Glenohumeral Joint

The Glenohumeral Joint, abbreviatedGH joint, is a triaxial, ball and socket (spheroidal) articulation formed between the large convex Head of the Humerus and the shallow concavity of the Scapulas Glenoid Fossa (SOURCE-12). The considerable size between the large Humeral Head and smaller Glenoid Fossa is accounted for by the Glenoid Labrum which deepens the socket and improves joint congruency (SOURCE-3). The highly mobile environment is supported is by the Synovial Membrane and numerous static and dynamic stabilisers. The Glenohumeral Joint is often considered the primary joint of The Shoulder Girdle of the 5 joints/ functional articulations that comrpise it.

Key Structures

Bone :

Muscle - also known as thedynamic stabilisers:

Connective Tissue - also known as thestatic stabilisers:

Nerve :

Fascia

Kinematics

The GH joint is a universal joint because movement occurs in all 3 degrees (triaxial) of freedom. Practically all motions of the GH joint involve motion at the Scapulothoracic Joint , as well as the associated movements at the Acromioclavicular Joint and Sternoclavicular Joint .Movements of GH joint

Stabilisers

The highly mobile Glenohumeral Joint relies on its architecture and many passive and dynamic tissues to afford it stability:

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-31). This phase is often marred by concomitant injury such as Avulsion Fractures (SOURCE-32):

  • 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-3). Similarly, the depth of the Fossa is approximately 40% of the radius of the Humeral Head (SOURCE-3). This concave articular surface is 20-30% larger in a vertical dimension than it is horizontally (SOURCE-3). 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-12):

      • 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-11+36+37).

      • 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-3). 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-38)

      • Humeral Retroversion - a reduced retroversion angle associated with anterior instability which may be reflective of adaptive changes in the anterior Glenohumeral Joint Capsule (SOURCE-9+38). Conversely, a positive correlation between retroversion and posterior capsule tightness (SOURCE-3)

  • Connective Tissue

  • 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-53). Stability is achieved through resistance to distraction and other translatory motions of the Humeral Head on the Glenoid Fossa (SOURE-53). The negative intra-articular pressure may diminish with certain Glenohumeral pathologies (SOURCE-53)

  • 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-12)

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-42). With this said, 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-43)

  • Deltoid - the most significant dynamic stabiliser against inferior translation, particularly at low Shoulder Elevation ranges (SOURCE-9+42). Akin to the Rotator Cuff, the Anterior Deltoid is considered a posterior stabiliser while the Middle and Posterior Deltoid an inferior stabiliser (SOURCE-42)

  • Long Head of Biceps - displayed a pre-engagement stabilising role and places an inferior distraction on the Humeral Head (SOURCE-16+44)

  • Coracobrachialis - affords significant dynamic stabilising against inferior translation and is considered a posterior humeral stabiliser (SOURCE-42)

  • Latissimus Dorsi - counters the superior pull of the Deltoid to decompress the Suprahumeral Joint (SOURCE-9)

  • Pectoralis Major - unopposed contraction produced an anteromedial bias on the Humeral Head (SOURCE-45)

  • 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-46+47+43+48)

    • 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-49)

    • 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-49)

Loss or disturbance of any of these contributing factors can lead to Glenohumeral Instability or Glenohumeral Dislocation when severe. The Connective Tissue that forms the Glenohumeral Joint Capsule is oriented in such a way that GH Joint - External Rotation and GH Joint - Abduction are most limited, the full extent of the two being considered the joints close-packed position.

Pathomechanics

The most notable pathologies of the Glenohumeral Joint are typically derived from an acute traumatic event or a chronic degenerative process with the potential for either to predispose the other.

Instability

The lack of bony congruence between the two articulating surfaces leaves the Glenohumeral joint at the whim of the dynamic and static stabilisers. When these tissues are compromised, joint arthrokinematics may be disturbed and Glenohumeral Instability may ensue. The relative position of the Humerus in the Glenoid lends credence to which specific tissues may be compromised. While these structures may not necessarily be the underlying cause of the pathology, they can provide useful insight for potential diagnosis (SOURCE-10+11):

Likewise, evaluating the direction of any Glenohumeral Instability can provide further insight into compromised tissues. Scapular Dyskinesis is described as a non-specific response to Shoulder Pain , with a reduction in Scapulothoracic Joint - Upward Rotation and reciprocal increase in Scapulothoracic Joint - Protraction considered a typical response to Glenohumeral Instability (SOURCE-13+14).

Degeneration

The predominant degenerative condition that affects the Glenohumeral Joint is Osteoarthritis which is considered primary if it is idiopathic and secondary if it is a sequela to other pathology. A diagnosis of Primary Osteoarthritis, therefore, may be made when no predisposing factors can be identified (SOURCE-24). In most instances predisposing factors such as trauma or chronic pathological states are identified, with Shoulder Osteoarthritis frequently attributed to shoulder injuries that involve Glenohumeral Dislocation or Rotator Cuff Tears (SOURCE-23). Irrespective of its onset, Osteoarthritis is described to follow a familiar path of joint degradation. Excess friction leads to a mechanical wearing of the joints articular Cartilage and a narrowing of the joint space (SOURCE-19+20+21). Mechanical stress is therefore relayed onto the underlying subchondral Bone which causesSclerosis(thickening/ stiffening) and necrosis of Osteocytes most prominent at sites of stress (SOURCE-19+20+22). As the articular Cartilage is relatively insensitive when compared to the synovium and subchondral Bone , this stage of degeneration may be associated with a marked increase in Pain (SOURCE-19). The upper two-thirds of the Head of Humerus are most frequently subject to this cartilaginous loss, a region in contact with the Glenoid Fossa between ~60-100º of GH Joint - Abduction (SOURCE-19). These compromised sites of Bone breakdown and exposed marrow spaces begin to fill with fluid, formingSubchondral Cystswhich further symptoms of Pain , Inflammation and stiffness (SOURCE-20+22). In instances where this fluid is Synovial Fluid, pseudocysts are formed (SOURCE-20). In an reparative attempt to stabilise the joint,Osteophytes(or bone spurs) form typically at the junction of soft-tissue with Bone such as the articular Cartilage , Synovial Membrane and Periosteum (SOURCE-20). Depending on the size and location of these Osteophytes, they may encroach on neighbouring soft-tissues and lead to their compromise. The anteroinferior and inferior aspects of the Humeral Head are most often affected, likely due to mechanical stress bestowed upon the Glenohumeral Capsular Ligaments and in severe cases a large inferior mass may collect on the Humeral Head (SOURCE-19+20). Degenerative changes may also lead to metaplastic Bone formation within the articular lip to form a smooth bony margin that surrounds the Glenoid Cavity (SOURCE-20).

Slightly removed from the Glenohumeral Joint, similar degenerative changes extend to the superior portion of the Bicipital Groove where Osteophyte formation encroaches on the Long Head of Biceps Tendon (SOURCE-20).

While Rotator Cuff pathology is a common cause of secondary Osteoarthritis, a significant enough tear may lead to joint degeneration through diverging mechanisms. A rupture or “massive” Rotator Cuff Tear may lead to superior migration of the Head of Humerus which encroaches on the subacromial space, this phenomenon being known as aRotator Cuff Arthropathy(SOURCE-25). The ensuing nonphysiologic friction between the Humeral Head and the undersurface of the Acromion causes erosion of the Greater Tuberosity and a pathologic reshaping of the Coracoacromial Arch (SOURCE-25). This not only affects the articular surface in a similar manner to that described for the Glenohumeral Joint but may escalate to compromise the Long Head of Biceps Tendon (SOURCE-25).

Rheumatoid Arthritis is a systemic Inflammation -based autoimmune arthropathy that similarly leads to degradation of the articular Cartilage and underlying subchondral Bone , although the mechanism and precise pattern of damage are divergent. Exposure to Inflammation becomes erosive, initially through microvascular compromise of the small blood vessels within the Synovium which provokes a cascade (SOURCE-28). In turn, the joint-fluid producing Synovial Cells undergo mild proliferation (multiply) in response to injury (SOURCE-28). The distinguishing feature of this autoimmune condition from Osteoarthritis isPerivascular Lymphocytosis, where immune cells accumulate at the injured vessels (SOURCE-28). The unrelenting presence of immune cells and inflammatory cytokines drives the disease state towards the formation of a hyperplastic Synovium, known as aPannus(SOURCE-28). Proliferating Synovial Cells and the accumulated inflammatory cells form a thick, abnormal tissue layer that has a highly destructive nature with the release of potent enzymes.

Another common degenerative state for the Glenohumeral Joint relates to impaired blood flow and may be derived from traumatic or nontraumatic means.Avascular Necrosis, orShoulder Osteonecrosis, describes the process of bone tissue deterioration and death that follows inadequate or ceased blood supply. The Head of the Humerus is one of the most common sites for Osteonecrosis to occur with both theAnterior and Posterior Humeral Circumflex Arteryvulnerable to compromise (SOURCE-26+27). Traumatic compromise is often an iatogenic complication of surgergical procedures such as internal fixation or the result of Proximal Humerus Fractures (SOURCE-26). Post-traumatic Osteonecrosis has an estimated prevalence of 0-25% for three-part fractures of the Humeral Head and 0-77% for four-part fractures (SOURCE-26). Nontraumatic Osteonecrosis of the Humeral Head may be attributed to a range of factors including dybaric conditions, alcohol consuption, corticosteroid use and Sickle-Cell Anemia, typically with their own mechanism of compromising blood-flow (SOURCE-26).

Crystaline Arthropathies, or crystal-induced arthritis, describe the process of Bone degeneration related to the abnormal deposition of crystals in bone and soft-tissue, with various conditions affecting distinct structures with distinct crystals. Of these conditions,Hydroxyapatite Deposition Disease (HADD)most commonly affects The Shoulder Girdle where Calcium Hydroxyapatite is deposited in the peri-articular Tendons near their bony attachment (SOURCE-29). One such example is Calcific Tendonitis in the Rotator Cuff , which may be idiopathic or occur secondary to certain diseases (SOURCE-29). Another considerably less common crystaline condition to affect the shoulder is Gout, where monosodium urate crystals are formed within the synovial fluid (SOURCE-30). Irrespective of the cause, calcific deposits are thought to abrade neighbouring soft-tissues or Bursa which incites an acute Inflammation response and associated Pain / symptoms (SOURCE-29).

Pathology

The following lists conditions that solely or primarily affect the Glenohumeral Joint, for an extensive list of pathologies that affect The Shoulder Girdle , see its respective page.

Rotator Cuff :

  • Rotator Cuff Strain or Tear - said to be one of the most common pathologies of the shoulder with a prevalence of ~22% and asymptomatic tears more common that symptomatic ones (SOURCE-7+8)

  • Rotator Cuff Tendinopathy - Point and annual prevalence of (2.4% - 21%) and (0.5% - 7.4%), respectively in general population (SOURCE-6)

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-16 (65, 37)).

Glenoid Labrum Tear - compromises the stability of the “socket-like” Glenoid Fossa which accepts the Head of Humerus , most often resulting in instability (SOURCE-15):

  • SLAP Lesion - accounts for 4-8% of all shoulder pathologies (SOURCE-5)

  • Bankart Lesion - anterioinferior Tear where the Labrum and Capsule become detached, highly associated with instability (SOURCE-18)

Glenohumeral Instability - while anterior instability is most common, can occur in posterior, inferior and multiple directions. Chronic Instability may induce composition changes and impaired performance in the local Connective Tissue and Muscle respectively. In turn these changes may predispose more severe injury:

  • Subluxation - could account for as many 85% of all instability events (SOURCE-4)

  • Glenohumeral Dislocation - most common Dislocation , accounting for almost half of the bodies total dislocations (SOURCE-2). Its estimated annual prevalence is estimated to be 0.17% in the general population (SORUCE-2)

  • Hill-Sachs Lesion - compression defect on the Humerus Head

Osteoarthritis - is reported to be present in ~5-15% of complainants shoulders and believed to be the underlying cause of shoulder Pain in 2-5% of cases (SOURCE-19+21). The prevalence appears to be population specific with Glenohumeral Osteoarthritis reported to be present in the vast majority (~94%) of women over the age of 80 (SOURCE-23).

Adhesive Capsulitis - often reported to have an incidence of 2-5% in the general population; however, this number may be inflated (SOURCE-1). The Glenohumeral Joint is the primary affected joint, with the majority of ranges expected to be restricted, in particular GH Joint - Abduction and GH Joint - External Rotation . The Synovial Membrane that lines the Glenohumeral Joint Capsule secretes ~20-40ml of Synovial Fluid into the joint space. A loss or reduction of this secretion can lead to Contracture s, typically within the Inferior Glenohumeral Ligament and eventually onto Adhesive Capsulitis (SOURCE-9)

Fracture :

Humeral Retroversion - influences the functional Glenohumeral Range of Motion , with greater Retroversion increasing the available GH Joint - External Rotation . This can be an adaptive response to repetitive movements and lead to thickening in the Posterior Glenohumeral Joint Capsule and/ or predispose injury in the Rotator Cuff or Glenoid Labrum .

Referred Pain from:

Assessment

Observation

With detailed observations for each of the Glenohumeral pathologies found on their respective pages, the following lists more common/ pronounced signs that may direct investigation:

Range of Motion

Range of Motion assessment for the Glenohumeral Joint involves Shoulder - Active Range of Motion , where the patient uses their muscles and Shoulder - Passive Range of Motion where the examiner moves the joint for them. When passive range exceeds that of active range, muscular insufficiency is implicated. Conversely when passive range is also restricted, static stabiliser restriction or a mechanical block is suspected. Joint Play forms an important part of the passive assessment of the Glenohumeral Joint as it evaluates joint motion not reproducible by the patient to determine the integrity of the Glenohumeral Joint Capsule and Glenohumeral Capsular Ligaments and mobility of the joint surfaces.

Orthopaedic Tests

For an extensive list of Orthopaedic Tests that can be used to evaluate the Glenohumeral Joint and related tissues/ joints see Shoulder - Special Tests .

Imaging

As imaging findings alone do not consistently correlate with a patients symptoms and findings are often identified in asymptomatic shoulders, they should be complimented by physical examination before reaching a diagnosis and establishing a treatment protocol (SOURCE-54).

Radiography (X-Ray)- often the first line of imaging for shoulder pathologies such as suspected Fractures of the Head of Humerus (SOURCE-55). Additionally useful for visualising Dislocation s, degenerative changes (joint space narrowing, osteophyte formation, periarticular cysts and subchondral sclerosis) and calcification, particularly in the later stages (SOURCE-19+23). As superimposed structures may impede ability to distinguish osseous structures, particular views are recommended for individual structures which are detailed on their respective pages. Unlike many of the other imaging techniques, X-rays are limited in their ability to visualise soft-tissues.

Ultrasonography (Ultrasound)- a highly accessible imaging modaility with real-time capabilities for the evaluation of soft-tissues including the Subacromial Bursa , Rotator Cuff and their Tendons . A major limitation of this modaility is that it is highly operator dependent.

Magnetic Resonance Imaging (MRI)- with the capacity for Bone and Soft-Tissue to be implicated in shoulder pathology, 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-56).

  • Proton Density Weighted Images (PD)- localise bone and soft-tissue pathology at the same time. The high water content in inflamed tissue causes this tissue to appear white (SOURCE-56)

Computed Tomography (CT) Scan- akin to MR-arthrography, used most often for the evaluation of Cartilage or the Glenoid Labrum (SOURCE-54). Typically reserved as a complement to other imaging modalities for the assessment of bony changes or when MRI’s are contraindicated (SOURCE-54). CT-Scans also have value for fracture classification and preoperative planning, particularly when a shear component is present (SOURCE-57+58). In particular CT-Scans may provide a better visualisation of subchondral fractures when compared to an MRI (SOURCE-26)

Dual X-Ray Absorptiometry (DEXA)- is considered the gold-standard for the evaluation of Bone Mineral Density which serves a marker for Osteoporosis (SOURCE-59+60)

Treatment

General treatment techniques for the Glenohumeral Joint are listed below. For more detailed procedures tailored to the specific pathology, see their respective pages.

Stretching

Stretching of the Glenohumeral Joint and neighbouring structures may be relevant in the treatment of certain joint pathologies, with appropriate techniques determined by the specific pathology and the presence of hypertonic Muscle s:

Simple:

Intermediate:

Advanced:

Strengthening

While many listed exercises may be progressed through load or time under tension, the following details movements in approximate order of most rudimentary to sophisticated that are relevant to the Glenohumeral Joint and the pathologies its subject to.

Initial Phase - typically used in the early phases of (p)rehabilitation to mitigate Muscle atrophy, provoke activity and cue appropriate joint motion:

Mid-Phase - simple strength exercises that may be relevant once Pain -free motion is achieved:

Late Phase - exercises at this stage should more closely reflect the activities/ demands of the patient. Relevant functional patterns should be promoted and exercises should be progressed in complexity and intensity:

Mobilisations

Through promoting appropriate joint arthrokinematics Mobilisations have been shown to be an effective treatment modality for many shoulder pathologies, often improving dysfunctional markers such as Pain , Range of Motion and Strength or functional deficits. For the Glenohumeral Joint specifically, mobilisations may be applied directly to the joint or to related structures such as the Scapulothoracic Joint , Cervical Spine or Thoracic Spine .

Joint Play - passive accessory movements performed without active movement

Mobilisation with Movement - the following Mulligan’s techniques may be relevant for conditions of the Glenohumeral Joint:

Dry Needling

The following tissues related to the Glenohumeral Joint have Dry Needling techniques detailed on their respective pages:

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