Flexor and Extensor Forearm
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Extensor and Flexor Forearm Dr. Andrew Deane MS5025Q Van Nuys Medical Center (317) 274-7802 [email protected] “Elbow Joint” • Composed of 3 separate synovial joints contained within a single joint capsule. Joint capsule is thin anteriorly and posteriorly. Reinforced laterally and medially by collateral (radial and ulnar, respectively) ligaments 1. Humeroulnar Joint Articulation between trochlea of humerus and trochlear notch of ulna. 2. Humeroradial Joint Articulation between capitulum of the humerus and the head of the radius. 3. Proximal Radioulnar Joint Articulation between the head of the radius and the radial notch of the ulna. Movement: rotation of the radial head within the cuff formed by the annular ligament and the radial notch of the ulna. “Elbow Joint” This is a synovial hinge joint that is primarily limited to flexion/extension. However, its continuity with the superior radioulnar joint introduces complexity. The joint capsule of a typical hinge joint is lax anteriorly and posteriorly but strengthened by collateral ligaments medially and laterally. Proximally the joint capsule surrounds the radial, coronoid and olecranon fossae. Distally it is attached to the margins of the trochlear notch and the annular ligament. The ulnar collateral ligament exhibits a triangular configuration. It extends between the medial epicondyle and the ulna with posterior and anterior bands extending to the olecranon and coronoid processes. The radial collateral ligament arises from the lateral epicondyle and is attached to the stationary annular ligament - not the radius. This structural arrangement does not impede independent rotation of the radius. supination pronation Radio-ulnar Joint Supination/pronation occurs in the forearm at the proximal and distal radioulnar joints - not at the wrist joint. The movements at these joints add enormously to the manipulative ability of the hand and their loss following injuries to the forearm is a serious disability. Proximal Radioulnar Joint The disc-like head of the radius rotates inside an osseo- fibrous ring formed by the radial notch of the ulna and the strong annular ligament. This synovial joint is continuous with that at the elbow. The head of the radius articulates with the capitulum just below the lateral epicondyle of the humerus superiorly, acting like a multiaxial ball-and-socket joint. Supination is the result of the action of the biceps brachii and supinator mm. Rotation in the opposite direction (pronation) is the result of the actions of the pronator teres and pronator quadratus mm. Partial dislocation of the head of the radius ("nursemaid's elbow") is common in children who have been lifted up by the pronated hand while the elbow is relaxed and in extension. Middle Radioulnar Joint The shafts of the radius and ulna are joined by the interosseous membrane. Its fibers extend downward and medially from radius to ulna +Elbow dislocation + Nursemaid’s elbow (radial dislocation; subluxation) Proximal incomplete temporary dislocation of the head of the radius. Child is suddenly lifted/jerked by the upper limb when the forearm is pronated. The immature radial head slips distally and partially out of the annular ligament. Treatment: Supination of the forearm while elbow is flexed, sling for 2 weeks and the annular ligament will heal. Distal Radio-ulnar Joint The ulnar articulates with the ulnar notch of the radius. At upper and lower joints the ulna remains stationary, here the lower end the radius rotates around the ulna. This is another synovial joint; a triangular fibrocartilage pad attaches the two bones and separates this lower radioulnar joint from the immediately inferior radiocarpal joint. Cubital Fossa Cubital fossa An inverted triangular region anterior to the elbow joint. Boundaries: Base: imaginary line through the medial and lateral epicondyle of the humerus cubital fossa Lateral: brachioradialis brachioradialis pronator teres Medial: pronator teres The roof of the fossa is skin, superficial and deep fascia. The median cubital v. lies in the superficial fascia of this region extending from the cephalic to basilic vv. • not uncommon site for dislocations and fracture dislocations of the elbow joint • access point to both venous and arterial blood • reflect its borders to visualize all the major nerves and vessels entering the forearm except the ulnar n. that passes behind the medial epicondyle of the humerus Cubital fossa Removal of the roof, and reflection of the two lateral aspects of the triangle, demonstrates the following structures: i. lateral cutaneous n. of the forearm appears between the biceps and brachialis. It becomes superficial over the lateral brachioradialis radial n. cutaneous n. ii. The brachioradialis forms the lateral brachioradialis border and when reflected exposes the radial n. as it enters the flexor compartment of the forearm biceps tendon iii. The tendon of the biceps iv. Crossing the tendon and deep to the radial a. bicipital aponeurosis is the brachial a. that ends by bifurcating into the radial and ulnar aa. ulnar a. Cubital fossa i. the median n. lies medial to the brachial a. ii. the medial cutaneous n. (not shown) of the forearm lies anterior to the pronator teres iii. the floor is formed mainly by the brachialis m. The supinator lies below and lateral median n. brachialis pronator teres supinator The Forearm Like the arm, the forearm has an anterior (flexor) compartment, and a posterior (extensor) compartment. However, to put the forearm in the anatomical position, it must be supinated. ulna The radius and ulna are connected by an interosseous membrane which separates the flexor and extensor compartments. Antebrachial fascia surrounds the forearm. Flexor i. Radial a.v.n ii. Ulnar a.v.n. iii. Median n. iv. Anterior interosseous a.v.n. Extensor i. Posterior interosseous a.v.n. supination pronation The Forearm Flexor Extensor The bulk of the flexor musculature arises from the medial epicondyle of the humerus and the anterior surfaces of the radius and ulna. The majority of muscles become tendinous at the wrist and continue down into the hand under the flexor retinaculum. The extensor muscles are arranged similarly except that their humeral origin is from the lateral epicondyle. Anterior Posterior Flexor forearm: superficial group A group of 5 muscles fan out over the flexor compartment from the medial supracondylar ridge and epicondyle of the humerus. From lateral to medial aspects they are: i. pronator teres ii. flexor carpi radialis iii. palmaris longus iv. flexor digitorum superficialis v. flexor carpi ulnaris* *only muscle in this group innervated by the ulnar n. All others are all innervated by the median n. The brachioradialis, which enters the flexor compartment, is also included. Flexor forearm: superficial group Pronator teres Origin: pronator teres Humeral head: medial epicondyle of humerus Ulnar head: coronoid process of ulna Insertion: Lateral surface of the radius Innervation: median n. flexor carpi radialis Action: pronates and flexes the forearm Flexor carpi radialis palmaris longus Origin: medial epicondyle Insertion: base of the 2nd metacarpal Innervation: median n. Action: flexes wrist, abducts the hand Palmaris longus Origin: medial epicondyle Insertion: flexor retinaculum + palmar aponeurosis Innervation: median n. Action: flexes wrist, tenses palmar aponeurosis Flexor forearm: superficial group Flexor carpi ulnaris Origin: Humeral head: medial epicondyle Ulnar head: medial margin of olechranon and upper ulna brachioradialis Insertion: Pisiform, hamate (via ligaments) + 5th metacarpal Innervation: ulnar n. Action: flexes wrist, adducts the hand Brachioradialis* Origin: upper 2/3 of lateral supracondylar ridge flexor Insertion: lateral aspect of the radial styloid carpi Innervation: radial n. ulnaris Action: flexes forearm when it is semipronated; stabilizer of the elbow * Brachioradialis is NOT part of the flexor group or part of the extensor group. It is innervated by the radial n. which supplies extensors, but acts as a flexor of the elbow. Simply put it is the orphan muscle of the forearm and does not fit comfortably in either compartment. Flexor forearm: superficial (intermediate) group Flexor digitorum superficialis Origin: Humeroulnar: medial epicondyle Radial head: anterior surface below tuberosity Insertion: By 4 tendons onto sides of the int. phalanx of digits 2 -5 Innervation: median n. Action: flexes wrist, int. and prox. phalanges flexor digitorum superficialis Flexor forearm: deep group The deep group lies mostly undercover of the superficial group. They include the following 3 muscles: i. flexor digitorum profundus ii. flexor pollicis longus iii. pronator quadratus Flexor digitorum profundus flexor digitorum Origin: Upper ¾ of the ant/med ulna and IO membrane profundus Insertion: Anterior surface of the base of the distal phalanx Innervation: median n. (IO branch) and ulnar n. Action: flexes wrist, prox., int. + distal phalanges Testing FDS and FDP • FDS: Flexion at PIP Joint • FDP: Only forearm flexor that FLEXES at the DIP Joints Essential Clinical Anatomy, Moore 4e. Fig. B6.11. Flexor forearm: deep group Flexor pollicis longus Origin: ant. surface of the radius and adjacent IO membrane Insertion: base of the distal phalanx of the thumb Innervation: median n. (IO branch) Action: flexes wrist, prox. + distal phalanges of pollex Pronator Quadratus Origin: distal 1/4th of the anterior surface of the ulna Insertion: distal 1/4th of anterior surface of the radius Flexor Innervation: median n. (IO branch) Pollicis