Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint

Development of a musculoskeletal shoulder model considering anatomic joint structures and soft-tissue deformation for dynamic simulation

The shoulder joint has a high degree of freedom and an extremely complex and unstable kinematic mechanism. Coordinated contraction of the rotator cuff muscles that stop around the humeral head and the deltoid muscles and the extensibility of soft tissues, such as the joint capsule, labrum, and ligaments, contribute to shoulder-joint stability. Understanding the mechanics of shoulder-joint movement, including soft-tissue characteristics, is important for disease prevention and the development of a device for disease treatment. This study aimed to create a musculoskeletal shoulder model to represent the realistic behavior of joint movement and soft-tissue deformation as a dynamic simulation using a rigid-body model for bones and a soft-body model for soft tissues via a spring-damper-mass system. To reproduce the muscle-contraction properties of organisms, we used a muscle-expansion representation and Hill's mechanical muscle model. Shoulder motion, including the movement of the center of rotation in joints, was reproduced, and the strain in the joint capsule during dynamic shoulder movement was quantified. Furthermore, we investigated narrowing of the acromiohumeral distance in several situations to induce tissue damage due to rotator cuff impingement at the anterior-subacromial border during shoulder abduction. Given that the model can analyze exercises under disease conditions, such as muscle and tendon injuries and impingement syndrome, the proposed model is expected to help elucidate disease mechanisms and develop treatment guidelines.

Anterolateral Acromioplasty Reduces Gliding Resistance Between the Supraspinatus Tendon and the Coracoacromial Arch in a Cadaveric Model

Purpose

To investigate the gliding resistance dynamics between the supraspinatus (SSP) tendon and the coracoacromial arch, both before and after subacromial decompression (anterolateral acromioplasty) and acromion resection (acromionectomy).

Methods

Using 4 fresh-frozen cadaveric shoulders, acromion shapes were classified (2 type I and 2 type III according to Bigliani). Subacromial bursa and coracoacromial ligament maintenance replicated physiologic sliding conditions. Gliding resistance was measured during glenohumeral abduction (0° to 60°) in internal rotation (IR) and external rotation (ER). Peak gliding resistance between the SSP tendon and the coracoacromial arch was determined and compared between intact, anterolateral acromioplasty, and acromionectomy.

Results

Peak SSP gliding resistance during abduction in an intact shoulder was significantly higher in IR than in ER (4.1 vs 2.1 N, P < .001). The mean peak SSP gliding resistance during 0° to 60° glenohumeral abduction in IR in the intact condition was significantly higher compared with the subacromial decompression condition (4.1 vs 2.8 N, P = .021) and with the acromionectomy condition (4.1 vs 0.9 N, P < .001). During 0° to 60° glenohumeral abduction in ER, mean peak SSP gliding resistance in the intact condition was not significantly different compared with the subacromial decompression condition (2.1 vs 2.0 N, P = .999). The 2 specimens with a hooked (i.e. type III) acromion showed significantly higher mean peak SSP gliding resistance during glenohumeral abduction in IR and ER when compared with the 2 specimens with a flat (i.e. type I) acromion (IR: 5.8 vs 3.0 N, P = .006; ER: 2.8 vs 1.4 N, P = .001).

Conclusions

In this cadaveric study, peak gliding resistance between the SSP tendon and the coracoacromial arch during combined abduction and IR was significantly reduced after anterolateral acromioplasty and was significantly higher in specimens with a hooked acromion.

Clinical Relevance

The clinical benefit of subacromial decompression remains unclear. This study suggests that anterolateral acromioplasty might reduce supraspinatus gliding resistance in those with a hooked acromion and in the typical "impingement" position.

Development of a more biofidelic musculoskeletal model with humeral head translation and glenohumeral ligaments

Computational musculoskeletal modeling is useful for understanding upper extremity biomechanics, especially when in vivo tests are unfeasible. A musculoskeletal model of the upper limb with increased biofidelity was developed by including humeral head translation (HHT) and ligaments. The model was validated and ligament contribution and effect of shoulder (thoracohumeral) elevation on HHT was evaluated. Humerus translated superiorly with increased elevation, with translations closely matching (avg. difference 2.83 mm) previous in vitro studies. HHT and ligament inclusion in the model will improve biomechanical predictions of upper extremity movements and study of conditions, like subacromial impingement, rotator cuff tear, or shoulder instability.

Anatomical, functional and biomechanical review of the glenoid labrum

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

Influential and Highest Cited Shoulder Instability Articles: A Bibliometric Analysis

Background

In orthopaedic surgery and other fields, the effect of influential journal articles has been evaluated by their citation counts and their correlation with methodological quality.

Purpose

To identify and characterize the 50 most cited articles on shoulder instability, examine trends in publication characteristics, and evaluate the correlation of citations with quality of evidence.

Study Design

Cross-sectional study.

Methods

The Web of Science and Scopus online databases were searched to identify the top 50 most cited articles on shoulder instability, based on the average number of citations from each database. Article characteristics were recorded, and level of evidence and methodological quality were assessed using the modified Coleman Methodology Score (mCMS), Jadad scale, and Methodological Index for Non-Randomized Studies (MINORS). Spearman correlation was used to evaluate relationships between citations or citation density (citations/y) and level of evidence or methodological scoring. Top cited articles from recent years were also aggregated.

Results

The top 50 most cited papers had a mean ± SD number of citations of 381.5 ± 166.7, with a mean of 15.0 ± 8.8 citations/y. Overall, 15 articles (30%) were biomechanical/cadaveric studies, and 15 (30%) were case series. Only 3 (6%) were considered to have level 1 evidence. The mean ± SD mCMS was 54.4 ± 12.7, mean ± SD Jadad score was 3.1 ± 1.4, and mean ± SD MINORS score was 10.5 ± 3.3. There were no significant correlations between citation rank or density and methodological assessments. There were weak correlations between citation rank and publication year (r _s = 0.32; P = .022) and between rank and level of evidence (r _s = -0.38; P = .047). The correlation between citation density and publication year was moderate (r _s = 0.70; P < .0001). There was no difference in citation density of the top 10 articles from 2010 to 2020 compared with the top 10 from the overall list (23.8 ± 5.3 vs 28.8 ± 9.5; P = .16).

Conclusion

Influential articles in shoulder instability included a high proportion of biomechanical/cadaveric studies. The majority of top cited articles had lower evidence levels and poorer methodological quality without strong correlation with citations or citation density. There was a moderate correlation between citation density and year of publication.

Anterior glenohumeral instability: Current review with technical pearls and pitfalls of arthroscopic soft-tissue stabilization

The glenohumeral joint (GHJ) allows for a wide range of motion, but is also particularly vulnerable to episodes of instability. Anterior GHJ instability is especially frequent among young, athletic populations during contact sporting events. Many first time dislocators can be managed non-operatively with a period of immobilization and rehabilitation, however certain patient populations are at higher risk for recurrent instability and may require surgical intervention for adequate stabilization. Determination of the optimal treatment strategy should be made on a case-by-case basis while weighing both patient specific factors and injury patterns (i.e., bone loss). The purpose of this review is to describe the relevant anatomical stabilizers of the GHJ, risk factors for recurrent instability including bony lesions, indications for arthroscopic vs open surgical management, clinical history and physical examination techniques, imaging modalities, and pearls/pitfalls of arthroscopic soft-tissue stabilization for anterior glenohumeral instability.

The glenohumeral ligaments: Superior, middle, and inferior: Anatomy, biomechanics, injury, and diagnosis

The three glenohumeral ligaments (superior, middle, and inferior) are discrete thickenings of the glenohumeral joint capsule and are critical to shoulder stability and function. Injuries to this area are a cause of significant musculoskeletal morbidity. A literature search was performed by a review of PubMed, Google Scholar, and OVID for all relevant articles published up until 2020. This study highlights the anatomy, biomechanical function, and injury patterns of the glenohumeral ligaments, which may be relevant to clinical presentation and diagnosis. A detailed understanding of the normal anatomy and biomechanics is a necessary prerequisite to understanding the injury patterns and clinical presentations of disorders involving the glenohumeral ligaments of the shoulder.

Shoulder biomechanics in normal and selected pathological conditions

The stability of the glenohumeral joint depends on soft tissue stabilizers, bone morphology and dynamic stabilizers such as the rotator cuff and long head of the biceps tendon. Shoulder stabilization techniques include anatomic procedures such as repair of the labrum or restoration of bone loss, but also non-anatomic options such as remplissage or tendon transfers.

Rotator cuff repair should restore the cuff anatomy, reattach the rotator cable and respect the coracoacromial arch whenever possible. Tendon transfer, superior capsular reconstruction or balloon implantation have been proposed for irreparable lesions.

Shoulder rehabilitation should focus on restoring balanced glenohumeral and scapular force couples in order to avoid an upward migration of the humeral head and secondary cuff impingement. The primary goal of cuff repair is to be as anatomic as possible and to create a biomechanically favourable environment for tendon healing.

Cite this article: EFORT Open Rev 2020;5:508-518. DOI: 10.1302/2058-5241.5.200006

Differences in Failure Mode Between Simple and Mattress Suture Configuration in Arthroscopic Bankart Repairs: A Cadaveric Study

Background

Traumatic anterior shoulder dislocations disrupt the anteroinferior labrum (Bankart lesion), leading to high rates of instability and functional disability, necessitating stabilization.

Purpose

To investigate modes and locations of repair failure between simple and horizontal mattress suture configurations after arthroscopic Bankart repair using suture anchors in a cadaveric model.

Study Design

Controlled laboratory study.

Methods

A total of 48 fresh-frozen human cadaveric shoulders from 48 specimens underwent creation of Bankart lesions from either the 3:00 to 6:00 o'clock position on the right glenoid or the 6:00 to 9:00 o'clock position on the left glenoid. Shoulder laterality between specimens was alternated and randomized to either simple or mattress suture repair configurations. In each shoulder, anchors were placed on the glenoid at the 3:00, 4:30, and 6:00 o'clock positions on the right or 6:00, 7:30, and 9:00 o'clock positions on the left and were secured via standard arthroscopic knot-tying techniques. Specimens were tested in the supine anterior apprehension position using a servohydraulic testing machine that was loaded to failure, simulating a traumatic anterior dislocation. After dislocation, open inspection of specimens was performed, and failure mode and location were documented. Differences in failure mode and location were compared using nominal multivariate generalized estimating equations.

Results

Simple suture repairs most frequently failed at the labrum, while mattress suture repair failed at the capsule. Regardless of configuration, repairs failed most commonly at the 3:00 o'clock position on the right shoulder and 9:00 o'clock position on the left shoulder. Compared with mattress suture repairs, simple suture repairs failed at a significantly higher rate at the 6:00 o'clock position.

Conclusion

Traumatic anterior shoulder dislocation after arthroscopic Bankart repair in a cadaveric model resulted in simple suture configuration repairs failing most commonly via labral tearing compared with capsular tearing in mattress repairs. Both repair configurations failed predominately at the anterior anchor position, with simple suture repairs failing more commonly at the inferior anchor position.

Clinical Relevance

Horizontal mattress suture configurations create a larger area of repair, decreasing the risk of repair failure at the labrum. The extra time required for mattress suture placement at the inferior anchor position is used effectively, resulting in lower biomechanical failure rates.

Comprehensive review of the physical exam for glenohumeral instability

Glenohumeral instability is a common pathology of the shoulder joint, especially among young athletes. Despite advancements in technology and the widespread use of diagnostic imaging, a careful history and physical examination still remain the cornerstone of diagnosing patients with shoulder instability. Due to the involvement of many static and dynamic stabilizers, proficient physical examination can be challenging. With a systematic approach to clinical evaluation, the clinician can recognize characteristic patterns of relevant signs and symptoms and make an accurate diagnosis.

Does arthroscopic preemptive extensive rotator interval release reduce postoperative stiffness after arthroscopic rotator cuff repair?: a prospective randomized clinical trial

BACKGROUND

To investigate whether preemptive extensive rotator interval (RI) release during arthroscopic rotator cuff repair (ARCR) would reduce postoperative stiffness.

METHODS

From July 2015 to September 2016, a total of 80 patients who were scheduled for ARCR were enrolled and randomly allocated into 2 groups: the preemptive extensive RI release group (group 1, n=40) and the RI nonrelease group (group 2, n=40). The American Shoulder and Elbow Surgeons scale, Constant score, Korean Shoulder Scale (KSS), visual analog scale (VAS) pain score, and range of motion (ROM) were evaluated before surgery; 3, 6, and 12 months after surgery; and at last follow-up. Magnetic resonance imaging was performed at postoperative 12 months.

RESULTS

The mean follow-up period was 26.5 months. The functional and pain scores in both groups were significantly improved at the last follow-up (P < .05). Group 1 showed a significantly higher sum of ROM with a difference of 27° and 1.6 vertebral level of internal rotation compared to group 2 at postoperative 3 months (P < .05). Constant score and KSS were significantly higher in group 1 than in group 2 at this time point (P < .05). Functional scores and ROM were not significantly different between 2 groups at postoperative 6 or 12 months or at the last follow-up (P > .05). The retear rate and pathologic change of the long head of the biceps tendon during follow-up were not significantly different between the 2 groups (P > .05).

CONCLUSION

Arthroscopic preemptive extensive RI release can reduce early postoperative shoulder stiffness after ARCR but does not significantly change the overall clinical outcome after surgery.

Rotator interval closure: inconsistent techniques and its association with anterior instability. A literature review

The Rotator interval (RI) is an anatomic space in the anterosuperior part of the glenohumeral joint. An incompetent or lax RI has been implicated in various conditions of shoulder instability and therefore RI has been frequently touted as an area that is important in preserving stability of the shoulder. Biomechanical studies have shown that repair of RI ligamentous and capsular structures decreases glenohumeral joint laxity in various directions. Clinical studies have reported successful outcomes after repair or plication of these structures in patients undergoing shoulder stabilization procedures. Although varieties of methods have been described for its closure, the optimal surgical technique is unclear with various inconsistencies in incorporation of the closure tissue. This in particular makes the analysis of the RI closure very difficult. The purposes of this study are to review the structures of the RI and their contribution to shoulder instability, to discuss the biomechanical and clinical effects of plication of RI structures in particular to anterior glenohumeral instability, to delineate the differences between an arthroscopic and open RI closure. Additionally, we have proposed a new classification system describing various techniques used during RI closure.

Scapular Upward Rotation During Passive Humeral Abduction in Individuals With Hemiplegia Post-stroke

Objective

To describe scapular upward rotation during passive humeral abduction in individuals with hemiplegia post-stroke compared to normal subjects.

Methods

Twenty-five individuals with hemiplegia post-stroke and 25 age- and gender-matched normal subjects voluntarily participated in this study. Scapular upward rotation during resting and passive humeral abduction at 30°, 60°, 90°, 120°, and 150° were measured using a digital inclinometer.

Results

In both groups, scapular upward rotation significantly increased as humeral abduction increased (p<0.001). Scapular upward rotation was significantly less in the hemiplegic group compared to that in the control at 90° (p=0.002), 120° (p<0.001), and 150° of humeral abduction (p<0.001). The mean difference in scapular upward rotation between these two groups ranged from 6.3° to 11.38°.

Conclusion

Passive humeral abductions ranging from 90° to 150° can significantly alter scapular upward rotation in individuals with hemiplegia post-stroke compared to those of matched normal subjects. The magnitude of reduction of the scapular upward rotation may potentially lead to the development of hemiplegic shoulder pain after prolonged repetitive passive movement. Scapular upward rotation should be incorporated during passive humeral abduction in individuals with hemiplegia post-stroke, especially when the humeral is moved beyond 90° of humeral abduction. Combined movements of scapular and humeral will help maintain the relative movement between the scapula and humerus. However, further longitudinal study in patients with shoulder pain post-stroke is needed to confirm these findings.

Shoulder crane: a concept of suspension, stability, control and motion

Framework and suspensory cascade

This novel model uses the structure and workings of the industrial crane as a simile to explain the function of the human shoulder. As a crane consists of a base, axial tower, boom and suspensory cascade that move and position loads in space, the base consists of the pelvic platform, with outriggers (legs) that provide stability in human body. The axial tower consists of an articulated spinal column and thoracic platform, which are stabilised by the core muscles. The clavicular boom articulates with the anterior thoracic platform and is elevated by the trapezius from the posterior tower. The ‘suspensory cascade’ extends from the skull and cervical spine to the trapezius and on to the clavicle, coracoclavicular ligaments, coracoid process, coracohumeral ligament and humeral head.

Motion

The rotator cuff muscles take origin from the scapula and coalesce with each other to form a multilayered rotator cuff tendon and cable, which cups to closely contain the humeral head. The four muscles insert into the common tendon and together share the load to stabilise and mobilise the arm in space. The coracoid is a pulley that allows the scapula to swivel on the coracoclavicular ligaments to enable adjustment of the angle of force transmission delivered by the rotator cuff to the humeral head.

Stability and control

The inferior glenoid and labrum are a fixed organ of compression, which coalesces with the hammock formed by the static inferior glenohumeral ligaments. The rotator cuff and deltoid compress the humeral head onto this static structure.

The biceps tendon passes adjacent to the condensations of the coracohumeral ligament to insert into the mobile superior labrum and glenoid. Contraction of the biceps pulls the mobile superior labrum onto the humeral head and tightens the glenohumeral ligaments that wrap around the humeral head at the extremes of motion. The coracohumeral ligament is a sensory organ that interfaces with these structures and is well positioned to work as a servomechanism to redirect the rotator cuff in providing stability, control and motion.

Level of evidence

Level V.

Biomechanical properties of transosseous bony Bankart repair in a cadaver model

INTRODUCTION

We compared two arthroscopic repair techniques to an intact shoulder using a biomechanical model of anterior shoulder dislocation with an anterior glenoid rim fracture (Ideberg IA fracture). We hypothesized that transosseous repair is sufficient to effectively stabilize the glenoid fracture. The primary objective was to define the mechanical properties of transosseous repair of an Ideberg IA fracture relative to an intact shoulder (control group). The secondary objective was to determine the contribution of supplemental anteroposterior screw fixation of the bone fragment.

MATERIALS AND METHODS

Fifteen fresh cadaver shoulders were divided into two groups: 5 specimens in the control group and 10 in the fracture fixation group, with sequential performance of transosseous repair followed by transosseous repair+screw fixation. A fracture at the inferior portion involving more than 30% of the glenoid's surface area was made.

RESULTS

The load to failure was 457 N in the control group, 277 N in the transosseous repair group and 325 N in the transosseous repair+screw fixation group. The stiffness of the constructs was 26.2N/mm for the control group, 14.6N/mm for transosseous repair and 24.6N/mm for transosseous repair+screw fixation. The difference between the two repair techniques was significant for the load to failure (p=0.02) and stiffness (p=0.001).

DISCUSSION/CONCLUSION

This study showed that transosseous repair restores the shoulder's anatomy but not the mechanical strength of the native glenoid. Adding screw fixation significantly improves the construct.

LEVEL OF EVIDENCE

IV, basic science study.

Reconstruction of the Superior Glenoid Labrum With Biceps Tendon Autograft: A Cadaveric Biomechanical Study

PURPOSE

To describe 2 superior labral reconstruction techniques using long head of the biceps (LHB) autograft and to investigate the ability of the 2 reconstruction techniques to restore superior restraint to the glenohumeral joint compared with superior labrum-deficient models.

METHODS

In this biomechanical study, 10 cadaveric shoulders were cycled on a servohydraulic machine while the force required to cause superior subluxation was recorded. Each specimen was cycled under 4 conditions: intact labrum, SLAP tear, posterior (9- to 12-o'clock position) labral reconstruction using LHB autograft (superior labral reconstruction 1 [SLR1]), and 180° (9- to 3-o'clock position) labral reconstruction using LHB autograft (superior labral reconstruction 2 [SLR2]).

RESULTS

The mean peak force required to cause superior subluxation in the intact labrum was 32.75 N versus 19.75 N in the SLAP tear (P = .0120). SLR1 required a mean peak force of 31.23 N versus 44.09 N for SLR2 (P = .0175). SLR1 required 94.96% of the force needed in the intact labrum to cause subluxation, whereas SLR2 required 140.6%. SLR1 and SLR2 required 34.21% higher (P = .0074) and 79.84% higher (P = .0033) forces, respectively, to generate subluxation compared with the SLAP tear state.

CONCLUSIONS

Both proposed superior labral reconstruction techniques increased the force needed for humeral head superior migration in the setting of a labral tear. SLR1 (posterior labral reconstruction) closely matched the constraint of an intact labrum, whereas SLR2 (180° labral reconstruction) provided greater superior constraint than an intact labrum.

CLINICAL RELEVANCE

The natural history of irreparable rotator cuff tears results in superior glenohumeral escape and eventual arthrosis. The superior glenoid labrum is an important contributor to superior glenohumeral constraint and is often degenerated in this setting. Clinical application of the 2 described superior labral reconstruction techniques may improve glenohumeral superior stability in patients with rotator cuff disease and superior labral deficiency.

The role of bone in glenohumeral stability

Shoulder stability depends on several factors, either anatomical or functional. Anatomical factors can be further subclassified under soft tissue (shoulder capsule, glenoid rim, glenohumeral ligaments etc) and bony structures (glenoid cavity and humeral head).

Normal glenohumeral stability is maintained through factors mostly pertaining to the scapular side: glenoid version, depth and inclination, along with scapular dynamic positioning, can potentially cause decreased stability depending on the direction of said variables in the different planes. No significant factors in normal humeral anatomy seem to play a tangible role in affecting glenohumeral stability.

When the glenohumeral joint suffers an episode of acute dislocation, either anterior (more frequent) or posterior, bony lesions often develop on both sides: a compression fracture of the humeral head (or Hill–Sachs lesion) and a bone loss of the glenoid rim. Interaction of such lesions can determine ‘re-engagement’ and recurrence.

The concept of ‘glenoid track’ can help quantify an increased risk of recurrence: when the Hill–Sachs lesion engages the anterior glenoid rim, it is defined as ‘off-track’; if it does not, it is an ‘on-track’ lesion. The position of the Hill–Sachs lesion and the percentage of glenoid bone loss are critical factors in determining the likelihood of recurrent instability and in managing treatment.

In terms of posterior glenohumeral instability, the ‘gamma angle concept’ can help ascertain which lesions are prone to recurrence based on the sum of specific angles and millimetres of posterior glenoid bone loss, in a similar fashion to what happens in anterior shoulder instability.

Cite this article: EFORT Open Rev 2018;3:632-640. DOI: 10.1302/2058-5241.3.180028

Outcomes After Arthroscopic Rotator Interval Closure for Shoulder Instability: A Systematic Review

PURPOSE

(1) To systematically assess the clinical outcomes of arthroscopic rotator interval closure (RIC) procedures for shoulder instability and (2) to report the different technical descriptions and surgical indications for this procedure.

METHODS

Two independent reviewers searched 4 databases (PubMed, Embase, Web of Science, and Cochrane) from database inception until October 15, 2017. The inclusion criteria were studies that reported outcomes of shoulder stabilization using arthroscopic RIC as an isolated or adjunctive surgical procedure. The methodologic quality of studies was assessed with the Methodological Index for Non-Randomized Studies tool and Grading of Recommendations Assessment, Development and Evaluation system for randomized controlled trials.

RESULTS

Fifteen studies met our search criteria (524 patients). Of the studies, 12 were graded Level IV evidence; 2, Level III; and 1, Level II. Six different RIC technique descriptions were reported, with 2 studies not defining the details of the procedure. The most common method of RIC was arthroscopic plication of the superior glenohumeral ligament to the middle glenohumeral ligament (8 of 15 studies). The most commonly used patient-reported outcome measure was the Rowe score, with all studies reporting a minimum postoperative score of 80 points. The rate of return to preinjury level of sport ranged from 22% to 100%, and the postoperative redislocation rate ranged from 0% to 16%.

CONCLUSIONS

The indications for RIC were poorly reported, and the surgical techniques were inconsistent. Although most studies reported positive clinical results, the heterogeneity of outcome measures limited our ability to make definitive statements about which types of rotator interval capsular closure are warranted for select subgroups undergoing arthroscopic shoulder stabilization.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II through IV studies.

The relationship between the glenoid track and the range of shoulder motion: A cadaver study

INTRODUCTION

The concept of the glenoid track has been proposed to evaluate the risk of dislocation. The glenoid track width was demonstrated to be 84% of the glenoid width in cadaveric shoulders and 83% in live shoulders.

HYPOTHESIS

The glenoid track width seems to be affected by the range of motion.

PURPOSE

The purpose of this study was to determine the relationship between the glenoid track and the range of shoulder motion.

METHODS

Ten fresh-frozen cadaveric shoulders were used. The specimen was fixed to a shoulder-positioning device. The anterior rim of the glenoid was marked on the humeral head using a Kirschner wire with the arm in 60° of abduction. This marking was repeated with the arm in (1) horizontal flexion/extension and (2) internal/external rotations (0° to max). The distances from the Kirschner wire markings to the footprint of the rotator cuff tendon were measured.

RESULTS

The greater the angle of the horizontal extension or external rotation, the smaller the glenoid track width, whereas the greater the angle of the horizontal flexion or internal rotation, the greater the glenoid track width. There was a negative relationship between them. The horizontal flexion/extension motion was demonstrated to affect the glenoid track width more than the internal/external rotation motion.

CONCLUSION

The glenoid track width decreased with the increase of horizontal extension. We should consider the range of horizontal extension angle when applying the glenoid track concept in clinical practice.

TYPE OF STUDY

Laboratory study.

Evaluation of the Translation Distance of the Glenohumeral Joint and the Function of the Rotator Cuff on Its Translation: A Cadaveric Study

PURPOSE

To evaluate the distance and position of humeral head translation during glenohumeral motion and to investigate the function of the rotator cuff in glenohumeral translation.

METHODS

Using 9 cadavers, glenohumeral translation during passive pendulum motion was tracked by an optical motion capture system. Tension was applied to 5 compartments of the rotator cuff muscles, and 7 different conditions of rotator cuff dysfunction were sequentially simulated. Three-dimensional glenohumeral structure was reconstructed from the computed tomography images of the specimens, and the distance and position of glenohumeral translation were compared among the conditions.

RESULTS

The average radius of glenohumeral translation was 10.6 ± 4.3 mm when static loading was applied to all rotator cuff muscles. The radius increased significantly in the models without traction force on the supraspinatus and total subscapularis tendons (P = .030). The position of the translation center did not change in the mediolateral direction (P = .587) and in the anteroposterior direction (P = .138), but it moved significantly superiorly in the models without supraspinatus and infraspinatus loading (P = .011) and in those without supraspinatus, infraspinatus, and teres minor loading (P < .001).

CONCLUSIONS

The distance and position of humeral head translation during glenohumeral motion changed with rotator cuff deficiency. The present study indicated that the subscapularis plays an important role in maintaining the central position of the humeral head, and that the infraspinatus acts as a major depressor of the humeral head during shoulder motion.

CLINICAL RELEVANCE

The results of this study suggest that extension of a tear into the subscapularis should be avoided to maintain the centering function of the glenohumeral joint in cases with rotator cuff tear.

Multidirectional instability of the glenohumeral joint: Etiology, classification, assessment, and management

Multidirectional instability of the shoulder is a type of glenohumeral joint shoulder instability. There are discrepancies in the definition and classification of this condition, which can make diagnosis and treatment selection challenging. Knowledge of contributing factors, the typical clinical presentation, and current best evidence for treatment options can assist in the diagnosis and appropriate treatment selection for this pathology. The purpose of this article is to present an overview of the current literature regarding the etiology, classification, assessment, and management of multidirectional instability of the glenohumeral joint.

The effect of rotator cuff malreduction on tendon tension: an evaluation of a custom-made digital tensiometer clamp

INTRODUCTION

Rotator cuff tears are common and good-to-excellent clinical outcome is reported after subsequent repair. However, the retear rate of rotator cuff repairs has been shown to be as high as 20%. The reasons for retear seem to be multifactorial, mainly comprised by mechanical and biological aspects. Regarding mechanical causes, the role of the tendon tension and malreduction is so far unknown. First, we hypothesized that the tendon tension depends on the technique of tendon reposition and that malreduction of the tendon results in an increased tendon tension. Second, we aimed to demonstrate the inter- and intraobserver reliability of a novel custom-made digital tensiometer clamp.

MATERIALS AND METHODS

A tendon defect of posterosuperior rotator cuff (reverse L-shaped) was simulated in seven cadaveric human shoulder specimens. By use of a custom-made tensiometer clamp, the supraspinatus tendon was reduced by pulling it in (1) an anterolateral direction (anatomical reduction) and (2) in a straight lateral direction (malreduction) until the footprint was completely covered. The reduction procedure was consecutively repeated to evaluate the inter- and intraobserver reliability.

RESULTS

The mean traction forces for anatomical reduction and malreduction were 16.02 N (SD 8.06) and 19.52 N (SD 9.95), respectively. The difference between the two groups was statistically significant (p = 0.028). The interobserver reliability showed a correlation of r = 0.757 [95% confidence interval (CI) 0.092-0.955]. The intraobserver reliability of the three surgeons was observed to be between r = 0.905 and 0.986.

CONCLUSIONS

The malreduction of the rotator cuff has a significant influence on the tendon tension and may therefore affect the healing rate of the tendon after the repair, so that a tension-balanced repair could improve the clinical results. Furthermore, the application of a novel custom-made tensiometer clamp showed good interobserver and excellent intraobserver reliabilities.

Contact pressure of the coracoacromial arch in shoulders with joint contracture: A cadaveric study

BACKGROUNDS

There have been many reports describing that the capsular fibrosis of the shoulder joint is the main cause of frozen shoulder, whereas others reported the significance of subacromial impingement as an etiological factor. The purpose of this study was to investigate the contact pressure between the coracoacromial arch and the rotator cuff tendons to clarify the contact phenomenon in shoulders with joint contracture.

METHODS

Fourteen fresh-frozen cadaveric shoulders were used. Specimens were divided into two groups: normal group (8 shoulders, definition: more than 61° of flexion and abduction and more than 21° of external rotation) and joint contracture group (6 shoulders, definition: less than 60° of flexion and abduction and less than 20° of external rotation). Contact pressure and area beneath the coracoacromial arch were measured by a flexible force sensor during flexion, abduction, internal and external rotation in adduction and abduction, extension and horizontal extension motions.

RESULTS

The peak contact pressure under the acromion was observed at 90° in flexion and abduction in the normal group, whereas that in the contracture group was observed at 30° in flexion (P = 0.037) and at 30° in abduction (P = 0.041). Contact pressure in the contracture group was significantly higher than that in the normal group at 20° and 30° of abduction (P = 0.043, P = 0.041, respectively). There were no significant differences of contact pressure during other motions. Although no significant differences of contact pressure beneath the coracoacromial ligament were observed, contact area significantly increased in extension and horizontal extension motion.

CONCLUSION

The contact between the acromion and the rotator cuff was observed in lower angles of flexion and abduction in shoulders with contracture than in those without. When treating patients with shoulder contracture, we need to perform rehabilitation taking such an abnormal movement into consideration.

Physical Exam and Evaluation of the Unstable Shoulder

Background:

The clinical evaluation of the patient with shoulder instability can be challenging. The pathological spectrum ranges from the straightforward “recurrent anterior dislocation” patient to the overhead athlete with a painful shoulder but not clear instability episodes. Advances in shoulder arthroscopy and imaging have helped in understanding the anatomy and physiopathology of the symptoms. The aim of this general article is to summarize the main examination manoeuvres that could be included in an overall approach to a patient with a suspicion of instability.

Material and Methods:

In order to achieve the above-mentioned objective, a thorough review of the literature has been performed. Data regarding sensibility and specificity of each test have been included as well as a detailed description of the indications to perform them. Also, the most frequent and recent variations of these diagnostic tests are included.

Results:

Laxity and instability should be considered separately. For anterior instability, a combination of apprehension, relocation and release tests provide great specificity. On the other hand, multidirectional or posterior instability can be difficult to diagnose especially when the main complain is pain.

Conclusion:

A detailed interview and clinical examination of the patient are mandatory in order to identify a shoulder instability problem. Range of motion of both shoulders, clicking of catching sensations as well as pain, should be considered together with dislocation and subluxation episodes. Specific instability and hyperlaxity tests should be also performed to obtain an accurate diagnosis.

Anatomy and Biomechanics of the Unstable Shoulder

PURPOSE

To review the anatomy of the shoulder joint and of the physiology of glenohumeral stability is essential to manage correctly shoulder instability.

METHODS

It was reviewed a large number of recently published research studies related to the shoulder instability that received a higher Level of Evidence grade.

RESULTS

It is reviewed the bony anatomy, the anatomy and function of the ligaments that act on this joint, the physiology and physiopathology of glenohumeral instability and the therapeutic implications of the injured structures.

CONCLUSION

This knowledge allows the surgeon to evaluate the possible causes of instability, to assess which are the structures that must be reconstructed and to decide which surgical technique must be performed.

The effect of scapular position on subacromial contact behavior: a cadaver study

BACKGROUND

Patients with subacromial impingement were reported to show abnormal scapular positions during shoulder elevation. However, the relationship between the scapular positions and subacromial impingement is unclear. The purpose of this study was to biomechanically determine the effect of scapular position on subacromial contact behavior by using fresh frozen cadavers.

METHODS

The peak contact pressure on the coracoacromial arch was measured with a flexible tactile force sensor in 9 fresh frozen cadaver shoulders. The measurement was performed during passive glenohumeral elevation in the scapular plane ranging from 30° to 75°. The scapular downward and internal rotations and anterior tilt were simulated by tilting the scapula in 5° increments up to 20°. The measurement was also performed with combination of scapular downward and internal rotations and anterior tilt positions.

RESULTS

The peak contact pressure decreased linearly with anterior tilt, and a significant difference between neutral scapular position (1.06 ± 0.89 MPa) and anterior tilt by 20° (0.46 ± 0.18 MPa) was observed (P < .05). However, the scapular positioning in the other directions did not change the peak contact pressure significantly. Furthermore, any combination of abnormal scapular positions did not affect peak contact pressure significantly.

CONCLUSION

Scapular anterior tilt decreased peak contact pressure during passive shoulder elevation. In addition, scapular downward and internal rotations had little effect on peak contact pressure. The abnormal scapular motion reported in previous studies might not be directly related to symptoms caused by subacromial impingement.

Management of the Stiff Shoulder With Arthroscopic Circumferential Capsulotomy and Axillary Nerve Release

Management of the stiff shoulder is a common and frequently daunting clinical scenario. Arthroscopic capsular release is usually an option for management of severe, chronic glenohumeral joint contractures when conservative treatment fails. Technical hurdles including a thickened capsule, reduction in joint volume, and difficulty with positioning the shoulder intraoperatively can make this procedure challenging. In addition, incomplete release and recalcitrant stiffness are frequent issues. We believe a complete release of the capsule entails special attention to the axillary pouch and requires identification and protection of the axillary nerve. We present a technique for a complete arthroscopic circumferential capsulotomy and detail our approach to safely dissect and protect the axillary nerve under arthroscopic visualization.

Anatomy of the capsulolabral complex and rotator interval related to glenohumeral instability

The glenohumeral joint with instability is a common diagnosis that often requires surgery. The aim of this review was to present an overview of the anatomy of the glenohumeral joint with emphasis on instability based on the current literature and to describe the detailed anatomy and anatomical variants of the glenohumeral joint associated with anterior and posterior shoulder instability. A review was performed using PubMed/MEDLINE using key words: Search terms were "glenohumeral", "shoulder instability", "cadaver", "rotator interval", "anatomy", and "anatomical study". During the last decade, the interest in both arthroscopic repair techniques and surgical anatomy of the glenohumeral ligament (superior, middle, and inferior), labrum, and rotator interval has increased. Understanding of the rotator interval and attachment of the inferior glenohumeral ligament on the glenoid or humeral head have evolved significantly. The knowledge of the detailed anatomy and anatomical variations is essential for the surgeon in order to understand the pathology, make a correct diagnosis of instability, and select proper treatment options. Proper understanding of anatomical variants can help us avoid misdiagnosis. Level of evidence V.

The Rotator Interval of the Shoulder: Implications in the Treatment of Shoulder Instability

Biomechanical studies have shown that repair or plication of rotator interval (RI) ligamentous and capsular structures decreases glenohumeral joint laxity in various directions. Clinical outcomes studies have reported successful outcomes after repair or plication of these structures in patients undergoing shoulder stabilization procedures. Recent studies describing arthroscopic techniques to address these structures have intensified the debate over the potential benefit of these procedures as well as highlighted the differences between open and arthroscopic RI procedures. The purposes of this study were to review the structures of the RI and their contribution to shoulder instability, to discuss the biomechanical and clinical effects of repair or plication of rotator interval structures, and to describe the various surgical techniques used for these procedures and outcomes.

Mechanical tradeoffs associated with glenosphere lateralization in reverse shoulder arthroplasty

BACKGROUND

Scapular notching in reverse shoulder arthroplasty occurs in up to 97% of patients. Notching is associated with decreased strength and reduced motion and may lead to long-term failure due to polyethylene wear. Many implant systems lateralize the glenosphere to address scapular notching, but the mechanical tradeoffs of lateralization have not been rigorously evaluated. We hypothesized that lateralization would decrease bony impingement but also decrease the mechanical advantage of the deltoid.

METHODS

Finite element models were created using the same implants with different amounts of glenoid lateralization: 5 mm of medialization to replicate glenoid erosion, as well as 2.5, 5, 7.5, and 10 mm of lateralization. Tests were performed with static and dynamic scapulae for motion in either the coronal or scapular plane. The angle of impingement between the scapula and the humeral polyethylene was recorded, as was the deltoid force required to elevate the arm.

RESULTS

Increasing lateralization decreased impingement while increasing the deltoid force required to elevate the arm. Differences were found between the static and dynamic scapulae, with the dynamic scapula model having increased humeral adduction before impinging. The impingement angle was also substantially affected by the bony prominences on the inferior scapula, showing how individual bony anatomy can affect impingement.

CONCLUSION

Lateralization is effective in increasing impingement-free range of motion but also increases the deltoid force required to perform identical tasks. In addition, impingement is determined by scapular motion, which should be included in all shoulder models.

Multidirectional instability of the shoulder: biomechanics, clinical presentation, and treatment strategies

Multidirectional instability (MDI) of the shoulder is a condition where the dislocation occurs in more than one direction with minimal or no causative trauma. Its pathoanatomy is complex and characterized by a redundant capsule, resulting in increased glenohumeral joint volume. The fact that several further factors may contribute to symptom onset complicates the diagnosis and hampers the identification of a therapeutic approach suitable for all cases. There is general agreement that the initial treatment should be conservative and that surgery should be reserved for patients who have not responded to an ad hoc rehabilitation program. We review the biomechanics, clinical presentation, and treatment strategies of shoulder MDI.

Effects of varying locations for biceps tendon tenotomy and superior labral integrity on shoulder stability in a cadaveric concavity-compression model

PURPOSE

The purpose of this study was to examine the location of biceps tenotomy and the integrity of the superior labrum as they relate to superior glenohumeral joint stability in a cadaveric concavity-compression model.

METHODS

Eight cadaveric glenoid labrums were mounted individually onto a load cell with the corresponding humerus fixed to the loading arm in the hanging-arm position. All surrounding soft tissue was removed except the labrum and proximal stump of the long head of the biceps (LHB) tendon, simulating a biceps tenotomy. A compressive load of 22 N was applied across the glenohumeral joint. The humerus was then translated superiorly until it subluxated over the glenoid labrum. The force resisting superior translation was characterized for each of 50 cycles. Each specimen was tested under the following conditions: (1) with a 4 cm biceps stump after tenotomy, (2) with a 0 cm biceps stump, (3) after full detachment of the superior labrum, and (4) after repair of the labrum.

RESULTS

Biceps tenotomy performed at the biceps-labral junction resulted in an average decrease in force required to superiorly subluxate the humeral head by 8.6% (P = .01) when compared with leaving 4 cm of biceps stump. Resection of the entire superior labrum resulted in a future decrease to 15.2% (P < .001) from baseline. Repair of the labrum resulted in restoration of stability with a mean of 101.1% (P = .82) and was not statistically different from baseline. The kinematics of the glenohumeral joint was affected by labral repair, with an earlier upslope on the force-to-displacement curve and alteration in the total energy required to cause subluxation of the humeral head noted.

CONCLUSIONS

In this study, location of the biceps tenotomy and integrity of the superior labrum affected glenohumeral stability during axial loading in the hanging-arm position. Repair of the labrum restored stability for superior subluxation but also changed the kinematics of the subluxation event.

CLINICAL RELEVANCE

Preservation of superior labrum after biceps tenotomy provides increased resistive force to superior translation in a unidirectional biomechanical model.

Pediatric and adolescent shoulder instability

Instability of the shoulder is a common issue faced by sports medicine providers caring for pediatric and adolescent patients. A thorough history and physical examination can help distinguish traumatic instability from multidirectional or voluntary instability. A systematic understanding of the relevant imaging characteristics and individual patient disease and goals can help guide initial treatment. Given the high risk of recurrent instability, young, active patients who seek to return to competitive contact sports should consider arthroscopic stabilization after a first-time instability event. MDI should be treated initially with conservative rehabilitation. Patients who fail extensive conservative treatment may benefit from surgical stabilization. Arthroscopic techniques may now approach the results found from traditional open capsular shift procedures. Future studies should be designed to examine the outcomes in solely pediatric and adolescent populations after both conservative and operative treatment of 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.

Role of the superior labrum after biceps tenodesis in glenohumeral stability

BACKGROUND

Little is known about the role that a torn superior labrum (SLAP) plays in glenohumeral stability after biceps tenodesis. This biomechanical study evaluated the contribution of a type II SLAP lesion to glenohumeral translation in the presence of biceps tenodesis. The authors hypothesize that subsequent to biceps tenodesis, a torn superior labrum does not affect glenohumeral stability and therefore does not require anatomic repair in an overhead throwing athlete.

METHODS

Baseline anterior, posterior, and abduction and maximal external rotation glenohumeral translation data were collected from 20 cadaveric shoulders. Translation testing was repeated after the creation of anterior (n = 10) and posterior (n = 10) type II SLAP lesions. Translation re-evaluation after biceps tenodesis was performed for each specimen. Finally, anatomic SLAP lesion repair and testing were performed.

RESULTS

Anterior and posterior SLAP lesions led to significant increases in glenohumeral translation in all directions (P < .0125). Biceps tenodesis showed no significance in stability compared with SLAP alone (P > .0125). Arthroscopic repair of anterior SLAP lesions did not restore anterior translation compared with the baseline state (P = .0011) but did restore posterior (P = .823) and abduction and maximal external rotation (P = .806) translations. Repair of posterior SLAP lesions demonstrated no statistical difference compared with the baseline state (P > .0125).

CONCLUSIONS

With no detrimental effect on glenohumeral stability in the presence of a SLAP lesion, biceps tenodesis may be considered a valid primary or revision surgery for patients suffering from symptomatic type II SLAP tears. However, biceps tenodesis should be considered with caution as the primary treatment of SLAP lesions in overhead throwing athletes secondary to its inability to completely restore translational stability.

The effect of the remplissage procedure on shoulder range of motion: a cadaveric study

PURPOSE

The purpose of this in vitro biomechanical study was to assess the effects of the remplissage procedure for small- and large-sized Hill-Sachs lesions (HSLs) on shoulder range of motion (ROM) with a special interest in the apprehension position.

METHODS

HSLs of 50% and 100% of the glenoid width were simulated in 7 cadaveric shoulders as small and large lesions, respectively, and the postoperative condition was reproduced by placing suture anchors on the articular surface and tying down the infraspinatus at the medial edge of the would-be lesion site. ROMs were measured in abduction, internal rotation, and external rotation with the humerus in the adducted and abducted position. In addition, the ROM was measured in the anterior apprehension position, in which 2 torques of external rotation and extension were applied simultaneously, and external rotation and horizontal extension ROMs were measured with the humerus in different abduction angles (20°, 40°, and 60°).

RESULTS

For standard ROMs, the procedure for the 50% HSL maintained complete ROMs, whereas the procedure for the 100% HSL significantly decreased external rotation ROM with the humerus in both the adducted and abducted positions, as well as abduction ROM. In the apprehension position, remplissage for the 50% HSL decreased extension ROM with the humerus abducted to 40° and 60°. Remplissage for the 100% HSL significantly decreased both external and extension ROMs regardless of the humeral abduction angle.

CONCLUSIONS

In the cadaveric model with an intact humeral head and the simulated postoperative condition, the remplissage procedure for a large HSL caused significant restrictions in ROM of abduction in the scapular plane and external rotation with the humerus in both adduction and abduction. It also caused significant restrictions in both external rotation and extension ROMs in the apprehension position.

CLINICAL RELEVANCE

The indication for the remplissage procedure for the larger HSL should be considered carefully, especially for the competitive throwing athlete who needs exceptional external rotation ROM for optimal overhead throwing performance.

An overview of shoulder instability and its management

The assessment and management of patients with instability of the shoulder joint can be challenging, due to the varying ways patients present, the array of different classification systems, the confusing terminology used and the differing potential management strategies. This review article aims to provide a clear explanation of the common concepts in shoulder instability and how they relate to the assessment and management of patients.

There are sections covering the mechanisms of shoulder stability, the clinical assessment of patients and imaging techniques. Beyond that there is a discussion on the common classifications systems used and the typical management options.

Some patients fall into reasonably well defined categories of classification and in these cases, the management plan is relatively easy to define. Unfortunately, other patients can elude simple classification and in these instances their management requires very careful consideration. Further research may help to facilitate a better understanding of management of the patients in this latter group.

Glenohumeral findings on magnetic resonance imaging correlate with innings pitched in asymptomatic pitchers

BACKGROUND

In recent years, there has been a documented increase in the number of professional baseball players on the disabled list and the total number of days on the disabled list. Pitchers account for the largest number of disabled list reports.

PURPOSE

To examine the relationship between magnetic resonance imaging (MRI) findings in asymptomatic professional pitchers and subsequent time on the disabled list (DL).

STUDY DESIGN

Cohort study (Prognosis); Level of evidence, 2.

METHODS

A total of 21 asymptomatic professional pitchers from a single Major League Baseball (MLB) organization underwent preseason MRIs of their dominant shoulder from 2001 to 2010. Asymptomatic was defined as no related DL stays in the 2 seasons before the MRI. These studies were reevaluated by a fellowship-trained musculoskeletal radiologist who was blinded to patient name, injury history, and baseball history. A second investigator who was blinded to the MRI results collected demographic data, total career number of innings pitched, and any subsequent DL reports for each subject.

RESULTS

The mean age at the time of MRI was 29.04 years (range, 20-39 years). Eleven of 21 pitchers had a rotator cuff tear (RCT): 9 had an articular surface tear (AST), and 2 had a full-thickness rotator cuff tear (FTT). Ten had superior labral anterior posterior (SLAP) tears, and 13 had either anterior or posterior labral tears. There was a statistically significant relationship between the number of innings pitched and presence of an RCT (AST + FTT). The mean number of career innings pitched by those with an RCT was 1014 compared with a mean of 729 innings pitched in pitchers without an RCT (P < .01). In addition, the number of career innings pitched was moderately correlated with presence of RCT (r = 0.46) and presence of superior and anterior/posterior labral tears (r = 0.43). There were no statistically significant findings between any single preseason MRI finding and subsequent time on the DL.

CONCLUSION

The MRI findings in asymptomatic MLB pitchers do not appear to be related to near future placement on the DL. However, there was a significant difference in numbers of innings pitched between pitchers who had an RCT and those who did not and a moderate correlation between innings pitched and the presence of RCT as well as the presence of labral lesions. This finding supports the notion that RCT and labral injury in pitchers may result from repetitive overhead motion with subsequent strain on the rotator cuff tendons and glenoid labrum. Asymptomatic shoulder lesions in professional baseball pitchers appear to be more frequent than previously thought.

THE ROLE OF NEGATIVE INTRA-ARTICULAR PRESSURE IN STABILIZING THE METACARPOPHALANGEAL JOINT

Negative intra-articular pressure (IAP) is a passive stabilizer during joint movement. In contrast to that of large joints, the IAP within the metacarpophalangeal (MCP) joint has not been well studied. The objective of this study was to evaluate the biomechanics of the MCP joint in terms of load–displacement relation and IAP during the application of long-axis distraction to fresh cadaver specimens. Nine fresh MCP joints specimens from four hands were used. A long-axis distraction load of 16 kg was applied to the cadaver MCP joint before and after venting of the joint capsule. In addition to load–displacement data, a pressure transducer was used to measure the IAP of the MCP joint during loading. After venting the capsule, significant increases were found in displacement at a load of 16 kg (4.60 ± 0.80 mm in an intact MCP joint and 5.22 ± 0.97 mm in a vented MCP joint) and in displacement at the cross-point (3.44 ± 0.82 and 4.01 ± 0.81 mm). No significant difference was found in the displacement difference between a load of 16 kg and the cross-point (1.16 ± 0.26 and 1.20 ± 0.33 mm) as well as stiffness at the terminal range under both the intact and venting conditions (12.59 ± 2.53 and 12.28 ± 2.70 kg/mm). The IAP decreased dramatically during the 5% to 10% total distraction of load. It was found that negative IAP of the MCP joint contributes significantly to initial stability.

Biomechanical comparison of open and arthroscopic Latarjet procedures

PURPOSE

To biomechanically compare the effectiveness of the standard open and arthroscopic techniques of the Latarjet procedure to address a critical anterior glenoid defect in combination with a capsular insufficiency.

METHODS

Translation testing of 12 human cadaveric shoulder specimens was performed in a robot-assisted setup under 3 different conditions: (1) intact/vented shoulder joint, (2) combined anterior glenoid bone and capsular defect, and (3) open and arthroscopic Latarjet procedures. Testing was performed for each condition in 2 test positions: 60° of glenohumeral abduction with neutral rotation (ABD position) and 60° of abduction and external rotation (ABER position). Each position was tested with a passive humerus load of 30 N in the anterior, inferior, and anteroinferior directions. Translational movement of the humeral head was evaluated with and without the application of a 10-N load to the conjoint tendon (CJT).

RESULTS

In the ABD position, translations after the open Latarjet procedure significantly differed from the arthroscopic technique in the anterior and anteroinferior directions when testing was performed with loading of the CJTs (CJT loading). Without CJT loading, the open Latarjet technique showed significantly lower translations in the anterior, inferior (P = .004), and anteroinferior (P = .001) testing directions in the ABD position. In the ABER position, the arthroscopic procedure showed no significant difference compared with the standard open procedure.

CONCLUSIONS

We found a superior stabilization effect of the open Latarjet technique in the ABD position. The difference is ascribed to the anterior capsular repair, which was performed within the open technique and omitted during the arthroscopic procedure.

CLINICAL RELEVANCE

The reduction of translation in a pure abduction position of the arm is more effectively performed with a conventional open Latarjet technique that includes a capsular repair. In combined ABER position, there was no difference found between the open and arthroscopic Latarjet techniques.

The effect of glenohumeral internal rotation deficit due to posterior capsular contracture on passive glenohumeral joint motion

BACKGROUND

To date, no study has investigated the biomechanical consequences of glenohumeral internal rotation deficit (GIRD) at values seen in symptomatic athletes. Hypothesis/

PURPOSE

The purpose of this study was to determine the biomechanical changes that occur with a full spectrum of GIRD in a cadaveric model with passive loading. We hypothesized that there is a critical percentage of GIRD that will result in a decrease in posterior glenohumeral translation and shift of the humeral head apex at the extreme ranges of motion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six specimens were tested using the following conditions: (1) native state ("intact"); (2) after external rotation (ER) stretch ("stretched"); and (3) GIRD of 5%, 10%, 15%, and 20%. For each condition, maximum ER, maximum internal rotation (IR), and total range of motion were measured. Kinematic data were obtained to determine the position of the humeral head apex (HHA), the highest point on the articular surface of the humeral head, relative to the geometric center of the glenoid. The amount of translation was measured in the anterior, posterior, superior, and inferior directions.

RESULTS

External rotation significantly increased compared with the intact condition for the stretched and 5% GIRD states, and IR decreased significantly beginning with 5% GIRD. At maximum ER, the HHA shifted significantly in the superior direction compared with the intact condition for all GIRD states, and at maximum IR, the HHA shifted significantly in the inferior direction compared with the intact and stretched conditions starting at 10% GIRD. The amount of posterior translation decreased significantly starting at 10% GIRD, and the amount of inferior translation decreased significantly starting at 20% GIRD.

CONCLUSION

Biomechanical changes of passive glenohumeral joint motion occur in the glenohumeral joint with as little as 5% GIRD.

CLINICAL RELEVANCE

Biomechanical changes of passive glenohumeral joint motion are noted with as little as 5% GIRD in this cadaveric model, and as the amount of GIRD increases, more substantial effects are noted.

Evaluation of dislocation position in patients with recurrent anterior shoulder dislocation

BACKGROUND

The usual mechanism of anterior shoulder dislocation is widely believed to be a combination of glenohumeral joint abduction, extension, and external rotation forces, even though no published reports to date have investigated the arm position of anterior shoulder dislocation in detail. Understanding the exact position of anterior shoulder dislocations is important for the management of anterior shoulder instability.

MATERIALS AND METHODS

The study included 40 shoulders of 38 patients (32 males, 6 females), aged 28.0 (range, 13-73) years with symptomatic post-traumatic recurrent anterior shoulder instability. While patients were under general anesthesia, but before shoulder-stabilizing surgery, we evaluated the angle of external rotation with 90° elevation in the scapular plane at which the humeral head showed anterior translations over the glenoid rim.

RESULTS

The center of anterior instability at 90° elevation in the scapular plane was at 25.9° of external rotation. Anterior translations were detected in the range of 3.4° of internal rotation to 55.1° of external rotation, and no shoulders (except one) showed anterior translation at maximal external rotation.

CONCLUSIONS

Gross anterior translation was seen in the middle range of rotation at approximately 25° of external rotation, and anterior translation decreased close to the end of external and internal rotation. Shoulders with grade III translation showed anterior translation in a wider range of rotation, especially in external rotation. These data will help to further our understanding of the management and the prevention of anterior shoulder dislocations.

Specificity of clinical examinations for testing glenohumeral ligament integrity: a computational study

An accurate diagnosis of glenohumeral joint (GHJ) instability is essential for an effective surgical intervention. There is presently no known comprehensive algorithm of clinical tests for the confirmation of the functional integrity of glenohumeral ligaments (GHLs). A validated computational GHL strain analyser was applied to a set of GHJ kinematics data from the literature to simulate 57 different physiological clinical examination manoeuvres. An algorithm that integrates the GHL pre-straining activities at the toe region of the stress-strain curve was developed for the quantification of ligament loading from prevailing strains. This was used to upgrade the strain analyser and applied to produce a matrix of the various GHL loadings and sensitivities during the manoeuvres. The investigation magnified the likely impact of anatomical variations of GHL attachments as possible causes of misdiagnoses during clinical examinations of GHJ dysfunction. This can serve as an assistive guide to ascertain the functional condition of a specific GHL during symptomatic clinical examinations.