Piyush Walia

Theoretical model of the effect of combined glenohumeral bone defects on anterior shoulder instability: A finite element approach†

The presence of either a Hill–Sachs or a bony Bankart defect has been indicated as a possible cause of subluxation and anterior shoulder dislocation. Previous studies investigated only the effects of isolated humeral or glenoid defects on glenohumeral instability. We investigated the effects on shoulder stability of both glenoid and humeral defects in the glenohumeral joint. A computer‐based finite element approach was used to model the joint. A generic model was developed for cartilage and bone of the glenoid and humerus, using previously published data, and experiments were analyzed using static analysis with displacement control in the anterior‐inferior direction. Simulations were run with a 50‐N compressive load in the presence of both isolated and combined defects to analyze reaction forces and distance to dislocation. The distance to dislocation for normal joint was 13.6 mm at 90° abduction, which reduced to 9.7, 0, and 0 mm for largest isolated humerus defect, glenoid defect, and certain combined defects, respectively. For combined defects, stability ratio was decreased to 0% from 43%. Our results suggest that in the setting of combined bone defects, stability may be reduced more than what is known for isolated defects alone.

Stability of the Glenohumeral Joint With Combined Humeral Head and Glenoid Defects A Cadaveric Study

Objectives: Shoulders with recurrent anterior shoulder instability often have combined defects of the humeral head and glenoid. The aim of this study is to define the relationship of combined humeral head and glenoid defects on anterior shoulder instability. We hypothesize that combined humeral head and glenoid defects will produce greater instability than either defect found alone, and that the size of humeral head and glenoid defects which are “critical” and need to be repaired in order to restore glenohumeral stability will be smaller when the defects are found together than when either defect is found alone. Methods: Eighteen shoulder specimens (mean age 57 years) were tested at 60° of glenohumeral abduction and 80° of glenohumeral external rotation (equivalent to 90° of abduction and 90° of external rotation relative to the trunk). Humeral head defect sizes included 6%, 19%, 31%, and 44% of the humeral head diameter. Glenoid defect sizes included 10%, 20%, and 30% of the glenoid width. Outcome measures included Percent of Intact Stability Ratio (stability ratio for a given trial divided by the stability ratio in the intact state for that specimen) and Percent of Intact Translation (distance to dislocation for a given trial divided by the distance to dislocation in the intact state for that specimen). Results: There was a progressive decrease in stability as humeral head defect size increased and as glenoid defect size increased. The decrease in Percent of Intact Stability Ratio reached statistical significance for humeral head defects of 44%, for glenoid defects of 30%, and additionally for a combined 19% humeral head defect with a 20% glenoid defect. The mean Percent of Intact Stability Ratio was 65% for a combined 19% humeral head defect with a 20% glenoid defect. The decrease in Percent of Intact Translation reached statistical significance for humeral head defects of 31% and 44%, for glenoid defects of 20% and 30%, and additionally for a combined 19% humeral head defect with a 10% glenoid defect. The mean Percent of Intact Translation was 69% for a combined 19% humeral head defect with a 10% glenoid defect. Conclusion: The humeral head and glenoid defect sizes required to produce instability are smaller when the defects are found together than when either defect is found alone. In patients with combined humeral head and glenoid defects bony reconstruction may be indicated for humeral head defects as small as 19% of the humeral head diameter and glenoid defects as small as 10-20% of the glenoid width.

The effects of Latarjet reconstruction on glenohumeral instability in the presence of combined bony defects: A cadaveric model

Objectives: Recurrent glenohumeral instability is often a result of underlying bony defects in the glenoid and/or humeral head. Anterior glenoid augmentation with a bone block (i.e. Latarjet) has been recommended for glenoid bone loss in the face of recurrent instability. However, no study has investigated the effect of Latarjet augmentation in the setting of both glenoid and humeral head defects (Hill-Sachs Defects (HSD)). The purpose of this study was to evaluate the stability achieved through a Latarjet procedure in the presence of combined bony defects. Our hypothesis was that Latarjet augmentation would increase shoulder stability for glenoid defects with small HSD, but have limited success in cases with large concomitant HSD. Methods: Eighteen fresh-frozen cadaveric specimens were tested at combinations of glenohumeral abduction (ABD) angles of 20°, 40°, and 60° and external rotation (ER) angles of 0°, 40°, and 80°. Each experiment applied a 50N medial load on the humerus to replicate the static load of soft tissues, and then simulated anterior dislocation by translating the glenoid in an anterior direction. Translational distance and medial-lateral displacement of the humeral head, along with horizontal reaction forces, were recorded for every trial. Specimens were tested in an intact condition (no defect), different combinations of defects, and with Latarjet augmentation. The Latarjet was performed for 20% and 30% glenoid defects by transferring the specimen’s coracoid process anterior to the glenoid flush with the articulating surface. Results: Results are summarized in Fig. 1. The vertical axis represents the normalized distance to dislocation with respect to the values of the intact joint. The horizontal axis represents the varying sizes and combinations of bony defects. Latarjet augmentation improved stability for every combination of bony defects. At 20° ABD, 0°ER, and 20% glenoid defect size, the percentage of intact translation did not change with increasing HSD size, and the Latarjet augmentation increased percent intact translation to greater than 100 percent for all cases (Fig. 1A). However, at 60° ABD, 80° ER, and 20% glenoid defect size, increasing HSD size caused decreased stability, and Latarjet augmentation did not increase the percent intact translation to normal levels for HSD sizes greater than 30% (Fig. 1B). Conclusion: This is first study to investigate and quantify the effect of Latarjet reconstruction on anterior shoulder instability in the presence of combined humeral head and glenoid defects. Clinically, these results demonstrate that some degree of stability can be regained for combined bony Bankart and Hill-Sachs defects with a Latarjet procedure. However, for humeral defects larger than 30%, the HSD led to persistent instability in the abducted externally rotated position, even after the Latarjet procedure. Thus, directly addressing the humeral defect to restore the articular surface should be considered in these cases.

The Reduction in Stability From Combined Humeral Head and Glenoid Bony Defects Is Influenced by Arm Position

Background: Combined defects of the glenoid and humeral head are often a cause for recurrent shoulder instability. Purpose/Hypothesis: The aim of this study was to evaluate the influence of combined bony lesions on shoulder instability through varying glenohumeral positions. The hypothesis was that instability due to combined defects would be magnified with increasing abduction and external rotation. Study Design: Controlled laboratory study. Methods: Eighteen cadaveric shoulders were tested. Experiments were performed at combinations of glenohumeral abduction angles of 20°, 40°, and 60° and external rotations of 0°, 40°, and 80°. The various glenoid defect sizes created were 10%, 20%, and 30% of the glenoid width. Four humeral head defects were created based on humeral head diameter (6%, 19%, 31%, and 44%). Each experiment consisted of translating the glenoid in a posterior direction to simulate an anterior dislocation under a 50-N load. The instability was measured as a percentage of intact translation (ie, loss in translational distance normalized to the no-defect condition). Results: At 20° of abduction, instability increased from 100% to 85%, 70%, and 43% with increasing glenoid defect sizes of 10%, 20% and 30%, respectively, with a 6% humeral head defect. However, at a functional arm position of apprehension, these values were significantly decreased (P < .05) for humeral head defect sizes of 19%, 31%, and 44%, with translation values of 49%, 27%, and 2%, respectively. Conclusion: A humeral defect leads to rotational instability with the arm rotated into a functional position rather than a resting position. However, a significant glenoid defect can lead to loss of translation independent of changes in arm position. Combined defects as large as 44% of humeral head and 20% glenoid did not show instability at 20° of abduction and neutral position; however, defects as small as 19% humeral defect and 10% glenoid defect led to significant instability in the position of apprehension. Clinical Relevance: Instability at lower levels of abduction and external rotation clinically indicates larger bony defects and may need to be directly addressed, depending on the patient’s age and function.

Subject-specific finite element analysis of the carpal tunnel cross-sectional to examine tunnel area changes in response to carpal arch loading

Background: Manipulating the carpal arch width (i.e. distance between hamate and trapezium bones) has been suggested as a means to increase carpal tunnel cross‐sectional area and alleviate median nerve compression. The purpose of this study was to develop a finite element model of the carpal tunnel and to determine an optimal force direction to maximize area. Methods: A planar geometric model of carpal bones at hamate level was reconstructed from MRI with inter‐carpal joint spaces filled with a linear elastic surrogate tissue. Experimental data with discrete carpal tunnel pressures (50, 100, 150, and 200 mm Hg) and corresponding carpal bone movements were used to obtain material property of surrogate tissue by inverse finite element analysis. The resulting model was used to simulate changes of carpal arch widths and areas with directional variations of a unit force applied at the hook of hamate. Findings: Inverse finite element model predicted the experimental area data within 1.5% error. Simulation of force applications showed that carpal arch width and area were dependent on the direction of force application, and minimal arch width and maximal area occurred at 138° (i.e. volar‐radial direction) with respect to the hamate‐to‐trapezium axis. At this force direction, the width changed to 24.4 mm from its initial 25.1 mm (3% decrease), and the area changed to 301.6 mm2 from 290.3 mm2 (4% increase). Interpretation: The findings of the current study guide biomechanical manipulation to gain tunnel area increase, potentially helping reduce carpal tunnel pressure and relieve symptoms of compression median neuropathy. Highlights:Carpal tunnel compliance allows for geometrical change with biomechanical manipulation.Narrowing of the carpal arch width results in an increase in carpal tunnel area.Patient‐specific finite element modeling predicted optimal force direction to achieve maximum area increase.Increase in overall area of the carpal tunnel potentially relieves median nerve compression.

A Simple Population-Based Finite Element Model Eliminates the Need for Patient-Specific Models to Predict Instability of the Shoulder

Objectives: Recurrent shoulder instability can significantly increase in the presence of bony Bankart and Hill-Sachs lesions. Therefore, it is important to understand the changes in shoulder biomechanics due to bony defects. Limitations of using cadaveric model to investigate the effects of combined bony defects on shoulder instability is inability to test all combination in a single specimen. Utilizing the flexibility of computational methodology like finite element (FE) model provides the advantage of testing all combinations at multiple arm positions. The aim of this study was to develop a simple FE model of combined bony lesions and its effect on anterior shoulder instability. In addition, we wanted to determine the need for patient (specimen) specific modeling. We hypothesized that the shoulder instability would be similar for all three models (population-based model, specimen-specific model, and cadaveric model). Methods: Three specimens were randomly selected from specimens tested in our previous study and Computed Tomography (CT) arthrogram images were taken before and after experimentation to develop FE models. We also developed a simple population-based model representing a spherical humeral head, which was developed using the radii values for cartilage and bone from literature. The sizes of humeral head lesions chosen were: 6%, 19%, 31%, and 44% of humeral head diameter and glenoid defect sizes were 10%, 20% and 30% of the glenoid width. All simulations were performed at glenohumeral abduction angles (ABD) of 20°, 40°, and 60° and external rotation of 0°, 40°, and 80°. Each simulation comprised of translating the humeral head leading to an anterior dislocation under a constant 50 N medial load. This compressive load simulated the static load of soft tissue. The percent intact translation (%IT) was computed by normalizing the distance to dislocation value for each defect condition w.r.t intact condition of each specimen. Stability Ratio (SR) was computed as a ratio of horizontal reaction force to the compressive load. Results: The individual specimen-specific model results comparison to the experimental data for %IT had a good agreement as the values were similar for defect created. However, results for SR were over predicted by the FE model, but they had similar linear decreasing trends for both specimen-specific and cadaveric model. In addition, the humeral head defect size of 44% reduced the %IT from 100% to nearly 0% for all three models. The results for the comparison of all three models with increasing size of humeral defect with a 20% glenoid defect are shown in Figure 1 at three arm position. Conclusion: This study proposed a simple population-based model that can be used to estimate the loss in stability due to combined defects to determine a threshold for defect augmentation in clinical practice. It was demonstrated that a smaller glenoid defect size of 10% combined with a 19% humeral head defect can cause significant instability. Similar to past studies, it was also shown that a glenoid defect would lead to loss of translation and a humeral head defect would lead to instability at a functional arm position of increased abduction and external rotation [5-6]. All three models predicted similar results during validation, which shows that the population based model can be utilized to estimate the stability, instead of needing patient-specific FE models. The limitation of the study is the absence of soft tissue restraints.

The Effects of Latarjet Reconstruction on Glenohumeral Instability in the Presence of Combined Bony Defects

Objectives: Recurrent glenohumeral instability is often as a result of underlying bony defects in the glenoid and/or humeral head. Anterior glenoid augmentation with a bone block (i.e. Latarjet) has been recommended for glenoid bone loss in the face of recurrent instability. However, no study has investigated the effect of Latarjet augmentation in the setting of both glenoid and humeral head defects (Hill-Sachs Defects (HSD)). The purpose of this study was to evaluate the stability achieved through a Latarjet procedure in the presence of combined bony defects. Methods: Eighteen fresh-frozen cadaveric specimens were tested at all combinations of glenohumeral abduction (ABD) angles of 20°, 40°, and 60° and three external rotation (ER) levels (0°, 40°, and 80°). Each experiment comprised of anterior dislocation by translating the glenoid under a 50N medial load applied on the humerus, simulating the static load of soft tissues. Translational distance and medial-lateral displacement of the humeral head, along with horizontal reaction forces were recorded for every trial. Specimens were tested in an intact condition (no defect), different combinations of defects, and with Latarjet augmentation. The Latarjet was performed for 20% and 30% glenoid defects by transferring the specimens coracoid process anterior to the glenoid flush with the articulating surface. Four different humeral head defects were created of sizes 6%, 19%, 31%, and 44% of humeral diameter. Repeated measures analysis of variance (ANOVA) was performed with statistical significance set at p <0.05. Results: Results are summarized in Fig. 1. The vertical axis represents the normalized distance to dislocation with respect to the values of the intact joint. The horizontal axis represents the varying sizes and combinations of bony defects. At 20° ABD and 0°ER, increasing HSD size did not affect percentage of intact translation with a constant glenoid defect of 20% before and after Latarjet augmentation (Fig. 1A). However, at an arm position of 60° ABD and 80° ER increasing HSD size led to a decrease in stability for both the defect state and post-Latarjet trials (Fig. 1B). Nevertheless, Latarjet augmentation helped in regaining stability for every combination of bony defects. With a HSD size of 44% the defect state had 0% intact translation for all 18 specimens. Conclusion: Clinically, these results demonstrate that some degree of stability can be regained for combined bony Bankart and Hill-Sachs defects with a Latarjet procedure. However, for humeral defects larger than 30%, the rotational effect of the HSD led to persistent instability. Thus, directly addressing the humeral defect to restore the articular surface should be considered in these cases. In conclusion, this study demonstrated that Latarjet procedure can restore the stability for combined defects, however for humeral defects greater than 31% may need attention.

Loss of Anterior Stability of Shoulder Across a Range of Motion Due to Combined Bony Defects: A Cadaveric Study

Objectives: Previous studies have analyzed only the effects of isolated glenoid or humeral head defects at limited arm positions. Literature data also suggests that instability might vary for envelop of motion. The aim of this study was to evaluate the effect of combined bony lesions on shoulder instability through varying glenohumeral positions. We hypothesized that the shoulder stability would significantly decrease with increasing defect size, and in the presence of combined defects. Furthermore, instability secondary to a humeral head defect will be magnified at functional arm positions. Methods: All experiments were performed at glenohumeral abduction angles (ABD) of 20°, 40°, and 60° and external rotations (ER) of 0°, 40°, and 80° for 18 specimens. Each experiment comprised of translating the glenoid in a posterior direction in order to cause an anterior dislocation under a 50N load. Translational distance of the glenoid and medial-lateral displacement of the humeral head, along with horizontal reaction force were recorded for every trial. Since it was not possible to test every defect combination in a single specimen, three different pathways were chosen (4 levels of glenoid defect and 5 levels of humeral defect) to maximize defect combinations. The sizes of humeral head lesions and glenoid defect were chosen similar to previous studies. Results: At 60° ABD and 80° ER, stability decreased from 100% to 85.2% and 73.7 % with isolated glenoid defect sizes of 10% and 20%, respectively. A combination of a 44% humeral head defect with 20% and 30% glenoid defect resulted in 1.6% and 1.4% intact translation, respectively. At 20° ABD and 0° ER, % intact translations were 69.0 ± 9.7, 64.3 ±12.9, 64.9 ± 11.1, 66.7 ± 8.8, 69.3 ± 13.9 for humeral defect sizes of 0%, 6%, 19%, 31%, 44% with a 20% glenoid defect, respectively. However, at a functional position of 60° ABD and 80° ER these values were significantly different (p < 0.05) for humeral head defects of size 19%, 31%, and 44% with translation values of 48.6 ± 24.2, 26.6 ± 25.2, and 1.6 ± 3.6, respectively. The % intact translation values for glenoid defects sizes 20% and 30% were significantly different (p < 0.05) for all arm positions. Combination of a smaller 6% humeral defect with increasing glenoid defects of size 0%, 10%, 20% and 30% has translation values 103.0 ± 2.9, 82.6 ± 16.4, 65.2 ± 12.9, and 40 ± 20.7, respectively. These values were similar at different arm positions. Conclusion: This study demonstrated that a smaller glenoid defect size of 10% combined with a 19% humeral head defect, can lead to a significant instability. Additionally, it was shown that a significant glenoid defect would lead to loss of translation independent of changes in the arm position. However, the loss of stability from a humeral head defect would lead to loss of translational stability significantly at a functional arm position of increased abduction and external rotation rather than a resting arm position. This rotational dependency of a humeral head defect further leads to a magnified instability during combined defects.

Anterior Instability of the Shoulder: Effect of Arm Position and Relative Contributions of Bony Bankart and Hill-Sachs Defects

Shoulder stability can be significantly reduced in the presence of bony defects. Bony Bankart and Hill-Sachs lesions are known causes for recurrent shoulder dislocation. It has been shown in literature that often these defects are present together during cases of recurrent dislocation.1 However, past studies have only analyzed the effects of isolated bony Bankart or Hill-Sachs lesions.2, 3 Recent studies have stated that a Hill-Sachs lesion that “engages” the anterior glenoid has a critical impact on shoulder stability.4 It is important to understand the relationship between these two bony defects, as this would lead to better management of the shoulders’ instability.Copyright