Determinants of the Maximal Nerve Cross‐Sectional Area and Its Role in the Separation of Entrapment and Compression Ulnar Neuropathies at the Elbow
Simon PodnarABSTRACT
Introduction/Aims
Nerve cross‐sectional area (CSA) is the most robust and sensitive ultrasonographic indicator of nerve pathology. The study aimed to identify predictors of maximal CSA (CSA max ) in ulnar neuropathy at the elbow (UNE) and to assess its utility in elucidating the mechanism of UNE, which is potentially important for patient referral to a surgeon.
Methods
In a group of prospectively recruited UNE patients, 11 demographic, clinical, and electrodiagnostic features were recorded. CSA max in the elbow segment was measured ultrasonographically. Explanatory variables for CSA max were determined using a backward stepwise method of multiple linear regression analysis. To determine the CSA max threshold with the best differentiation of retrocondylar compression and cubital tunnel entrapment (i.e., the UNE mechanism), a ROC curve was constructed.
Results
We studied 130 patients (94 men), aged 27–88 years (median 62 years). The only significant predictor of CSA max was the mechanism of UNE (CSA max = 7.49 + 6.89 UNE mechanism, SE 1.04, (adjusted) R 2 = 0.25, p < 0.0001). The best differentiation between UNE mechanisms was obtained at the CSA max of 16 mm 2 (sensitivity 0.80, positive predictive value 0.71).
Discussion
In UNE, the main determinant of CSA max was the mechanism of neuropathy. In the UNE of unclear mechanism, CSA max larger than 16 mm 2 is more in favor of a cubital tunnel entrapment. These findings suggest that US is more sensitive in the diagnosis of entrapment compared with compression neuropathies.