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Steroid Injection, Carpal Tunnel

Overview
Carpal tunnel syndrome (CTS) is a compressive focal mononeuropathy that is brought on by compression of the median nerve as it travels through the carpal tunnel. Patients commonly experience pain, paresthesias, and weakness in the median nerve distribution. Carpal tunnel steroid injection at the wrist is used to treat the symptoms of carpal tunnel syndrome by injecting a steroid solution into the ulnar bursa surrounding the median nerve.
For mild to moderate carpal tunnel syndrome, carpal tunnel steroid injection can be used in conjunction with other conservative measures such as splinting, physical therapy, ergonomic modifications, rest, and regular exercise.^{[1, 2, 3, 4, 5]} Conservative modalities, including median nerve steroid injections, should generally be attempted prior to pursuing surgical options.^[6] Historically, carpal tunnel steroid injections were typically used for only mild median nerve entrapment (as documented by electroneurography) as well as for temporary pain relief in anticipation of definitive flexor retinaculum surgical release. In general, injected corticosteroids appear effective in reducing subjective symptoms for 1-3 months when compared to placebo.^[7] While short-term relief of symptoms after injection appears superior to relief after carpal tunnel release surgery, the advantage is lost over the course of a year.^[8]
Electrodiagnostic studies such as nerve conduction studies and electromyography are typically obtained to determine the severity of nerve damage prior to performing the procedure.^{[9, 10]} Steroid injections should be avoided prior to planned electrodiagnostic testing, as the presence of steroids may alter test results. Several clinical tests can be used to diagnose carpal tunnel syndrome. One is Tinel's sign, which is done by over the median nerve at the volar crease at the wrist to reproduce the paresthesia. The Phalen test involves holding the flexed wrists against each other for several minutes to provoke the symptoms in the median nerve distribution. Manual carpal compression testing is done by applying pressure over the transverse carpal ligament and evaluating for paresthesia within 30 seconds of applying pressure.^[11]
Carpal tunnel anatomy
The carpal tunnel of the wrist is defined anatomically by the transverse carpal ligament on the volar surface and the carpal bones on the dorsal surface. The transverse carpal ligament, also known as the flexor retinaculum, attaches radially to the trapezium and scaphoid tuberosity and ulnarly to the hamate and pisiform. The contents of the carpal tunnel include the 4 flexor digitorum profundus tendons, the 4 flexor digitorum superficialis tendons, the flexor pollicis longus tendon, and the median nerve. See images below.
Carpal tunnel anatomy. Carpel tunnel anatomy, cross-section.
There are 2 bursae in the wrist. The radial bursa contains the flexor pollicis longus tendon. The ulnar bursa, also known as the common flexor sheath, holds the flexor digitorum superficialis and profundus tendons. When the hand is supinated, the 4 superficialis tendons lay on top of the 4 profundus tendons, forming a U-shaped structure referred to as the ulnar bursa. On top of the ulnar bursa, and below the transverse carpal ligament, lies the median nerve. Although the median nerve itself has 2 sensory branches and 1 motor branch, only 1 sensory branch and the motor branch traverse through the carpal tunnel and are affected by carpal tunnel syndrome. This sensory branch is responsible for sensory innervation of the thumb, index finger, middle finger, and radial half of the ring finger. 
Indications

• Carpal tunnel syndrome not relieved by conservative measures
• Electrodiagnostic changes consistent with mild-to-moderate median nerve entrapment

Contraindications

• Adverse reaction to injectable steroid or anesthetic
• Uncontrolled diabetes mellitus
• Active systemic or local infection
• Compromised skin integrity over the area
• Immunosuppression
• Planned electrodiagnostic study

Anesthesia

• Lidocaine (Xylocaine) 1% without epinephrine, 2-3 mL
• Bupivacaine (Marcaine) 0.25%, 2-3 mL
• For more information, see Local Anesthetic Agents, Infiltrative Administration.

Equipment

• Needle, 1 in, 27 or 30 gauge (ga)
• Syringe, 5 mL
• Antiseptic solution with skin swabs
• Small rolled towel
• Triamcinolone acetonide (Kenalog), 10-20 mg; or methylprednisolone acetate (Depo-Medrol), 10-20 mg
• Lidocaine 1% or bupivacaine 0.25%

Positioning

• Patient should be positioned comfortably in a seated or supine position.
• The affected arm should be supinated with the dorsal aspect of the wrist resting over a small rolled towel.

Technique

• First, locate the flexor carpi radialis (FCR) and palmaris longus (PL) tendons. The palmaris longus tendon is medial to the flexor carpi radialis and is best located by opposing the thumb and fifth digit while the wrist is flexed. The image below depicts relevant anatomy and landmarks. For more information, see Flexor Tendon Anatomy. Solid blue line - palmaris longus tendon; solid red line - flexor carpi radialis tendon; dotted blue line - proximal palmar crease.
• Carefully disinfect the skin.
• Draw up 1 mL of 1% lidocaine and make a skin wheal ulnar to the palmaris longus and proximal to the proximal wrist crease.
• In another syringe, draw up the steroid with or without lidocaine or bupivacaine.
• Insert the needle 1 cm proximal to the proximal wrist crease and directly ulnar to the palmaris longus tendon at the skin wheal. Direct the needle distally toward the ring finger at an angle of 30 degrees. See image below. Needle placement - Medial of palmaris longus tendon.
• Advance the needle approximately 1.5-2 cm or until the tendon is touched.
• Aspirate to verify that no vasculature is affected, and inject the steroid solution with little or no resistance.
• Lastly, remove the needle and place the wrist in a gravity-dependent position.
• Advise the patient to actively move the fingers for several minutes to distribute the solution evenly.

Pearls

• Some people do not have a palmaris longus (PL) tendon.^{[12, 13]} In these cases, the needle is inserted at the midline between the radial and ulnar aspects of the wrist, proximal to the wrist crease, and is directed toward the ring finger (see image below). Needle placement in absence of palmaris longus tendon.
• If contact is made with the palmaris longus tendon while advancing the needle, retract slightly and redirect.
• The use of a needle smaller in diameter may require increased effort and slower injection time but dramatically reduces pain at the site of injection.
• Sudden worsening pain or paresthesia indicates the possibility of improper needle placement. If this occurs, retract the needle and redirect more medially (ulnar).
• To avoid potential complications of vascular or nerve ischemia, tissue necrosis, and serious damage to nerve, lidocaine with epinephrine should not be used. 

Complications

• Bleeding
• Infection
• Injury to nerve^{[14, 15]}
• Tendon rupture^[16]
• Temporary paresthesia
• Alteration in blood glucose levels in patients with diabetes mellitus
• Pain^[17]  

http://emedicine.medscape.com/article/103333-overview#a01