Patients with carpal tunnel symptoms typically have numbness and tingling in the thumb and first finger and part of the middle finger. This is most commonly caused by repetitive use injury of the median nerve at the carpal tunnel in the wrist where the nerve has to bend as the wrist is flexed. This repetitive stress causes inflammation and subsequent fibrosis of the nerve leading to symptoms.
The median nerve on the right side of the picture before it goes into the carpal tunnel is normal. Once the nerve goes into the carpal tunnel you can see that it is thickened and swollen and has lost its normal “honeycomb” appearance. The patient also experienced reproduction of the symptoms during the exam at this location but not at the other parts of the median nerve.
Patients that have carpal tunnel syndrome can benefit from ultrasound diagnosis from experienced radiologists trained in musculoskeletal ultrasound. Ultrasound can identify if there is a mass or other cause of the symptoms in case of an abnormal EMG before going to carpal tunnel surgery. Ultrasound can also be used with EMG or by itself to diagnose carpal tunnel.
When a patient comes to Ultrasound First they will sit in a comfortable chair with their arm in a comfortable position while the median nerve is evaluated. Gel is placed on the arm and a probe is placed in strategic locations along the nerve. The nerve is evaluated for changes in its shape and architecture. A normal nerve has a “honey comb” appearance. As fibrosis builds up in the nerve at a point of entrapment, this honeycomb disappears as the normal lining of the nerve fascicles is replaced. The nerve is also measured at key locations. A wrist-to-forearm ratio of 1.4 or more showed 100% sensitivity for detecting patients suffering from CTS (carpal tunnel syndrome).
Ultrasound is especially helpful to identify pronator teres syndrome which is entrapment of the median nerve at the pronator teres muscle near the elbow. This can be visualized on the ultrasound in real time. We follow the entire length of the nerve from the wrist to the arm.
The examination takes between 10-20 minutes. Using MRI for the same thing would take 45 minutes and may or may not show the problems.