal reaction, cortical disruption and hypervascularity associated with the periosteal reaction (Figure 3) [44]. At times fracture is incidentally diagnosed when ultrasound is ordered to evaluate for a soft tissue injury [46].

Figure 3:

Greyscale US images without (A) and with (B) power Doppler in longitudinal orientation to the 3rd metatarsal shows hypoechoic, hyperemic callus diagnostic of stress fracture (white arrows). Follow up radiographs obtained two weeks (C) later show maturing callus at the same location (yellow arrow). MT, metatarsal.

Ligament tears

Ligament tears in the foot and ankle during pregnancy are more prevalent due to hormonal influences, particularly increased relaxin levels, which soften ligaments and increase joint laxity, heightening the risk of injury. Common symptoms include sudden, sharp pain at the time of injury, followed by swelling, bruising, and a feeling of instability in the affected joint, making weight-bearing activities particularly painful. Early diagnosis and management are crucial to prevent chronic instability and pain, which can significantly impact mobility and quality of life.

The ultrasound diagnosis of ligament tears during pregnancy offers a safe and effective method for evaluating soft tissue injuries without exposing the patient to ionizing radiation. Ultrasound imaging is particularly advantageous for pregnant women due to its real-time visualization capabilities, allowing for dynamic assessments of the affected area. In the case of a suspected ligament tear, the ultrasound can detect changes in the echogenicity and continuity of the ligament fibers. It also provides valuable information about the severity of the tear, whether it be a partial or complete rupture, and the presence of associated injuries such as edema or hematoma. During the examination, high-resolution probes and appropriate positioning are used to enhance the diagnostic accuracy. The procedure is non-invasive and can be repeated as needed to monitor the healing process or guide therapeutic interventions, making it an indispensable tool in the management of musculoskeletal injuries in the pregnant population. This diagnostic approach not only ensures maternal and fetal safety but also aids in the prompt and appropriate management of ligament injuries, thereby improving clinical outcomes and maternal comfort.

Ultrasound for ligament tears in pregnancy has the advantage of an examination targeted to the area of symptoms which can decrease examination times and increase patient comfort over MRI. In addition, dynamic maneuvers can be performed which can improve detection of tears [51]. It is highly accurate for the diagnosis of anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) tears, with a combined sensitivity of 100 % and specificity of 93 % (Figure 4) [51, 52]. Ultrasound is less accurate for detection of posterior talofibular ligament (PTFL), deltoid and syndesmotic ligament tears, likely because portions of these ligaments are partially obscured by overlying bone [51].

Figure 4:

The anterior talofibular ligament (ATFL) is diffusely thickened and focally discontinuous at mid-substance (arrow), diagnostic of tear.

Synovitis

During pregnancy, many women with autoimmune diseases such as rheumatoid arthritis often experience a temporary improvement in symptoms, likely due to maternal immune suppression that accommodates paternal antigens expressed by the fetus. For instance, studies show that 75–90 % of pregnant women with rheumatoid arthritis report a reduction in symptoms [53]. However, some patients with severe or rapidly progressive diseases may experience flares, and new diagnoses during pregnancy are also reported [54]. The common symptoms of rheumatological diseases – fatigue, joint pain, and swelling – can mimic normal physiological changes in pregnancy, particularly in the third trimester, making diagnosis challenging. Active disease during pregnancy increases the risk of premature delivery and lower birth weights, underscoring the importance of accurately diagnosing conditions like synovitis for both maternal and fetal health.

Ultrasound is a preferred diagnostic tool for detecting synovitis, especially in accessible joints like those in the foot and ankle, due to its ability to visualize active synovial inflammation without the need for gadolinium-based contrast agents (GBCAs) used in MRI (Bowen). GBCAs, which cross the placental barrier and enter the fetal circulation, have an unconfirmed safety profile during pregnancy and are associated with potential risks including stillbirth and neonatal death [55, 56]. Consequently, the American College of Radiology advises against routine GBCA administration in pregnant patients.

Ultrasound imaging of synovial hypertrophy shows hypoechoic, poorly compressible intra-articular tissue, while active synovitis appears hyperemic on color Doppler imaging, with the intensity indicating the severity of inflammation [57, 58]. Ultrasound can also detect erosions, joint effusion, rheumatoid nodules, enthesitis, and crystal deposits, allowing for a comprehensive examination of multiple joints in a single session – a capability not matched by MRI. Comparative studies suggest that ultrasound and MRI have similar sensitivity (80–97 %) and specificity (60–98 %) for various pathologies [59]. Ultrasound is particularly sensitive for inflammatory arthritis, boasting an 89 % negative predictive value for detecting arthralgia in patients without visible synovitis [60]. Moreover, sonographic assessments can reveal specific features such as flexor tenosynovitis, periarticular soft tissue edema, and extensor enthesitis in patients with psoriatic arthritis, and “icing” in chondrocalcinosis, indicative of gout tophi [60].

For treatment, ultrasound-guided intra-articular corticosteroid injections enhance the precision and efficacy compared to palpation-guided injections. Ultrasound can also facilitate diagnostic arthrocentesis and synovial biopsy, making it an invaluable tool in the management of rheumatological conditions during pregnancy.

Tendon tears/tenosynovitis/paratenonitis

Tendon tears, tenosynovitis, and paratenonitis represent a spectrum of tendon pathologies that can manifest during pregnancy due to hormonal changes, increased joint laxity, and altered biomechanics. These conditions often result in localized tenderness, swelling, and pain during movement, significantly impacting the musculoskeletal comfort of pregnant women. Ultrasound is a highly effective diagnostic tool for evaluating these tendon issues (Figures 5 and 6), offering detailed visualization of tendon structure, identifying tears, and assessing inflammation within the tendon sheath and surrounding paratenon. Accurate diagnosis and appropriate management of these conditions are essential to maintaining maternal well-being and functional capacity throughout pregnancy [7, 48, 61]. These conditions can result in symptoms ranging from localized tenderness and swelling to pain during movement or palpation.

Figure 5:

Grayscale images with power Doppler show acute synovitis at the 1st MTP (A) and TMT (B) joints characterized by thickened hyperemic synovium (arrows).

Figure 6:

Longitudinal greyscale ultrasound image with Doppler (A) shows hyperemia of the Achilles at the insertion and expansion of the retrocalcaneal bursa (arrowheads), diagnostic of Achilles enthesitis and retrocalcaneal bursitis, respectively. Transverse greyscale image (B) shows an erosion in the calcaneus (yellow arrow). RB, retrocalcaneal bursa.

The incidence of tendon tears, tenosynovitis, and paratenonitis in pregnancy is not well-documented as isolated conditions. However, these tendon pathologies are relatively common due to the increased joint laxity and altered biomechanics that occur during pregnancy. The hormonal changes, particularly the increase in relaxin, lead to softer ligaments and increased risk of injury and they are a recognized cause of musculoskeletal discomfort during this period, necessitating careful clinical evaluation and management to ensure maternal well-being and functional capacity.

Ultrasound is a highly effective diagnostic tool for evaluating tendon pathologies such as tendon tears, tenosynovitis, and paratenonitis. It allows for detailed visualization of tendon structure, offering insights into tendon thickness, echogenicity, and integrity. Ultrasound can detect more subtle injuries to the ankle tendons than MRI due to its superior spatial resolution [62]. As the tendons change orientation as they course from the lower leg into the foot, the transducer can be changed in orientation as well to provide orthogonal imaging of each tendon along its entire course, decreasing confounding artifacts which limit MRI such as magic angle and volume averaging.

Ultrasound can distinguish between partial and complete tears and identify the presence of fluid within the tendon sheath in cases of tenosynovitis or inflammation of the surrounding paratenon in paratenonitis (Figure 7). Its dynamic imaging capability facilitates assessment during tendon movement, enhancing diagnostic accuracy. Additionally, ultrasound can guide therapeutic interventions, such as injections or aspirations, making it not only a diagnostic modality but also a tool for treatment facilitation. This imaging technique is particularly valuable as it avoids ionizing radiation, is cost-effective, and can be easily repeated to monitor treatment progress.

Figure 7:

Partial tear of the extensor hallucis longus (EHL) tendon involving the dorsal fibers with gapping of the torn fibers (arrows). MT, metatarsal.

Tendinosis, or tendon degeneration, is characterized by tendon thickening, decreased echogenicity and loss of the normal fibrillar architecture (Figure 8). Tendon tears may be partial or complete, depicted as partial or complete discontinuity of fibers, respectively (synvoviture 7). Tenosynovitis is diagnosed by visualization of tenosynovial fluid which circumferentially surrounds the tendon and/or hypervascular tenosynovial thickening (Figure 8). In rheumatological conditions, proliferative synovitis, tenosynovitis of and enthesitis are common [58]. The Achilles tendon lacks a tendon sheath, therefore painful inflammation surrounding this tendon is termed peritendinitis or paratenonitis and is depicted on ultrasound as hypoechoic soft tissue thickening, hypoechoic fluid, and/or hyperemia surrounding the Achilles tendon (Figure 9).

Figure 8:

Greyscale ultrasound image with power Doppler in transverse orientation to the posterior tibial tendon (PT) shows tenosynovitis with trace fluid, and hyperemia (arrows).

Figure 9:

Greyscale ultrasound images without (A) and with power Doppler (B) demonstrate and intact Achilles tendon with thickening of the paratenon (arrows), indicating Achilles paratentonitis is the cause.

Plantar fasciitis

Plantar fasciitis is a common condition during pregnancy, presenting in an estimated 1 in 10 pregnant women, with symptoms that typically include sharp heel pain and arch discomfort, often most pronounced during the first steps after a period of rest. It is a degenerative process usually caused by repetitive microtrauma [63]. Pregnancy induced weight gain increases stress across the plantar fascia; therefore, plantar fasciitis is common in this population. The increased incidence of plantar fasciitis during pregnancy is attributed to weight gain, altered gait, and hormonal changes that affect ligamentous laxity and foot structure.

Ultrasound is an invaluable diagnostic tool for plantar fasciitis, especially during pregnancy when traditional imaging modalities such as X-rays are best avoided [64], [65], [66], [67], [68]. Ultrasound imaging allows for the direct visualization of the plantar fascia, providing crucial information about its thickness, echogenicity, and any potential tears or calcifications (Figure 10). Plantar fasciitis typically occurs at the calcaneal origin and is characterized by increased thickness (>4 mm) and hypoechoic echotexture [69, 70] which are indicative of inflammation associated with plantar fasciitis. This technique also helps in assessing the involvement of surrounding structures and the presence of heel spurs, which are commonly associated with the condition. Additionally, ultrasound can be used dynamically to assess the mechanical behavior of the plantar fascia under stress. Its non-invasive nature, absence of radiation exposure, and the ability to perform repeated examinations make ultrasound particularly suited for diagnosing and monitoring plantar fasciitis in pregnant patients, ensuring both maternal and fetal safety.

Figure 10:

Longitudinal greyscale US image of the plantar fascial origin show a full-thickness tear (yellow arrow), with thickened, hypoechoic residual fibers (white arrows).

Ultrasound not only precisely identifies plantar fascial tears, intrafascial calcifications, and fibromas but also enhances diagnostic accuracy when used in conjunction with elastography, although this technology remains less accessible [63]. For therapeutic interventions, ultrasound-guided perifascial corticosteroid injections have been demonstrated to alleviate symptoms in the short term [72]. Studies indicate that deeper injections are more efficacious than superficial ones [72]. Additionally, incorporating fascial needle fenestration into the procedure has been shown to further improve treatment outcomes [73]. In more recent applications, Platelet-Rich Plasma (PRP) treatments for plantar fasciitis have been explored, with some research suggesting superior long-term results compared to steroid injections [74].

Morton’s neuroma

Morton’s neuroma, a painful condition affecting the nerves between the toes, can become symptomatic or exacerbated in pregnancy, likely due to increased pressure on the forefoot and hormonal changes affecting soft tissue [75]. Characterized by sharp, burning pain or numbness in the toes, its incidence in pregnancy, while not clearly defined, is believed to be influenced by gestational weight gain and edema. It is caused by perineural fibrosis, vascular proliferation, endoneurial edema and axonal degeneration [76]. The incidence of Morton’s neuroma in the general population is estimated to be around 33 per 100,000 annually, with a higher prevalence in women compared to men. However, specific data on the incidence of Morton’s neuroma during pregnancy is not well-documented in the medical literature. The condition’s symptoms may be mistaken for or masked by other common foot-related discomforts during pregnancy, such as edema or generalized foot pain due to increased weight bearing and accurate diagnosis and management are essential to alleviate discomfort and improve quality of life for expectant mothers.

Ultrasound is highly effective in diagnosing and often treating Morton’s neuroma, with various studies reporting sensitivity rates ranging from 85 to 95 % and specificity rates from 77 to 100 %, considered equivalent to MRI [77], [78], [79], [80], [81] The dynamic capability of ultrasound also assists in differentiating neuromas from other intermetatarsal lesions by applying transverse pressure to displace the neuroma, enhancing diagnostic confidence.

The typical sonographic appearance is of a hypoechoic soft tissue mass with or without a component of anechoid bursal fluid measuring less than 20 mm in length (Figure 11). Continuity with the digital nerve and plantar bulging of the neuroma producing a click (sonographic Mulder sign) can sometimes be seen which increases diagnostic confidence [76]. It can also be used to guide therapeutic injections and exclude alternative diagnoses. Ultrasound-guided steroid injections (UGSI) are superior to blind injections as they induce greater pain relief, are associated with fewer complications and referrals for surgical excision [78]. One third of patients experience pain relief lasting over 2 years. Repeat injection may be needed to achieve pain relief for large neuromas (>6 mm).

Figure 11:

Longitudinal ultrasound image of the 2nd webspace (A) demonstrates a large Morton’s neuroma (solid arrows), contiguous with the plantar digital nerve (dashed arrows). Ultrasound-guided injection was performed (B) resulting in marked improvement of symptoms. Needle, arrowheads.

Foreign bodies

Foreign bodies in the foot and lower legs are common clinical challenges that can lead to significant morbidity if not promptly and accurately diagnosed. These injuries typically occur from stepping on or being struck by objects and can range from superficial to deeply embedded items.

The incidence of foreign bodies in the foot and ankle specifically during pregnancy is not commonly detailed in isolation in medical literature. However, pregnant women may be at a slightly increased risk of sustaining injuries, including foreign bodies in the foot and ankle, due to changes in balance, increased weight, and potential for reduced visibility of the feet due to the enlarged abdomen.

Usually, the patient will be able to localize the foreign body and recall the implantation event, such as a laceration or stepping on an object. Occasionally, the patient will present instead with cellulitis or abscesses that fail to respond to adequate treatment and ultrasound will reveal the occult object. When foreign bodies do occur, ultrasound is frequently used as the first mode of detection due to its safety profile for the fetus. Both radiopaque (visible on radiographs) and non-radiopaque foreign bodies are readily diagnosed on ultrasound when superficial (Figure 12). Visible materials include metal, glass, ceramic, stone, wood, and plastic [82]. The relationship between the foreign object and adjacent vessels and nerves is readily demonstrated. Objects as small as 0.5 mm in diameter can be detected, appearing as an echogenic, often shadowing body in the soft tissues, with glass and metal objects generating reverberation artifact.

Figure 12:

Ultrasound shows echogenic wood splinters (white arrows) surrounded by hypoechoic phlegmon (red arrows) just deep to the skin surface in longitudinal (A) and transverse (B) dimensions.

Ultrasound is highly sensitive and specific in the detection of foreign bodies in the foot, particularly effective for identifying materials such as glass, metal, and wood [83], [84], [85], [86], [87], [88]. Studies have shown ultrasound to have a sensitivity ranging from 85 to 98 % and specificity as high as 99 % for detecting these materials. This imaging modality is favored for its ability to provide real-time feedback and distinguish between types of foreign bodies, guiding appropriate surgical or conservative management.

Conclusions

Foot and ankle disorders commonly occur during pregnancy. Diagnostic ultrasound is an invaluable tool to assess clinical evaluation and therapeutic management. Despite the superiority of ultrasound for most foot and ankle disorders in pregnancy, X-rays may be sometimes necessary for diagnosing certain foot and ankle disorders in pregnancy, especially when bone abnormalities or specific alignment issues are suspected, and when ultrasound may not provide sufficient detail such as: fractures, osteoarthritis, osteochondritis dissecans, severe ankle sprains, and congenital deformities [86, 89, 90].

In conclusion, we have provided evidence-based insights and practical guidance for ultrasound implementation in clinical practice, supporting improved diagnosis and clinical outcomes and enhancing the quality of life for pregnant patients suffering from these common disorders.