Week 9: Upper limb analysis

Primary role of the shoulder girdle

Provides a stable but mobile base so the hand can be placed, grasp, lift, push, and manipulate objects effectively.

Secondary functions of the shoulder girdle

Assists forced inspiration/expiration and can elevate the body (e.g., during crutch walking).

Three bony articulations of the shoulder girdle

Sternoclavicular (SC), acromioclavicular (AC), and glenohumeral (GH) joints.

Functional articulation of the shoulder girdle

Scapulothoracic joint (scapula moving over the thoracic cage).

Unique characteristic of the sternoclavicular (SC) joint in the skeletal system

It is the only bony connection between the entire upper limb and the trunk.

Structural classification of the sternoclavicular (SC) joint

Saddle-shaped synovial joint with fibrocartilage.

Primary source of stability for the sternoclavicular (SC) joint

Strong ligamentous and capsular support (rather than bony congruence).

Resting (open-pack) position of the sternoclavicular (SC) joint

Arm by the side.

Closed-pack position of the sternoclavicular (SC) joint

Full shoulder-girdle elevation.

Capsular pattern of the sternoclavicular (SC) joint

Pain at extremes of shoulder elevation and horizontal adduction.

Accessory glide used to assess or mobilise the sternoclavicular (SC) joint

Anterior-to-posterior (AP) glide of the clavicle relative to the sternum.

Movements occurring at the sternoclavicular (SC) joint

Clavicular elevation/depression, protraction/retraction, and anterior/posterior rotation.

Bony structures forming the acromioclavicular (AC) joint

Flattened lateral end of the clavicle and the acromion of the scapula.

Structural classification of the acromioclavicular (AC) joint

Plane synovial joint with fibrocartilage.

Role of the acromioclavicular (AC) joint during shoulder elevation

Allows the shoulder girdle to move through ranges greater than about $100^\bullet$.

Primary stabilising structures of the acromioclavicular (AC) joint

Coracoclavicular ligament, superior and inferior AC ligaments, and joint capsule.

Two divisions of the coracoclavicular ligament

Conoid and trapezoid ligaments.

Deformity resulting from severe coracoclavicular ligament injury

Step deformity, caused by elevation of the clavicle relative to the acromion.

Resting (open-pack) position of the acromioclavicular (AC) joint

Arm by the side.

Closed-pack position of the acromioclavicular (AC) joint

Shoulder abduction to $90^\bullet$.

Capsular pattern of the acromioclavicular (AC) joint

Pain at extremes of shoulder elevation and horizontal adduction.

Structural classification of the glenohumeral (GH) joint

Multiaxial ball-and-socket synovial joint.

Anatomical reason for high mobility at the glenohumeral (GH) joint

Minimal bony containment of the humeral head by the shallow glenoid.

Anatomical cause of relative instability at the glenohumeral (GH) joint

Limited bony congruence, requiring reliance on passive and dynamic stabilisers.

Primary functions of the glenoid labrum

Deepens the glenoid, increases contact area, and improves joint stability.

Role of intra-articular negative pressure in the glenohumeral (GH) joint

Creates a suction effect holding the humeral head against the glenoid.

Clinical consequence of damage to the glenohumeral (GH) capsule

Loss of joint stability and increased risk of recurrent dislocation.

Main passive stabilisers of the glenohumeral (GH) joint

Joint capsule, glenohumeral ligaments, coracohumeral ligament, coracoacromial arch, labrum, and intra-articular negative pressure.

Main dynamic stabilisers of the glenohumeral (GH) joint

Rotator cuff muscles and the long head of biceps brachii.

Four muscles constituting the rotator cuff

Supraspinatus, infraspinatus, teres minor, and subscapularis.

Resting (open-pack) position of the glenohumeral (GH) joint

About $35^\bullet \text{--} 55^\bullet$ abduction in the scapular plane (scaption) with slight horizontal adduction.

Closed-pack position of the glenohumeral (GH) joint

Full abduction with external rotation.

Capsular pattern of limitation at the glenohumeral (GH) joint

External rotation is most limited, followed by abduction, then internal rotation.

Biomechanical reason external rotation is required for full shoulder abduction

Clears the greater tubercle from beneath the acromion to avoid bony impingement.

Accessory glides used to assess or mobilise the glenohumeral (GH) joint

• AP glide: a small push from the front toward the back, moving the humeral head backwards relative to the socket.

• Lateral distraction: a gentle pull that draws the humeral head straight out from the socket, across the joint space.

• Longitudinal distraction: a gentle pull along the length of the arm, away from the shoulder socket—roughly down the arm.

Structural classification of the scapulothoracic joint

Functional sliding articulation rather than a true anatomical bony joint.

Movements occurring at the scapulothoracic joint

Elevation/depression, protraction/retraction, upward/downward rotation, internal/external rotation, and anterior/posterior tilt.

Scapulohumeral rhythm

Coordinated kinematic movement between the glenohumeral and scapulothoracic joints during arm elevation.

Scapular-setting phase

Initial $\thicksim 30^\bullet$ of shoulder abduction, where movement occurs primarily at the GH joint.

GH to ST ratio after the initial setting phase

Approximately $2:1$ (2 degrees of GH movement for every 1 degree of scapulothoracic movement).

Kinematic movement of the clavicle during shoulder elevation

Elevates initially, then rotates posteriorly as elevation continues.

Three joints comprising the elbow complex

Ulnohumeral, radiohumeral, and superior (proximal) radioulnar joints.

Structural classification of the ulnohumeral and radiohumeral joints

Synovial hinge joints.

Structural classification of the superior radioulnar joint

Synovial pivot joint.

Primary movements occurring at the superior radioulnar joint

Pronation and supination of the forearm.

Primary stabilisers of the proximal radioulnar joint

Annular ligament and interosseous membrane.

Primary factor limiting full elbow flexion

Soft-tissue bulk.

Primary factor limiting elbow extension

Bony approximation/articulation.

Primary ligament resisting valgus stress at the elbow

Medial (ulnar) collateral ligament.

Primarhy muscle of elbow flexion?

Brachialis.

Reason brachialis serves as the primary workhorse of elbow flexion

Flexes the elbow effectively regardless of forearm position (pronation or supination).

Forearm position in which biceps brachii is most effective as an elbow flexor

Supination.

Forearm position in which brachioradialis is most effective as an elbow flexor

Mid-position between pronation and supination.

Primary muscles producing forearm pronation

Pronator teres and pronator quadratus.

Primary muscles producing forearm supination

Biceps brachii and supinator.

Four carpal bones of the proximal row

Scaphoid, lunate, triquetrum, and pisiform.

Four carpal bones of the distal row

Trapezium, trapezoid, capitate, and hamate.

Midcarpal joint

Articulation between the proximal and distal rows of carpal bones.

Key passive structures providing stability to the wrist and carpal bones

Intercarpal ligaments, transverse carpal ligament (flexor retinaculum), and surrounding capsuloligamentous structures.

Anatomical side of the wrist where the TFCC is located

Ulnar side.

Primary function of the triangular fibrocartilaginous complex (TFCC)

Stabilises the distal radioulnar joint and the ulnar side of the wrist.

Thumb opposition

Combined movement bringing the thumb across the palm toward the fingers, involving abduction and rotation.

Structural classification of the first carpometacarpal (CMC) joint

Saddle joint.

Primary stabilisers of the thumb MCP joint

Radial collateral ligament, ulnar collateral ligament, and volar plate.

Skier's thumb

Injury to the ulnar collateral ligament of the thumb MCP joint, typically caused by a valgus force.

Common term for metacarpophalangeal (MCP) joints

Knuckles.

Structural classification of the finger metacarpophalangeal (MCP) joints

Biaxial ellipsoid joints (capable of flexion/extension and abduction/adduction).

Structural classification of interphalangeal (PIP and DIP) joints

Synovial hinge joints.

Power grip

Grasping pattern where the thumb is adducted to hold an object against curled fingers (e.g., holding a hammer).

Precision grip

Grasping pattern where the thumb is abducted and opposed to one or more fingers (e.g., picking up a coin).

Prehension

The general term for gripping, grasping, or manipulating objects with the hand.

Functional wrist position required for maximum grip strength

About $20^\bullet \text{--} 30^\bullet$ wrist extension, with slight finger flexion and about $45^\bullet$ thumb abduction.

Biomechanical cause of reduced grip strength during wrist flexion

Finger flexors undergo active insufficiency (over-shortened) and finger extensors undergo passive insufficiency (over-stretched).

Mechanism by which radial nerve injury impairs functional grip

Paralyses wrist extensors, preventing the wrist from reaching optimal extension required for effective finger flexor force.

Functional benefit of a wrist splint for wrist drop

Holds the wrist in extension, allowing the finger flexors to generate an effective grip without active insufficiency.