Movements of the forearm
Movements of fingers
The fingers can undergo flex/ext at MCP and IP joints
They can undergo abd/add at MCP joints
- Midline is 3rd digit
Movements of the thumb
Muscles of forearm
The interosseous membrane and deep fascia separate into 2 compartments.
Posterior (extensor) compartment
- extensor muscle
- supinator mucsle
- innervated by radial nerve from posterior cord
Anterior (flexor) compartment
- flexor muscles
- pronator muscles
- innervated by median and ulnar nerves from median and lateral cords
- radial and ulnar arteries
Anterior forearm muscles
Superficial - 4 muscles
- pronator teres
- flexor carpi radialis
- palmaris longus
- flexor carpi ulnaris
Intermediate - 1 muscle
- flexor digitorum superficialis
Deep - 3 muscles
- flexor digitorum profundus
- flexor pollicis longus
- pronator quadratus
Muscles of the hand
Hypothenar
- abductor digiti minimi
- flexor digiti minimi
- opponens digiti minimi
Thenar
- abductor pollicis brevis
- flexor pollicis brevis
- opponens pollicis
Central
- lumbricals
Palmar aponeurosis
- Thick, triangular shaped fascia covering central palm
- Protects underlying tendons and neurovasculature
- Palmaris longus inserts into the fascia as its apex
- The distal end splits into 4 slips that are continuous with digital sheaths of digits 2-5
Dupuyten’s contracture
- Progressive thickening and shortening of the palmar aponeurosis on the medial side of the hand which pulls the 4th and 5th digits into partial flexion at MP and PIP joints
- Contracture is often bilateral and occurs in men over 50
- Cause is unknown, but evidence points to a hereditary predisposition
- treatment usually involves surgical excision of all fibrotic parts of the aponeurosis to free the fingers
- similar to ulnar claw but MCP is flexed
Median nerve
- Exits cubital fossa passing between 2 heads of pronator teres
- Gives off anterior interosseous nerve which innervates deep muscle layer
- Courses in plane between FDP and FDS
- Becomes more superficial near wrist as it approaches carpal tunnel
- Innervates all muscles of forearm except: FCU and medial half of FDP
Innervation of median nerve
Motor to lumbricals 1-2
Sensory branches:
- common and proper palmar digital branch
- nail beds of digits 1-4
- all of palmar hand except ulnar area
Recurrent branch:
- motor to thenar muscles
- very superficial making it vulnerable to cut injuries of the hand
Ulnar nerve
- enters forearm after passing posterior to medial epicondyle
- courses in plane between FCU and FDP, which it innervates
- joins ulnar artery midway down forearm
- crosses wrist through Guyon’s tunnel
Ulnar nerve innervation
Motor branches to:
- 3 hypothenar muscles
- adductor pollicis
- all interosei
- lumbricals 3-4
Sensory branches to:
- common and proper palmar digital branch
- pinky and medial finger
- medial side of hand
Crossing the wrist
Radial artery passes posterior to CMC joint of thumb to cross anatomical snuff box; superficial branch joins superficial palmar arch
Ulnar artery and nerve pass through Guyon’s tunnel
Median nerve passes through carpal tunnel
FDP, FDS, and FPL tendons - 9 tendons pass through carpal tunnel
FCP tendon passes lateral to carpal tunnel.
Palmaris longus passes superficial to carpal tunnel.
Carpal tunnel syndrome
Flexor retinaculum stretches between tubercles of trapezium/scaphoid and pisiform/hook of hamate
Carpal tunnel - passageway deep to the flexor retinaculum
Contains:
- median nerve
- 4 FDS tendons
- 4 FDP tendons
- FPL tendon
Tendon sheaths
Synovial sheaths around each tendon
Reduces friction as tendons slide with muscle action
Compression of medial nerve as it passes through carpal tunnel
Cause: swelling of synovial sheaths due to repetitive motion of flexor tendons
Symptoms:
- weakness/atrophy of thenar mm.
- inability to oppose thumbs
- parasthesia in palmar skin over lateral 3.5 digits
Treatment:
- overnight wrist brace to immobilize joint
- carpal tunnel release - surgical cut of flexor retinaculum to relieve pressure in tunnel
Guyon’s Canal
Ulnar nerve and artery pass through ulnar tunnel.
Ulnar canal syndrom - compression
Symptoms:
- parasthesia of medial 1.5 digits
- weakness of most intrinsic hand muscles
The paralysis of the interossei and 3rd and 4th lumbricals leading to “claw hand” deformity
- In “claw hand” the MCP joints are hyperextended due to unopposed action of the extensors; IP joint extension isn’t possible.
The other major site for ulnar damage is the medial epicondyle. Lesions there will affect both hand and forearm mm.
