Carpal Tunnel Syndrome (CTS) is a common condition caused by the compression of the median nerve as it travels through the narrow passageway in the wrist. This compression typically results in symptoms like numbness, tingling, and weakness in the hand and fingers, often worsening at night. When initial treatments such as wrist splinting or oral anti-inflammatory medications are insufficient, a cortisone injection becomes a non-surgical option. This targeted treatment delivers an anti-swelling agent directly to the source of the pressure. The goal is to reduce inflammation within the confined space of the carpal tunnel, alleviating pressure on the median nerve.
Mechanism of Action
The cortisone used in these injections is a type of corticosteroid, a synthetic version of hormones naturally produced by the body with anti-inflammatory properties. The carpal tunnel houses nine flexor tendons and the median nerve. These tendons are covered by the synovium, a lubricating membrane that often becomes inflamed and swollen in CTS, contributing to cramped conditions inside the tunnel.
Once injected, the corticosteroid concentrates around the median nerve and the inflamed subsynovial connective tissues. Its primary action is to suppress the inflammatory response that causes the swelling of the tendon sheaths. By reducing this inflammation and associated fluid buildup, the drug effectively increases the available space within the carpal tunnel.
The therapeutic effect may also involve a change in the tissue quality itself, beyond just reducing volume. Some research suggests the steroid works by inhibiting fibrosis, which softens the thickened subsynovial tissue. This change in consistency further relieves the mechanical stress placed on the median nerve. This localized application is more effective at addressing the compression than oral steroids, which diffuse throughout the body.
The Injection Procedure and Immediate Recovery
The cortisone injection is performed as a quick outpatient procedure, typically in a clinic or office setting. The process begins with applying a local anesthetic to numb the skin and underlying tissue, minimizing discomfort. A small needle is then used to deliver the medication directly into the carpal tunnel space at the wrist.
To ensure safety and accuracy, the injection is often administered with the guidance of an ultrasound machine. This imaging allows the clinician to visualize critical structures, including the median nerve and surrounding tendons, in real-time. Ultrasound guidance confirms the precise placement of the medication and helps avoid accidental injury to the nerve or tendons during the procedure.
Following the injection, patients are advised to rest the treated wrist for 24 to 48 hours, avoiding strenuous activity or heavy lifting. Applying ice to the injection site can help manage any immediate soreness or localized pain. Patients should use the hand gently for daily tasks but refrain from repetitive or overusing motions for a few days to allow the medication to settle and begin working.
Expected Results and Longevity
The initial effect often comes from the local anesthetic mixed with the cortisone, providing immediate but short-lived numbness. The anti-inflammatory effect of the corticosteroid generally takes a few days to a week to become noticeable. The greatest relief is typically experienced within two to four weeks. The injection serves as both a therapeutic intervention and a diagnostic tool, as a good response helps confirm the diagnosis of carpal tunnel syndrome.
The level and duration of relief are highly variable among individuals. For many, the injection provides significant symptom relief, often lasting for several months or sometimes even a year. However, it is not considered a permanent cure, especially in cases where nerve compression is severe or caused by chronic issues.
Symptoms will eventually return in a substantial number of cases, necessitating further treatment. Studies indicate that while the injection can provide long-term relief for about one-third of patients, the majority will require additional intervention over several years. For those who experience a return of symptoms, the injection may still delay the need for carpal tunnel release surgery.
Potential Side Effects and Limitations
While generally considered a safe procedure, patients should be aware of several potential side effects. The most common immediate concern is a temporary increase in pain at the injection site, sometimes called a “steroid flare.” This soreness can last for one to two days before the beneficial effects begin. This temporary pain can usually be managed with rest and ice application.
Localized side effects are also possible, including changes to the skin and underlying tissues near the injection site. These can manifest as skin discoloration, such as lightening or thinning of the skin, or fat atrophy (a slight depression in the tissue). These effects are typically cosmetic and not medically serious, though they can be more noticeable in individuals with darker skin tones.
Rare but more serious risks include infection, which is minimized by sterile technique, and injury to the median nerve or tendon. The risk of injury is significantly reduced when ultrasound guidance is used. Corticosteroids can potentially weaken tendons, which is why repeat injections are limited. Physicians generally advise against receiving more than two or three cortisone injections in the same wrist per year due to the risk of tissue damage.