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Utility of Ultrasonography versus EMG/NCS in the Diagnosis of Cubital Tunnel Syndrome
Raghuveer Muppavarapu, MD; Kenneth Brock, MD; Michael Gottschalk, MD; Anthony Sapienza,MD
NYU Hospital for Joint Diseases, New York, NY

Introduction: Electrodiagnostic testing (EDT) is the most common test used to confirm the diagnosis of ulnar nerve entrapment at the elbow. In comparison to EDT, the diagnostic accuracy of ultrasonography (US) is unknown. We hypothesize that US has a higher correlation to clinical examination findings and is more accurate at detecting ulnar nerve entrapment at the elbow than EDT.
Methods: Between January 2012 and January 2015, 51 patients were identified who underwent ulnar nerve decompression at the elbow by the same surgeon. 32 patients met the inclusion criteria of having a pre-operative EDT. 24 of those 32 patients also had an US evaluation of the ulnar nerve. Pertinent pre and post-operative clinical examination included: Tinel, elbow flexion compression test, Semmes Weinstein, 2-point discrimination, intrinsic muscle strength, and FDP strength testing. Chi square and fisher exact test were used for nominal variables. Wilcoxon / Kruskal Wallis tests were used for continuous variables. Statistical significance was set at a p-value of 0.05.
Results: 15 patients had a positive EDT result and 17 had a negative EDT result. All 24 patients who had US evaluation of the ulnar nerve at the elbow had a positive finding of ulnar nerve compression. There was a positive correlation between intrinsic strength improvement and FDP strength improvement for the patients with a positive EDT result (Table 1). All patients had an improvement in their DASH score with an average pre-operative DASH score of 51.04 and average post-operative DASH score of 20.67 (Table 2).
Conclusion: Ultrasonography is a fast, inexpensive, and accurate screening tool for diagnosing ulnar nerve compression at the elbow. EDT testing had an unacceptably high false negative detection rate of ulnar nerve compression at the elbow. US can be used to improve the diagnosis of ulnar nerve compression at the elbow and potentially change the current standards for diagnostic evaluation.

TABLE 1 CLINICAL TESTING

EDT result Percussion of ulnar nerve at elbow (Tinels) Elbow Flexion Compression test Semmes Weinstein

(improvement)

2-pt disc

(improvement)

Intrinsic Strength

(improvement)

FDP Strength

(improvement)

Positive (n = 15) 13   (86.7%) 10

(66.67%)

11

(73.3%)

14

(93.3%)

14

(93.3%)

12

(80%)

Negative (n = 17) 15

(88.2%)

15

(88.2%)

11

(64.7%)

10

(58.8%)

8

(47%)

6

(35.3%)

p-value 1 0.107 0.857 0.107 0.005 0.02

TABLE 2 - DASH

  Positive EDT, Positive US Negative EDT, Positive US All patients
Mean

Preop DASH

58.029 46.05 51.04
Mean

Postop DASH

24.66 17.82 20.67


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