Overview
This lecture covers carpal tunnel syndrome (CTS): its definition and prevalence, the anatomy of the median nerve and the carpal tunnel itself, the causes of nerve compression, the symptoms, signs and investigations used to diagnose it, and the treatment options and their complications. The lecture opens and closes with the same reflective question, inviting the reader to consider where CTS sits on the biopsychosocial/spiritual spectrum rather than treating it as a purely anatomical problem.
Definition and prevalence
- Carpal tunnel syndrome is compression of the median nerve within the carpal tunnel.
- It is the most common compressive neuropathy involving a peripheral nerve: 6-9% of women and <1% of men.
- Other compressive neuropathies for context: the ulnar nerve at the elbow, the common peroneal nerve at the fibular neck, and the posterior tibial nerve in the tarsal tunnel.
Median nerve anatomy
- The median nerve is the main sensory nerve of the hand.
- Course from the brachial plexus down the arm, it gives branches (in sequence) to: pronator teres (humeral head), an articular branch, flexor carpi radialis, palmaris longus, pronator teres (ulnar head), flexor digitorum superficialis, and via the anterior interosseous nerve the lateral part of flexor digitorum profundus (the medial part of FDP is supplied by the ulnar nerve), flexor pollicis longus, and pronator quadratus, then a palmar branch before entering the hand.
- In the hand it supplies: the thenar muscles - abductor pollicis brevis (always), flexor pollicis brevis (superficial head; the deep head is supplied by the ulnar nerve), and opponens pollicis; the 1st and 2nd lumbricals; branches to the dorsum of the middle and distal phalanges; and the common and proper palmar digital nerves. An anastomotic branch connects it to the ulnar nerve.
- At the wrist, the median nerve and its palmar cutaneous branch run alongside the radial and ulnar arteries and their superficial/deep palmar arches, with a communication between the median and ulnar nerves also present.
- Sensation: radial side of the hand to the middle of the ring finger; the palmar cutaneous branch supplies the skin of the thenar eminence.
- Motor: thenar muscles - abductor pollicis brevis (always), flexor pollicis brevis (usually), opponens pollicis (usually) - plus the radial two lumbricals.
The source Netter-style diagrams of median nerve anatomy (course down the limb, and the volar hand vasculature/nerves) had very fine print labelling; the label text above is a best-effort transcription and some minor wording may not be exact.
Anatomy of the carpal tunnel
- The floor of the tunnel is formed by the carpal bones (visible on a plain AP wrist radiograph).
- Viewed from the wrist surface looking distally towards the palm, the carpal bones are: pisiform, triquetral, lunate, scaphoid, trapezium, trapezoid, capitate, hamate.
- The flexor surface of the carpus is deeply concave, and this arch is maintained by the flexor retinaculum, which bridges across the arch from the trapezium/pisiform side to the hamate side to form the roof of the tunnel.
- Contents of the tunnel: tendons, tendon sheaths, and the median nerve. Structures at the wrist are grouped as: the “median duo” (median nerve and palmaris longus tendon); the “radial trio” (radial artery, flexor carpi radialis tendon, and flexor pollicis longus tendon in the radial bursa); the “two tendon quartet” (flexor digitorum superficialis and flexor digitorum profundus tendons in the ulnar bursa); and the “ulnar trio” (ulnar artery, ulnar nerve, flexor carpi ulnaris tendon).
The diagrams of the carpal bone arch and of the flexor tendons/arteries/nerves at the wrist (repeated for the tenosynovitis slide) also had fine print labels; transcribed to the best of legibility.
Aetiology
Two general mechanisms cause compression: swelling of the tunnel’s contents, and encroachment on the tunnel space.
Swelling of contents:
- Tenosynovitis
- Rheumatoid arthritis (joint swelling and finger deformity/deviation)
- Hypothyroidism
- Diabetes
- Pregnancy
- Acromegaly
Encroachment on the tunnel:
- Colles fracture - a dorsally displaced/angulated distal radius fracture producing a “dinner-fork” deformity
- Dislocated lunate
Other causes:
- Occupational: repetitive use of the hands, e.g. meat workers, carpenters
- Idiopathic
Clinical features
Symptoms due to irritation of the nerve: tingling, pain, and electric shock feelings, e.g. with grasping activities (tools, steering wheel), knitting, reading, and at night.
Symptoms due to dysfunction of the nerve: numbness and weakness, e.g. difficulty gripping, dropping cups or a teapot, clumsiness, and stiffness/loss of use of the fingers.
Signs on examination:
- Look: drier skin (loss of sympathetic input), wasting of the thenar eminence
- Feel: lack of sweat, diminished sensation
- Move: decreased power of thumb abduction
Investigations
Provocative tests:
- Phalen’s test - wrist flexed to maximum for 60 seconds - 88% sensitivity
- Tinel’s test - tapping over the transverse carpal ligament - 67% sensitivity
- Both look for pain, anaesthesia, or paraesthesia
Electrodiagnostic tests (nerve conduction studies, EMG): used for confirmation rather than diagnosis.
Treatment and complications
Treatment options, typically escalating:
- Rest / avoidance of activities
- Splint in slight wrist extension
- NSAIDs
- Steroid injection
- Surgical release (endoscopic or open)
Complications:
- Permanent weakness / numbness
- Weakness of grip post-surgery
- Accidental division of the palmar cutaneous or recurrent motor branch
- Painful scar
- Pain syndrome
Self-test
- Define carpal tunnel syndrome, stating which nerve is compressed and where.
- Compare the prevalence of carpal tunnel syndrome in men and women, and name three other compressive neuropathies mentioned as context.
- Describe the sensory distribution of the median nerve in the hand, including the area supplied by its palmar cutaneous branch.
- List the thenar muscles supplied by the median nerve, noting which one is always innervated by it.
- Name the eight carpal bones forming the floor of the carpal tunnel, and describe the structure that maintains the arch of the carpus.
- List the tendons and neurovascular structures that pass through the carpal tunnel.
- Give four causes of carpal tunnel syndrome due to swelling of the tunnel’s contents.
- Give two causes of carpal tunnel syndrome due to encroachment on the tunnel, with an example condition for each.
- Distinguish the symptoms caused by irritation of the median nerve from those caused by dysfunction of the median nerve in carpal tunnel syndrome.
- Describe the look/feel/move signs of carpal tunnel syndrome on examination.
- Describe how Phalen’s test and Tinel’s test are performed, and state which has the higher sensitivity.
- Explain the role of electrodiagnostic tests (nerve conduction studies, EMG) in carpal tunnel syndrome.
- List the treatment options for carpal tunnel syndrome in order of escalation.
- List the possible complications of carpal tunnel surgery.
- A meat worker presents with night-time tingling in the thumb, index and middle fingers, difficulty gripping a knife, and thenar wasting on examination. Explain how her occupation links to these findings, and outline the likely diagnostic and management pathway.
Answers
Reveal answers
- Compression of the median nerve within the carpal tunnel at the wrist.
- 6-9% of women vs <1% of men; other compressive neuropathies are the ulnar nerve at the elbow, the common peroneal nerve at the fibular neck, and the posterior tibial nerve in the tarsal tunnel.
- Radial side of the hand to the middle of the ring finger; the palmar cutaneous branch supplies the skin over the thenar eminence.
- Abductor pollicis brevis (always), flexor pollicis brevis (usually), and opponens pollicis (usually); it also supplies the radial two lumbricals.
- Pisiform, triquetral, lunate, scaphoid, trapezium, trapezoid, capitate, hamate; the flexor retinaculum bridges the deeply concave flexor surface (trapezium/pisiform side to hamate side) to maintain the arch and form the roof of the tunnel.
- Flexor tendons (flexor pollicis longus in the radial bursa; flexor digitorum superficialis and profundus in the ulnar bursa) with their tendon sheaths, and the median nerve.
- Any four of: tenosynovitis, rheumatoid arthritis, hypothyroidism, diabetes, pregnancy, acromegaly.
- Colles fracture (dorsally displaced/angulated distal radius fracture with a dinner-fork deformity) and dislocated lunate.
- Irritation produces tingling, pain and electric shock feelings (e.g. with grasping activities, tools, steering wheel, knitting, reading, at night); dysfunction produces numbness and weakness (e.g. difficulty gripping, dropping cups/teapot, clumsiness, stiffness/loss of use of the fingers).
- Look: drier skin (loss of sympathetic input) and thenar wasting. Feel: lack of sweat and diminished sensation. Move: decreased power of thumb abduction.
- Phalen’s test: wrist flexed to maximum for 60 seconds (88% sensitivity). Tinel’s test: tapping over the transverse carpal ligament (67% sensitivity). Phalen’s is more sensitive.
- They are used for confirmation of the diagnosis rather than for making it.
- Rest/avoidance of activities, then splinting in slight wrist extension, then NSAIDs, then steroid injection, then surgical release (endoscopic or open).
- Permanent weakness/numbness, weakness of grip post-surgery, accidental division of the palmar cutaneous or recurrent motor branch, painful scar, and pain syndrome.
- Repetitive hand use is an occupational cause of median nerve compression in the carpal tunnel. Irritation of the nerve’s sensory fibres produces tingling in its territory (thumb, index and middle fingers), typically worse at night; dysfunction of its motor fibres to the thenar muscles produces weak grip and thenar wasting. The pathway would be provocative testing (Phalen’s/Tinel’s), electrodiagnostic confirmation (nerve conduction studies/EMG), then conservative management (rest, splinting, NSAIDs, steroid injection) escalating to surgical release if this fails.