ELBOW JOINT

 ANATOMY OF ELBOW JOINT

MUSCLES

• Brachialis
• Brachio radialis
• Biceps
• Supinator
• Triceps
• Anconeus
• Pronator teres
• Pronator quadratus

BRACHIALIS MUSCLE

INNERVATION

 Musculocutaneous(C5–C7)

ORIGIN: Distal half of humerus, anterior surface

INSERTION: Coronoid process and ulnar tuberosity of the ulna

ACTION

Flexion, assists with supination

RANGE: 90° to 100° of elbow flexion

 BICEP BRACHI

The bicep brachi muscle has two heads (long head, short head)

ORIGIN

Long head: supraglenoid tubercle of scapula

Short head: coracoid process of scapula

INSERTION:  Radial tuberosity

INNERVATION 

 Musculocutaneous nerve (C5, C6)

ACTION

Elbow flexion, forearm supination

During supination, the biceps muscle contracts and essentially “unwraps” or “untwists” the forearm. It is most effective in supination when the elbow is in approximately 90 degrees of flexion, and it loses its effectiveness as the elbow is extended. This is because the muscle’s moment arm is greatest at 90 degrees; therefore, its angular force is also greatest. As the elbow is extended, the moment arm decreases, as does angular force, and the stabilizing force increases.

RANGE: 90° to 110° of flexion

BRACHIORADIALIS MUSCLE

INNERVATION Radial nerve (C5, C6)

ORIGIN: Lateral supracondylar ridge on the humerus

INERTION: Styloid process of the radius

ACTION Elbow flexion

The brachioradialis muscle is most effective as an elbow flexor when the forearm is in a neutral position. This is because its line of pull is vertical with essentially no diagonal component and goes through the axis for pronation and supination.

RANGE: 100° to 120° of elbow flexion

TRICEP BRACHI MUSCLE

The triceps muscle has three heads

ORIGIN

Long head: infraglenoid tubercle of scapula

Lateral head: inferior to greater tubercle on posterior humerus

Medial head: posterior surface of humerus

INSERTION: Olecranon process of ulna

INNERVATION: Radial nerve (C7, C8)

ACTION: Elbow extension and it has no attachment on the radius, it can play no role in pronation or supination.

RANGE: 70° to 90° of elbow flexion.

ANCONEUS MUSCLE

It is a small muscle and attaches to triceps assisting it in performing function.

INNERVATION: Radial nerve (C7, C8)

ORIGIN: Lateral epicondyle of humerus

 INSERTION: Lateral and inferior to olecranon process of ulna

ACTION: Not a prime mover in any joint action; assists in elbow extension

PRONATOR TERES

INNERVATION: Median nerve (C6, C7)

ORIGIN: Medial epicondyle of humerus and coronoid process of ulna

INSERTION: Lateral aspect of radius at its midpoint

ACTION: Forearm pronation, assistive in elbow flexion

PRONATOR QUADRATUS

It is a small, flat, quadrilateral muscle located deep on the anterior surface of the distal forearm; therefore, cannot be palpated. It attaches from the distal one-fourth of the ulna to the distal one-fourth of the radius. It has a horizontal line of pull, and works with the pronator teres muscle to pronate the forearm.

INNERVATION: Median nerve (C8, T1)

ORIGIN: Distal one-fourth of ulna

INSERTION: Distal one-fourth of radius

ACTION: Forearm pronation

SUPPINATOR

INNERVATION: Radial nerve (C6)

ORIGIN: Lateral epicondyle of humerus and adjacent ulna

INSERTION: Anterior surface of the proximal radius

ACTION: Forearm supination. It combines with the biceps muscle as a prime mover in forearm supination

ELBOW COMPLEX

The elbow complex includes three bones, three ligaments, two joints, and one capsule.

ELBOW JOINT

The articulation of the humerus with the ulna and radius is commonly called the elbow joint

TYPE OF JOINT

The elbow is a uniaxial hinge joint that allows only flexion and extension.

FLEXION

145 degrees of flexion

EXTENSION

0-degree position of extension

RADIOULNAR JOINT

The articulation between the radius and ulna is known as the radioulnar joint

TYPE OF JOINT

 The radioulnar joint is a uniaxial pivot joint, allowing only pronation and supination of the forearm

PRONATION

Measured from the neutral or mid-position, there are approximately 80 degrees of pronation

SUPINATION

Measured from the neutral or mid-position, there are approximately 90 degrees of supination

Humeroulnar Joint

TYPE OF JOINT: The humeroulnar is hinge joint at the elbow.

 ARTICULATION: The humeral trochlea articulates with the trochlear fossa at ulna.

CLOSE-PACK POSITION: The close pack position is Extension.

STABILITY: The join is more stable in close pack position.

MOVEMENTS: Flexion and Extension

Humeroradial Joint

TYPE OF JOINT: The humeroradial joint is Gliding joint

ARTICULATION:  It is formed between the spherical capitellum of the humerus and the proximal end of the radius

MOVEMENTS: Flexion, Extension, Supination

CLOSE PACK POSITION: Flexion at 90° and the forearm is supinated about 5°

CARRYING ANGLE OF ELBOW

The longitudinal axes of the humerus and forearm form an angle called the carrying angle This angle tends to be greater in women than in men. Normal carrying angle measures approximately 5 degrees in males and between 10 and 15 degrees in females.

WHY DOES CARRYING ANGLE OCCUR?

Angle occurs because the distal end of the humerus is not level. The medial side (trochlea) is lower than the lateral side (capitulum). Therefore, as the ulna and radius rotate around the trochlea and capitulum of the humerus, they do not rotate in a straight line like a typical hinge joint, in which the long axis of the lower segment is in line with the long axis of the upper segment.

RANGE The carrying angle ranges from 10° to 15° in adults and tends to be larger in females than in males.

CONCAVE-CONVEX RULE OF ELBOW

The concave-convex rule has the convex joint surface moving in a direction opposite to the movement of the body segment and the concave joint surfacing moving in the same direction as the body segment.

END FEEL AT ELBOW JOINT

FLEXION

With flexion, the end feel is soft because the muscle bulk of the arm and forearm compresses together and limits further motion. This is called soft tissue approximation

EXTENSION

The end feel for extension is just the opposite. It is described as hard due to bone on-bone contact as the olecranon process of the ulna moves into the olecranon fossa of the humerus, limiting further motion. This is called a bony end feel.

SUPINATION

In supination, the end feel is firm because of muscle and ligament tension. This is called soft tissue stretch.

PRONATION

Pronation end feel is hard (bony) due to contact between the radius and ulna. This bony end feel is more subtle than that felt during elbow extension.

MOVEMENTS AT ELBOW

The movements at elbow include Flexion, Extension, Pronation and Supination.

FLEXION

The flexion is initiated by the Elbow flexors (muscle crossing the anterior side of elbow are called elbow flexors). Muscles assisting in elbow flexion are BRACHIALIS (effective when the forearm is in supination or pronation.), BICEP BRACHI (effectively to flexion when the forearm is supinated) and BRACHIORADIALIS (pronation from supinated position to neutral, supination from pronated position to neutral)

EXTENSION

The movement of flexion is initiated by Elbow Extensors (muscle at the posterior side of elbow) The major extensor of elbow is TRICEPS, it has three heads Long head, Lateral head and Medial head. The triceps is effectively working during extension.

PRONATION and SUPINATION

These movements involve the rotation of radius around ulna.  The movements are initiated by three bony articulation of radioulnar joint i.e. proximal, distal, middle radioulnar joint.

PRONATION MUSCLES: The major pronator is the pronator quadratus and pronator teres

SUPINATION MUSCLES: The supinator is the muscle primarily responsible for supination. When the elbow is flexed to 90° or less, the biceps is positioned to serve as a supinator.

Closed Kinematic Chain Motion at the Elbow Complex

  The bony configuration and joint’s ligaments provide the elbow’s stability in full extension, the demand for stability transfers to the joint’s flexor and extensor muscles when the elbow is even slightly flexed these muscle groups contract to provide this stability in a CKC (closed kinematic chain) activity.

ONE JOINT MUSCLE

the brachialis is a one-joint muscle it is recruited before multi joint muscles the brachialis is recruited in all tasks requiring elbow flexion. The body desires efficiency by design and function; it is inefficient to use the biceps brachi if the task simply requires elbow flexion or an isometric contraction with a low load because supination would have to be neutralized by the pronators so additional muscles would have to be recruited for simple elbow flexion

MULTI-JOINT MUSCLE

When the muscle crosses more than one joint it is known as multi-joint muscle and it has effect on each joint side it crosses.

The bicep brachi is Three joint muscle

The triceps and pronator teres are Two joint muscles

ACTIVE INSUFFICIENCY OF MUSCLE

When a muscle contracts to its shortest length, the muscle is at a weakened length since it is at its minimum on the length-tension curve; when this occurs in multi-joint muscles, it is called active insufficiency

Bicep active insufficiency: The biceps is at its point of active insufficiency with full shoulder flexion, elbow flexion, and supination with the palm touching the back of the shoulder. Testing the maximum force of supination in this position compared to when the arm is at the side and the elbow is in 90° of flexion demonstrates the marked loss of biceps force.

Triceps active insufficiency: Active insufficiency of the long head of the triceps occurs at end-range shoulder and elbow extension

Pronator teres active insufficiency:  The pronator teres is actively insufficient with the elbow in flexion and pronation.

LOADS ON ELBOW

The elbow is not a weight bearing joint but does sustain large loads in daily task performed by an individual. some of the activities are listed below such as

Eating and dressing: The elbow sustains a compressive load of 300N and can bears a weight of 67lb.

Standing from chair: the force of 1700N is required

Puling table: 1900N force is required while pulling

COMPRESSIVE FORCE ON ELBOW

The attachment of the triceps tendon to the ulna is closer to the elbow joint center than the attachments of the brachialis on the ulna and the biceps on the radius, the extensor moment arm is shorter than the flexor moment arm. This means that the elbow extensors must generate more force than the elbow flexors to produce the same amount of joint torque. This translates to larger compression forces at the elbow during extension than during flexion when movements of comparable speed and force requirements are executed. Because of the shape of the olecranon process, the triceps moment arm also varies with the position of the elbow, the triceps moment arm is larger when the arm is fully extended than when it is flexed past 90°.