3.1 Forearm: bones and muscles Flashcards
What is a ‘Colles’ fracture of the radius?
Fracture of distal end of radius - fall on outstretched arm.
Can lead to dinner fork deformity.
Distal radius (with clavicle) are the most commonly fractured upper limb bone, especially in elderly (osteoporotic).
What does the interosseous membrane do?
Made from the periosteum of the radius and ulna, it connects these two forearm bones and transmits forces from the hand up the arm. The downwardly oriented fibres transmit the force from radius to ulna.
What are the consequences of a dislocation and/or fracture of ulna?
Usually proximal end of ulna is more susceptible to fracture, ie. flexed elbow hits ground can result in avulsion of olecranon and elbow dislocation.
Susceptible structures include median nerve and brachial artery.
- compromise of flexor muscle function
- avascular necrosis, Volkman’s ischemia due to loss of blood supply
Fascial compartments of the forearm?
- Fascia of arm/forearm (brachial/antebrachial) tightly bind down muscles
- Fascia forms retinaculum at wrist/ankles, forms palmar aponeurosis
- Facilitates muscle contraction, aids venous return to heart and blood supply to work within region.
- A sig. rise in P can lead to compression of contents known as compartment syndrome (carpal tunnel syndrome)
Which of the following is likely to be initially affected by compartment syndrome?
- Veins & lymphatics
- Arteries
- Superficial nerves
- Deep nerves
Cubital fossa
- B/w medial and lateral epicondyles, PT (medial) and brachioradialis (lateral)
- Roof: bicipital aponeurosis
- Floor: brachialis muscle
- Contains: median cubital vein, cutaneous nerves, ulnar and radial arteries, median and radial nerves
What is the difference between flexors and extensors in your forearm?
- Flexors and more powerful than extensors
- Skin overlying flexor muscles is more sensitive than that over extensors
- Supplied by 3 nerves (median, ulnar and radial)
What are the superficial muscles of the anterior flexor compartment?
All arise from common flexor origin (CFO)
- pronator teres (PT)
- flexor carpi radialis (FCR)
- pulmaris longus (PL)
- flexor carpi ulnaris (FCU)
What are the intermediate layer muscles of the anterior flexor compartment?
Flexor digitorum superficialis (FDS)
- from medial epicondyle & shaft of radius, inserting into the base of middle phalanges
- flexes at the 1st interphalangeal joint on hand
- from CFO, radius & ulna
What are the deep layer muscles of the anterior flexor compartment?
- Flexor pollicis longus (FPL)
- Flexor digitorum profundus (FDP): works with FDS
- Pronator quadratus (PQ)
*all from radius, ulna +/- IO membrane
Pronators & Supinators
PT, PQ: Pronator teres, pronator quadratus work together to pronate forearm
Supinator: supination is the more powerful action, also produced by biceps
*Testing radius-ulna motion is best done with elbow flexed at 90deg - prevents involvement of the shoulder
Median nerve
from medial and lateral cords: C5-T1
Muscles - all but 1.5 muscles of anterior compartment of forearm
PT, FCR, PL
FDS
FDP (lateral 2 tendons), FPL, PQ
- Passes via a muscle (PT) to forearm & carpal tunnel to hand
- Recurrent branch of the median nerve supplies thenar muscles
- Anterior interosseous nerve supplies deep muscles on front of forearm FPL & PQ (but not ulnar 0.5 of FDP)
Compression at elbow
- functional deficit
- hand of benediction (unopposed extension of medial fingers, flexed lateral fingers)
Ulnar nerve
from medial cord (C8-T1)
Muscles: supplies 1.5 muscles in anterior compartment of forearm
- FCU
- FDP medial 2 heads
Susceptible to compression and/or stretch across back of medial epicondyle
- functional deficits
- Claw hand
What muscles lie in the superficial layer of the posterior extensor compartment?
Brachioradialis Extensor carpi radialis longus (ECRL) Extensor carpi radialis brevis (ECRB) Extensor digitorum communis (EDC) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU) Anconeus
*most arise from CEO
What are the deep layer muscles of the posterior extensor compartment of the forearm?
Supinator Abductor pollicis longus (APL) Extensor pollicis brevis (EPB) Extensor pollicis longus (EPL) Extensor indicis (EI)
*Most arise from ulna +/- radius and IO membrane
