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Variation in the Glenoid Origin of the Anteroinferior Glenohumeral Capsulolabrum

Eberly, Vance, C.*; McMahon, Patrick, J.*,**; Lee, Thay, Q*

Clinical Orthopaedics and Related Research: July 2002 - Volume 400 - Issue - p 26-31
SECTION I SYMPOSIUM: Recent Basic Science and Clinical Advances in Anterior Glenohumeral Instability
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Restoration of the anteroinferior capsulolabrum, including the labrum and origin of the anterior band of the inferior glenohumeral ligament is crucial during Bankart repair. The purpose of the current study was to describe variations in this anatomy near the glenoid. The histologic and gross anatomy were studied in 10 fresh-frozen glenohumeral joints from adult cadavers. Each joint was placed in the apprehension position of abduction, external rotation, and horizontal abduction because anterior dislocation occurs in this shoulder position. The joints then were sectioned serially in the transverse plane from cephalad to caudad. Three glenohumeral joints were embedded in Techovit 7200 resin, polymerized, and then mounted onto an acrylic slide. Ground sections were prepared by attaching a microscope slide to the face of each and cutting 200 μm-thick sections. The thin sections were ground to a thickness of 30 μm. Finally, sections were stained with 1% toluidine blue zero in 1% sodium tetraborate for light microscopic examination. The other seven glenohumeral joints were frozen in the apprehension position and held with a custom jig while sectioned serially at 3-mm intervals. The surfaces then were recorded with a tabletop computer and a scanning device. Two distinct patterns of the anteroinferior capsulolabrum attachment to the glenoid were identified. In eight joints (80%) it had its major origin from the labrum with some fibers extending onto the glenoid neck, a Type I origin. In two joints (20%), it emanated solely from the glenoid neck, a Type II origin. Failure to repair the glenoid origin of the anteroinferior capsulolabrum, the location of the anterior band of the inferior glenohumeral ligament, because of variations in its anatomy may be a reason for failure after Bankart repair.

From the *Orthopaedic Biomechanics Laboratory, VA Healthcare System, Long Beach, CA, and University of California, Irvine; and the **University of Pittsburgh, Pittsburgh, PA.

Reprint requests to Patrick J. McMahon, MD, University of Pittsburgh, Center for Sports Medicine, 3200 Water Street, Pittsburgh, PA 15203.

Understanding of the anatomy and function of the anterior glenohumeral capsulolabrum improved with the description of three glenohumeral ligaments that provide its structural support. Variations from caudad to cephalad in the superior, middle, and inferior glenohumeral ligaments were described by DePalma and coworkers. 9 Although the prevalence of each capsulolabral type as reported by DePalma et al has been disputed, variations in this anatomy later were confirmed. 13,32 The inferior glenohumeral ligament resists anterior translation of the humeral head on the glenoid 34 with the shoulder in the apprehension position of abduction, external rotation, and horizontal abduction, where anterior dislocation occurs. The inferior glenohumeral ligament was additionally delineated into three discrete regions, an anterior band, a posterior band, and an axillary pouch. 26 Histologically, the anterior and posterior bands were composed of dense, longitudinal collagen fibers whereas the intervening pouch lacked this organization.

The capsulolabral lesions after initial dislocation of the glenohumeral joint in vivo include glenoid origin detachment (the Bankart lesion), 1,2,7,22,23 capsuloligamentous tearing, 2,7,11 and humeral insertion avulsion. 11 The Bankart lesion 3,29 now is known to include injury to the glenoid origin of the anterior band of the inferior glenohumeral ligament.

Traditional, open techniques of Bankart lesion repair from outside the glenohumeral joint involve plication of the capsule and reattachment of the capsulolabral structures to the glenoid bone yielding less than 5% recurrent instability. 5,21 Arthroscopic repair techniques of the Bankart lesion involve repair of the labrum to the glenoid, visible from inside the joint. Unfortunately, results have been less satisfactory, with recurrent instability reported in 8% to 20% of patients. 1,28,30,37 Both techniques sometimes are ineffective at restoration of normal function. 5,17,21,31

All Bankart lesions are not alike yet understanding of variations in this pathoanatomy, important for successful outcome, necessitates understanding of the normal glenoid origin of the anterior band of the inferior glenohumeral ligament. Previous studies found the glenoid origin to be from the labrum, rim, and neck. 8,15,24,25,30,40 Before birth, attachment was primarily from the glenoid neck in 23% and from the labrum in 77% of glenohumeral joints. 35 Because it has implications for repair of the Bankart lesion, variation in the anatomy of the glenoid origin of the anteroinferior capsulolabrum in the glenohumeral joint of adults was evaluated.

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METHODS

Ten fresh-frozen glenohumeral joints from cadavers were thawed at room temperature and then dissected of all soft tissue except the rotator cuff musculature and the capsuloligamentous structures.

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Histologic Evaluation

Three glenohumeral joints were positioned at 60° abduction and at the limit of external rotation before being refrozen. This position of abduction was chosen because 90° shoulder abduction, where anterior instability is common, corresponds to 30° scapulothoracic and 60° glenohumeral abduction. 10,12,16 The joints then were sectioned in a plane perpendicular to the glenoid through the midportion, creating inferior and superior halves. A second section, in a plane perpendicular to the first plane through the 12 o’clock and the 6 o’clock glenoid locations, left four parts. Histologic sections were obtained using an accelerated tissue-processing technique described by Ohland and coworkers. 27 The anteroinferior and anterosuperior parts were thawed in 70% alcohol, fixed for 14 days, dehydrated, cleared, and embedded in Techovit 7200 resin (Exact Technologies Inc, Oklahoma City, OK). After 10 days of infiltration, the resin was polymerized by a combination of light and heat. The polymerized blocks were mounted onto an acrylic slide and serially sectioned perpendicular to a plane containing the anterior and posterior rims of the glenoid. Ground sections then were prepared by attaching a microscope slide to the face of each block and cutting 200-μm thick sections. These thin sections were ground to a thickness of 30 μm. Finally, sections were stained with 1% toluidine blue zero in 1% sodium tetraborate for light microscopic examination. This method of preparation provided the necessary anatomic detail for study but it was time-consuming and costly.

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Gross Evaluation

Seven glenohumeral joints were positioned at 60° abduction and at the limit of external rotation before being refrozen. A custom jig held the frozen joints while they were sectioned serially at 3-mm intervals perpendicular to a plane containing the anterior and posterior rims of the glenoid. Both surfaces of each section then were recorded with a tabletop computer, scanning device.

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RESULTS

In all 10 joints, the anteroinferior capsulolabrum had attachments to labrum and bone at the glenoid origin but two distinctly different patterns of these attachments were found. Eight joints (80%) had an attachment primarily from the labrum (Fig 1) with transitional zones of fibrocartilage and mineralized fibrocartilage being present (a Type I origin). The longest portion of the fibrocartilage zone (approximately 2 mm) was at the 3 o’clock location and was progressively shorter with each section inferiorly. At the 5 o’clock location, there was no apparent fibrocartilage zone and the collagen fibers near the labrum were disorganized. There also was attachment to the glenoid rim and neck, more so cephalad than caudal but always slight in comparison with the labral attachment. In two joints (20%), the anteroinferior capsulolabrum origin was primarily from the glenoid rim and neck (a Type II origin) (Fig 2). The collagen fibers ran principally in a longitudinal direction, becoming thicker and denser at the articular margin, before attaching at an acute angle along the rim and neck of the glenoid bone. Some fibers attached directly to bone, and some ran parallel to the bone surface, blending with the periosteum. This attachment was thickest and longest at the 3 o’clock location, inserting for a distance of more than 10 mm on the glenoid, and then became thinner and smaller with each section inferior. Near the 5 o’clock location, the collagen was disorganized in appearance and attached to the rim of the glenoid bone.

Fig 1A–C.

Fig 1A–C.

Fig 2A–B.

Fig 2A–B.

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DISCUSSION

There were two types of origin of the anteroinferior capsulolabrum at the glenoid of the glenohumeral joint in adults. In 80%, the attachment was primarily from the labrum, showing similarities to other direct ligament or tendon insertion sites, such as that of the supraspinatus. 4 Characteristic of these direct insertion sites, the collagen fibers met the attachment at a right angle in a sequence of four distinct zones (ligament, fibrocartilage, mineralized fibrocartilage, and bone). 38 This labral attachment of the anterior band of the inferior glenohumeral ligament was relatively long, 19 especially the zone of fibrocartilage at the anterosuperior margin of the anterior band of the inferior glenohumeral ligament, in contrast to other direct insertion sites. At more caudal locations, the capsulolabrum appeared disorganized near the glenoid, likely representing a change in direction of the collagen bundles. Here the orientation was no longer longitudinal as at the midsubstance, but was primarily in a radial fashion 13 to form the circular system of collagen bundles of the labrum. The fibrous glenoid labrum was formed by the origin of the capsuloligamentous structures to be an extension of the articular cavity for added joint stability.

In 20% of the glenohumeral joints, the anteroinferior capsuloligamentous structures originated primarily from the glenoid bone. Especially at the 3 o’clock location, it was similar to the tibial insertion of the medial collateral ligament as described by Woo and coworkers. 39 Dense collagen fibers met the attachment at the bone at an acute angle as an indirect insertion. Superficial and deep fibers were present. The superficial fibers ran parallel to the bone surface, blending in with the periosteum and the deep fibers attached straight to the bone.

The anteroinferior capsuloligamentous structures have been reported to have labral origin. 24,25,32 Others described the anterior band of the inferior glenohumeral ligament as being intimately attached to the labrum and the rim of glenoid bone, 8 implying it was not consistent. However, when there was an attachment to the neck of the glenoid it was described as well-developed, rather than simply a thickening in the capsule. Gohlke and coworkers 13 also reported that the origin of fibers at the 3 o’clock location on the glenoid was anchored most commonly to the glenoid bone. In their description, these fibers inserted mostly at an acute angle but were part of the middle glenohumeral ligament. Histologic cross sections of the glenohumeral joint as reported in 1962 by Moseley and Overgaard 24 also showed attachments to the glenoid bone.

The fibers described in the current study were from sections through and inferior to, the 3 o’clock location on the glenoid. Although the relationship of these fibers to the anterior capsular ligaments was difficult to ascertain from the histologic sections, fibers in this location on the glenoid correspond to the origin of the anterior band of the inferior glenohumeral ligament. 8,36 One histologic study found two attachments of the anterior band of the inferior glenohumeral ligament at the glenoid, one into the labrum and another into the anterior glenoid rim and neck. 19 Study of joints from humans before birth found the origin solely from the labrum in 77% and from the glenoid neck in 23%. 35 This correlated very closely with the results of the current study in glenohumeral joints from adults indicating that variation in origin of the anterior band of the inferior glenohumeral ligament is congenital and not acquired. Because joints from elderly individuals were studied, this also indicates there is little change with aging.

A severe Bankart lesion, poor tissue quality, too few repair sutures, failure to properly plicate the capsuloligamentous structures, recurrent injury from contact sports, large number of preoperative dislocations, and mistreatment of multidirectional instability have been associated with failure after surgical repair. 6,14,18,20,28,33 Variation in pathoanatomy from different anteroinferior capsulolabral origin types also may account for some failures. In the majority of joints, the anterior band of the inferior glenohumeral ligament ruptures with the labrum when dislocation occurs. However, if the anterior band of the inferior glenohumeral ligament originated primarily from the glenoid, it may rupture, stretch, or tear but leave the labrum intact. Repair focused on the labrum may then neglects the anterior band of the inferior glenohumeral ligament injury so that it no longer can function as the primary static restraint to anterior instability. Misunderstanding of this anatomy also may partly explain the discrepancy in results between the traditional open technique of Bankart lesion repair, from outside the glenohumeral joint, and arthroscopic repair which involves repair from the inside. In the first, both attachments are repaired routinely whereas in the latter the labral attachment is repaired and depending on the surgical technique the glenoid attachment may or may not be repaired.

In adults, there are two types of origin of the anteroinferior capsulolabrum, the location of the anterior band of the inferior glenohumeral ligament. A Type I origin, where the ligament arises from the glenoid rim, labrum and neck, occurs in 80% of cases. The second, is a Type II origin, where the ligament arises entirely from the glenoid neck and occurs in 20% of cases. This variability should be considered when selecting the technique of repair for surgical treatment of anterior glenohumeral dislocation.

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Section Description

Patrick J. McMahon, MD; and Thay Q. Lee, PhD—Guest Editors

© 2002 Lippincott Williams & Wilkins, Inc.