Ans. is 'a' i.e., Median nerve f Ref: Basics of orthopaedics 2nd/e p. 718]Carpal tunnel syndromeo Carpal tunnel syndrome is the most common and widely known entrapment neuropathy in which the body's peripheral nerve is compressed or traumatized. Carpal tunnel syndrome occurs when the median nerve is compressed in the carpal tunnel below flexor retinaculum. The carpal tunnel is a narrow rigid passage way of ligament and bones at the base of hand, in front of distal part of wrist. Carpal tunnel houses the median nerve and 9 tendons (4 FDS, 4 FDP & FPL).Causes of carpal tunnel syndromeo There are many causes of carpal tunnel syndrome : -Idiopathic : - This is the most common cause.Pregnancy and menopauseMetabolic : - Gout, Diabetes mellitus4} Endocrine : - Hypothyroidism, Myxedema, Acromegaly, Hyperparathyroidism.Deposition disorder Amyloidosis, Sarcoidosis, Rheumatid arthritis, Leukemia, CRF, Nlucopoly saccharoidosis.AlcoholismLocal causes : - Malunited colie's fracture, osteo-arthritis of the carpal bones, synovitits of flexor tendon sheath, hematoma.Clinical features of carpal tunnel syndromeo Carpal tunnel syndrome is more common in women and occurs between 35-50years.o Symptoms usually start gradually, writh frequent burning, tingling,paresthesia and numbness in the distribution of median nerve, i.e., lateral three & half of fingers and lateral 2/3rd of palm,o The symptoms often first appear during night, since many people sleep with flexed wrists. (Flexion decreases the space in carpal tunnel which results in increased pressure over median nerve),o Sensory symptoms can often be reproduced by percussing over median nerve (Tinel's sign) or by holding the wrist fully flexed for a minute (Pltalen's test).o As the disease progresses, clumsiness of hand and impairment of digital function develop,o Later in the disease, there is sensory loss in median nerve distribution and obvious wasting of thenar eminence.Clinical Tests for Carpal tunnel syndromeo There are some provocative tests which act as important screening methods : -Wrist flexion (Phalen's test) : - The patient is asked to actively place the wrist in complete flexion. If tingling and numbness develop in the distribution of median nerve, the test is positive. This is the most sensitive provocative testTourniquet test : - A pneumatic BP cuff is applied proximal to the elbow' and inflated higher than the patient's systolic BP. The test is positive if there is paresthesia or numbness in the region of median nerve distribution in hand.Median nerve percussion test (Ttnel's sign) : - The median nerv e is gently tapped at the wrist. The test is positive if there is tingling sensation.;Median nerve compression test: - Direct pressure is exerted equally over both wrists by the examiner. If symptoms of carpal tunnel syndrome appear, the test is positive.