Elbow Joint Anatomy and Biomechanics

• The elbow complex allows hand mobility and provides stability for skilled movements. Humeroulnar, humeroradial, and radioulnar joints are linked to shoulder and wrist function.

Elbow Joint

• The elbow joint is a modified hinge with one degree of freedom. ABD/ADD and rotation are seen in flexion and extension. Flexion and extension occur in the sagittal plane.

Humeroulnar (HU) Joint

• The Trochlea on the humerus articulates with the Trochlear notch of the ulna. Motion is mainly the Trochlear notch sliding on the Trochlea.
  • During flexion, the Ulna slides unit the Coronoid process enters Coronoid fossa during full flexion.
  • During extension, Ulna slides until the Olecranon process enters the Olecranon fossa.
• Full contact between Trochlea and the deepest portion of the Trochlear notch occurs when joint is heavily loaded, but there is no contact between the Trochlea and the deepest portion of Trochlear notch from 30°-120° of elbow flexion when unloaded the contact is primarily on the side of the notch

Humeroradial (HR) Joint

• Concave radial head slides over the convex Capitulum.
  • Rim of the Radial head slides into the radial fossa during full flexion.
  • No contact occurs between the articulating Radial head and Capitulum when the arm is unloaded, especially during full extension.

Radioulnar Joints

• Proximal and distal RU joints function together to rotate the forearm with 1 degree of freedom. (pronation/supination)
  • The proximal RU joint shares a capsule with the HU and HR joints.

Joint Capsule of Elbow

• HU, HR, and proximal RU joints share a capsule with capsular attachments

• Proximal capsular attachment is just superior to coronoid and radial fossa

• Distal capsular attachment is along the margin of coronoid process of ulna, blending with annular ligament

• Medial and lateral attachments are continuous with collateral ligaments

• Posterior capsular attachment is along upper edge of olecranon fossa and to the back of medial epicondyle; just inferior to annular ligament

Joint Capsule

Relatively large and loose capsule.

• Reinforced laterally and medially by collateral ligaments with synovial membrane which allows full ROM. It can become inflamed, causing pain

Ligamentous Function

• Ligaments provide additional support to the elbow joint.

Terminology

• Valgus is lateral projection of a distal bone or joint segment. Varus is a medial projection of a distal bone segment

Valgus and Varus forces

• Valgus force: tension on elbow, compression on the lateral joint. Varus creates tension on the lateral side of the elbow, with compression on the medial. Valgus stress can occur from a laterally directed force to distal forearm when the upper arm is fixed, or medially directed force with the forearm fixed.

Ligaments of the Elbow

• Medial (ulnar) collateral ligaments consists of anterior/posterior bundles. The transverse bundle is also part of this ligament (Cooper's ligament). The lateral (radial) collateral ligament complex consists of radial collateral/ulnar collateral, and annular ligaments.

Medial (Ulnar) Collateral Ligament Complex

• Stabilizes against Valgus forces, and limits hyperextension. Guides joint motion and assists with resisting longitudinal distraction for joint surfaces

• Anterior bundle is the primary ligamentous restraint during valgus stress from 20° - 120° of elbow flexion posterior bundle - Less significant role in providing valgus stability

• Transverse (oblique) bundle plays a role in approximation of joint surfaces but contribute little to valgus stability

Lateral Collateral Ligament Complex

• The lateral Collateral Ligament complex stabilizes against varus and supination and reinforces the HR joint. Assists with resisting longitudinal distraction, posterolateral rotatory stability, and stabilizes radial head rotation

• The radial collateral ligament reinforces the HR joint and resists varus stress assisting in resisting longitudinal distraction of the joint

• The ulnar collateral ligament resists combined forced varus And supination stresses

• Annular ligament resists distraction of radius and stabilizes radial head against ulna

Carrying Angle of the Elbow

• Forearm lies lateral to the humerus when elbow is fully extended. The normal carrying angle of the elbow is 8-15°; usually greater in females. Cubital (cubitus) Valgus is an excessive carrying angle, >15°. Cubital (cubitus) Varus is a reduced carrying angle, <5°.

Cubitus Varus

• The term is used when the deformity results from a malunion following a broken humerus

Axis of Motion

• Axis of motion for flexion and extension is oblique and runs through trochlea's middle.

Axis of Rotation

• Ulna is guided medially from extension to full flexion.

Axis of Rotation: Flexion of Elbow

• Typical = Forearm is in line with humerus in passive flexion. Cubital Valgus = Forearm rests slightly medial to humerus during passive flexion

Musculature of Elbow Joint

• Muscles that cross anterior to the elbow joint are elbow flexors (Brachialis, Biceps Brachii, & Brachioradialis. FCR, FCU, FDS, & palmaris longus have primary functions at the wrist/hand, serving as weak elbow flexors.

Musculature

Mobility muscles include Biceps Brachii, Brachialis while the stabilizing muscles that help with joint compression include the brachoradialis.

Brachialis

• Mobility muscle has insertion close to axis of rotation which helps for a larger arc of motion, it has large potential for force generation and is greatest at 100° of elbow flexion.

Biceps brachii

• Mobility muscle that inserts close to axis with force production related to the shoulder. Elbow flexion > 100°, action changes in the elbow joint . Most active during unresisted supination or neutral forearm positions during unresisted with weight and active in all forearm positions

Brachioradialis

• Stability muscle has insertions far from the joint, with the most force going to jt compression peak force produced between 100-120 degrees with activity increasing with faster speed when loaded in neutral or fully pronated.

Muscles Posterior to the Elbow Joint

• The main extensors are the Triceps brachii, along with and Anconeus. The Extensors of the wrist, ECRL, ECRB, ED, ECU and EDM, originate at the lateral epicondyle and provide stability in the elbow. Note that ECRL/ECRB can assist elbow flexion.

Actions of Triceps

• Primary elbow extensor, which acts as stabilizers and synergist. The long head's force ability is related to shoulder position. the max torque is achieved at ~90 elbow flex

Actions of Anconeus

• Assists in elbow extension and acts as stabilizer for all activity.

Factors impacting flexion/extension motion at elbow

   - Type of motion (active or passive), position of the forearm (pronation/supination), body mass index (BMI), and position of the shoulder

Factors Contributing to Stability at Elbow Joint

• Configuration of joint surfaces, ligaments, joint capsule, and active/passive tension via muscles

Stability at Elbow Joint

• Bony components oppose to varus and valgus stresses in full extension with Olecranon process compressing with Olecranon fossa to limit extension. HU joint is close-packed - Anterior capsule aids with resisting anter. Displacement. capsule & ligment. Note the Soft tissues Provide support, and is limited with distal distraction of joint

Medial Collateral Ligament

• Provides resistance to distraction and valgus. osseous structures offer 2 degree of restriction.

Stability in full Flex

• Approximation of coronoid process/fossa and radial head/fossa. limits extremes of flexion

Radioulnar Joints

• Proximal and distal RU joints function as 1 joint that provides a rotational movement of the forearm.

Proximal RU Joint

• Articulation = radial notch of ulna (covered with hyaline cartilage), annular ligament with anterior and posterior edges of the radial notch, rim of the radial head (covered in hyaline cartilage), and fovea of radial head and Capitulum

• During Pronation/supination, the Radial head spins against capitulum with axis of rotation, pulling radius proximally against the capitulum.

Ligamentous Support: Proximal RU Joint

• Annular, and quadrate, and Oblique cord are used for support The annular ligament helps with maintaining position and the quadrate limits supination/pronation. The Oblique cord is a ventral flat band in the ventral forearm that helps stabilizes radius and is unimportant.

Distal Radioulnar Joint (DRUJ)

• Functions to transmit compressive forces from the hand to forearm.

• Articular Surface Includes: Concave ulnar notch of radius, convex Radial head and, joint capsule that connects to radius, with Anterior palmer and posterior (dorsal).

• Supination and Pronation Supination - Tenses palmer side, loosening posterior Pronation- Tenses posterior side, loosening palmer

Triangular Fibrocartilage Complex

• Stabilizes the joint and is ~20% that pass through TFFC Components include Articular disc Discal R joints Palmer U and UCL Fascial Sheath

Muscle Control at Radioulnar Joints

• Supination
  • supinator, the biceps brachii
• Pronators
  • Pronator teres, pronator quadratus
• Pronator Teres; Major action at RU joints but also stabilizes RU.
• Stabilizes radius and ulnar during movements

Muscle Actions- Acts as a stabilizer

Functions of Muscle Actions Slow sup is supination, but when fast, all positions of the elbow, the biceps work. Flex to 90 helps when against force,

Axis of Rotation is longitudinal to the joint

Motion in RU joints

• In open-chain movement, the primary movement occurs as the radius rotates around the ulna

• Motion occurs in the ulna as well When Pronating The head shifts back and laterally. Ventrally or Dors. When Supinating The head shifts ventrally/ anterior, head shifts Prox

Amt of Radioulnar Motion

 Total ~150 deg

Elbow Flex – Sup=90 – Pro= 60 Elbow Extended – Sup=50 – Pro= 100

• Joint capsule & the interosseous membrane contribute to RU joint stability.

Proximal radioulnar joint

• The annular and quadrate ligaments, plus the interosseous membrane contribute to stability

Muscular Structures

• Passive tension in biceps when elbow is fully extended is a factor in this stability- Pronator teres (helps maintain contact of radial head & capitulum)
• Pronator quadratus, anconeus, extensor carpi ulnaris / pronator teres

Arthrokinematics: Humeroulnar

• Flexion- Ulna Slides + Rolls Ventral & Superior
• Extension- Ulna Slides + Rolls Dors & inf.

Arthrokinematics + Humeroradial Humerus

• Flex- Rad Slides + Rolls V+S
• Extension- Rad Slides + Rolls D + Inf"

Arthrokinematics of the Radioulnar Joints

• Radius and Hand rotation, when fixed the ulna Radius = Spinning on a track by the annular lig and Radial Notch with Radius & Hand are mobile

WeightBearing

• Radius and Hand mobile the Radius and ulna at Radial Head with Roll/Slide- Roll - Slide with both Both are concaved.

DRUJ - Distal U heads pull the styloid to head apex side Fixed ulna and has little to no rotation- Conc outside With all sides The styloid process moves in that direction. The whole unit spins

Arthrokinematics of Radioulnar Joints: Pronation

• PRUJ: Radial head spins on Ulna. - Maybe is an ant-roll with and post slides on unit
• DRUJ-The radius rolls and all in with Ulna on both sides; with the Palmar joint.

Arthrokinematics Radioulnar Joints: Supernation

PRUJ = Has Posterior-Roll slide DRUJ = On radial and slide posterior

• Result to shoulder. Results from GH which cause the HU jt

GH, HU, Elbow are ER and IR. GH in fixed and rotation will cause humeral and ulnar to to go the a single link

• Closed Chain Kinematics in Action Pronation =ER Supination = IR*

Closed Chain = ER/IR cause a fix - Supination = GH and IR

Closed/ Open Packed Positions HU = 70 with 10 with IR/ER, in both. Hr = Both sides Pr= Flex IR supination Dis = Just opposite.

An overview of the elbow joint's structure and function, including the humeroulnar joint. It explores the articulation between the humerus and ulna, detailing the sliding motion and contact points during flexion and extension. The elbow complex is critical for hand mobility and stability.