Anterior Glenohumeral Translation Research Articles

Dynamic anterior shoulder stabilization using the long head of the biceps tendon: a biomechanical study: DAS: a biomechanical study

Objectives A new concept of dynamic anterior shoulder stabilization (DAS) combining Bankart repair with the additional sling effect of the long head of the biceps (LHB) tendon to treat anterior glenohumeral instability has recently been introduced. The purpose of this study was to biomechanically investigate the stabilizing effect of the DAS technique in comparison to standard Bankart repair in different defect models. Methods Twenty-four fresh frozen cadaver shoulders (average ± SD: age 60.1 ± 8.6 years) were mounted in a shoulder-testing system allowing 6 degrees of freedom. According to cross sectional area ratios the rotator cuff muscles and the LHB tendon were loaded with 40 N and 10 N, respectively. Glenohumeral translation was tested in 60° abduction and 60° external rotation (ABER position) while forces of 20 N, 30 N and 40 N were applied. The translation was measured using a 3D-digitizer and the total translation and the relative translation in relation to the native starting position were determined. Maximal external and internal rotation after application of 1.5 Nm torque to the humerus were measured. All specimens went through for 4 different conditions (Intact, defect, isolated Bankart repair, DAS) and were randomized to 3 different defect groups (Isolated Bankart lesion; 10% anterior glenoid defect; 20% anterior glenoid defect). Results Both surgical techniques resulted in decreased anterior glenohumeral translation in comparison to the defect conditions in all defect groups. In comparison with isolated Bankart repair DAS showed significant less relative anterior translation in 10% glenoid defects (30 N: 2.6 ± 3.4 mm vs. 5.3 ± 4.2 mm; p=0.044) and in 20% glenoid defects (40 N: 2.1 ± 6.6 mm vs. 6.0 ± 5.7 mm; p=0.035). However, in 20% defects DAS led to a relevant posterior and inferior shift of the humeral head in ABER position and to a relevant increase of inferior glenohumeral translation. Both surgical techniques did not limit the rotational range of motion. Conclusion In the context of minor glenoid bone defects the DAS technique demonstrates superior results in comparison to isolated Bankart repair.

Dynamic Anterior Shoulder Stabilization With the Long Head of the Biceps Tendon: A Biomechanical Study

Background: The concept of dynamic anterior shoulder stabilization (DAS) combines a Bankart repair with the additional sling effect of the long head of the biceps (LHB) tendon to treat anterior glenohumeral instability. This surgical technique was created to close the gap between the indications for isolated Bankart repair and those requiring bone transfer techniques. Purpose: To biomechanically investigate the stabilizing effects of the DAS technique in comparison with the standard Bankart repair in different defect models. Study Design: Controlled laboratory study. Methods: Twenty-four fresh-frozen cadaveric shoulders (mean ± SD age, 60.1 ± 8.6 years) were mounted in a 6 degrees of freedom shoulder testing system. With cross-sectional area ratios, the rotator cuff muscles and LHB tendon were loaded with 40 N and 10 N, respectively. Anterior and inferior glenohumeral translation was tested in 60° of abduction and 60° of external rotation (ABER position) while forces of 20 N, 30 N, and 40 N were applied to the scapula in the posterior direction. Total translation and relative translation in relation to the native starting position were measured with a 3-dimensional digitizer. Maximal external rotation and internal rotation after application of 1.5-N·m torque to the humerus were measured. All specimens went through 4 conditions (intact, defect, isolated Bankart repair, DAS) and were randomized to 1 of 3 defect groups (isolated Bankart lesion, 10% anterior glenoid defect, 20% anterior glenoid defect). The DAS was performed by transferring the LHB tendon through a subscapularis split to the anterior glenoid margin, where it was fixed with an interference screw. Results: Both surgical techniques resulted in decreased anterior glenohumeral translation in comparison with the defect conditions in all defect groups. As compared with isolated Bankart repair, DAS showed significantly less relative anterior translation in 10% glenoid defects at translation forces of 20 N (0.3 ± 1.7 mm vs 2.2 ± 1.8 mm, P = .005) and 30 N (2.6 ± 3.4 mm vs 5.3 ± 4.2 mm, P = .044) and in 20% glenoid defects at all translation forces (20 N: –3.2 ± 4.7 mm vs 0.8 ± 4.1 mm, P = .024; 30 N: –0.9 ± 5.3 mm vs 4.0 ± 5.2 mm, P = .005; 40 N: 2.1 ± 6.6 mm vs 6.0 ± 5.7 mm, P = .035). However, in 20% defects, DAS led to a relevant posterior and inferior shift of the humeral head in the ABER position and to a relevant increase in inferior glenohumeral translation. Both surgical techniques did not limit the rotational range of motion. Conclusion: In the context of minor glenoid bone defects, the DAS technique demonstrates less relative anterior translation as compared with an isolated Bankart repair at time zero. Clinical Relevance: The new DAS technique seems capable of closing the gap between the indications for isolated Bankart repair and bone transfer techniques.

Lower shoulder abduction during throwing motion may cause forceful internal impingement and decreased anterior stability

Internal impingement and decreased anterior stability, which result from shoulder capsular loosening, are common shoulder pathologies in throwing athletes. The purpose of this study was to assess the effect of shoulder abduction angle on shoulder internal impingement and anterior shoulder stability during the simulated throwing motion. Eight cadaveric shoulders were tested by simulating the late-cocking and acceleration phases of the throwing motion for intact and thrower's shoulder conditions. The maximal glenohumeral external rotation, anterior translation, location of the rotator cuff insertion with respect to the glenoid, length and site of internal impingement, and glenohumeral contact pressure were measured. All data were compared between shoulder abduction angles of 80°, 90°, and 100°. Decreasing shoulder abduction in the simulated late-cocking phase shifted the humeral head posteriorly (P < .03) and superiorly (P < .001), decreasing the total internal impingement area between the greater tuberosity and glenoid (P = .04) and increasing the glenohumeral contact pressure during internal impingement (P = .02). In the simulated acceleration phase, anterior glenohumeral translation significantly increased as the shoulder abduction angle decreased (P < .001). Decreasing shoulder abduction significantly increased the contact pressure during internal impingement in the simulated late-cocking phase of the throwing motion. During the simulated acceleration phase of the throwing motion, anterior glenohumeral translation significantly increased as shoulder abduction decreased.

Lower Shoulder Abduction During Throwing Motion May Cause Forceful Internal Impingement and Decreased Anterior Stability

Background Internal impingement and decreased anterior stability, which result from shoulder capsular loosening, are common shoulder pathologies in throwing athletes. The purpose of this study was to assess the effect of shoulder abduction angle on shoulder internal impingement and anterior shoulder stability during the simulated throwing motion. Methods Eight cadaveric shoulders were tested by simulating the late-cocking and acceleration phases of the throwing motion for intact and thrower's shoulder conditions. The maximal glenohumeral external rotation, anterior translation, location of the rotator cuff insertion with respect to the glenoid, length and site of internal impingement, and glenohumeral contact pressure were measured. All data were compared between shoulder abduction angles of 80°, 90°, and 100°. Results Decreasing shoulder abduction in the simulated late-cocking phase shifted the humeral head posteriorly (P Conclusion Decreasing shoulder abduction significantly increased the contact pressure during internal impingement in the simulated late-cocking phase of the throwing motion. During the simulated acceleration phase of the throwing motion, anterior glenohumeral translation significantly increased as shoulder abduction decreased.

The Effects of Posterior Rotator Cuff Cable Tears on Glenohumeral Biomechanics in a Cadaveric Model of the Throwing Shoulder

Objectives:The rotator cuff cable has been postulated to be the primary load bearing substructure of the superior part of the rotator cuff. Tears of the posterior rotator cable are frequently seen in overhead throwing athletes. Although the biomechanical significance of the anterior rotator cable has been well described, our current understanding of the relevance of the posterior cable is limited. The purpose of this study was to examine how partial-thickness tears and full-thickness tears of the posterior rotator cable would alter glenohumeral biomechanics and kinematics in cadaveric shoulder models.Methods:Eight fresh-frozen cadaveric shoulder specimens were prepared and tested. To simulate the sequence of glenohumeral positions during the throwing motion, specimens were mounted on a custom shoulder testing system with the humerus positioned at 90° of abduction (30° scapular upward rotation, 60° glenohumeral abduction) and tested at 30, 60, 90, and 120 degrees of external rotation. After a circumferential capsulotomy was performed, rotator cuff muscles were loaded based on physiologic cross-sectional area ratios, and testing for each specimen was performed on each the following three conditions: intact posterior cable, partial-thickness (50%) articular-sided posterior cable tear, and full-thickness posterior cable tear. Primary outcome measures tested for each condition under the various degrees of glenohumeral rotation were: 1) anterior and total glenohumeral translation after application of a 30N anterior force; 2) path of glenohumeral articulation; 3) glenohumeral joint force.Results:With a 30N anterior force at 120° of external rotation, there was a significant increase in anterior glenohumeral translation between intact and full-thickness tear specimens (7.28±2.00mm and 17.49±3.75mm, respectively; p<0.05). Similarly, total joint translation at 120° of external rotation significantly increased between intact and full-thickness tear specimens (10.37±3.18mm and 23.37±5.05mm, respectively; p<0.05). No significant differences were apparent at other degrees of rotation (30, 60, 90 degrees), or with partial-thickness tears. Changes in the path of glenohumeral articulation were likewise most evident at 120° of external rotation, with a progressively anterior, inferior, and lateral shift in articulation with sequential sectioning of the posterior cable. Lastly, with regards to alterations in glenohumeral joint force, no significant changes were seen in any of the conditions.Conclusion:In this cadaveric shoulder model of the throwing shoulder, tears of the posterior rotator cuff cable lead to altered glenohumeral biomechanics and kinematics. These changes were most profound at 120° of external rotation, suggesting the importance of an intact posterior cable as a potential stabilizer during the late-cocking phase of throwing.

Inter-rater and intra-rater reliability of a movement control test in shoulder

BackgroundMovement faults are commonly observed in patients with musculoskeletal pain. The Kinetic Medial Rotation Test (KMRT) is a movement control test used to identify movement faults of the scapula and gleno-humeral joints during arm movement. Objective tests such as the KMRT need to be reliable and valid for the results to be applied across different clinical settings and patient populations. The primary objective of the present study was to determine the intra-rater and inter-rater reliability of KMRT in subjects with and without shoulder pain. MethodsSixty subjects were included in this study based on specific inclusion and exclusion criteria. Two musculoskeletal physiotherapists with different levels of clinical experience performed the tests. The intra-rater reliability was tested in twenty asymptomatic subjects by a single assessor at two week intervals. An equal number of subjects with and without shoulder pain were tested by both the assessors to determine the inter-rater reliability. Both components of the KMRT, the Gleno- Humeral Anterior Translation (GHAT) and the Scapular Forward Tilt (SCFT) were tested. ResultsThe Kappa values for inter-rater reliability of the GHAT and SCFT were K = 0.68 & K = 0.65 respectively in subjects with shoulder pain. In asymptomatic subjects, the inter-rater reliability of GHAT was K = 0.61 and SCFT was K = 0.85. Intra-rater reliability ranged from K = 0.66 for GHAT to K = 0.87 for SCFT. ConclusionOur study found substantial agreement in inter-rater reliability of KMRT in subjects with shoulder pain, whereas substantial to near perfect agreement was found in intra-rater and inter-rater reliability of KMRT in subjects without shoulder pain.

Biomechanical Analysis of Articular-Sided Partial-Thickness Rotator Cuff Tear and Repair

Background: Articular-sided partial-thickness rotator cuff tears are common injuries in throwing athletes. The superior shoulder capsule beneath the supraspinatus and infraspinatus tendons works as a stabilizer of the glenohumeral joint. Purpose: To assess the effect of articular-sided partial-thickness rotator cuff tear and repair on shoulder biomechanics. The hypothesis was that shoulder laxity might be changed because of superior capsular plication in transtendon repair of articular-sided partial-thickness rotator cuff tears. Study Design: Controlled laboratory study. Methods: Nine fresh-frozen cadaveric shoulders were tested by using a custom shoulder-testing system at the simulated late-cocking phase and acceleration phase of throwing motion. Maximum glenohumeral external rotation angle, anterior translation, position of the humeral head apex with respect to the glenoid, internal impingement area, and glenohumeral and subacromial contact pressures were measured. Each specimen underwent 3 stages of testing: stage 1, with the intact shoulder; stage 2, after creation of articular-sided partial-thickness tears of the supraspinatus and infraspinatus tendons; and stage 3, after transtendon repair of the torn tendons by using 2 suture anchors. Results: Articular-sided partial-thickness tears did not significantly change any of the shoulder biomechanical measurements. In the simulated late-cocking phase, transtendon rotator cuff repair resulted in decreased maximum external rotation angle by 4.2° (P = .03), posterior shift of the humeral head (1.1-mm shift; P = .02), decreased glenohumeral contact pressure by 1.7 MPa (56%; P = .004), and decreased internal impingement area by 26.4 mm2 (65%; P < .001) compared with values in the torn shoulder. In the acceleration phase, the humeral head shifted inferiorly (1.2-mm shift; P = .03 vs torn shoulder), and glenohumeral anterior translation (1.5-mm decrease; P = .03 vs torn shoulder) and subacromial contact pressure (32% decrease; P = .004 vs intact shoulder) decreased significantly after transtendon repair. Conclusion: Transtendon repair of articular-sided partial-thickness supraspinatus and infraspinatus tears decreased glenohumeral and subacromial contact pressures at time zero; these changes might lead to reduced secondary subacromial and internal impingements and consequently progression to full-thickness rotator cuff tear. However, repair of the tendons decreased anterior translation and external rotation and changed the positional relationship between the humeral head and the glenoid. Clinical Relevance: Careful attention should be paid to shoulder laxity and range of motion when transtendon repair is chosen to treat articular-sided partial-thickness rotator cuff tears, specifically in throwing athletes.

Anteroposterior translation of the glenohumeral joint in various pathologies: differences between shoulder MRI in the adducted neutral rotation and abducted externally rotated positions

The present study was performed to determine the translation of the glenohumeral joint in patients with and without shoulder lesions by comparing the magnetic resonance images obtained in the conventional adducted neutral rotation position with those obtained in the abducted externally rotated position. Two hundred and eighty-five consecutive shoulders without rotator cuff tears that had been subjected to magnetic resonance imaging (MRI) without arthrography in the abducted externally rotated position were reviewed retrospectively. Among them, 50 shoulders without pathology were selected at random to be compared with three shoulder pathology groups, comprising shoulders with superior labrum, anterior-to-posterior (SLAP) lesions without range of motion (ROM) limitation (group I, 47 shoulders), with massive rotator cuff tears without ROM limitation (group II, 20 shoulders), and with full-thickness subscapularis tendon tears without ROM limitation (group III, 20 shoulders). Glenohumeral translation in the anterior-to-posterior direction relative to the glenoid face was evaluated using a method based on the glenohumeral contact point (CP) and humeral head centre (HHC) in the adducted neutral rotation and abducted externally rotated views, which were measured by three orthopaedic surgeons. For each shoulder, the differences in translation for the glenohumeral CP and HHC between the adducted neutral rotation and abducted externally rotated views were calculated as relative posterior translation in millimetres. The differences in ΔCP and ΔHHC between group I and the normal control group were not statistically significant. The differences in ΔCP (P = 0.001) and ΔHHC (P = 0.001) between group II and the normal control group were statistically significant. Additionally, the differences in ΔCP and ΔHHC between group III and the normal control group were not statistically significant. The MRI in abducted externally rotated view in patients with SLAP lesions or full-thickness subscapularis tendon tears diagnosed by conventional MRI alone showed no significant glenohumeral posterior translation relative to the adducted neutral rotation view in the present study. However, the abducted externally rotated view in patients with massive rotator cuff tears showed significant glenohumeral anterior translation relative to the adducted neutral rotation view.

Conjoined Tendon Transfer vs Modified Bristow in a Glenoid Bone Loss Model: A Biomechanical Study

Objectives:Over the last ten years there has been a resurgent interest in the use of coracoid transfer procedures for the treatment of traumatic, anterior glenohumeral instability of the shoulder. Bankart repair, whether arthroscopic or open, is the gold standard for treatment of the majority of anterior glenohumeral instability cases. Coracoid transfer procedures, on the other hand, are effective for patients with significant bony defects, those with poor quality anterior capsulolabral tissues, and in collision athletes with higher risk of instability after simple soft-tissue repair. Despite high rates of success in most studies involving the Bristow and other coracoid transfer procedures, complications have been reported. Screw breakage, nerve injury, non-union of the coracoid fragment, and arthritis related to improper placement of the bone block have all been documented. Eliminating the bone block would help to decrease the number of potential complications associated with the procedure. For this reason, we sought to evaluate whether the Bristow procedure or the conjoined tendon transfer (CTT) would be more effective in restoring kinematics of the glenohumeral joint in a glenoid bone loss model for anterior shoulder instability. This is the first study to our knowledge comparing a bone block with its attached musculotendinous sling to a sling alone in a glenoid bone loss model.Methods:Utilizing fresh frozen cadavers, biomechanical testing was undertaken comparing anterior glenohumeral translation in two groups of ten specimens each with a 25% anterior glenoid bone defect. Group 1 consisted of a tensioned conjoined tendon transfer (CTT) into the defect. Group 2 consisted of a Modified Bristow bone block (BB) transfer. Cyclic testing was performed with the shoulder at 90 degrees of external rotation in both 60 and 90 degrees of abduction.Results:At 60 degrees of abduction, the conjoined tendon transfer showed a 43% reduction in anterior humeral head translation from the unstable or deficient state, while the bone block transfer showed a 12% reduction. This difference was statistically significant. At 90 degrees of abduction, the conjoined tendon transfer showed a 59% reduction in anterior humeral head translation from the unstable or deficient state, while the bone block transfer showed a 38% reduction. This difference trended towards significance. (Please see table 1. for full details/data)Conclusion:A tensioned conjoined trendon transfer in the setting of 25% anterior glenoid bone loss exhibited a statistically significant reduction in anterior glenohumeral translation at 60 degrees of abduction and a nonsignificant reduction at 90 degrees of abduction versus a Modified Bristow bone block transfer. Biomechanically, we feel the musculotendinous sling of the conjoined tendon functions in place of the anterior and anterior/inferior capsulolabral structures, including the anterior band of the IGHL, which are typically deficient in the setting of recurrent anterior instability. This represents the initial step in determining if this procedure could be a viable alternative to a bone block transfer in the setting of anterior glenohumeral instability with glenoid bone loss.

Arthroscopic Suture Anchor Capsulorrhaphy Versus Labral-Based Suture Capsulorrhaphy in a Cadaveric Model

The purpose of this study was to establish whether suture anchor capsulorrhaphy (SAC) is biomechanically superior to suture capsulorrhaphy (SC) in the management of recurrent anterior shoulder instability without a labral avulsion. Twelve matched pairs of shoulders were randomized to either SC or SAC. Specimens were mounted in 60° of abduction and 90° of external rotation. Testing was conducted on an MTS servohydraulic load testing device (MTS, Eden Prairie, MN). A compressive load of 22 N was applied, followed by a 2-N anterior and posterior force to establish a 0 point. Translation with 10-N anterior and posterior loads was recorded for baseline laxity measurement. Arthroscopic capsulorrhaphy was performed with either 3 solitary sutures or 3 suture anchors. Specimens were remounted and returned to the 0 point. Translation was measured with 10-N anterior and posterior loads to determine reduction in translation. Specimens were then loaded to failure to the 0 point at a rate of 0.1 mm/s. Load to failure was significantly greater (P = .02) in the SC group (13.6 ± 1.0 N) versus the SAC group (20.5 ± 2.8 N). No differences were found between SC (2.7 ± 0.7 mm) and SAC (2.3 ± 0.6 mm) when we compared reduction of anterior translation with a 10-N load. The percent reduction of anterior displacement with a 10-N load was similar for the SC (49.9%) and SAC (49.6%) groups. The dominant mode of failure in the study was suture pull-through of the capsular tissue. Our study indicates that labral-based SC and SAC similarly reduce anterior glenohumeral translation at low loading conditions. Load-to-failure studies indicate that SAC exhibits significantly greater resistance to translation at higher loading conditions. Our study suggests that the use of a suture anchor when one is performing a capsulorrhaphy may provide biomechanical advantage at high loading conditions. Our study suggests that when one is performing capsulorrhaphy, the use of a suture anchor may provide biomechanical advantages at high loading conditions.

Arthroscopic Suture Anchor Capsulorrhaphy Versus Suture Capsulorrhaphy in a Cadaveric Model (SS-01)

Introduction Recurrent anterior glenohumeral instability is challenging to treat. Arthroscopic capsulorrhaphy utilizing either a solitary suture or suture anchor has proven effective in alleviating instability symptoms. To date, no study was found that determined whether suture capsulorrhaphy or suture anchor capsulorrhaphy is more effective at reducing anterior translation. Thus, the purpose of this study is to establish whether there is biomechanical benefit for the use of anchor capsulorrhaphy versus suture capsulorrhaphy in the management of anterior shoulder instability. Methods Twelve matched pairs of fresh, frozen shoulders were randomized to either anchor or suture capsulorrhaphy group. Specimens were mounted in 60-degrees of abduction and 90-degrees of external rotation in the plane of the scapula. Testing was conducted on an MTS with the use of Vicon motion capture system. Compressive load of 22N was applied to each shoulder and subsequent 2N anterior and posterior force was applied to establish zero point. Translation with 10N anterior and posterior loads was then recorded. Arthroscopic capsulorrhaphy was performed with either three solitary sutures or three suture anchors. Specimens were remounted and returned to the zero-point. A 10N anterior force, 10N posterior force, and an anterior load to failure force were applied, respectively. Translation from zero was measured. Load to failure was defined as the amount of force required to return to preoperative zero point. Specimens were loaded-to-failure at a rate of 0.1mm/sec. Data were reported in millimeters ±SEM with significance set at p Results Load-to-failure was significantly greater (p=0.02) in the anchor capsulorrhaphy group (20.5N±2.8) versus suture capsulorrhaphy group (13.6N±1.0). When comparing reduction of anterior translation with a 10N load, no differences were found between suture capsulorrhaphy (2.7mm±0.7) and anchor capsulorrhaphy (2.3mm±0.6). Percent reduction of anterior displacement with a 10N load was not different for the suture capsulorrhaphy (49.9%) versus anchor capsulorrhaphy (49.6%) groups. Tissue pull-through of the suture was the dominant mode of failure in the study. Conclusion Suture capsulorrhaphy and anchor capsulorrhaphy reduce anterior glenohumeral translation at low loading conditions. Load-to-failure studies indicate that anchor capsulorrhaphy exhibits significantly greater resistance to translation at higher loading conditions. Thus, it is concluded that the use of arthroscopic suture anchors is more effective than suture capsulorrhaphy in reducing catastrophic anterior glenohumeral translation in cadavers. Our study suggests that the use of a suture anchor when performing a capsulorrhaphy may provide biomechanical advantage at high loading conditions. Potential benefits of suture anchor capsulorrhaphy include increased resistance to glenohumeral translation and higher load to failure. This may represent better clinical outcomes and a reduction in the rate of recurrent instability as a result.

Biomechanical Assessment of TYPE II Superior Labral Anterior-Posterior (SLAP) Lesions Associated with Anterior Shoulder Capsular Laxity as Seen in Throwers

Background Type II superior labral anterior-posterior lesions in throwers are often associated with anterior shoulder capsular laxity. Hypothesis Shoulder instability in patients with type II superior labral anterior-posterior lesions may result from the associated shoulder capsular laxity rather than the superior labral anterior-posterior lesion alone. Study Design Controlled laboratory study. Methods Six cadaveric shoulders were externally rotated to 20% beyond the maximum humeral external rotation at 60° of glenohumeral abduction, which simulated 90° of shoulder abduction, to detach the superior labrum and elongate the anterior shoulder capsular ligaments. The detached labrum was then repaired to isolate the effect of the detached superior labrum and that of the capsular laxity. Rotational range of motion was measured at 60° of glenohumeral abduction. Anterior-posterior glenohumeral translation was measured at 30° and 60° of glenohumeral abduction. Superior-inferior glenohumeral translation was measured at 0° and 60° of glenohumeral abduction. Results The experimentally created type II superior labral anterior-posterior lesion and capsular laxity significantly increased anterior translation at 30° (mean difference, 1.0 ± 0.8 mm; P < .05) and 60° (mean difference, 2.2 ± 2.0 mm; P < .05) of glenohumeral abduction. Subsequent superior labral anterior-posterior repair restored the anterior translation but only at 30° of glenohumeral abduction (mean difference, 0.9 ± 0.6 mm; P < .05). Conclusion Because of the anterior capsular laxity associated with type II superior labral anterior-posterior lesions, superior labral anterior-posterior repair of the peeled-back superior labrum may not restore anterior glenohumeral translation at 90° of shoulder abduction. Clinical Relevance Anterior shoulder capsular laxity associated with type II superior labral anterior-posterior lesions may cause anterior shoulder instability at 90° of shoulder abduction in throwers even after superior labral anterior-posterior lesion repair.

Anterior Translation at the Glenohumeral Joint

Background Lesions to the axillary artery are reported in overhead athletes. One speculated cause is repeated transient compression by the humeral head due to excessive laxity at the glenohumeral joint. Hypotheses (1) Anterior translation of the glenohumeral joint alters axillary artery diameter and blood flow characteristics, and (2) individuals demonstrating inducible axillary artery compression with the arm in an overhead position (as indicated by diameter and blood flow characteristics) will demonstrate greater magnitudes of anterior translation. Study Design Descriptive laboratory study. Methods After receiving ethical approval and screening for problematic conditions/injuries, 26 subjects were tested (10 men and 16 women; mean age [standard deviation], 25 years [4]). Axillary artery diameter and peak systolic velocity were measured with B-mode and Doppler ultrasound before, during, and after glenohumeral anterior translation at 90° of abduction, 60° of external rotation, and 30° of horizontal flexion, and at baseline and a simulated overhead throwing position (120° of abduction, 90° of external rotation, and 30° of horizontal extension). The magnitude of anterior translation was captured with B-mode ultrasound using a posterior transverse approach. Results Application of the glide resulted in a significant (F2,21 = 9.965, P = .001) reduction in axillary artery diameter and a significant increase in peak systolic velocity (F2,21 = 5.286, P = .014). Subjects demonstrating clinically significant levels of axillary artery compression (>50% reduction in vessel diameter with the arm in the overhead throwing position) exhibited significantly (t = −2.260, P = .040) greater ranges of anterior translation at the glenohumeral joint than the 9 subjects who exhibited <10% reduction in arterial diameter. Conclusions This investigation provides the first empirical support for the clinical opinion that glenohumeral anterior translation could be a mechanism for inducible axillary artery compression. Clinical Relevance The response of axillary artery hemodynamics in normal, healthy individuals is the first step in the process of determining whether the finding of inducible axillary artery compression in overhead athletes with arterial pathology is related to glenohumeral translation.

Intrarater reliability of the KT1000 arthrometer in determining anterior translation of the glenohumeral joint

Taylor JD, Bandy WD. Intrarater reliability of the KT1000 arthrometer in determining anterior translation of the glenohumeral joint. Arch Phys Med Rehabil 2005;86:826–9. Objectives To establish intrarater reliability of the KT1000 arthrometer in determining glenohumeral anterior translation and to determine if a difference existed between measurements of glenohumeral anterior translation in 2 testing positions. Design Intrarater reliability study. Setting Academic laboratory. Participants Convenience sample of 15 unimpaired volunteers (mean age ± standard deviation, 25±4y). Interventions Not applicable. Main outcome measures Subjects were positioned supine with the shoulder in 20° of abduction and 0° of external rotation (position 1) and 90° of abduction and 90° of external rotation (position 2). The KT1000 was placed on the shoulder with the tibia sensor pad near the joint line and the patella sensor pad over the coracoid process. Testing involved an anteriorly directed force of 67N. Testing procedures were repeated after 1 week. Results The intraclass correlation coefficients (ICCs) for intrarater reliability for position 1 (ICC=.93; 95% confidence interval [CI], .81–.98) and for position 2 (ICC=.93; 95% CI, .80–.97) were excellent. The degree of anterior translation measured in position 1 was significantly greater than in position 2 ( t=4.79, P<.01). Conclusions Use of the KT1000 to measure glenohumeral anterior translation in the 2 testing positions appears to be a relatively simple, reliable method. Because testing position 1 allowed significantly greater anterior translation than testing position 2, the 2 positions should not be used interchangeably.

Glenohumeral joint translation after arthroscopic thermal capsuloplasty of the posterior capsule

Treatment of recurrent posterior or multidirectional glenohumeral instability in athletes with traditional operative management has produced variable results at long-term follow-up. The purpose of this study was to determine whether an arthroscopic thermal capsuloplasty of the posterior capsule with a radiofrequency probe significantly decreases anterior-posterior glenohumeral translation. Successive posterior and anterior loads of 10, 15, and 20 N were applied sequentially to 7 cadaveric shoulder joints that were mounted in a translation testing apparatus with an electromagnetic tracking device measuring posterior and anterior glenohumeral translation. Arthroscopic thermal capsuloplasty was then performed on the posterior capsular tissue with a radiofrequency probe. The identical posterior-anterior loading protocol was then repeated, and translations were recorded. The results demonstrated no statistically significant differences in the mean posterior translation measurements before and after arthroscopic thermal capsuloplasty of the posterior capsule for the 10-N (+8.9%), 15-N (−3.1%), or 20-N (−1.8%) load ( P > .50 to .62). Slightly greater changes occurred in anterior translation after posterior capsuloplasty at 10 N (−1.0%), 15 N (−6.0%), and 20 N (−10.3%). However, these changes were not found to be significant either ( P = .06 to .62). The results of this study demonstrated that neither posterior nor anterior glenohumeral translation was significantly decreased by thermal capsuloplasty of the posterior capsule. Perhaps the lack of substantial collagenous material in the thin posterior capsule accounts for the inability of thermal capsuloplasty to be effective in this region.

Effects of simulated scapular protraction on anterior glenohumeral stability.

We evaluated the effect of simulated scapular protraction on anterior glenohumeral translation and in situ inferior glenohumeral ligament strain. Five fresh-frozen cadaveric glenohumeral joints were tested in the position of apprehension while simulating scapular protraction using a custom translation testing device and a differential variable reluctance transducer. The results showed a statistically significant decrease in anterior glenohumeral translation as the scapula was increasingly rotated to simulate 20 degrees of scapular protraction. With 15 N of thorax-based, anteriorly directed load, the mean anterior translation was 6.3 +/- 1.6 mm (mean +/- SEM). With 10 degrees of simulated scapular protraction, translation decreased to 4.1 +/- 1.0 mm; with 20 degrees of simulated scapular protraction, it decreased further to 2.5 +/- 0.5 mm. For each of the other anteriorly directed loads, translations also decreased when 20 degrees of scapular protraction was simulated. Concurrently for each of the anteriorly directed loads, there was increased in situ strain of the anterior band of the inferior glenohumeral ligament with increased simulated scapular protraction. These results suggest that repetitive or chronic protraction of the scapula may result in excessive strain and, ultimately, insufficiency in the anterior band of the inferior glenohumeral ligament.

Strategies for an anterior capsular shift of the shoulder. A biomechanical comparison.

We evaluated the effect of two different anterior capsular shift strategies on load-induced multidirectional glenohumeral motion. Nine cadaveric shoulders were tested on a special test apparatus in which three motions were constrained but which allowed simultaneous measurement of three translations: anteroposterior, mediolateral, and superoinferior. A simulated Bankart lesion was created by detaching the inferior glenohumeral ligament and labrum from the anterior glenoid from 5 mm superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The two types of medial-based anterior capsular shifts were performed sequentially using fixation via a transglenoid drill hole and No. 2 suture. One shift medialized the anterior capsule on the glenoid by 5 mm; the other one shifted the anterior capsule 5 mm superior on the anterior glenoid. Biomechanical testing was done in two positions of humeral elevation in the scapular plane, three positions of humeral rotation, and with an externally applied joint compression load of 22 N. Glenohumeral motion was measured in the intact state, after creation of the simulated Bankart lesion, and after each of the two anterior capsular shifts. Both the superior and medial shifts of the capsule decreased anterior glenohumeral translation to equivalent extents. For posterior and inferior translation at 45 degrees elevation, the superior shift significantly decreased translation to a greater extent than did the medial shift.