CASE 16451 Published on 16.09.2019

A considerable overlook of rotator cuff avulsion fracture on ultrasound

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Yaqun Tang2, Langqing Zeng1, Weiwen Chen2, Heng Zhang3, Jing Huang2, Jinping Sun3, Wei Li4

1 M.D., Division of Orthopedics, Zhuhai People’s Hospital, Zhuhai Hospital Affiliated to Jinan University
2 M.D., Department of Ultrasound, Zhuhai People’s Hospital, Zhuhai Hospital Affiliated to Jinan University
3 B.D., Department of Ultrasound, Zhuhai People’s Hospital, Zhuhai Hospital Affiliated to Jinan University
4 B.D., Department of Radiology, Zhuhai People’s Hospital, Zhuhai Hospital Affiliated to Jinan University

Patient

53 years, female

Categories
Area of Interest Musculoskeletal bone, Musculoskeletal soft tissue ; Imaging Technique CT, MR, Ultrasound
Clinical History

A 53-year-old female patient, presenting with pain and functional weakness of right shoulder after rolling on the ground, was admitted to our hospital. On physical examination, there were no visible contusions, but moderate tenderness and dysfunction of abduction and flexion on the shoulder. No prior injury or medical history was reported.

Imaging Findings

Preoperative plain radiograph evaluation of the right shoulder showed some strip-shaped high density in the subacromial space, supra-posterior to the humerus head (Fig 1). The followed CT scan assessment showed the strip-shaped high density was located in subacromial space, arranging around the medial and posterior margin of the proximal humerus (Fig 2A-C). The MRI showed an abnormal signal on the whole thickness of the supraspinatus tendon (Fig 2D-F). Ultrasonography showed an irregular bone cortex of the greater tuberosity of the humerus (Fig 3D). The supraspinatus tendon was thin and minimally elastic, where there was a hypoechoic area, involving both the bursal and articular sides of the tendon (Fig 3A). Besides, the focal structure of the infraspinatus tendon was disorganised and discontinuous. Dense spot-shaped echo shadows were dispersedly distributed in the region of both the supraspinatus tendon and infraspinatus tendon. A strong arc-shaped echo was observed at the junction area of the muscle and tendon of infraspinatus next to the mesoscapula (Fig 3E, 3F). It was confirmed to be a rotator cuff avulsion fracture operatively (Fig 4).

Discussion

Avulsion fracture of the greater tuberosity of the proximal humerus associated with rotator cuff tear is rare, usually owing to excessive traction of the attachment of rotator cuff caused by high-energy trauma, such as proximal humeral fracture and anterior dislocation of the shoulder [1-3]. The superiorly displaced bone fragments on rotator cuff avulsion fracture will cause shoulder impingement, leading to shoulder pain and malfunction, even retorn cuff, which may further cause traumatic articular adhesion and so on [4]. At present, the academic community believes that the fracture of the humerus with a displacement of more than 5mm should be performed with surgical treatment [5-8]. As for calcific tendinitis, no intervention is required for asymptomatic individuals and surgical removal is feasible when conservative treatment is invalid for symptomatic patients [9-11]. Therefore, it is important to identify avulsion fracture and calcific tendinitis to avoid unnecessary complementary examinations and aggressive surgery.

For patients with shoulder trauma, it is usually necessary to take a series of plain films [12]. If a fracture is suspected on films, a computed tomography (CT) scan is often needed for further detecting the degree of comminution and loss of local bone mass [13,14]. A minority of fractures involving soft tissue injuries such as rotator cuff are necessary for magnetic resonance imaging (MRI). However, few works of literature reported the sonographic assessment of avulsion fractures. Paramanathan et al. revealed that ultrasound correctly detected a rare occult triceps avulsion fracture rupture case missed by plain films [15]. Alnaif et al. reported ultrasound accurately diagnosed an isolated extensor carpi radialis longus via detecting the avulsed bony fragment attached to the tendon [16]. To our knowledge, this is the first case of rotator cuff avulsion fracture both misdiagnosed by CT and ultrasound as calcific tendinitis.

The purpose of this case report is to analyse the possible reason of misdiagnosis on ultrasound to further provide more cautions for sonographers on differentiating rotator cuff tendon avulsion fracture from calcific tendinitis and degeneration because of the different clinical management.

The argues in sonographic diagnosis focus on the irregular cortical bone of the greater tuberosity and the arc-shaped strong echo on the posterior medial aspect of the humeral head, just below the mesoscapula. The preliminary consideration is to differentiate the degeneration and the calcific tendinitis from the avulsion fracture. The greater tuberosity was carefully examined with only a relatively flat area and no obvious discontinuity on the cortical bone (Fig. 2D). Besides, the bone fracture should have been located superior to the mesoscapula for the case was mainly involved in the supraspinatus tendon if it is an avulsion fracture. Besides, the well-defined curvilinear strong echo was much more similar to the dense calcification and there is some scattered spotted strong echo within the tendon. Therefore, the sonographer was prone to diagnose calcific tendinitis and degeneration. 

As for the reasons for misdiagnosis, the author believes that there are two aspects. Firstly, the lack of sufficient recognition on the morphology of the greater tuberosity and the characteristics of various fracture lines is the key point. The normal cortex of greater tuberosity is a smooth, curvilinear, strong-echo surface with obvious posterior acoustical shadowing [17]. Just as White et al. reported, the sonographer in the present case thought the presence of a sharply demarcated defect or a significant discontinuity of the bone cortex strongly indicates a fracture [18]. However, in the present case, neither of these two signs appeared. Instead, the greater tuberosity was morphologically abnormal in the case with a small sharp bony prominence adjacent to the “flat area” at the avulsion area on the greater tuberosity of right humerus via retrospective analysis on ultrasound (Fig. 2D), which was overlooked during the examination. The sonographer misinterpreted the abnormal morphological changes of greater tuberosity as degeneration. Although degenerative irregularity is usually a smoother unevenness change, no sharp bony prominence, and the dome-shaped greater tuberosity can be roughly outlined (Fig. 2B, 2C), it is still difficult for ultrasound to distinguish the degenerative irregularity of the tuberosity from a fracture [19]. The lack of visualisation of obvious discontinuity on the cortical bone of the greater tuberosity, just as the defect but still continuous cortex bone (Fig. 2D) in the present case, may contribute to the misinterpretation. Further, advance the understanding of the characteristics of various fracture lines is beneficial for recognition of the corresponding ultrasonic signs. Actually, the fracture line of avulsion fracture is horizontal [20], consistent with the “flat area” in the present case. Besides, avulsion fractures are usually involved in the superficial cortex of bone and the residual cortical layer can still be continuous, which can better explain the appearance of the defect but still continuous cortex bone. Retrospectively analyzing the ultrasonogram of the “flat area” in this case carefully, an “equal-like” strong echo can be seen between the sharp bony prominence and the “flat area” (Fig. 2D). Research has reported that this sign named “double-line sign” with the incidence rate of about 93% and high positive predictive value in the fracture, was conducive to improve the detection rate of occult fracture missed by plain film [21]. Due to the lack of understanding, the sonographer missed the sign.

In addition, there is insufficient understanding of the spatial adjacent structure of the supraspinatus muscle. Since the bone fragment was located inferior to mesoscapula, we considered the arc-shaped strong echo as a lesion within infraspinatus muscle. Considering the majority of complete torn cuff being supraspinatus tendon, the arc-shaped strong echo should have been above the mesoscapula if it was an avulsion bone fragment, so avulsion fracture was excluded from the diagnosis combined with the overlooked fracture signs. However, it was confirmed that the bone fragment was avulsed from the attachment area of the supraspinatus tendon intraoperatively. The reason for misinterpretation may be attributed to the insufficient understanding of the spatial adjacent structure of the supraspinatus tendon. Actually, the mesoscapula is an oblique bony structure outstretching superiorly and laterally, and its terminal end is acromion. Since the supraspinatus tendon runs through the subacromial space, and the posterior superior part is the acromion, the retraction path goes through the space below the acromion. When the displacement of the avulsion bone fragment is mild, it can be located just below the scapula. Therefore, the doubt of this case was solved.

In summary, besides the trauma history and rotator cuff injury, deepening the understanding on morphology and corresponding sonographic features of the greater tuberosity and the various fracture lines in avulsion fracturelike the "horizontal line sign" and "double-line sign" and sharp bony prominence besides the defect on the greater tuberosity, and the spatial adjacent structure of the supraspinatus muscle, can make it simple to identify avulsion fracture quickly and accurately for sonographers.

 

Written informed patient consent for publication has been obtained.

Differential Diagnosis List
Rotator cuff avulsion fracture
Calcific tendinitis combined with degeneration
Enthesopathy combined with degeneration
Epiphysis (juvenile; special site)
Final Diagnosis
Rotator cuff avulsion fracture
Case information
URL: https://www.eurorad.org/case/16451
DOI: 10.35100/eurorad/case.16451
ISSN: 1563-4086
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