Presentation and diagnosis
Carpal tunnel syndromeis probably the most common nerve entrapment disorder, affecting more women than men. It is caused by compression of the median nerve as it enters the palm posterior to the flexor retinaculum. It typically presents as pain radiating up the arm from the wrist, and paraesthesia affecting the median nerve distribution in the palm – namely the thumb, index and predominantly the middle finger and lateral half of the ring finger, paroxysmally affecting the patient in the night and being relieved on moving the arm and hand. If left untreated, the condition may deteriorate and produce muscle wasting in the thenar eminence of the palm.
This is a reliable diagnostic test. Percuss lightly over the flexor retinaculum with a tendon hammer, particularly between the palmaris longus tendon and the flexor carpi radialis tendons. The test is positive if the patient describes a tingling sensation in the median nerve distribution.
This further test is recommended for cases in doubt. Hold the wrist in acute flexion for up to one minute – this usually reproduces the pain and typical paraesthesia. Diagnosis may be confirmed by electromyography.
Initial treatment of a mild carpal tunnel syndrome may be simple weight-lossadvice together with a daily diuretic tablet. Night splints are helpful and may be thepreferred management in early pregnancy. If these measures fail, steroid injection will be helpful in over 60% of cases.
The patient sits facing you, with the palm of the affected hand facing upwards and resting on a firm surface. By flexing the wrist against resistance, the palmaris longus tendon is clearly seen. Make a thumbnail indentation or skin mark on the radial side of the tendon precisely at the distal crease of the wrist; this is the best injection site. Inject, where possible, through a skin crease as this ensures less pain. If you cannot demonstrate the palmaris tendon, which is absent in 13% of patients, palpate the gap between the tendons of the flexor digitorum superficialis and the flexor carpi radialis and then mark the skin at the distal crease. Avoid any surface veins.
Use 1ml steroid – for example, triamcinolone acetonide alone – in a 2ml volume syringe. Use a 2.5cm needle. No local anaesthetic is added, because it may cause an uncomfortable numbness in the fingers and palm in the median nerve distribution that can last for several hours.
With the wrist now straight, advance the needle almost to the hilt, pointing distally and at an angle of 45 degrees. This ensures the steroid solution is deposited in the carpal tunnel immediately behind the flexor retinaculum. Ask the patient if this is comfortable and ensure no pain is felt. Inadvertent needling of a digital branch of the median nerve will cause pain in the palm and referred along a finger. If this occurs, withdraw the needle slightly before injecting. Aspirate to exclude any intravascular injection. You should then be able to inject the steroid with little resistance. Inject slowly, as this will ensure the least pain or discomfort.
The median nerve lies posterior to the palmaris longus tendon. If the needle insertion causes immediate paraesthesia, indicating it has entered the substance of the median nerve, withdraw the needle slightly and reinsert it laterally. This will ensure that no damage is caused to the nerve itself.
Some acute pain may be experienced for up to 48 hours after the injection. Advise simple analgesia and instruct the patient to rest the arm for 24 to 48 hours.
Symptoms should resolve within a few days. If the condition is bilateral, inject one side initially and await the clinical result. Where no improvement in symptoms is noted, a second injection about three weeks later is justified. If there is no response to steroid injection (after two or three successive injections) or – very importantly – if there is evidence of median nerve damage, such as thenar eminence muscle wasting, refer for surgical decompression.1
- Agarwal V et al. A prospective study of the long term efficacy of local methyl prednisolone acetate injection in the management of mild carpal tunnel syndrome. Rheumatol 2005;44:647-50
This extract is taken from Joint and Soft Tissue Injection 5th Edition, by Dr Trevor Silver which is now available to purchase from Radcliffe Publishing with an exclusive 20% discount available until 30th September – simply quote PULSETS12.
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