Elbow Complex Notes

Carpal Bones

  • There are typically eight carpal bones, but two may be fused, resulting in seven.

  • Mnemonic devices can be used to remember the order of the carpal bones (e.g., "So long to pinky, here comes a thumb").

  • It's important to understand the direction in which the mnemonic describes the bones.

Carpal Bone Order

  • Scaphoid: Called the "talus" of the wrist (analogous to the talus in the ankle).

  • Lunate: Named for its moon-like shape.

  • Triquetrum

  • Pisiform: Sits on top of the triquetrum and can be easily moved.

  • Capitate

  • Trapezium

  • Trapezoid: Resembles a quadrilateral or four-sided structure.

  • Hamate

Radial and Ulnar Sides

  • Knowing the medial (ulnar) and lateral (radial) sides of the carpal bones is crucial.

  • For example, extensor carpi radialis longus indicates a muscle on the radial side, which helps determine its attachment point.

Reminder

  • Staphoid, lunate, triquetrum, episcophor, hamate, capitate, trapezoid, trapezoid are the carpal bones.

  • If a muscle is on the radial side, its attachment point is likely on a carpal bone on the radial side.

Forearm Muscles

  • Extrinsic Muscles: Originate outside the hand and attach within the hand, contributing to hand function.

  • Intrinsic Muscles: Originate and end within the hand.

  • Muscles discussed previously (presumably on Monday) are extrinsic muscles.

Pronator Teres

  • Has two heads, with a branch of the median nerve passing between them.

  • Compression of this nerve can occur due to pronation exercises in the gym.

  • Attaches to the medial epicondyle.

  • The flexor digitorum superficialis also attaches to the medial epicondyle.

Posterior Forearm Muscles

  • Superficial posterior forearm muscles include:

    • Extensor carpi radialis longus

    • Extensor carpi radialis brevis

    • Extensor carpi ulnaris

    • Extensor digitorum (for the digits)

    • Extensor digiti minimi (for the small finger, also called the "tea-drinking muscle").

Lateral Epicondyle

  • The common extensor origin is located at the lateral epicondyle.

  • Before the epicondyle, the radial nerve splits into superficial and deep branches.

  • The superficial branch is generally sensory.

Muscle Function

  • Muscles on the radial side tend to be involved in generating grip strength.

  • Muscles on the extensor side are more involved in fine motor control, such as pointing or moving the thumb.

  • The supinator muscle also has two heads, with the deep radial nerve passing between them.

  • The deep branch can be impinged upon.

  • After passing through the supinator, the nerve becomes the posterior interosseous nerve (PIN).

Quick Tests

  • Rock, paper, scissors is used for quick tests.

    • Rock = Medium.

    • Paper = Radial.

    • Scissors = Ulnar/ PIN (Posterior Interosseous Nerve).

Blood Supply to the Forearm

  • The brachial artery is the primary blood supply, branching medially and laterally near the elbow.

  • Branches supply both the front and back of the interosseous membrane.

  • The blood supply reunites in the hand.

  • A similar pattern occurs in the lower limb with the tibia and fibula.

Anatomical Regions

  • Anatomists define regions to understand what structures (nerves, vessels, etc.) pass through them.

    • Cubital Fossa: Located on the anterior aspect of the elbow.

      • Contains: Brachial artery, median cubital vein (where blood is drawn), biceps tendon, and radial nerve.

Ulnar Nerve

  • The ulnar nerve can be impinged by sleeping with the elbows flexed, causing numbness and tingling in its distribution.

Muscle Attachment

  • Start with the muscle name to infer attachment points and function.

  • Example: Flexor carpi ulnaris is a flexor on the ulnar side that attaches to the carpals on the ulnar side, causing flexion and ulnar deviation.

  • Group muscles functionally.

  • Flexors work as a group, while extensors require more individual digit control.

Flexor Digitorum

  • Flexor digitorum superficialis splits, while flexor digitorum profundus is underneath the split.

Elbow Complex

Bones

  • The elbow complex involves the humerus, radius, and ulna.

  • Newman divides the elbow into four joints due to the distal radial ulnar joint (DRUJ).

  • The DRUJ is considered part of the elbow complex but will be discussed with the wrist.

Articulations

  • The ulna's concavity articulates with the humerus's convexity.

  • The radius also articulates with the humerus with a concave radial head on the convex humerus.

  • Flexion and extension follow the same rule for both the ulna and radius.

  • The elbow's rule is "same," meaning the direction of roll and slide are the same.

Pronation and Supination

  • Involve the radius moving on the ulna.

  • The ulnar notch is concave, so pronation and supination follow an "opposite" rule because it's convex on concave.

  • The DRUJ also follows the opposite rule.

Mechanics

  • The elbow is mechanically simple: problems with pronation and supination indicate a radial-ulnar issue, while flexion and extension issues indicate a humeral-ulnar problem.

  • If both are impaired, the entire elbow complex is affected.

  • Pseudo Hinge: The elbow is not a true hinge joint because the ulna abducts during flexion due to the humerus's torsion and the angle of the supracondylar ridge.

  • During elbow flexion, there is compensatory abduction.

Radius

  • The radial head's shape allows for a pure spin during pronation and supination.

Ulna

  • The trochlear notch of the ulna articulates with the humerus, creating a congruent joint that locks during elbow extension due to compression from the olecranon process which slides back and hooks. Therefore, tightness in front of the elbow limits elbow extension.

  • Inability to lock the elbow suggests a fracture between the ulna and humerus.

Elbow Dislocation

  • Elbow dislocations are not common.

  • Dislocations typically occur medially when the elbow is straight due to force.

  • Landing with an arm to the side or behind the body (like a FOOSH injury) can cause dislocation.

  • Gymnasts and weightlifters may also experience dislocations, with the elbow tending to go forward and medially during weightlifting.

Angle of Forearm

  • Carrying Angle: The angle of the forearm relative to the humerus; generally greater in women.

    • A large carrying angle can make weightlifting appear dangerous.

Elbow Ligaments

  • Ulnar Collateral Ligament (UCL) aka Lateral Collateral Ligament: The ligament commonly injured, particularly in baseball players (medial collateral ligament).

    • Injuries occur during the cocking (flexion) and deceleration (extension) phases of throwing.

    • Deceleration forces can reach 4g4g.

      • 4g4g force example: Spinning a goniometer four full circles in one second.

    • Repetitive stress can cause the UCL to stretch and eventually tear.

Tests

  • Moving Valgus Stress Test: A test for UCL tears where the forearm is put under tension and then stressed to see if the ulna "pops."

    • Anterior fibers are loaded during elbow extension, while posterior fibers are loaded during flexion.

    • The UCL is involved with valgus stress in both flexion and extension.

Angular Ligaments

  • The Annular Ligament: Surrounds the radial head, allowing it to spin on the ulna and articulate with the humerus. Attaches all the way around and is a key stabilizer.

    • If torn, the radius can slip superiorly and inferiorly, causing lateral elbow pain, particularly when carrying objects. Therefore, it helps with lateral stability.

    • Works as a buttress (architectural support that disperses force laterally).

  • Torn ligaments are not painful.

Cubitus Varus

  • Cubitus Varus: Decreased carrying angle. Also known as a gunstock deformity. This typically occurs if someone broke their elbow as a child before skeletal maturity, leading to abnormal elbow mechanics.

Falls

  • Falling forward and catching oneself with extended wrists and supinated forearms can lead to fractures.

  • The interosseous membrane is for dispersing forces up into the weight-bearing center of the humerus.

Movement and ADLs

  • Most ADLs (Activities of Daily Living): Are possible with at least 30 degrees of pronation and supination. This minimum range is required for basic hygiene tasks.

  • IADLs (Instrumental Activities of Daily Living): require 50 degrees. Need at least 90 degrees flexion for eating, etc.

In Feels

  • End Feel for elbow extension should be hard (bony).

  • End Feel for elbow flexion should be soft tissue approximation (muscle).

  • Bicep hypertrophy is a risk indicator for elbow problems.

More on the Elbow

  • Arthrokinematics: Flexion/extension follows the same-same rule; pronation/supination follows the opposite rule.

  • Pronation/supination is a pure spin, arthrokinematically.

Measuring Pronation and Supination

  • Measure pronation and supination with the elbow flexed at 90 degrees.

  • The elbow is more straightforward than the shoulder in terms of movements.

Function of the Elbow

  • The primary function of the elbow is to bring the hand to the face.

  • Extrinsic muscles (starting in the forearm) enable gross motor movements, while intrinsic muscles (starting in the hand) fine-tune hand shapes.

Elbow Flexors

  • Brachioradialis: Is the workhorse for elbow flexion based on moment arm.

  • The Law of Parsimony: The body recruits the smallest muscle necessary for a task to conserve energy.

Muscle Involvement

  • Elbow flexors based on moment arm: Brachialis gets recruited first (smallest), then brachioradialis, then biceps (last).

Pronator Quadratus

  • The smallest muscle and gets turned on first followed by pronator teres which gets recruited when you need faster movement, added resistance or both.

Elbow Extension

Brachialis gets recruited first because it's smallest/ has the smallest moment arm, followed by the brachioradialis, then the bicep.

  • Triceps : The workhorse in elbow extension is lateral head, that that gets turned on all the time is the medial head, and anconius get recruited first.

Elbow Stability

Slow, unresisted exercises for extension engage the anconeus for stability.

  • To target the bicep, add resistance and perform supination.

  • Exercises such as curls (bicep flexor) pick on the bicep and engage the shoulder flexor and the brachialis.

Power

  • Supination is the power movement, aided by the biceps brachii.

  • This emphasizes the coupling between forearm and hand movements, influencing grip strength.

  • Moms lifting toddlers often experience elbow and thumb pain due to this coupling.

Elbow Injuries

  • Elbow injuries and thumb pain relate with gripping and power!