What Is Lithotripsy?

Lithotripsy is a medical procedure that uses focused acoustic energy to fragment concretions, most commonly kidney stones, within the body without requiring open surgery. The term derives from the Greek words for stone and crushing. In extracorporeal shock wave lithotripsy (ESWL), the most widely practiced form, a device outside the body generates high-amplitude pressure pulses that are focused through tissue onto the stone, inducing spallation, cavitation, and fatigue fracture that break it into fragments small enough to pass through the urinary tract. ESWL was introduced clinically in West Germany in 1980 and became standard of care for kidney stone treatment within a decade.

The procedure can treat most stones in the kidney and upper ureter without anesthesia or incision, making it one of the earliest examples of minimally invasive therapeutic ultrasound. Johns Hopkins Medicine describes extracorporeal shock wave lithotripsy as effective for stones up to roughly 2 centimeters in diameter, with outcomes depending on stone composition, location, and density.

Shock Wave Mechanics

A lithotripsy shock wave is a sharp, unipolar compressive pressure pulse with a rise time on the order of tens of nanoseconds, a positive peak pressure typically between 30 and 100 megapascals, and a negative trailing phase that drives cavitation. The positive phase fractures the stone by spallation, in which compressive waves reflect off the distal stone surface as tensile waves. The negative phase generates cavitation bubbles in the fluid surrounding the stone; the collapse of these bubbles produces localized microjet impacts and secondary pressure pulses that contribute to fragmentation. Effective fragmentation therefore depends on both the peak pressure and the acoustic field geometry at the stone's location, which drives the design of the ellipsoidal reflectors and acoustic lenses used in lithotriptors.

The number of shock waves delivered per session typically ranges from 1,500 to 3,500, at pulse repetition rates between 0.5 and 2 Hz. Lower repetition rates allow cavitation bubbles to dissipate before the next pulse, reducing collateral tissue damage. Research on shock wave focusing and cavitation control has examined how focused ultrasound can produce more controllable fragmentation compared with broad-focus lithotripsy systems.

Imaging and Targeting

Precise targeting of the stone is required to concentrate shock wave energy on the concretion rather than surrounding renal parenchyma. Clinical lithotripsy systems integrate either fluoroscopy, which uses X-ray imaging to locate radiodense stones in real time, or diagnostic ultrasound, which can visualize radiolucent stones and avoids ionizing radiation. Dual-imaging systems that combine both modalities allow continuous stone tracking during treatment, compensating for respiratory motion that shifts kidney position by up to several centimeters per breath cycle.

Ultrasound-based targeting also enables direct monitoring of fragmentation progress during the session, allowing the operator to confirm that the stone is breaking and to adjust focal depth or coupling as needed. Advances in image guidance have been reviewed in Springer's Focused Ultrasound and Lithotripsy chapter, which covers the physics of tissue-stone interaction and imaging requirements across lithotriptor configurations.

Applications

Lithotripsy has applications across several areas of urological and related medical practice, including:

• Fragmentation of kidney stones (renal calculi) to enable spontaneous passage
• Treatment of upper ureteral stones without ureteroscopic intervention
• Gallstone fragmentation in combination with bile acid dissolution therapy
• Salivary gland stone (sialolith) treatment using lower-energy extracorporeal devices
• Research into broader therapeutic shock wave applications for tendinopathy and bone healing