Glenohumeral Instability is a condition of The Shoulder Girdle marked by excessive movement of the Head of the Humerus relative to the Glenoid Fossa of the Scapula , causing the shoulder joint to be unstable. The extent of instability varies from slight displacement of the Glenohumeral Joint to Subluxation or full Glenohumeral Dislocation . Instability of this joint may be reflected statically and dynamically in any or many directions by both traumatic and inscidious means.
The inherently unstable structure of the Glenohumeral Joint leaves it dependent on external stabilisers which forms many avenues for its demise. The direction and extent of instability implicates specific structures, with anterior instability most common:
Static Stabilisers- while increasingly prevalent with chronicity or recurrence, only trivial elongation of the static stabilisers is present in the initial phase of instability (SOURCE-6). This phase is often marred by concomitant injury such as Avulsion Fractures (SOURCE-5):
Bony Architecture - the significant size disparity of this ball and socket joint affords significant mobility at the expense of stability.
Scapula - provides an articulating surface with the Glenoid Fossa while the Acromion forms a protective bony ceiling. Morphologies of either have the capacity to impact joint stability:
Glenoid Fossa - the much smaller Glenoid Fossa accounts for 25-30% of the surface area of the Humeral Head during articulation (SOURCE-40). Similarly, the depth of the Fossa is approximately 40% of the radius of the Humeral Head (SOURCE-40). This concave articular surface is 20-30% larger in a vertical dimension than it is horizontally (SOURCE-40). Although determined by the position of the Scapula , the slight inclination or medial tilt of the fossa creates a compressive stabilising effect at the joint between gravity and certain stabilisers such as the Superior Glenohumeral Ligament at rest (SOURCE-67):
Glenoid Anteversion predisposes injury to posterior rotator cuff (SOURCE-36). Additionally in the apprehension position of combined GH Joint - External Rotation and GH Joint - Abduction , Glenoid Anteversion increases strain on the anterior band of the Inferior Glenohumeral Ligament (SOURCE-46)
Glenoid Retroversion - generally predispose anterior cuff tears, signifcantly more common - although for For every 1º of increased retroversion there was a 17% increased risk of posterior shoulder instability (SOURCE-36+37)
Acromion - mophologies such as a hooked acromion are assocaited with higher signs of degeneration and ossification of the Coracoacromial Ligament , Subacromial Impingement and Rotator Cuff Tears (SOURCE-20+34+35).
Coracohumeral Distance - every 1mm greater accounts for a 20% increased risk in instability events
Posterior Chondrolabral Cleft - 2.8x more likely anterior instability event
Head of Humerus - only ~25-30% of the much larger Humeral Head is articulating with the Glenoid Fossa at any point, leaving it vulnerable to instability (SOURCE-40). Morphologies of the Humerus have been found to perpetuate this risk:
Morphologies of the Bicipital Groove are associated with pathologic states of the proximal Long Head of Biceps Tendon , which may compromise its stabilising role and inferior glide bias (SOURCE-43)
Humeral Retroversion - a reduced retroversion angle associated with anterior instability which may be reflective of adaptive changes in the anterior Glenohumeral Joint Capsule (SOURCE-17+38). Conversely, a positive correlation between retroversion and posterior capsule tightness (SOURCE-3)
Glenoid Labrum - as the Labrum deepens the Glenoid Fossa by 50% to improve joint congruency, it is a major source of static stability and aids in the maintenance ofViscoelatic Piston Effectwhich forms a seal around the joint to maintain a negative intra-articular pressure (SOURCE-39+40). The Labrum also serves as the attachment site for several other static and dynamic stabiliers
Glenohumeral Joint Capsule - the various portions of the joint capsule provide static stability in all directions. Restriction in one portion may correspond with increased stress in another portion which may lead to instability. With increasing chronicity this may lead to degenerative changes which further perpetuates instability
Glenohumeral Capsular Ligaments
Superior Glenohumeral Ligament - while this ligament displays the most consistent tension through shoulder movement it is pulled most taut during GH Joint - Adduction and GH Joint - External Rotation (SOURCE-41). Excessive laxity in this ligament may lead to inferior instability, particularly is the Coracohumeral Ligament is also compromised (SOURCE-4)
Middle Glenohumeral Ligament - tension increases incrementally from 0-90º of GH Joint - Abduction and GH Joint - External Rotation , particularly when combined (SOURCE-41). The MGL serves to resist anterior translation of the Humeral Head, although its relative contribution is less than the other capsular ligaments (SOURCE-39)
Inferior Glenohumeral Ligament - comprised of three distinct components, the IGL forms a hammock to resist anterior, inferior and posterior translation of the Humeral Head (SOURCE-42). The ligament is similarly pulled taught during GH Joint - Abduction and with bands on either side of the Humerus, the anterior and posterior IGL restrict GH Joint - External Rotation and GH Joint - Internal Rotation , respectively. This ligament is a major static stabiliser, particularly at 90º GH Joint - Abduction and is often damaged during anterior Glenohumeral Dislocation (SOURCE-5+42)
Coracohumeral Ligament - one of the larger Glenohumeral ligaments that blends with several neighbouring ligaments and tendons. All fibres are pulled taut during GH Joint - Adduction and resist inferior translation of the Humerus. Addtionally, the anteiror fibres restrict the extremes of GH Joint - External Rotation and GH Joint - Extension while the posterior fibres restrict the opposing GH Joint - Internal Rotation and GH Joint - Flexion (SOURCE-6)
Negative Intra-articular pressure - the soft-tissue envelope formed by the Glenohumeral Joint Capsule and Glenohumeral Capsular Ligaments establishes negative intra-articular pressure which is a passive contributor to stability (SOURCE-68). Stability is achieved through resistance to distraction and other translatory motions of the Humeral Head on the Glenoid Fossa (SOURE-68). The negative intra-articular pressure may diminish with certain Glenohumeral pathologies (SOURCE-68)
Gravity - the downwards force of gravity pulls the Humerus down the inclined face of the Fossa until the Superior Glenohumeral Ligament is pulled taut (SOURCE-67)
Dynamic Stabilisers- with Muscle tone more acutely variable than that of Connective Tissue , dynamic stabilisers may play a more notable role in non-traumatic Glenohumeral instability, particularly in the initial phase
Rotator Cuff - are the primary stabilisers of the Glenohumeral Joint . Unlike the more superficial muscles, the Rotator Cuff has little shear bias in any direction (SOURCE-18). With this said, smaller cross-sectional areas of the posterior rotators ( Infraspinatus and Teres Minor ) are related to anterior instability while anterior rotators ( Subscapularis ) are related to posterior instability (SOURCE-55)
Deltoid - the most significant dynamic stabiliser against inferior translation, particularly at low Shoulder Elevation ranges (SOURCE-17+18). Akin to the Rotator Cuff, the Anterior Deltoid is considered a posterior stabiliser while the Middle and Posterior Deltoid an inferior stabiliser (SOURCE-18)
Long Head of Biceps - displayed a pre-engagement stabilising role and places an inferior distraction on the Humeral Head (SOURCE-27+28)
Coracobrachialis - affords significant dynamic stabilising against inferior translation and is considered a posterior humeral stabiliser (SOURCE-18)
Latissimus Dorsi - counters the superior pull of the Deltoid to decompress the Suprahumeral Joint (SOURCE-17)
Pectoralis Major - unopposed contraction produced an anteromedial bias on the Humeral Head (SOURCE-29)
Scapula r Stabilisers
Serratus Anterior - a significant Scapular stabilser at rest and throughout Scapulohumeral Rhythm , muscular insufficency could compromise the scapulas stable base for articulation and reduce its functional range which exacerbates stress on other stabilisers such as the Rotator Cuff (SOURCE-30+31+32+33)
Trapezius - with extensive attachment to the Scapula and a notable source of stability at rest and throughout Scapulohumeral Rhythm , the Trapezius may share a bidirectional relationship with Glenohumeral Instability where dysfunction may predispose or exacerbate instability or vice versa
Rhomboids - smaller muscles that perfoms a variety of contractions to either stabilise or move the Scapula. Restrictions in thes muscles has been relfected in the Glenohumeral Joint where GH Joint - Abduction and GH Joint - Flexion were also restricted (SOURCE-45)
Levator Scapulae - in a similar fashion to the Rhomboids, stabilises the Scapula through a variety of movements and through hypertonicity has displayed a capacity to restrict elevation at the glenohumeral joint (SOURCE-45)
With such an array of stabilisers, there is even greater potential causes for instability in the shoulder. Diagnosis must rely on potentially subtle indicators that help differentiate the origins of the pathology. Despite the varied onset disturbed Scapulohumeral Rhythm are likely to eventuate as too for a a reduction in Scapulothoracic Joint - Upward Rotation and reciprocal increase in Scapulothoracic Joint - Protraction (SOURCE-21).
The extent of instability varies from slight displacement of the Glenohumeral Joint to Subluxation or full Glenohumeral Dislocation . Similarly the acuteness typically correlates with the severity (or grade) of instability, where traumatic-derived instability often results in dislocation (SOURCE-7). The onset of injury also bares implications for the direction of instability as unidirectional instability typically follows trauma while multidirectional instability usually relates to ligamentous laxity and insufficient Muscle control (SOURCE-46).
Traumatic Anterior Dislocations account for the vast majority (~85-98%) of initial Glenohumeral Dislocations (SOURCE-48). This form of traumatic injury is most often derived from indirect mechanisms where the arm is suddenly loaded in a variable position of combined GH Joint - Abduction , GH Joint - External Rotation and GH Joint - Extension (SOURCE-46+48). Common examples of this position include activities that reflect the Apprehension Test such as overhead throwing or a posterior FOOSH (SOURCE46+48). Given the traumatic nature of this injury, anterior dislocations often occur (~80%) concomitantly with Hill-Sachs Lesions (SOURCE-46). While most Hill-Sachs Lesions effect less that 30% of the proximal Humerus ’ articular surface, those that exceed this number are expected to play a notable role in recurrence (SOURCE-46). The sequelae that follows a traumatic anterior dislocation typically includes (SOURCE-46+49):
Detachment of the Anterior Glenoid Labrum
Pathologic changes in the Glenohumeral Joint Capsule and Inferior Glenohumeral Ligament
Proprioception Deficits - attributed at least in part to capsulolabral integrity
Brachial Plexus - courses with Subclavian Vein between First Ribs and Clavicle leaving it vulnerable to injury from an anteriorly displaced Humeral Head
Forming a positive feedback-loop, these symptoms predispose further events of instability.
Although considerably less represented, the second most common form of Glenohumeral Dislocation is the Posterior Dislocation, accounting for ~2-5% of all shoulder dislocations (SOURCE-49+50). Similarly, these dislocations are often attributed to high velocity impacts (such as motor vehicle accidents), strong muscle contractions (such as a Seizure) or direct trauma to the anterior Humeral Head (SOURCE-49+50). The mechanism behind posterior dislocations typically involves forceful GH Joint - Adduction with GH Joint - Internal Rotation and there is associations with Reverse Hill-Sachs Lesions (SOURCE-49+50). Posterior Dislocations are often (~50-79%) misdiagnosed at initial presentation (SOURCE-49+50).
Inferior Dislocations, also known asLuxatio Erecta, are the least common form of Glenohumeral Dislocation , accounting for 0.5-1% (SOURCE-51+52). This injury is most often attributed to Hyperabduction from a significant GH Joint - Abduction force which causes the Neck of the Humerus to straighten against the Acromion to compromise the inferior Glenohumeral Joint Capsule and cause inferior migration of the Humeral Head (SOURCE-51+52). Another less reported mechanism involves axial loading of the abducted arm (SOURCE-51). In either instance the vast majority (~80%) of Inferior Dislocations are accompanied by concomitant injury to the following structures (SOURCE-51+52):
Fractures - roughly 60% of inferior dislocations are associated with fractures to the Humeral Head or Greater Tuberosity of Humerus or the Glenoid Fossa of Scapula
Soft-Tissue - Tears or Avulsion Fractures of the Rotator Cuff and Glenohumeral Joint Capsule (in particular Inferior Glenohumeral Ligament ) are likely and may disrupt other local musculature. One MRI study found 75% of inferior dislocations to be accompanied by Rotator Cuff Lesions (SOURCE-52)
Neurovascular Compromise - while Axillary Nerve is most often affected, Brachial Plexus , Radial Nerve , Ulnar Nerve and Median Nerve have also been reported. Nervous compromise is associated with 60% of inferior dislocations and recovery varies from two weeks to one year
The most common long-term complication to follow inferior dislocations is Adhesive Capsulitis (SOURCE-52).
In lieu of trauma instability may still ensue, although its presentation tends to be less isolated to a single direction. While all instability is defined by a failure of the Head of the Humerus to be adequately contained within the Glenoid Fossa; Multidirectional instability occurs when this failure leads to recurrent involuntary Subluxations in more than one direction (SOURCE-53). Intuitively, the insidious onset of this instability subtype is more frequently attributed to degenerative changes or chronic pathologic states rather than traumatic injury. Poor Muscle control and generalised ligamentous laxity within The Shoulder Girdle are considered major factors contributing to multidirectional instability (SOURCE-46+53). This forms the basis for bidirectional relations with Scapular Dyskinesis where aberrant Scapula mechanics may increase humeral translations and consequent stress on static stabilisers which may perpetuate Glenohumeral Instability, while instability may predispose Scapular Dyskinesis (SOURCE-53). One MRI study reported disturbed scapular movement patterns in ~57-80% of MDI patients. The following pathomechanics have been attributed to MDI:
Arm Elevation - during arm elevation patients with MDI display decreased Scapulothoracic Joint - Upward Rotation and a corresponding increase in Scapular Internal Rotation, Posterior Tilting (from 0-60º) and humeral elevation (SOURCE-53). Altered scapular movement is reflected in the activity of attaching Muscle s. Generally, there is reduced activity of the Biceps Brachii and Anterior Deltoid , while there is in an increase for the Infraspinatus (SOURCE-53). The active duration of these muscles is also disrupted in MDI. During elevation in the scapular plane, those with MDI sustained prolonged activity in the Infraspinatus , Supraspinatus , Biceps Brachii and Triceps Brachii while the activity of the Pectoralis Major and all portions of the Deltoid was reduced (SOURCE-53).
Horizontal Pull / Horizontal Push - during both directions of movement those with MDI have a reduced contribution from the Biceps Brachii , Middle Deltoid and Pectoralis Major (SOURCE-53). Additionally for Horizontal Pull, there was a reduction in Anterior Deltoid and Triceps Brachii while Posterior Deltoid and Upper Trapezius increased (SOURCE-53).
Overhead Throwing - during overhead throwing those with MDI display an overactive Infraspinatus and Upper Trapezius (SOURCE-53). The Posterior Deltoid also became notably active during a slow overhead throw (SOURCE-53)
GH Joint - External Rotation - those with MDI display a delay in engagement of the Posterior Deltoid (SOURCE-53)
These findings have been stipulated to reflect a compensatory increase in both the activity and duration of humeral stabiliser engagement (SOURCE-53). There also appears a cautionary compensatory response where the activity of arm/ shoulder accelerators are diminished while activity of muscles that decelerate and control these movements is increased (SOURCE-53). Compared to other forms of instability, Multidirectional Instability is less often associated with a Glenoid Labrum Tear or Bankart Lesion but may still fall into cascade of discomfort, apprehension and chronic shoulder Pain (SOURCE-46+53).
The extent of instability may be graded accordingly (SOURCE-20):
Normal Laxity - 0-25% of Humeral Head translation relative to the Glenoid Fossa
Grade-I - Humeral Head encroaches on the Glenoid Rim but does not dislocate (~25-50% translation)
Grade-II - Humeral Head exceeds the Glenoid Rim but is able to relocate without intervention (spontaneous reduction) (~>50% translation)
Grade-III - Humeral Head exceeds the Glenoid Rim but is unable to relocate on its own, requiring manual reduction (~>50% translation)
The recurrence of Glenohumeral Instability events is a significant concern as it is both common and associated with a sequelae. Recurrence rates following acute-traumatic Glenohumeral Dislocation were found to be as high as 47% following non-operative management and most often occurred within a year of the initial event (SOURCE-8 (13). For those who underwent surgery, recurrence rates may still be as high as 26% (SOURCE-10). Recurrence is roughly 3 times more likely in males and 13x more likely in those under the age of 20 (SOURCE-8 (13). Recurrent instability is associated with an increased risk of degeneration of the Glenoid, Humeral Head and Glenohumeral Joint Capsule and the number of events was correlated to the extent of damage (SOURCE-8). Bone loss is present in 70-90% of recurrent instability cases (SOURCE-10). Similar degenerative changes were seen in the Synovial Membrane and Collagen structure of those with a history of traumatic instability, which included a denuded Synovial Membrane and Subsynovial Edema (58% of cases), increased vascularity (83%) and increased cellularity (25%) (SOURCE-12).
Glenoid or Humeral Head Bone loss is common following recurrent episodes of Glenohumeral Dislocation , particularly in adolescents (SOURCE-21). This phenomenon further perpetuates the risk of recurrence in a proportional manner where the greater the bone loss the greater the risk (SOURCE-21).
Establishing the true prevalence of Glenohumeral Instability in the general population is difficult as it often goes undiagnosed, particularly for lower grade instability.
Glenohumeral Dislocation - various studies have estimated the prevalence in the general population to be 0.0123% to 0.0563% (12.3 - 56.3 cases per 100,000 people years) (SOURCE-8)
Glenohumeral Joint Subluxation - a study on military academy students found Subluxations to account for 85% of all instability events (SOURCE-8+9)
The prevalence of instability increases dramatically sports, particularly those that involve contact, or labour intensive professions such as the military (SOURCE-7+8)
Non-Modifiable:
Sports or labour intensive professions - chronic or accumulated stress is a known predisposing factor to instability, particularly when these activities frequently involve the apprehension position ( GH Joint - External Rotation and GH Joint - Abduction ) as seen in overhead throwing (SOURCE-46). Repetitive stain in such positions may lead to attenuation of the anteroinferior static stabilisers and consequently, instability (SOURCE-46). In athletes, trauma accounts for almost all onset of instability (~97.8%), with anterior instability being the most common (82.6%), then posterior (16.9%) and lastly inferior (0.5%) (SORUCE-7). In these populations, the severity was a full Glenohumeral Dislocation in half of cases (SOURCE-7).
Age - a steep incline in Glenohumeral Instability incidence occurs after the age of 10 with a peak in the late teens/ early 20’s (SOURCE-8). An obvious explanation for such a trend is attributed to sports and physical activity; however, other contributing factors have been identified. Expression of Elastic Fibres is shown to be significantly higher in those <22 years of age and in those with multidirectional instability (SOURCE-11). Additionally, the proportion of Collagen fibres changes as we age from predominately Type III to Type I (SOURCE-46). The sulphur groups in Type I fibres increase the likelyhood of cross-links formation between filaments, making the relevant Tendons or Ligaments more stable and less elastic (SOURCE-46)
Glenoid Labrum Tear - lesions that alter articulation are associated with an increased risk of recurrence (SOURCE-10)
Elastic Fibres - significantly higher Elastin density and percentage of surface area accounted for by Elastic Fibres was identified in those with multidirectional shoulder instability (SOURCE-11). It is thought the increased playability of these fibres may be a predisposing and maintaining factor for instability. Similarly hyperlaxity is a known risk factor for instability and recurrence (SOURCE-21)
Modifiable:
Rotator Cuff - weakness was associated with anterior instability and recurrence (SOURCE-14). Conversely, the following factors were associated with acute traumatic posterior instability events:A consensus is yet to be established on whether greater Rotator Cuff Strength was a compensatory response to the instability or a sequela (SOURCE-13).
Greater GH Joint - External Rotation Strength at 0º and 45º GH Joint - Abduction
Greater GH Joint - Internal Rotation Strength at 0º GH Joint - Abduction
Ratio of External to Internal Rotation at 45º GH Joint - Abduction
(SOURCE-13)
Connective Tissue - given the morphologic responses of relevant connective tissue to exercise it could be postulated the emphasis of certain movement paterns could restore appropriate tone to static stabilisers (described above) and Fascia l connections:
The following list contains pathologies that often relate to glenohumeral instability, as either predisposing factors, concomitant conditions, or sequelae:
Glenohumeral Dislocation - considered the natural progression of chronic Glenohumeral Instability.
Subacromial Impingement - shares a complex, reinforcing and often bidirectional relationship with instability of the Glenohumeral Joint . The implied insufficient action from the Rotator Cuff may lead to excessive superior translation of the Head of Humerus which reduces the subacromial space either at rest or through movements such as arm elevation. Conversely, chronic impingement increases friction on muscles such as the Rotator Cuff and Long Head of Biceps on their course through the subacromial space and compromises their ability to accurately centre the Humeral Head within the Glenoid Fossa, leading to instability.
Scapular Dyskinesis - as displayed in Scapulohumeral Rhythm , the Scapulothoracic Joint and Glenohumeral Joint share the complex but coordinated task of appropriately positioning the Glenoid Fossa to maximise stability of The Shoulder Girdle in a highly mobile environment. Insufficiency from one joint appears to be compensated for by the other, however this appears to come at the expense of movement quality and may compromise associated soft-tissues. Glenohumeral Instability often results in reduced Scapulothoracic Joint - Upward Rotation and a corresponding increase in Scapulothoracic Joint - Protraction , particularly if instability is multidirectional (SOURCE-21). Asymmetric Scapulothoracic motion is also disproportionately higher in those with anteroinferior instability (SOURCE-46).
Glenoid Labrum Tear - anterior tears predominantly presented with Instability, with Pain as the main a symptom in less than a quarter of instances (SOURCE-2). Conversely, for posterior tears Pain was the primary complaint in the majority of cases, with instability only accounting for 21% (SOURCE-2).
Bankart Lesion - following a traumatic episode 97% of patients with anterior instability were found to have a Bankart Lesion (SOURCE-4+5)
SLAP Lesion - third most common soft-tissue lesion that occurs following traumatic anterior dislocation, associated with roughly a quarter (~23%) (SOURCE-65)
Humeral Avulsion of the Glenohumeral Ligaments - estimated to be associated with 7.5-9.3% of primary dislocations and a larger proportion of initial dislocations in those over the age of 35 (SOURCE-66)
Rotator Cuff Tear - shares a similar bidirectional relationship with Glenohumeral Joint instability as other shoulder pathologies. Rotator Cuff weakness is associated with anterior instability and recurrence of unstable events (SOURCE-14). Conversely, instability may alter the length-tension relationship of these muscles and predispose injury. Rotator Cuff Tears often occur concomitantly with Dislocations (SOURCE-22).
Long Head of Biceps Tendinopathy / Absence - those with absent or impaired LHB tendons displayed superior translation of the Head of Humerus , which is throught to lead to instability (SOURCE-3).
Hill-Sachs Lesion - impression Fractures of the Head of the Humerus are associated with 65-71% Glenohumeral Dislocations and 100% of recurrent Instability (SOURCE-15).
Osteoarthritis - Glenohumeral instability has been shown to increase rates of arthritis with 20-60% of patients developing the condition at long-term follow up (SOURCE-7+8+10).
Rotator Cuff Tear / Tendinopathy / Weakness
Adhesive Capsulitis - early “freezing” stage may mimic instability
Neuropathy - may lead to Rotator Cuff weakness and pseudoinstability
Radiculopathy - likely C4 , C5 and/or C6
Ligament ous Conditions
Systemic Conditions such as Hypermobility Syndrome
Local ligamentous laxity
Bone Defects
Scapulohumeral Rhythm - reduced Scapulothoracic Joint - Upward Rotation likely with instability, particularly in the first 90º of elevation (SOURCE-15)
Sulcus Sign - may indicate multidirectional instability (SOURCE-20)
Shoulder Displacement - may indicate Glenohumeral Dislocation
Posterior Dislocations may be observed as an GH Joint - Internal Rotation deformity, enlarged posterior and a prominent Coracoid Process (SOURCE-50)
Inferior Dislocations - often presents in the “Hands Up” position with full GH Joint - Abduction , Elbow - Pronation and partial Elbow - Flexion and supported by the head (SOURCE-52)
The direction(s) of instability will determine which Range of Motions are either Pain ful or lax/vulnerable. Posterior Dislocations for example, limit or ruin GH Joint - Abduction and GH Joint - External Rotation while these same ranges become excessive with Anterior instability (SOURCE-16+50). Near end-range the unstable shoulder may relocate, indicating at least a partial Subluxation of the Head of Humerus . Two or more directions of instability would indicate multidirectional instability which should then be followed up by a screening of unrelated joints to screen for systemic laxity:
Posterior Glide on Humerus - excessive movement indicates Posterior Instability
Anterior Glide on Humerus - excessive movement indicates Anterior Instability
Long Arm Traction on Humerus - excessive movement as indicated by presence of Sulcus Sign indicates inferior instability
Lateral Distraction on Humerus - excessive movement indicates Inferior Instability
The following Shoulder - Special Tests can be used to evaluate the presence and grade of instability in various directions:Anterior:
Anterior Drawer Test (shoulder) - high specificity for anterior instability
Apprehension Test - high specificity for anterior instability
Jobe Relocation Test - high sensitivity for anterior instability
Load & Shift Test - evaluates instability in any direction with high specificity
Posterior:
Jerk Test - evaluates integrity of posteroinferior Glenoid Labrum and therefore posteroinferior instability
Kim Test - evaluates integrity of posteroinferior Glenoid Labrum and therefore posteroinferior instability
Inferior:
Sulcus Sign - predominately an indicator for inferior instability but may also be valid for multidirectional, particularly when GH Joint - External Rotation is added
Jerk Test - evaluates integrity of posteroinferior Glenoid Labrum and therefore posteroinferior instability
Kim Test - evaluates integrity of posteroinferior Glenoid Labrum and therefore posteroinferior instability
Multidirectional:
Sulcus Sign - external rotation variant
Dynamic Rotary Stability Test - evaluates dynamic stabilisers
The following Muscles may be weak or inhibited with instability:
Supraspinatus - active resisted GH Joint - Abduction either seated or supine
Infraspinatus - active resisted GH Joint - External Rotation while lying prone in 90º GH Joint - Abduction
Teres Minor - same as Infraspinatus
Subscapularis - active resisted GH Joint - Internal Rotation while lying prone in 90º GH Joint - Abduction
Serratus Anterior - Punch Out Test perfomed either supine or standing
Trapezius - differentiation between Upper, Middle and Lower Fibres detailed on its page
Biceps Brachii - active resisted 90º Elbow - Flexion with Elbow - Supination
While the diagnosis of Glenohumeral Instability is predominately based on clinical findings, imaging may be used to evaluate concomitant or contributing pathology:
Magnetic Resonance Imaging (MRI)- with the capacity for Bone and Soft-Tissue to be implicated in instability, MRIs may be preferable due to their ability to produce clear images of both. High sensitivity for the detection of edema also allows MRIs to recognise pathologies in their early phase (SOURCE-19). When compared to 1.5-T MRIs, the stronger 3-T MRIs offer enhanced accuracy for visualizing subtle soft tissue and bony lesions, which can be crucial for differentiating structural and dynamic pathologies related to shoulder instability and associated conditions like impingement (SOURCE-24).
MR-Arthrography - the complement of contrast injections distends the joint and sequesters into tears for better visualisation. For acute injury this may not be necessary as joint effusion may play a similar revealing role (SOURCE-44). MR-Arthrography is considered the modaility of choice for imaging of the Glenoid Labrum and Glenohumeral Capsular Ligaments . Injury to the Capsulo-Labro-Ligamentous Complex may be identified by the contrast fluid (or joint effusion) that distinguishes the previously attached structures (SOURCE-44). In chronic injury, displaced tissue may scar into a round mass known as theGlenoid Labrum Ovoid Mass (GLOM)which can also be visualised on MRI’s (SOURCE-44). Galolinium-based contrast material may afford a more favorable contrast-to-noise ratio and intraarticular injections may allow for better joint distension and delineation of labral lesions when compared to intravenous injections (SOURCE-44).
Radiographs (X-Rays) - are highly accessible and provide clear images of osseous structures. X-Rays may be relevant for the diagnosis of Glenohumeral Dislocation or the evaluation of secondary bony lesions of the Humerus or Glenoid Fossa, including Hill-Sachs Lesion s, Bankart Lesions or other Avulsion Fractures (SOURCE-44). In the acute setting, the following views may be relevant (SOURCE-44+46+50):
Anteroposterior (Grashey) View
Transscapular (Scapular-Y) View
Garth View (X-ray beam orientated 45º caudally from AP view) - demonstates anteroinferior margins of Glenoid and posterosuperior aspect of Humeral Head without requiring abduction
West Point View - recommended for suspected Bankart Lesion
Stryker Notch View - recommneded for suspected Hill-Sachs Lesion
In certain instances the addition of dynamic stress radiographs may provide better insight into the instability of the shoulder (SOURCE-44).
Computed Tomography (CT) Scan - while generally used as an alternative to MRI’s when they are contraindicated, they appear to boast similar accuracy for Glenoid Labrum assessment (SOURCE-44). The detail of CT scans allows for the evaluation of osseous structures to a standard where bone loss may be quantified (eg. glenoid index) and congential bone alterations are recognised (SOURCE-44). Glenoid Dysplasia, for example, is often visualised as a blunting and convexity of the posterior Glenoid Rim in the axial plane - a.k.a. “Lazy-J-Sign” (SOURCE-44). For CT-Arthrography, single contrast methods may be prefered at a dilution radiologist dependent (SOURCE-44). A dilution of 10ml of Ionic contrast material (320 mg of iodine per milliliter), diluted with 5 mL of local anesthetic has been described (SOURCE-44).
Such high levels of recurrence stresses the importance of primary prevention in Glenohumeral Instability; however, for many it is too little too late and further stages of prevention are required (SOURCE-8):
Primary Prevention - prevent the condition from ever occurring
Secondary Prevention - intervene at the initial phase of a condition, including conservative and surgical intervention
Tertiary Prevention - prevent or minimise chronicity
Typically surgical intervention is reserved for those with recurrent episodes of dislocations; however, the patients activity levels may indicate surgery even following a single episode. For example, adolescents participating in contact sports may require surgery to prevent otherwise likely recurrence (SOURCE-21). In these cases conservative management should still first be attempted which usually involves immobilisation of 4-6 weeks before commencing a physical therapy program (SOURCE-21). The position of immobility may also effect patient outcomes as patients immobilised in GH Joint - External Rotation appear to have lower recurence (SOURCE-54). Pain -free Range of Motion is carefully progressed and then followed by a progressive Strength program. Only once full Pain -free range and Strength is obtained should the athlete consider returning to sport. Some authors have suggested in-season return to sport following a severve instability event such as an anterior dislocation can be made in 1-3 weeks; however, this may increase risk of recurrence and perpetuate instability (SOURCE-54).
Stretching techniques may be relevant to improve joint mechanics; however, given the nature of instability caution must be taken when selecting which tissues are lengthened as it may perpetuate instability. Muscle hypertonia has been shown to cause superior migration of the Head of the Humerus and instability of the Glenohumeral Joint and Scapulothoracic Joint (SOURCE-24):
Posterior Glenohumeral Joint Capsule and Posterior Deltoid - chronic instability may lead to adaptive changes such as capsular thickening and restriction. This may eventuate to increased anterosuperior stress in the Glenohumeral Joint (SOURCE-23+25):
Genie Stretch - rudimentary horizontal adduction stretch
Sleeper Stretch - greater emphasis on GH Joint - Internal Rotation
Sleeper Stretch MWM - sleeper stretch with added Humerus Mobilisation
Pectoralis Minor - the restoration of length may improve associated Scapular Dyskinesis if present (SOURCE-25+56)
Scapula Stretch - a Scapulothoracic Joint - Retraction and posterior tilt can be passively applied by a practitioner directly to the Scapula. This may be indicated as other stretching positions may be provoke symptoms (SOURCE-25)
Scapular Stretch with ~90º GH Joint - Abduction and GH Joint - External Rotation (SOURCE-26)
Door Frame Shoulder Stretch - Pectoralis Minor variation
Short Head of Biceps (SOURCE-56)
Split Stance Biceps Stretch - Short Head variant
Levator Scapulae (SOURCE-25)
Door Frame Neck Stretch - Levator Scapulae variant
Rhomboids (SOURCE-25)
Latissimus Dorsi - hypertonicity may lead to a destabilising inferior pull on the Humeral Head (SOURCE-56)
Conservative managment that emphasises the Strength ening of the following Muscles has displayed good to excellent outcomes in the treatment of traumatic and atraumatic instability (SOURCE-25+46):
Rotator Cuff - general weakness associated with anterior instability and recurrence (SOURCE-14). Additionally, smaller cross-sectional areas of the posterior rotators ( Infraspinatus and Teres Minor ) are related to anterior instability while smaller anterior rotators ( Subscapularis ) are related to posterior instability (SOURCE-55)
Deltoid - unlike the compressive action of the Rotator Cuff, the Deltoids generate substantial superior shear forces to either stabilise or destabilise the Humerus depending on contextual factors such as arm position and exernal load (SOURCE-18). The Deltoids notable resistance to inferior translation of the humerus increasingly diminishes as the arm elevates (SOURCE-18)
Coracobrachialis - affords a similar superior shear force on the Humerus as the Deltoid and is considerd a posterior stabiliser (SOURCE-18)
Scapula Stabilisers
Serratus Anterior - reduced activity has been displayed in several pathologies of The Shoulder Girdle , including Glenohumeral Instability (SOURCE-1).
Lower/ Middle Trapezius
Exercise selection should always be considerate of exercise selection as to not perpetuate overactive muscles (SOURCE-25).
Initial Phase - should address the altered neuromuscular control by promoting appropriate muscle recruitment with particular focus on the Rotator Cuff and other Scapula stabilisers (SOURCE-25). Strength may be increasingly emphasised as neuromuscular function is restored. In chronic or pathologic states such as a Tendinopathy , eccentric Muscle Contractions may be relevant (SOURCE-25).
Rotator Cuff - begining with Proprioception cueing and rhythmic stabilisation/ activation exercises and potentially progressing to move patient specific movements such as emphasising eccentric rotations for overhead throwing athletes (SOURCE-25+56):
Rotator Cuff Pendulums - oscillatory motion that afford a distracting glide to the Humeral Head
Banded Unilateral Lat Activations - a contingently relevant Lat exercise which may draw the head of the Humerus posteroinferiorly
Scapula Plane Elevation with:
Y-Raise - light isotonic exercise that emphasises Trapezius, particularly mid/low fibres
Standing Shoulder External Rotations - incorporates upright torso posture
Rotator Cuff Banded Rotations - light low range isotonic rotation exercises
Prone Shoulder External Rotations - adds gravity or light load to Apprehension Test position
Banded Horizontal Adduction - low load isotonic horizontal adduction exercise, indicated for posterior instability
Scapula Orientation Exercises
Pattern Correction - cue appropriate postural/ movement patterns relevant to the Scapula, in particular those that emphasise Scapulothoracic Joint - Retraction . May additionally benefit from the use of mirros to provide visual feedback:
Lawnmower- empathises the bodies diagonal pattern and retraction of the scapula. In a braced (slightly flexed) posture, reach from roughly the contralateral knee to reach over the ipsilateral shoulder
Cat-Cow - promotes movement and mild activity of all Trapezius fibres
Bird-Dog - bodyweight exercise that emphasises full arm elevation and the Posterior Sling
Push-Up Plus - starting with wall variation, a bilateral isotonic exercise for Scapular Protractors
Circumduction Row - isotonic exercise for Scapular Retractors
Band Pull-Apart - basic isotonic exercise for Scapular Retractors
Mid-Phase - adequate muscle activation and active Range of Motion should now be achieved and exercise selection may begin to address specific deficits and demands of the patient (SOURCE-25). This may include rudimentary versions of Barbell, Dumbbell and machine exercises:
Scapular Pinches - Swiss Robbery Pinches w/ DB’s variation - isometric, moderate load Scapular retraction exercise
Seated Row - or High Row variation - moderate-to-high load isotonic Scapula retraction exercise
Lat Pulldown - isotonic exercise that promotes downwards rotators of Scapula
Face Pulls - bilateral isonotic horizontal pull exercise that emphasises GH Joint - External Rotation
Upright Row - weighted isotonic vertical pull exercise that emphasises Upper Trapezius , Deltoid and external rotators
Overhead Press - isotonic strength exercise that approaches maximum range overhead
DB Shoulder Press - overhead press variation that loads each side independently
Late Phase - with basic asymmetries, deficits and movement quality now addressed, the patient is ready to undertake advanced stability and strength exercises throughout complex, circumstance (or sport) specific movements (SOURCE-25). Exercise selection should emphasise relevant functional patterns or kinetic chains with increasing difficulty, through parameters such as load, speed or instability (SOURCE-25).
Functional Patterns
Diagonal Patterns - similar to those described in Anterior Sling , Posterior Sling and Spiral Line . Although specific exercises can emphaises these continuities, sometimes simple modifications to familiar exercises may be relevant. For example, standing on the contralateral leg increases activity of Scapula musculature (SOURCE-25)
Half DB Bench Press - unilateral pressing motion that emphasises Anterior Sling and Posterior Sling
Bird-Dog Row - unilateral unstable exercise that emphasises scapular retraction and the Posterior Sling
Reverse Woodchopper - isotonic exercise that emphasises Serratus Anterior and Mid/Low Trapezius through a movement that promotes Scapulohumeral Rhythm
Bottoms-Up Kettlebell Walk - emphasises Scapular Stabilisers
Split Stance Landmine Press - unilateral, body-wide, explosive isotonic exercise through large overhead range
Medball Pullover Throw - explosive low load, large shoulder and thoracic range exercise
Shoulder Rotation Ball Plyometrics - low load and range, repetitive movements that emphasise shoulder rotation in various functional positions that involve overhead throwing
Bear Crawl on Swiss Ball - legs on ball, hands crawl in/ out while maintaining neutral spine
Seated Pike Lift - isometric holds emphasising Scapular stabilisers
DB Hang Clean - unilateral clean progression, often performed explosively
Prone Lat Pulldown - variation that emphasises scapular stractors and thoracic extension
Push Press - explosive overhead press progression that incorporates the lowerbody
Kneeling Landmine Press - explosive isotonic exercise through large overhead range
Given the multifaceted and often concomitant origins of Glenohumeral Instability, Mobilisations of the Scapula , Glenohumeral Joint , Cervical Spine and Thoracic Spine may be relevant. As Glenohumeral Instability is often associated with soft-tissue laxity, mobilisations applied directly to the Glenohumeral Joint should be performed at a low grade to help maintain joint health and neuromodulate Pain through the stimulation of Mechanoreceptors without approaching end-range and stretching soft-tissues (SOURCE-64). Joint Play
Acromioclavicular Joint - mobilsations for stiffness advocated by Maitland for instability (SOURCE-16)
Acromioclavicular Anterior Glide - can be used to treat general Pain (SOURCE-16)
Acromioclavicular Posterior Glide - appropriate for Pain following injury, Subluxation or Fracture of Clavicle (SOURCE-16)
Acromioclavicular Inferior Glide - advocated by Maitland for general joint Pain or restriction (SOURCE-16)
Acromioclavicular Superior Glide - recommended when the other joint play motions fail to alleviate symptoms (SOURCE-16)
Cervical Spine - in addition to a PACVP , PAUVP or TVP applied to a desired Cervical segment, the following techniques may be of relevance for a suspected Radiculopathy :
Glenohumeral Joint - low grades used to promote Proprioception prior to functional stability training (SOURCE-16)
Posterior Glide on Humerus - advocated for by Maitland in the treatment of anterior Subluxation (SOURCE-16). Posterior shoulder stiffness likely most common adaptation seen in overhead athletes (SOURCE-25)
Anterior Glide on Humerus - may be indicated for posterior instability
Scapulothoracic Joint - with compensatory action between the two joints, Glenohumeral Instability may result in abnormal or restricted motion of the Scapula :
Mobilisation with Movement - in a similar fashion to joint play mobilisations, MWM techniques are generally not indicated for instability; however they may be used to treat secondary hypomobility so long as it is Pain -free and not aimed towards the direction of instability:
Shoulder - MWM 1 - corrects Scapula motion through arm elevation
Shoulder - MWM 2 - mid range variation of MWM 1
Shoulder - MWM 3 - applies posterolateral glide to Humeral Head through elevation
Shoulder - MWM 4 - applies posterolateral and inferior glide on Humerus through mid-range elevation
Shoulder - MWM 5 - applies posterolateral and inferior glide on Humerus through end-range elevation
Shoulder - MWM 8 - applies posterolateral and inferior glide on Humerus through GH Joint - External Rotation or GH Joint - Internal Rotation
Sleeper Stretch MWM - self-guided inferior glide on Humerus with GH Joint - Internal Rotation
Cervical - MWM Techniques - in addition to NAGS or SNAGS applied to a relevant Cervical segment, the following techniques may be indicated with suspected Radiculopathy :
SMWAM - cerivcal mobilisation with arm movement
Neurodynamic SMWAM - cervical mobilisation with neurodynamic tensioner
Cervical SNAGS - cervical posteroanterior mobilisation with neck movement
C6-T1 Transverse SNAGS - cervical transverse mobilisation with neck movement
As a general trend first-time acute Dislocations are managed conservatively with immobilisation through the use of a sling, afterwhich treatment techniques such as those describe above may be implemented (SOURCE-25). In a similar fashion, conservative management is recommended for multidirectional instability through Strength ening before surgical capsule tightening should be considered (SOURCE-25). Surgical intervention becomes increasingly indicated with Dislocation reccurence, particularly when associated with contact or elite sport (SOURCE-25). Broadly speaking there are several surgical techniques that may be relevant for those with Glenohumeral Instability, including:
Arthroscopic Surgery
Open Surgery
Shoulder Arthroplasty
Fracture Fixation
Tendon Transfer
In terms of specific procedures, theBankartandLatarjetprocedures are most commonly utilised for the treatment of Glenohumeral Instability which represent a combination of the aforementioned techniques (SOURCE-25):
Bankart Procedure - as the name suggests this procedure is designed to repair a Bankart Lesion that occurs following Glenohumeral Dislocation . While traditionally performed through open surgery, is now more commonly performed arthroscopically (SOURCE-57+58). In either instance, the Bankart procedure retentions the Anterior Glenohumeral Joint Capsule and repairs the avulsed Glenoid Labrum using sutures or anchor sutures (SOURCE-58). While this procedure is often used as the surgical first line of attack for instability, it is reserved for less severe instances where bone loss is minimal (SOURCE-58+63)
Latarjet Procedure - also known as theCoracoid Bone Block Procedure, transfers the portion of the Coracoid Process of Scapula where the Conjoint tendons (formed by fusion of Short Head of Biceps and Coracobrachialis tendons) attach to the Anterior Glenoid Rim through the use of screws (SOURCE-58). In contrast to Bankart procedure, the Latarjet requires open surgery and is therefore more invasive; however, it appears to boast superior outcomes in the settings of notable boneloss and is more effective at preventing reccurent instability symptoms over the long-term (SOURCE-58+61).
For the majority of outcome measures including rates or timing of return to sport, return to pre-injury level, Range of Motion and functionality there appears to be no significant difference between the two procedures (SOURCE-59+61). The less invasive Bankart procedure did however boast significantly higher reccurrence and reoperation rates (SOURCE-60+62+63).
Following surgery The Shoulder Girdle is typically immobilised for approximately 4 weeks, with only active-assisted exercises within a “safe-zone” permitted (SOURCE-25). Other post-surgical recommendations include (SOURCE-25):
Glenohumeral Joint Mobilisations may commence after 4 weeks with the aims of full Range of Motion after 2 months
Proprioception Training may commence after 4 weeks
Stabilisation/ Rotator Cuff Strength ening may commence at roughly the 2 month mark
Forced passive GH Joint - External Rotation should be avoided for up to 3 months
Return to sport is likely possible between 4 and 6 months post surgery
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