Introduction[edit | edit source]

The shoulder complex is the connection of the upper arm and the thorax. Comprising numerous ligamentous and muscular structures, composed of the clavicle, scapula, humerus and sternum, and an intricately designed combination of four joints, the Glenohumeral (GH) Joint, the Acromioclavicular (AC) Joint and the Sternoclavicular (SC) Joint, and a "floating joint", known as the Scapulothoracic (ST) joint. The shoulder allows for a large range of motion due to the spheroid shape of the glenohumeral joint but this (i.e. a large ball in a small socket) renders it prone to dislocation and other injuries.[1]

1. anatomical neck of humerus 2. greater tuberosity 3. lesser tuberosity 4. surgical neck of humerus 5. humeral shaft 6. humeral head 7. glenoid fossa 8. acromion 9. acromioclavicular joint 10. coracoid process 11. clavicle 12. superior angle of scapula 13. medial border of scapula 14. inferior angle of scapula 15. lateral border of scapula 16. scapula

Freedom of Movement[edit | edit source]

Shoulder: freedom of movement

The GH, AC and SC joints link the upper extremity to the axial skeleton at the thorax. The ST joint allows for the scapula to glide over the contours of the posterior thoracic wall. All four joints work collectively together to achieve normal shoulder girdle movements. [2] Movements of the shoulder complex represent a complex dynamic relationship between muscle forces, ligament constraints, and bony articulations. The articular structures of the shoulder complex, in particular the GH Joint, are designed primarily for mobility, allowing us to move and position the hand through a wide range of space, allowing the greatest range of motion of any joint in the body.[2] [3]

The freedom of movement has been developed at the expense of stability (commonly known as the mobility-stability trade-off), and it is these competing mobility and stability demands, combined with an intricate structural and functional design, which makes the shoulder complex highly susceptible to dysfunction and instability (ultimately to injury). The shoulder demonstrates a unique functional balance between mobility and stability through active forces, known as Dynamic Stabilisation, which is the reliance on active forces or dynamic muscular control rather than passive stabilisation through passive forces such as articular surface configuration, capsule, or ligaments. Thus within the shoulder complex, it is muscle forces which serve as the primary mechanism for securing the shoulder girdle to the thorax and providing a stable base of support for upper extremity movements. [2] [3]


Anatomy[edit | edit source]

Osteology[edit | edit source]

The osseous segments of the shoulder complex comprise of the clavicle, scapula (shoulder blade), the humerus and the sternum (the link to the thoracic cage).

Joints[edit | edit source]

Shoulder Joint Articulations

In all, there are four major articulations associated with the Shoulder Complex involving the sternum, clavicle, ribs, scapula, and humerus, which work together to provide large ranges of motion to the upper extremity in all three planes of motion. Movement at the Shoulder Complex occurs as a result of movement at each of these four joints, listed below.

  1. Glenohumeral Joint,
  2. Acromioclavicular Joint
  3. Sternoclavicular Joint
  4. Scapulothoracic Joint

The interplay of 4 articulations (Glenohumeral Joint, Acromioclavicular Joint, Sternoclavicular Joint and Scapulothoracic Joint) of the shoulder complex, results in a coordinated movement pattern of the arm elevation. The involved movements at each joint are continuous, although occurring at various rates and at different phases of arm elevation.  

Bursae[edit | edit source]

A bursa is a synovial fluid-filled sac, which acts as a cushion between tendons and other joint structures. In the shoulder region, we have 8 bursae, the most of any single joint in our body. The bursae have both a nerve supply and mechanoreceptors which aid proprioceptive information of shoulder joint position. [5] This shows that bursae don’t strictly function as a lubricator between tissues. The upper limits of the bursae are the coracoacromial ligament, acromion bone and the deltoid. The lower limits are the humeral head, the shoulder joint and the supraspinatus.[6]

1. Subacromial-subdeltoid bursa 2.Subscapular recess 3. Subcoracoid bursa 4. Coracoclavicular bursa 5. supraacromial bursa. 6 medial extension of subacromial-subdeltoid bursa
  • Subscapular Bursa or the Scapulothoracic Bursa: between the tendon of the subscapularis muscle and the shoulder joint capsule.
  • Subdeltoid Bursa: between the deltoid muscle and the shoulder joint cavity.
  • Subacromial Bursa: below the acromion process and above the greater tubercle of the humerus. 
  • Subcoracoid Bursa: between the coracoid process of the scapula and the shoulder joint capsule.
  • Infraspinatus Bursa: between the infraspinatus tendon and the capsule of the joint.
  • Subcutaneous Acromial Bursa: is located above the acromion just beneath the skin.

The Subacromial and the Subdeltoid Bursa are often taken as a single bursa, the Subacromial Deltoid Bursa. [7]

Soft Tissue: Static & Dynamic[edit | edit source]

The shoulder complex is comprised of an impressive amount of soft tissue. Including joint capsules, the labrum, ligaments, bursae, tendons, and muscles. Due to the high mobility of the shoulder complex, it relies on the coordination of both static (non-contractile, for example, ligaments) and dynamic (contractile, for example, tendons and muscles) tissues, for it' stability.

Shoulder stability is achieved through the interplay of both static and dynamic stabilisers, which work in synchrony to maintain shoulder stability during movements of the shoulder. Understanding the complex interplay between these static and dynamic components are key for effective assessment and management of shoulder conditions.

Static: Non-Contractile[edit | edit source]

Articular Surfaces and Bony Geometry[edit | edit source]

The bony geometry of the glenohumeral joint is conducive to excessive joint mobility but sacrifices osseous stability. It is thicker at the periphery and provides the foundation for the concavity-compression effect of Rotator Cuff Muscles.

Glenoid Labrum[edit | edit source]

The Glenoid labrum is a fibrocartilaginous, ridge-like connective tissue which increases articular surface area for the humeral head by deepening the glenoid fossa.  It provides the primary attachment for the glenohumeral ligaments and gives rise to the long head biceps tendon, capsule, and scapular neck. It conforms to the curvature of the humeral head and as such contributes to approximately 50% of the depth of the shoulder joint. Stretches out anteriorly with external rotation, stretches out posteriorly with internal rotation. A loss of labrum integrity has been shown to decrease the resistance to the translation by 20%

Joint Capsule[edit | edit source]

The joint capsule that surrounds the glenohumeral joint is also an important passive stabilizer of the shoulder joint. The glenohumeral joint capsule is thickened at the front of the capsule and is twice the size of the humeral head. It provides most of its extensibility anteriorly and inferiorly and it “Winds up” during abduction and external rotation. The joint capsule and glenohumeral ligaments are intimately adherents anatomically and mainly function as stabilizers at the extremes of motion. This static end-range stabilization is very important when all other stabilizing mechanisms are overwhelmed. The joint capsule has an inherent negative intra-articular pressure that holds the joint together.

Ligaments[edit | edit source]

Ligaments of the shoulder anterior aspect Primal.png

Glenohumeral Ligaments[edit | edit source]

Illustration of glenohumeral ligaments lateral view Primal.png

There are 3 main ligaments in the glenohumeral joint:

  1. Superior Ligament limits ER and inferior translation of the humeral head and parallels the course of the coracohumeral ligament.
  2. Middle Ligament limits ER and Anterior Translation at 45° of Abduction.
  3. Inferior Ligament is the thickest of the ligaments and consists of 3 different portions: anterior band, posterior band, and the axillary pouch

Coracohumeral Ligament

Covers the superior glenohumeral joint anteriorly-superiorly, and fills the space between the tendons of the Supraspinatus and Subscapularis Muscles, uniting these tendons. Limits anterior and inferior translation at lower levels of elevation, extension, and extension with adduction (Izumi et al 2011)

Coracoacromial Ligament

Consists of a strong triangular band, extending between the coracoid process and the acromion, that together with these structures, forms a vault for the protection of the head of the humerus.

Dynamic Musculature: Contractile[edit | edit source]

The dynamic stabilisers of the shoulder complex include the active, contractile tissues. This includes the rotator cuff muscles, the deltoid muscles, the scapular muscles, which control the scapulohumeral rhythm and the associated sensorimotor system involved with proprioception (joint position sense, kinaesthesia (sense of movement), sense of force, sense of vibration and sense of velocity). For optimal shoulder stabilization, the dynamic stabilizers must function in an efficient synergistic fashion. These dynamic stabilisers assist with the maintenance of the central position of the humeral head within the glenoid fossa during movement.[8] The deltoid muscle is a powerful abductor and elevator of the shoulder joint. However, it’s the line of pull in isolation means it draws the head of the humerus superiorly upwards towards the coracoacromial arch. It is essential that the rotator cuff muscles (infraspinatus, teres minor, supraspinatus and subscapularis) activate in synergy with the deltoid during overhead activities to pull the humeral head inferiorly or downwards and upward drift of the humerus. Dynamic stabilization results in a wide range of mobility for the shoulder complex and provides adequate stability when the complex is functioning normally.  

Dynamic stability occurs as a result of three key factors: [9]

  1. Resistance to translation from opposite side pull of muscles;
  2. Support of same side structures through muscle stiffness/capsular tensioning;
  3. Synergistic force coupling for an efficiently controlled axis of rotation/motion.

There are an impressive array of muscles which attach and act on the four joints of the shoulder complex. They include:

  1. Infraspinatus
  2. Supraspinatus
  3. Teres minor
  4. Subscapularis
  5. Teres major
  6. Deltoid muscle (anterior / middle / posterior)
  7. Serratus anterior
  8. Subclavius
  9. Pectoralis minor
  10. Pectoralis major
  11. Sternocleidomastoid
  12. Levator scapulae
  13. Triceps (3 heads)
  14. Biceps brachii (long head / short head)
  15. Coracobrachialis
  16. Rhomboid major
  17. Rhomboid minor
  18. Trapezius (upper / middle / lower)
  19. Latissimus dorsi

Intrinsic muscles: Known as the scapulohumeral muscular group, are deeper muscles which originate from the scapula and /or the clavicle and insert on the humerus.

Extrinsic muscles are larger, more superficial muscles originate on the thorax and attach to the bones of the shoulder complex (the humerus, clavicle and scapula).

There are also other muscles that act on the shoulder joint, which act as secondary movers. They are generally in the pectoral area of the body or the upper arm.

Video[edit | edit source]


Primary Dynamic Stabilisers[edit | edit source]

  • Rotator Cuff Muscles (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis). While these muscles have quite a small cross-sectional area and size, are closer to the centre of rotation on which they act, with a short lever arm, and generate small forces, they play a major role in the dynamic stabilisation of the shoulder.  They also blend with the joint capsule which also assists to reinforce the joint capsule.
  • Long Head of Biceps
  • The Deltoid function includes prevention of subluxation or dislocation of the head of the humerus particularly when carrying a load and is the prime mover in shoulder abduction.

Secondary Dynamic Stabilisers[edit | edit source]

  • Teres Major is a small muscle that runs along the lateral border of the scapula. It forms the inferior border of both the triangular space and quadrangular space. It's sometimes called "lat's little helper" because of its synergistic action with the latissimus dorsi.[11]
  • Latissimus Dorsi whose name means “broadest muscle of the back,” is one of the widest muscles in the human body. Also known as the “lat,” it is a very thin triangular muscle that is not used strenuously in common daily activities but is an important muscle in many exercises such as pull-ups, chin-ups, lat pulldowns, and swimming.[12]
  • Pectoralis Major is a thick, fan-shaped muscle, situated at the chest which makes up the bulk of the chest muscles and lies under the breast.

Scapulohumeral Rhythm[edit | edit source]

The actions of the shoulder are paired with actions of the scapula. This serves to both increase the available range of motion of the upper extremity and allows the glenoid fossa to be positioned in a more stable position in relation to the humeral head. Scapulohumeral rhythm is the kinematic interaction between the scapula and the humerus, first published by Codman in the 1930s. [13] This interaction is important for the optimal function of the shoulder. [14]  Scapulohumeral rhythm or ratio is significantly greater (less scapular motion and more humeral motion) in the sagittal plane than other planes. Consistent with the findings, the dominant side demonstrates significantly higher values for SH rhythm than the non-dominant side but only in the coronal and scapular planes. [15]

The scapulohumeral rhythm is therefore defined as the ratio of the glenohumeral movement to the scapulothoracic movement during arm elevation. This is most often calculated by dividing the total amount of shoulder elevation (humerothoracic) by the scapular upward rotation (scapulothoracic). [16] In the literature Scapulohumeral rhythm is described as a ratio of humeral elevation: scapulothoracic rotation. The overall ratio of 2:1 during arm elevation is commonly used. According to the 2-to-1 ratio frame-work, flexion or abduction of 90° in relation to the thorax would be accomplished through approximately 60° of GH and 30° of ST motion. [17]

Scapulohumeral rhythm is a common metric for assessing muscle function and shoulder joint motion.[18] There is a three-dimensional scapular kinematic pattern during normal arm elevation that includes upward rotation, posterior tilting and varying internal/external rotation dependent on the plane and angle of elevation. [13] [14] When there is a change of the normal position of the scapula related to the humerus, this can cause dysfunction of the scapulohumeral rhythm, often referred to as scapular dyskinesia.

A 2022 study of male students, aged 18-25, found a significant correlation between an existing thoracic kyphosis with scapular upward rotation and scapulohumeral rhythm ratio. This correlation highlights the importance of proper spinal alignment in the prevention of shoulder joint disorders.[19]

Clinical Examination[edit | edit source]

  • Clinical Prediction Rules (CPR) for Cervico-Thoracic Manipulation

Outcome Measures[edit | edit source]

Conditions[edit | edit source]

Procedures[edit | edit source]

  • Acromioclavicular Joint Stabilisation (Weaver Dunn)
  • Anterior Inferior Capsular Shift
  • Arthroscopic Capsular Release
  • Arthroscopic Posterior Stabilisation
  • Arthroscopic Subacromial Decompression
  • Open Bankart Repair
  • Arthroscopic Bankart Repair
  • Biceps Tenodesis
  • Biceps Tenotomy
  • Bipolar Hemiarthroplasty
  • Capsular Shrinkage
  • Excision of the Acromioclavicular Joint Arthroscopic
  • Excision of the Lateral End of the Clavicle
  • Hemiarthroplasty
  • Long Thoracic Nerve Release
  • Manipulation Under Anaesthetic
  • Release of the Coraco-Humeral Ligament Arthroscopic
  • Rotator Cuff Debridement
  • Rotator Cuff Repair
  • Shoulder Fracture Fixation
  • Shoulder Resurfacing Arthroplasty
  • SLAP Repair Arthroscopic
  • Open Subacromial decompression
  • Total Shoulder Replacement Rotator Cuff Intact
  • Total Shoulder Replacement Rotator Cuff Repair

Interventions[edit | edit source]

References[edit | edit source]

  1. Radiopedia Shoulder Joint Available: (accessed 14.4.2022)
  2. 2.0 2.1 2.2 Levangie PK, Norkin CC. Joint structure and function: a comprehensive analysis.
  3. 3.0 3.1 Veeger HE, Van Der Helm FC. Shoulder function: the perfect compromise between mobility and stability. Journal of biomechanics. 2007 Jan 1;40(10):2119-29.
  4. Randale Sechrest. Shoulder Anatomy Animated Tutorial. Available from: [last accessed 13/01/2021]
  5. Hsieh LF, Hsu WC, Lin YJ, Wu SH, Chang KC, Chang HL. Is ultrasound-guided injection more effective in chronic subacromial bursitis?. Medicine & Science in Sports & Exercise. 2013 Dec;45(12):2205-13.
  6. Conduah AH, Baker III CL, Baker Jr CL. Clinical management of scapulothoracic bursitis and the snapping scapula. Sports Health. 2010 Mar;2(2):147-55.
  7. Hitzrot JM. Surgical diseases of the shoulder bursae. Annals of surgery. 1933 Aug;98(2):273.
  8. Guerrero P, Busconi B, Deangelis N, Powers G. Congenital instability of the shoulder joint: assessment and treatment options. journal of orthopaedic & sports physical therapy. 2009 Feb;39(2):124-34.
  9. Wilk KE, Arrigo CA, Andrews JR. Current concepts: the stabilizing structures of the glenohumeral joint. Journal of Orthopaedic & Sports Physical Therapy. 1997 Jun;25(6):364-79.
  10. Kenhub - Learn Human Anatomy. Shoulder joint: Movements, bones and muscles - Human Anatomy. Available from: [last accessed 14/01/2021]
  11. Biel A (2005). Trail Guide to the Body (2nd ed). Boulder, CO: Books of Discovery.
  12. Heydemann A. Severe murine limb‐girdle muscular dystrophy type 2C pathology is diminished by FTY720 treatment. Muscle & nerve. 2017 Sep;56(3):486-94.
  13. 13.0 13.1 Codman EA: The Shoulder,Boston: G.Miller &amp Company,1934
  14. 14.0 14.1 Ben Kibler W. The role of the scapula in athletic shoulder function. The American journal of sports medicine. 1998 Mar;26(2):325-37.
  15. Barnes CJ, Van Steyn SJ, Fischer RA. The effects of age, sex, and shoulder dominance on range of motion of the shoulder. Journal of Shoulder and Elbow Surgery. 2001 May 1;10(3):242-6.
  16. Struyf F, Nijs J, Baeyens JP, Mottram S, Meeusen R. Scapular positioning and movement in unimpaired shoulders, shoulder impingement syndrome, and glenohumeral instability. Scandinavian journal of medicine & science in sports. 2011 Jun;21(3):352-8.
  17. Inman B, Saunders J, Abbott L: Observations of the function of the shoulder joint. J Bone Joint Surg Br 2004; 26:1. Level of Evidence: 4.
  18. McQuade KJ, Smidt GL. Dynamic scapulohumeral rhythm: the effects of external resistance during elevation of the arm in the scapular plane. Journal of Orthopaedic & Sports Physical Therapy. 1998 Feb;27(2):125-33.
  19. Hosseinimehr SH, Anbarian M. The Relationship between Thoracic Kyphosis with Scapular Upward Rotation and Scapulohumeral Rhythm Ratio. medical journal of mashhad university of medical sciences. 2022 Jul 23;65(3).