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1 Department of Radiology, Keller Army Community Hospital, 900 Washington Rd.,
West Point, NY 10996-1197.
2 Department of Radiology, Division of Radiologic Sciences, Wake Forest
University School of Medicine, Medical Center Blvd., Winston-Salem, NC
27157-1088.
3 Department of Radiology, Uniformed Services University of the Health Sciences,
Bethesda, MD 20814-4799.
4 Orthopaedic Surgery Service, Keller Army Community Hospital, West Point, NY
10996-1197.
Received July 20, 2001;
accepted after revision February 19, 2002.
The opinions and assertions contained herein are those of the authors and
should not be construed as official or as representing the opinions of the
Department of the Army or the Department of Defense.
Abstract
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MATERIALS AND METHODS. A retrospective review of six cases of HAGL lesion diagnosed at our institution from October 1996 to February 2001 was performed. We reviewed the radiology reports, radiologic examinations, medical records, and operative notes. All patients had undergone radiography, and four patients had undergone MR imaging of the shoulder before diagnostic arthroscopy.
RESULTS. All the patients were men who ranged in age from 19 to 41 years (mean, 26 years). Four patients (67%) had an anterior shoulder dislocation. Three of the HAGL lesions (50%) were detected on radiologic examinations, either by radiography or MR imaging. One patient had a bony HAGL. All patients had associated injuries. The most common associated abnormalities were osteochondral injury of the humeral head (n = 3), rotator cuff tear (n = 3), Bankart lesion (n = 3), Hill-Sachs lesion (n = 2), avulsion of the middle glenohumeral ligament (n = 1), partial tear of the biceps brachii tendon (n = 1), and comminuted fracture of the clavicle (n = 1).
CONCLUSION. With an incidence of 7.5% and 9.4% in two large series of patients, the HAGL lesion is an important cause of anterior instability of the glenohumeral joint. The majority (68%) of patients with an HAGL lesion have associated injuries.
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The MR imaging examinations of the shoulder performed at our institution included the following sequences: axial gradient-echo (TR/TE, 449/13; flip angle, 30°), axial proton density—weighted with fat suppression (2409/17), oblique coronal T1-weighted (509/14), oblique coronal fast spin-echo T2-weighted with fat suppression (2500/60), and oblique sagittal fast spin-echo T2-weighted with fat suppression (2500/60). We used an 18-cm field of view, 4-mm slice thickness, and 0.4-mm spacing. The MR imaging examinations of the shoulder performed at the outside institution included the following sequences: axial T1-weighted (600/15), axial proton density—weighted with fat suppression (3500/16), axial T2-weighted (3500/98), oblique sagittal proton density—weighted (2400/45), oblique sagittal T2-weighted (2400/90), oblique coronal T2-weighted with fat suppression (3000/90), oblique coronal T1-weighted (550/15), and oblique coronal proton density—weighted (2200/20). The outside imaging facility used a 14- to 18-cm field of view, 4-mm slice thickness, and 0.4-mm spacing.
A fellowship-trained musculoskeletal radiologist retrospectively reviewed all radiologic examinations. A literature search of the MEDLINE database was conducted using the PubMed search engine of the National Library of Medicine and National Center for Biotechnology Information [9].
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Three (50%) of the six HAGL lesions were detected on radiologic examinations, either at radiography or MR imaging. One patient had a bony HAGL that was seen on radiography (Fig. 1A,1B). However, the interpreting radiologist did not recognize its origin or the significance of the avulsion fracture. On radiography, bony HAGL appears as an avulsion fracture from the medial cortex of the humeral neck. A thin radiolucency is seen inferior to the anatomic neck of the humerus, the donor site of the bony HAGL. In four patients (67%), radiographs showed associated injuries: Bankart lesion (n = 1) (Fig. 2A,2B), comminuted fracture of the clavicle (n = 1) (Fig. 3A,3B,3C), greater tuberosity fracture (n = 1), and osteochondral fracture of the humeral head (n = 1) (Fig. 4).
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Two HAGL lesions were diagnosed on MR imaging. The MR imaging criteria for the diagnosis of an HAGL lesion are conversion of a fluid-distended U-shaped axillary pouch into a J-shaped structure and extravasation of contrast material or joint effusion across the torn humeral attachment [8]. One patient had complete disruption of the anterior capsule, resulting in a subscapularis tendon tear, a tear of the anterior glenoid labrum, and an HAGL lesion (Fig. 3A,3B,3C). One patient had a partial tear of the biceps brachii tendon and an osteochondral injury of the humeral head in addition to the HAGL lesion (Fig. 4). The other two MR examinations did not reveal the HAGL lesion. However, MR imaging showed other associated injuries: Hill-Sachs lesion and tear of the anterior glenoid labrum in one patient and osteochondral injury, focal full-thickness tear of the supraspinatus tendon, and Bankart lesion in another patient (Fig. 5A,5B).
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All but one patient underwent diagnostic arthroscopy that confirmed the diagnosis of HAGL lesion and immediately underwent open repair. One patient did not have arthroscopy because his symptoms improved with nonoperative therapy. In this series of patients, the associated abnormalities seen with that HAGL lesion include osteochondral injury of the humeral head (n = 3, 50%), Bankart lesion (n = 3, 50%), rotator cuff tear (n = 3, 50%; two supraspinatus tendon tears and one subscapularis tendon tear), Hill-Sachs lesion (n = 2, 33%), partial tear of the biceps brachii tendon (n = 1, 17%), middle gleno-humeral ligament avulsion (n = 1, 17%), and clavicular fracture (n = 1, 17%).
Our literature search using the PubMed search engine of the National Library of Medicine and National Center for Biotechnology Information yielded six articles [2,3,4, 6,7,8]. Two additional articles were found in the references of these six articles [1, 5]. Combined, these articles discuss the diagnosis of HAGL lesion in 59 patients. The average age was 27 years, and age ranged from 12 to 50 years. There were 57 males (97%) and two females. Most (52%) of the patients were participating in rugby when injured. The other patients were injured when diving; playing football, basketball, or volleyball; surfing; skiing; or involved in a motor vehicle crash. Twelve patients (20%) had a bony HAGL. Eight patients (14%) had prior orthopedic surgery of the same injured shoulder. The majority (68%) of the patients with an HAGL lesion had associated injuries. The associated abnormalities were rotator cuff tear (n = 16, 27%), Bankart lesion (n = 13, 22%), Hill-Sachs lesion (n = 6, 10%), multidirectional laxity (n = 4, 7%), and labral tear (n = 3, 5%).
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Bokor et al. [6] cited Nicola [12] as the first researcher to describe capsular avulsion from the humerus in patients with shoulder dislocations. In a subsequent cadaveric study, Nicola noted that the articular capsule is torn from the humerus as a result of hyperabduction and external rotation, whereas a Bankart lesion occurs as a result of hyperabduction and associated impaction. In 1992, a study by Bigliani et al. [13] described the tensile property of the inferior glenohumeral ligament labral complex. The bone—ligament—bone complex was tested to mechanical failure at three sites: the glenoid labrum failed 40% of the time; the intrasubstance of the inferior glenoid ligament, 35% of the time; and the humeral insertion site, 25% of the time. In the two largest clinical series in the literature, the incidence of the HAGL lesion was 7.5% and 9.4% [2, 6], which is lower than the incidence projected by Bigliani et al. on the basis of their biomechanical study. One explanation for the discrepancy is that the cadaveric testing conditions may differ greatly from the clinical environment. Also, the cadaveric studies tested elderly specimens [14]. Lastly, the HAGL lesion may not be recognized at either diagnostic arthroscopy or an open stabilization procedure of the shoulder. In our series, the incidence of the HAGL lesion was 2%, much lower than the incidence cited in the other published series. This discrepancy may reflect differences among the patient populations and mechanisms of injury in each series.
At arthroscopy, an HAGL lesion can be overlooked if the appropriate area is not searched specifically for this finding [5]. Bach et al. [1] stated that in the absence of ligamentous laxity and glenoid damage, the possibility of a disruption of the lateral capsule must be excluded. The cardinal arthroscopic sign of an HAGL lesion is the visualization of the fibers of the subscapularis muscle through the avulsed inferior joint capsule, an exposed subscapularis muscle [2]. Bokor et al. [6] found disruption of the "wave" that is formed by the reflection of the inferior capsule onto the humeral neck a reliable arthroscopic sign.
An open stabilization procedure of a shoulder with anterior instability requires exposure of the joint for an inferior capsular shift. A risk associated with open repairs that use a medial capsulotomy is that an HAGL lesion might be overlooked. During open stabilization procedures that use lateral capsulotomy, disruption of the lateral capsule can be overlooked if the subscapularis muscle and the capsule are divided together. Detection of an HAGL lesion requires careful blunt dissection to separate the subscapularis muscle from the capsule. Otherwise, exposure of the HAGL lesion may be misinterpreted as an iatrogenic breach of the capsule rather than an injury. The HAGL lesion is located below the level of the subscapularis muscle in the inferior pouch of the shoulder and appears as a thickened, rolled edge in the capsular defect [6].
Because an HAGL lesion can be overlooked during either arthroscopy or an open stabilization procedure, correct preoperative diagnosis of the HAGL lesion on imaging is important and has a significant clinical implication. At our institution, an HAGL lesion diagnosed on imaging and confirmed at diagnostic arthroscopy requires open repair.
HAGL lesions can occur without (80%) or with (20%) bony avulsion from the medial cortex of the humeral neck. A combined Bankart lesion and lateral capsule avulsion has been termed the floating anterior inferior glenohumeral ligament [5]. In the literature, the frequency of HAGL, floating anterior inferior glenohumeral ligament, and bony HAGL is 59%, 22%, and 20%, respectively [1,2,3,4,5,6,7]. HAGL lesion has a male predominance of 97% [1,2,3,4,5,6,7]. In patients undergoing an operation to manage shoulder instability, the mean age of the patients with an HAGL lesion was slightly greater than those without an HAGL lesion [6]. HAGL lesions occurred most often in rugby players (52%). This finding reflects the patient population in the largest series of HAGL to date [6]. However, the HAGL lesion is found in patients who participate in many other activities and sports.
Fourteen percent of the HAGL lesions reported in the literature occurred in shoulders that had prior orthopedic surgery. The duration between shoulder surgery and the injury that resulted in the HAGL lesion was not given for all the patients. Therefore, whether prior surgery placed patients at risk for subsequent injury is not known. One of our patients had an open anteroinferior capsular shift 6 weeks before being involved in a motor vehicle crash that resulted in a comminuted fracture of the clavicle and complete disruption of the anterior capsule. Recently having undergone capsular surgery likely predisposed him to the HAGL lesion.
The majority (68%) of the patients with HAGL lesions had associated abnormalities. This percentage was calculated from the statistics included in all the articles published to date about the HAGL lesions [1,2,3,4,5,6,7]. A rotator cuff tear is the most common associated injury, 94% of which involve the subscapularis tendon [6]. Other associated injuries in descending order of frequency are floating anterior inferior glenohumeral ligament, Hill-Sachs lesion, and tear of the glenoid labrum.
Our series mirrors the literature. All our patients were men. The average age of our patients was 26 years, which is similar to the findings reported in the literature. Seventeen percent of our cases were bony HAGL, compared with 20% reported in the literature. All our patients had associated injuries, which were osteochondral injury of the humeral head (n = 3), rotator cuff tear (n = 3), Bankart lesion (n = 3), Hill-Sachs lesion (n = 2), avulsion of the middle glenohumeral ligament (n = 1), partial tear of the biceps brachii tendon (n = 1), and comminuted fracture of the clavicle (n = 1). Osteochondral injury denotes a defect in the humeral head that is not in the typical location of a Hill-Sachs lesion. Diagnostic arthroscopy did not identify a Hill-Sachs lesion in two of the patients with osteochondral injury of the humeral head. The third patient with osteochondral injury did not undergo arthroscopy because his symptoms responded with conservative therapy.
Little has been written about the HAGL lesion in the radiology literature. To our knowledge, only Stoller [8] has described the HAGL lesion on MR arthrography of the glenohumeral joint. Stoller stated that identification of the HAGL lesion on MR images requires either the presence of a joint effusion or the use of MR arthrography. MR arthrography of the HAGL lesion shows that the axillary pouch is converted from a fluid-distended U-shaped structure to a J-shaped structure as the anterior band of the inferior glenohumeral ligament labral complex drops inferiorly. Additionally, extravasation of contrast material can be seen across the torn humeral attachment.
The HAGL lesion is detected on radiography in only 20% of the cases when there is associated bony avulsion from the humeral neck, known as bony HAGL and first described by Bach et al. [1]. On radiography, a small linear bony fragment is seen medial to the neck of the humerus that is associated with a linear radiolucency in the humeral neck, the donor site (Fig. 1A,1B). Oberlander et al. [3] reported that the bony fragment of the bony HAGL lesion was best visualized on a Garth view of the glenohumeral joint, which is a 15° oblique radiograph in the anterior plane of the shoulder. The bony HAGL lesion may mimic a bony Bankart lesion (Fig. 8A) or a calcified intraarticular loose body. An axillary or a West Point view will allow a bony HAGL to be distinguished from a Bankart lesion. On either of these views a bony Bankart lesion is seen in the anterior half of the glenoid cavity (Fig. 8B), whereas the bony fragment of the bony HAGL lesion is seen superimposed on the proximal humerus. Oberlander et al. also described the CT appearance of a bony HAGL lesion. CT arthrography of the shoulder joint showed a linear bony fragment posterior to the middle glenohumeral ligament and contrast extravasation anterior to the bony HAGL lesion.
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Two of the HAGL lesions in our series were detected during routine MR imaging of the shoulder, which was performed the day after injury. We agree with Stoller [8] that the presence of a joint effusion is critical for the detection of an HAGL lesion on MR imaging. We have found oblique coronal and sagittal T2-weighted sequences with fat suppression to be most helpful. On oblique coronal T2-weighted MR images obtained with fat suppression, the HAGL lesion appears as a J-shaped anterior band of the inferior glenohumeral ligament, and extravasation of joint fluid across the humeral detachment can be seen (Figs. 3A,3B,3C and 4). On oblique sagittal T2-weighted MR images obtained with fat suppression, fluid extravasation, edema, or both are seen anterior to the humeral neck. In the other two patients, the MR examinations were performed more than 1 week after the injury and did not reveal the HAGL lesion. The HAGL lesion may have healed in place. Consequently, in the absence of joint distention by effusion or MR arthrography, the humeral detachment may not be detected on routine MR examination of the shoulder.
Management of an HAGL lesion depends on the presence of associated injuries. An isolated HAGL lesion may be treated with conservative therapy: sling immobilizer for 4 weeks followed by a shoulder-strengthening program [3]. Other researchers advocate surgical repair of HAGL lesions by either arthroscopy or open repair [2, 5, 6]. At our institution, all patients with first-time traumatic anterior shoulder dislocation or recurring dislocations are offered arthroscopy because in our young (<24 years) athletic patient population, the recurrence rate for patients treated nonoperatively is 90% [14]. All our patients with an HAGL lesion first underwent diagnostic arthroscopy and then had open repair. If the anterior glenoid labrum is not damaged, then repair can be performed by closing the defect. The goal is to secure good healing of the capsule to the bone, particularly inferiorly [1]. Lesions associated with bony HAGL are reattached to the humerus using nonabsorbable sutures or Mitek anchoring sutures [3].
In conclusion, the HAGL lesion is an important cause of anterior instability of the glenohumeral joint, with an incidence of 7.5% and 9.4% in two large series of patients. Most (68%) patients with an HAGL lesion have associated injuries. Radiologists should be familiar with the radiologic appearance of the HAGL lesion and the injuries commonly associated with this finding.
Acknowledgments
We thank John Donlon for his technical expertise, Etthie Galliard, and the
Directorate of Information Management of the United States Military Academy
for its assistance with the photographs.
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