Transarterial embolization (TAE) is a novel treatment option for chronic musculoskeletal pain (MSK
pain), particularly beneficial for patients unresponsive to conservative therapies or unsuitable for surgical
intervention. This minimally invasive technique, which targets and embolizes aberrant neovascularization,
relies heavily on the precise information provided by various imaging modalities to ensure effi cacy and safety.
While TAE’s adoption is on the rise, the application of these imaging modalities throughout the procedure—
ranging from plain radiography and ultrasonography to computed tomography and magnetic resonance
imaging—remains underexplored. Through a comprehensive literature review, we delve into the utilization of
these imaging modalities from pre-procedural planning to post-procedural assessment of TAE, highlighting
their contribution to the treatment’s success. Ultimately, the article aims to equip interventional clinicians with
the insights needed to effectively utilize these imaging modalities, thereby enhancing treatment outcomes for
patients with chronic MSK pain through a more refi ned process of TAE.

imaging modalities, musculoskeletal pain, transarterial embolization

Since its pioneering introduction by Okuno et al. [1-3] in 2013, transarterial embolization (TAE) has been increasingly recognized for its effi cacy, gaining widespread adoption as an innovative treatment for musculoskeletal pain (MSK pain). Targeting both appendicular and a few axial locations, TAE has shown promising results for conditions such as osteoarthritis (OA), adhesive capsulitis, epicondylitis, and plantar fasciitis, offering significant improvements in pain, function, and quality of life [4-7]. Additionally, its minimally invasive nature makes it particularly beneficial for patients who have found little relief from conservative treatments or are unsuitable for surgical intervention [8,9].

Central to the effectiveness of TAE in reducing MSK pain is its ability to address aberrant neovascularization observed in areas such as the synovium and osteochondral junction. This pathological neovascularization fosters the ingrowth of nerves into typically non-innervated tissues and is known to be associated with painful conditions like synovitis and osteochondral damage [10]. TAE eradicates these abnormal vessels through precise catheterization and disruption of their feeding arteries using microspheres. Ultimately, embolization of these vessels results in decreased inflammation and promotes ischemic neurolysis of newly grown sensory nerves [11], thus contributing to the reduction of MSK pain.

Despite the increasing application of TAE for MSK pain, the absence of universally endorsed guidelines highlights a significant gap, particularly regarding its indications and contraindications. This gap underscores the importance of careful patient selection and risk evaluation to ensure procedural safety and efficacy. Currently, several broadly accepted contraindications, including local infection, severe atherosclerosis, infectious arthritis, malignancy, and pain related to compressive neuropathy, are acknowledged within the field [5,7,12,13].

To optimize the procedure and minimize adverse effects, thorough evaluations of anatomic structures are also required before TAE. Multiple studies demonstrate the complexity and variability of genicular arteries [14-17], emphasizing the importance of understanding vascular anatomy to maximize treatment effect and minimize the risks of nontarget embolization. Common adverse effects of non-target embolization include transient tissue ischemia and paresthesia, which typically resolve within hours to a few days, and are more prominent with the use of permanent embolic agents [8,18,19].

Taken together, the success of TAE hinges on several key factors: a thorough understanding of vascular anatomy to accurately target pathological angiogenesis, careful consideration of vessel anastomoses, awareness of the embolization endpoint, and meticulous pre-procedural planning and patient selection. Central to ensuring these factors are imaging modalities. Their roles in guiding each step of the TAE process, from planning to execution and post-procedural evaluation, are indispensable in achieving optimal outcomes.

Through a comprehensive review of current literatures, this article delves into the roles of various imaging modalities—including plain radiography, ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI), and fluorodeoxyglucose-positron emission tomography (FDG-PET)— in enhancing each step of TAE for managing chronic MSK pain. Each section individually introduces the application of a specific imaging modality, spanning from pre-procedural planning to post-procedural out comes, with the aim of refining TAE procedures and improving patient outcomes.

Plain radiography is typically used to assess patients with pain in peripheral joints and is commonly acquired for those who do not respond to conservative therapies [20,21]. It is primarily chosen for its accessibility, cost-effectiveness, and ability to delineate both bone integrity and gross osseous changes.

Plain radiographs are helpful for diagnosing knee OA and are considered the gold standard for imaging hand OA [22,23]. It distinguishes OA from conditions that may require surgery such as tumors, fractures, or infections [24-28]. The Kellgren-Lawrence (KL) grading system quantitatively assesses the severity of OA through radiographs, guiding patient categorization in TAE studies [23,25,29]. While TAE is effective in managing pain and improving function for patients with knee OA [8,9,18,30-32], its efficacy decreases in severe cases (KL Grade 4) due to the mechanical stresses of bone contact [30,31,33,34]. This highlights the significance of optimizing patient selection based on pre-procedural radiographic features.

The diagnosis of medial and lateral epicondylitis is typically based on clinical history and physical examination, as elbow radiographs often show normal results or only occasionally reveal calcification near the epicondyle. However, radiographs are typically obtained to exclude other pathologies in refractory cases, namely in patients for whom conventional therapies have failed and who are now being considered for TAE or surgical intervention [35,36].

Similarly, patients with adhesive capsulitis are usually diagnosed clinically. The role of radiography is to exclude common mimics, such as fractures, that are not indicated for TAE treatment [37].

Prior to TAE for plantar fasciitis, radiography is recommended to exclude other painful pathological conditions, such as fractures or bony tumors. Nonweight-bearing lateral foot radiographs can also reveal findings supportive of plantar fasciitis, including increased thickness of the plantar fascia near the medial calcaneal origin, narrowing or absence of the fat pad beneath the fascia, presence of calcaneal spurs, and changes in the calcaneal cortex like lucency and sclerosis [38,39].

Radiography was particularly useful for the preliminary evaluation of post-total knee arthroplasty (TKA) pain. It can reveal conditions such as fractures or osteolysis and detect hemarthrosis through the presence of joint effusion and tendon displacement [40,41]. In a recent pilot study on TAE for chronic pain following TKA, participants underwent thorough diagnostic assessments, including knee radiography and advanced imaging, to exclude complications such as septic or aseptic loosening [42]. This diagnostic process is vital for elucidating the exact etiology of post-TKA pain, enabling physicians to determine whether to opt for TAE or other interventions.

In conclusion, while candidates for embolization usually have an identifi ed pain etiology, it is always recommended to obtain radiographs of the affected area before proceeding. This precaution ensures the exclusion of conditions that may require alternative therapies and helps assess the severity of OA in affected patients [24-28,35-37,42].

Plain radiography falls short of reflecting the clinical outcomes after TAE for OA, as the therapeutic mechanisms of TAE do not involve direct repair of cartilage and bone. This is evident when post-TAE radiographs revealed no notable changes or progression, despite a signifi cant reduction in pain [43] (Figure 1). The treatment outcomes of TAE are typically evaluated through physical examinations, patient-reported outcomes, and pain scales corresponding to the affected body parts. Post-TAE imaging evaluations are usually reserved for research purposes unless there is a worsening of pain or suspicion of complications [25].

In a review of TAE for refractory overuse sports injuries, a slight increase in vascularity was observed in the area adjacent to a nonunion Jones fracture in a patient. Following the TAE procedure, subsequent radiography clearly demonstrated that the previously nonunion fracture had achieved fusion over time [44].

The limited sensitivity of plain radiography in assessing soft tissue often necessitates the adoption of alternative imaging modalities for a more comprehensive evaluation. When patients present with suspected soft tissue abnormalities, US or MRI is typically the preferred choices for a more accurate diagnosis.

Figure 1. Radiographic Progression of Hip Osteoarthritis (OA) After Transarterial Embolization (TAE)

Hip radiographs of a 69-year-old man experiencing chronic pain in the right hip joint before (A) and 4 years after (B) TAE to the right hip. (A) The right hip joint demonstrates marginal sclerosis, osteophyte formation, and joint space narrowing, indicative of OA. (B) The patient visited our outpatient department 4 years after TAE due to leg length discrepancy and left hip pain. Notably, while the patient reported sustained pain relief in the right hip after TAE over the years, radiographic progression of OA in the right hip persisted.

US is highly valuable for diagnosing musculoskeletal disorders and plays a vital role in the TAE process. The non-invasive nature, rapid image acquisition, and no risk of radiation exposure make US a favorable choice for both clinicians and patients. Additionally, US is not affected by metal artifacts, which is an advantage it holds over MRI in certain clinical scenarios.

US excels in visualizing soft tissues and peripheral structures, offering detection of knee OA mani festations such as effusions, synovitis, erosions, and osteophytes [45,46]. These capabilities are crucial, as radiographic findings of OA may not correlate with early-stage symptoms. In patients with shoulder pain, US tells adhesive capsulitis apart from other causes [47]. Moreover, in cases of suspected epicondylitis, US is beneficial for ruling out collateral ligament injuries and ulnar neuropathy, both of which may resemble or coexist with epicondylitis but may not be suitable for TAE [48]. Additionally, ultrasound is a reliable tool for assessing the thickness of the plantar fascia, facilitating the diagnosis of patients with plantar fasciitis [49].

In the pre-procedural stage of TAE, a specific application for US is spotting high-grade arterial stenosis located distal to the artery access site, a condition often resulting from peripheral arterial occlusion diseases or anomalies like a persistent sciatic artery (Figure 2). Such stenosis can signifi cantly hamper or even prevent the necessary catheterization process for TAE, leading to the explicit exclusion of these patients from multiple studies focused on TAE for MSK pain [2,8,50]. Patients presenting with clinical signs and symptoms of peripheral arterial disease, such as claudication, rest pain, and skin changes, particularly warrant a pre-TAE ultrasound evaluation to assess potential distal arterial stenosis [51]. Pulse Doppler effectively detects severe peripheral arterial stenosis by revealing a single-phase pattern in the spectral waveform [52]. Ultimately, US facilitates better patient selection for TAE and potentially aids in avoiding procedural complications.

Figure 2. Case Example of Congenital Vasculature Anomaly

During transarterial embolization for a patient with osteoarthritis of the left knee, a hypoplastic superfi cial femoral artery (arrow) was identifi ed following vascular puncture at the left femoral site, which precluded the continuation of the procedure. Later, a persistent sciatic artery (arrowheads) was confi rmed to give rise to the genicular arteries instead.

During the execution of TAE, real-time ultrasound guidance facilitates arterial puncture by visualizing the needle’s path as it penetrates the vessel. This capability allows for immediate adjustments during the procedure, ensuring the optimal placement of the catheter for effective embolization.

Despite its strengths, US has limitations, including heavy reliance on operator skill and a restricted field of view. These considerations emphasize the importance of skilled operation and the necessity for complementary imaging techniques in actual practice.

Fluoroscopic angiography is a cornerstone technology for performing TAE. It enables the 2D visualization of vascular structures, particularly the aberrant neovascularization associated with MSK pain. Digital subtraction angiography (DSA) is an advanced imaging technique that eliminates non-vascular structures from the original fl uoroscopic angiography, resulting in a clearer view of the vasculature and reducing the need for contrast agents.

Numerous studies on TAE for MSK pain have characterized the aberrant neovascularization as tumor blush-type enhancements observed during angiography [6-8,42,50,53,54]. The technical success or procedural endpoint of TAE for MSK pain involves embolizing aberrant neovascularization until a reduction or absence of blush areas is achieved [7,9,54] (Figure 3).

During TAE procedures, careful instillation of embolic material is often needed to prevent non-target embolization. In a prospective pilot study of TAE for knee OA, there are instances in which patients were not embolized because of noticeable cutaneous blood supply or anastomoses between the target vessel and the popliteal artery [9]. Similarly, in low back pain treatment, a study underscored the need to identify and spare anterior segmental medullary arteries derived from lumbar arteries to prevent spinal cord infarction [55]. In TAE procedures targeting the hip joint, artery branches that supply the femoral head should be preserved to avoid bone necrosis [56]. Collectively, these studies demonstrate the importance of fluoroscopic angiography in avoiding non-target embolization and safely carrying out TAE. We present another case to demonstrate the identifi cation and avoidance of non-target arteries to prevent complications (Figure 4).

The application of fl uoroscopic angiography extends to recognizing intraprocedural complications, as highlighted in a review article [19]. For instance, specific angiographic patterns, such as fibrillar staining and pooling of contrast agents, may indicate extravasation within muscle tissue or fat planes related to microartery perforations. Furthermore, an abrupt luminal narrowing or saccular outpouchings of the artery may indicate different types of arterial dissections.

A study has shown a correlation between the degree of pre-procedural angiographic enhancement and pain reduction following embolization [57]. Despite the potential, further studies are needed to validate whether specific findings in fluoroscopic imaging could serve as predictive markers for treatment outcomes.

The limitations of fl uoroscopic angiography are notable, particularly in identifying small, tortuous, or overlapping vessels. It was suggested in a study focusing on the angiographic anatomy of the genicular artery that the resolution limitations of DSA may hinder the detection of the medial genicular artery and its branches [15]. Additionally, the effectiveness of DSA can be infl uenced by the laminar fl ow dynamics of the contrast medium, which could result in preferential opacifi cation of certain arteries and potentially compromise the overall clarity of the angiographic image [58].

Figure 3. Digital Subtraction Angiography (DSA) During Transarterial Embolization (TAE) for Right Adhesive Capsulitis
DSA findings before (A) and after (B) TAE in a 63-year-old male with right adhesive capsulitis. (A) Abnormal “tumor blush” (arrowheads) was identified following selective angiography of the right anterior circumflex humeral artery. (B) The post-embolization DSA demonstrated the elim-ination of the abnormal vessels.

Figure 4. Case Example of Refractory Hip Pain Treated With Transarterial Embolization (TAE)
Angiography image of the left obturator artery in a 57-year-old female who underwent TAE for left ischial pain, demonstrating the acetabular branch (arrowheads) that gives rise to the artery of the ligamentum teres. As the artery of the ligamentum teres contributes to the vascular perfusion of the femoral epiphysis, it is important to preserve the acetabular branch of the obturator artery to prevent femoral head necrosis.

CT scans excel in detecting bone abnormalities, yet radiographs can provide comparable insights with less radiation. In cases of soft tissue conditions such as epicondylitis, adhesive capsulitis, or plantar fasciitis, US or MRI are preferred due to their superior soft tissue visualization [37]. Consequently, CT scans are not routinely acquired in the pre-TAE assessment due to being overshadowed by other modalities in various aspects.

Similarly, while CT angiography (CTA) is accurate in detecting peripheral arterial diseases or anomalies before TAE, its use is limited by radiation concerns. It is considered a secondary option when US does not provide clear results regarding distal arterial stenosis [59].

In TAE procedures for MSK pain, rotational cone-beam CT (CBCT) is frequently employed alongside DSA to better identify target and non-target vessels [58,60]. CBCT is particularly benefi cial when targeting lower extremities, where variant branching patterns and overlapping vessels pose signifi cant challenges when relying solely on DSA for guidance. The concurrent use of fluoroscopy and CBCT provides detailed 3D angiography and facilitates the identification of the optimal angle for visualizing the origin of arteries [12,14]. This fusion imaging technique also improves procedural planning, facilitates error identifi cation during the intervention, and ultimately reduces fl uoroscopy duration [61] (Figure 5).

Nevertheless, the use of CBCT is limited when targeting the upper extremities for TAE due to spatial constraints. In such cases, pre-procedural MRI can be utilized to provide 3D guidance for TAE.

Figure 5. 3D Cone-Beam Computed Tomography (CT) During Knee Transarterial Embolization (TAE)
3D cone-beam CT effectively elucidates the complex and overlap-ping vasculature of the genicular arteries, as demonstrated in this image captured during knee TAE in a 74-year-old female.

MRI is widely recognized as the leading modality for the assessment of musculoskeletal conditions. Its detailed imaging capabilities and safety from radiation make it increasingly preferred for evaluating patients with chronic MSK pain.

MRI effectively delineates structural abnormalities in knee disorders, including cartilage damage, osteophytes, subchondral cysts, joint effusions, ligament and tendon tears, Baker’s cysts, synovitis, meniscal tears, and subchondral bone marrow lesions [62-64]. In shoulder pain cases, MRI detects detail changes in the synovium and joint capsule, helping to determine the optimal treatment method by differentiating disorders such as adhesive capsulitis, rotator cuff tear, tendinitis, OA, subacromial impingement, and occult fractures [65,66].

Studies have explored how initial MRI findings in knee OA correlate with clinical outcomes observed within months following TAE. A retrospective study highlights that the presence and severity of a full-thickness cartilage defect at baseline were the most significant predictors of reduced pain relief after TAE [33]. Furthermore, the presence and increased severity of effusion synovitis, bone marrow lesions, osteophytes, and cartilage surface area scores at baseline are also associated with less favorable clinical outcomes. The presence of Hoffa synovitis did not show a significant association with the clinical outcome after TAE. Other studies suggest that extensive bone marrow lesions, severe meniscal damage, and concurrent subchondral insufficiency fractures of the knee are indicative of poor responses to TAE [67,68]. These insights suggest MRI’s utility in identifying potential non-responders ahead of TAE.

Contrast-enhanced MRI (CE-MRI) is instrumental in diagnosing adhesive capsulitis by identifying enhancement in the joint capsule and synovial membrane. This is particularly helpful to confirm the diagnosis in cases of refractory shoulder pain before TAE [65,69]. In a recent case series regarding TAE for MSK pain, patients exhibiting enhancement on pre-procedural CE-MRI experienced more significant pain relief [70]. Moreover, a higher proportion of patients with enhancement (89.5%) reported pain reduction compared to those without enhancement (61.5%). These findings emphasize the usefulness of CE-MRI in predicting treatment outcomes of TAE.

Additionally, pre-procedural MRI is helpful for screening conditions requiring surgical intervention, such as fractures and malignancies [12]. The early detection of these conditions can be crucial in avoiding medical disputes and ensuring that patients receive timely and appropriate treatment.

A recent study showcases the application of MRI fusion imaging for TAE for MSK pain [61]. By incorporating pre-procedural non-contrast 3D magnetic resonance angiography (MRA) with fluoroscopic imaging, this technique effectively overcomes challenges caused by overlapping arteries, ensuring precise catheterization. Opting for non-contrast MRA instead of CBCT for 3D guidance is equally effective and offers additional benefits, such as avoiding radiation exposure and the risks associated with contrast agents. The acquisition of non-contrast 3D MRA occurs before TAE, which also helps reduce the overall procedural duration.

MRI is invaluable for assessing the outcomes of TAE, with studies showing significant reductions in contrast enhancement in areas like the rotator interval, axillary pouch, and internodal groove following TAE for frozen shoulder [71]. For knee TAE, various MRI techniques are utilized to assess changes in osteoarthritic features post-TAE, including synovial thickness alterations observed through CE-MRI, joint effusion on non-CE-MRI, and synovial perfusion changes captured by dynamic CE-MRI [25].

In clinical settings, MRI is selectively employed when complications are suspected, providing accurate identification and assessment of conditions such as bone marrow edema, aggressive cartilage loss, tendon rupture, ligament rupture, or muscle atrophy [8,9,12,25].

In summary, MRI is a versatile tool for diagnosing MSK pain, guiding TAE procedures, and identifying post-TAE complications. The capacity to offer detailed visualization of anatomical structures and tissue alterations is particularly invaluable throughout the entire process of TAE for MSK pain.

In a retrospective cohort study, FDG-PET/CT was utilized to investigate the underlying mechanism of the therapeutic effect of TAE on frozen shoulder [71]. Baseline FDG-PET/CT scans of patients with frozen shoulders revealed increased FDG uptake in the rotator interval and axillary pouch, indicating inflammation [72] (Figure 6). MRI scans confirmed these findings by showing contrast enhancement in the same regions. The notable FDG uptake on PET/ CT and the corresponding contrast enhancement on MRI both demonstrated resolution after TAE of the aberrant neovascularization at the affected shoulder. These results suggest that the therapeutic effect of TAE may be attributed to reduced inflammation in the corresponding supplying area of the target vessels and underscore the potential of FDG-PET/CT for quantitatively assessing the efficacy of TAE procedures [9,32,57].

This review article underscores the multifaceted role of various imaging modalities at each stage of TAE for chronic MSK pain. From plain radiography to more advanced MRI and PET scans, these imaging modalities not only enhance the effi cacy of TAE but also deepen our understanding of pain mechanisms. They aid in patient selection, personalize treatment, and enable thorough outcome assessments. The continuous integration and advancement of these imaging tools, along with refi nement at each stage of TAE, are pivotal for optimizing patient outcomes and advancing progress in the fi eld.