Standardized ultrasound assessment with a classification system in greater trochanteric pain syndrome: a pilot study

Introduction

Greater trochanteric pain syndrome (GTPS) is a common cause of chronic lateral hip pain (1), which is recognized as a syndrome including trochanteric/sub-gluteus maximus or sub-gluteus medius bursitis, gluteus medius (GMED) and/or gluteus minimus (GMIN) tendinopathy or rupture, and/or ilio-tibial band pathology (2). The diagnosis of GTPS is mostly clinical based on history, pain on palpation, and findings from provocative physical examination such as the flexion, abduction, and external rotation (FABER) test (3,4).

Pelvis and hip X-rays are often the initial investigation in primary care to rule out common differentials such as hip osteoarthritis, osteonecrosis, and femoroacetabular impingement. Both ultrasound (US) and magnetic resonance imaging (MRI) provide high soft-tissue resolution to assess bursa and tendon abnormalities, representing the second-tier imaging techniques for GTPS. Although MRI has been reported to have good accuracy for diagnosis of gluteal tendon tears (5), pelvic MRI is associated with a significant number of false-positive signals, probably because of the high incidence of peritrochanteric abnormalities in asymptomatic hips (2,6,7). US is a cost-effective, widely available imaging modality which allows dynamic imaging, playing an important role in evaluating musculoskeletal disorders including GTPS, as well as guiding the therapeutic interventions (8-10).

Although previous studies have described the value of US in assessing gluteal tendinopathy and peritrochanteric pathology (11-15), standardized US procedures and definitions for the reliable evaluation of lateral hip pain are lacking. Given that optimal management of GTPS relies on detailed morphological grading, endoscopic classification (16,17) and MRI-based scoring systems (18) have been developed to stratify disease severity and guide therapeutic decision-making. Nevertheless, a standardized US-based classification system for GTPS has not been well established. Therefore, in this pilot study, we performed standardized US procedure, made clear definitions to assess the underlying pathologies of GTPS, and proposed a novel US grading system to better understand GTPS progression and severity. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1491/rc).

Methods

Patients

This prospective cross-sectional study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Sichuan Provincial People’s Hospital (No. 2023-416) and informed consent was provided by all individual participants. Patients diagnosed with GTPS by orthopedic surgeons according to the symptoms and physical examinations were prospectively included between October 2023 and December 2024. All patients were positive to the following pain provocation tests: “jump sign” after direct palpation of the greater trochanter (GT) and the “single leg stance” test (19). All patients underwent plain radiography to exclude severe hip osteoarthritis, femoroacetabular impingement, and fractures. The patient inclusion criteria were as follows: (I) aged above 18 years; and (II) typical clinical symptoms including tenderness on the outer side of the hip, Trendelenburg gait, and limited external rotation of hip abduction. The exclusion criteria were as follows: (I) severe hip osteoarthritis; (II) patients with hip replacement; and (III) patients treated with corticoid injection in the past 3 months.

The visual analogue scale (VAS) score was used to assess patient-report pain, with 0 representing “no pain” and 10 representing “worst pain”.

Standardized US examination procedure of the lateral hip

A radiologist with 10 years’ (Y.W.) experience in musculoskeletal US performed all standardized US examinations and interpreted all images. We used 2 US systems (RS80A, Samsung, Suwon, Korea; EPIQ5, Philips, Amsterdam, The Netherlands) equipped with high frequency (5–12 MHz) linear array transducers. Patients lay on the examination table in a lateral position with both the hips and knees slightly flexed in a comfortable position. The US scanning of the lateral hip is guided by the bony morphologic characteristics of the GT, which is divided into anterior, lateral, posterior, and superior-posterior facet. The GMIN tendon attaches onto the anterior facet; the anterior band of the GMED tendon attaches onto the lateral facet; and the posterior band of GMED tendon attaches onto the superior-posterior facet (12,14). The posterior facet is covered by the GT bursa and void of an attachment of tendon.

Firstly, the transducer was positioned in an anatomic oblique transverse plane perpendicular to the anterior facet (Figure 1A) to show the short-axis image of the GMIN tendon (appearing as hyperechoic above the anterior facet) (Figure 1B). Then, the transducer was rotated 90° in an anatomic oblique coronal plane (Figure 1C) parallel to the anterior facet to obtain the long-axis view of the GMIN tendon (Figure 1D). At the long-axis view of the GMIN, the GMED muscle can be seen superficial and slightly oblique to the GMIN tendon. Subsequently, the transducer was moved posteriorly slowly in an anatomic slightly anterior coronal oblique orientation to an anatomic coronal plane (Figure 2A), the lateral facet then appeared, and the entirety of the anterior band of GMED tendon came into view (Figure 2B). Notedly, there is a small region on the anterior aspect of the lateral facet where no tendon can be visualized, corresponding to the bare spot, which should not be mistaken as a tear. Continuing to scan posteriorly on the lateral facet (Figure 2C), the long-axis view of posterior band of the GMED tendon that inserts onto the superoposterior facet of the GT was obtained (Figure 2D). A careful adjustment of the transducer was made to optimize visualizing both the anterior and posterior bands of the GMED from the muscle-tendon units to the GT insertions respectively. Finally, the transducer was rotated 90° to show the short-axis view of both the anterior and posterior bands of GMED tendons located above the lateral and superoposterior facets, respectively (Figure 2E).

Figure 1 Long- and short-axis of the GMIN. (A) Transducer position and (B) corresponding short-axis image of the GMIN tendon. The hyperechoic GMIN tendon (black arrows) lies above the AF. The hyperechoic GMED tendon (red arrows) lies above the LF. (C) Transducer position and (D) corresponding long-axis image of the GMIN. The GMIN tendon (white arrows) insertion onto the AF whereas the AB-GMED (red arrows) lies over the GMIN tendon. AB-GMED, anterior band of GMED; AF, anterior facet; GMED, gluteus medius; GMIN, gluteus minimus; LF, lateral facet.

Figure 2 Long- and short-axis of the GMED tendon. (A) Transducer position and (B) corresponding short-axis view of the anterior band of the GMED tendon. The anterior (black arrows) and posterior bands (red arrows) of the GMED tendon located superficial to the GT-L and GT-SP respectively. (C) Transducer position and (D) corresponding long-axis view of the anterior band tendon is located in a relatively deep position (arrows) within the muscle and moves to a superficial position and inserts onto the GT-L. (E) Long-axis view of the posterior band of the GMED tendon, which has a relatively straight course (arrows) before inserting onto the GT-SP. Gmax, gluteus maximus; GMED, gluteus medius; GT, greater trochanter; GT-L, lateral facet of greater trochanter; GT-SP, superoposterior facet of greater trochanter.

Definitions of pathologic US findings in GTPS

Tendinosis is defined as an alteration in tendon thickness (i.e., swelling, thickening) and/or echogenicity (i.e., hypoechoic, heteroechoic, loss of fibrillar pattern) with or without vascularity on color Doppler. Intratendinous calcifications appearing as a hyperechogenic arciform shape and others showing nodular echogenicity are also considered as tendinosis. A partial-thickness tear is defined as a hypoechoic or anechoic defect on the superficial or deep surface of the tendon, with interruption of the fibrillar pattern. A full-thickness tear is defined as an anechoic defect extending to both tendon surfaces with possible tendon retraction. Dynamic hip maneuvers such as passive adduction to stretch the tendon, passive abduction to fold the tendon, or active abduction to place tension on the tendon are helpful in identifying tendon tears (14). Additional abnormal US findings including bursitis and bony alterations are recorded. Bursitis is defined as an anechoic fluid collection in the GT bursa, subgluteus medius bursa, or minimus bursa. Bony alterations are defined as cortical irregularities along the GT and/or the presence of enthesophytes (15). Any detection of blood flow signal in the gluteal tendon on color Doppler or power Doppler is defined as vascularity. Any abnormality should be confirmed in at least 2 imaging planes. Moreover, a contralateral comparison examination is performed to confirm these abnormal US findings on the painful hip.

US classification system of GTPS

Patients with GTPS are classified into 1 of 4 categories based on the pathologic findings seen on US (Table 1). Briefly: type I, isolated bursitis; type II, tendinosis of gluteal tendon with or without bursitis; type IIIA, partial-thickness tear; and type IIIB, full-thickness tear.

Another 2 radiologists (X.G. with 13 years’ experience in musculoskeletal US and K.C. with 5 years’ experience in musculoskeletal US) who were blinded to patients’ symptom severity were asked to make retrospective evaluation of images and grade all patients in order to assess the interobserver reliability of this US classification system.

Statistical analysis

The demographic data were expressed as frequencies and mean ± standard deviation. Either the t or analysis of variance (ANOVA) test was used to compare continuous variables, and Chi-squared test was used to compare categorical variables. Interobserver agreement of US classification system of GTPS was assessed using Cohen’s kappa statistic. Univariate and multivariate analyses were performed using linear regression to analyze the relationships between patients’ VAS score and the pathologic US findings in GTPS. A P value <0.05 was considered statistically significant. All statistical analyses were performed with the software SPSS 27.0 (IBM Corp., Armonk, NY, USA).

Results

Patient demographics

In total, 53 patients with 55 hips (with the bilateral hips involved in 2 patients) who satisfied both the inclusion and exclusion criteria were included in this study. There were 15 (28.3%) male and 38 (71.7%) female patients with a mean age and VAS score of 54.6±13.84 years and 6.1±1.42, respectively. All patients performed US examination and assessment successfully.

Pathologic US findings

Table 2 shows the US findings of the study groups by age, sex, and VAS score. Gluteus tendon abnormality was the most common (90.9%, 50/55) finding in patients with GTPS, of which 44 of 50 (88.0%) and 6 of 50 (12.0%) were tendinosis (Figure 3) and tendon tear (Figure 4), respectively. Patients with gluteal tendon tear had worse pain than those with tendinosis (VAS score: 8.0±0.63 vs. 6.0±1.33, P<0.001). A minority of patients (9.1%) had isolated bursitis (Figure 5), who had significantly lower VAS score than patients with tendon abnormalities (4.6±0.55 vs. 6.2±1.43, P<0.001). There was no difference in age (49.4±7.64 vs. 55.7±14.42, P=0.341) and sex (female: 100% vs. 70%, P=0.363) between patients with isolated bursitis compared with patients with gluteal tendon abnormalities. Of the 50 hips with gluteal tendon abnormalities, the GMED tendon (94.0%) was the most commonly involved. Patients with the presence of calcification or vascularity in the gluteus tendon showed significantly greater VAS score than those without these findings (P=0.031, P<0.001, Table 2). Fluid collection in peritrochanteric bursa was evident in 32.7% (18/55) hips, with 15 involving the GT bursa, 1 involving the subgluteus medius bursa, and 1 involving the subgluteus minus bursa. Meanwhile, bony abnormality in GT was evident in 72.7% (40/55) patients, among whom 62.5% had cortical irregularities and 37.5% had enthesophytes. As shown in Table 2, patients had normal US appearance of GT were younger and had less pain as compared to patients with abnormal US appearance of GT.

Figure 3 US images from a 68-year-old man with GMIN tendinosis (categorized into type II). (A) Long-axis image of a normal-appearing GMIN tendon (arrows) in the unaffected side. (B) Long-axis image reveals a thickened heterogeneous GMIN tendon (red arrows) with an echogenic calcification (yellow arrow) in the affected side. An irregularity on cortical surface of the anterior facet (green arrow) is also observed. AF, anterior facet of greater trochanter; GMIN, gluteus minimus; US, ultrasound.

Figure 4 US images from a 67-year-old woman with partial-thickness GMED tendon tear (categorized into type IIIA). (A) Short-axis image of the posterior band of GMED tendon demonstrates a thickened tendon with loss of fibrillar pattern (arrows) in the affected side. (B) Short-axis image of a normal-appearing posterior band of GMED tendon (arrows) in the contralateral side. (C) Long-axis image of the posterior band of GMED tendon (arrows) shows an undersurface partial-thickness tear (yellow arrow). (D) The undersurface partial-thickness tear (survey mark) is also observed in the short-axis image. Arrows indicated the thickened posterior band of GMED tendon. GMED, gluteus medius; GT-SP, superoposterior facet of greater trochanter; US, ultrasound.

Figure 5 US images from a 38-year-old woman with isolated bursitis (categorized into type I). Both (A) short-axis image and (B) long-axis image shows anechoic fluid accumulation in the greater trochanter bursa (arrows). The cortical surface of GT is smooth and normal. GT, greater trochanter; US, ultrasound.

We performed universal regression analyses to evaluate the relationships of pathologic US findings with patients’ self-reported pain (VAS score). As shown in Table 3, the appearance of tendon abnormalities (B =1.73, P<0.001), tendon calcification (B =1.13, P=0.031), tendon vascularity (B =2.59, P<0.001), and bony abnormalities of the GT (B =0.77, P=0.003) on US predicted greater pain intensity (all P<0.05). The presence of bursitis negatively correlated with VAS score (B =−0.82, P=0.046). Multivariate regression analysis showed that tendon abnormality, tendon calcification, and tendon vascularity were significantly correlated with VAS score (Table 3); the following equation was incorporated to describe their relationship, Y = 3.36 + 0.96 * X₁ + 1.44 * X₂ + 2.51 * X₃. Y, VAS score; X₁, tendon abnormality (1= normal, 2= tendinosis, 3= tendon tear); X₂, tendon calcification (1= presence, 0= absence); X₃, tendon vascularity (1= presence, 0= absence).

According to this model, the VAS score increased by 5.87 point in patients with the presence of gluteal tendon tear, tendon calcification, as well as vascularity, as compared to patients with normal tendon (with bursitis alone) on US.

US classifications and inter-observer reliability

As shown in Table 4, there were 5, 44, and 6 hips with GTPS categorized into type I, type II, and type III, respectively. There was no significant difference in age and sex among patients with different US classifications (P=0.312, P=0.179). Of note, patients with type I had significantly lower VAS score than those with type II and type III (4.6±0.55 vs. 6.0±1.33 vs. 8.0±0.63, P<0.001). Among 44 hips with US type II GTPS, 31 (70.5%) had gluteal tendinosis alone, and 13 (39.5%) had gluteal tendinosis with bursitis. There was no significant difference in the age (56.1±15.32 vs. 51.8±13.73, P=0.392), sex (female: 67.7% vs. 84.6%, P=0.151), and VAS score (6.0±1.37 vs. 5.8±1.28, P=0.73) between these two groups. Univariate regression analysis demonstrated that patients’ VAS score positively correlated with the US classifications system [B =1.73, 95% confidence interval (CI): 0.98–2.47, P<0.001]. The association is described by the following equation: pain = 2.57 + 1.73 * (1= US type I, 2= US type II, 3= US type III). Therefore, our US classification system could potentially represent the severity of GTPS. Between the two radiologists with experience (13 years) and less experience (5 years) in musculoskeletal US, the interobserver agreement for the US classification system for assessment of GTPS was good (weighted k =0.77, 95% CI: 0.58–0.97, P<0.001).

Discussion

US is a valuable imaging modality for diagnosing the underlying cause of GTPS and guiding percutaneous interventions according to specific pathological findings for treatment of GTPS. In this pilot study, we performed standardized US examination in patients with lateral hip pain, and assessed the reliability of a novel US classification system to describe the severity of GTPS. The findings indicated that the proposed US classification system is a reliable tool, demonstrating both excellent interobserver reliability and a significant association with pain severity in patients with GTPS.

In this study, women were 2.5 times more likely than men to have GTPS, in keeping with the higher prevalence of GTPS associated with women. Previous studies had indicated that gluteus tendinosis, gluteal tendon tear, GT bursitis, the presence of intratendinous calcifications, and bony alterations of GT are the common sonographic findings in patients with GTPS. Our data show that 90.9% of hips had gluteal tendon abnormalities, of which 88% were tendinosis, and 10.9% were tendon tears. This is consistent with other studies that have demonstrated gluteus tendinopathy is the most prevalent pathology in patients with lateral hip pain (18,20). However, few patients with GTPS in our study had full-thickness gluteus tendon tears. Notably, abnormalities of the GMED tendon were more common than those of the GMIN tendon. The low incidence of isolated bursitis (9.1%) observed in our study is consistent with the retrospective analysis by Long et al. (11), who reported a similar rate (8.1%) in a large cohort. These findings challenge the historical notion of “bursitis” as the primary cause of GTPS. Vascularity in the gluteus tendon on color Doppler was present in 9 of 55 hips, associating with pain intensity. Moreover, bony abnormalities of GT on US including cortical irregularities and enthesophytes were frequently seen, especially in older patients, and related to patients’ pain severity. The prevalence of calcium deposits has been reported to range from 10% to 97% (15,21). Herein, US detected calcification within the gluteal tendon in 16.4% hips with GTPS, and its presence predicted a more severe pain. The multivariate linear regression analysis indicated that the pathologic US findings of tendon abnormalities, the presence of calcification, and vascularity were associated with pain.

MRI is widely regarded as the gold standard for the assessment of musculoskeletal disorders (22). It has been reported to have a poor-to-moderate correlation with pain in GTPS (7,23), with a sensitivity and specificity of 73% and 95%, respectively, in diagnosing gluteal tendon tears (4). Unfortunately, it was not feasible to perform MRI for all participants in this study due to its high cost and prolonged waiting times. Consequently, it was not possible to evaluate the sensitivity and specificity of US in assessing GTPS, owing to the absence of a gold standard reference and an appropriate control group (e.g., asymptomatic hips). Further case-control studies using MRI as a reference standard are encouraged to establish the diagnostic accuracy of US and broaden its generalizability in the assessment of GTPS.

Recently, Tso et al. Al reported an MRI scoring system to grade the severity of gluteus tendinopathy (18). They provided each patient an overall Melbourne Hip MRI Score (MHIP) score ranging from 0 to 17 (most severe) according to the extent of tendon pathology, muscle atrophy, trochanteric bursitis, cortical irregularity, and bone marrow edema. Similarly, we categorized GTPS into 4 types based on ultrasonographic findings of isolated bursitis, tendinosis, and partial- and full-thickness tendon tear, which represent the disease severity. This US classification system demonstrated a positive correlation with patient VAS score, and showed excellent interobserver reliability between two radiologists with differing experience in musculoskeletal US. Although the VAS score was used in this study to evaluate pain severity, the Victorian Institute of Sports Assessment-Gluteal (VISA-G) questionnaire, which provides a more comprehensive assessment of both pain and functional impairment in GTPS (24), would have been more appropriate for correlating with the US classification. Ideally, the application of a standardized US examination and US classification system could provide clinicians a reliable tool for assessing GTPS severity, and may facilitate a more targeted treatment strategy. For instance, grade I (isolated bursitis) may respond to intrabursal corticosteroid injection (22), grade II (gluteus tendinosis) to US-guided percutaneous needle tenotomy (25), and grade III (gluteus tendon tear) to surgical repair (26). However, these applications remain speculative at present, and further studies are necessary to validate the role of US classification in guiding personized treatment decisions and predicting therapeutic outcomes.

This study has several limitations. Firstly, the relatively small sample size may limit the generalizability of the findings and could potentially introduce selection bias. Secondly, although the proposed US classification system demonstrated excellent interobserver agreement, its reproducibility across other institutions remains uncertain. Furthermore, the absence of established diagnostic standards (e.g., MRI or surgical confirmation), as previously discussed, precluded determination of the diagnostic accuracy for the proposed classification types of GTPS. Finally, the use of a comprehensive clinical assessment tool such as the VISA-G questionnaire, would have been valuable to correlate with the US classification. Despite these limitations, this study proposes a standardized US examinations and classification system for the assessment of GTPS. Further large-scale, multicenter studies are warranted to validate this US classification and to confirm its generalizability across diverse clinical settings.

Conclusions

Standardized US examinations and definitions are available in the assessment of GTPS. Our results revealed that pathological US findings of gluteus tendon abnormalities, the presence of calcification, and vascularity in gluteus tendons were associated with pain intensity. The proposed US classification system, which is based on the presence of isolated bursitis and specific gluteus tendon abnormalities, may offer clinicians a reliable tool for evaluating GTPS severity and could potentially help guide more targeted treatment strategies.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1491/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1491/dss

Funding: This work was supported by the Sichuan Science and Technology Program (No. 2024NSFSC0535).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1491/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Sichuan Provincial People’s Hospital (No. 2023-416) and informed consent was obtained from all individual participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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