Percussion is one of the most important techniques of physical examination. Percussion sets the chest wall and underlying tissues in motion, producing audible sound and palpable vibrations. Percussion helps you establish whether the underlying tissues are air-filled, fluid-filled, or consolidated. 

The percussion blow penetrates only 5 to 7 cm into the chest, however, and will not aid in detection of deep-seated lesions.

The technique of percussion can be practiced on any surface. As you practice, listen for changes in percussion notes over different types of materials or different parts of the body. The key points for good technique, described for a right handed person, are detailed below:

■ Hyperextend the middle finger of your left hand, known as the pleximeter finger. Press its distal interphalangeal joint firmly on the lung surface to be percussed (Fig. 1). Avoid surface contact by any other part of the hand because this dampens out 

vibrations. Note that the thumb and second, fourth, and fifth fingers are not touching the chest wall.

FIGURE 1. Press the pleximeter finger firmly on the chest wall.

■ Position your right forearm quite close to the surface, with the hand cocked upward. The middle finger should be partially flexed, relaxed, and poised to strike.

■ With a quick, sharp but relaxed wrist motion, strike the pleximeter finger with the right middle finger, called the plexor finger (Fig. 2). Aim at your distal interphalangeal joint. Your goal is to transmit vibrations through the bones of this joint to the 

underlying chest wall. Use the same force for each percussion strike and the same pleximeter pressure to avoid changes in the percussion note due to your technique rather than underlying findings.

FIGURE 2. Strike the pleximeter finger with the right middle finger.

■ Strike using the tip of the plexor finger, not the finger pad. The striking finger should be almost at right angles to the pleximeter. A short fingernail is recommended to avoid injuring your knuckle.

■ Withdraw your striking finger quickly to avoid damping the vibrations you have created (Fig. 3).

FIGURE 3. Withdraw the striking finger quickly.

In summary, the movement is at the wrist. It is directed, brisk, yet relaxed and slightly bouncy

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