What is the bun test used to measure?

The Bun Test

The Bun test, also known as the Bun-Crossed Sign test, is a clinical examination used to assess the integrity of the lateral femoral cutaneous nerve (LFCN). The LFCN provides sensory innervation to the anterolateral aspect of the thigh.

Procedure

The patient is asked to lie in the supine position with their knee extended and their foot externally rotated. The examiner then lightly pinches the skin over the anterolateral thigh, just below the inguinal ligament. If the patient feels the pinch, the test is negative and the LFCN is functioning properly. If the patient does not feel the pinch, the test is positive and the LFCN may be damaged.

Indications

The Bun test is commonly performed to evaluate patients with suspected LFCN palsy. LFCN palsy can occur as a result of trauma, surgery, or other medical conditions. Symptoms of LFCN palsy include numbness or tingling in the anterolateral thigh, difficulty perceiving light touch, and difficulty with walking.

Interpretation

A positive Bun test indicates that the LFCN is not functioning properly. However, a negative Bun test does not necessarily rule out LFCN palsy. Other tests, such as electromyography (EMG) and nerve conduction studies (NCS), may be necessary to definitively diagnose LFCN palsy.

Treatment

Treatment for LFCN palsy depends on the underlying cause. In some cases, conservative treatment such as rest, ice, and pain relievers may be sufficient. In other cases, surgery may be necessary to repair the damaged nerve. Prognosis for LFCN palsy is variable, but most patients eventually recover full function.