Position and anatomical landmarks
The injections are administered in or just proximally to the carpal tunnel, 3-4 cm proximally to the distal wrist fold.
The skin is disinfected locally and covered. The needle is inserted near the distal wrist fold on the ulnar side of the tendon of the palmaris longus muscle. The wrist is kept in slightly dorsal flexion. The needle is inserted in the direction of the base of the middle finger at an angle of approximately 450 so that it reaches the carpal tunnel through the transverse carpal ligament. The needle should be retracted and reinserted 1 cm further proximally if the patient's fingers start to tingle. Alternatively, the needle can be inserted initially either in a more ulnar position in the tendon of the palmaris longus muscle, or between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle. In the latter case, the needle should be inserted at an angle of 300. When the needle tip is in the carpal tunnel, rather than in a tendon, the needle and injection will meet minimal resistance.
During injection proximally to the carpal tunnel, the risk of damaging the median nerve is less if the needle is inserted 3 cm proximally to the distal wrist fold. This is due to the fact that, at that site, the nerve is less fixated (more mobile) than it is inside the carpal tunnel. The 3-cm-long injection needle is inserted in a more ulnar position in relation to the tendon of the palmaris longus muscle, or between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle at an angle of 100 to 200, towards the third interosseous space.
The thermocouple is inserted after perforation of the skin. The median nerve is located by means of stimulation of 50 Hz, 0.5 V, until the patient feel paraesthesia in the first three fingers. Thereafter, two PRF treatments will be performed with 45 V for 120 seconds at a maximum temperature of 42o C.
- The most serious complication after the injection is infection.
- Small subcutaneous bleedings may result in a temporary increase in pain after the injection.