Anatomic study of the glenoid labrum

ArUco-based stylus reliability for reproductible 3D digitalisation of shoulder cartilage contours

Imaging techniques in anatomy have developed rapidly over the last decades through the emergence of various 3D scanning systems. Depending on the dissection level, non-contact or tactile contact methods can be applied on the targeted structure. The aim of this study was to assess the inter and intra-observer reproducibility of an ArUco-based localisation stylus, that is, a manual technique on a hand-held stylus. Ten fresh-frozen, unembalmed adult arms were used to digitalise the glenoid cartilage related to the glenohumeral joint and the contour of the clavicle cartilage related to the acromioclavicular joint. Three operators performed consecutive digitalisations of each cartilage contour using an ArUco-based localisation stylus recorded by a single monocular camera. The shape of each cartilage was defined by nine shape parameters. Intra-observer repeatability and inter-observer reproducibility were computed using an intra-class correlation (ICC) for each of these parameters. Overall, 35.2 ± 2.4 s and 26.6 ± 10.2 s were required by each examiner to digitalise the contour of a glenoid and acromioclavicular cartilage, respectively. For most parameters, good-to-excellent agreements were observed concerning intra-observer (ICC ranging between 0.81 and 1.00) and inter-observer (ICC ranging between 0.75 and 0.99) reproducibility. To conclude, through a fast and versatile process, the use of an ArUco-based localisation stylus can be a reliable low-cost alternative to conventional imaging methods to digitalise shoulder cartilage contours.

Anatomical, functional and biomechanical review of the glenoid labrum

The glenohumeral joint is the most mobile joint in the human skeleton, supported by both active and passive stabilisers. As one of the passive stabilisers, the glenoid labrum has increasingly been recognised to play an important role in stability of the glenohumeral joint, acting to maintain intraarticular pressure, centralise the humeral head and contribute to concavity-compression stability. Several studies have investigated the macro- and micro-anatomical features of the labrum as well as its biomechanical function. However, in order to better understand the role of the labrum and its mechanics, a comprehensive anatomical, functional and biomechanical review of these studies is needed. Therefore, this article reviews the current literature detailing anatomical descriptions of the glenoid labrum, with an emphasis on its function(s) and biomechanics, as well as its interaction with neighbouring structures. The intimate relationship between the labrum and the surrounding structures was found to be important in glenohumeral stability, which owes further investigation into the microanatomy of labrum to better understand this relationship.

Reconciling arthroscopic and anatomic morphology of the humeral insertion of the inferior glenohumeral ligament

PURPOSE

To clarify the morphology of the humeral insertion of the inferior glenohumeral ligament (IGHL).

TYPE OF STUDY

Cadaveric and arthroscopic anatomic analysis.

METHODS

The morphology of the humeral insertion was studied in 200 nonembalmed cadavers through open dissection (100 specimens), by arthroscopy (50 specimens), or both (50 specimens). In addition, the morphology was studied in 100 living subjects with stable shoulders undergoing shoulder arthroscopy.

RESULTS

On the humeral side, the insertion of the inferior capsular fibers is usually in the form of a V, the point of which is covered by the tendon of the latissimus dorsi. When viewed intra-articularly, the inferior insertion usually gives a collar-like impression because the capsular recess is filled with frenula capsulae.

CONCLUSIONS

Our description corresponds with that found in the classic literature. Our results are, however, in contrast with those of others who have observed about 50% of V-shaped insertions. This difference may be explained by the method of observation and by the small numbers of specimens studied. The form of the humeral insertion of the IGHL is linked to the formation of a supporting hammock that can accommodate the humeral head during movement as described by several authors.

CLINICAL RELEVANCE

We believe that the difference between arthroscopic and anatomic observation of the humeral insertion may have 2 major clinical implications. An observed tear of the frenula capsulae may not necessarily represent a humeral avulsion of the glenohumeral ligaments (HAGL). In the case of a HAGL, the capsule may have to be reattached in its V-form to adequately retension the inferior capsule.

Biomechanical evaluation of multidirectional glenohumeral instability and repair

The purpose of the current study was to create a multidirectional glenohumeral instability model and compare anterior capsulolabral reconstruction with inferior capsular shift with respect to their effects on glenohumeral translation and rotational range of motion. Ten fresh frozen cadaveric shoulders were used with a custom shoulder translation testing jig. To create the multidirectional instability model the capsule was stretched an additional 20% from the initial rotational range of motion in apprehension and neutral positions. Shoulders were repaired using anterior capsulolabral reconstruction (n = 5) or an inferior capsular shift (n = 5). Anterior, posterior, inferior, and superior translations were measured along with the rotational range of motion for intact, stretched, and repaired conditions. All specimens showed increased translations and rotations after stretching. Both repair techniques significantly reduced anterior, posterior, and inferior translation. The inferior capsular shift was more effective in reducing inferior translation in the apprehension position; however, postoperative rotational range of motion was restricted significantly when compared with anterior capsulolabral reconstruction, and posterior subluxation of the humeral head was seen in all specimens. These results indicate that a vertical capsulorrhaphy with a medial to lateral shift of the glenohumeral capsule, as in the inferior capsular shift repair, significantly reduces rotational range of motion when compared in vitro with the horizontal shift of the anterior capsulolabral reconstruction.

Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression : an in vitro study

BACKGROUND

Although the glenohumeral joint is the most mobile articulation of the human body, it is known to exhibit ball-and-socket kinematics. Compression into the glenoid labral concavity keeps the humeral head centered. The purpose of the present study was to determine the effects of joint position on glenohumeral stability through concavity-compression.

METHODS

Ten cadaveric shoulders were tested. The glenoid was mounted horizontally onto a six-component load-cell while the humerus was clamped to a vertically unconstrained slide. An x-y stage translated the load-cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of 20, 40, and 60 N were applied. The tests were repeated in 0 degrees, 30 degrees, 60 degrees, and 90 degrees of glenohumeral abduction with and without the labrum. Relative translations between the glenoid and the humeral head and the forces resisting translation were recorded. Then the stability ratio, defined as the peak translational force divided by the applied compressive force, was calculated.

RESULTS

The average stability ratio was higher in the hanging-arm position than it was in glenohumeral abduction. The highest stability ratio was detected in the inferior direction (59.8% 7.7%) when the labrum was intact and in the superior direction (53.3% 7.9%) when the labrum had been resected. Under both conditions, the anterior direction was associated with the lowest stability ratio (32.0% 4.4% with the labrum and 30.4% 4.1% without the labrum). Resection of the glenoid labrum resulted in an average decrease in the stability ratio of 9.6% 1.7%. With increasing compressive load, the average stability ratio slightly decreased.

CONCLUSIONS

Glenohumeral stability through concavity-compression was greater in the hanging-arm position than it was in glenohumeral abduction. The average contribution of the labrum to glenohumeral stability through concavity-compression was approximately 10%, about one-half of the value previously reported. With the labrum intact, the glenohumeral joint was most stable in the inferior direction. Without the labrum, it was most stable in the superior direction. Under both conditions, it was least stable in the anterior direction. Glenohumeral joint stability through concavity-compression decreases with higher compressive loads.

Multidirectional instability: current concepts

Multidirectional instability (MDI) of the shoulder is a complex problem that is not yet well understood. Instability in several directions is termed MDI, but the precise definition, classification, cause, and optimal method of treatment remains elusive. The cause appears to be multifactorial, with biochemical and biomechanical abnormalities present in shoulders with MDI. The biomechanical factors responsible for preventing MDI include bony architecture, concavity-compression from the deepening of the glenoid by the labrum, stability from the ligaments, primarily the inferior glenohumeral ligament complex and the superior capsular structures, and muscular control by use of force couples, especially stabilization of the scapula. Current recommended treatment is initially nonoperative, with aggressive physical therapy aimed at strengthening the rotator cuff and the scapular stabilizers. Patients who fail to respond to a nonoperative regimen often improve with surgical stabilization, which is usually an inferior capsular shift or a variant of that procedure. After this surgery immobilization of the operated shoulder for 6 to 8 weeks is recommended by most authors.