DOI: 10.1148/radiol.2202001723
(Radiology. 2001;220:601-605.)
© RSNA, 2001
Ulnar Nerve Dislocation and Snapping Triceps Syndrome: Diagnosis with Dynamic Sonography—Report of Three Cases1
Jon A. Jacobson, MD,
Peter J. L. Jebson, MD,
Andrew W. Jeffers, MD,
David P. Fessell, MD and
Curtis W. Hayes, MD
1 From the Departments of Radiology (J.A.J., D.P.F., C.W.H.) and Orthopedic Surgery (P.J.L.J., A.W.J.), University of Michigan Medical Center, 1500 E Medical Center Dr, TC-2910G, Ann Arbor, MI 48109-0326. Received October 27, 2000; revision requested December 18; revision received January 31, 2001; accepted February 26. Address correspondence to J.A.J. (e-mail: jjacobsn@umich.edu).
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ABSTRACT
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Initial experience with the use of dynamic sonography of the elbow for diagnosing ulnar nerve dislocation and snapping triceps syndrome is reported. Cases of three consecutive patients who underwent sonographic evaluation of the elbow and subsequent open elbow surgery for symptomatic ulnar nerve dislocation were reviewed. Dynamic sonography of the elbow was used to aid in the accurate diagnosis of and differentiation between ulnar nerve dislocation and snapping of the medial triceps muscle.
Index terms: Elbow, 422.482 • Muscles, US, 422.482 • Nerves, 422.42 • Ultrasound (US), 422.12989
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INTRODUCTION
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Causes of medial elbow pain and/or ulnar neuropathy are many, and they include ulnar nerve compression within the cubital tunnel, ulnar nerve subluxation or dislocation, and snapping triceps syndrome (1,2). Ulnar nerve dislocation represents abnormal movement of the ulnar nerve out of the cubital tunnel and over the medial epicondyle during elbow flexion (3). Snapping triceps syndrome represents medial dislocation of the medial head of the triceps muscle over the medial epicondyle during elbow flexion (2). These latter two abnormalities of the medial elbow may produce a transient snapping sensation with elbow flexion that is palpable at physical examination (2). Because ulnar nerve dislocation with and without accompanying snapping triceps syndrome may be clinically indistinguishable, imaging is often needed to assist in the diagnosis (2). Accurate diagnosis is essential; ulnar nerve transposition surgery for ulnar nerve dislocation without appropriate treatment for unrecognized snapping triceps syndrome will result in persistent symptoms (4,5).
Ulnar nerve dislocation from the cubital tunnel over the medial epicondyle typically occurs during elbow flexion and is reduced with elbow extension (3). Similarly, medial dislocation of the medial head of the triceps muscle in snapping triceps syndrome also occurs with elbow flexion and is reduced with elbow extension (2). Although magnetic resonance (MR) imaging has been used with success in the evaluation of elbow abnormalities, the transient nature of ulnar nerve dislocation and snapping triceps syndrome with normal appearances with elbow extension make routine MR imaging inadequate for these diagnoses. Nonroutine MR imaging with the elbow in various degrees of flexion for making the diagnosis of snapping triceps syndrome has been described (6).
Given the limitations of routine MR imaging in these clinical settings, we explored the use of sonography to assist in the diagnosis of ulnar nerve dislocation and snapping triceps syndrome. The purpose of our study was to report our initial experience with the use of dynamic sonography of the elbow to aid in the diagnosis of ulnar nerve dislocation and snapping triceps syndrome.
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Sonographic Procedure
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Preoperative sonography of the elbow was completed by a musculoskeletal radiologist (J.A.J.) who was experienced in musculoskeletal sonography. The radiologist was given a clinical history of possible ulnar nerve dislocation and/or snapping triceps syndrome. A 10-MHz linear transducer (Advanced Technology Laboratories, Bothell, Wash) was used. A liberal amount of acoustic transmission gel was used in place of a standoff pad.
For sonographic evaluation of the cubital tunnel, the patient sat on a stool and placed the extended elbow on the examination table, with slight external rotation of the shoulder to enable visualization and palpation of the medial epicondyle and olecranon. The transducer was placed in the transverse plane over the posteromedial aspect of the elbow; one end of the transducer was placed over the olecranon process and the other end was placed over the medial epicondyle (Fig 1a).
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Figure 1a. (a) Photograph of the elbow in an asymptomatic healthy volunteer demonstrates positioning of the transducer between the medial epicondyle (black dot, arrowhead) and olecranon (black dot, arrow) with the elbow in extension for a sonographic examination. Right side of image is proximal, and left side is distal. Corresponding (b) transverse sonogram and (c) illustration show the normal ulnar nerve (straight arrow) posterior to the medial epicondyle apex (arrowhead). Note olecranon (curved arrow) and common flexor tendon origin (F). The brackets in c indicate the sonographic field of view as depicted in b. Left side of image is posterior, and right side of image is anterior. (d) Photograph shows elbow flexion, and the transducer remains stabilized to the medial epicondyle (black dot, arrowhead) while the olecranon (black dot, arrow) moves distally away from the transducer. Right side of image is proximal and left is distal. (e) Corresponding transverse sonogram shows the ulnar nerve (solid arrow) and medial head of the triceps (open arrows) in normal position posterior to the medial epicondyle apex (arrowhead). Note common flexor tendon origin (F). Left side of image is posterior, and right side of image is anterior.
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Figure 1b. (a) Photograph of the elbow in an asymptomatic healthy volunteer demonstrates positioning of the transducer between the medial epicondyle (black dot, arrowhead) and olecranon (black dot, arrow) with the elbow in extension for a sonographic examination. Right side of image is proximal, and left side is distal. Corresponding (b) transverse sonogram and (c) illustration show the normal ulnar nerve (straight arrow) posterior to the medial epicondyle apex (arrowhead). Note olecranon (curved arrow) and common flexor tendon origin (F). The brackets in c indicate the sonographic field of view as depicted in b. Left side of image is posterior, and right side of image is anterior. (d) Photograph shows elbow flexion, and the transducer remains stabilized to the medial epicondyle (black dot, arrowhead) while the olecranon (black dot, arrow) moves distally away from the transducer. Right side of image is proximal and left is distal. (e) Corresponding transverse sonogram shows the ulnar nerve (solid arrow) and medial head of the triceps (open arrows) in normal position posterior to the medial epicondyle apex (arrowhead). Note common flexor tendon origin (F). Left side of image is posterior, and right side of image is anterior.
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Figure 1c. (a) Photograph of the elbow in an asymptomatic healthy volunteer demonstrates positioning of the transducer between the medial epicondyle (black dot, arrowhead) and olecranon (black dot, arrow) with the elbow in extension for a sonographic examination. Right side of image is proximal, and left side is distal. Corresponding (b) transverse sonogram and (c) illustration show the normal ulnar nerve (straight arrow) posterior to the medial epicondyle apex (arrowhead). Note olecranon (curved arrow) and common flexor tendon origin (F). The brackets in c indicate the sonographic field of view as depicted in b. Left side of image is posterior, and right side of image is anterior. (d) Photograph shows elbow flexion, and the transducer remains stabilized to the medial epicondyle (black dot, arrowhead) while the olecranon (black dot, arrow) moves distally away from the transducer. Right side of image is proximal and left is distal. (e) Corresponding transverse sonogram shows the ulnar nerve (solid arrow) and medial head of the triceps (open arrows) in normal position posterior to the medial epicondyle apex (arrowhead). Note common flexor tendon origin (F). Left side of image is posterior, and right side of image is anterior.
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Figure 1d. (a) Photograph of the elbow in an asymptomatic healthy volunteer demonstrates positioning of the transducer between the medial epicondyle (black dot, arrowhead) and olecranon (black dot, arrow) with the elbow in extension for a sonographic examination. Right side of image is proximal, and left side is distal. Corresponding (b) transverse sonogram and (c) illustration show the normal ulnar nerve (straight arrow) posterior to the medial epicondyle apex (arrowhead). Note olecranon (curved arrow) and common flexor tendon origin (F). The brackets in c indicate the sonographic field of view as depicted in b. Left side of image is posterior, and right side of image is anterior. (d) Photograph shows elbow flexion, and the transducer remains stabilized to the medial epicondyle (black dot, arrowhead) while the olecranon (black dot, arrow) moves distally away from the transducer. Right side of image is proximal and left is distal. (e) Corresponding transverse sonogram shows the ulnar nerve (solid arrow) and medial head of the triceps (open arrows) in normal position posterior to the medial epicondyle apex (arrowhead). Note common flexor tendon origin (F). Left side of image is posterior, and right side of image is anterior.
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Figure 1e. (a) Photograph of the elbow in an asymptomatic healthy volunteer demonstrates positioning of the transducer between the medial epicondyle (black dot, arrowhead) and olecranon (black dot, arrow) with the elbow in extension for a sonographic examination. Right side of image is proximal, and left side is distal. Corresponding (b) transverse sonogram and (c) illustration show the normal ulnar nerve (straight arrow) posterior to the medial epicondyle apex (arrowhead). Note olecranon (curved arrow) and common flexor tendon origin (F). The brackets in c indicate the sonographic field of view as depicted in b. Left side of image is posterior, and right side of image is anterior. (d) Photograph shows elbow flexion, and the transducer remains stabilized to the medial epicondyle (black dot, arrowhead) while the olecranon (black dot, arrow) moves distally away from the transducer. Right side of image is proximal and left is distal. (e) Corresponding transverse sonogram shows the ulnar nerve (solid arrow) and medial head of the triceps (open arrows) in normal position posterior to the medial epicondyle apex (arrowhead). Note common flexor tendon origin (F). Left side of image is posterior, and right side of image is anterior.
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At sonography, the position of the ulnar nerve with respect to the medial epicondyle was noted (Fig 1b, 1c), and the cross-sectional area of the ulnar nerve was measured in the transverse plane at the level of the medial epicondyle in the cubital tunnel. The ulnar nerve was identified on the basis of its parallel hypoechoic neuronal fascicles separated by hyperechoic connective stroma (7). This produced a speckled echogenicity that appeared hypoechoic relative to the surrounding hyperechoic fat in an imaging plane transverse to the ulnar nerve (Fig 1b).
The normal speckled appearance of the ulnar nerve may be less apparent if the ultrasound beam is not perpendicular to the nerve fibers due to anisotropy. Identification of the ulnar nerve may be confirmed with scanning proximal and distal to the cubital tunnel and noting the expected location and echotexture of the ulnar nerve. Color or power Doppler sonography may also be used to differentiate the ulnar nerve from a vascular structure, although the latter is typically smaller in diameter when compared with the ulnar nerve.
Once the ulnar nerve was identified in the transverse plane, the patient then actively flexed the elbow, with the transducer remaining stationary relative to the medial epicondyle (Fig 1d). With dynamic imaging throughout elbow flexion, the positions of the ulnar nerve and medial head of the triceps muscle were assessed relative to the medial epicondyle (Fig 1e). The triceps muscle was identified on the basis of its predominantly hypoechoic echotexture with internal hyperechoic fibroadipose septa. Imaging continued with active elbow extension in the same imaging plane. Typically, a focused sonographic examination of the cubital tunnel region can be completed in less than 5 minutes. Imaging of the contralateral elbow was not performed.
At sonography, a diagnosis of ulnar nerve dislocation was made when the ulnar nerve dislocated over the apex of the medial epicondyle with elbow flexion. The apex of the medial epicondyle was defined as the point where the two nearly flat cortical surfaces of the humerus formed an angle of approximately 80°–100°; sonographic identification was aided by finding the common flexor tendon origin located immediately anterior to the apex of the medial epicondyle (Fig 1c). Of note, the common flexor tendon typically appears relatively hypoechoic in the transverse plane with elbow extension due to anisotropy (Fig 1b), whereas with elbow flexion, a fibrillar hyperechoic echotexture can be appreciated (Fig 1e). The diagnosis of snapping triceps syndrome was made when the hypoechoic medial muscle belly of the triceps muscle dislocated over the apex of the medial epicondyle with elbow flexion. Ulnar nerve dislocation and snapping triceps syndrome were excluded if the ulnar nerve and medial head of the triceps muscle remained posterior to the apex of the medial epicondyle during full active elbow flexion (Fig 1e).
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Surgical Diagnosis
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Although the sonographic results were available to the orthopedic surgeon (P.J.L.J.), the decision to proceed with surgical treatment was based on the clinical history, physical examination findings, and results of nerve conduction analysis and electromyography.
Surgery was performed by the orthopedic surgeon who was experienced in elbow surgery. At open elbow surgery, dislocation of the ulnar nerve was diagnosed if the ulnar nerve was abnormally located over the medial epicondyle with elbow flexion. The diagnosis of snapping triceps syndrome was made when visible and palpable snapping of the medial triceps muscle was noted over the medial epicondyle during elbow flexion. Surgical treatment was performed for each abnormality, if present.
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Case Reports
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Institutional review board approval was obtained to retrospectively search patient records, and informed consent was not required. By using the patient information database of one orthopedic surgeon, three consecutive patients were identified as having (a) open elbow surgery for symptomatic ulnar nerve dislocation with or without snapping triceps syndrome and (b) a preoperative sonographic examination of the elbow between June 1999 and July 2000. In addition, institutional review board approval and informed consent were obtained to image the elbow of a healthy volunteer with sonography.
Case 1
A 52-year-old woman had clinical and electromyographic findings consistent with ulnar neuritis and a dislocating ulnar nerve of the right elbow. Sonographic findings demonstrated that the ulnar nerve was in a normal position with elbow extension (Fig 2a), and it was 0.24 x 0.21 cm in cross section (area, 0.05 cm2). With active elbow flexion, the ulnar nerve dislocated over the apex of the medial epicondyle and superficial to the common flexor tendon origin (Fig 2b), which produced a painful snap that was felt through the transducer. The hypoechoic medial head of the triceps muscle remained posterior to the medial epicondyle and was visualized only in the cubital tunnel with elbow flexion. The real-time sonographic finding was interpreted as an isolated ulnar nerve dislocation. The diagnosis was confirmed by findings at surgery.
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Figure 2a. Case 1. Isolated ulnar nerve dislocation. (a) Transverse sonogram shows the ulnar nerve (straight arrow), which is in its normal position posterior to the medial epicondyle apex (arrowhead), with the elbow in extension The olecranon is indicated by the curved arrow. F = common flexor tendon origin. (b) Transverse sonogram shows that with elbow flexion, the ulnar nerve (solid arrow) is dislocated anteriorly over the medial epicondyle apex (arrowhead) and superficial to the common flexor tendon origin (F). Note separation of the medial head of the triceps muscle (open arrows) from the dislocated ulnar nerve. Left side of image is posterior, and right side of image is anterior.
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Figure 2b. Case 1. Isolated ulnar nerve dislocation. (a) Transverse sonogram shows the ulnar nerve (straight arrow), which is in its normal position posterior to the medial epicondyle apex (arrowhead), with the elbow in extension The olecranon is indicated by the curved arrow. F = common flexor tendon origin. (b) Transverse sonogram shows that with elbow flexion, the ulnar nerve (solid arrow) is dislocated anteriorly over the medial epicondyle apex (arrowhead) and superficial to the common flexor tendon origin (F). Note separation of the medial head of the triceps muscle (open arrows) from the dislocated ulnar nerve. Left side of image is posterior, and right side of image is anterior.
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Case 2
A 34-year-old woman had a snapping sensation and ulnar nerve symptoms consistent with compression of the ulnar nerve at the elbow (cubital tunnel syndrome). Sonographic findings demonstrated that the ulnar nerve was posterior to the medial epicondyle apex with elbow extension (Fig 3a). In addition, with elbow extension, the medial head of the triceps muscle was identified within the cubital tunnel. The cubital tunnel appeared crowded because both the medial head of the triceps muscle and the ulnar nerve were near the medial epicondyle apex.
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Figure 3a. Case 2. Snapping triceps syndrome. (a) Transverse sonogram shows the ulnar nerve (solid arrow) slightly medially displaced, although posterior to the medial epicondyle apex (arrowhead). Note depiction of the medial head of the triceps muscle (open arrows) within the cubital tunnel with elbow extension. F = common flexor tendon origin. (b) Transverse sonogram shows that with elbow flexion, both the ulnar nerve (solid arrow) and medial head of the triceps muscle (open arrows) are displaced over the medial epicondyle (arrowhead) and are superficial to the common flexor tendon origin (F). Note that the ulnar nerve and medial head of the triceps muscle remain in close continuity. Left side of image is posterior, and right side of image is anterior.
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Figure 3b. Case 2. Snapping triceps syndrome. (a) Transverse sonogram shows the ulnar nerve (solid arrow) slightly medially displaced, although posterior to the medial epicondyle apex (arrowhead). Note depiction of the medial head of the triceps muscle (open arrows) within the cubital tunnel with elbow extension. F = common flexor tendon origin. (b) Transverse sonogram shows that with elbow flexion, both the ulnar nerve (solid arrow) and medial head of the triceps muscle (open arrows) are displaced over the medial epicondyle (arrowhead) and are superficial to the common flexor tendon origin (F). Note that the ulnar nerve and medial head of the triceps muscle remain in close continuity. Left side of image is posterior, and right side of image is anterior.
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The ulnar nerve was 0.6 x 0.25 cm at the level of the epicondyle (area, 0.15 cm2). With elbow flexion (Fig 3b), abnormal dislocation of the ulnar nerve and the medial head of the triceps muscle occurred over the apex of the medial epicondyle and superficial to the common flexor tendon origin, which produced two painful snaps that were felt through the transducer. The dislocated ulnar nerve and medial head of the triceps muscle returned to the normal position with elbow extension. Both the medial head of the triceps muscle and the ulnar nerve remained in contact with each other throughout dislocation and relocation. The real-time sonographic findings were interpreted as ulnar nerve dislocation and snapping triceps syndrome. These findings were confirmed by findings at open elbow surgery.
Case 3
A 17-year-old girl presented with a painful snapping sensation at the medial aspect of the right elbow during elbow flexion. The patient had previously undergone decompression and anterior ulnar nerve transposition surgery but had continued to have medial elbow pain. With transposition surgery, the ulnar nerve is surgically relocated anterior to the medial epicondyle for treatment of cubital tunnel syndrome. Sonography depicted a normal-appearing ulnar nerve, located anterior to the medial epicondyle, that was 0.5 x 0.25 cm (area, 0.125 cm2). With elbow extension, the triceps muscle was identified within the cubital tunnel. With elbow flexion, the medial head of the triceps muscle dislocated over the apex of the medial epicondyle, which caused a painful snap that was felt through the transducer. The dislocated medial triceps muscle reduced with elbow extension. Findings at open elbow surgery confirmed the presence of snapping triceps syndrome.
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Discussion
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Our results show that dynamic sonography of the elbow can be used to help demonstrate abnormal dislocation of the ulnar nerve, with and without snapping triceps syndrome. The dynamic imaging allows continual visualization of the ulnar nerve and triceps muscle throughout active elbow flexion and extension. Knowledge and accurate diagnosis of ulnar nerve and/or medial triceps muscle dislocation as causes for medial elbow snapping are important so that proper surgical treatment may be prescribed. This point is emphasized in patient 3 of this study; this subject required open elbow surgery twice because the diagnosis of snapping triceps syndrome was not initially made in conjunction with presumed ulnar nerve compression.
Dislocation of the ulnar nerve from the cubital tunnel of the elbow has been reported (3) in approximately 16% of healthy subjects. One proposed cause is congenital absence of the cubital tunnel retinaculum, a fibrous band extending from the olecranon process to the medial epicondyle and forming the roof of the cubital tunnel (1). Dislocation of the ulnar nerve over the medial epicondyle may cause ulnar nerve irritation due to friction as it passes over the medial epicondyle (3). An abnormal ulnar nerve location over the medial epicondyle also places the nerve at risk for direct injury (3).
To our knowledge, snapping triceps syndrome was first described as a distinct entity in 1970 (4). Although not uncommon, the prevalence of this syndrome is not known, possibly due to ambiguous clinical findings that cause it to remain unrecognized (2). The clinical presentation is variable and includes medial elbow pain, snapping, neuropathy, or a combination of symptoms (2). Two palpable "snaps" may be detected clinically, with the first representing dislocation of the ulnar nerve and the second representing dislocation of the medial head of the triceps muscle (2).
The cause of snapping triceps syndrome is unknown. However, both acquired and congenital causes have been implicated (2). For example, bodybuilding may increase the bulk of the triceps muscle, which causes medial dislocation (2). Posttraumatic osseous abnormalities may also be associated with dislocation of the ulnar nerve and triceps muscle (2). Congenital accessory triceps tendon and abnormal medial triceps muscle have also been suggested as causes (2). Symptoms may be exacerbated with overhead activities, such as pitching and weight lifting (2).
The MR imaging findings of snapping triceps syndrome have been described (6). It should be noted, however, that elbow flexion is required to demonstrate both dislocation of the ulnar nerve and dislocation of the medial head of the triceps muscle (6). Dynamic sonography permits continual visualization of the ulnar nerve and medial head of the triceps muscle throughout active elbow flexion and extension. This dynamic evaluation with sonography is one advantage, as opposed to static evaluation with routine MR imaging. In addition, any palpable snap can be directly correlated with the sonographic findings to confirm the diagnosis. This is also important because not all cases of ulnar nerve and medial triceps muscle dislocation are symptomatic.
The sonographic results in this study demonstrated that ulnar nerve dislocation and snapping triceps syndrome were correctly diagnosed during elbow flexion (Figs 2, 3). We used the apex of the medial epicondyle, located immediately posterior to the common flexor tendon origin, as the landmark to diagnose abnormal dislocation (Fig 1c, 1e). In each of our cases, the ulnar nerve and/or medial head of the triceps muscle dislocated medial to the epicondyle apex and superficial to the common flexor tendon origin during elbow flexion (Figs 2b, 3b).
We have noted that when ulnar nerve dislocation is secondary to snapping triceps syndrome, the medial head of the triceps muscle and the ulnar nerve remain in close continuity as they dislocate over the medial epicondyle (Fig 3b). In contrast, in the case of isolated ulnar nerve dislocation, the medial head of the triceps muscle and the ulnar nerve separate from each other (Fig 2). Mild medial displacement of the triceps muscle normally occurs with elbow flexion; however, the muscle remains posterior to the medial epicondyle (Fig 1e) (6). In addition, in the two cases of snapping triceps syndrome, we noted visualization of the medial triceps muscle within the cubital tunnel with elbow extension (Fig 3a). This finding was not present in the healthy volunteer (Fig 1) and in the patient with isolated ulnar nerve dislocation (Fig 2).
With ulnar nerve dislocation, the abrupt movement of the dislocating ulnar nerve between the ultrasound transducer and the medial epicondyle produced a snapping sensation felt through the transducer. One potential pitfall is that excessive transducer pressure may inhibit the ulnar nerve from dislocating, thus resulting in misdiagnosis. This can be avoided by intermittently decreasing transducer pressure on the soft tissues throughout the dynamic examination.
Sonography has been used to detect ulnar nerve dislocation in healthy volunteers and has been used in the evaluation of ulnar neuritis and ulnar nerve compression in the cubital tunnel (8–10). It has been shown (9) that ulnar nerve cross-sectional area increases in the cubital tunnel in control subjects, and an area greater than 0.075 cm2 at the level of the epicondyle indicates cubital tunnel syndrome. It has also been shown (8) that the ulnar nerve flattens during elbow flexion, and this flattening is most marked with ulnar nerve subluxation. In this study, the ulnar nerve cross-sectional area was 0.05 cm2 in patient 1, 0.15 cm2 in patient 2, and 0.125 cm2 in patient 3.
By using 0.075 cm2 as the threshold value for area, the second and third patients met the sonographic criterion for cubital tunnel syndrome (9). Both patients had symptoms of ulnar nerve compression at the elbow. Although the first patient met the electrodiagnostic criterion for ulnar nerve compression, the nerve itself was not enlarged at sonography. It is unclear why this discrepancy was present. It is possible that the conservative treatment prior to surgery reduced the ulnar nerve irritation and decreased nerve size to less than the threshold value.
The limitations of this study include the small number of subjects. This is primarily because the intraoperative surgical findings were used as the standard of reference and because snapping triceps syndrome is an uncommon and often unrecognized clinical condition. Further studies are required to confirm our findings in a larger subject population. In addition, interobserver variability could not be calculated because only one radiologist performed each sonographic examination.
In summary, dynamic sonography of the elbow was used to aid in the diagnosis of and differentiation between ulnar nerve dislocation and snapping of the medial triceps muscle. Although accurate in this small series, a larger prospective study would be required to determine the sensitivity and specificity of sonography to assist in making these diagnoses.
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FOOTNOTES
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Author contributions: Guarantors of integrity of entire study, J.A.J., P.J.L.J.; study concepts and design, all authors; literature research, J.A.J., P.J.L.J.; clinical and experimental studies, J.A.J., P.J.L.J., A.W.J., D.P.F.; data acquisition, J.A.J., P.J.L.J., A.W.J., D.P.F.; data analysis/interpretation, all authors; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, all authors.
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TOP
ABSTRACT
INTRODUCTION
