Apprehension Position Research Articles

Comment on the Classics

We examined the architectural properties of the rotator cuff muscles in 10 cadaveric specimens to understand their functional design. Based on our data and previously published joint angle-muscle excursion data, sarcomere length operating ranges were modeled through all permutations in 75 masculine medial and lateral rotation and 75 masculine abduction at the glenohumeral joint. Based on physiologic cross-sectional area, the subscapularis would have the greatest force-producing capacity, followed by the infraspinatus, supraspinatus, and teres minor. Based on fiber length, the supraspinatus would operate over the widest range of sarcomere lengths. The supraspinatus and infraspinatus had relatively long sarcomere lengths in the anatomic position, and were under relatively high passive tensions at rest, indicating they are responsible for glenohumeral resting stability. However, the subscapularis contributed passive tension at maximum abduction and lateral rotation, indicating it plays a critical role in glenohumeral stability in the position of apprehension. These data illustrate the exquisite coupling of muscle architecture and joint mechanics, which allows the rotator cuff to produce near maximal active tensions in the midrange and produce passive tensions in the various end-range positions. During surgery relatively small changes to rotator cuff muscle length may result in relatively large changes in shoulder function.

Innervation patterns of the inferior glenohumeral ligament: Anatomical and biomechanical relevance

Although the Inferior Glenohumeral Ligament (IGHL) has a well known mechanical and proprioceptive relevance in shoulder stability, the interrelation of the ligament's anatomical disposition/innervation has not actually been described previously. The purpose of the study was to determine the IGHL innervation patterns and relate them to dislocation. Forty-five embalmed and 16 fresh-frozen human cadaveric shoulders were studied. Masson's Trichrome staining detailed the intraligamentous nerve fiber arrangements. The effect on the articular nerves of an anteroinferior dislocation of the shoulder joint and the position of 60 degrees abduction and 45 degrees external rotation was studied dynamically. The axillary nerve provided IGHL innervation in 95.08% of the cases. We saw two distinct innervation patterns originating from the axillary nerve. In Type 1, one or two collaterals diverged later from the main trunk to enter the ligament. Type 2 showed innervation to the ligament provided by the posterior branch for three to four neural branches. In both cases, these branches enter the ligament near the glenoid rim and at the 7 o'clock position (right shoulder). The radial nerve (Type 3 innervation pattern) provided IGHL innervation in 3.28% of the cases. Microscopic analysis revealed wavy intraligamentous neural branches. The articular branches relaxed and separated from the capsule at the apprehension position and stayed intact after dislocation. These results showed a special predisposition to avoid possible denervation and suggested that the neural arch probably remains unaffected after most dislocations. Knowledge of the neural anatomy of the shoulder will clearly help in avoiding its injury in surgical procedures.

Significance of the latissimus dorsi for shoulder instability. II. Its influence on dislocation behavior in a sequential cutting protocol of the glenohumeral capsule

In a cadaveric instability model that leaves all muscles intact initially, the latissimus dorsi seemed to play a role when complete section of the glenohumeral capsuloligamentous structures did not result in a locked anteroinferior dislocation. The present study was carried out to determine whether the latissimus dorsi does truly affect dislocation in a modified cutting protocol, and to find an anatomic explanation for this apparent behavior. This article (Part II) details the results of a sequential cutting study and relates these results with the anatomic findings of Part I. In 75 shoulders, the influence of the latissimus dorsi on dislocation behavior in the apprehension position after section of all capsuloligamentous structures was examined. After cutting all capsuloligamentous structures, either on the glenoid or on the humeral side, the tendon of either the latissimus dorsi or the subscapularis was cut. Capsular lesions on the glenoid side (20 shoulders) resulted in a locked dislocation in 16 specimens. In the other four shoulders, there was a metastable dislocation after cutting the entire capsule, which did not change after cutting either tendon. With lesions on the humeral side (55 shoulders), three possibilities arose: metastable (17 shoulders), locked anterior (9 shoulders) or locked anteroinferior (29 shoulders) dislocation. This difference in dislocation behavior was related to the variability of the tendon-cartilage distance (TCD) and the type of scapular connection of the latissimus dorsi. A locked anteroinferior dislocation was always observed when the TCD was more than 20 mm, regardless of the type of scapular connection. With a TCD < 20 mm, a metastable dislocation was the result when there was a type 1 scapular connection and a locked anterior dislocation was seen when there was a type 2 scapular connection. The tendon of the latissimus dorsi can restrain the humeral head from dropping inferiorly or can lead to a spontaneous reduction of a dislocation, depending on its anatomy. This effect can only take place in the infrequent situation of humeral avulsion of the glenohumeral ligaments. This may be an explanation for the relative paucity of these lesions in clinical instability series.

Active stability of the glenohumeral joint decreases in the apprehension position

Background. Muscle forces that compress the glenohumeral joint during mid-ranges of motion may lead to increased translational forces in end-range positions, such as the apprehension position, where symptoms of anterior instability occur. Objective. The objective of this study was to quantify active stability provided by eight shoulder muscles in mid-range and end-range positions through muscle force vector analysis. Methods. Lines of action were derived from a geometric model and muscle force magnitudes were estimated with electromyography-based techniques. Resultant muscle force vectors were calculated by summing individual muscle force vectors. Results. Compared to mid-range positions, lines of action of resultant force vectors were more anteriorly directed in end-range positions compared to 15° of abduction, up to 26°. Consequently, anterior stability was lowest in the apprehension position. The magnitudes of the resultant force vectors were comparable to other studies. Based on a sensitivity analysis, lines of action of resultant force vectors vary up to 6° within the population. Conclusions. Data obtained from this model will improve conservative management, post-surgical rehabilitation, and strength training protocols. Relevance. In the apprehension position, muscle forces may promote anterior humeral head translation, predisposing the glenohumeral joint to anterior instability when other stabilizing mechanisms such as the glenohumeral capsule are not functioning normally.

Shoulder Muscle Reflex Latencies Under Various Levels of Muscle Contraction

Previous research in relaxed muscles shows that muscle reflex latencies are too slow to protect the shoulder. However, during athletic activity when injury occurs, some level of shoulder muscle contraction typically exists. The purpose of the current study was to assess shoulder muscle reflex latencies under various levels of muscle contraction. Seventeen healthy subjects participated. A perturbation consisting of an external rotation collision force to the anterior forearm in a position of apprehension under various levels of muscle contraction (0%, 20%, and 50% of a maximum voluntary muscle contraction) was applied. Muscle reflex latencies were measured as the time from perturbation application to onset of muscle activity. Electromyography measured activity onset of the rotator cuff muscles and the primary humeral movers. During 0%, the latissimus dorsi muscle reflex latency was significantly slower than most other muscles. No difference existed between muscles in the 20% and 50% conditions. For the rotator cuff muscles, the reflex latencies significantly quickened for 20% and 50% compared with the relaxed state (0%). Overall, introducing muscle contraction significantly quickened muscle reflex latencies. These results provide clinicians with a better understanding of the role that these reflexes play in joint stability in a position of injury vulnerability like a position of apprehension.

A novel cadaveric model for anterior-inferior shoulder dislocation using forcible apprehension positioning.

A novel cadaveric model for anterior-inferior shoulder dislocation using forcible apprehension positioning is presented. This model simulates an in vivo mechanism and yields capsulolabral lesions. The scapulae of 14 cadaveric entire upper limbs (82 +/- 9 years, mean +/- standard deviation) were each rigidly fixed to a custom shoulder-testing device. A pneumatic system was used with pulleys and cables to simulate the rotator cuff and the deltoid muscles (anterior and middle portions). The glenohumeral joint was then positioned in the apprehension position of abduction, external rotation, and horizontal abduction. A 6-degree-of-freedom load cell (Assurance Technologies, Garner, North Carolina) measured the joint reaction force that was then resolved into three orthogonal components of compression force, anteriorly directed force, and superiorly directed force. With the use of a thrust bearing, the humerus was moved along a rail with a servomotor-controlled system at 50 mm/s that resulted in horizontal abduction. Force that developed passively in the pectoralis major muscle was recorded with an independent uniaxial load cell. Each of the glenohumeral joints dislocated anterior-inferior, six with avulsion of the capsulolabrum from the anterior-inferior glenoid bone and eight with capsulolabral stretching. Pectoralis major muscle force as well as the joint reaction force increased with horizontal abduction until dislocation. At dislocation, the magnitude of the pectoralis major muscle force, 609.6 N +/- 65.2 N was similar to the compression force, 569.6 N +/- 37.8 N. A cadaveric model yielded an anterior dislocation with a mechanism of forcible apprehension positioning when the appropriate shoulder muscles were simulated and a passive pectoralis major muscle was included. Capsulolabral lesions resulted, similar to those observed in vivo.

Variation in the glenoid origin of the anteroinferior glenohumeral capsulolabrum.

Restoration of the anteroinferior capsulolabrum, including the labrum and origin of the anterior band of the inferior glenohumeral ligament is crucial during Bankart repair. The purpose of the current study was to describe variations in this anatomy near the glenoid. The histologic and gross anatomy were studied in 10 fresh-frozen glenohumeral joints from adult cadavers. Each joint was placed in the apprehension position of abduction, external rotation, and horizontal abduction because anterior dislocation occurs in this shoulder position. The joints then were sectioned serially in the transverse plane from cephalad to caudad. Three glenohumeral joints were embedded in Techovit 7200 resin, polymerized, and then mounted onto an acrylic slide. Ground sections were prepared by attaching a microscope slide to the face of each and cutting 200 microm-thick sections. The thin sections were ground to a thickness of 30 microm. Finally, sections were stained with 1% toluidine blue zero in 1% sodium tetraborate for light microscopic examination. The other seven glenohumeral joints were frozen in the apprehension position and held with a custom jig while sectioned serially at 3-mm intervals. The surfaces then were recorded with a tabletop computer and a scanning device. Two distinct patterns of the anteroinferior capsulolabrum attachment to the glenoid were identified. In eight joints (80%) it had its major origin from the labrum with some fibers extending onto the glenoid neck, a Type I origin. In two joints (20%), it emanated solely from the glenoid neck, a Type II origin. Failure to repair the glenoid origin of the anteroinferior capsulolabrum, the location of the anterior band of the inferior glenohumeral ligament, because of variations in its anatomy may be a reason for failure after Bankart repair.

Effects of simulated scapular protraction on anterior glenohumeral stability.

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

Age related biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex

Objective. To quantify the biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex for the two age groups. Design. In vitro human cadaver study evaluating the biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex for a younger group ( n=5, mean age 38.5, SD 0.5 years) and an older group ( n=7, mean age 74.8, SD 5.3 years). Background. Glenohumeral instability is more of a problem in younger than in older individuals, primarily because recurrence is much more common at a young age. Methods. Tensile testing was performed on the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex in the shoulder apprehension position using a custom jig, Instron machine and a video digitizing system. Results. In the younger individuals disruption of the complex most often occurred at the glenoid–labrum region of the glenoid insertion site. In the older individual, disruption most often occurred at the midsubstance region. The load and the stress at failure of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex showed that the older group was only 61% and 46% of the younger group, respectively. Conclusions. The structural properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex and the material characteristics of the anterior band of the inferior glenohumeral ligament for the younger group were significantly superior than the older group. Relevance A stronger and more extensive repair, such as the traditional open technique, may be necessary for younger individuals with glenohumeral instability whereas in older individuals, a different repair technique, such as an arthroscopic technique, may be sufficient.

The anterior band of the inferior glenohumeral ligament. Assessment of its permanent deformation and the anatomy of its glenoid attachment.

Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 +/- 1.3 MPa and stress at failure, 9.2 +/- 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 +/- 0.8 mm. The strain at yield was 13.0 +/- 0.7% and at failure, 15.4 +/- 1.2%; therefore permanent strain was only 2.4 +/- 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.

The anterior band of the inferior glenohumeral ligament

Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 ± 1.3 MPa and stress at failure, 9.2 ± 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 ± 0.8 mm. The strain at yield was 13.0 ± 0.7% and at failure, 15.4 ± 1.2%; therefore permanent strain was only 2.4 ± 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.

Humeroscapular positions in a shoulder range-of-motion-examination

Positions of the arm are traditionally described in relation to the thorax. Yet shoulder pathology most often lies in and about the glenohumeral joint, which then becomes the focus of treatment. Little is known about the relative motion between the humerus and the scapula primarily because there is no clinically accepted method for assessing and describing these positions. This paper proposes a clinical method for describing and measuring humeroscapular positions based on an anatomic definition of the plane of the scapula. Humeroscapular positions achieved by 75 normal subiects during a conventional (humerothoracic) shoulder range-of-motion examination are presented. Identification of the plane of the scapula is based on four palpable anatomic landmarks: (7) the inferior pole of the scapula, (2) the medial border of the scapula at the level of the scapular spine, (3) the posterolateral corner of the acromion, and (4) the tip of the coracoid. The plane of the scapula is defined by the line connecting the first two of these points and a point midway between the last two. Humeroscapular positions are specified by the plane of elevation and the angle of elevation in relation to this mobile scapular plane. Measurement of these positions was done with a goniometer facilitated by a "scapula-locating device" designed for this study. Maximal humerothoracic elevation of the arm was achieved with the humerus lust behind the scapular plane at 90° of humeroscapular elevation. Cross-body adduction positioned the humerus in a plane 51° anterior to the plane of the scapula, with most of the cross-body motion occurring between the scapula and thorax. External rotation at 90° of elevation in the coronal plane of the body (the apprehension position) positioned the humerus in a plane 17° posterior to the scapular plane. Humerothoracic extension and reaching up the back took place at very low angles of humeroscapular elevation.

Thoughts on orthodontic teaching with practical results

T H E invitation to give a paper before this Society finds me in a position of apprehension. The difficulty is the choice of a subject. To choose anyone special part of the great specialty of orthodontia and present anything new, may only involve us in a debate, which will have no definite result, and the value be lost in side issues which bulk so largely in any discussion. Experience of twenty years of orthodontic study and practice and some ten years of active and definite teaching has led me to some conclusions which I venture to put before you this evening, in the hope that something may result which will afford us an interest which is at the moment lacking. I do not propose to enter into any questions tonight of treatment, diagnosis or apparatus, but to generalize on the question of orthodontia and the attitude the profession takes in regard to its practice. Is it one of silent' contempt due to many causes ~ Or, is the lack of interest due to the great amount of work which awaits us and prevents research in this and so many branches of our specialty ~ May I digress for a moment and ask your permission to state briefly the position of orthodontia in this country ~ This Society was formed by a few enthusiasts to study orthodontia as a live science, and one may assume thereby to be helpful to the profession and through it to the nation. After years, what is the result-a very small Society doing a useful work in a very limited sphere-its meetings largely confined to individual criticism and ideas of treatment-no enlarged view of the usefulness of work that may be done and should be encouraged-and in consequence still an indefinite idea in the mind of the average general practitioner that orthodontia is anything more than a fad and only for the specialist, and cannot be undertaken save at great personal worry and disappointment. With this attitude I entirely agree and for this reason that no endeavor has been made by individual or school to educate and instruct the profession or public in the value of skilled treatment. It must be remembered that the bulk of practitioners do not read any great amount of current dental literature. A difficulty to combat is the lack of appreciation of the principles involved in the discussion of any point (apart from the obviously simple), which is so entirely essential in the study and practice of orthodontia, and with all respect to some, treatment so often follows a line of compromise that the underlying principles probably get lost in the transaction. Too often difficulties are foreseen which never arise, likewise too, cases are regarded as quite