The Value of Clustering CTS Tests
The Value of Clustering Carpal Tunnel Tests
Carpal Tunnel Anatomy
The carpal tunnel is an osteofibrous canal of the wrist. It is defined by the boundaries of the carpal bones and the flexor retinaculum. Within the carpal tunnel are nine tendons and the median nerve. The latter being a significant structure since one of the hallmark signs is edema which puts a back-pressure on the median nerve to produce burning, tingling, and numbness into the palm, thumb, and/or index and middle fingers. Individuals with diabetes, hypertension, high sodium intake, sedentary lifestyles, smoking, and high body mass index (BMI) have as increased risk of carpal tunnel syndrome (CTS).
Clinical Predictor Rules
Research by Wainner et al (2005) and Childs and Cleland (2006) have contributed to the development of Carpal Tunnel Clinical Predictor Rules. The following are the parameters identified as the clinical predictors:
- Flick Test relieves symptoms (discussed below)
- Wrist ratio (Anterior-Posterior width / Medial-Lateral width) > 0.67
- Symptoms Severity Scale > 1.9
- Diminished sensation of thenar eminence
- Age > 45 years old
The likelihood of having CTS is influenced by the number of the signs/symptoms present. As one can see, the more positive tests, the greater the likelihood of a diagnosis of CTS.
Carpal Tunnel Clinical Tests
There are at least 5 carpal tunnel tests in the literature. We will discuss the performance of these tests, the metrics, and the influence of clustering various tests. These tests include: Phalens, Reverse Phalens, Flick, Carpal Tunnel Compression, and Tinel sign.
Phalen & Reverse Phalen Test
These tests aim to compress the median nerve in the carpal tunnel with endrange flexion or extension, respectively. For the Phalen test, the patient puts the back of both hands together with his/her arms elevated at the level of the shoulder. For the Reverse Phalen test, the patient puts the palms together with his/her arms elevated at the level of the shoulder. An easy way to remember the positions for these two tests is: Phalen Test by ‘Fingers-Falling.’ In contrast, the Reverse Phalen is “fingers Rising.” A positive test is numbness or tingling into the median nerve distribution, i.e. palmar surface of digits 1, 2, and 3.
The Flick Maneuver is an interesting test. It does exactly what is sound like…..it involves flicking the wrist. Where most tests look to reproduce the symptoms, this test is positive when the symptoms (paresthesias into the median nerve distribution) subside as a result of the repeated flicking maneuver of the wrist. As per the summary statistical chart below, sensitivity and specificity have a wide range. This may be due to the interpretation of the magnitude of the symptom relief being highly variable.
Carpal Tunnel Compression Test
The carpal tunnel compression test simply involves positioning the wrist in at least 60° of flexion and maintaining the position for 30 seconds. This position is essentially the same as a Phalen test without addressing the position of the shoulder. A positive test is numbness or tingling into the median nerve distribution. Thus, it is not a surprise to learn the statistics are almost exactly the same as the Phalen test.
A Tinel sign is a common sign used in a variety of locations of the body and indicates that a nerve is irritated. This test can be performed at the elbow, shoulder, ankle, and wrist. A Tinel sign is positive when light percussing over the nerve elicits tingling into the distribution of the nerve. When performing this test on the wrist, one taps over the anterior aspect of the wrist to incriminate the median nerve.
The statistics for this individual test is highly variable. This may be attributed to the interpretation of the magnitude of the paresthesias produced. However, when coupled with the Phalen test or Flick maneuver, the diagnostic metric improves.
CTS Test Statistics
When assessing the results of a test, it is always helpful when you have a contralateral structure to which you can compare. Obviously it is always desirable to obtain positive results from at least two tests for a given tissue to provide some reassurance of the diagnosis. Notwithstanding the high variability of the statistical data for the individual tests, there is slightly better data with the clustering of carpal tunnel tests. The chart below displays these results.
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