https://upoj.org/wp-content/uploads/v20/v20_15.pdf

The thrower's shoulder.

Pathology of the superior glenoid labrum is a common source of musculoskeletal pain and disability. One of the proposed mechanisms of injury to the labrum is superior humeral head migration, which can be seen with rotator cuff insufficiency. Due to the size, anatomical location, and complex composition of the labrum, laboratory experiments have many methodological difficulties. The purpose of this study was to develop and validate a finite element model of the glenoid labrum. The model developed includes the glenoid labrum, glenoid cartilage, glenoid bone, and the humeral head cartilage. Labral displacements derived from the finite element model were compared to those measured during a controlled validation experiment simulating superior humeral head translations of 1, 2, and 3 mm. The results of the finite element model compared well to experimental measurements, falling within one standard deviation of the experimental data in most cases. The model predicted maximum average strains in the superior labrum of 7.9, 10.1, and 11.9%, for 1, 2, and 3 mm of humeral translation, respectively. The correspondence between the finite element model and the validation experiment supports the use of this model to better understand the pathomechanics of the superior labrum.

Development and Validation of a Finite Element Model of the Superior Glenoid Labrum

OBJECTIVE: The purpose of this study was to establish if, in elite junior tennis players, there is a difference between the dominant and nondominant shoulders in the internal and external range of motion (ROM) of the shoulder and to examine the effect of taping the dominant shoulder on glenohumeral internal and external rotation ROM. DESIGN: Measurement of glenohumeral rotational ROM was performed on the dominant and nondominant shoulders in supine with the humerus abducted to 90 degrees. SETTING: Training room at the New South Wales Institute of Sport tennis center, Homebush, New South Wales, Australia. PARTICIPANTS: Eleven asymptomatic male subjects and 10 asymptomatic female subjects from an elite junior training squad participated in the study. INTERVENTION: Humeral head repositioning with tape. MAIN OUTCOME MEASURE: Glenohumeral ROM. RESULTS: A statistically significant decrease in internal rotation for both the male and female groups between the dominant and nondominant shoulders, but only the female group had a significant increase in external rotation in the dominant compared with the nondominant shoulder. There was also a statistically significant increase in range between the tape and no tape conditions for each rotation condition. CONCLUSIONS: The specific application of tape to the glenohumeral joint can immediately increase rotational ROM in the dominant arm of tennis players.

The effect of tape on glenohumeral rotation range of motion in elite junior tennis players.

The glenoid labrum is an integral component of the glenohumeral capsule's insertion into the glenoid, and changes in labrum geometry and mechanical properties may lead to the development of glenohumeral joint pathology. The objective of this research was to determine the effect that changes in labrum thickness and modulus have on strains in the labrum and glenohumeral capsule during a simulated physical examination for anterior instability. A labrum was incorporated into a validated, subject-specific finite element model of the glenohumeral joint, and experimental kinematics were applied simulating application of an anterior load at 0 deg, 30 deg, and 60 deg of external rotation and 60 deg of glenohumeral abduction. The radial thickness of the labrum was varied to simulate thinning tissue, and the tensile modulus of the labrum was varied to simulate degenerating tissue. At 60 deg of external rotation, a thinning labrum increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 10.5% average strain) and anterior band (increased 7.5% average strain). These results suggest a cause-and-effect relationship between age-related decreases in labrum thickness and increases in labrum pathology. A degenerating labrum also increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 15.5% strain) and anterior band (increased 10.4% strain). This supports the concept that age-related labrum pathology may result from tissue degeneration. This work suggests that a shift in capsule reparative techniques may be needed in order to include the labrum, especially as activity levels in the aging population continue to increase. In the future validated, finite element models of the glenohumeral joint can be used to explore the efficacy of new repair techniques for glenoid labrum pathology.

The Impact of Glenoid Labrum Thickness and Modulus on Labrum and Glenohumeral Capsule Function

Shoulder labral pathomechanics with rotator cuff tears

Superior labrum tears are common injuries in the throwing athlete. Sever contributing factors have been identified; however, the effects of instability on the superior labrum have not been studied. The goal of this cadaver study was to determine the effect of instability on superior labral strain in a model of the throwing motion. Six cadaver shoulders were mounted on an MTS machine with a strain gauge placed on the superior labrum. The shoulder was brought into the late cocking phase and strain measured before and after the introduction of a lesion to the inferior glenohumeral ligament to create anterior instability. Labral strain increased linearly in the late cocking phase of throwing in all specimens. Posterosuperior labral strain increased 160% in the unstable shoulders. This was a significant difference (P = .02). Instability increases strain in the posterosuperior labrum in the late cocking phase of throwing. This increased strain may render the labrum more prone to injury in the throwing or overhead athlete.

Anterior Instability Increases Superior Labral Strain in the Late Cocking Phase of Throwing

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Anterior Instability Increases Superior Labral Strain in the Late Cocking Phase of Throwing