The Hidden Burden of Entheseal Pathology in Lower-Limb Pain: A Real-World Ultrasound Study of 667 Adults

Abstract

Objective

To address the limited recognition of structural causes of lower-limb pain and the lack of real-world data on entheseal pathology, we evaluated ultrasound-detected entheseal and tendinous abnormalities in an unselected outpatient population, highlighting the underuse of musculoskeletal ultrasound (MSK US) in early diagnostic assessment despite the frequent misclassification of these conditions as nonspecific soft-tissue or degenerative disorders.

Patients and Methods

We conducted a retrospective analysis of 667 consecutive adults undergoing standardized MSK US for lower-limb pain in a general ambulatory orthopedic clinic. Fourteen predefined entheseal and tendinous sites across the hip, knee, and ankle–foot regions were evaluated using Outcome Measures in Rheumatology criteria. Prevalence, anatomical distribution, bilaterality, and clinical predictors were assessed using descriptive statistics and multivariable logistic regression.

Results

Ultrasound-confirmed enthesopathy or tendinopathy was present in 152 of 667 patients (22.8%). Lesions most frequently involved the gluteus medius tendon and plantar fascia (5.5% each, n=37), followed by the semimembranosus (2.8%, n=19), patellar (2.6%, n=17), and Achilles tendons (4.2%, n=28). Abnormalities were predominantly unilateral (<10% bilateral). Increasing age was the only independent predictor of entheseal pathology (adjusted OR 1.26 per 10-year increase; 95% CI, 1.08-1.47). Sex, body mass index, diabetes, and rheumatologic disease were not relatively associated with pathology.

Conclusion

Entheseal and tendinous abnormalities are common among symptomatic adults in everyday outpatient practice. Systematic integration of MSK US as a first-line assessment tool could improve diagnostic precision and enable targeted management strategies. These findings provide population-relevant evidence to inform musculoskeletal care pathways and health system decision-making.

Musculoskeletal disorders are among the leading causes of pain, disability, and health care utilization worldwide.^1,2 Lower-limb pain generates substantial primary and specialist care visits, work absenteeism, and diagnostic imaging costs.³ Within this broad spectrum, enthesopathies and tendinopathies represent a frequent but often under-recognized source of symptoms. In routine practice, they are commonly labeled as nonspecific hip, knee, or heel pain, and their true contribution to the clinical burden across outpatient settings remains poorly quantified.^4,5

Patients presenting to ambulatory orthopedic clinics constitute a heterogeneous group, ranging from young adults with sports-related overload injuries to older individuals with degenerative, metabolic, or inflammatory conditions.⁶ Most existing data on entheseal pathology come from narrowly defined cohorts, such as competitive athletes or patients with spondyloarthritis and psoriasis. These disease-specific studies report high prevalence of ultrasound-detectable entheseal abnormalities but provide limited insight into how often such lesions occur in unselected symptomatic adults seen in everyday practice.^7,8 Practice-based epidemiological data are needed to inform diagnostic pathways, triage decisions, and rational use of imaging and rehabilitation resources.

Entheses are specialized anatomical structures that anchor tendons, ligaments, fasciae, and joint capsules to bone, acting as biological stress buffers that distribute mechanical loads. Disruption of this adaptive capacity—through repetitive microtrauma, age-related degeneration, or metabolic dysregulation—can lead to microdamage, fibrocartilaginous metaplasia, and failed healing, processes collectively referred to as enthesopathy.^9,10 Experimental and imaging studies suggest that mechanical stress interacts with inflammatory and immune pathways, including prostaglandin E₂ signalling and the IL-23/IL-17 axis, to drive local tissue remodeling and, in some cases, aberrant new bone formation.¹¹ Fibrocartilaginous entheses of the lower limb, such as the gluteus medius, patellar tendon, Achilles tendon, and plantar fascia, are particularly vulnerable to these load-related injuries.¹²

Musculoskeletal ultrasound (MSK US) is widely available, relatively inexpensive, and capable of visualizing structural and inflammatory changes at the tendon–bone interface in real time. Despite these advantages, it remains underused as a first-line diagnostic tool for lower-limb pain.¹³ In clinical practice, trochanteric pain is often attributed to bursitis rather than gluteus medius enthesopathy, and semimembranosus insertional lesions are rarely considered as a cause of posterior knee pain. Such diagnostic biases create a gap between underlying structural pathology and the labels applied in the clinical record, potentially delaying targeted interventions and contributing to chronic symptoms and repeated healthcare contacts.14, 15, 16, 17 Systematic integration of ultrasound into outpatient assessment could help close this gap by directly linking anatomical pathology with clinical presentation and by clarifying which patients truly benefit from rehabilitation, injections, or further imaging.^18,19

Against this backdrop, we conducted a large, real-world observational study in an unselected cohort of adults referred for lower-limb ultrasound in a general orthopedic outpatient clinic. The primary objective was to determine the prevalence and anatomical distribution of ultrasound-confirmed enthesopathies and tendinopathies in symptomatic outpatients. A secondary objective was to identify demographic and metabolic factors associated with active entheseal pathology. By characterizing the hidden burden and pattern of these conditions in routine care, our study aims to inform clinical guidelines and health system strategies for the diagnostic work-up of lower-limb pain.

Patients And Methods

Study Design and Participants

This retrospective observational study included consecutive adult patients who underwent MSK US of the lower limb from January 1, 2021 to December 30, 2022, in a general orthopaedic outpatient clinic within a European community health care setting. Patients were referred for ultrasound due to nonspecific lower-limb pain localized to the hip, knee, ankle, or foot, without predefined diagnostic categories, reflecting routine first-contact orthopedic practice. The clinic serves a broad regional population and functions as a first-contact specialty service for lower-limb pain.

Eligible participants were identified through electronic medical records. Inclusion criteria were: (1) age ≥18 years; (2) complete ultrasound documentation; and (3) clinical symptoms localized to the hip, knee, ankle, or foot.

Exclusion criteria comprised: (1) history of prior orthopedic surgery involving the examined limb and (2) incomplete imaging records or clinical data.

The study was conducted in accordance with the Declaration of Helsinki. Ethical approval was waived due to the retrospective nature of the analysis, in line with national regulations for non-interventional studies. All patients provided written consent for the use of anonymized imaging and clinical data for research and publication purposes.

This design enabled the evaluation of real-world diagnostic patterns in an unselected symptomatic outpatient population and allowed a translational interpretation of ultrasound findings in the context of routine clinical decision-making.

Ultrasound protocol

All examinations were performed using high-resolution ultrasound systems equipped with linear (3-12 MHz) and, when needed, convex (1-6 MHz) transducers. Patients were positioned according to standardized protocols specific to the anatomical region examined.

Power Doppler settings were optimized for low-flow detection. Longitudinal and transverse planes were acquired routinely, maintaining the transducer perpendicular to the tendon axis to minimize anisotropy. All scans were performed by experienced musculoskeletal sonographers following a uniform protocol used in routine ambulatory care.

The imaging protocol was designed to replicate real-life clinical conditions rather than experimental imaging conditions, thereby enhancing the external validity and generalizability of the findings.

Diagnostic Criteria

Active enthesopathy was defined in accordance with the Outcome Measures in Rheumatology (OMERACT) consensus¹⁶ as the presence of ≥1 of the following sonographic features: (1) entheseal thickening, (2) hypoechogenicity, (3) loss of normal fibrillar architecture, and (4) increased vascularity on Power Doppler imaging. No predefined quantitative thresholds were applied for entheseal thickening or Doppler signal. All abnormalities were assessed qualitatively in accordance with OMERACT definitions, reflecting routine clinical practice. To reduce variability, examinations were performed by experienced musculoskeletal sonographers using a standardized imaging protocol. Isolated enthesophytes, calcifications, or cortical irregularities without inflammatory features were not classified as active enthesopathy. Tendinopathy was diagnosed when abnormalities were confined to the tendon structure (thickening, echotexture loss, or calcification) without adjacent bony involvement. The use of standardized OMERACT definitions was intended to ensure consistency and reproducibility across both clinical and research settings.^16,20

Data Collection

Clinical and demographic characteristic variables including age, sex, BMI, presence of diabetes mellitus, and rheumatologic comorbidities were extracted from medical records.

Each ultrasound examination was systematically assessed for the presence or absence of active enthesopathy or tendinopathy at 14 predefined anatomical sites across 3 anatomical regions: hip (gluteus medius/minimus, proximal adductor, and proximal hamstrings), knee (semimembranosus, patellar tendon, biceps femoris, iliotibial band, pes anserinus, and quadriceps tendon), ankle/foot (plantar fascia, Achilles tendon (proximal, midportion, and insertion), and tibialis posterior tendon). For each site, laterality (unilateral/bilateral) was recorded. All data were entered into a structured database for subsequent statistical analysis. Imaging findings were based on direct assessment of ultrasound examinations performed according to a standardized protocol, rather than solely on written reports.

Statistical Analyses

Analyses were performed using R software (version 4.3.1). Continuous variables were expressed as mean ± SD, and categorical variables as counts and percentages. Statistical significance was set at P<.05 (two-sided). Baseline characteristics were summarized for the overall cohort and stratified by the presence of ultrasound-confirmed enthesopathy. Overall prevalence and site-specific prevalence (with Wilson 95% CIs) were calculated. Comparative analyses were performed to assess differences between groups. Categorical variables, such as sex, were compared using the χ² test or Fisher’s exact test, as appropriate. Differences in age distributions between groups were evaluated using the Mann–Whitney U test. Trends in prevalence across age categories were assessed using the Cochran–Armitage test for trend.

Multivariable analysis was performed using binary logistic regression to identify independent predictors of active enthesopathy. The model included the following prespecified covariates: age, sex, BMI, presence of diabetes mellitus, and rheumatologic disease. Adjusted odds ratios (ORs) with 95% confidence intervals were reported. Model performance fit was assessed using the Hosmer–Lemeshow test. Multicollinearity among covariates was evaluated using variance inflation factors with a threshold of <2 indicating acceptable levels.

To account for multiple comparisons, P-values were adjusted using the Benjamini–Hochberg false discovery rate method. Sensitivity analyses were conducted by excluding patients with rheumatologic comorbidities and those with a history of contralateral orthopedic surgery, to test the robustness of findings. This analytical framework was designed to identify clinically meaningful predictors and generate evidence applicable to real-world diagnostic pathways for lower-limb pain.

Results

Cohort Characteristics

A total of 667 adults were included, of whom 342 (51.3%) were women. The mean age was 52.4±16.2 years. The mean BMI was 28.1±4.2 kg/m², with 58.0% of participants classifies as overweight or obese. Diabetes mellitus was present in 8.0% of the cohort, whereas rheumatologic disease was identified in 1.5%. Baseline characteristics are summarized in Table 1.

Table 1.

Baseline Characteristics of the Study Population (N=667)

Characteristic	Value
Age (y), mean ± SD	52.4 ± 16.2
Sex, n (%)	Women: 342 (51.3%); Men: 325 (48.7%)
BMI, kg/m2 (mean ± SD)	28.1 ± 4.2
Overweight/obesity, n (%)	387 (58.0%)
Diabetes mellitus, n (%)	53 (8.0%)
Rheumatologic disease, n (%)	10 (1.5%)

Abbreviations: BMI, body mass index.

Prevalence and Anatomical Distribution of Entheseal Pathology

Active enthesopathy or tendinopathy was identified in 152 of 667 patients, corresponding to an overall prevalence of 22.8%. The number of affected sites per patient ranged from 1 to 4 (median 1). Lesions were distributed across the hip (25.7% of all abnormalities), knee (29.6%), and ankle/foot regions (44.7%). The most frequently affected structures were: gluteus medius tendon 5.5% (n=37), plantar fascia 5.5% (n=37), Achilles tendon (any portion) 3.9% (n=26), semimembranosus tendon 2.8% (n=19), and patellar tendon 2.6% (n=17).

Detailed site-specific prevalence data are presented in Table 2, while the overall anatomical distribution is illustrated in Figure 1. Bilateral involvement was infrequent across all examined sites. Bilateral abnormalities were observed in the gluteus medius tendon in 3 of 37 cases (8.1%), plantar fascia in 2 of 37 cases (5.4%), and Achilles tendon (any portion) in 2 of 28 cases (7.1%). All other anatomical sites reported low rates of bilateral involvement (<5%).

Table 2.

Frequency and Prevalence of Entheseal and Tendinous Lesions by Anatomical Site (N=667)

Anatomical Site	Number of cases (n)	Prevalence (%)
Gluteus medius tendon	37	5.5
Proximal adductor attachment	1	0.2
Proximal hamstrings attachment	1	0.2
Semimembranosus tendon	19	2.8
Patellar tendon	17	2.6
Biceps femoris attachment	4	0.6
Iliotibial band	3	0.5
Pes anserinus tendons	1	0.2
Quadriceps tendon	1	0.2
Plantar fascia	37	5.5
Achilles tendon–distal	14	2.1
Achilles tendon–proximal	12	1.8
Achilles tendon–insertion	2	0.3
Tibialis posterior tendon	3	0.5

Figure 1.

Prevalence of enteseal and tendinous lesions by anatomical site (N=667).

Age and Sex Patterns

Patients with ≥1 entheseal or tendinous lesion were older than those without pathology (mean age 56.1±14.7 vs 51.2±16.4 years; P=.002). The prevalence of enthesopathy increased progressively across age quartiles (P for trend=.004): Q1 (≤38 years) 15.2%; Q2 (39-52 years) 20.5%; Q3 (53-63 years) 24.7%; and Q4 (≥64 years) 31.0%. Women exhibited a slightly higher prevalence of any enthesopathy (24.6%) compared with men (21.0%); however, this difference was not statistically significant (P=.28).

Predictors of Entheseal Pathology

In multivariable logistic regression, age was the only independent predictor of active entheseal pathology (adjusted OR 1.26 per 10-year increase; 95% CI, 1.08-1.47; P=.003). Sex, BMI, diabetes mellitus, and rheumatologic disease were not statistically significantly associated with the outcome in adjusted models (all P>.2). Model calibration was satisfactory (Hosmer–Lemeshow P=.47), and multicollinearity was minimal (variance inflation factor<1.6). Detailed regression results are shown in Table 3, with corresponding effect estimates illustrated in Figure 2.

Table 3.

Multivariable Logistic Regression for Predictors of Entheseal Pathology

Characteristic	Adjusted OR	95% CI	P
Age (per 10-year increase)	1.26	1.08-1.47	.003
Sex (female)	1.18	0.87-1.62	>.2
BMI (per 1 kg/m2)	1.04	0.99-1.09	.09
Diabetes mellitus	1.21	0.72-2.07	>.2
Rheumatologic disease	1.33	0.41-4.29	>.2

Figure 2.

Predictors of entheseal pathology (multivariable model).

Excluding patients with known rheumatologic disease (n=10) did not change prevalence estimates or the importance of predictors. When analyses were restricted to patients with single-site lesions (n=118), the same age-related gradient was observed, confirming the robustness of the findings across clinically relevant subgroups.

Discussion

In this large real-world cohort of 667 symptomatic adults referred for lower-limb assessment, nearly one in 4 patients reported active enthesopathy or tendinopathy on ultrasound. The distribution of lesions—predominantly involving the gluteus medius tendon and plantar fascia—highlights specific anatomical sites that may be systematically overlooked during routine clinical evaluation. Most lesions were unilateral and mechanically driven, and increasing age emerged as the only independent predictor of pathology. These findings reveal a substantial diagnostic gap in the assessment of lower-limb pain in ambulatory care. Although musculoskeletal disorders are a major contributor to global morbidity and health service use, the underlying structural causes of symptoms often remain unidentified in first-line clinical pathways.^2,21 Our results suggest that entheseal pathology constitutes a hidden but clinically relevant component of this burden.

Existing research on enthesopathy has largely focused on narrowly defined populations, particularly patients with spondyloarthritis, psoriasis, or high-level athletic activity.7, 8, 9^,17,22 These studies consistently report a high prevalence of entheseal abnormalities, especially at lower-limb insertion sites, and have established enthesitis as a key lesion in inflammatory spondyloarthropathies.^9,17,23, 24, 25 However, the applicability of these findings to general ambulatory practice is limited because participants are typically recruited from specialist rheumatology or sports medicine clinics. Only a small number of investigations have attempted to characterize the burden of entheseal pathology in unselected symptomatic populations, despite lower-limb pain being one of the most common reasons for consultation across primary and secondary care.^2,7 The 22.8% prevalence observed in the present cohort is consistent with registry-based and community data showing that tendinopathies and insertional disorders occur frequently in the general population, particularly at the knee and Achilles tendon.^7,8,26 The predominance of gluteus medius and plantar fascia involvement reflects functional biomechanics during gait and common load-distribution patterns in adults with sedentary lifestyles, elevated BMI, or age-related muscle weakening, in line with contemporary tendinopathy models.^27,28 Conversely, the relatively low frequency of Achilles and patellar tendon lesions—structures often studied in athletic cohorts—highlights that the clinical epidemiology of tendinopathies differs substantially between sports-related and general outpatient populations.^8,26,28

Population-level imaging data on entheseal abnormalities remain scarce. Existing epidemiological work has predominantly examined tendon-specific registries (eg, Denmark) or disease-focused rheumatology cohorts, leaving the general ambulatory population insufficiently characterized.^14,22,29,30 These gaps underscore the need for real-world imaging studies to refine diagnostic algorithms for lower-limb pain, particularly in nonspecialized clinical environments where misclassification is common. The consistent association between enthesopathy and age in our cohort aligns with models in which cumulative mechanical stress, microvascular compromise, and impaired tissue repair contribute to degenerative changes at the tendon–bone interface.^9,27,28 With increasing age, fibrocartilaginous entheses become less resilient to repetitive loading, leading to microdamage, maladaptive remodelling, and, in some cases, aberrant new bone formation.^9,28 Our findings support the notion that most entheseal abnormalities in community-dwelling adults are not driven by systemic inflammation but rather by localized, load-dependent processes.

This observation has implications for clinical prioritization. In many health systems, persistent lower-limb pain in older adults is initially attributed to osteoarthritis or nonspecific soft-tissue pain.² Our data suggests that entheseal pathology may account for a meaningful proportion of these presentations and could improve diagnostic precision and reduce ineffective or unnecessary interventions. From a health systems perspective, several implications emerge. First, the high background prevalence of ultrasound-detectable enthesopathy suggests that a considerable proportion of patients with lower-limb pain may be inaccurately triaged when diagnostic pathways rely solely on clinical examination or plain radiography.^2,7,31 Conditions such as trochanteric pain syndrome or posterior knee pain may be misattributed to bursitis or degenerative joint disease, delaying appropriate management, despite evidence that enthesopathy is a frequent structural correlate of symptoms in these regions.^22,29,31 Second, the identification of specific high-frequency sites—particularly the gluteus medius and plantar fascia—may help clinicians prioritize targeted ultrasound assessment in patients with persistent or diagnostically unclear symptoms. This focused approach can reduce diagnostic uncertainty and enable earlier referral to physiotherapy, load-modification strategies, or image-guided interventions.^30,32,33 Third, the lack of meaningful associations between entheseal pathology and diabetes, obesity, or sex suggests that demographic characteristics and metabolic characteristics alone are insufficient to guide diagnostic decisions. Real-time visualization of structural abnormalities through ultrasound provides actionable information that can be directly integrated into clinical decision-making and is increasingly reflected in international recommendations for the use of imaging in spondyloarthritis and related conditions.14, 15, 16^,20,30

Finally, integrating MSK US into early diagnostic workflows could reduce unnecessary imaging (eg, magnetic resonance imaging), prevent repeated consultations, and optimize resource allocation. Given the widespread availability and favorable cost profile of ultrasound, its broader adoption represents a scalable and context-appropriate strategy for improving musculoskeletal care across health care systems.^20,30 Strengths of this study include its large sample size, standardized imaging protocol, and strict use of OMERACT criteria for enthesopathy, which enhance reproducibility and generalizability.^15,16 The exclusive reliance on real-world outpatient data provides insight into diagnostic patterns that are directly relevant to clinical practice and health care planning.

Several limitations warrant consideration. The retrospective design and single-center setting may limit external validity, although the nonspecialized nature of the clinic and its broad catchment population increase applicability to community settings. The lack of magnetic resonance imaging or histopathology as reference standards restricts the ability to distinguish inflammatory from purely mechanical lesions, though this reflects the pragmatic nature of most real-world diagnostic workflows.^22,29 Interobserver variability was not formally assessed, although experienced sonographers performed all examinations using a uniform protocol. Finally, because only symptomatic patients were included, the true population prevalence of entheseal pathology is likely lower than reported here. Despite these limitations, the study provides one of the most comprehensive datasets describing the epidemiology of lower limb entheseal abnormalities in general ambulatory practice. Future research should include multicenter prospective studies integrating clinical, functional, and imaging outcomes to clarify the prognostic relevance of entheseal pathology. Incorporating patient-reported outcome measures and health utilization metrics could help determine how ultrasound-guided diagnosis influences recovery trajectories and healthcare demand. Emerging techniques such as shear-wave elastography and other quantitative ultrasound methods may offer biomarkers of tendon stiffness and enthesis integrity and assist in monitoring treatment response.34, 35, 36

At a systems level, studies evaluating diagnostic pathways—with and without routine ultrasound—could help quantify potential reductions in referrals, imaging costs, and time to definitive diagnosis.^20,32,36 Integrating imaging data with wearable technology, gait analysis, or biomechanical modeling may further advance personalized approaches to lower-limb pain. The results underscore a diagnostic gap in the management of lower-limb pain across ambulatory care. Structural causes of symptoms—particularly gluteus medius and semimembranosus enthesopathy—are often misclassified or overlooked, leading to delays in targeted treatment and increased health care utilization. Musculoskeletal ultrasound serves as a translational tool that links real-time tissue pathology to clinical decision-making. Beyond its diagnostic utility, ultrasound facilitates image-guided treatment, enables monitoring, and may help healthcare systems implement streamlined, cost-effective pathways for musculoskeletal care.

This study reports that entheseal pathology is common, under-recognized, and strongly associated with mechanical load and aging in symptomatic adults. By identifying patterns of disease that are frequently missed during routine assessment, our findings highlight the potential for MSK US to enhance diagnostic accuracy and support more efficient, evidence-informed care pathways.^{9,17,20,27,28,30} In the context of global efforts to reduce the burden of musculoskeletal conditions.² Integrating targeted ultrasound assessment into lower-limb pain pathways could improve patient outcomes while using existing imaging resources more effectively.

Conclusion

In a large, unselected cohort of adults presenting with lower-limb pain, ultrasound revealed that entheseal and tendinous pathologies are common, predominantly mechanical, and frequently overlooked during routine clinical assessment. Age emerged as the primary determinant of disease, supporting the concept that cumulative load and impaired tissue resilience—rather than systemic inflammation—drive most entheseal changes in community-dwelling adults.

These findings underscore the value of MSK US as an accessible, first-line diagnostic tool capable of identifying structural causes of pain that often remain hidden in standard clinical pathways. Earlier and more systematic incorporation of ultrasound into outpatient assessment may improve diagnostic precision, reduce unnecessary downstream imaging, and facilitate timely, targeted interventions.

By clarifying the burden and distribution of entheseal pathology in routine practice, this study provides evidence to inform clinical decision-making, optimize resource allocation, and support the development of more efficient, patient-centered musculoskeletal care pathways.

Potential Competing Interests

The authors report no competing interests.

Ethics Statement

The study was conducted in accordance with the Declaration of Helsinki. Ethical approval was waived due to the retrospective, non-interventional nature of the study, in accordance with applicable national regulations. All patients provided written informed consent for the use of anonymized imaging and clinical data for research and publication purposes.

Declaration of Generative AI and AI-Assisted Technologies in the Writing Process

During the preparation of this work the authors used ChatGPT (OpenAI, GPT-5.1 Thinking) in order to assist with language editing and improving clarity of the manuscript. After using this tool, the authors reviewed and edited the content as needed and takes full responsibility for the content of the publication.