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Original Report |
1 Department of Radiology, UCSD and VAHCS, 3350 La Jolla Village Dr., La Jolla,
CA 92161.
2 La Jolla Radiology, 8400 Miramar Rd., Ste. 200, San Diego, CA 92123.
3 Childrens' Hospital and Health Center, 3020 Childrens' Way, San Diego, CA
92123.
Received September 30, 2003;
accepted after revision February 13, 2004.
Presented at the 2002 annual meeting of the Radiological Society of North
America, Chicago, IL.
Abstract
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CONCLUSION. Humeral avulsion or insufficiency of the posterior band of the inferior glenohumeral ligament can be easily detected using MR arthrography. This ligamentous abnormality may be seen in isolation, or it may occur in conjunction with posterior or, less often, anteroinferior capsulolabral abnormalities. The presence of this lesion in a subgroup of patients with the clinical diagnosis of multidirectional instability may offer insight into the causes and pathogenesis of this complex entity.
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The purposes of this study were to describe the MR arthrography findings of humeral avulsion of the posterior band of the inferior glenohumeral ligament and to correlate these imaging findings with the presence of coexisting structural abnormalities (n = 17), clinical presentation (n = 17), and arthroscopic evaluation (n = 8) in an attempt to elucidate the clinical importance of this finding.
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Arthrography was performed using an anterior approach in all cases. Patients were placed in the supine position on the fluoroscopy table with an arm in external rotation. Sterile technique was used. The junction of the superior two thirds and inferior one third of the articulation was localized fluoroscopically. A 20-gauge spinal needle was placed into the articulation, and approximately 12 mL of a 1-mmol/L solution of gadodiamide was instilled into the articulation. The solution was composed of equal parts of an iodinated contrast agent (Omnipaque [iohexol], Nycomed Amersham) and a 2-mmol/L gadodiamide solution prepared by diluting Omniscan (Nycomed Amersham) with saline.
All MRI studies were performed on a 1.5-T unit (Magnetom Symphony, Siemens Medical Solutions) using a dedicated extremity coil for image acquisition within 1 hr of arthrography. MRI was performed with the patient supine, arm at the side in neutral position (thumb directed to the ceiling). Fat-saturated fast spin-echo T1-weighted images (TR range/TE range, 580–800/10–12; field of view, 14 cm; matrix, 192 x 256; slice thickness, 3 mm; acquisitions, 2) of the shoulder in the abducted and externally rotated position were obtained in the axial, coronal oblique, and sagittal oblique planes. An additional fat-saturated fast spin-echo T2-weighted sequence (3,600–3,900/88–98; field of view, 14 cm; matrix, 192 x 256; slice thickness, 3 mm; acquisitions, 2) in the coronal oblique plane was performed.
The diagnosis of avulsion of the posterior band of the inferior glenohumeral ligament from the humerus on MR arthrography was established by identification of a detachment of the ligament from its humeral attachment site with or without abnormal distribution of contrast material along the distal humeral shaft (Figs. 1A and 1B). This designation was made on both coronal and sagittal images. On the basis of image analysis, 17 of 29 patients met the criteria for avulsion of the posterior band of the inferior glenohumeral ligament from the humerus.
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Images were further assessed for characterization of the capsular attachment (anterior capsule only) or the presence of capsular abnormality. Anterior capsular attachment was described by its attachment site with respect to the glenoid labral junction: at or adjacent to the labrum, more than 1 cm medial to the labrum, or more than 2 cm medial to the labrum. The labrum was evaluated for abnormalities in signal intensity and morphology. The rotator cuff was examined for the presence of a full-thickness tear. The osseous structures were examined for abnormalities in signal intensity and morphology.
The medical records of the patient population were acquired and reviewed with specific attention to patient demographics, clinical history, presenting symptoms, physical examination findings, and course of treatment. Arthroscopic correlation was available in eight patients.
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Thirteen of the 17 patients presented with chronic shoulder pain and reported no history of an acute traumatic episode. Of this subgroup of patients, seven showed evidence of multidirectional instability at physical examination. These patients were athletically active and included an amateur weightlifter, professional baseball player, yoga instructor, competitive high school volleyball player, competitive high school football player, and recreational racquetball player; the seventh patient was both a swimmer and a "throwing" athlete. The remaining patients in this subgroup (n = 6) gave no definite clinical history that documented a source of repetitive microtrauma, either recreational or occupational.
Four of the 17 patients presented with a history of an acute traumatic episode no more than 12 weeks before undergoing imaging. In this group, one patient showed evidence of anterior instability at physical examination.
In 13 of the 17 patients, a capsular attachment 1 cm or more from the glenoid labral junction was present (Figs. 3A, 3B, and 3C). This finding was seen in all the patients with a history of trauma and in nine of the patients with no history of trauma, including all those with physical examination findings of multidirectional instability (n = 7).
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In eight of the 17 patients, a medial insertion of the posterior superior capsule was identified (Figs. 4A and 4B). This finding was seen in a patient from the group with a history of trauma. Five of the seven patients with this finding in the atraumatic group were among those with multidirectional instability at physical examination. In this subgroup, the finding of a medial capsular insertion was confirmed at arthroscopy.
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Labral abnormalities were identified in four of the 17 patients on MR arthrography. In the patient population with a history of trauma, one patient with instability at physical examination presented with a Bankart lesion that was confirmed and treated at arthroscopy. In the atraumatic patient population, three labral abnormalities were identified. A posterior labral tear was noted in the professional baseball player, and anterior inferior labral degeneration was present in the recreational swimmer. These findings were confirmed at arthroscopy. In an additional patient, an anterior inferior labral tear was diagnosed on MR arthrography, but arthroscopy was declined by the patient (Figs. 5A and 5B).
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No full-thickness tear of the rotator cuff was present in either patient population. A Hill-Sachs lesion was detected in the patient with a posttraumatic Bankart lesion confirmed at arthroscopy and instability at physical examination. Nonspecific cystic changes in the region of the greater tuberosity were seen in three of the patients in the atraumatic population, including the swimmer and professional baseball player.
Arthroscopy was performed in eight patients: the patient with posttraumatic anterior instability and the seven patients with multidirectional instability. In the former, repair of the Bankart lesion and capsular shift were performed with imbrication of the rotator cuff interval. In the latter, thermal capsulorrhaphy was performed with imbrication of the rotator cuff interval. In all cases, the arthroscopy findings confirmed those seen on MR arthrography.
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Undoubtedly, because of the relative frequency of anterior dislocation with subsequent failure of the superior and anterior bands of the inferior glenohumeral ligament complex, extensive biomechanical testing, imaging, and clinical characterization of lesions of this part of the capsule have been performed. Bigliani et al. [6] showed that three failure sites exist for the components of the inferior glenohumeral ligament complex: glenoid insertion, ligament mid substance, and humeral insertion. In the case of the posterior band, ligament failure occurred at the glenoid in 25% of specimens, mid substance in 44%, and humerus in 31% [6]. These findings suggest a higher frequency of failure of the ligament at the humeral attachment for the posterior band than for its anterior counterparts, which is consistent with the fact that the posterior band is the thinnest component of the inferior glenohumeral ligament complex with the least strength and stiffness [6, 7]. This biomechanical milieu provides a plausible backdrop for our study in that the majority of patients reported no history of trauma and one expects minor trauma or repetitive microtrauma to preferentially affect relatively vulnerable points in the capsule.
Although primary lesions of the posterior band of the inferior glenohumeral ligament have received little attention in the literature, the MRI findings, clinical diagnosis, and treatment of failure of the anterior band have been described in the realm of anterior instability [8–10]. The MRI diagnosis of humeral avulsion of the anterior band of the inferior glenohumeral ligament is established by direct visualization of discontinuity of the ligament and extravasation of contrast material in the region of capsular avulsion [10] that results in an abnormal distribution of fluid within the articulation—the conversion of a U-shaped recess to a J-shaped recess. We used the same imaging criteria in this study to localize abnormalities to the posterior band of the inferior glenohumeral ligament.
Although the concept of glenohumeral joint stability is both complex and controversial, it is largely accepted that the articulation has both static and dynamic stabilizers for which activation depends on arm position as well as mechanism of injury. In the case of anterior stability, the association of the humeral avulsion of the anterior band of the inferior glenohumeral ligament is established [8–10]. On the contrary, however, consensus about the clinical diagnosis, classification, and treatment for multidirectional instability has not been reached [11, 12]. The entity is, however, gaining attention in the orthopedics literature and is believed to be a debilitating condition in young athletic people [11]. A history of repetitive microtrauma with generalized ligamentous laxity at physical examination is thought to be a common presentation. The hallmark abnormality is believed to be inferior capsular laxity [11, 12], which may or may not have associated lesions of the labrum–ligament complex in either an anterior or posterior distribution. The physical examination findings may be subtle and are ill-appreciated outside the realm of the subspecialized orthopedic surgeon. Likely a reflection of the variability in the clinical presentation of multidirectional instability, no set imaging findings have been associated with this clinical entity.
In our patient population, seven patients with the finding of humeral avulsion of the posterior band of the inferior glenohumeral ligament presented with multidirectional instability, one with anterior instability, and the remaining nine patients with a history of shoulder pain and no demonstrable instability at physical examination. The clinical presentation is admittedly nonspecific in more than half of our patient population, paralleling the spectrum of abnormalities that can exist with multidirectional instability [11].
This study is limited by the inherent weakness of its retrospective design, the lack of a gold standard in all cases, the lack of longterm imaging and clinical follow-up, and the incompletely developed understanding of the clinical entity of multidirectional instability.
Despite these limitations, the primary imaging finding of insufficiency of the posterior band of the inferior glenohumeral ligament outside the realm of acute trauma and posterior dislocation is a unique finding. Moreover, this structural lesion may offer insight into the spectrum of imaging pathology that could correspond to the spectrum of pathology encountered at clinical presentation.
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