Corticosteroid injections are a common non-surgical option for managing Carpal Tunnel Syndrome (CTS), providing temporary relief from the pain, numbness, and tingling associated with the condition. CTS occurs when the median nerve, which runs through a narrow passageway in the wrist, becomes compressed or squeezed. The injection delivers anti-inflammatory medication directly into the carpal tunnel space, reducing swelling around the irritated nerve. This localized treatment alleviates pressure on the median nerve, often delaying or eliminating the need for surgical intervention.
The Medications Used in the Injection
The injectate is typically a mixture of a corticosteroid and a local anesthetic. The corticosteroid is the primary therapeutic agent, targeting the inflammation that causes median nerve compression. Commonly used long-acting corticosteroids include Triamcinolone acetonide or Methylprednisolone acetate, which provide sustained anti-inflammatory effects within the confined space of the carpal tunnel.
A local anesthetic, such as lidocaine or bupivacaine, is almost always added to the mixture. This numbing agent offers two immediate benefits: it provides rapid, temporary pain relief and allows the physician to confirm the needle placement. Immediate symptom relief helps confirm the injection was delivered to the correct location near the median nerve. The total volume of the injectate, which combines the steroid, anesthetic, and sometimes saline, is usually kept low, often ranging from 1 to 3.5 milliliters.
Factors That Determine Steroid Dosage
Physicians typically aim for the lowest effective dose to maximize local anti-inflammatory action while minimizing potential side effects. For Triamcinolone acetonide, a common dosage falls between 10 milligrams (mg) and 40 mg per injection. For example, 40 mg of Methylprednisolone is also a frequently reported dose.
The final dosage and volume chosen depend on several patient-specific and procedural factors. Studies suggest that lower doses, such as 10 mg of Triamcinolone, can be as effective as higher 40 mg doses in providing symptom improvement. The physician considers the severity of CTS, the patient’s body mass index (BMI), and any history of prior injections.
The total volume of the injectate is also a critical consideration. Research indicates that a larger volume, around 3 to 4 milliliters, may be associated with a reduced rate of treatment failure after one year. A larger volume may help mobilize the median nerve through a process called hydrodissection and better distribute the medication throughout the carpal tunnel. The total amount of steroid is calculated by its concentration and the overall volume of the mixture, ensuring the medication spreads optimally around the compressed nerve.
Administration Techniques and Placement
The effectiveness of the steroid dose depends heavily on its precise placement within the carpal tunnel, proximal to the wrist crease. The injection targets the space inside the carpal tunnel, avoiding direct contact with the median nerve and surrounding tendons. Incorrect placement, such as an intraneural injection, can lead to nerve injury or persistent dysesthesias.
Two primary techniques guide the needle placement. The traditional landmark-guided technique relies on external anatomical knowledge, typically inserting the needle just ulnar to the palmaris longus tendon. The ultrasound-guided injection technique is increasingly preferred because it allows the physician to visualize the needle tip in real-time.
Ultrasound guidance ensures the medication is accurately delivered into the carpal tunnel and away from the nerve, significantly reducing the risk of accidental nerve trauma or tendon injury. Visually confirming placement with ultrasound may lead to better long-term outcomes and allow for smaller, more precise volumes of medication, particularly in patients with unusual wrist anatomy.
Post-Injection Care and Treatment Frequency
After the injection, patients may experience immediate numbness from the local anesthetic, which wears off within a few hours. The injection site may become temporarily sore or symptoms may worsen slightly for up to 72 hours, a reaction sometimes called a “steroid flare,” before the corticosteroid begins its therapeutic effect. Physicians typically advise temporary rest and reduced activity involving the hand and wrist for a few days following the procedure.
The beneficial anti-inflammatory effects of the steroid usually become noticeable within two to seven days. Because repeated steroid exposure risks local tissue damage, such as fat atrophy or weakening of tendons, the frequency of injections is carefully limited. Most physicians recommend a maximum of two to three injections in the same wrist per year, with a minimum interval of three to six months between treatments. This limitation underscores the importance of the initial dosage calculation to ensure the maximum possible benefit from each treatment.