Elbow Complex Anatomy and Function

Elbow Complex Objectives

• Identify the elbow complex components.
• Discuss factors impacting the stability and mobility of the elbow complex.
• Describe the elbow musculature's roles and effects of varying joint loads.
• Describe the open and close packed positions of the elbow and forearm complex.
• Discuss radioulnar joints' structure and function.
• Describe the arthrokinematics of the elbow and forearm.

Overall Function

• Allows hand mobility in space
• Provides stability for skilled/forceful manual activities
• Linked to shoulder/wrist function via muscles crossing those joints

Components

• Humeroulnar (HU) joint
• Humeroradial (HR) joint
• Proximal and distal radioulnar (RU) joints

Elbow Joint

• It is a modified hinge joint.
• There is a small amount of ulna rotation and ABD/ADD during flexion and extension.
• It has 1 degree of freedom.
• Flexion/extension occurs in the sagittal plane.

Humeroulnar (HU) Joint

• Articulating surfaces: Trochlea of humerus and trochlear notch of ulna

Humeroradial (HR) Joint

• Articulating surfaces: Capitulum of humerus and head of radius (fovea)

Humeroulnar Joint Motion

• The primary motion is trochlear notch sliding on the trochlea of the humerus.
• During flexion, the ulna slides along the trochlea until the coronoid process enters the coronoid fossa in full flexion.
• During extension, sliding of the ulna occurs until the olecranon process enters the olecranon fossa.
• The trochlea only contacts the deepest notch portion when the joint is heavily loaded.
• In unloaded conditions, contact primarily occurs on notch sides.
• The contact area expands toward the trochlear notch's depth when loaded.
• There is no contact between trochlea and the deepest portion of the trochlear notch from 30°-120° of flexion.

Humeroradial Joint Motion

• The primary motion is sliding of the concave radial head over the convex capitulum surface.
• In full flexion, the radial head rim slides into the radial fossa.
• In full extension, there's no contact between the articulating radial head and the capitulum when the arm is unloaded/NWBing.

Radioulnar (RU) Joints

• Proximal and distal RU joints are linked and function as one joint
• They act together to produce forearm rotation.
• They are uniaxial, diarthrodial pivot joints with 1 degree of freedom.
• Pronation/supination occurs in the transverse plane.
• The proximal RU joint shares a capsule with HU and HR joints.

Joint Capsule

• HU, HR, and proximal RU joints share a capsule
• Capsular attachments:
  • Proximal: just superior to the coronoid and radial fossa
  • Distal: along the coronoid process margin of the ulna, blending with the annular ligament
  • Medial/Lateral: continuous with collateral ligaments
  • Posterior: along the upper edge of the olecranon fossa and to the back of the medial epicondyle, just inferior to the annular ligament
• The capsule is relatively large and loose, weaker anteriorly and posteriorly, and reinforced laterally and medially by collateral ligaments.
• Synovial membrane folds allow expansion for full ROM and can become inflamed and hypertrophied, causing pain.

Terminology

• Valgus: lateral projection of the distal segment of a bone or joint
• Varus: medial projection of the distal segment of a bone or joint
• Valgus force creates tension on the medial elbow aspect and increases compression at the lateral joint.
• Varus force creates tension on the lateral elbow aspect and increases compression medially.

Ligaments

• A varus or valgus force can be applied distally or at the joint itself
• Valgus Collateral Ligament complex:
  • Stabilizes against valgus forces at the medial elbow
  • Limits hyperextension
  • Guides joint motion throughout flexion ROM
  • Some resistance to longitudinal joint surface distraction
  • It has an anterior bundle, posterior bundle, and transverse (oblique) bundle.
  • The anterior bundle is the primary restraint to valgus stress from 20°-120° of elbow flexion.
  • The posterior bundle has a less significant role in providing valgus stability than the anterior bundle.
  • The transverse (oblique) bundle, aka Cooper's ligament, contributes little to valgus stability and plays a role in the approximation of joint surfaces.
• Lateral (radial) collateral ligament complex:
  • Stabilizes elbow against varus forces and combined varus/supination.
  • Reinforces the HR joint.
  • It has a lateral collateral ligament, lateral ulnar collateral ligament, and annular ligament.
  • Provides some resistance to longitudinal joint distraction.
  • Maintains posterolateral rotatory stability.
  • Stabilizes the radial head rotation (annular ligament).
  • Lateral (radial) Collateral Ligament: reinforced the HR joint, resists varus stress at elbow, and assists in resisting longitudinal distraction of jt.
  • Lateral Ulnar Collateral Ligament: 2° restraint to combined forced varus & supination stresses and assists in resisting varus stress.
  • Annular Ligament: resists distraction of the radius and stabilizes the radial head against ulna at PRUJ.

Carrying Angle

• The forearm typically lies slightly lateral to the humerus when the elbow is fully extended in anatomic position.
• "Carrying angle" is the angle of the elbow, which is normally 8-15°.
• Females tend to have higher carrying angles than males.
• Cubital (cubitus) valgus is an excessive carrying angle (>15°), and cubital (cubitus) varus is a reduced carrying angle (<5°) or reversed.
• Cubitus Varus: Aka "gunstock deformity", and it results from a malunion after a supracondylar fracture of the humerus.

Axis of Motion

• The axis of motion for flexion/extension is an oblique axis of rotation that runs through the middle of the trochlea.
• The Ulna is guided medially when moving from extension to full flexion (2° to oblique axis)
• Typical carrying angle is caused when the forearm rests in line with the humerus.
• Cubital valgus occurs when the forearm rests medial to the humerus in full flexion.
• Cubital varus occurs when the forearm rests lateral to the humerus.

Musculature of the Elbow Joint

• Muscles crossing anterior to the elbow joint include primary elbow flexors: brachialis, biceps brachii, & brachioradialis
• FCR, FCU, FDS, & palmaris longus primarily function at the wrist/hand but can serve as weak elbow flexors.
• Supinator & pronator teres primarily function at RU joints
• Biceps brachii & brachialis provide mobility.
• Brachialis: A mobility muscle with its insertion close to the rotation axis, favoring a large motion arc and generates force. The MA is greatest at ~100° elbow flexion.
• Biceps Brachii: It is a mobility muscle that inserts close to the rotation axis. Active in all forearm positions. The shoulder position affects its force production, and the MA is greatest between 80-100° flexion.
• The brachialis has a large CSA and contributes a large force. With >100° elbow flexion, the line of action changes, which creates distraction force. The muscle is less active when the forearm is pronated, and most active when it is in a supinated or neutral position.
• Brachioradialis:
  • It is a stability muscle.
  • The insertion point is at a greater distance from the joint axis
• The largest force component goes to joint compression with Relatively small CSA along with large avg peak MA compared to other flexors and The peak MA occurs b/w 100° - 120° of elbow flexion.
• Posterior Elbow Musculature:
  • Triceps brachii has three heads, that the long head crosses the shoulder joint
  • Anconeus and ECRL, ECRB, ED, ECU and EDM originate at the lateral epicondyle & primarily act at the wrist/hand
• Its effect at the elbow is predominantly compressive for stabilization.
• Triceps act as primary extensors, and the shoulder joint position affects the long head's force production ability.
• The long head's force production ability is impacted by shoulder position. The medial and lateral heads are not impacted by shoulder position.
• Maximum torque production at ~90 deg elbow flexs. This will vary depending upon the shoulder position and it will Acts as a stabilizer & synergist.
• Anconeus assists in elbow extension, which contributes ~ 15% of the total extension torque at the elbow
• It acts as a stabilizer during activity

Mobility of the Elbow

• This is impacted by the type of motion (active or passive), position of the forearm (pronation/supination), body mass index (BMI), and position of the shoulder
• Passive flexion is typically greater than active flexion. Flexion will be greater when the forearm is supinated.
• Higher BMI can lower the flexion ROM due to tissue approximation
• The position of the shoulder and active or passive insufficiency of 2 joint muscles can impact elbow motion.

Stability of the Elbow

• This is contributed by the configuration of joint surfaces, ligaments, joint capsule, and active/passive tension in muscles crossing the joint.
• Inherent articular stability occurs at end-range flexion & extension, which contribute to stabilization via compression & co-contraction.
• Co-contraction of muscles at the elbow assists in creating a stable base for forceful wrist/finger motions.
• In full extension, bony components resist varus/valgus stress, the Olecranon process contacts the olecranon fossa limiting extension and the HU joint is in the close-packed position Additional resistance to varus/valgus forces comes from the capsule and ligaments. Resistance to joint distraction is provided entirely by soft tissue and The anterior capsule provides major resistance to anterior humerus displacement.
• At 90° of flexion, the anterior portion of the MCL provides 1º resistance to distraction & valgus stresses and a majority of resistance to varus stress occurs by osseous joint structures (with slight contribution from LCL and the capsule).

Radioulnar Joints

• Proximal and distal RU joints are linked and function as one joint.
• They act together to produce forearm rotation.
• They are uniaxial, diarthrodial pivot joints with 1 degree of freedom.
• Pronation/supination occurs in the transverse plane around longitudinal axis.
• Articulating surfaces: Radial notch (ulna), covered in hyaline cartilage and Annular ligament (attaches to ant./post. edges of radial notch and Completes fibro-osseous ring around the joint, radius and Rim of radial head. The fovea radial head spins with the capitulum, and pronator teres pulls the radius proximally against the capitulum as it contracts
• Oblique cord- flat fascial band on forearm and extends from anterolateral coronoid process to insert just below the bicipital (radial) tuberosity & Functional importance is unclear and Potentially assists in preventing separation of radius and ulna.
• Distal Radioulnar Joint (DRUJ): The DRUJ functions to transmit loads from the hand to the forearm. The DRUJ is an uniaxial pivot joint and consists of the distal radius & ulna, and articular disc (TFCC). Itis a triangular fibrocartilage complex, acting as its main stabilizer
• Components of TFCC includes: Articular disc (triangular fibrocartilage), Distal radio-ulnar joint capsular ligaments, Palmar ulnocarpal ligament: (Ulnotriquetral and Ulnolunate), Ulnar collateral ligament and Fascial sheath enclosing ECU tendon
• Total radio ulnar motion is ~ 150. The amount of pronation vs supination is related to elbow flexion
• Structures Contributing to Stability at RU Joints:
  • The ligaments included are: Annular & quadrate ligaments, Oblique cord and Interosseous membrane
  • The muscles included are: Passive tension in biceps (when elbow is fully extended) and Pronator teres
• Structures which provide resistance to Distal radioulnar joints: Interosseous membrane, Dorsal radioulnar ligament, Palmar radioulnar ligament and Triangular fibrocartilage
• Muscles: Pronator quadratus, Anconeus Extensor carpi ulnaris and Pronator teres

Arthrokinematics

The Proximal RUJ- weight bearing: Annular ligament and radial notch of the ulna rotate around a fixed radial head -Non Weight Bearing, radial head rotates (spins) w/in a ring formed by annular ligament and radial of ulna Distal RUJ- With weight on the Radius/hand- Convex ulnar head rolls and slides in opposite directions on the concave ulnar radius notch Non Weigth Bearing-
Concavity of ulnar radius notch rolls / slides in same direction on the head ###Closed-Chain Kinematics at Radioulnar Joints Radius & hand are fixed with the ground, forearms pronated from EH humuerus/ Ulna Full-Supinated by internal rotation of elbow via Humerus/ and ulna

DRJU- pronatiion: una slides Ventrally / dorsally/ Supination- ULuna Slide dorsally /vetnrallly

###Open Packed /Closed Packed Positions. Each joint and its corresponding open /close position:

• Humeroulnar Joint: 70° flexion & 10° supination / Full extension & full supination
• Humeroradial: Full extension & full supination / 90° elbow flexion & 5° supination
• Proximal RU:70° flexion & 35° supination / 5° supination
• Distal RU: 10° supination / 5° supination