The Use of Ultrasound to Quantify Muscle Overlying the Carpal Tunnel

Introduction:

The pathophysiology of carpal tunnel syndrome (CTS) is in all probability multifactorial including many parameters that ultimately increase the pressure within the carpal tunnel. It is likely that the increased pressure then causes injury to the median nerve and the signs and symptoms of CTS. The relationship between the size or dimensions of the hand and the occurrence of CTS has been evaluated and "square-shaped" hands have also been examined to determine if there is an increased tendency to develop CTS. The literature remains inconclusive at this time. Other static anatomical parameters that have been evaluated include the size of the carpal tunnel and the thickness and biomechanical properties of the transverse carpal ligament again without absolute consensus in the literature.

Additional studies have evaluated the role of the intrinsic musculature within and surrounding the carpal tunnel in the etiology of CTS. Most of these studies have evaluated the muscles as space occupying lesions that add to the pressure within the carpal tunnel. The investigators believe that some of the muscles described, specifically those that are found within the transverse carpal ligament and that cross the area of the carpal tunnel, actually have a dynamic role in the etiology of CTS, especially in manual laborers that use their hands in a forceful manner in a repetitive fashion. It is also possible that this anatomic variant (muscles crossing the area of the carpal tunnel) is related to the "square "hand configuration and that this dynamic contribution to the pressure within the carpal tunnel is the reason for the increased incidence of CTS in these patients. The purpose of this study is to quantify the amount of muscle crossing the area of the carpal tunnel in normal individuals and to compare it to the amount of muscle in the wrists of patients with CTS.

Hypothesis: Participants with CTS will have more muscle crossing the carpal tunnel that normal controls (without CTS).

Purpose: To compare the amount of muscle crossing the carpal tunnel in normal controls (without CTS) and in patients with CTS

Specific aims:

1. To develop a system to quantify the amount of muscle crossing the carpal tunnel area using ultrasound of the wrist area.
2. To compare this measurement in normal wrists and in wrists with CTS
3. To compare the measurements in the CTS patients to intraoperative evaluation of the amount of muscle crossing the carpal tunnel area .
4. To compare these measurements to the external measurements of the hand (palm width/palm length)

Methods:

Fifty participants will be recruited for the study. Twenty five participants with no CTS- and twenty five with CTS.

The CTS group inclusion criteria:

The diagnosis of CTS will include:

1. Signs and symptoms of CTS: nighttime numbness and tingling or numbness and tingling in a median nerve distribution with a positive phalen or tinel or forearm compression test
2. A nerve conduction test and electromyography (NCT and EMG) that is positive for CTS.

The participants without CTS inclusion criteria:

1) Individuals that do not have any signs and or symptoms of CTS.

Exclusion criteria:

1. Individuals that have a known history of peripheral neuropathy or other condition in the hand including recent significant trauma.
2. Patients with incomplete or unclear evaluation and tests.
3. Individuals unwilling to sign a consent form to participate in the study.

Patients that meet the inclusion criteria and that are sent for carpal tunnel release surgery will be consented and examined on the day of surgery. Their US results, external palmar measurements as well as the amount of overlying muscle will be recorded as well as demographic data. Demographic information, occupational history, history of hand diagnoses and procedures as well as history pertinent to CTS (nighttime numbness and tingling, pain, perceived pinch weakness, and duration of symptoms) will be collected. Results of nerve conduction testing (NCT) will be recorded.

Physical examination findings pertinent to CTS will be collected including pinch strength, grip strength, 2-point discrimination, and the hand measurements of palm width (PW), palm length (PL).

External measurements: PL is measured as the vertical length from the midline of the distal wrist crease to the proximal middle finger. PW is measured as the horizontal length from the base of the 1st metacarpophalangeal (MP) joint along the proximal palmar crease.