Carpal Tunnel Syndrome

CARPAL TUNNEL SYNDROME

· clinical syndrome manifested by characteristic signs and symptoms resulting from an entrapment neuropathy of the median nerve at the wrist

· most common compression neuropathy in the upper extremity.

Anatomy

· Space enclosed by the concavity of the carpus and the overlying flexor retinaculum

· Flexor retinaculum has 3 components

· deep forearm fascia (deep to FCR and FCU)

· transverse carpal ligament

· distal aponeurosis between thenar and hypothenar muscles

· Mean width

· 25mm at proximal end

· 20mm at the narrowest region at the level of the hook of hamate

· 26mm at the distal end

· Mean widening of the transverse carpal arch after carpal tunnel release is 10.4% or 2.7 mm

· Volume measure 5ml. Generally smaller in females

· Contents

· 4 tendons of flexor digitorum superficialis (FDS)

· 4 tendons of flexor digitorum profundus (FDP)

· All 8 share a common synovial sheath – Ulnar bursa. The sheath does not invest them completely but is reflected/open from the radial side. Arteries gain access to the tendons at these points

· 1 tendon of flexor pollicis longus, median nerve

· Other structures

§ Palmaris profundus arises from the interosseus membrane in the forearm and passes through the carpal tunnel to insert onto the dorsal surface of the palmar aponeurosis. Rare finding. Reported in 1:1600 dissections

§ Lumbricals usually originate form FDP tendons distal to the tunnel, but when fingers are flexed they may be pulled back into the tunnel

§ Small persistent median artery – dominant blood supply to median nerve in 30% and may significantly contribute to blood supply of index and middle fingers

§ Anomalous palmar cutaneous branch

MRI distal cross section

· Transverse Carpal ligament

· Medial – pisiform and hamate ( hook and radial surface)

· Lateral – scaphoid tuberosity and medial surface/ridge of trapezium.

· Integrity of the TCL is not a major factor in the maintenance of the carpal arch.

· Palmar cutaneous nerve

· From radiopalmar aspect of nerve, 5cm proximal to wrist crease

· Separates from main nerve after 2cm and travels underneath antebrachial fascia between PL and FCR

· Emerges through fascia 0.8cm proximal to wrist crease and divides into radial and ulnar branches

· Median Nerve

· Enters the canal in the middle or slightly to the radial side of midline, directly under or dorso-radial to the palmaris longus tendon

· Enclosed by a parietal and visceral layers of loose connective tissue. This allows it to shift as the hand changes position.

· Shape of the nerve varies as is passes through the tunnel. It starts out oval and then flattens out.

· With the wrist in a neutral position, the median nerve is seen anterior to the flexor digitorum superficialis tendon of the index finger or posterolaterally between the flexor digitorum tendon of the index finger and flexor pollicis longus tendon.

· May move as much as 20mm in flexion-extension

· The nerve can sometimes be split by an accessory lumbrical or the median artery. The division may be equal or unequal. Sometimes they rejoin distally.

· Motor fascicles are generally on the radial side. 78% of cases motor fascicles occupy radiopalmar position in the nerve, 22% in central palmar portion

· Divides into 6 branches distally – recurrent, 2 common and 3 proper

· 1st lumbrical supplied by radial side proper digital nerve to IF, 2nd lumbrical supplied by common digital nerve to 2nd cleft

· In 56%, the thenar branch travels in a separate fascial tunnel. The thenar branch commonly comes off distal to the TCL(extraligamentous). Sometimes it branches off within the tunnel (subligamentous) and sometimes it perforates the TCL in its own tunnel (transligamentous).

A – Extraligamentous and recurrent (most common 45-90%)

B – Subligamentous (31%)

C – Transligamentous (23%)

D – Originate from ulnar border of median nerve

E – Lie on top of TCL

Topographical landmarks

1. Distal wrist crease is the proximal origin of the transverse carpal ligament (TCL). The proximal wrist crease corresponds to the radiocarpal joint.

2. Kaplan’s cardinal line – line drawn parallel to the ulnar side of the abducted thumb and the hypothenar space.

3. The distal end of TCL is at the intersection of the cardinal line and the line of the ring finger axis.

4. Superficial palmar arch lies 5mm distal to the above point.

5. Hook of hamate is 1cm distal and radial to the pisiform.

6. Kaplan’s landmark is the intersection of the cardinal line and a line drawn from index/middle finger interspace. This point identifies the motor branch of the median nerve.

History

· 1854 - Sir James Paget first reported median nerve compression at the wrist following a distal radius fracture

· 1913 - Pierre Marie and Charles Foix described the pathology of median nerve compression underneath the transverse carpal ligament

· 1924- Galloway and Mackinnon in Winnipeg, Canada, did the first TCL release in a patient with a posttraumatic neuropathy. Complicated by neuroma of PCN

· 1933 - Sir James Learmonth reported TCL release to treat median nerve compression at the wrist.

· 1951 – Phalen advocated transverse incision at the distal wrist crease, with proximal and distal extension as needed

· 1970 – Taleisnik popularised vertical incision in line with 4th ray

Epidemiology

· Prevalence 1-5% of general population

· prevalence among working individuals is somewhat lower, about 0.5% - suggests that the majority of cases occur in the non-working population

· 50% bilateral

· F>M 3-5:1

o relationships between CTS and women (OC use, menstrual disorders, and obesity) may be related to pressure on the median nerve due to fat or edema near the carpal tunnel.

· Most common 4th to 6th decades of life

· Risk factors

1. female sex

2. obesity (BMI>30)

3. age 41-60

4. diabetus mellitus

5. square (width=height) wrists (as opposed to rectangular)

· Smoking is not strongly associated

· Males tend to have worse disease

· Diabetus mellitus is a significant risk factor for bilateral lesions.

· American Society for Surgery of the Hand has issued a statement that the current literature does not support a causal relationship between specific work activities and the development of diseases such as CTS.

Aetiology

· Approximately one-third of patients with carpal tunnel symptoms have associated medical conditions such as inflammatory arthritis, diabetes, pregnancy, amyloidosis, hypothyroidism and acromegaly (NEJM 1993)

· Local and Systemic factors

o Systemic factors act to directly or indirectly affect microcirculation, pressure thresholds for nerve conduction, nerve cell body synthesis, and axon transport or interstitial fluid pressures.

· Acute vs Chronic

Trauma-related structural changes

1. Distal radius fracture

2. Lunate dislocation

3. Posttraumatic arthritis/osteophytes

4. Edema

5. Hemorrhage

6. Burns

Systemic diseases

1. Rheumatoid arthritis

2. Diabetes mellitus

a. Reduces threshold for developing symptoms

Thyroid imbalance (especially hypothyroidism)
Consider this if recurrent presentation after surgery
Causal relationship not clear

4. Amyloidosis

5. scleroderma

Hemophilia
Alcoholism
Raynaud's phenomenon
Paget's disease
Gout
Chronic renal failure/hemodialysis

12. Glycogen storage diseases in children

Anomalous anatomic structures

1. Aberrant muscles (eg, reversed palmaris, palmaris profundus)

2. Unusually extensive lumbricals or FDS/FDP bellies

3. Median artery thrombosis

4. Enlarged persistent median artery

Hormonal changes

1. Pregnancy

up to 17% of pregnant women, mostly in third trimester
weight gain increases risk
most resolve spontaneously after delivery
11% of women reported CTS six months after delivery and 4.3% still had the condition a year afterward

2. Menstrual disorders

3. Menopause

4. Oral contraceptive pill

Acromegaly

Infections

Tumors/neoplasms

1. Lipoma

Ganglion
Fibroma
Aneurysm of median artery

Mechanical overuse

Vibrating machinery

Differential Diagnosis

1. Cervical radiculopathy (double crush syndrome)

2. Thoracic outlet syndrome

3. Pronator teres syndrome

4. De Quervain’s syndrome

5. RSD

6. Tenosynovitis

Pathophysiology

· Compression leads to

1. swelling of tenosynovium

2. thickening of transverse carpal ligament

3. focal demyelination of median nerve.

4. Axonal loss in more severe cases

· initial insult is a reduction in epineural blood flow and venous congestion, which occurs with 20 to 30 mm Hg compression.

· Intracarpal canal pressures in patients with CTS routinely measure at least 33 mm Hg and often up to 110 mm Hg with wrist extension.

· Continued or increased pressure eventually causes edema in the epineurium and endoneurium.

· If applied for 2 hours, pressure of 50 mm Hg will cause epineural edema, and if applied for 8 hours, it will increase endoneural fluid pressure fourfold and block axonal transport.

· As further injury occurs to the capillary endothelium, more protein leaks out into the tissues, which become more edematous, and a vicious cycle ensues. The effects are most pronounced within the endoneurium, since more exudate and edema accumulate there, unable to diffuse across the perineurium.

· The perineurium resists pressure changes because of its higher tensile strength and acts as a diffusion barrier creating in effect a "compartment syndrome" within the nerve.

Histopathology

· Path of flexor tenosynovium shows inflammation in only 10%, but oedema and vascular sclerosis in 98%

Diagnosis

History

· most common symptom is paresthesias in the distribution of the median nerve – middle and index most common

· Other symptoms include feelings of clumsiness and weakness in the affected hand, often made worse with activity.

· Proximal radiation of pain or paresthesias to the elbow or even the shoulder is not uncommon

· Night pain is a consistent symptom. Theories:

o Phalen postulated that when the hand and wrist are at rest during sleep, engorgement and relative venostasis occur in the small vessels within the flexor synovialis, producing swelling, more nerve compression within the tunnel, and worse pain. Active motion of the fingers and wrist decreases venous engorgement and relieves pain, a phenomenon consistent with many patients' histories and their need to shake or exercise their hands to relieve night pain. It is an interesting theory that emphasizes the vascular etiology of the disorder, but there is no published evidence to prove the hypothesis.

o Patients hold their wrists flexed while sleeping, thus increasing the pressure on the median nerve and causing pain. Therefore, preventing wrist flexion would be expected to decrease symptoms, and may be why many patients find it beneficial to wear neutral-position wrist splints at night.

Examination

· thorough physical examination of the neck and upper extremity should be performed

· Sensory findings (threshold tests best):

1. Semmes-Weinstein pressure monofilaments: Values greater than 2.83 may be indicative of CTS.

2. Vibratory sensibility: A vibrating 256-cycle per second tuning fork is placed against the patient's fingertips. The median and ulnar fingers of both hands are tested. The test is considered positive if decreased sensation is perceived.

3. Static and moving 2-point discrimination: Failure to discriminate more than 6 mm (static) or 5 mm (moving) is a positive finding – this is a late finding as can remain normal until nearly all sensory conduction has ceased.

· Thenar atrophy is a sign of advanced CTS of long-standing duration.

· Provocation tests

Tinel’s
Sensitivity - 25 to 79%
Specificity – 60-95%
One study showed Tinels to be the most specific (84 percent), but the least sensitive (32 percent) of all the provocation tests
Phalens (wrist flexion)
patient's elbows are placed on a table, the forearms are perpendicular to the table, and the wrists are flexed for 60 seconds. The test is positive if numbness or paresthesias develop in radial-sided digits
Sensitivity - 42 to 85%
Specificity – 54-98%
reverse Phalen's (wrist extension)
carpal compression
vibration testing
Durkan’s pressure test
Applies a known standard pressure (150mmHg) over the TCL
10% false positive rate

· No one test is diagnostic

Investigations

Investigations for systemic diseases – hypothyroidism, diabetes

Nerve conduction studies

· most appropriate role for electrodiagnostic testing is as an adjunct to the clinical assessment in instances where the diagnosis is not clear

· Distal motor latencies of 4.5 millisecs and sensory latencies of 3.5millisecs abnormal

· Difference between hands of 1 ms (motor) or 0.5 ms (sensory) abnormal

· Electromyography of thenar helpful for signs of denervation

· There is no relationship between the nature or duration of pre-operative symptoms and the severity of the electrophysiological impairment.

· There is no relationship between pre-operative nerve conduction impairment and either successful outcome of surgery (defined as complete symptom relief) or time to resolution of symptoms after surgery

Imaging studies

· Xray wrist – arthropathy, post trauma deformities

· US and MRI not routinely performed unless masses suspected

· MRI may be useful to assess recurrent symptoms post repair

o following adequate carpal tunnel release, MRI may demonstrate an increase in carpal tunnel volume of up to 24%, often accompanied by a change in shape from oval to circular, resulting in increased anteroposterior and mediolateral diameters.

o incomplete surgical release of the flexor retinaculum can occur and be detected by a residual increase in T2 signal of the median nerve within the carpal tunnel and by direct visualization of the still-connected fibers of the retinaculum.

o Other changes include excessive fat within the carpal tunnel, neuromas, scarring, and persistent neuritis.

Management

Nonoperative

1. splinting in neutral

o initial trial of full-time splinting for 3 to 4 weeks followed by part-time night splinting is recommended.

2. NSAIDs

3. diuretics to reduce oedema

o little evidence to support effectiveness

4. treat underlying disease

o often resolves symptoms in hypothyroidism

5. Vit B6 was thought to be good but doesn’t modify disease

6. Steroids – 80% relief (transient), 22% symptom free at 1 year

o Most likely to benefit are those with symptoms <1yr; diffuse and intermittent numbness; normal 2 point discrimination; no weakness or atrophy; <1-2ms prolongation in latency for M and S