De Quervain tenosynovitis was first described by Swiss physician Fritz de Quervain, in 1895, in a series of case reports. [1, 2] This common condition is caused by inflammation of the tendons in the first dorsal compartment of the wrist. The tendons involved are the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons (see the image below). 
Repetitive radial and ulnar deviation of the wrist, associated with flexion of the thumb, causes thickening of the tendon sheath and pain when the inflamed tendons cross the distal radial styloid.
Patients who report these symptoms often have occupations that involve repetitive gripping and grasping with the thumb or pastimes such as racquet sports, golf, or disc throwing. According to a 2009 report, risk factors include the following  :
Age over 40 years
Physical examination is significant for tenderness at the distal radial styloid.  The Finkelstein test is positive in these patients—that is, pain is elicited when the patient makes a fist with the thumb tucked in and the wrist is rotated in the ulnar direction. Steroid injection is efficacious when standard conservative treatment fails.
Indications and contraindications
Thumb injection is indicated for the treatment of de Quervain tenosynovitis. Contraindications include local infection and allergy to the chosen anesthetic or corticosteroid.
Equipment used for thumb injection includes the following:
Syringe, 3 mL
Needle, 1 in. (to draw up into the syringe)
Needle, 27 gauge, 0.5 in. (to inject)
Sterile examination gloves
Povidone-iodine skin preparation with sterile gauze
Corticosteroid, 1-2 mL (eg, triamcinolone acetonide or methylprednisolone acetate; see the image below)
Local anesthetic agents (eg, bupivacaine 0.5% or lidocaine 1%) may be used. The local anesthetic can be mixed with the corticosteroid.
For proper positioning, identify the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons by having the patient extend the thumb (see the image below). Mark the gap between the tendons, distal to the radial styloid. Place the patient's hand vertically with the radial side up in a relaxed position.
Conservative treatment for this condition includes rest, ice, stretching and strengthening exercises, nonsteroidal anti-inflammatory drugs (NSAIDs), and thumb spica wrist splinting. [6, 7] If these measures fail, studies have proven the efficacy of steroid injections in treating these symptoms.  It has been suggested that the combination of steroid injection with thumb spica casting may yield better results than injection alone. 
A pooled literature evaluation demonstrated an 83% cure rate with injection alone.  However, if symptoms recur or do not resolve after two injections, surgical consultation is indicated. Surgery involves decompressing the first dorsal compartment by making an incision through the tendon sheath. For more information on surgical technique, see De Quervain Tenosynovitis.
Obtain informed consent. Prepare the steroid/anesthetic mixture (0.5-1 mL of local anesthetic with 1-2 mL of corticosteroid). Position the patient as described previously (see Periprocedural Care), and mark the area to be injected. Sterilize the area with povidone-iodine solution.
With sterile technique, use a 27-gauge 0.5-in. needle to inject the steroid-anesthetic solution. Hold the needle at a 45º angle in line with the two tendons (see the image below). Advance the needle until it strikes the tendons, then withdraw slightly. Inject the solution. The injected material should flow in easily. If it does not, the needle may be in the tendon. Do not inject if the needle is in the tendon; instead, withdraw slightly and inject when less resistance is met.
Ultrasonography is a valuable asset in the diagnosis and treatment of de Quervain tenosynovitis. Not only does it show the thickening of the tendons, but it allows direct visualization of the needle entering the tendon sheath. It helps decrease cases of intratendinous injection and some complications of subcutaneous corticosteroid injection, such as fat atrophy and skin hypopigmentation. It is especially beneficial in confirming injection into the correct subcompartment when a dividing septum is present in the tendon sheath. [11, 12]
After the injection, compress the area and apply a bandage. Apply ice for 10-15 minutes every 4-6 hours after the procedure. (See the videos below.)
Complications of thumb injection include the following:
Local skin hypopigmentation (white spot around the injection site)
Fat atrophy (depression of skin at the location of the injection  )