Effect of joint compression on inferior stability of the glenohumeral joint

To determine the relative importance of negative intraarticular pressure, capsular tension, and joint compression on inferior stability of the glenohumeral joint we studied 17 fresh, normal adult cadaver shoulders using a "3 degrees of freedom" shoulder test apparatus. Translations were measured in intact and vented shoulders while a 50-N superior and inferior directed force was applied to the shoulder. Three different joint compressive loads (22 N, 111 N, 222 N) were applied externally. Tests were performed in 3 positions of humeral abduction in the scapular plane (0 degree, 45 degrees, 90 degrees) and in 3 positions of rotation (neutral, maximal internal, and maximal external). After tests of the intact and vented shoulder, the glenohumeral ligaments were sectioned and tests were repeated. With minimal joint compression of 22 N, negative intraarticular pressure and capsular tension limited translation of the humeral head on the glenoid. Increasing the joint compressive load to 111 N resulted in a reduction of mean inferior translation from 11.0 mm to 2.0 mm at 0 degree abduction, from 21.5 mm to 1.4 mm at 45 degrees abduction, and from 4.5 mm to 1.2 mm at 90 degrees abduction. With a compressive load of 111 N, venting the capsule or sectioning of glenohumeral ligaments had no effect on inferior stability. Clinical relevance: Glenohumeral joint compression through muscle contraction provides stability against inferior translation of the humeral head, and this effect is more important than negative intraarticular pressure or ligament tension.     

Superoinferior translation in the intact and vented glenohumeral joint

The purpose of this investigation was to measure inferior translation in the intact and vented shoulder in different positions of abduction and rotation. Fifteen shoulders from adult cadavers were tested before and after venting of the joint capsule on an apparatus that permitted unconstrained translation when a 50 N inferior force was applied to the humeral shaft. The greatest inferior translation in the intact shoulder occurred at 45° abduction in neutral rotation. Venting the capsule significantly increased inferior translation in all positions but 45° abduction, and the greatest effect was seen at 0° glenohumeral abduction in neutral rotation. The so-called "sulcus sign" is the result of intraarficular vacuum effect and capsular laxity. Venting the capsule results in a significant increase in inferior translation. This is an important effect to consider during procedures for repairing instability of the shoulder, because failure to appreciate the normal "play" in inferior glenohumeral translation might lead the surgeon to believe that perceived laxity represents actual instability.     

Determination of in vivo glenohumeral translation using fluoroscopy and shape-matching techniques

The purpose of this study was to investigate glenohumeral translation in-vivo during active shoulder abduction in the scapular plane. Three-dimensional (3D) models of 9 shoulders were created from CT scans. Fluoroscopic views aligned to the plane of the scapula were recorded during active arm abduction with neutral rotation. 3D motions were determined using model-based 3D-to-two-dimensional (2D) registration. Humeral translation was referenced to the glenoid center in the superior/inferior direction. The humerus moved an average of 1.7 mm superior with arm abduction, from an inferior location to the glenoid center. The humeral head was centered within 1 mm from the glenoid center above 80 degrees abduction. Variability in glenohumeral translation between shoulders decreased significantly from initial to final arm abduction. Our findings agree with some authors' observations of inferior-to-central translation of the humerus and behavior as a congruent ball and socket. We believe this information will help improve the understanding of shoulder function.     

Dynamic capsuloligamentous anatomy of the glenohumeral joint

Though many anatomic and biomechanical studies have been performed to elucidate capsuloligamentous anatomy of the glenohumeral joint, no previous studies have evaluated capsuloligamentous anatomy during rotator cuff contraction. The purpose of this study was to define and document the orientation and interrelationship between the glenohumeral ligaments during simulated rotator cuff contraction. Six fresh cadaveric shoulders were arthroscoped to document and grade ligamentous anatomy. The superior and middle glenohumeral ligaments and the anterior and posterior bands of the inferior glenohumeral ligament complex were labeled by an arthroscopicassisted technique with a linked metallic bead system. Shoulders were then placed onto an experimental apparatus that simulated rotator cuff function through computer-controlled servo-hydrolic actuators attached to the rotator cuff and biceps by a clamp and cable-and-pulley system. Simulated rotator cuff action and manual placement allowed shoulders to be placed into three positions of rotation (neutral, internal, and external) in three positions of scapular plane abduction (0°, 45°, 90°). Anteroposterior and axillary lateral plane radiographs were taken in each position to document orientation of all four ligaments. Both the superior and middle glenohumeral ligaments were maximally lengthened in 0° and 45° abduction and external rotation and appeared to shorten in all positions of abduction. The anterior and posterior bands of the inferior glenohumeral ligament complex maintained a cruciate orientation in all positions of abduction in the anteroposterior plane, except at 90° abduction and external rotation, where they are parallel. This cruciate orientation is due to the different location of the glenoid origin and humeral insertion of each band and may allow reciprocal tightening of each during rotation. The glenohumeral capsule is composed of discreet ligaments that undergo large charges in orientation during rotation. The superior and middle glenohumeral ligaments appear to complement the inferior glenohumeral ligaments, with the former tightening in adduction and the latter tightening in abduction. This relationship permits the large range of motion normally seen in the glenohumeral joint.     

Normal and abnormal motion of the shoulder.

The roentgenographic parameters of motion in normal and abnormal shoulders, including the movement of the scapula, arm angle, glenohumeral angle, scapulothoracic angle, excursion of the humeral head, and instant center of motion for abduction in the plane of the scapula, were determined in twelve normal subjects and fifteen patients. The scapula rotated externally with abduction. The ratio of glenohumeral to scapulothoracic movement was 5:4 after about 30 degrees of abduction. The center of rotation of the glenohumeral joint for abduction in the plane of the scapula was located within six millimeters of the geometric center of the humeral ball. The average excursion of the humeral ball on the face of the glenoid in the superoinferior plane between each 30-degree arc of motion was less than 1.5 millimeters in normal subjects. Significant previous injury resulting in abnormal mechanics of the shoulder joint was associated with abnormal values for excursion of the instant center and of the humeral head. An abnormal glenohumeral-to-scapulothoracic ratio was associated with significant pain in the shoulder. The fact that these various parameters were sensitive indicators of normal and abnormal motion raises the possibility of diagnostic clinical application.     

骨性缺损对肩关节稳定性影响的研究

目的探讨肩关节骨性缺损对关节稳定性的影响,为临床提供理论依据。方法分别制作肩胛盂及肱骨头缺损模型并逐渐增加缺损程度;以盂肱关节旋转中立位、60°外展位为起始位置,逐渐增加外旋角度至盂肱关节脱位,测量脱位发生前肱骨头前移距离;保持盂肱关节外展60°,分别在旋转中立位及外旋60°位时增加轴向应力,直至盂肱关节脱位,测量脱位前肱骨头的应力强度变化。结果随着肩胛盂及肱骨头缺损程度增加,外旋角度增加,肩关节稳定性下降,肱骨头位移不断增大,各组间呈显著性差异(P<0.01);盂肱关节外展60°、旋转中立位时,肱骨头应力强度随着骨缺损增大而不断增大,正常应力强度从1.68 Mpa迅速增加至4.62 Mpa,各组间呈显著性差异(P<0.01);盂肱关节外展60°、外旋60°时,正常应力强度为1.94 Mpa,骨缺损时迅速增加至6.65 Mpa,各组间呈显著性差异(P<0.01);肩关节不同缺损时,其接触力学特性证实了对肩关节稳定性有较大的影响,肩关节不稳定现象十分突出。结论随着肩胛盂及肱骨头缺损范围的增大,肩关节稳定性不断下降,肱骨头位移和应力强度不断增加,以致发生提前脱位。     

A three-dimensional scapular motion analysis in patients with arthroscopic anterior capsulolabral repair of the shoulder: The effect of scapular stabilization taping

BackgroundThe aim of this study was to investigate the scapular kinematics during dynamic humeral movements in patients with arthroscopic anterior capsulolabral repair of the shoulder along with the potential biomechanical corrective effects of scapular stabilization taping.MethodsTwenty patients with unilateral traumatic anterior shoulder instability and arthroscopic anterior capsulolabral repair participated in the study. Dynamic shoulder kinematics were assessed during the scapular plane shoulder elevation for both the operated and non operated shoulders and also under two conditions: no-taping and taping. Statistical analysis to compare sides and conditions was performed with analysis of variance models.ResultsThe scapula was more internally rotated position in operated shoulders than in non operated shoulders. Furthermore, the scapula was less internally rotated and more downwardly rotated at 120° of elevation in the taping condition.ConclusionsOperated shoulders demonstrated kinematics alterations when compared to non operated shoulders underwent arthroscopic anterior capsulolabral repair. Additionally, changes in the scapular orientation with the taping was very small but followed a pattern, which would be suggested to be an orientation that potentially produce more scapular stability and to increase stress on the inferior glenohumeral ligament.     

Pathomechanics in atraumatic shoulder instability: scapular positioning correlates with humeral head centering

The objective was to analyze three-dimensional scapular positioning and glenohumeral centering of normal and atraumatic unstable shoulders. We hypothesized that changes of humeral head position correlate with alterations of scapular positioning. The shoulders of 28 healthy volunteers and 14 patients with atraumatic instability were examined in various arm positions using open magnetic resonance imaging. After segmentation and three-dimensional reconstruction, three-dimensional analyses of scapular positioning and humeral head position relative to the glenoid were done. The coefficient of correlation (r) between both parameters was determined using the correlation z test. The glenohumeral to scapulothoracic ratio in the scapular plane was increased in nine of 14 patients and decreased in three patients, whereas the scapular internal rotation in the transverse plane was increased in all unstable shoulders. The unstable shoulders also had malcentering (greater than two times the standard deviation in the healthy volunteers) of the humeral head in the direction of instability during various arm positions. In healthy and unstable shoulders, the correlation between scapular position and glenohumeral positioning was high during passive elevation (r = 0.60-0.87). The high correlation suggests that scapular positioning is relevant for humeral head decentering. Therefore, physiotherapeutic strategy should consider the malpositioning of the scapula and be adapted to the direction of instability.     

Neer Award 2006: Biomechanical assessment of inferior tuberosity placement during hemiarthroplasty for four-part proximal humeral fractures

Tuberosity malpositioning commonly occurs and is associated with a decline in clinical function after prosthetic shoulder reconstruction for proximal humeral fractures. This study assesses the biomechanical effects of inferior tuberosity position on glenohumeral joint forces and humeral head position at multiple positions. Eight fresh-frozen cadaveric shoulders were tested. Hemiarthroplasty was performed with preservation of anatomic tuberosity height and with 10 mm and 20 mm of inferior tuberosity displacement. The rotator cuff, deltoid, pectoralis major, and latissimus dorsi muscles were statically loaded. Contact forces and humeral head position were recorded within a functional range of motion. Glenohumeral joint forces shifted significantly superiorly (P < .05) at 30 degrees of abduction after both 10 mm and 20 mm of tuberosity displacement. At 60 degrees of glenohumeral abduction, glenohumeral joint forces remained significantly altered after tuberosity displacement of 10 mm and 20 mm compared with the intact height (P < .005). This study demonstrates that, during hemiarthroplasty performed for proximal humeral fractures, malpositioning the tuberosities inferiorly results in significant superior glenohumeral joint force displacement. These findings suggest that the mechanical advantage of the shoulder abductor muscles is compromised with inferior tuberosity malpositioning and may help to explain inferior functional results seen in these patients.     

Consequences of a Perthes-Bankart lesion in twenty cadaver shoulders

This study investigated whether an anteroinferior capsulolabral lesion is sufficient to allow the humeral head to dislocate and whether a limited inferior approach for creating the lesions influenced the results compared with an all-arthroscopic approach. Four ligamentous zones of the glenohumeral capsule were sequentially detached from the glenoid neck and labrum in 20 cadaver shoulders through an inferior approach. Before and after each resection step, inferior stability was tested using a sulcus test and anterior stability using a drawer test and an apprehension maneuver. Dislocation was only possible when at least 3 zones were cut. This study confirmed that superior and posterior extension of the classic anteroinferior Perthes-Bankart lesion is necessary before the capsular restraint in external rotation and abduction is overcome and dislocation occurs. Lesions other than the Perthes-Bankart need to be investigated when recurrent dislocation is treated, because this anteroinferior injury is most probably not the sole factor responsible for the instability.     

Effect of rotator interval closure on glenohumeral stability and motion: a cadaveric study

The effect of rotator interval closure, which is performed as an adjunct to arthroscopic stabilization of the shoulder, has not been clarified. Fourteen fresh-frozen cadaveric shoulders were used. The position of the humeral head was measured using an electromagnetic tracking device with the capsule intact, sectioned, and imbricated between the superior glenohumeral ligament and the subscapularis tendon (SGHL/SSC closure) or between the superior and middle glenohumeral ligaments (SGHL/MGHL closure). The direction of translational loads (10, 20, and 30 N) and arm positions were (1) anterior, posterior, and inferior loads in adduction; (2) anterior load in abduction/external rotation in the scapular plane; and (3) anterior load in abduction/external rotation in the coronal plane. The range of motion was measured using a goniometer under a constant force. Both methods reduced anterior translation in adduction. Only SGHL/MGHL closure reduced anterior translation in abduction/external rotation in the scapular plane and posterior translation in adduction. Both methods reduced the range of external rotation and horizontal abduction. Rotator interval closure is expected to reduce remnant anterior/posterior instability and thereby improve the clinical outcomes of arthroscopic stabilization procedures.     

Modifizierte Technik der Verpflanzung des Musculus trapezius zur Funktionsverbesserung bei Armplexusschäden

OBJECTIVE: Increase of shoulder stability. Elimination of inferior subluxation of the humeral head. Increase of active abduction. Better control of the paralyzed arm. Decrease or elimination of shoulder pain. INDICATIONS: Palsy of deltoid and supraspinatus muscles with weak abduction, multidirectional shoulder instability and subluxation of the humeral head after complete neurosurgical therapy (neurolysis, reconstruction of the brachial plexus). No essential active function of the elbow and hand. CONTRAINDICATIONS: Weakness of trapezius muscle. Incomplete rehabilitation after neurosurgical procedure. Stiffness of the glenohumeral joint. Arthritis of the glenohumeral joint. SURGICAL TECHNIQUE: The cranial part of the trapezius muscle is detached from the scapular spine and the clavicle. Its insertion at the acromion is left untouched. The acromion is freed from the scapular spine and the lateral end of the clavicle by oblique osteotomies and then transferred to the proximal humerus. Under maximum tension the deltoid muscle is sutured on top of the trapezius muscle. POSTOPERATIVE MANAGEMENT: Immobilization of the arm in an abduction support (75 degrees of abduction) for 6 weeks. The physiotherapy program starts on the 1st postoperative day with assisted and active training of elbow, hand, and fingers. During the 1st postoperative week, the abduction support is removed for physiotherapy, abduction is maintained during the exercises. After 6 weeks, progressive adduction to remove the abduction support is commenced. RESULTS: The procedure was performed in 104 cases. 80 patients were followed up on average after 2.4 years (0.8-8 years). In all cases, the transfer resulted in an increase of function and in 95% in a decrease of multidirectional shoulder instability. The modification of the original technique in the latest 22 cases was superior in terms of shoulder stability. In all these cases, a decrease of instability was achieved and inferior subluxation was abolished.     

Bilateral irreducible inferior shoulder dislocation: A case report

IntroductionBilateral inferior shoulder dislocation is rare; but the dislocation is almost always reducible by closed means. We present a unique case of irreducible bilateral inferior shoulder dislocation.Presentation of caseA 35-year old male fell down from height. Direct axial loading while both shoulders were fully abducted resulted in bilateral inferior shoulder dislocation. All attempts of closed reduction failed. Open reduction revealed that the cause of irreducibility was the entrapment of the humeral head in a button-hole through the inferior joint capsule and the surrounding soft tissue envelope. At 6 months, there was almost full range of motion and no pain.DiscussionThe direct axial loading resulted in a narrow defect in the inferior joint capsule/soft tissue envelope; and this may have led to button-hole entrapment of the dislocated humeral head and irreducibility. Open reduction required widening of the button-hole while protecting the axillary neurovascular bundle.ConclusionWe present a rare case of bilateral irreducible inferior shoulder dislocation. We highlight the pathomechanics of irreducibility: button-hole entrapment of the humeral head. We emphasize technical tips during open reduction such as widening of the button-hole and protection of the axillary neurovascular bundle. The outcome is good although some limitation of shoulder abduction is to be expected.     

Static stabilizers of the shoulder joint

Anatomic dissection of 220 cadaver shoulders was performed to find out more about the static stabilizers of the shoulder joint. The static stabilizers, i.e. the glenohumeral ligaments, were always found to be present and strong in healthy shoulders. It was revealed that in anatomic preparations with all the organs removal except the synovial capsule, the capsule ligaments completely stabilized the joint. Anterior dislocation at 45 degrees of abduction was prevented by the superior and medial glenohumeral ligaments, while at 90 degrees of abduction the inferior glenohumeral ligament prevented dislocation. When anterior dislocation has occurred even the coracohumeral ligament must be ruptured. A new finding recorded is that the glenoid labrum is the origin of the inferior glenohumeral ligament and not a triangular static organ enlarging the socket and having a similar function to the menisci in the knee. This ligament is the most important ventral stabilizer of the humeral joint. With the conventional arthrotomy technique the medial and inferior ligaments are immediately cut through and therefore cannot be seen. The inferior glenohumeral ligament must be reconstructed in cases of anterior recurrent dislocation.     

Shoulder capsule shrinkage and consequences on shoulder movements

A study was designed to find landmarks to avoid restriction of range of motion or insufficient shortening of the ligaments after thermal shoulder capsule shrinkage. In 15 nonembalmed shoulders from cadavers, shrinkage was done in three steps: (1). the middle glenohumeral ligament, (2). the anterior part of the inferior glenohumeral ligament, and (3). the posterior part of the glenohumeral ligament. Before and after each step passive range of motion of the glenohumeral joint was studied. Results indicated that flexion and the external rotation were not affected. External rotation in the scapular plane with 45 degree elevation diminished after shrinkage of the middle glenohumeral ligament. External rotation in full abduction diminished after shrinkage of the anterior part of the inferior glenohumeral ligament. Abduction diminished after shrinkage of the anterior and posterior parts of the inferior glenohumeral ligament. Internal rotation in full abduction was restricted after shrinkage of the posterior part of the inferior glenohumeral ligament. These results show a constant relation between the reduction of a given movement and the shrunken area, by providing useful landmarks to reduce the passive hyperabduction that is constant in anterior shoulder instability and to control the immediate effects on the other ranges of motion. To control the immediate consequences of shrinkage may help avoid excessive restriction of motion or insufficient reduction of capsular redundancy.     

The effect of capsular venting on glenohumeral laxity

Anesthetized shoulders are frequently stable against forces applied during drawer and sulcus tests, even though the shoulder muscles are inactive and do not contribute to stability. This passive stability is also evident in the glenohumeral joints of anatomic specimens. The translational laxity of anatomic specimen shoulders was measured, and it was demonstrated that this laxity was substantially increased when air was admitted into the capsule. Eight shoulders, aged 57-87 years, including six contralateral pairs, were analyzed using a six degrees-of-freedom force transducer and a six degrees-of-freedom spatial tracker. Capsules were vented by admitting air ad libitum through an 18-gauge needle. Venting reduced the force necessary to translate the humeral head with respect to the glenoid fossa by an average of 15.3 N (55%) for anterior forces, 10.8 N (43%) for posterior forces, and 19.0 N (57%) for inferior forces. It is likely that passive stability will also be diminished by a similar mechanism in patients with intact but excessively lax capsules. The principle of limited joint volume should be considered and tested when investigating glenohumeral stability.     

Prosthetic replacement in rotator cuff-deficient shoulders

We reviewed a series of 30 shoulders in 25 patients who had glenohumeral arthritis and rotator cuff deficiency and who underwent prosthetic replacement. Nineteen shoulders underwent humeral head replacement, and 11 shoulders had total shoulder arthroplasty. Meticulous mobilization and reconstruction of the deficiencies in the thin atrophic rotator cuff tissues were attempted in all shoulders. Emphasis was placed on anteroposterior stability, and this was achieved in all shoulders; superior coverage was fully achieved in 15 shoulders and was partially achieved in 11. All shoulders had less pain after surgery, and 93% achieved satisfactory pain relief. Total shoulder arthroplasty and humeral hemiarthroplasty were found to provide similar results with respect to pain relief, functional improvement, and patient satisfaction. Shoulders with hemiarthroplasty gained significantly more active elevation (+52° vs + 2°) after surgery. Cuff repair was easier when a humeral head prosthesis alone was used because less lateralization of the humerus occurred. Also, operative time, anesthesia time, and blood loss were decreased with hemiarthroplasty. Because the lack of glenoid resurfacing did not adversely affect pain relief or function and avoided the potential problem of glenoid loosening, we favor humeral hemiarthroplasty as a treatment for glenohumeral arthritis in the rotator cuff-deficient shoulder.     

The influence of handheld weight on the scapulohumeral rhythm

Scapulohumeral rhythm (SHR) provides insight to neuromuscular control and fundamental biomechanics of the shoulder. This rhythm often is disrupted in pathologic shoulders. As the first step, we sought to quantify SHR in healthy subjects for diagnostic assessment of shoulder function. Ten healthy shoulders were studied. Three-dimensional models of the humerus and scapula were created from computed tomography scans. Dynamic shoulder motion was recorded by use of single-plane fluoroscopy during arm abduction with 0-kg and 3-kg handheld loads. Shoulder kinematics were quantified by use of model-based 3-dimensional-to-2-dimensional registration techniques. SHR decreased (more scapular motion) with increasing abduction. With a 3-kg load, scapulothoracic motion was significantly reduced through the range of 35 degrees to 45 degrees of glenohumeral motion. Muscular stabilization of the scapula increased with external loading, as shown by decreased SHR during early lifting. Dynamic scapular stabilization provides a critical platform for upper extremity activity.     

MRI-based 3-D analysis of the glenohumeral translation in patients with shoulder instability

AIM: Until now, pathological translation of the glenohumeral joint could not be assessed three-dimensionally and in functionally important arm positions in the living. The objektive of this study was therefore to develop an MR-based technique for determining the three-dimensional glenohumeral translation in functionally relevant positions in vivo. METHOD: In an open MR scanner both shoulder joints of 5 volunteers with an unilateral traumatic instability were examined in different positions of abduction and rotation. After semiautomatic segmentation, 3D reconstruction of the bony structures of the shoulder girdle was performed and the center of mass of the glenoid cavity was determined and used as reference point. In a virtual reality, the midpoint of the humeral head was assessed and its position relative to the center of mass of the glenoid cavity was calculated. RESULTS: At 30 degrees of abduction, in both shoulders, the humeral head was positioned inferior and posterior relative to the glenoid cavity (healthy: 0.42 +/- 1.1 inf., 0.75 +/- 1.0 mm post.; unstable: 1.31 +/- 0.87 mm inf., 0.51 +/- 1.28 mm post.) The maximal translation (to anterior and inferior) was observed both on the healthy side (mean 1.0 mm, max. 1.8 mm) and in the unstable shoulders (mean 2.5 mm, max. 4.6 mm) with the arm in 90 degrees of abduction and external rotation, thus being 1.7 to 2.5 times higher in the pathological shoulders. CONCLUSIONS: With this technique the glenohumeral translation can be quantified three-dimensionally in functionally important positions and without projectional artefacts. In the future, this method can be applied to patients with different entities of shoulder instability.     

Glenohumeral movement patterns after puncture of the joint capsule: An experimental study

In on experimental series comprising 22 shoulder specimens obtained at autopsy, we investigated the influence of an intact capsule on glenohumeral stability. Puncture of the capsule resulted in significant glenohumeral translation in unloaded and loaded specimens during shoulder abduction. A maximum of 16.6 mm of distal translation was observed at 20° of abduction. Concomitant with this translation the humerus spontaneously rotated externally, with a maximum rotation of 15.8° at 50° of abduction. After venting the capsule, anterior and posterior translation and external rotation were increased significantly. Maximum total increase in anteroposterior translation was 14 mm at 30° of abduction. The external rotation was increased up to 7.1° at 40° of abduction. These findings indicate that studies evaluating glenohumeral instability are compromised unless the translations resulting from capsular venting ore corrected. Evaluation of shoulder stability should be performed before violation of the intraarticular pressure mechanisms.