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Median Nerve Entrapment Workup

  • Author: Bardia Amirlak, MD; Chief Editor: Harris Gellman, MD  more...
Updated: Feb 24, 2016

Laboratory Studies

Some evidence suggests that there is a higher prevalence of concurrent conditions, such as diabetes mellitus and rheumatoid arthritis, in patients with carpal tunnel syndrome (CTS). At present, however, there is not enough evidence to warrant routine laboratory screening for such conditions in all patients with newly diagnosed CTS.[70]


Imaging Studies

Both ultrasonography and magnetic resonance imaging (MRI) may be useful in the evaluation of patients with upper-extremity neuropathies.[71, 72] Atrophy can be appreciated in the involved muscles. Signal changes can also point to the affected muscles. Ultrasonography can similarly identify the affected muscles by looking at the muscle mass, perfusion on Doppler ultrasonography, and active contraction of affected muscles.[73, 74]  For diagnosis of CTS, peripheral nerve ultrasonography may be particularly useful in combination with electrodiagnostic studies (see Diagnostic Procedures).[75, 76]


Diagnostic Procedures

Electrodiagnostic examination

Major limitations are associated with electrodiagnostic examination. False-positive and false-negative results are common. Patients with a positive clinical diagnosis of CTS and negative findings on electrodiagnostic studies improve with carpal tunnel release.[77]

Although electrodiagnostic studies provide quantifiable values, they are particularly dependent on the proficiency of the examiner.[78] These studies should only complement the clinical evaluation by helping to localize the level and severity of the injury and to monitor the progression of the disease when it is being managed conservatively. Electrodiagnostic studies are not generally helpful in confirming a diagnosis of more proximal lesions.

Needle electromyography

Needle electrodes are placed into muscle to record fibrillation potentials; sharp waves and increased insertional activity indicate advanced nerve compression. However, electromyography (EMG) cannot differentiate a median nerve lesion at the pronator teres from a more proximal lesion.[79] In addition, proximal median neuropathy is frequently normal preoperatively.[63]

Measurement of nerve conduction velocity

The velocity of motor and sensory nerve conduction is measured across definite landmarks. Latency greater than 3.5 ms or asymmetry of conduction velocity greater than 0.5 ms as compared with that of the opposite hand indicates possible entrapment neuropathy. Each segment of the upper extremity can be isolated for specific measurement.

Generally, an increase in sensory latency is observed first, and upon progression of the disease, an increase in the latency of motor fibers is seen. These studies assess only the large myelinated fibers, not the small ones that mediate pain. Nerve conduction studies may be less dependable when there is multiple levels of damage or when a systemic polyneuropathy is present.

Sensibility testing

Sensibility tests can be used to identify compressive neuropathies associated with sensory loss. These include two-point discrimination, Semmes-Weinstein monofilament (SWM) testing, and Strauch's ten test. The SWM test is more reliable, but it is time-consuming.[80]

Contributor Information and Disclosures

Bardia Amirlak, MD Assistant Professor of Plastic Surgery, Director of Residency Cosmetic Clinic, Director of Plastic Surgery Global Health Program, University of Texas Southwestern Medical Center at Dallas; Chief of Hand and Peripheral Nerve Surgery, Dallas Veterans Affairs Medical Center

Bardia Amirlak, MD is a member of the following medical societies: American College of Surgeons, American Society of Plastic Surgeons, American Society of Reconstructive Transplantation, Kleinert Society

Disclosure: Nothing to disclose.


Thomas W Wolff, MD Associate Clinical Professor of Hand Surgery, University of Louisville School of Medicine; Director, Christine M Kleinert Institute for Hand and Microsurgery

Thomas W Wolff, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Medical Association, American Society for Surgery of the Hand, American Society for Reconstructive Microsurgery, Indiana State Medical Association, Kentucky Medical Association, American Association of Clinical Anatomists

Disclosure: Nothing to disclose.

Omar Ahmed, MD Senior Fellow in Hand and Microvascular Surgery, Department of Surgery, Kleinert Institute

Omar Ahmed, MD is a member of the following medical societies: American Association for Hand Surgery, American Medical Association, American Society for Surgery of the Hand, American Society for Reconstructive Microsurgery

Disclosure: Nothing to disclose.

K Prashant Upadhyaya, MBBS, MS Resident, Department of General Surgery, Creighton University Medical Center

Disclosure: Nothing to disclose.

Tsu-Min Tsai, MD Clinical Professor of Surgery, University of Louisville School of Medicine; Consulting Surgeon, Kleinert, Kutz and Associates Hand Care Center, PLLC

Tsu-Min Tsai, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Association for Hand Surgery, American College of Surgeons, American Medical Association, American Society for Surgery of the Hand, American Society for Reconstructive Microsurgery, Arthroscopy Association of North America, Kentucky Medical Association

Disclosure: Nothing to disclose.

Luis R Scheker, MD Assistant Clinical Professor, Division of Plastic and Reconstructive Surgery, University of Louisville School of Medicine; Assistant Consulting Professor, Department of Surgery, Duke University Medical Center; Consulting Staff, Kleinert, Kutz and Associates Hand Care Center, PLLC

Luis R Scheker, MD is a member of the following medical societies: American Medical Association, Kentucky Medical Association

Disclosure: Nothing to disclose.

Georges N Tabbal, MD Resident Physician, Department of Plastic and Reconstructive Surgery, University of Texas, Southwestern Medical Center at Dallas, Southwestern Medical School

Georges N Tabbal, MD is a member of the following medical societies: Texas Society of Plastic Surgeons

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Harris Gellman, MD Consulting Surgeon, Broward Hand Center; Voluntary Clinical Professor of Orthopedic Surgery and Plastic Surgery, Departments of Orthopedic Surgery and Surgery, University of Miami, Leonard M Miller School of Medicine, Clinical Professor, Surgery, Nova Southeastern School of Medicine

Harris Gellman, MD is a member of the following medical societies: American Academy of Medical Acupuncture, American Academy of Orthopaedic Surgeons, American Orthopaedic Association, American Society for Surgery of the Hand, Arkansas Medical Society

Disclosure: Nothing to disclose.

Additional Contributors

Michael S Clarke, MD Clinical Associate Professor, Department of Orthopedic Surgery, University of Missouri-Columbia School of Medicine

Michael S Clarke, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Arthroscopy Association of North America, American Academy of Pediatrics, American Association for Hand Surgery, American College of Surgeons, American Medical Association, Clinical Orthopaedic Society, Mid-Central States Orthopaedic Society, Missouri State Medical Association

Disclosure: Nothing to disclose.

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Anatomy of median nerve along its course in upper extremity.
Ligament of Struthers.
Lacertus fibrosus (bicipital aponeurosis).
Pronator teres.
Fibrous arch of flexor digitorum superficialis.
Gantzer's muscle.
Traditional open carpal tunnel incision.
Lighted retractor allows direct visualization of transverse carpal ligament, which can be divided under direct vision with knife or scissors.
Blade (swivel knife) and blade guide (grooved Mickey Mouse director) are used to divide transverse carpal ligament when minimally invasive incision is made.
Two red lines show correct locations of incisions for endoscopic carpal tunnel surgery. FCR=flexor carpi radialis tendon; H=hook of hamate; P=pisiform; PL=palmaris longus tendon.
Cannula is inserted inside carpal space, with groove of instrument facing up.
Endoscope is inserted in cannula attached to endoscopic knife. Knife is pushed forward along cannula's groove, and carpal ligament is divided under direct vision.
Type of endoscopic knife used in carpal tunnel surgery.
Instruments used in endoscopic carpal tunnel surgery. From left to right: endoscopic camera, endoscopic knife, cannula, scraper, custom-made plastic tube, and elevator.
Incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) exposure.
Alternative incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) is marked by horizontal thickened lines. Relative locations of underlying pertinent structures are marked on skin. Bicep=biceps tendon; BR=ulnar border of brachioradialis; LABN=lateral antebrachial cutaneous nerve; MABN=medial antebrachial cutaneous nerve; PT=radial border of pronator teres.
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