Fiber components of the shoulder superior labrum

Histology, vascularity and innervation of the glenoid labrum

BACKGROUND

Although the glenoid labrum has an important role in shoulder stability, little is known about its composition, vascularity and innervation. The aims of this study were therefore to evaluate the histology, vascularity and innervation of the glenoid labrum.

MATERIALS AND METHODS

Ten glenoid labrum specimens (three male, two female: mean age 81.2 years, range 76-90 years) were detached at the glenoid neck. Following decalcification, sections were cut through the whole thickness of each specimen perpendicular to the glenoid labrum at 12 radii corresponding to a clock face superimposed on the glenoid fossa. Then they were stained using haematoxylin and eosin, a silver nitrate protocol or subjected to immunohistochemistry using anti-protein gene protein 9.5 to demonstrate neuronal processes.

RESULTS

The labrum was fibrocartilaginous, being more fibrous in its free margin. There was a variable distribution of blood vessels, being more vascular in its periphery, with many originating from the fibrous capsule and piercing the glenoid labrum. Immunohistochemistry revealed positive staining of nerve fibres within the glenoid labrum.

CONCLUSION

The glenoid labrum is fibrocartilaginous, being more fibrous in its periphery, and is vascularized, with the anterosuperior aspect having a rich blood supply. Free sensory nerve fibres were also present; no encapsulated mechanoreceptors were observed. The presence of sensory nerve fibres in the glenoid labrum could explain why tears induce pain. It is postulated that these sensory fibres could play a role in glenohumeral joint proprioception.

Imaging the Glenoid Labrum and Labral Tears

The shoulder joint is the most unstable articulation in the entire human body. While this certainly introduces vulnerability to injury, it also confers the advantage of broad range of motion. There are many elements that work in combination to offset the inherent instability of the glenohumeral joint, but the glenoid labrum is perhaps related most often. Broadly, clinical unidirectional instability can be subdivided into anterior and posterior instability, which usually raise concern for anteroinferior and posteroinferior labral lesions, respectively. In the special case of superior labral damage, potential dislocation is blocked by structures that include the acromion; hence, while damage elsewhere commonly manifests as clinical instability, damage to the superior labrum is often described by the term microinstability. In this particular case, one of the radiologist's main concerns should be classic superior labral anteroposterior lesions. The glenoid labrum is also subject to a wide range of normal variants that can mimic labral tears. Knowledge of these variants is central to interpreting an imaging study of the labrum because misdiagnosis of labral variants as tears can lead to superfluous surgical procedures and decreased shoulder mobility. This article reviews labral anatomy and normal labral variants, describes their imaging features, and discusses how to discriminate normal variants from labral tears. Specific labral pathologic lesions are described per labral quadrant (anteroinferior, posteroinferior, and superior), and imaging features are described in detail. Online supplemental material is available for this article. ^©RSNA, 2016.

Anatomical study for SLAP lesion repair

PURPOSE

The purpose of this study was to meticulously observe the structures around the origin of the long head of the biceps tendon (LHB) in order to propose a method of anatomical superior labrum anterior and posterior repair.

METHODS

Twenty-eight shoulders of 16 cadavers with intact LHB origin were macroscopically investigated. Among them, 20 shoulders with an intact superior labrum were additionally observed, to determine whether the anterior edge of LHB on the labrum (point 'A') was anterior to the supraglenoid tubercle. Serial sections vertical to LHB were observed using ordinary light and polarized microscopy in three glenoids and scanning acoustic microscopy in one.

RESULTS

The labrum had a meniscal appearance, and no LHB fibre was sent anterior to the anterior edge of the supraglenoid tubercle. 'A' was not located more posterior than the supraglenoid tubercle. All specimens had the so-called 'the sheet-like structure', in which the portion closer to the LHB origin tends to be stiffer. Fibres of the sheet-like structure ran vertically to LHB.

CONCLUSION

Fibre orientation and the stiffness of the sheet-like structure suggest its support of LHB. As LHB fibres do not anteriorly cross over 'A', 'A' could be a landmark for the anterior border of LHB, independent from the sheet-like structure. Considering a previous report mentioning that the horizontal mattress suture maintains the meniscus-like structure which might be sufficient for proper motion of the normal superior labrum, the horizontal mattress suture not crossing over 'A' should be recommended from the viewpoint of functional anatomy.

Fibrocartilage in various regions of the human glenoid labrum. An immunohistochemical study on human cadavers

PURPOSE

The nature and the distribution of fibrocartilage at the human glenoid labrum are unclear, and a better understanding may help to restore its function in open and arthroscopic Bankart repair. Aim of this study was to describe the fibrocartilage extent within the labrum at clinically relevant sites of the glenoid in order to relate the molecular composition of the labrum to its mechanical environment.

METHODS

Twelve fresh frozen human cadaveric shoulders (mean age 38 years) were obtained, and sections perpendicular to the glenoid rim at the 12, 2, 3, 4, 6 and 9 o' clock position were labelled with antibodies against collagen I and II, aggrecan and link protein.

RESULTS

A fibrocartilaginous transition zone with a characteristic collagen fibre orientation was found in 81% of cases, evenly distributed (83-92%) around the glenoid rim. The percentage of labrum cross-sectional area comprised of fibrocartilage averaged 28% and ranged from 26% at 12 o'clock on the glenoid clock face to 30% at 3 o'clock. The highest amount of fibrocartilage (82%) was found in the region neighbouring the hyaline articular cartilage. In the region beyond the bony edge of the glenoid, fibrocartilage cross-sectional area did not exceed 12-17%.

CONCLUSION

Fibrocartilage is present at all examined positions around the glenoid rim and constitutes up to 1/3 of the cross-sectional area of the labrum. In turn, the percentage of fibrocartilage in different regions of its cross-section varies considerably. The findings suggest that the penetration of fibrocartilaginous tissue may be reduced by avoiding the highly fibrocartilage transition zone during restoration of labral detachment.

The rotator interval and long head biceps tendon: anatomy, function, pathology, and magnetic resonance imaging

The rotator interval is an anatomically defined triangular area located between the coracoid process, the superior aspect of the subscapularis, and the anterior aspect of the supraspinatus. It is widely accepted that the rotator interval structures fulfill a role in biomechanics and pathology of the glenohumeral joint and long head biceps tendon. However, there is ongoing debate regarding the biomechanical details and the indications for treatment. A better understanding of rotator interval anatomy and function will lead to improved treatment of rotator interval abnormalities, and guide the indications for imaging and surgical intervention.