Pathophysiology

1. Pressure on nerve results on blood flow obstruction in vasa nervorum
2. Results in venous congestion and oedema
3. With time, fibroblast proliferation occurs in nerve leading to inefficiency of cell transport mechanisms and impairment of nerve conduction 

Approach

• Expose to elbows
• Place palms upwards on a pillow
• Conduct a directed examination

1. Look
   • Wasting of thenar muscles
   • Scar from previous surgery over transverse carpal ligament
2. Feel
   • Sensory assessment - test light touch over thumb, index and middle fingers - deficiency implies median nerve invovlemet
   • Motor assessment: LOAF muscles (lateral 2 lumbricals, opponens, abductor pollicus brevis, flexor pollicis brevis)

     Arm - none
     Elbow: Pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis
     Forearm: Flexor digitorum profundus I/II, flexor pollicis longus, pronator quadratus
     Hand: Abductor pollicis brevis, flexor pollciis brevis, oppones pollicis, 1/2 lumbricals

3. Move

Completion

1. Tinels: tap test over median nerve - tingling sensation in distribution of nerve
2. Phalen's test: maximal felxion of wrist for 1 minute exacerbates symptoms - relived when flexion discontinued
3. Duran's test: Flexion compression test - maximal flexion and direct digital compression of the median nerve at the wrist reproduces symptoms

Causes of carpal tunnel syndrome

1. Idiopathic
2. Anatomical
   • Bone - previous fractures, acromegaly
   • Soft tissues - lipomas, ganglia
3. Physiological
   • Inflammatory - Rheumatoid arthritis, gout
   • Alterations to fluid balance - pregnancy, menopause, hypothyroidism, obesity, amyloidosis, renal failure
   • Neuropathic - DM, alcoholism

Management

1. Investigations
   • Nerve conduction studies - symptoms can be mimicked by higher lesions of the median nerve (higher lesions characterised by loss of sensation over the thenar eminence due to involvement of the palmar cutnaeous branch and loss of forearm flexors)
   • Neck imaging - may be due to compression of a nerve root
2. Treatments
   • Removal of underlying causes
   • Wrist splints in neutral position (especially night time)
   • Local steroid injection just proximal to carpal tunnel
   • Surgical decomrpession

Complications of surgical decompression

1. Scar
2. Scar tenderness
3. Wound infection
4. Nerve injury - palmar cutaneous branch of median nerve (lies superficial to retinaculum) and motor branch to the thenar muscles (usually leaves radial side of the median nerve towards the distal extent of the standard incision).  Risk of nerve injury decreased if skin icnision is made on the ulnar side of the palmar crease
5. Recurrence of symptoms

Boundaries of the carpal tunnel

• Pisiform
• Hook of hamate
• Scaphoid
• Trapezium
• Transverse carpal ligament

Sites of compression of the median nerve

1. Wrist
2. Entrapment of the anterior interosseous branch of the median nerve, usually at origin of pronator teres
   • Nerve supplies FPL leading to loss of precise pinch but no sensory signs
3. Pronator syndrome
   • Compression by the ligament of struthers (fibrous band arising from the medial epicondyle of the humerus that passes medially and upwards to attach to a supratrochlear spur on the lower anterior humerus)