Joints of the Upper Limb

Shoulder Joint Complex

Introduction and Components

Shoulder joint movement occurs through the integrated action of three distinct joints:

  • Sternoclavicular Joint
  • Glenohumeral Joint
  • Scapulothoracic Movement

Sternoclavicular Joint

  • Classification: It is categorized as a synovial double-plane joint.
  • Articulation: Occurs between the sternal end of the clavicle, the manubrium sterni, and the first costal cartilage.
  • Innervation: Provided by the supraclavicular nerve and the nerve to the subclavius muscle.
  • Anatomical Structure:     1. Capsule     2. Ligaments     3. Articular disc     4. Synovial membrane

Acromioclavicular Joint

  • Classification: A synovial plane joint.
  • Articulation: Occurs between the acromion of the scapula and the lateral end of the clavicle.
  • Innervation: Provided by the suprascapular nerve.
  • Anatomical Structure:     1. Capsule     2. Ligaments: Superior and inferior acromioclavicular ligaments.     3. Accessory Ligament: Coracoclavicular ligament.     4. Disc: Fibrocartilaginous disc.     5. Synovial membrane

Glenohumeral Joint

  • Classification: A synovial ball-and-socket joint.
  • Articulation: Occurs between the rounded head of the humerus and the shallow, pear-shaped glenoid cavity of the scapula.
  • Articular Surfaces: Covered with hyaline articular cartilage.
  • Glenoid Labrum: A fibrocartilaginous rim that deepens the glenoid cavity to improve the fit and stability of the humeral head.
  • Innervation: Provided by the axillary and suprascapular nerves.
  • Anatomical Structure:     1. Capsule     2. Ligaments:         * The glenohumeral ligaments (three in total).         * The transverse humeral ligament.         * The coracohumeral ligament.     3. Accessory Ligaments: Coracoacromial ligament.     4. Synovial membrane

Movements of the Glenohumeral Joint

  • Abduction: Involves the middle fibers of the deltoid, assisted by the supraspinatus.
  • Adduction: Performed by the pectoralis major, latissimus dorsi, teres major, and teres minor muscles.
  • Flexion: Produced by the anterior fibers of the deltoid, pectoralis major, biceps, and coracobrachialis muscles.
  • Extension: Produced by the posterior fibers of the deltoid, latissimus dorsi, and teres major muscles.
  • Internal Rotation: Performed by the pectoralis major, latissimus dorsi, teres major, and teres minor muscles.
  • External Rotation: Performed by the infraspinatus, the teres minor, and the posterior fibers of the deltoid muscle.
  • Circumduction: A combination of the above movements.

Scapulohumeral Rhythm and Ratios

Movement at the shoulder involves specific ratios between the glenohumeral joint and the scapulothoracic interface:

  • 0∘0^{\circ} to 30∘30^{\circ} of Abduction: Primarily involves glenohumeral movement.
  • 60∘60^{\circ} of Forward Flexion: Primarily involves glenohumeral movement.
  • Beyond 30∘30^{\circ} of Abduction: The ratio of scapulothoracic to glenohumeral movement is 2:12:1.
  • Beyond 120∘120^{\circ} of Abduction: The ratio is approximately 1:11:1.

Shoulder Ligaments

Intracapsular Ligaments

These consist of three fibrous bands situated between the glenoid labrum and the humerus. They are continuous with the fibrous capsule and provide anterior reinforcement. They are:

  1. Superior glenohumeral ligament
  2. Middle glenohumeral ligament
  3. Inferior glenohumeral ligament
Extracapsular Ligaments
  1. Coracoacromial Ligament: Links the acromion and the coracoid process.
  2. Coracohumeral Ligament: Passes from the base of the coracoid process to the anterior part of the greater tubercle of the humerus.
  3. Transverse Humeral Ligament: Functions to hold the tendon of the long head of the biceps in place during shoulder movement.

Stability Factors of the Shoulder Joint

Stability is provided through a combination of static and dynamic factors:

Static Factors
  • Structural Features: Humeral head and glenoid version, glenoid arc, labrum, glenohumeral ligament and capsule, and the coracohumeral ligament.
  • Functional Features:     * Conformity of articular surfaces.     * Vacuum Effect: Includes intra-articular pressure, suction effect, and adhesion-cohesion forces.     * Surface area coverage.
Dynamic Factors
  • Structural Features: Scapular rotators, rotator cuff muscles, biceps, and deltoid.
  • Functional Features: Proprioception.
Additional Stability Elements
  • Tendons of the rotator cuff (providing support anteriorly, posteriorly, and superiorly).
  • Coraco-acromial arch (providing superior stability).
  • Splinting effect of the long head of the biceps (above) and the long head of the triceps (below).

Scapulothoracic Movements

  • Protraction (Forward Movement): Produced primarily by the serratus anterior muscle (moving the clavicle forward).
  • Retraction (Backward Movement): Produced by the trapezius and rhomboid muscles.
  • Elevation: Produced by the trapezius (descending/superior part), sternocleidomastoid, levator scapulae, and rhomboid muscles.
  • Depression: Produced by the pectoralis minor, subclavius, inferior trapezius, and latissimus dorsi muscles.
  • Rotation elevating glenoid cavity: Driven by the descending trapezius, inferior trapezius, and inferior part of the serratus anterior.
  • Rotation depressing glenoid cavity: Driven by the levator scapulae, rhomboids, and pectoralis minor.

Elbow Joint Complex

Component Joints

Elbow joint movements occur through three integrated joints:

  1. Humero-ulnar Joint
  2. Radio-capitellar Joint
  3. Proximal Radio-ulnar Joint

Humero-ulnar Joint

  • Classification: Synovial hinge joint.
  • Articulation: Occurs between the trochlea and capitulum of the humerus and the trochlear notch of the ulna and the head of the radius. Articular surfaces are covered with hyaline cartilage.
  • Innervation: Branches from the median, ulnar, musculocutaneous, and radial nerves.
  • Structure: Capsule, synovial membrane, and ligaments (Medial [3 bands] and Lateral).
  • Movements: Flexion and Extension.
  • Carrying Angle: Defined as the angle between the long axis of the extended forearm and the long axis of the arm.

Radio-capitellar Joint

  • Articulation: Formed by the radial head (radius bone) articulating with the capitellum (rounded end of the humerus).
  • Function: Allows for forearm rotation (pronation/supination) and contributes to flexion/extension.
  • Stability: The annular ligament stabilizes the radial head against the ulna within the common elbow joint capsule.

Proximal Radio-Ulnar Joint

  • Classification: Synovial pivot joint.
  • Articulation: Between the circumference of the head of the radius, the annular ligament, and the radial notch on the ulna.
  • Innervation: Branches of the median, ulnar, musculocutaneous, and radial nerves.
  • Function: Responsible for pronation and supination of the forearm.
  • Structure: Capsule, Annular ligament, and synovial membrane.

Wrist and Hand Joints

Wrist Joint Complex

Wrist movement occurs through two primary joints:

Distal Radio-Ulnar Joint (DRUJ)
  • Classification: Pivot type of synovial joint.
  • Mechanism: The radius moves around the relatively fixed distal end of the ulna.
  • Exclusion: The ulna is excluded from the joint by an articular disc.
  • Innervation: Anterior interosseous nerve and the deep branch of the radial nerve.
  • Structure: Capsule, ligaments, articular disc, and synovial membrane.
Radio-Carpal Joint (RCJ)
  • Classification: Synovial ellipsoid (condyloid) joint.
  • Articulation: Lies between the distal end of the radius and the articular disc above, and the scaphoid, lunate, and triquetral bones below.
  • Innervation: Anterior interosseous nerve and the deep branch of the radial nerve.
  • Movements: Flexion, extension, abduction (radial deviation), adduction (ulnar deviation), and circumduction.
  • Structure:     * Capsule: Attached to distal radius, ulna, and proximal carpal row.     * Ligaments: Anterior, posterior, medial (ulnar collateral), and lateral (radial collateral).     * Synovial membrane

Hand Joints Classification and Articulations

Intercarpal Joints (ICJ)
  • Type: Plane synovial joint.
  • Articulation: Between carpal bones of the proximal row and joints between carpal bones of distal row.
  • Midcarpal Joint: Synovial joint between proximal and distal rows of carpal bones; allows flexion and abduction of the hand.
  • Pisiform Joint: Separate synovial joint between the pisiform and triquetrum.
  • Ligaments: Carpal bones are united by anterior, posterior, and interosseous ligaments.
Carpometacarpal (CMC) and Intermetacarpal (IM) Joints
  • General CMC/IM: Plane synovial joints.
  • CMC of Thumb (1st Digit): A specialized Saddle-shaped synovial joint between the trapezium and the base of the first metacarpal bone.
  • Thumb CMC Movements:     * Flexion: Flexor pollicis brevis and opponens pollicis.     * Extension: Extensor pollicis longus and brevis.     * Abduction: Abductor pollicis longus and brevis.     * Adduction: Adductor pollicis.     * Rotation (Opposition): The thumb is rotated medially by the opponens pollicis.
  • Mobility of Digits 2-5:     * 2nd and 3rd: Almost no movement.     * 4th: Slightly mobile.     * 5th: Very mobile.
Metacarpophalangeal Joints (MCP)
  • Type: Synovial condyloid joints.
  • Articulation: Heads of metacarpals with the bases of proximal phalanges.
  • Innervation: Digital nerves from ulnar and median nerves.
  • Ligaments:     * Strong palmar ligaments.     * Deep transverse metacarpal ligaments (unite 2nd-5th joints, holding metacarpal heads together).     * Collateral ligaments (pass from heads of metacarpals to bases of phalanges).
  • Movements: Flexion-extension, abduction-adduction, and circumduction (restricted in the thumb).
Interphalangeal Joints (IPJ)
  • Type: Synovial hinge joints.
  • Articulation: Heads of phalanges with bases of more distally located phalanges.
  • Innervation: Digital nerves from ulnar and median nerves.
  • Movements: Flexion and extension.