Carpal tunnel syndrome is a median nerve neuropathy due to compression as it passes through the carpal tunnel in the wrist.
Carpal tunnel syndrome (CTS) is due to compression of the median nerve as it passes through the carpal tunnel in the wrist leading to median nerve neuropathy. It is considered the most common upper limb mononeuropathy.
CTS is common and usually presents with paraesthesia and/or sensory loss of the first three fingers (thumb, index finger, middle finger), lateral half of the fourth finger (ring finger). As the condition progresses, there is loss of motor function with hand weakness, wasting of the thenar eminence, and weakness in thumb abduction. Symptoms are characteristically worse at night and may disrupt sleep.
Treatment can be with non-surgical measures (e.g. steroid injections, wrist splints) or surgical measures (e.g. carpal tunnel decompression) depending on the severity.
CTS is common and may be bilateral.
CTS is common in adults with a prevalence as high as 5% in the general population. There is an estimated 3:1 female-to-male ratio. Bilateral involvement is commonly observed.
CTS is due to compression of the median nerve as it passes through the carpal tunnel in the wrist.
As the median nerve crosses the wrist, it passes through the carpal tunnel. Compression here is typically due to anatomic compression and inflammation. Several risk factors have been identified that increase the risk of median nerve compression in this region.
The carpal tunnel has two key boundaries superiorly and inferiorly:
Through the carpal tunnel runs the median nerve and nine flexor tendons.
The median nerve is derived from the lateral and medial cords of the brachial plexus (C5-T1). It enters the upper arm at the axilla and travels alongside the brachial artery into the cubital fossa. It then travels in the anterior forearm before passing through the carpal tunnel to supply some intrinsic muscles of the hand.
The median nerve provides sensory innervation to the hand. This includes the palmar and distal dorsal aspects of the lateral three-and-a-half digits (thumb, index, middle, and half of the ring finger) and central palm. The sensation of the palm is provided by the median nerve and a small sensory branch known as the palmar cutaneous, which branches before the carpal tunnel.
In the forearm, the median nerve provides innervation for:
A branch of the median nerve known as the anterior interosseous arises within the forearm and provides innervation for:
Within the hand, the median nerve provides motor innervation to the thenar eminence muscles and two lateral lumbricals that can be remembered as ‘2LOAF’. This is why prolonged compression can lead to thenar eminence wasting
There are a number of risk factors associated with the development of CTS. These include:
There is also limited data on the role of genetic factors and environmental factors such as repetitive hand and wrist use or work with vibrating tools.
The precise cause of increased pressure within the carpal tunnel is unknown. However, evidence suggests it may be related to anatomic compression (e.g. fibrosis of the flexor tendons, mass lesion, or an anatomically small tunnel) and inflammation of the nerve itself in response to the compressive injury.
CTS is characterised by pain and/or paraesthesia in the distribution of the median nerve.
Early symptoms of CTS are those of pain and/or paraesthesia. As the disease progresses, overt sensory loss can develop in the distribution of the median nerve in association with hand weakness and thenar eminence muscle wasting.
Sensory symptoms are usually limited to the median-innervated fingers (thumb, index, middle, and lateral half of ring finger). Symptoms may be unilateral or bilateral.
Initial symptoms are often noted at night and may wake patients from sleep. CTS may progress becoming noticeable during the day as well. Symptoms are usually exacerbated by activities that promote extended periods of wrist extension or flexion (e.g. driving).
Overt sensory loss and muscle weakness are usually late signs.
Pressure within the carpal tunnel increases if the hand is extended or fully flexed, which can exacerbate symptoms. The tunnel is under the least amount of pressure when the hand is hand is in a neutral (i.e. flat) or slightly flexed position.
Several bedside tests can be performed in an attempt to provoke symptoms of CTS and improve the likelihood of making a clinical diagnosis. The two main tests are Phalen and Tinel.
The diagnosis of CTS is usually made clinically but can be confirmed on electrodiagnostic tests.
CTS is usually a clinical diagnosis based on characteristic signs and symptoms. Clinical features can be used to determine the severity of CTS.
Electrodiagnostic tests include both nerve conduction studies and electromyography:
Electrodiagnostic tests are usually reserved for the following groups:
If nerve conduction studies are completed it will show impaired conduction across the carpal tunnel. These can be combined with electromyography, especially if there is concern about another pathology (e.g. plexopathy, radiculopathy) or surgical management is being considered because EMG can grade the severity.
Imaging (e.g. US or MRI) is usually reserved for patients with a suspected structural abnormality such as a cyst or tumour.
Treatment of CTS can be non-surgical or surgical.
The choice between non-surgical or surgical options in CTS depends on the severity and response to any previous treatments.
Non-surgical options include wrist splints, physical therapy, and/or corticosteroids. These options are generally indicated for patients with mild-to-moderate CTS. Wrist splints help to hold the wrist in a neutral position and thus reduce the pressure within the carpal tunnel. They are often worn at night but can be worn continuously throughout the day.
Corticosteroids can be injected into the region of the carpal tunnel for short-term relief of symptoms. They are generally given at most once every six months and if symptoms recur after two injections other options should be considered (e.g. surgery).
Surgical decompression is highly effective for CTS and should be offered to patients with evidence of severe median nerve injury or those who have failed to respond to non-surgical measures. Surgery should generally not be offered during pregnancy because symptoms usually improve a few weeks after delivery.
A variety of different surgical techniques can be used to release pressure within the carpal tunnel. These include:
The most frequent complication of CTS surgery is incomplete release and this may lead to reoperation. Other complications include:
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