Carpal Tunnel Injection: Procedure, Benefits, and Recovery

Carpal tunnel syndrome (CTS) causes pain, numbness, and tingling in the hand due to pressure on the median nerve. When conservative treatments like splinting or physical therapy fail, corticosteroid injections can reduce inflammation and swelling, offering relief.

This minimally invasive procedure is often attempted before surgery. Understanding how these injections work, their benefits, and what to expect during recovery can help individuals make informed treatment decisions.

Anatomy Of The Wrist And Carpal Tunnel

The wrist is a complex structure of bones, ligaments, tendons, and nerves that facilitate movement. The carpal tunnel, a narrow passageway formed by the carpal bones and the transverse carpal ligament, houses the median nerve and nine flexor tendons. Due to its rigid boundaries, any swelling or structural changes can compress the median nerve, leading to CTS symptoms.

The median nerve originates from the brachial plexus in the neck and travels through the carpal tunnel into the hand. It provides sensation to the thumb, index, middle, and part of the ring finger while controlling motor function in several hand muscles. Unlike other nerves, it has little surrounding soft tissue for protection, making it especially vulnerable to compression. Even minor increases in pressure from inflammation or repetitive strain can impair function.

Carpal tunnel dimensions vary, and a smaller cross-sectional area increases CTS risk. Normal tunnel pressure ranges from 2 to 10 mmHg, but in CTS patients, it can exceed 30 mmHg, particularly during wrist movement. Prolonged pressure disrupts blood flow, causing ischemia and demyelination, which result in pain, tingling, and weakness. Chronic compression can lead to permanent nerve damage, emphasizing the importance of early intervention.

Corticosteroid Mechanisms In Nerve Sheath

Corticosteroid injections relieve CTS symptoms by reducing inflammation around the median nerve. The perineurium, a protective layer surrounding nerve fascicles, helps regulate fluid exchange. When inflamed, it increases pressure within the carpal tunnel, worsening nerve compression. Corticosteroids like methylprednisolone and triamcinolone suppress pro-inflammatory cytokines such as TNF-α and IL-6, reducing pain and swelling.

Once injected, corticosteroids diffuse through nerve layers, inhibiting phospholipase A2, which reduces prostaglandin and leukotriene production. These mediators contribute to pain and vascular permeability, so their suppression decreases swelling and improves microcirculation. Additionally, corticosteroids stabilize capillary membranes, preventing further fluid accumulation that could intensify compression.

Beyond inflammation control, corticosteroids affect sodium and potassium channels in the median nerve, reducing abnormal nerve signaling. Studies show they downregulate voltage-gated sodium channels, decreasing hyperexcitability and spontaneous discharges that cause pain and tingling. By restoring a balanced nerve function, corticosteroid injections can not only relieve symptoms but also slow nerve deterioration in mild to moderate cases.

Ultrasound Techniques For Needle Placement

Ultrasound technology has improved the accuracy of corticosteroid injections for CTS, allowing real-time visualization of anatomical structures. Unlike blind techniques, ultrasound guidance ensures precise needle placement while minimizing the risk of nerve or vascular injury. The median nerve appears as a hypoechoic, oval structure within the carpal tunnel, and adjusting the transducer angle enhances clarity.

A key factor in ultrasound-guided injections is selecting the best approach to avoid critical structures. The in-plane technique, where the needle is inserted parallel to the transducer, provides continuous visualization and greater control over depth and trajectory, reducing the risk of intraneural injection. The out-of-plane approach, where the needle is perpendicular to the transducer, offers a shorter path but requires greater precision. Studies show the in-plane method has a higher accuracy rate, exceeding 95% in achieving safe perineural placement.

Ultrasound also allows dynamic assessments of median nerve mobility and compression patterns. By having patients move their fingers during scanning, clinicians can identify entrapment sites and optimize injection placement. Doppler imaging can assess vascular flow, helping avoid inadvertent injection into the median artery, a variant found in some individuals.

Composition Of Injection Solutions

Corticosteroid injections for CTS are formulated to balance potency, duration, and safety. Commonly used steroids include triamcinolone acetonide, methylprednisolone acetate, and betamethasone. Particulate steroids like triamcinolone and methylprednisolone remain longer in the tissue, providing sustained effects, while non-particulate options like dexamethasone are absorbed faster but carry a lower risk of intraneural deposition.

Corticosteroids are typically suspended in a sterile carrier solution, often saline or lidocaine. Lidocaine, a local anesthetic, provides immediate relief by temporarily blocking sodium channels in nerve fibers. This helps differentiate mechanical compression from inflammatory pain, as rapid symptom relief suggests a favorable response to corticosteroid therapy. However, lidocaine concentration must be carefully controlled to prevent neurotoxicity, particularly in cases of inadvertent intraneural injection.