Ultrasonographic Evaluation of the Optimal Needle Position in the Supinator Muscle

Investigating the supinator muscle (SUP) is important for diagnosing radial neuropathy or cervical radiculopathy in needle electromyography (EMG). However, different authors have proposed several locations for needle EMG placement in the SUP. This study aimed to determine the optimal needle insertion position for examining the SUP via needle EMG under ultrasonographic guidance.

This study included 16 male (32 upper limbs) and 15 females (30 upper limbs). In the supine position, the line connecting the midpoint of the dorsal wrist to the upper margin of the radial head (RH) (RH_WRIST line) was measured while the forearm was pronated. Under ultrasonographic guidance, the thickness of the SUP was measured at 1-cm intervals from the RH to 4 cm along the RH_WRIST line. Moreover, the horizontal distance (HD) from the RH_WRIST line to the posterior interosseous nerve (PIN) and the distance from the RH to the point where the RH_WRIST line and the PIN intersected (VD_PIN_CROSS) were measured.

VD_PIN_CROSS was 51.25±7.0 mm (mean±SD). The muscle was the thickest at 3 cm (5.6±0.8 mm) and 4 cm (5.4±1.0 mm) from the RH. The distances from the PIN to these points were 14.1±3.9 mm and 9.0±4.3 mm, respectively.

Our findings suggest that the optimal needle placement is at 3 cm from the RH.