Tensile properties of the superior glenohumeral and coracohumeral ligaments

Effect of subscapularis repair on joint contact forces based on degree of posterior-superior rotator cuff tear severity in reverse shoulder arthroplasty

Massive irreparable rotator cuff tears (RCTs) affect the clinical outcomes of reverse shoulder arthroplasty (RSA). However, the effects of subscapularis repair on the outcomes of RSA, based on the degree of posterior-superior RCTs, are unclear. This study aimed to examine the effect of subscapularis repair on three-dimensional joint contact forces (JCFs) based on the degree of posterior-superior RCT severity in RSA. Ten human in vivo experimental data were used as input to the musculoskeletal model. A six-degrees-of-freedom (DOF) anatomical shoulder model was developed and validated against three-dimensional JCFs. The 6-DOF musculoskeletal shoulder model of RSA was then developed by importing the reverse shoulder implant into the validated anatomical shoulder model. Based on the various types of posterior-superior RCT severity, inverse dynamic simulations of subscapularis-torn and subscapularis-repaired models of RSA were performed: from isolated supraspinatus tears to partial or massive tears of the infraspinatus and teres minor. The intact rotator cuff model of RSA was also simulated for comparison with the different types of models. Our results showed that the more posterior-superior RCTs progressed in RSA, the more superior JCFs were observed at 90°, 105°, and 120° abduction in the subscapularis-torn model. However, subscapularis repair decreased the superior JCF at those angles sufficiently. In addition, the teres minor muscle-tendon force increased as infraspinatus bundle tears progressed in both the subscapularis-torn and -repaired models, in order to compensate for the reduced force during abduction. However, the teres minor muscle-tendon force was not as high as that of the infraspinatus muscle-tendon, which could result in muscle force imbalance between repaired subscapularis and teres minor. Therefore, our results suggest that repairing the subscapularis and the repairable infraspinatus during RSA can improve glenohumeral joint stability in the superior-inferior direction by restoring muscle force balance between the anterior cuff (i.e., subscapularis) and posterior cuff (i.e., infraspinatus and teres minor). The findings of this study can help clinician decide whether to repair the rotator cuff during RSA to enhance joint stability.

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.

Dynamic Analysis of the Coracohumeral Ligament Using Ultra-Sonography in Shoulder Contracture

The coracohumeral ligament (CHL) is related to the range of motion of the shoulder joint. The evaluation of the CHL using ultrasonography (US) has been reported on the elastic modulus and thickness of the CHL, but no dynamic evaluation method has been established. We aimed to quantify the movement of the CHL by applying Particle Image Velocimetry (PIV), a technique used in the field of fluid engineering, to cases of shoulder contracture using the US. The subjects were eight patients, with 16 shoulders. The coracoid process was identified from the body surface, and a long-axis US image of the CHL parallel to the subscapularis tendon was drawn. The shoulder joint was moved from 0 degrees of internal/external rotation to 60 degrees of internal rotation at a rhythm of one reciprocation every 2 s. The velocity of the CHL movement was quantified by the PIV method. The mean magnitude velocity of CHL was significantly faster on the healthy side. The maximum magnitude velocity was significantly faster on the healthy side. The results suggest that the PIV method is helpful as a dynamic evaluation method, and in patients with shoulder contracture, the CHL velocity was significantly decreased.

Association of damage to the coracohumeral ligament with anterosuperior rotator cuff degeneration revealed by anatomical dissection

The coracohumeral ligament (CHL) is an important structure of the biceps pulley which also merges with the rotator cuff. Which role it actually plays in the pathogenesis of rotator cuff degeneration (RCD) and rotator cuff tears (RCT) is still a point of discussion. The hypothesis of this study was, that macroscopic injury to the anterosuperior part of the rotator cuff also includes parts of or the whole CHL. Forty fresh-frozen shoulders were dissected and examined, the morphology of the rotator cuff and the coracohumeral ligament were evaluated and existing lesions documented. 27.5% of the shoulder joints showed an anterosuperior full-thickness RCT. 57.5% of all examined shoulder girdles showed at least a partial rupture of the CHL. A highly significant correlation (p < 0.001, rho = 0.529) between the presence of rotator cuff tears and ruptures of the CHL was found. Cartilage damage within the anterosuperior section of the humeral head was observed in 20% cases. In rotator cuff degeneration and atraumatic rotator cuff tears of the elderly population, the pathomechanism of full-thickness RCT is based on repetitive anterosuperior glenoid impingement. This is especially supported by the identification of a higher frequency of CHL lesions compared to RCT reported in this study. No intact CHL was identified in shoulders with damaged rotator cuff tendons.

Elasticity of the coracohumeral ligament in patients with frozen shoulder following rotator interval injection: a case series

Aim of the study: To evaluate changes in the elasticity of the coracohumeral ligament in patients with adhesive capsulitis of the shoulder treated with ultrasound-guided rotator interval injections. Methods: Shear wave elastography was used to evaluate elasticity of the coracohumeral ligament in symptomatic and asymptomatic shoulders in the shoulder-neutral position and 30° external rotation. A total of 24 shoulders were assessed. Symptomatic shoulders were treated with targeted steroid injection via the rotator interval and manipulation under local anaesthetic block. Follow-up assessment of the elasticity of the coracohumeral ligament was obtained at 10 weeks post-injection. Results: In all subjects, the coracohumeral ligament elastic modulus was larger at 30° external rotation than in the neutral position. In patients with adhesive capsulitis, the coracohumeral ligament thickness and elastic modulus was significantly greater in the symptomatic shoulder in the neutral position and 30° ER. Treated patients had an excellent response with improved Oxford Shoulder Score and reduced visual analogue scale pain scores. Median Oxford Shoulder Score was 13.5 pre-injection and 34 at 10 weeks post-injection. Median visual analogue scale pain scores measured 8.5 pre-injection, 3.5 at 1 day, 2 at 1 week, and 2.5 at 10 weeks. Improved Oxford Shoulder Score and visual analogue scale pain score was associated with a trend to normalisation of the elastic modus of the coracohumeral ligament. Conclusion: In patients with adhesive capsulitis of the shoulder, shear wave elastography demonstrated the coracohumeral ligament is stiffer in the symptomatic shoulder than in the unaffected shoulder. Treatment with the ultrasound-guided rotator interval injection is associated with improved Oxford Shoulder Score, reduced visual analogue scale pain scores, and reduced stiffness in the coracohumeral ligament.

Mapping of the Inferior Glenohumeral Ligament for Suture Pullout Strength: A Biomechanical Analysis

Background

Suture pullout during rehabilitation may result in loss of tension in the inferior glenohumeral ligament (IGHL) and contribute to recurrent instability after capsular plication, performed with or without labral repair. To date, the suture pullout strength in the IGHL is not well-documented. This may contribute to recurrent instability.

Purpose/Hypothesis

A cadaveric biomechanical study was designed to investigate the suture pullout strength of sutures in the IGHL. We hypothesized that there would be no significant variability of suture pullout strength between specimens and zones. Additionally, we sought to determine the impact of early mobilization on sutures in the IGHL at time zero. We hypothesized that capsular plication sutures would fail under low load.

Study Design

Descriptive laboratory study.

Methods

Seven fresh-frozen cadaveric shoulders were dissected to isolate the IGHL complex, which was then divided into 18 zones. Sutures in these zones were attached to a linear actuator, and the resistance to suture pullout was recorded. A suture pullout strength map of the IGHL was constructed. These loads were used to calculate the load applied at the hand that would initiate suture pullout in the IGHL.

Results

Mean suture pullout strength for all specimens was 61.6 ± 26.1 N. The maximum load found to cause suture pullout through tissue was found to be low, regardless of zone of the IGHL. Calculations suggest that an external rotation force applied to the hand of only 9.6 N may be sufficient to tear capsular sutures at time zero.

Conclusion

This study did not provide clear evidence of desirable locations for fixation in the IGHL. However, given the low magnitude of failure loads, the results suggest the timetable for initiation of range-of-motion exercises should be reconsidered to prevent suture pullout through the IGHL.

Clinical Relevance

From this biomechanical study, the magnitude of force required to cause suture pullout through the IGHL is met or surpassed by normal postoperative early range-of-motion protocols.

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.

Functional and Surgical Anatomy of the Upper Limb: What the Radiologist Needs to Know

The anatomy of the upper limb is complex and allows for exceptional functionality. The movements of the joints of the shoulder, elbow, and wrist represent a complex dynamic interaction of muscles, ligaments, and bony articulations. A solid understanding and of the characteristics and reciprocal actions of the anatomic elements of the joints of the upper limb helps explain the mechanisms and patterns of injury. This article focuses on the anatomy and functionality of the shoulder, elbow, and wrist, with emphasis on the stabilizing mechanisms, to set the foundation for understanding the occurrence of pathologic conditions.

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.

Spatial Dependency of Glenohumeral Joint Stability during Dynamic Unimanual and Bimanual Pushing and Pulling

Degenerative wear to the glenoid from repetitive loading can reduce effective concavity depth and lead to future instability. Workspace design should consider glenohumeral stability to prevent initial wear. While stability has been previously explored for activities of daily living including push-pull tasks, whether stability is spatially dependent is unexplored. We simulated bimanual and unimanual push-pull tasks to 4 horizontal targets (planes of elevation: 0º, 45º, 90º, and 135º) at 90º thoracohumeral elevation and 3 elevation targets (thoracohumeral elevations: 20º, 90º, 170º) at 90º plane of elevation. The 45º horizontal target was most stable regardless of exertion type and would be the ideal target placement when considering stability. This target is likely more stable because the applied load acts perpendicular to the glenoid, limiting shear force production. The 135º horizontal target was particularly unstable for unimanual pushing (143% less stable than the 45º target), and the applied force acts parallel to the glenoid, likely creating shear forces. Pushing was less stable than pulling (all targets except sagittal 170º for both task types and horizontal 45º for bimanual) (p<0.01), which is consistent with prior reports. For example, unimanual pushing at the 90º horizontal target was 197% less stable than unimanual pulling. There were limited stability benefits to task placement for pushing, and larger stability benefits may be seen from converting pushing to pulling rather than optimizing task layout. There was no difference in stability between bimanual and unimanual tasks, suggesting no stability benefit to bimanual operation.

Correlations between Capsular Changes and ROM Restriction in Frozen Shoulder Evaluated by Plain MRI and MR Arthrography

Background:

Evaluation of the Range Of Motion (ROM) is one of the important procedures for shoulder disorders. The purpose of this study was to investigate correlations between capsular changes and ROM restrictions evaluated by both plain magnetic resonance imaging (MRI) and Magnetic Resonance Arthrography (MRA) in the same patients with frozen shoulder.

Methods:

Between March 2015 and June 2016, 24 patients with frozen shoulders (13 male and 11 female patients, mean age 60.5) with severe ROM restriction who underwent both MRI and MRA on the same affected side were evaluated. We evaluated 1) ROM, 2) the coracohumeral ligament (CHL) thickness, 3) the joint capsule thickness in the axillary recess (humeral and glenoid sides), 4) the area of the axillary recess, and 5) the capsular area of the axillary recess.

Results:

Positive correlations were found between the axillary area and forward flexion (FF) (R = 0.43, P = 0.035), lateral elevation (LE) (R = 0.66, P<0.001), external rotation (ER)(R = 0.43, P = 0.035), 90° abduction with external rotation (AER)(R = 0.56, P = 0.004), and hand behind the back (HBB)(R = 0.6, P = 0.002) on MRA. Negative correlations were found between the joint capsule at the glenoid side and ER and HBB in both MRI and MRA.

Conclusion:

The axillary area was significantly correlated with ROM restriction in FF, LE, ER, AER, and HBB on MRA. Thickness of the joint capsule at the glenoid side is an important factor for ROM restriction in frozen shoulder.

Level of Evidence:

Level 3, Study of Diagnostic Test.

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.

Mechanical Considerations for Electrospun Nanofibers in Tendon and Ligament Repair

Electrospun nanofibers possess unique qualities such as nanodiameter, high surface area to volume ratio, biomimetic architecture, and tunable chemical and electrical properties. Numerous studies have demonstrated the potential of nanofibrous architecture to direct cell morphology, migration, and more complex biological processes such as differentiation and extracellular matrix (ECM) deposition through topographical guidance cues. These advantages have created great interest in electrospun fibers for biomedical applications, including tendon and ligament repair. Electrospun nanofibers, despite their nanoscale size, generally exhibit poor mechanical properties compared to larger conventionally manufactured polymer fiber materials. This invites the question of what role electrospun polymer nanofibers can play in tendon and ligament repair applications that have both biological and mechanical requirements. At first glance, the strength and stiffness of electrospun nanofiber grafts appear to be too low to fill the rigorous loading conditions of these tissues. However, there are a number of strategies to enhance and tune the mechanical properties of electrospun nanofiber grafts. As researchers design the next-generation electrospun tendon and ligament grafts, it is critical to consider numerous physiologically relevant mechanical criteria and to evaluate graft mechanical performance in conditions and loading environments that reflect in vivo conditions and surgical fixation methods.

Correlations of coracohumeral ligament and range of motion restriction in patients with recurrent anterior glenohumeral instability evaluated by magnetic resonance arthrography

BACKGROUND

Evaluation of range of motion (ROM) restriction before treatment of shoulder disorders is important for predicting the final functional outcomes. The purpose of this study was to investigate correlations of thickness of the coracohumeral ligament (CHL) and ROM restriction in patients with recurrent anterior glenohumeral instability.

METHODS

Between January 2005 and March 2015, 181 shoulders (137 male and 44 female patients; mean age, 29.3 years) with recurrent anterior glenohumeral instability treated with an arthroscopic Bankart repair were enrolled in this study. We evaluated preoperative ROM, thickness of the CHL, and obliteration of the subcoracoid fat triangle on magnetic resonance arthrography. ROM measurements, including forward flexion (FF), external rotation with the arm at the side (ER), and hand behind the back (HBB), were made in a standing position.

RESULTS

There were significant negative correlations between FF and age (P < .001) and between HBB and age (P < .001) but not between ER and age (P = .11). The thickness of the CHL significantly increased with age (P < .001). FF, ER, and HBB were significantly restricted in patients with obliteration compared with those without obliteration (P < .001, P = .004, P < .001, respectively).

CONCLUSIONS

Obliteration of the subcoracoid fat triangle and the thickness of the CHL positively correlated with ROM restrictions, and these changes were greater with age in patients with recurrent anterior glenohumeral instability.

High-Pressure Balloon-Assisted Stretching of the Coracohumeral Ligament to Determine the Optimal Stretching Positions: A Cadaveric Study

BACKGROUND

The coracohumeral ligament (CHL) is a thick capsular structure and markedly thickened when affected by adhesive capsulitis. Therapeutic stretching is the most commonly applied treatment for adhesive capsulitis, but optimal stretching postures for maximal therapeutic effects on the CHL have not been fully investigated.

OBJECTIVE

To investigate the most effective stretching direction for the CHL by measuring the stretching intensity in 5 different directions and to determine whether the stretching intervention resulted in loosening of the ligament by comparing the changes of CHL tightness before and after stretching.

DESIGN

Biomechanical cadaver study.

SETTING

Academic institution cadaver laboratory.

PARTICIPANTS

Nine fresh frozen cadaveric shoulders.

METHODS

A high-pressure balloon catheter inserted under the CHL and intraballoon pressure was measured, to evaluate CHL tightness without ligament damage as well as to augment and monitor stretching intensity. To find the optimal stretching direction, the glenohumeral joint was stretched from the neutral position into 5 directions sequentially under pressure-monitoring: flexion, extension [EX], external rotation [ER], EX+ER, and EX+ER+adduction [AD] directions.

MAIN OUTCOME MEASUREMENTS

CHL tightness was determined by a surrogate parameter, the additional pressure created by the overlying CHL. The pressure increase (ΔP_str) by a specific directional stretch was considered as the stretching intensity.

RESULTS

ΔP_str by the 5 directions were mean (standard deviation) values of 0.03 ± 0.07 atm, 0.87 ± 1.31 atm, 1.13 ± 1.36 atm, 1.49 ± 1.32 atm, and 2.10 ± 1.70 atm, respectively, revealing the highest ΔP_str by the EX+ER+AD stretch (P < .05). The balloon pressure by the overlying CHL was decreased from 0.45 ± 0.35 atm to 0.18 ± 0.14 atm (P = .012) before and after the stretching manipulation.

CONCLUSIONS

EX+ER+AD of the glenohumeral joint resulted in the greatest increase in balloon pressure, implying that it could be the most effective stretching direction. A series of stretching manipulations assisted with an underlying pressure balloon were capable of decreasing CHL tightness. With further development and modification, high-pressure balloon-assisted stretching can be a potential therapeutic option to release tight CHL, including the advantage of augmenting and monitoring stretching intensity.

LEVEL OF EVIDENCE

II.

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.

Anatomy and histology of the transverse humeral ligament

The classic literature describes the transverse humeral ligament (THL) as a distinct anatomic structure with a role in biceps tendon stability; however, recent literature suggests that it is not a distinct anatomic structure. The purpose of this study was to evaluate the gross and microscopic anatomy of the THL, including a specific investigation of the histology of this ligament. Thirty frozen, embalmed cadaveric specimens were dissected to determine the gross anatomy of the THL. Seven specimens were evaluated histologically for the presence of mechanoreceptors and free nerve endings. Two tissue layers were identified in the area described as the THL. In the deep layer, fibers of the subscapularis tendon were found to span the bicipital groove with contributions from the coracohumeral ligament and the supraspinatus tendon. Superficial to this layer was a fibrous fascial covering consisting of distinct bands of tissue. Neurohistology staining revealed the presence of free nerve endings but no mechanoreceptors. This study's findings demonstrate that the THL is a distinct structure continuous with the rotator cuff tendons and the coracohumeral ligament. The finding of free nerve endings in the THL suggests a potential role as a shoulder pain generator.

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.

In-vivo glenohumeral translation and ligament elongation during abduction and abduction with internal and external rotation

Study Design

Basic Science. To investigate humeral head translations and glenohumeral ligament elongation with a dual fluoroscopic imaging system.

Background

The glenohumeral ligaments are partially responsible for restraining the humeral head during the extremes of shoulder motion. However, in-vivo glenohumeral ligaments elongation patterns have yet to be determined. Therefore, the objectives of this study were to 1) quantify the in-vivo humeral head translations and glenohumeral ligament elongations during functional shoulder positions, 2) compare the inferred glenohumeral ligament functions with previous literature and 3) create a baseline data of healthy adult shoulder glenohumeral ligament lengths as controls for future studies.

Methods

Five healthy adult shoulders were studied with a validated dual fluoroscopic imaging system (DFIS) and MR imaging technique. Humeral head translations and the superior, middle and inferior glenohumeral ligaments (SGHL, MGHL, IGHL) elongations were determined.

Results

The humeral head center on average translated in a range of 6.0mm in the anterior-posterior direction and 2.5mm in the superior-inferior direction. The MGHL showed greater elongation over a broader range of shoulder motion than the SGHL. The anterior-band (AB)-IGHL showed maximum elongation at 90° abduction with maximum external rotation. The posterior-band (PB)-IGHL showed maximum elongation at 90° abduction with maximum internal rotation.

Discussion

The results demonstrated that the humeral head translated statistically more in the anterior-posterior direction than the superior-inferior direction (p = 0.01), which supports the concept that glenohumeral kinematics are not ball-in-socket mechanics. The AB-IGHL elongation pattern makes it an important static structure to restrain anterior subluxation of the humeral head during the externally rotated cocking phase of throwing motion. These data suggest that in healthy adult shoulders the ligamentous structures of the glenohumeral joint are not fully elongated in many shoulder positions, but function as restraints at the extremes of glenohumeral motion. Clinically, these results may be helpful in restoring ligament anatomy during the treatment of anterior instability of the shoulder.

Reliability of a set of protractors for direct anatomical measurements around the glenoid and humeral head rims

Functional biomechanics studies of the glenohumeral (GH) soft tissues require an understanding of their sites of bony attachment. Anatomical positions of GH capsular structures have often been quantified relative to the rims of the glenoid and humeral head (HH). The aim of this study was twofold: (1) to quantify the reliability of a set of protractors that directly fit on to the glenoid and HH rims and (2) to use this to determine direct angular position referencing of landmarks and soft tissue attachment points. Three assessors independently used the protractors to assess nine prescribed landmarks on 30 dry bone specimens (15 glenoids and 15 HHs) recording the angular positions of the structures relative to the glenoid and HH. The collected data showed high levels of validity as indicated by the protractor's intra- and inter-assessor reliabilities: 98.2 and 98.7% for the glenoid component, and 96.2 and 96.5% for the humeral component, respectively. The device could be useful in anatomical studies, description of defects and pathologies on glenohumeral articulation, and planning of scapular reconstructive surgery.

Development and validation of a model for quantifying glenohumeral ligament strains during function

Analysis of the function of glenohumeral ligaments (GHLs) during physical joint manipulations is hindered by an inability to adequately image these tissues during the movements. This restricts functional biomechanics studies only to the manoeuvres that may be replicated cadaverically. There is, however, a clinical imperative to be able to investigate complex manoeuvres that exacerbate symptoms but cannot be easily conducted physically in the laboratory. The aim of this study was to develop and validate an algorithm for a computer simulation model that allows the quantification of glenohumeral ligament lengths during function. Datasets of the humerus and scapula pair were segmented to provide individual surface meshes of the bones and insertion points of each glenohumeral ligament on both bones. An algorithm was developed in which the glenohumeral ligament attachment-to-attachment length was divided into two straight lines, plus an arc overlaying the spherical wrapping portions. The model was validated by simulating two classical cadaveric studies from the literature and comparing results. Predictions from the model were qualitatively similar to the results of the two cadaveric studies by a factor of 91.7% and 81.8%, respectively. Algorithm application will allow investigation of functional loading of the glenohumeral ligaments during simulated complex motions. This could then be used to provide diagnostic understanding and thus, inform surgical reconstruction.

Magnetic resonance imaging in glenohumeral instability

The glenohumeral joint enables tremendous range of motion at the expense of stability. Functional stability is maintained by the synchronous coordination of complex static and dynamic structures. Symptomatic glenohumeral instability most often results from injury to the inferior labral-ligamentous complex, the primary passive stabilizer of the shoulder. This article reviews the structures important in glenohumeral stabilization and illustrates their normal appearances and the abnormalities associated with anterior, posterior, and multidirectional instability. These lesions are discussed in the context of therapeutic decision making.

Soft tissue structures resisting anterior instability in a computational glenohumeral joint model

The glenohumeral joint is the most dislocated joint in the body due to the lack of bony constraints and the dependence on soft tissue for stability. The roles that various structures provide to joint function are important for understanding injury treatment and orthopaedic device design purposes. The goal of this study was to develop a computational model of the glenohumeral joint whereby joint behaviour was dictated by articular contact, ligamentous constraints, muscle loading and external perturbations. The bone structure of the computational model consisted of assembled computer tomographic images of the scapula, humerus and clavicle. The soft tissue elements were composed of forces and tension-only springs that represented muscles and ligaments. Validation of this model was achieved by comparing computational predictions to the results of a cadaveric experiment in which the relative contribution of muscles and ligaments to anterior joint stability was examined. The computational model predicted an anterior subluxation force that was similar to the cadaveric experimental results in humeral external rotation. The individual structure results showed the subscapularis to be critical to stabilisation in both neutral and external rotations, the biceps stabilised the joint in neutral but not in external rotation, and the inferior glenohumeral ligament resisted anterior displacement only in external rotation. The model's predictions were similar to the conclusions of the cadaveric experiment and the literature. Knowledge gained from this type of model could assist in further understanding the contribution of soft tissue stabilisers to joint function, pre-operative planning or the design of orthopaedic implants.

Multimedia article. The rotator interval: pathology and management

The rotator interval describes the anatomic space bounded by the subscapularis, supraspinatus, and coracoid. This space contains the coracohumeral and superior glenohumeral ligament, the biceps tendon, and anterior joint capsule. Although a definitive role of the rotator interval structures has not been established, it is apparent that they contribute to shoulder dysfunction. Contracture or scarring of rotator interval structures can manifest as adhesive capsulitis. It is typically managed nonsurgically with local injections and gentle shoulder therapy. Recalcitrant cases have been successfully managed with an arthroscopic interval release and manipulation. Conversely, laxity of rotator interval structures may contribute to glenohumeral instability. In some cases this can be managed with one of a number of arthroscopic interval closure techniques. Instability of the biceps tendon is often a direct result of damage to the rotator interval. Damage to the biceps pulley structures can lead to biceps tendon subluxation or dislocation depending on the structures injured. Although some authors describe reconstruction of this tissue sling, most recommend tenodesis or tenotomy if it is significantly damaged. Impingement between the coracoid and lesser humeral tuberosity is a relatively well-established, yet less common cause of anterior shoulder pain. It may also contribute to injury of the anterosuperior rotator cuff and rotator interval structures. Although radiographic indices are described, it appears intraoperative dynamic testing may be more helpful in substantiating the diagnosis. A high index of suspicion should be used in association with biceps pulley damage or anterosuperior rotator cuff tears. Coracoid impingement can be treated with either open or arthroscopic techniques. We review the anatomy and function of the rotator interval. The presentation, physical examination, imaging characteristics, and management strategies are discussed for various diagnoses attributable to the rotator interval. Our preferred methods for treatment of each lesion are also discussed.

Stretching positions for the coracohumeral ligament: Strain measurement during passive motion using fresh/frozen cadaver shoulders

BACKGROUND

Contracture of the coracohumeral ligament is reported to restrict external rotation of the shoulder with arm at the side and restrict posterior-inferior shift of the humeral head. The contracture is supposed to restrict range of motion of the glenohumeral joint.

METHODS

To obtain stretching position of the coracohumeral ligament, strain on the ligament was measured at the superficial fibers of the ligament using 9 fresh/frozen cadaver shoulders. By sequential measurement using a strain gauge, the ligament strain was measured from reference length (L0). Shoulder positions were determined using a 3 Space Tracker System. Through a combination of previously reported coracohumeral stretching positions and those observed in preliminary measurement, ligament strain were measured by passive external rotation from 10° internal rotation, by adding each 10° external rotation, to maximal external rotation.

RESULTS

Stretching positions in which significantly larger strain were obtained compared to the L0 values were 0° elevation in scapula plane with 40°, 50° and maximum external rotation (5.68%, 7.2%, 7.87%), 30° extension with 50°, maximum external rotation (4.20%, 4.79%), and 30° extension + adduction with 30°, 40°, 50° and maximum external rotation (4.09%, 4.67%, 4.78%, 5.05%)(P < 0.05). No positive strain on the coracohumeral ligament was observed for the previously reported stretching positions; ie, 90° abduction with external rotation or flexion with external rotation.

CONCLUSIONS

Significant strain of the coracohumeral ligament will be achieved by passive external rotation at lower shoulder elevations, extension, and extension with adduction.

In vivo three-dimensional evaluation of the functional length of glenohumeral ligaments

BACKGROUND

Glenohumeral ligaments play an important role in stabilizing the shoulder. However, it is impossible to know how they function in vivo during shoulder motion. To help elucidate this stabilizing role, we studied the in vivo three-dimensional kinematics of the normal shoulder joint using a markerless bone-registration technique.

METHODS

Our technique utilized image registration to determine corresponding relations between several image volumes represented at different coordinates. Magnetic resonance images of 14 shoulder joints of seven healthy volunteers were acquired for seven isometric abduction orientations between 0 degrees and 180 degrees . We then calculated three-dimensional shortest path between the origin and insertion of each ligament based on anatomical study in each abduction orientation.

FINDINGS

At 0 degrees of abduction, the posterior band of the coracohumeral ligament displayed the maximum length. At 30 degrees of abduction, the superior glenohumeral ligament displayed the maximum length. At 60 degrees of abduction, the anterior band of the coracohumeral ligament and the middle glenohumeral ligament displayed the maximum length. At 120 degrees of abduction, the anterior band of the inferior glenohumeral ligament displayed the maximum length.

INTERPRETATION

Based on progressive abduction of the arm, each ligament had different pattern in change of length. At different arm orientation of abduction, each ligament displayed the maximum length. We think that each ligament might play an important role in stabilizing the shoulder at different arm orientation.

Functional anatomy of the superior glenohumeral and coracohumeral ligaments and the subscapularis tendon in view of stabilization of the long head of the biceps tendon

BACKGROUND

Various findings in the lateral rotator interval to support the long head of the biceps tendon have been reported. The purpose of this study was to clarify the functional anatomy regarding the stabilization of the biceps tendon.

MATERIAL AND METHODS

Twenty embalmed shoulders were used for anatomic study, and 5 specimens of the anterosuperior part of the glenohumeral joint were histologically studied.

RESULTS

Anatomically, the most superior part of the subscapularis tendon was attached to the upper margin of the lesser tuberosity and extended as a thin tendinous slip to the fovea capitis of the humerus. The superior glenohumeral ligament ran spirally along the biceps tendon. Histologically, the superior glenohumeral ligament was attached to the tendinous slip. There was no clear boundary between the superior glenohumeral and coracohumeral ligament.

CONCLUSION

To keep the biceps tendon in place and stabilized, tension in the superior glenohumeral ligament and the buttress support of the most superior insertion point of the subscapularis from behind the ligament may be necessary.

LEVEL OF EVIDENCE

Basic Science.

The glenohumeral capsule should be evaluated as a sheet of fibrous tissue: a validated finite element model

The function of the glenohumeral capsule has typically been evaluated by isolating several discrete, ligamentous regions during experimental and computational investigations. However, recent data suggests that the regions of the glenohumeral capsule have significant interactions and function multiaxially. Therefore, examining the function of the inferior glenohumeral ligament as a discrete structure may not be appropriate. The objective of this work was to validate the predicted strain distribution and deformed shape of the inferior glenohumeral ligament using experimental data for two subject-specific finite element models: (1) a continuous model including all capsular regions, and (2) a discrete model including only the inferior glenohumeral ligament. The distribution of maximum principal strain and deformed shape of the glenohumeral capsule was determined for a cadaveric shoulder in a joint position frequently associated with dislocation (60 degrees of glenohumeral abduction, 52 degrees of external rotation, and a 25 N anterior load applied to the humerus). The experimental kinematics were then applied to the two finite element models constructed from the geometry and material properties from the same cadaveric shoulder and the predicted strain distributions and deformed shapes were determined. For the continuous model, the average difference between predicted strains and experimental strains was less than 5%. The predicted deformed shape was also similar to experimental data, with the anterior band of the inferior glenohumeral ligament clearly wrapped around the humeral head. In contrast, large differences existed between the strains predicted by the discrete model when compared to the experimental strains for this joint position (average difference from experimental data was 20%). In addition, the predicted deformed shape of the inferior glenohumeral ligament did not wrap around the humeral head. These differences may be attributed to neglecting the complex interactions between the anterior band of the inferior glenohumeral ligament with the neighboring capsular regions. Thus, the glenohumeral capsule should not be evaluated as several discrete structures. Rather, it should be evaluated as a single sheet of fibrous tissue.

Material properties of the axillary pouch of the glenohumeral capsule: is isotropic material symmetry appropriate?

Inconclusive findings regarding the collagen fiber architecture and the material properties of the glenohumeral capsule make it unclear whether the material symmetry of the glenohumeral capsule is isotropic or anisotropic. The overall objective of this work was to use a combined experimental and computational protocol to characterize the mechanical properties of the axillary pouch of the glenohumeral capsule and to determine the appropriate material symmetry. Two perpendicular tensile and finite simple shear deformations were applied to a series of tissue samples from the axillary pouch of the glenohumeral capsule. An inverse finite element optimization routine was then used to determine the material coefficients for an isotropic hyperelastic constitutive model by simulating the experimental conditions. There were no significant differences between the material coefficients obtained from the two perpendicular tensile deformations or finite simple shear deformations. Furthermore, stress-stretch relationships predicted by utilizing the material coefficients from one direction were able to predict the responses of the same tissue sample in the perpendicular direction. These similarities between the longitudinal and transverse material behaviors of the tissue imply that the capsule may be considered an isotropic material. However, differences did exist between the material coefficients obtained from the tensile and shear loading conditions. Therefore, a more advanced constitutive model is needed to predict both the tensile and shear responses of the material.

An anatomic and histologic study of the coracohumeral ligament

Although the anatomy and histology of the coracohumeral ligament (CHL) play an important role in the diagnosis and treatment of frozen shoulder, they remain unclear. Our objective was to study the anatomic features of the CHL and analyze its histology. Twenty-six fresh-frozen, normal cadaveric shoulders were used to examine the position and morphology of the CHL and their relationship with the superior glenohumeral ligament and to determine the CHL's histologic features in comparison with the joint capsule and coracoacromial ligament. The CHLs were all located in the rotator interval, with an irregular trapezoidal structure. The subacromial bursa was above the CHL, and the subcoracoid bursa was below the it. The CHLs in all shoulders originated from the lateral aspect of the base of the coracoid process. In 11 shoulders, it inserted into the supraspinatus tendon, whereas in 11 other shoulders, it inserted into the rotator interval. In 3 shoulders, the CHLs were split and inserted into both the supraspinatus and subscapularis tendons, respectively. Finally, the CHL in 1 shoulder only inserted into the subscapularis tendon. We also observed that the pectoralis minor tendons in 4 shoulders passed over the coracoid process top and inserted into the CHLs. In 11 shoulders, a complex of the CHL and the superior glenohumeral ligament was formed. Histologically, the CHL was found to be similar to the joint capsule without any ligament features. The position, morphology, and origin of the CHL did not change much, but its insertion varied greatly. In addition, the CHL had the histologic feature of a capsule, not a ligament.

Biomechanics and anatomy of the proximal biceps tendon

With the role of the biceps tendon being the source of considerable controversy, the treatment of its disease has been even more confusing. Our understanding of its role in shoulder pathology has ranged from describing it as a vestigial structure, to a vital structure of shoulder function with distinct disease pathology. This chapter analyzes the anatomic and biomechanical functions of the proximal biceps tendon.

An analysis of the rotator interval in patients with anterior, posterior, and multidirectional shoulder instability

PURPOSE

To describe anatomic measurements of the rotator interval (RI) on magnetic resonance arthrogram (MRA) images and to assess the relationship between increased dimensions of the RI and instability conditions of the shoulder.

METHODS

Three groups of patients with clinical instability were treated arthroscopically (anterior [A = 19 patients], posterior [P = 14 patients], and multidirectional [M = 13 patients]), and a group of 10 control patients without clinical instability were also identified. The MRAs of all groups were randomized, and 5 blinded reviewers recorded RI anatomic measurements of: (1) sagittal measures of the distance between the subscapularis (SSc) and supraspinatus (SS) tendons at 3 anatomic landmarks across the RI, and (2) the sagittal position of the long head of the biceps (LHB) relative to the most anterior aspect of the SS.

RESULTS

The rotator interval distance between the SS and SSc tendons was nearly identical for all groups of instability, and was also not different from control groups. On the sagittal oblique sequences, the distance from the LHB tendon to the anterior edge of the SS tendon was significantly increased in posterior (7.4 mm) instability versus both the control group (2.4 mm; P = .025) and those with anterior instability (4.5 mm; P = .041), with the LHB in a consistent anterior position. The remainder of the measures was not statistically different between the groups.

CONCLUSIONS

The distance between the SS and SSc and the overall size of the RI was well preserved in all instability patterns and control conditions. The LHB tendon assumes a more anterior position relative to the supraspinatus tendon in patients with posterior instability versus those patients with anterior instability or those without clinical instability. Additional work is necessary to further define objective radiographic evidence of RI insufficiency in patients with shoulder instability.

LEVEL OF EVIDENCE

Level III, prognostic case-control study.

Definition of the capsular insertion plane on the proximal humerus

The aim of this work was quantitatively to establish the relationship between the plane that hosts the humeral head lateral margin (anatomical neck) and that of the capsular insertion. Eight cadaveric shoulders were used. These were dissected, exposing the humeral head margin and the root of the capsular humeral insertion to extract digitally their outlines using a mechanical 3-d digitizer. The datasets of the digitized outlines were applied and the geometric planes they best fitted mathematically calculated. Vector analysis techniques were finally applied to the two planes to quantify the relationship between them. The humeral head margin is circular (+/- 2.2% of radius), having each of its outlining points on the same plane (within +/- 1.5 mm.) The capsular attachment outlining points also insert on a plane (+/- 1.4 mm). The two planes are related to one another by an inclination of 14.5 +/- 3.6 degrees. The relationship described here would allow for in vivo prediction of humeral attachment of capsular structures by using radiological datasets of the anatomical neck. This would be useful in patient-specific modelling to study and understand the glenohumeral ligament kinematics during clinical examinations and to plan surgical reconstructive procedures.

Variations in the superior capsuloligamentous complex and description of a new ligament

Although the rotator cuff interval and the adjacent ligaments are gaining interest because of their importance for glenohumeral instability and adhesive capsulitis, there seems to be some confusion about their anatomy. This study reinvestigates the superior capsular structures in 110 cadaveric shoulders by a combination of arthroscopy, dissection, histology, and functional analysis. The structure of the superior capsule was found to be more complex than suspected until now. The coracohumeral, coracoglenoid, and superior glenohumeral ligaments joined with a circular transverse band to form the anterior limb of a suspension sling. This was 9 to 26 mm wide at its midportion. In 90% of the specimens, there also was a posterior limb composed of a broad fibrous sheet, 6 to 26 mm wide at its midportion. This hitherto unrecognized posterosuperior glenohumeral ligament joined posterolaterally with the circular transverse band. Four types of configuration for the superior complex could be identified. The suspension sling formed by the superior complex functions in the same way as the hammock formed by the inferior glenohumeral ligament complex. The posterior limb seems to restrict internal rotation, like the anterior limb restricts external rotation. The expanded knowledge of the superior capsular complex increases the understanding of the pathology involved in anterosuperior and posterosuperior impingement, as well as articular-sided rotator cuff tears. It also has clinical implications for rotator cuff interval and biceps pulley lesions, because these areas are bordered by the anterior limb of the superior complex, as well as for adhesive capsulitis, where we can now understand why internal rotation is limited and why the release needs to be extended posterosuperiorly.

Arthroscopic versus open rotator interval closure: biomechanical evaluation of stability and motion

PURPOSE

The purposes of this study were to investigate the differences between open and arthroscopic closure of the rotator interval (RI) on glenohumeral translation and range of motion. We also sought to determine if the addition of either an open or arthroscopic RI closure increases stability of the shoulder.

METHODS

Fourteen fresh-frozen (10 paired) cadaveric shoulder specimens were mounted in a custom testing apparatus, and glenohumeral translation and rotation were obtained by using an optoelectric tracking system (Optotrak Certus; Northern Digital, Ontario, Canada). Specimens were randomly allocated to either open (n = 7) or arthroscopic (n = 7) plication of the RI. The following were measured first with an intact and vented specimen and subsequently after an RI closure using either open or arthroscopic techniques: (1) range of motion in neutral and 90 degrees abduction; (2) anterior and posterior translation at neutral rotation; (3) anterior translation at 90 degrees abduction with external rotation; and (4) posterior translation at 90 degrees flexion with internal rotation.

RESULTS

Posterior stability was not improved from the intact state by either open (1.0-mm change) or arthroscopic (0.1-mm change) repair. The sulcus stability was improved in the open group (5.7 mm to 2.9 mm, P = .028), but not arthroscopically (5.1 to 4.1 mm, P = .499). Neutral anterior stability was improved after open repair (7.2 to 2.6 mm, P = .018), but not arthroscopically (2.3 to 2.4 mm, P = 0.5). However, anterior stability in external rotation (ER) at 90 degrees abduction was improved in the arthroscopic repair group (5.5 to 3.1 mm, P = .006). The mean loss of ER in neutral was greater in the open group (40.8 degrees) versus the arthroscopic group (24.4 degrees, P = .0038). The arthroscopic group showed an 11.7 degrees loss of ER in 90 degree abduction (P = .018) versus the open group loss of 4.8 degrees. There were no significant differences in loss of IR in either neutral or 90 degree abduction.

CONCLUSIONS

Posterior stability was not improved by either open or arthroscopic rotator interval repair, and sulcus stability only improved with the open technique. Anterior stability in neutral was improved after open repair and in the arthroscopic repair group with the arm abducted. There was a large loss of external rotation with both techniques.

CLINICAL RELEVANCE

This study suggests that arthroscopic RI closure adds little to the overall posterior and inferior stability of the shoulder joint, although anterior stability may be improved. There is a potentially large loss of external rotation after either repair method.

The rotator interval: anatomy, pathology, and strategies for treatment

Over the past two decades, it has become accepted that the rotator interval is a distinct anatomic entity that plays an important role in affecting the proper function of the glenohumeral joint. The rotator interval is an anatomic region in the anterosuperior aspect of the glenohumeral joint that represents a complex interaction of the fibers of the coracohumeral ligament, the superior glenohumeral ligament, the glenohumeral joint capsule, and the supraspinatus and subscapularis tendons. As basic science and clinical studies continue to elucidate the precise role of the rotator interval, understanding of and therapeutic interventions for rotator interval pathology also continue to evolve. Lesions of the rotator interval may result in glenohumeral joint contractures, shoulder instability, or in lesions to the long head of the biceps tendon. Long-term clinical trials may clarify the results of current surgical interventions and further enhance understanding of the rotator interval.

Structural and mechanical properties of the glenohumeral joint posterior capsule

The purpose of this study was to quantify regional variations in material properties of the glenohumeral joint posterior capsule and to compare these data with the anterior band of the inferior glenohumeral ligament (AB-IGHL). Mechanical properties were determined for individual bands of the AB-IGHL, superior posterior capsule (SUP-PC), middle posterior capsule (MID-PC), and inferior posterior capsule (INF-PC). Significant differences in tissue thickness were found among the 3 posterior capsular regions and the AB-IGHL. The AB-IGHL was thicker than the MID-PC (P=.03) and INF-PC (P=.01), and the SUP-PC was thicker than the INF-PC (P=.02). Except for significant differences in failure strains, material properties were not significantly different among the 4 tissue regions. There were no significant differences between tissue bands in modulus (P=.2), maximum stress (P=.46), or strain energy density (P=.62). Specimens failed primarily near the glenoid insertion (75%), with 4 specimens failing at the humeral insertion and 2 others failing in the tissue's mid substance.

MR arthrography of rotator interval, long head of the biceps brachii, and biceps pulley of the shoulder

The rotator interval and the long head of the biceps brachii tendon are anatomically closely associated structures believed to confer stability to the shoulder joint. Abnormalities of the rotator interval may be acquired or congenital and are associated with instability of the long head of the biceps brachii tendon. Clinical and arthroscopic diagnoses of rotator interval abnormalities and subtle instability patterns of the long head of the biceps brachii tendon are difficult. Magnetic resonance arthrography, owing to its superior depiction of ligaments with distention of the joint capsule, may be the procedure of choice, barring open surgery, for help in diagnosis of these conditions.

Pathomechanics of acquired shoulder instability: a basic science perspective

Normal asymptomatic glenohumeral motion is dependent on the coordinated function of dynamic and static stabilizers. Data from both selective sectioning studies of the capsuloligamentous components and tensile testing of the inferior glenohumeral ligament have provided important insights into the in situ function of these structures. However, little is known regarding the mechanism of microdamage accumulation in acquired shoulder instability. Recent findings suggest that cyclic subfailure loading of the inferior glenohumeral ligament may induce gradual stretching of the anteroinferior capsule, compromising its capacity to restrain excessive humeral translations. Further studies elucidating the mechanism of load transmission in the capsule during physiologic arm motion, as well as data on the intrinsic healing response of the capsular ligaments, are required to more fully characterize the pathoetiology of acquired shoulder instability.

Unusual attachment of the pectoralis minor muscle

The authors report a presumably unusual bony attachment of the pectoralis minor muscle in an adult cadaver. The specimen's left pectoralis minor had no attachment to the coracoid process of the scapula but attached directly to the fibrous capsule of the glenohumeral joint. Some have theorized that the coracohumeral ligament represents fibers of the pectoralis minor that attach to this bone in some animals but that has degenerated in man. This case report seems to support this possibility.

Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations

BACKGROUND

Surgical treatments of complete acromioclavicular joint dislocations replace or reconstruct the coracoclavicular ligaments with a single structure and do not account for the anatomical variance of each ligament in the design.

PURPOSE

To evaluate the cyclic behavior and structural properties of an anatomic tendon reconstruction of the coracoclavicular ligament complex after a simulated acromioclavicular joint dislocation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cyclic loading followed by a load-to-failure protocol (simulated dislocation) of the normal coracoclavicular ligament complex was performed and repeated after an anatomic reconstruction on the same specimen (n = 9). The anatomical reconstruction consisted of a semitendinosus tendon that replicated the direction and orientation of both the trapezoid and conoid ligaments.

RESULTS

The coracoclavicular ligament and anatomical reconstruction complexes had clinically insignificant (<3 mm) permanent elongation after cyclic loading. The stiffness and ultimate load of the coracoclavicular ligament complex (60.8 +/- 12.2 N/mm and 560 +/- 206 N) were significantly greater than for the anatomical reconstruction complex (23.4 +/- 5.2 N/mm and 406 +/- 60 N), respectively (P < .05). Further analysis of the complexes revealed a 40% decrease in the bending stiffness of the clavicle after the simulated dislocation and failure of the normal coracoclavicular ligament complex (P < .05), which contributed to the diminished properties of the anatomic reconstruction.

CONCLUSIONS

The low level of permanent elongation after cyclic loading suggests that the anatomic reconstruction complex could withstand early rehabilitation; however, the decrease in the structural properties and stiffness of the clavicle should be considered in optimizing the anatomic reconstruction technique.

CLINICAL RELEVANCE

Despite the differences compared to the normal coracoclavicular ligament complex, the anatomical reconstruction complex more closely approximates the stiffness of the coracoclavicular ligament complex than current surgical constructs, and the incorporation of biological tissue could improve the overall structural properties with healing.

Mechanical Properties of the Shoulder Ligaments under Dynamic Loading

Thirty-three fresh human cadaver shoulders were harvested and bone-ligament-bone specimens of acromioclavicular joint, coracoclavicular joint and sternoclavicular joint were obtained. A test fixture and clamps specifically designed for this ligament study and a high-speed Instron machine were used. One quasi-static rate (nominally 0.1 %/sec) and two high rates (nominally, high rate 1 = 40,000 %/sec and high rate 2 = 15,000 %/sec) were used in this study. In the acromioclavicular joint tests, ligament failure was the most common failure mode. Bone fractures occurred most often at the clavicle rather than acromion. In the coracoclavicular joint tests, the majority of specimens failed at the ligament and bone fractures occurred at the coracoid. In the sternoclavicular joint tests, the specimen failed at the bone in most cases. In the acromioclavicular joint and coracoclavicular joint tests, high rate 2 tests and quasi-static tests had more bone fracture cases than high rate 1 tests. Cross sectional area, deflection at failure, load at failure, strain at failure, stress at failure and Young's modulus of these three shoulder joints were found. The Young's modulus, ultimate stress and ultimate load of the three joints were found to be significantly lower in the quasi-static rate tests compared to the high rate 2 tests but not significantly different between high rate 1 and high rate 2 tests. There are no significant relationships between cross-sectional area and age, height or weight, nor between the mechanical properties of the shoulder joint and age, height or weight.

Viscoelastic behavior and structural properties of the coracoclavicular ligaments

During contact sports such as football, hockey or rugby, the coracoclavicular ligaments are commonly ruptured. Currently, the limited biomechanical data on the properties and function of these ligaments have led to debate on the "gold standard" treatment for these injuries. Therefore, the objective of this study was to characterize the geometry, viscoelastic behavior and structural properties of the coracoclavicular ligaments (n=11). The trapezoid and conoid were found to have similar length (9.6+/-4.4 vs. 11.2+/-4.1 mm) and cross-sectional area (103+/-43 vs. 69+/-51 mm2), respectively (P>0.05). Static and cyclic stress relaxation tests were then performed, followed by uniaxial tensile testing with the insertions of each ligament aligned to ensure a uniform distribution of load across the fibers. No significant differences were observed for the trapezoid and conoid during the static (36+/-8% vs. 31+/-7%) and cyclic (23+/-12% vs. 16+/-6%) stress relaxation tests, respectively (P>0.05). Similarly, no statistically significant differences were found between the trapezoid and conoid for linear stiffness (83+/-40 vs. 70+/-23 N mm(-1)), ultimate load (312+/-133 vs. 266+/- 108 N), energy absorbed at failure (820+/-576 vs. 752+/- 410 N mm), percent elongation (74+/-47% vs. 62+/-22%) and elongation at failure (5.8+/-2.2 vs. 6.1+/-1.6 mm), respectively (P>0.05). A comparison of our data to previous studies suggests that the complex fiber orientation of these ligaments has a significant role in determining the maximum load that can be transferred between the clavicle and scapula by each bone-ligament-bone complex. Our findings also further confirm the functional role of the coracoclavicular ligaments in supporting the upper extremity, and provide data for reconstruction and rehabilitation protocols as well as computational models.

Tensile properties of the porcine temporomandibular joint disc

Despite the significant morbidity associated with the temporomandibular joint (TMJ), little is known about the pathophysiology of this complex joint. TMJ disc degeneration plays a central role in the progression of TMJ disorders, and therefore disc regeneration would be a crucial treatment modality. Unfortunately, scarce information about the structural and functional characteristics of the TMJ disc is available. The current study aims to provide a standard for the biomechanical behavior of the TMJ disc for future tissue engineering studies. The disc was loaded under uniaxial tension in two directions, mediolateral and anteroposterior, and in three locations per direction. In the mediolateral direction, the posterior band was 2.5 times stiffer, 2.4 times tougher (energy to maximum stress), and 2.2 times stronger than the anterior band, which was in turn 16 times stiffer and 5.7 times stronger than the intermediate zone. In the anteroposterior direction, the central and medial regions were 74% and 35% stiffer and 56% and 59% stronger than the lateral region, respectively, although similar to each other in strength and stiffness. There was no significant difference in toughness between regions in the anteroposterior direction. These results correlated qualitatively with collagen fiber orientation and fiber size obtained using polarized light microscopy.