Bun Test: Assessing Lateral Femoral Cutaneous Nerve Function

The Bun test (Bun-Crossed Sign) evaluates the lateral femoral cutaneous nerve (LFCN), which supplies sensation to the anterolateral thigh.

Procedure

Patient lies supine, knee extended, foot externally rotated. Examiner lightly pinches skin over anterolateral thigh below inguinal ligament. Negative = pinch felt (LFCN intact). Positive = no sensation (possible LFCN damage).

Indications

Suspected LFCN palsy from trauma, surgery, or medical conditions. Symptoms: anterolateral thigh numbness/tingling, light-touch loss, walking difficulty.

Interpretation & Treatment

Positive test suggests LFCN dysfunction; negative doesn't rule it out—EMG/NCS may be needed. Treatment depends on cause: conservative (rest, ice, pain relief) or surgical repair. Prognosis variable; most recover fully.