Anterior Forearm Dissection Guide
A comprehensive guide to dissecting the anterior compartment of the forearm, including the superficial and deep flexor muscles, median nerve, ulnar nerve, and associated vasculature. Master the anatomy essential for understanding carpal tunnel syndrome and nerve injuries.
Learning Objectives
- ✓Identify all muscles of the superficial and deep flexor compartments
- ✓Trace the median and ulnar nerves through the forearm
- ✓Identify the radial and ulnar arteries and their branches
- ✓Understand the relationship between flexor tendons at the wrist
- ✓Appreciate the anatomy relevant to carpal tunnel syndrome
Prerequisites
- • Completed arm dissection (brachial artery, median nerve in arm)
- • Understanding of brachial plexus terminal branches
- • Knowledge of superficial venous anatomy
- • Review of forearm muscle attachments
Equipment Needed
- • Scalpel with #22 blade
- • Dissecting scissors (sharp and blunt)
- • Forceps (toothed and smooth)
- • Probe
- • Retractors
- • Dissecting tray and pins
Dissection Steps
Step 1:Skin Incision and Reflection
Make a longitudinal incision from the cubital fossa to the wrist along the midline of the anterior forearm. Make transverse incisions at both ends. Carefully reflect the skin laterally and medially, preserving the superficial veins and cutaneous nerves in the superficial fascia.
Key Structures
Step 2:Remove Deep Fascia
Identify the deep (antebrachial) fascia covering the muscles. Make a longitudinal incision through it and reflect it to expose the underlying muscles. Note the bicipital aponeurosis (lacertus fibrosus) at the proximal end.
Key Structures
Step 3:Identify Superficial Flexor Muscles
Identify the five superficial muscles from lateral to medial: pronator teres, flexor carpi radialis, palmaris longus (absent in 15% of people), flexor digitorum superficialis, and flexor carpi ulnaris. All share a common origin from the medial epicondyle.
Key Structures
Step 4:Expose the Median Nerve
Locate the median nerve entering the forearm between the two heads of pronator teres. Trace it distally as it passes deep to the fibrous arch of FDS. The nerve lies between FDS and FDP in the middle of the forearm and becomes superficial at the wrist.
Key Structures
Step 5:Identify Deep Flexor Muscles
Retract or reflect the superficial muscles to expose the three deep muscles: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. Note that FDP has dual innervation (median and ulnar).
Key Structures
Step 6:Trace the Ulnar Nerve
Find the ulnar nerve entering the forearm by passing posterior to the medial epicondyle and between the two heads of flexor carpi ulnaris. Trace it distally along the medial side of the forearm, lateral to FCU.
Key Structures
Step 7:Identify Arterial Anatomy
Locate the brachial artery in the cubital fossa and trace it to its bifurcation into radial and ulnar arteries. Follow the ulnar artery deep to pronator teres, then trace it distally. Follow the radial artery along the lateral forearm under brachioradialis.
Key Structures
Step 8:Examine the Wrist
At the wrist, identify the flexor retinaculum (transverse carpal ligament) and the structures passing deep to it forming the carpal tunnel. Note the superficial position of the median nerve and tendons.
Key Structures
Clinical Correlations
- •Carpal tunnel syndrome: compression of median nerve under flexor retinaculum causing pain, numbness in lateral 3.5 digits, and thenar weakness
- •Pronator syndrome: median nerve compression between heads of pronator teres causing forearm ache and sensory changes
- •Anterior interosseous syndrome: pure motor loss to FPL, FDP (2-3), and pronator quadratus - unable to make "OK" sign
- •Volkmann's ischemic contracture: compartment syndrome causing flexor muscle necrosis and fibrosis
Common Mistakes to Avoid
- ✗Cutting the bicipital aponeurosis before identifying structures in the cubital fossa
- ✗Mistaking palmaris longus for flexor carpi radialis (FCR is lateral and larger)
- ✗Confusing the median nerve with the anterior interosseous vessels
- ✗Missing the dual innervation of FDP (median to lateral, ulnar to medial)
Study Questions
- What muscles does the median nerve innervate in the forearm?
- How would you test for anterior interosseous nerve function?
- What are the boundaries of the carpal tunnel?
- Why is the palmaris longus tendon often used for tendon grafts?
- What is the clinical significance of the dual innervation of FDP?
FAQs
Common questions about this dissection
Approximately 15% of people (varying by ethnicity) are missing palmaris longus. It's tested by opposing thumb to little finger while flexing the wrist - the tendon becomes prominent at the midline.
FDS tendons split to allow FDP tendons to pass through (chiasma tendinum). At the wrist, FDS is superficial and FDP is deep. FDS can flex the PIP joint independently; FDP flexes the DIP.