Abstract
Objective:
To compare the detection capability and reported diagnostic indicators of Doppler ultrasonography (DUS) and contrast-enhanced ultrasound (CEUS) to detect neovascularisation in Achilles tendinopathy, as well as assess the diagnostic relevance in relation to symptoms and treatment outcomes.
Materials and Methods:
A systematic literature search was conducted using the EBSCO host databases for studies published between 2004 and 2024, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies involving adults with Achilles tendinopathy assessed with DUS and/or CEUS were included. Data extraction was performed using a structured form, and study quality was evaluated using the Critical Appraisal Skills Programme (CASP) tool. Due to methodological heterogeneity, a narrative synthesis was executed.
Results:
Eight studies met the inclusion criteria, all using DUS, with two additionally incorporating CEUS. The CEUS appeared to demonstrate greater detection capability for microvascular flow compared to DUS, particularly in complex clinical cases. The DUS remained more accessible and clinically feasible. Evidence linking neovascularisation with symptom severity was inconsistent, although some studies reported vascular changes following treatment.
Conclusion:
Both DUS and CEUS have been shown to detect neovascularisation in Achilles tendinopathy. Based on published evidence, CEUS provides enhanced microvascular assessment, while DUS remains a practical primary diagnostic tool. The diagnostic role of neovascularisation as a clinical biomarker remains uncertain.
Introduction
Achilles tendinopathy is a commonly overused condition characterised by pain, swelling, and impaired functionality of the Achilles tendon. It is frequently diagnosed in athletes and physically active individuals but also affects non-athletic patients. The condition is typically caused by repetitive strain or mechanical overload of the tendon, resulting in degenerative changes at both cellular and structural levels. 1
Epidemiologically, the burden of Achilles tendinopathy is considerable. In the United Kingdom, the incidence of Achilles tendon rupture, an associated condition, has been reported at 8 per 100 000 people per year. 2 A notable gender discrepancy exists, with up to 79.2% of cases occurring in males. The average age of onset is approximately 40 years, 3 and the prevalence is higher in sports that involve repetitive loading, such as running, jumping, and basketball. Interestingly, the rate of tendinopathy in basketball players alone is estimated at 4.3%, 4 indicating a significant impact on athletic performance and quality of life.
At the tissue level, Achilles tendinopathy is characterised by collagen disorganisation, increased tendon thickness, and alterations in tendon vascularity.5,6 In clinical practice, these vascular changes can be detected using ultrasonography, Doppler ultrasonography (DUS), and contrast-enhanced ultrasound (CEUS), which are commonly employed to evaluate tendon microvascular activity. The DUS is a widely accessible non-invasive diagnostic tool that measures blood flow by detecting Doppler frequency shifts produced by moving red blood cells. 7 It enables dynamic assessment of intratendinous vascularisation and has become a cornerstone of musculoskeletal imaging. The DUS encompasses both colour Doppler and power Doppler applications. Colour Doppler provides information on flow direction and velocity but is limited by angle dependency and reduced sensitivity to low-volume blood flow. Power Doppler addresses some of these limitations by detecting the amplitude of flow signals independent of direction, thereby improving sensitivity to slow and microvascular flow. Despite these advantages, power Doppler remains susceptible to technical factors such as gain settings, probe pressure, and tissue relaxation, which may introduce artefacts or result in underestimation of microvascular activity. 8
To overcome these limitations, CEUS has emerged as an advanced diagnostic imaging method. The CEUS uses injectable microbubble contrast agents that enhance the echogenicity of blood flow allowing for the visualisation of small slow-flowing vessels in the microvasculature. 9 Its ability to detect microvascular flow has been validated in several musculoskeletal applications. 10 Despite these advantages, CEUS has lesser utilisation due to higher costs, limited availability, and the need for specialised training and equipment. 11
Although both DUS and CEUS can detect vascular signals within the tendon, the physiological phenomenon being identified is hyperaemia or hypervascularity, which is typically defined as an increase in blood volume or perfusion within a tissue relative to normal baseline levels. 12 Such findings may reflect a range of underlying biological processes, including inflammation, tissue repair, or mechanical loading responses. 13 However, in the context of Achilles tendinopathy, the most implicated mechanism is neovascularisation, defined as the formation or ingrowth of new blood vessels through angiogenic processes. 14 This vascular process is believed to be a reactive or compensatory mechanism aimed at facilitating tendon repair by improving oxygen and nutrient delivery. 15 However, neovascularisation has also been implicated in pain generation and chronic symptoms, particularly when accompanied by nerve ingrowth. 16
The clinical relevance of imaging-detected neovascularisation remains controversial. Some studies suggest that neovascularisation correlates with pain intensity and functional impairment, supporting its potential role as a biomarker of disease severity. 17 Other findings, however, report weak or inconsistent associations between vascularity and symptoms raising questions about its utility in predicting outcomes. 18 Despite this, neovascularisation continues to attract research attention because of its potential value in tracking treatment response. For example, the success of interventions such as sclerotherapy, high-volume saline injections, and shockwave therapy is often evaluated based on the reduction or elimination of neovessels. 19 These vascular changes have also been observed post-treatment in studies of clinical survalence. 20
Previous systematic reviews have examined imaging in tendinopathy or evaluated individual ultrasound techniques in isolation. However, the comparative performance of DUS and CEUS for detecting neovascularisation in Achilles tendinopathy has not been systematically synthesised. Given the distinct technical capabilities, accessibility, and costs associated with these techniques, clarification of their relative detection capability and clinical utility is clinically relevant.
The role of neovascularisation in Achilles tendinopathy remains debated, particularly regarding its association with symptoms and response to treatment. A synthesis of the existing evidence comparing DUS and CEUS is therefore necessary to support informed interpretation of diagnostic imaging findings and appropriate technical selection for clinical practice. For the purposes of this review, the primary outcome of interest was the comparative detection capability and reported diagnostic indicators of DUS and CEUS in detecting neovascularisation, including measures such as sensitivity and specificity where reported, as well as relative detection capability. Secondary outcomes included the reported associations between neovascularisation and clinical symptoms, as well as changes in vascular findings following therapeutic intervention.
Materials and Methods
This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The aim of this review was to evaluate and compare the detection capability and reported diagnostic indicators of DUS and CEUS in assessing neovascularisation, in adults with Achilles tendinopathy. A review protocol was developed prior to the search and data collection process and followed throughout. Due to expected heterogeneity in study design, diagnostic imaging protocols, and outcome reporting, a narrative synthesis approach was adopted. The term sensitivity in this review refers to the relative detection capability of the diagnostic imaging technique unless otherwise specified as diagnostic accuracy measures reported by the original studies. This allowed for a structured qualitative summary of findings across diverse studies, without statistical pooling or meta-analysis.
Eligibility Criteria
Studies were selected based on a predefined eligibility framework, based on the patient, problem, or population, intervention, comparison, and outcome (PICO) model. The review included adult individuals aged 18 to 65 years diagnosed with Achilles tendinopathy. To meet the inclusion criteria, studies had to involve the use of DUS or CEUS to detect and assess neovascularisation. Studies comparing these two diagnostic imaging techniques were eligible, as were those using either technique independently. Relevant outcome measures included detection of neovascularisation and any reported associations with pain, function, or treatment outcomes.
Eligible study designs included diagnostic accuracy studies, cohort studies, cross-sectional studies, and randomised controlled trials. Only studies published in English were considered. Studies focusing on other tendons, not evaluating neovascularisation, or using other diagnostic imaging techniques such as magnetic resonance imaging (MRI), computed tomography (CT), or without DUS or CEUS were excluded. Reviews, meta-analyses, case reports, and editorials were also excluded.
The PICO framework used to guide inclusion is visually summarised in Table 1.
The PICO Framework Used to Formulate the Literature Search.
Search Strategy
A search strategy was developed using keyword combinations and Boolean operators. The search terms included “neovascularisation,” “angiogenesis,” “blood vessel formation,” “Doppler ultrasound,” “contrast-enhanced ultrasound,” “Achilles tendinopathy,” “tendonitis,” and related synonyms. Both British and American spellings were incorporated to maximise retrieval.
The following electronic databases were searched via the EBSCO host platform: MEDLINE, CINAHL Complete, AMED, SPORTDiscus, and Academic Search Complete, covering literature published from January 2004 to December 2024.
Grey literature sources were explored through hand-searching the reference lists of included studies and manually screening key journals. Additional sources such as conference proceedings, dissertations, and clinical trial registries were considered; however, only peer-reviewed full-text studies meeting the eligibility criteria were included in the final synthesis. Duplicates were removed using the RefWorks citation management software.
Study Selection
A study selection process was implemented in accordance with PRISMA. The process was carried out in two stages. First, titles and abstracts of all identified records were screened against the predefined inclusion criteria. Studies that did not meet the eligibility requirements, such as incorrect population, intervention, or outcome, were excluded at this stage.
Second, full-text articles of potentially relevant studies were reviewed to assess whether they met all eligibility criteria, including the use of DUS or CEUS to assess neovascularisation in Achilles tendinopathy. Only studies that provided relevant and sufficient data were included in the final synthesis.
The outcomes of the selection process, including the number of records screened, excluded, and included, are illustrated in the PRISMA flow diagram (See Figure 1).
Power Doppler ultrasound image demonstrating intratendinous vascularity (neovascularisation) in Achilles tendinopathy, with associated tendon thickening and hypoechoic changes.
Data Extraction
An extraction form was developed to systematically record relevant information from each included study. 22 Key data fields included study aim and design, population characteristics, sample size, intervention details (DUS or CEUS), outcome measures, and key results. Additional information, such as methodological limitations and risk of bias, was also recorded (See Table 2).
Data Characteristics and Risk of Bias Assessment of the Included Published Studies Under Review.
Prior to full implementation, the form was piloted on a small subset of studies to confirm clarity and reliability. This approach enabled uniform data collection and facilitated meaningful comparison across studies. 28
Quality Appraisal
To ensure methodological rigour, the quality of all included studies was assessed using the Critical Appraisal Skills Programme (CASP) checklists. The CASP randomised controlled trial (RCT) checklist was applied to randomised controlled trials, while other tools from the CASP suite were used for observational and cohort studies, depending on study design. 29
The appraisal process was used not to exclude studies but to provide a structured assessment of the methodological strengths and limitations of each study. 30 Studies were evaluated for potential risks of bias, including selection bias, performance bias, detection bias, and attrition bias. Key features assessed included randomisation, blinding, sample size, and completeness of follow-up.
Bias management was integrated throughout the review process. Eligibility criteria, a standardised data extraction form, and adherence to PRISMA methodology were used to reduce subjectivity and ensure consistency. The outcomes of the quality assessment informed the narrative synthesis and contextual interpretation of study findings, helping to ensure that conclusions are grounded in evidence. 31
Literature Search
The literature search was conducted across five databases using the EBSCOhost platform: MEDLINE (n = 136), Academic Search Complete (n = 103), CINAHL Complete (n = 72), SPORTDiscus (n = 55), and AMED (n = 5). In addition, reference lists of included articles were manually screened, yielding a further 14 records. This resulted in a total of 385 records identified prior to deduplication.
Duplicate records were removed using a combination of automated and manual processes across EBSCOhost (n = 185), RefWorks (n = 4), and Covidence (n = 5). Following deduplication, 191 unique records remained and were screened at the title and abstract level against the predefined eligibility criteria.
Title and abstract screening were conducted by the primary reviewer, with eligibility decisions and exclusions subsequently reviewed by a second reviewer to ensure consistency with inclusion criteria. At this stage, 146 records were excluded based on population characteristics, imaging modality, or lack of relevance to neovascularisation. Forty-five full-text articles were sought for retrieval. Of these, 15 could not be accessed despite attempts through institutional database subscriptions and inter-library loan services.
Thirty full-text articles were subsequently assessed for eligibility. Full-text screening decisions were verified by a second reviewer, with any uncertainties resolved through discussion. Twenty-two studies were excluded at this stage: nine due to inappropriate study design, six due to an incorrect population, three due to an irrelevant intervention, and four due to the absence of outcome data related to neovascularisation. Eight studies met all eligibility criteria and were included in the final synthesis.
Screening was conducted by a primary reviewer with subsequent verification by a second reviewer to ensure consistency with the predefined inclusion criteria. Formal inter-rater agreement statistics were not calculated, as independent dual screening was not performed.
Data Extraction
Data extraction was performed by the primary reviewer using a predefined, structured extraction form. Extracted data were subsequently reviewed by a second reviewer for accuracy and completeness. Any discrepancies or uncertainties were resolved through discussion and consensus.
Of the eight included studies, observational designs were most common (n = 3), followed by pilot studies (n = 2), with one prospective study (n = 1), one experimental study (n = 1), and one reliability study (n = 1). Most investigations were conducted in clinical or sports medicine settings in Europe and North America, with publication dates ranging from 2007 to 2020.
All studies investigated adult patients with clinically diagnosed Achilles tendinopathy. Populations varied in activity level, chronicity of symptoms, and recruitment setting. Sample sizes ranged from 9 to 64 participants, with most involving fewer than 40 individuals. While some studies focused exclusively on symptomatic tendons, others included comparisons with asymptomatic limbs.
All eight studies used DUS to assess neovascularisation. Two studies additionally incorporated CEUS, either as a primary method or in comparison with DUS. The studies differed in their specific imaging objectives and applications, including quantifying vascular flow, assessing vascular changes post-intervention, and evaluating neovascular patterns under activity-related conditions.
Most studies were rated as having a moderate risk of bias, while three were assessed as low risk. Common methodological limitations included small sample sizes, lack of blinding, and limited reporting of reliability measures. An overview of study characteristics, imaging modalities, and key outcomes is provided in Table 3.
Summary of the Diagnostic Detection Rates and Clinical Associations for Utilising Doppler and CEUS.
Data Synthesis
A narrative synthesis approach was employed to analyse and present the findings from the included studies. This method was selected due to the considerable heterogeneity across studies in terms of imaging protocols, study design, outcome measures, and reporting styles; hence, statistical pooling was not feasible. 32
The synthesis was organised thematically around three core areas. First, the comparative detection capability of DUS and CEUS in detecting neovascularisation was compared across studies. Second, the characteristics of neovascularisation, such as its extent, anatomical distribution, and vascular patterns, were summarised. Finally, the relationship between neovascularisation and clinical symptoms, such as pain and function, and treatment outcomes was explored.
Differences in sample cohorts, sonographic techniques, assessment criteria, and reporting contributed to heterogeneity across the studies. These variations were acknowledged when interpreting results and drawing comparisons. 33 Where homogeneity existed, such as similar imaging protocols or outcome definitions, findings were grouped to enhance consistency. 34
Results
All eight included studies utilised DUS to assess neovascularisation, while two studies additionally employed CEUS. Among the DUS studies, neovascularisation was detected in approximately 1.6%–90% of symptomatic tendons. In one study, a Doppler signal was identified in 63% of 63 symptomatic tendons. 19 In contrast, another investigation detected Doppler flow in only 2 of 128 tendons, 25 illustrating substantial variability in reported findings across cohorts and clinical contexts (See Figure 2).
Detection rates were extracted from studies reporting baseline prevalence data. Several included studies reported quantitative vascular measures, reliability outcomes, or treatment-related changes rather than detection prevalence and were therefore not represented in this figure. Detection denominators varied across studies (per tendon or per participant) and should be interpreted cautiously. CEUS, contrast-enhanced ultrasound; DUS, Doppler ultrasound.
In studies using CEUS, neovascularisation was detected more frequently in symptomatic tendons. Within a single cohort, CEUS identified vascular flow in 83% of cases, compared with 54% using DUS. 14 In a separate study, CEUS-derived microvascular volume was reported to be more sensitive than standard Doppler techniques and showed a moderate association with clinical symptoms. 18
Formal diagnostic accuracy measures such as sensitivity, specificity, predictive values, or contingency table data were inconsistently reported across studies, precluding pooled analysis or standardised accuracy comparisons; therefore, comparisons between diagnostic imaging techniques are based primarily on reported detection rates and relative detection capability. In addition, detection rates should be interpreted with caution due to heterogeneity in reporting denominators, with some studies presenting outcomes per tendon and others per participant, alongside variation in study populations ranging from athletic cohorts to clinical samples.
Characteristics of Neovascularisation
Neovascularisation was predominately located in the mid-portion of the Achilles tendon or within the adjacent paratenon. Low-velocity Doppler signals were observed in degenerative tendon regions in one study, with vessel counts decreasing over time during conservative management. 24 In another investigation, Doppler signal intensity was shown to reduce immediately following physical activity, suggesting an acute load-related vascular response. 23 In contrast, microvascular volume was reported to remain stable over time in a separate cohort, supporting its association with chronic pathology rather than transient loading effects. 18
Studies employing CEUS provided greater anatomical detail of neovascularisation, including visualisation of vessel morphology and branching patterns that were not clearly distinguishable using Doppler techniques alone. 14
Association With Symptoms and Clinical Outcomes
The relationship between neovascularisation and clinical symptoms, including pain and functional limitation, was inconsistent across studies. No significant association between Doppler-detected neovascularisation and pain intensity was observed in asymptomatic or symptomatic athletes in one investigation. 25 Similarly, substantial vascular flow identified with CEUS was reported alongside wide variability in symptom severity in another study. 14
In contrast, several studies suggested potential clinical relevance of neovascularisation for monitoring purposes rather than diagnostic prediction. Reductions in neovascular signal following focused extracorporeal shockwave therapy were accompanied by improvements in pain in one cohort. 27 Elsewhere, vascular surface area quantification was proposed as a tool for tracking rehabilitation progress rather than establishing diagnosis. 26 Finally, although baseline vascularity did not predict treatment outcomes, longitudinal changes in neovascularisation were moderately associated with clinical improvement after 12 weeks in another study. 19
Discussion
This systematic review synthesised evidence from eight studies evaluating the diagnostic utility of DUS and CEUS in detecting neovascularisation in Achilles tendinopathy. All eight studies employed DUS, while two studies additionally incorporated CEUS. Both diagnostic techniques identified neovascularisation in symptomatic tendons, yet their diagnostic sensitivity and clinical relevance varied, influenced by imaging depth, signal resolution, and methodological design.
The DUS was the more frequently used diagnostic technique, likely due to its wide availability, non-invasive nature, and ease of application in clinical practice. Power Doppler was particularly effective in visualising vascularity in the mid-portion of tendons, often correlating with morphologically degenerated regions. 32 However, limitations were noted in detecting microvascular flow, particularly in deeper or subtler regions of pathology. De Vos et al 19 suggested that DUS may underestimate neovascularisation, particularly in chronic cases or where flow is minimal. Moreover, the signal produced by DUS is susceptible to machine settings, transducer pressure, and operator variability, which can compromise consistency. 35
The CEUS, although investigated in only two included studies, appeared to demonstrate greater detection capability of neovascularisation. Evidence from broader musculoskeletal imaging literature, including studies not meeting the specific inclusion criteria of this review, similarly indicates that contrast-enhanced techniques improve visualisation of microvascular perfusion compared with conventional Doppler methods, particularly in low-flow or deep tissue environments. This wider evidence base supports the observed trend towards enhanced vascular detection with CEUS while reinforcing the need for further direct comparative research, specifically in Achilles tendinopathy. Across the included studies, CEUS identified more extensive vascular flow patterns, including deep or low-flow vessels, compared with DUS.14,18 This improved detection is likely due to CEUS’s ability to visualise tissue perfusion at the capillary level via microbubble contrast agents, enabling direct assessment of blood volume and flow kinetics. 36 In contrast, DUS measures Doppler shifts caused by moving red blood cells, which limits its sensitivity in low-volume or slow-flow environments. In addition, CEUS provides contrast-specific imaging modes that reduce artefact and improve spatial resolution, making it less susceptible to the operator-dependent variability that limits DUS. 37
Although CEUS showed greater diagnostic imaging sensitivity, this conclusion must be interpreted with caution. The current evidence base for CEUS is small and methodologically uneven, with only two studies meeting the inclusion criteria. Both were observational and differed in imaging protocols, contrast agent administration, and interpretation methods. Therefore, while CEUS shows promise as an advanced imaging tool, these findings should not be overgeneralised until further high-quality research validates its clinical utility.
When comparing CEUS and DUS across diagnostic themes, several patterns emerged. Importantly, the utility of the imaging modality itself should be distinguished from the clinical utility of the biomarker being measured, as enhanced detection capability does not necessarily translate into improved diagnostic or prognostic value. Regarding depth of vascularity, CEUS was uniquely capable of detecting fine vessel branching and deep microvascular networks that DUS often failed to visualise. 14 In terms of symptom correlation, neither modality demonstrated a consistent association between vascular signal and pain or functional limitation. Vascularity was frequently observed in tendons irrespective of symptom severity in two studies.14,25 Notably, De Marchi et al 14 reported abundant neovascularisation detected by CEUS but found no significant correlation between vascularisation and pain or disability, further highlighting the inconsistent clinical relevance of vascular findings across studies. In relation to treatment outcomes, changes in Doppler-detected vascular signals were reported following therapeutic interventions or physical activity in several studies, suggesting that vascular imaging may be more informative for monitoring rehabilitation than for establishing an initial diagnosis.23,27 This pattern supports the view that imaging biomarkers such as neovascularisation may function more effectively as indicators of biological activity or treatment response rather than definitive markers of pathology and aligns with broader literature on tendinopathy imaging, which has consistently questioned the reliability of neovascularisation as a biomarker for pain. 38 A recent review by Rabello and colleagues 20 emphasised the importance of integrating clinical findings with imaging and discouraged over-reliance on vascular signal alone. Imaging consensus papers have likewise called for standardisation in ultrasound protocols, both in equipment settings and interpretation thresholds. 39
Across the included studies, variation in imaging methodology was a persistent limitation. Differences in Doppler settings including probe pressure, patient positioning, and operator training limited comparability. Beyond technical variability, both DUS and CEUS are inherently operator-dependent diagnostic imaging techniques. Image acquisition, optimisation of machine settings, probe positioning, and interpretation of vascular signals rely on operator expertise and training. Although CEUS may reduce some artefacts through contrast-specific imaging modes, it still requires precise timing of contrast administration, consistent acquisition protocols, and subjective interpretation of perfusion patterns. Inadequate standardisation or variability in operator experience may therefore affect reproducibility and limit generalisability across clinical settings. 40 Van der Vlist et al 26 addressed this issue by developing a surface area quantification (SAQ) method to improve objectivity. Similarly, CEUS studies varied in microbubble contrast dose and image capture protocols, limiting direct comparisons. These inconsistencies highlight the need for standardised imaging protocols, particularly if CEUS is to be integrated more widely into clinical workflows.
Ultimately, while DUS remains the most practical primary diagnostic imaging tool, due to its accessibility and cost-effectiveness, CEUS appears to offer superior visualisation of microvascular changes. It may even be more informative in complex or ambiguous cases.
The findings of this review have implications for both clinical practice and future research. The results reinforce that ultrasound-detected neovascularisation should be interpreted as an adjunct to clinical assessment rather than a standalone diagnostic marker, with Doppler techniques remaining appropriate for routine evaluation and CEUS potentially offering additional value in complex cases. The review also highlights the need for standardised imaging protocols, consistent outcome definitions and adequately powered comparative studies incorporating validated clinical measures. Establishing clear methodological frameworks will be essential to determine whether neovascularisation functions more effectively as a treatment-response biomarker rather than a diagnostic indicator.
Limitations
As with all evidence syntheses, this review is subject to limitations. Although CEUS demonstrated greater sensitivity for detecting microvascularity compared with Doppler techniques in the included studies, the evidence base remains limited, with only two studies employing CEUS. This restricts the strength of comparative inferences and precludes definitive conclusions regarding modality superiority. Therefore, findings should be interpreted as preliminary indications of differential detection capability rather than conclusive evidence of diagnostic advantage. Eligibility criteria were restricted to English-language publications and participants aged 18–65 years, which may limit generalisability. Language restrictions can introduce publication bias and reduce representation of studies conducted in non-English-speaking regions, while exclusion of older adults may reduce applicability to populations with age-related tendon degeneration commonly encountered in clinical practice. In addition, CEUS availability varies geographically and is more frequently implemented in tertiary or research settings than in community sonography environments, potentially influencing external validity across health care systems and practice contexts. Only a small number of studies directly compared CEUS and DUS, and diagnostic accuracy metrics were inconsistently reported; consequently, comparisons primarily reflect relative detection capability rather than definitive diagnostic accuracy. Imaging protocols varied widely, including Doppler settings, operator technique, and contrast use, which reduced comparability. Most studies had small sample sizes and lacked blinding. Independent dual screening with calculation of inter-rater agreement statistics was not performed, which may introduce reviewer selection bias despite secondary verification of eligibility decisions. In addition, some potentially relevant studies could not be retrieved despite attempts through institutional database access and inter-library loan services. Publication bias cannot be excluded. Although grey literature sources were explored, unpublished and non-peer-reviewed studies were not included in the final synthesis, which may have contributed to the over-representation of studies demonstrating detectable neovascularisation. These limitations highlight the need for standardised imaging protocols and larger, high-quality comparative trials.
Conclusion
This systematic review compared the detection capability and reported diagnostic indicators of DUS and CEUS for identifying neovascularisation in patients with Achilles tendinopathy. The findings demonstrate that both diagnostic imaging techniques can identify neovascular changes, with CEUS showing greater detection of microvascularity, particularly for small or deeply located vessels. However, DUS remains the more accessible and practical option for routine clinical use due to its availability, ease of application, and lower cost.
Neovascularisation was commonly identified in symptomatic tendons, confirming its role as a frequent feature of Achilles tendinopathy. However, its association with pain and functional limitation was inconsistent. This reinforces the need for clinicians to interpret vascular findings alongside clinical symptoms and patient-reported outcomes, rather than relying on diagnostic imaging alone for diagnosis or treatment decisions.
While CEUS may provide greater detail in complex or inconclusive cases, it is not widely implemented in standard musculoskeletal practice. Its potential lies more in research settings or advanced clinical evaluations. Both diagnostic imaging techniques may play a more meaningful role in monitoring treatment progress, where changes in vascularity appear to correspond with symptom improvement in some studies.
Further research is required to strengthen the evidence base comparing DUS and CEUS in Achilles tendinopathy. Future studies should prioritise direct comparative diagnostic accuracy designs with larger, adequately powered samples, blinded assessment of imaging findings, and standardised acquisition and interpretation protocols. Such methodological rigour is essential to determine the true diagnostic value of neovascularisation and to clarify how advanced ultrasound techniques should be integrated into routine clinical practice. When applied within a patient-centred framework, sonography remains a valuable tool for both assessment and monitoring of Achilles tendinopathy.
Footnotes
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.