Glenohumeral Abduction Research Articles

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.

Stability of the Glenohumeral Joint with Combined Humeral Head and Glenoid Defects

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.

Effect of Anterior Capsular Laxity on Horizontal Abduction and Forceful Internal Impingement in a Cadaveric Model of the Throwing Shoulder

Background: Excessive anterior capsular laxity (elongation of the anterior capsular ligaments) causes shoulder subluxation during acceleration of the throwing motion, leading to a disabled throwing shoulder. Few biomechanical studies have investigated the relationship between anterior capsular laxity and internal impingement, another cause of the disabled throwing shoulder. Purpose/Hypothesis: The purpose of this study was to assess the effect of anterior capsular laxity on forceful internal impingement during the late cocking phase. The hypothesis was that excessive anterior shoulder laxity caused by elongation of the anterior capsular ligaments will increase the horizontal abduction angle to increase glenohumeral contact pressure. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric shoulders were tested with the shoulder abducted to 90° and at maximal external rotation to simulate the late cocking phase of the throwing motion. The angle of external rotation, anterior translation, angle of horizontal abduction, locations of the articular insertion of the rotator cuff tendons (supraspinatus and infraspinatus) on the greater tuberosity relative to the glenoid, and the glenohumeral contact pressure and area during internal impingement were measured. All data were compared between intact and elongated anterior capsule, which was created by repeatedly applying external rotational stretching. Results: Elongation of the anterior capsular ligaments was confirmed by the increase in glenohumeral external rotation and anterior translation after our stretching technique. Location data showed that the posterior half of supraspinatus tendon, the entire infraspinatus tendon, and the posterosuperior labrum were impinged between the greater tuberosity and glenoid. Maximal glenohumeral horizontal abduction (2.2% increase; P = .003) and glenohumeral contact pressure (27.3% increase; P = .04) were significantly increased in the shoulder joint with increased anterior capsular laxity as compared with the intact condition. Conclusion: Increased anterior capsular laxity created by applying repetitive excessive external rotational torque significantly increased horizontal abduction and contact pressure in the glenohumeral joint. Concurrently, the supraspinatus and infraspinatus tendons and posterosuperior labrum were impinged between the greater tuberosity and glenoid. Clinical Relevance: Increased anterior capsular laxity may exacerbate forceful internal impingement during the late cocking phase of the throwing motion.

Scapular Kinematics During Late Cocking of a Simulated Throwing Activity in Baseball Players With Shoulder Injury: A Cross-Sectional Study Using a 3D-to-2D Registration Technique.

Abnormal scapular kinematics during throwing motion in baseball players with shoulder disorders has not yet been clarified, although altered scapular position has been suggested to be associated with shoulder disorder. To determine if the shoulders of baseball players with throwing disorders demonstrate abnormal scapular kinematics during the simulated arm-cocking phase of throwing activity. Cross-sectional study. Laboratory. Eleven baseball players (age 21.1 ± 1.2 y) with a unilateral shoulder disorder volunteered to participate, including 9 players at the college level and 2 at the adult level. The mean playing experience was 12.1 ± 2.7 y. Scapular upward/downward rotation, anteroposterior tilting, and external/internal rotation during simulated arm-cocking motion were analyzed using a 3-to-2-dimensional registration technique. Scapular external rotation in the throwing shoulder was significantly smaller by 2.0-6.0° than that of the contralateral shoulder. There were no detectable differences in scapular upward/downward rotation or anteroposterior tilting between the throwing and contralateral shoulders. Compared with that in the contralateral shoulder, scapular external rotation was smaller in the throwing shoulder, which would increase glenohumeral horizontal abduction during the arm-cocking phase and be related to the throwing-shoulder disorder.

Limited glenohumeral cross-body adduction in children with brachial plexus birth palsy: a contributor to scapular winging.

Approximately 1 of every 1000 live births results in life-long impairments because of a brachial plexus injury. The long-term sequelae of persistent injuries include glenohumeral joint dysplasia and glenohumeral internal rotation and adduction contractures. Scapular winging is also common, and patients and their families often express concern regarding this observed scapular winging. It is difficult for clinicians to adequately address these concerns without a satisfying explanation for why scapular winging occurs in children with brachial plexus birth palsy. This study examined our proposed theory that a glenohumeral cross-body abduction contracture leads to the appearance of scapular winging in children with residual brachial plexus birth palsy. Sixteen children with brachial plexus injuries were enrolled in this study. Three-dimensional locations of markers placed on the thorax, scapula, and humerus were recorded in the hand to mouth Mallet position. The unaffected limbs served as a control. Scapulothoracic and glenohumeral cross-body adduction angles were compared between the affected and unaffected limbs. The affected limbs demonstrated significantly greater scapulothoracic and significantly smaller glenohumeral cross-body adduction angles than the unaffected limbs. The affected limbs also exhibited a significantly lower glenohumeral cross-body adduction to scapulothoracic cross-body adduction ratio. The results of this study support the theory that brachial plexus injuries can lead to a glenohumeral cross-body abduction contracture. Affected children demonstrated increased scapulothoracic cross-body adduction that is likely a compensatory mechanism because of decreased glenohumeral cross-body adduction. These findings are unique and better define the etiology of scapular winging in children with brachial plexus injuries. This information can be relayed to patients and their families when explaining the appearance of scapular winging. Level II.

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

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 Effect of a Combined Glenoid and Hill-Sachs Defect on Glenohumeral Stability

Background: Bone loss in anterior glenohumeral instability occurs on both the glenoid and the humerus; however, existing biomechanical studies have evaluated glenoid and humeral head defects in isolation. Thus, little is known about the combined effect of these bony lesions in a clinically relevant model on glenohumeral stability. Hypothesis/Purpose: The purpose of this study was to determine the biomechanical efficacy of a Bankart repair in the setting of bipolar (glenoid and humeral head) bone defects determined via computer-generated 3-dimensional (3D) modeling of 142 patients with recurrent anterior shoulder instability. The null hypothesis was that adding a bipolar bone defect will have no effect on glenohumeral stability after soft tissue Bankart repair. Study Design: Controlled laboratory study. Methods: A total of 142 consecutive patients with recurrent anterior instability were analyzed with 3D computed tomography scans. Two Hill-Sachs lesions were selected on the basis of volumetric size representing the 25th percentile (0.87 cm3; small) and 50th percentile (1.47 cm3; medium) and printed in plastic resin with a 3D printer. A total of 21 cadaveric shoulders were evaluated on a custom shoulder-testing device permitting 6 degrees of freedom, and the force required to translate the humeral head anteriorly 10 mm at a rate of 2.0 mm/s with a compressive load of 50 N was determined at 60° of glenohumeral abduction and 60° of external rotation. All Bankart lesions were made sharply from the 2- to 6-o’clock positions for a right shoulder. Subsequent Bankart repair with transosseous tunnels using high-strength suture was performed. Hill-Sachs lesions were made in the cadaver utilizing a plastic mold from the exact replica off the 3D printer. Testing was conducted in the following sequence for each specimen: (1) intact, (2) posterior capsulotomy, (3) Bankart lesion, (4) Bankart repair, (5) Bankart lesion with 2-mm glenoid defect, (6) Bankart repair, (7) Bankart lesion with 2-mm glenoid defect and Hill-Sachs lesion, (8) Bankart repair, (9) Bankart lesion with 4-mm glenoid defect and Hill-Sachs lesion, (10) Bankart repair, (11) Bankart lesion with 6-mm glenoid defect and Hill-Sachs lesion, and (12) Bankart repair. All sequences were used first for a medium Hill-Sachs lesion (10 specimens) and then repeated for a small Hill-Sachs lesion (11 specimens). Three trials were performed in each condition, and the mean value was used for data analysis. Results: A statistically significant and progressive reduction in load to translation was observed after a Bankart lesion was created and with the addition of progressive glenoid defects for each humeral head defect. For medium (50th percentile) Hill-Sachs lesions, there was a 22%, 43%, and 58% reduction in stability with a 2-, 4-, and 6-mm glenoid defect, respectively. For small (25th percentile) Hill-Sachs lesions, there was an 18%, 27%, and 42% reduction in stability with a 2-, 4-, and 6-mm glenoid defect, respectively. With a ≥2-mm glenoid defect, the medium Hill-Sachs group demonstrated significant reduction in translation force after Bankart repair (P < .01), and for the small Hill-Sachs group, a ≥4-mm glenoid defect was required to produce a statistical decrease (P < .01) in reduction force after repair. Conclusion: Combined glenoid and humeral head defects have an additive and negative effect on glenohumeral stability. As little as a 2-mm glenoid defect with a medium-sized Hill-Sachs lesion demonstrated a compromise in soft tissue Bankart repair, while small-sized Hill-Sachs lesions showed compromise of soft tissue repair with ≥4-mm glenoid bone loss. Clinical Relevance: Bipolar bony lesions of the glenoid and humeral head occur frequently together in clinical practice. Surgeons should be aware that the combined defects and glenoid bone loss of 2 to 4 mm or approximately 8% to 15% of the glenoid could compromise Bankart repair and thus may require surgical strategies in addition to traditional Bankart repair alone to optimize stability.

Rocking-horse phenomenon of the glenoid component: the importance of inclination

Abnormal glenoid version positioning has been recognized as a cause of glenoid component failure caused by the rocking horse phenomenon. In contrast, the importance of the glenoid inclination has not been investigated. The computed tomography scans of 152 healthy shoulders were evaluated. A virtual glenoid component was positioned in 2 different planes: the maximum circular plane (MCP) and the inferior circle plane (ICP). The MCP was defined by the best fitting circle of the most superior point of the glenoid and 2 points at the lower glenoid rim. The ICP was defined by the best fitting circle on the rim of the inferior quadrants. The inclination of both planes was measured as the intersection with the scapular plane. We defined the force vector of the rotator force couple and calculated the magnitude of the shear force vector on a virtual glenoid component in both planes during glenohumeral abduction. The inclination of the component positioned in the MCP averaged 95° (range, 84°-108°) and for the ICP averaged 111° (range, 94°-126°). A significant reduction in shear forces was calculated for the glenoid component in the ICP vs the MCP: 98% reduction in 60° of abduction to 49% reduction in 90° of abduction. Shear forces are significantly higher when the glenoid component is positioned in the MCP compared with the ICP, and this is more pronounced in early abduction. Positioning the glenoid component in the inferior circle might reduce the risk of a rocking horse phenomenon.

Glenohumeral abduction contracture in children with unresolved neonatal brachial plexus palsy.

Following neonatal brachial plexus palsy, the Putti sign-obligatory tilt of the scapula with brachiothoracic adduction-suggests the presence of glenohumeral abduction contracture. In the present study, we utilized magnetic resonance imaging (MRI) to quantify this glenohumeral abduction contracture and evaluate its relationship to shoulder joint deformity, muscle atrophy, and function. We retrospectively reviewed MRIs of the thorax and shoulders obtained before and after shoulder rebalancing surgery (internal rotation contracture release and external rotation tendon transfer) for twenty-eight children with unresolved neonatal brachial plexus palsy. Two raters measured the coronal positions of the scapula, thoracic spine, and humeral shaft bilaterally on coronal images, correcting trigonometrically for scapular protraction on axial images. Supraspinatus, deltoid, and latissimus dorsi muscle atrophy was assessed, blinded to other measures. Correlations between glenohumeral abduction contracture and glenoid version, humeral head subluxation, passive external rotation, and Mallet shoulder function before and after surgery were performed. MRI measurements were highly reliable between raters. Glenohumeral abduction contractures were present in twenty-five of twenty-eight patients, averaging 33° (range, 10° to 65°). Among those patients, abductor atrophy was present in twenty-three of twenty-five, with adductor atrophy in twelve of twenty-five. Preoperatively, greater abduction contracture severity correlated with greater Mallet global abduction and hand-to-neck function. Abduction contracture severity did not correlate preoperatively with axial measurements of glenohumeral dysplasia, but greater glenoid retroversion was associated with worse abduction contractures postoperatively. Surgery improved passive external rotation, active abduction, and hand-to-neck function, but did not change the abduction contracture. A majority of patients with persistent shoulder weakness following neonatal brachial plexus palsy have glenohumeral abduction deformities, with contractures as severe as 65°. The abduction contracture occurs with abductor atrophy, with or without associated adductor atrophy. This contracture may improve global shoulder abduction by positioning the glenohumeral joint in abduction. Glenohumeral and scapulothoracic kinematics and muscle pathology must be further elucidated to advance an understanding of the etiology and the prevention and treatment of the complex shoulder deformity following neonatal brachial plexus palsy. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

PS8-11 The Effect of Rotator Cuff Imbalance during Glenohumeral Abduction(PS8: Poster Short Presentation VIII,Poster Session)

PS8-11 The Effect of Rotator Cuff Imbalance during Glenohumeral Abduction(PS8: Poster Short Presentation VIII,Poster Session)

Effect of glenohumeral abduction on supraspinatus repair tension

A pilot x-ray study was performed on three healthy subjects using a x-ray fluoroscopy InSight (Hologic, Inc. Bedford, MA, USA) in true anterior-posterior (AP) view, to determine what position the shoulder is placed in when wearing a sling only (Donjoy Ultrasling II (DJO, Normanhurst, NSW, Australia)), sling with small abduction pillow (Donjoy Ultrasling II (DJO)) and sling with large abduction pillow (ProCare Shoulder Abduction Kit (DJO)). Figure 1: AP view of a shoulder X-Ray

Effect of shoulder abduction on the fixation of humeral greater tuberosity fractures: a biomechanical study for three types of fixation constructs

An abduction brace and abduction exercises are commonly employed after humeral greater tuberosity fracture repair. However, the effects of glenohumeral abduction on the biomechanical strength have seldom been elucidated. We studied 24 pairs of female fresh frozen porcine shoulders randomly divided into 3 groups. After creation of a greater tuberosity fracture on each shoulder, 3 fixation techniques were used for the 3 groups: double-row suture anchor fixation (DR), suture bridge technique (SB), and 2-screw fixation (TS). This biomechanical study was conducted to compare the forces that create 3- and 5-mm displacements and the ultimate failure load at the simulated shoulder abduction angles of 0° and 45° among the 3 groups. In the DR group, the mean forces to create 3- and 5-mm displacements and the failure load at 0° were higher than those at 45° (P = .036, P = .012, P = .027). By contrast, in the SB group, the mean forces to create 3- and 5-mm displacements at 45° were greater than those at 0° (P = .012, P = .012). There were no significant differences in the forces to create 3- and 5-mm displacements and construct failure between 0° and 45° in the TS group (P = .575, .327, .478). The DR group had greatest initial fixation strength at a low abduction angle, whereas the SB group had the highest initial fixation strength at a high abduction angle. The TS group appeared unaffected by the abduction angle.

Muscular Activation During Plyometric Exercises in 90° of Glenohumeral Joint Abduction

Background:Plyometric exercises are frequently used to increase posterior rotator cuff and periscapular muscle strength and simulate demands and positional stresses in overhead athletes. The purpose of this study was to provide descriptive data on posterior rotator cuff and scapular muscle activation during upper extremity plyometric exercises in 90° of glenohumeral joint abduction.Hypothesis:Levels of muscular activity in the posterior rotator cuff and scapular stabilizers will be high during plyometric shoulder exercises similar to previously reported electromyographic (EMG) levels of shoulder rehabilitation exercises.Study Design:Descriptive laboratory study.Methods:Twenty healthy subjects were tested using surface EMG during the performance of 2 plyometric shoulder exercises: prone external rotation (PERP) and reverse catch external rotation (RCP) using a handheld medicine ball. Electrode application included the upper and lower trapezius (UT and LT, respectively), serratus anterior (SA), infraspinatus (IN), and the middle and posterior deltoid (MD and PD, respectively) muscles. A 10-second interval of repetitive plyometric exercise (PERP) and 3 repetitions of RCP were sampled. Peak and average normalized EMG data were generated.Results:Normalized peak and average IN activity ranged between 73% and 102% and between 28% and 52% during the plyometric exercises, respectively, with peak and average LT activity measured between 79% and 131% and between 31% and 61%. SA activity ranged between 76% and 86% for peak and between 35% and 37% for average activity. Muscular activity levels in the MD and PD ranged between 49% and 72% and between 12% and 33% for peak and average, respectively.Conclusion:Moderate to high levels of muscular activity were measured in the rotator cuff and scapular stabilizers during these plyometric exercises with the glenohumeral joint abducted 90°.

Fluoroscopic, magnetic resonance imaging, and electrophysiologic assessment of shoulders with massive tears of the rotator cuff

It was the purpose of this paper to analyze structural, functional, and electrophysiologic variables that may determine preserved overhead function for patients with massive rotator cuff tears. Nineteen patients (20 shoulders) were prospectively included in either the pseudoparalytic (n = 9) or the non-pseudoparalytic group (n = 11). Fatty infiltration was graded according to Goutallier, and anterior (subscapularis) and posterior (infraspinatus and teres minor) tear extension was graded 0 (no involvement) to 4 (full tear) on magnetic resonance imaging. Glenohumeral and scapulothoracic rhythm was assessed by fluoroscopic motion analysis, and electromyographic evaluation of the deltoid muscle was performed. We found no significant difference of fatty infiltration of the supraspinatus (3.9 vs 3.6), infraspinatus (3.9 vs 3.8), and teres minor (1.7 vs 0.6) or of the posterior tear extension (2.6 vs 2.0) between pseudoparalytic and non-pseudoparalytic shoulders. Global tear extension in the parasagittal plane (205° vs 163°) and subscapularis involvement (2.6 vs 1.2), however, showed significant differences between the two groups, and no patient with a full-thickness supraspinatus and infraspinatus tear with extension into the inferior half of the subscapularis was able to lift the arm to 90°. Fluoroscopic assessment revealed almost total loss of active glenohumeral abduction in the pseudoparalytic group. Despite global tear extension, the single most important predictor for preserved shoulder function is the integrity of the inferior subscapularis insertion. Furthermore, electromyographic evaluation identifies a well-differentiated deltoid innervation as beneficial for a well-preserved shoulder function, but it does not protect from pseudoparalysis.

Wear rates of highly cross-linked polyethylene humeral liners subjected to alternating cycles of glenohumeral flexion and abduction

Although short-term outcomes of reverse total shoulder arthroplasty have been promising, long-term success may be limited due to device-specific complications, including scapular notching. Scapular notching has been explained primarily as mechanical erosion; however, the generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching. A 12-station hip simulator was converted to a reverse total shoulder arthroplasty wear simulator subjecting conventional and highly cross-linked ultra-high-molecular-weight polyethylene humeral liners to 5 million cycles of alternating abduction-adduction and flexion-extension loading profiles. Highly cross-linked polyethylene liners (36.5±10.0mm(3)/million cycle) exhibited significantly lower volumetric wear rates compared with conventional polyethylene liners (83.6±20.6mm(3)/million cycle; P<.001). The flexion-extension loading profile exhibited significantly higher wear rates for conventional (P<.001) and highly cross-linked polyethylene (P<.001) compared with the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional polyethylene (P<.001). Highly cross-linked polyethylene liners significantly reduced polyethylene wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked polyethylene may lead to increased device longevity and fewer complications but must be weighed against the effect of reduced mechanical properties.

The Effect of Combined Glenoid and Humeral Head Defects on Glenohumeral Translation

Objectives:Bone loss in anterior glenohumeral instability has significant clinical implications and is responsible for surgical failure. Previous work has focused on glenoid and humeral head defects separately. There is no prior biomechanical work evaluating the combined effect of these lesions. The purpose of this study is to determine the effect of the combination of humeral head and glenoid bone loss on glenohumeral joint translation in a bipolar bone loss model with a Bankart lesion and after Bankart repair. Our hypothesis is that when both humeral head and glenoid defects occur together, the amount of bone loss required to compromise soft tissue Bankart repair is less than compared to when glenoid and humeral head lesions occur in isolation.Methods:Eight cadaveric shoulders were dissected to expose the intact capsule and glenohumeral joint. The set-up and testing was as described by Itoi ,Sekiya and Yamamoto1,2,3.The humeral shaft and scapula were potted and the shoulder mounted on a custom shoulder testing device permitting 6 degrees of freedom. The test positions were 60 degrees of glenohumeral abduction and 60 degrees of external rotation. A 50N compressive load was applied to the glenohumeral joint. A MTS 858 Servohydraulic test system (MTS Systems, Eden Prairie, MN) was used to translate the humeral head anteriorly 10mm at a rate of 2.0mm/sec. The peak force required to translate the humeral head 10mm was recorded. Three trials were performed in each condition, and the mean value was used for data analysis. All Bankart lesions were made sharply from the 2 o’clock to 6 o’clock position for a right shoulder. Bankart repair was made with transosseous tunnels using high strength suture. A digital micrometer was used to measure and create glenoid defects with a saw parallel to the anterior glenoid. Hill-Sachs lesions were made from 3D models created from a clinical database of computerized tomographic images of 142 patients with shoulder instability (Figure 1). A bell-shape curve was created and the 50th percentile lesion for size and location was selected, 1.47 cm3. Testing was conducted in the following sequence for each specimen:(1) intact (2)posterior capsulotomy, (3)bankart lesion, (4)bankart repair, (5) 2mm glenoid defect with Bankart lesion, (6)bankart repair, (3) Hill Sachs (1.47cm3) lesion, bankart lesion and 2mm defect, (7)bankart repair, (8) 4mm defect with Hill Sachs defect and Bankart lesion,(9)bankart repair, (10)6mm glenoid defect with Hill Sachs, defect and Bankart lesion (11)bankart repair.Results:A linear mixed-effects approach was used to examine force needed to translate for each condition. A statistically significant reduction in force needed to translate was observed with Bankart repair performed with a 1.47 cm3 Hill-Sachs defect and a 2mm (p=0.01) and 4mm (p=0.04) glenoid bone loss compared to Bankart repair with glenoid bone loss alone (Figure 2). A 2mm glenoid defect with the Hill-Sachs defect resulted in a 25% reduction in stability. A 6mm glenoid defect with the Hill-Sachs lesion resulted in a 50% reduction in load to translation compared to a Bankart repair with no bone loss.Conclusion:As little as a 2mm glenoid defect together with a Hill-Sachs lesion of the dimensions observed in 50% of an actual clinical practice will compromise a soft tissue Bankart repair alone. Combined lesions , even when small, may require surgical strategies that address bone defects to optimize outcomes.

The biomechanical effect of shoulder remplissage combined with Bankart repair for the treatment of engaging Hill-Sachs lesions.

The purpose of this study was to determine the biomechanical effects of the remplissage repair combined with Bankart repair for engaging Hill-Sachs lesions on range of motion (ROM), translation, and glenohumeral kinematics. Six cadaveric shoulders were tested using a custom shoulder testing system. ROM, kinematics, and anterior-posterior (AP) and superior-inferior glenohumeral translations were quantified at 0° and 60° glenohumeral abduction. Six conditions were tested: intact, Bankart lesion, Bankart with 40 % Hill-Sachs lesion, Bankart repair, Bankart repair with remplissage, and remplissage repair alone. Humeral external rotation (ER) and total range of motion increased significantly after the creation of the Bankart lesion at both 0° and 60° abduction. The Bankart repair restored ER to intact values at 0° and 60° abduction, and the addition of the remplissage repair did not significantly alter range of motion from the Bankart repair alone. AP translation increased following the creation of the Bankart and Hill-Sachs lesions and was restored with the Bankart repair; the remplissage did not alter translation from the Bankart repair alone. At maximum ER at 60° abduction, the apex of the humeral head shifted posteriorly and inferiorly with remplissage repair. The addition of the remplissage procedure combined with Bankart repair for treatment of large Hill-Sachs lesions had no statistically significant effect on ROM or translation, but altered the kinematics of the glenohumeral joint. Thus, by addressing the humeral bone defect following an anterior shoulder dislocation, the remplissage technique with concurrent Bankart repair may be a relatively minimally invasive option for converting engaging Hill-Sachs lesions to non-engaging and promoting shoulder stability, though further biomechanical and clinical studies are warranted.

Biomechanical analysis of the modified Bristow procedure for anterior shoulder instability: is the bone block necessary?

Anterior shoulder instability with bone loss can be treated successfully with the modified Bristow procedure. Opinions vary regarding the role of the soft-tissue sling created by the conjoined tendon after transfer. Therefore, the aim of this study was to determine the effect of the modified Bristow procedure and conjoined tendon transfer on glenohumeral translation and kinematics after creating anterior instability. Eight cadaveric shoulders were tested with a custom shoulder testing system. Range-of-motion, translation, and kinematic testing was performed in 60° of glenohumeral abduction in the scapular and coronal planes under the following conditions: intact joint, Bankart lesion with 20% glenoid bone loss, modified Bristow procedure, and soft tissue-only conjoined tendon transfer. A Bankart lesion with 20% bone loss resulted in significantly increased external rotation and translation compared with the intact condition (P<.05), as well as an anterior shift of the humeral head apex at all points of external rotation. Both the modified Bristow procedure and soft-tissue Bristow procedure maintained the increase in external rotation but resulted in significantly decreased translation (P<.05). There was no difference in translation between the 2 reconstructions. The increase in external rotation suggests that the modified Bristow procedure does not initially restrict joint motion. Translational stability can be restored in a 20% bone loss model without a bone block, suggesting the importance of the soft-tissue sling.

Glenohumeral Contact Pressure With Simulated Anterior Labral and Osseous Defects in Cadaveric Shoulders Before and After Soft Tissue Repair

Background: Glenoid rim fractures and erosion can result from traumatic and repeated shoulder dislocations, leading to glenoid bone loss. Traditional instability surgery includes Bankart repair to restore soft tissue anatomy, although a recent trend is to address glenoid bone deficiency when appropriate with a bone block procedure. Hypothesis/Purpose: The purpose of this study was to quantify glenohumeral joint contact pressures as a function of anterior labral detachment, progressive anterior glenoid bone loss, and labral repair. The hypothesis was that a critical glenoid defect size exists whereby labral repair alone cannot restore joint contact pressures, therefore favoring bone block augmentation over soft tissue repair. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric shoulders were tested under a 440-N compressive load simulating glenohumeral abduction positions of 30° and 60° in neutral rotation and 60° with 90° of external rotation. Glenohumeral joint contact pressures were recorded with a Tekscan pressure sensor system in these configurations: (1) intact specimen, (2) Bankart lesion, (3) 10% anterior rim bone defect, (4) 10% bone defect with labral repair, (5) 20% bone defect, (6) 20% bone defect with labral repair, (7) 30% bone defect, and (8) 30% bone defect with labral repair. The joint contact pressures were compared at all configurations. Results: The Bankart lesion and 10%, 20%, and 30% glenoid defects showed significant (P < .05) increases in mean contact pressures over baseline values. Labral repair at 10% bone loss reduced mean contact pressures to below the intact state, and labral repair of 20% defects demonstrated normalized mean contact pressures. However, mean contact pressures remained statistically elevated compared with baseline values after labral repair of 30% glenoid defects. Conclusion: Glenohumeral joint contact pressures were restored to baseline values after labral repair of 10% and 20% anterior glenoid bone defects. Conversely, labral repair at 30% glenoid bone loss did not restore glenohumeral contact mechanics, yielding elevated contact pressures despite repair. Further study is warranted to investigate the stability (resistance to dislocations) of the glenohumeral joint after labral repair and bone block augmentation. Clinical Relevance: A critical glenoid defect size exists in which labral repair alone does not restore normal glenohumeral contact pressures. Surgeons should carefully evaluate glenoid bone loss before selecting a surgical treatment for shoulder instability.

The effect of different humeral prosthesis fin designs on shoulder stability: A computational model

Humeral prostheses commonly use a fin structure as an attachment point for the supraspinatus muscle in total shoulder arthroplasty (TSA), but these fins may cause injury to the muscle during implantation, inadvertently influencing stability. In order to prevent supraspinatus injury, the effect of different humeral prostheses on shoulder joint stability needs to be investigated. A commercially available prosthesis and two modified humeral prostheses that substituted the fin structure for 2 (2H) or 3 holes (3H) were evaluated using computational models. Glenohumeral abduction was simulated and the superioinferior/anterioposterior stability of the shoulder joint after TSA was calculated. The results revealed that the 2H design had better superioinferior stability than the other prostheses, but was still less stable than the intact shoulder. There were no obvious differences in anterioposterior stability, but the motion patterns were clearly distinguishable from the intact shoulder model. In conclusion, the 2H design showed better superioinferior stability than the 3H design and the commercial product during glenohumeral joint abduction; the three prostheses show similar results in anterioposterior stability. However, the stability of each tested prosthesis was not comparable to the intact shoulder. Therefore, as a compromise, the 2H design should be considered for TSA because of its superior stability.