Carpal tunnel. Please note the recurrent branch and palmar cutaneous branch of median nerve. (Reprinted with permission from Philip Peng Educational Series)
Diagnosis begins with a complete history characterizing the type of pain and its location. The history should correlate with expected findings of median nerve compression as it passes through the tunnel at the wrist. These include burning pain associated with numbness and tingling of the volar surface of the thumb, index finger, middle finger, and radial half of the ring finger. The palm and little finger are often spared. Symptoms often worsen at night and after repeated use. Traditional physical exam maneuvers to reproduce nerve compression including Tinel’s sign and Phalen’s test are neither highly sensitive nor specific. Thenar atrophy can help to rule in. Diagnostic testing includes electrodiagnostic studies (nerve conduction and electromyography) and ultrasound measurements of median nerve cross-sectional area.
Position: Seated with forearm supinated with hand resting comfortably on the table. Rolled towel can support wrist in mild extension.
Probe: High-frequency linear array transducer (10 MHz+); Hockey stick linear probe is preferred.
Short axis over the distal wrist crease (Fig. 21.3)
The borders of the tunnel seen are the scaphoid and trapezium laterally and the hamate and pisiform medially. The roof of the tunnel is the flexor retinaculum (marked with ∗). Identify the flexor carpi radialis (FCR) and the palmaris longus (PL) located superficial to the flexor retinaculum. The median nerve (MN) will appear honeycomb-like in the tunnel along with the hypoechoic tendons of the flexor digitorum profundus (flexor tendons), flexor digitorum superficialis (flexor tendons), and flexor pollicis longus (FPL). To clearly identify the nerve, scan proximally and distally. The ideal injection will have the median nerve identified at the level of the pisiform under the transverse carpal ligament. Use color flow to mark the location of the ulnar artery (UA) as in the right lower diagram. The left diagram shows the position of the probe and the underlying structures.
Needles: 25G–27G 1.5 inch needle
Drugs: 1–3 mL local anesthetic (0.25% plain bupivacaine)
0.5 mL steroid (depomedrol)
In-plane approach is performed from ulnar to radial inserting the needle 1–3 cm away and parallel to probe just radial or deep to the ulnar nerve and artery at a shallow angle (Fig. 21.4). The needle (arrows) will be visualized in the canal. Here, the needle is next to and under the median nerve (MN). The injectate can now be administered. As the space is enclosed, the medicine will spread and saturate the nerve.
Short axis over the distal wrist crease (Fig. 21.5). With the probe target just ulnar to the median nerve, an out-of-plane approach is performed by inserting needle perpendicular to the probe at a steep angle directed just off to the ulnar side of the median nerve (MN). A small hyperechoic dot will be seen on the ulnar side of the nerve (needle tip depicted by arrowhead). Use caution with out-of-plane injections to ensure tip is under the transducer. Inject next to the nerve.
To visualize the median nerve, isolate a relatively hypoechoic area surrounded by hyperechoic tendons in cross-sectional view.
Tilt/angle the probe or have patient flex and extend their hand: the nerve will remain relatively unchanged because the tendons are more subject to anisotropy.
Look for adhesions, which can be treated by hydrodissection.
Track nerve proximally up the arm if difficult to visualize.
Use gel standoff technique if wrist is too small to achieve a shallow needle trajectory.
Use color flow to aid in identifying vascular structures such as a persistent medial artery.
Advise patients to refrain from driving secondary to possible temporary hand numbness/weakness.
Ultrasound-guided injections at the carpal tunnel allow the practitioner to visualize the median nerve, assess for any structural abnormalities or masses, and ultimately place medicine in the correct position without damaging the nerve. Median nerve blocks are proven to provide pain relief in patients suffering from carpal tunnel syndrome. Ultrasound-guided corticosteroid injections targeting the median nerve are more accurate over direct approach and demonstrate significant improvements in post-injection monofilament testing, sensory nerve conduction velocity, and digit-4 comparison study (comparing ulnar to medial sensory latency at the dually innervated fourth digit). The American Academy of Orthopedic Surgeons suggests the use of local steroid injections prior to considering surgery for carpal tunnel syndrome. Recent studies demonstrate that in-plane ulnar approach proves to be superior over out-of-plane injection.
De Quervain’s Tenosynovitis
Pain or tenderness in the first extensor compartment of the radial wrist at the styloid process produced by a tendinopathy of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) is known as De Quervain’s tenosynovitis (Fig. 21.6). These tendons are involved in radial abduction and extension of the thumb. Through progressive rubbing, these tendons become irritated causing symptoms.
Locate the abductor pollicis longus and extensor pollicis brevis tendon at the first dorsal compartment at the radial styloid process (Fig. 21.7). The APL originates at the ulna and inserts at the base of the metacarpal of the first digit. The EPB originates at the lower third of the radius and inserts at the base of the proximal phalanx of the first digit.
Patients present with radial sided wrist pain at the thumb base with histories of overuse often without direct acute trauma. There is a higher prevalence in the dominant wrist. Tenderness is common over the location of the APL and EPB tendons.
Classically, the Finkelstein maneuver will reproduce symptoms as the two thumb tendons are elongated by flexing the thumb and ulnar deviating the wrist (Fig. 21.8). Imaging is not routinely useful as x-rays are expected to be unremarkable. With ultrasound, one can demonstrate a thickened extensor retinaculum indicating possible synovitis.
Position: Seated with elbow flexed with radial styloid facing up and arm resting comfortably on the table
Probe used: High-frequency linear array transducer (10 MHz+); Hockey stick probe is preferred.
Over the radial styloid process, the transducer is placed transversely, short axis to visualize the first extensor compartment (Fig. 21.9). The abductor pollicis longus (APL) and extensor pollicis brevis (EPB) are seen. Extensor retinaculum (outlined by ∗) lies superficially to tendons and radius (RAD) is seen deep to tendons. Note location of the radial artery prior to injection.
Longitudinal View of Radial Styloid and APL Tendon
Over the radial styloid process, the transducer is rotated longitudinally (Fig. 21.10). Abductor pollicis longus (APL) and extensor pollicis brevis (EPB) are seen along their long axis above the radius.