Kidney stones are broken up using one of three main approaches: shock waves aimed from outside the body, a laser threaded up through the urinary tract, or a surgical instrument inserted through a small incision in the back. The right method depends mostly on the stone’s size, location, and composition. Stones smaller than about 5 mm often pass on their own with the help of medication, while anything larger typically needs an active procedure.
Shock Wave Lithotripsy (ESWL)
Shock wave lithotripsy uses a machine outside the body to send focused pressure waves through the skin and into the stone. These waves break the stone apart through several physical forces at once: tiny gas bubbles form in the fluid around the stone and collapse with enough energy to chip its surface, internal cracks develop as waves bounce off the stone’s inner walls, and repeated pulses exploit weak points in the stone’s layered structure until it crumbles into sand-like fragments. Those fragments then pass out naturally through urine over the following days or weeks.
ESWL works best on stones smaller than 10 mm. Stones between 10 and 20 mm can sometimes be treated this way, but success drops significantly, and stones larger than 20 mm are generally not good candidates. Location matters too. For lower pole kidney stones larger than 1 cm, or non-lower pole stones larger than 2 cm, clinical guidelines recommend against using shock waves as first-line treatment because fragments have a harder time draining from those positions.
One session of ESWL clears the stone about 37% of the time for proximal ureteral stones. A second session brings that to roughly 65%, and a third pushes it to about 85%. So multiple treatments are common. Nearly all patients see blood in their urine afterward, which is expected and usually resolves quickly. Kidney bruising (hematoma) is the main complication, reported anywhere from less than 1% to about 20% of cases depending on imaging method and the type of machine used. Serious complications like damage to nearby organs are rare but documented.
The procedure can be done under sedation or general anesthesia, and most people go home the same day.
Laser Lithotripsy Through a Scope
Ureteroscopy, often called URS, involves passing a thin, flexible scope up through the urethra, bladder, and ureter to reach the stone directly. Once the scope is in position, a laser fiber is threaded through it and used to break the stone into tiny fragments or dust it into powder fine enough to flush out on its own.
The standard laser for this procedure has long been the holmium laser, but a newer thulium fiber laser is gaining ground. In pooled clinical data, the thulium laser achieved higher stone-free rates, shorter operating times, and less stone migration (where fragments bounce away during treatment). Because the thulium fiber is thinner, it allows better flexibility and irrigation flow through the scope, improving the surgeon’s view. Both lasers have similar complication rates and hospital stays.
For stones under 10 mm in the distal ureter, ureteroscopy and ESWL are both reasonable first options. Ureteroscopy tends to clear stones in a single session at rates comparable to three rounds of shock wave treatment. For stones under 10 mm, single-session ureteroscopy clears about 94% of proximal ureteral stones, compared to about 88% after three ESWL sessions.
After ureteroscopy, many surgeons place a temporary ureteral stent, a small tube that holds the ureter open to help remaining fragments pass and prevent swelling from blocking the kidney. Up to 80% of patients receive one, though guidelines suggest it isn’t always necessary. Stents typically stay in for three to seven days. They can cause flank pain, blood in the urine, and urinary urgency while in place. Some patients are instructed to remove the stent at home on a scheduled date by pulling an attached string.
Ureteroscopy can be performed under local anesthesia with intravenous sedation, though general anesthesia is also used depending on stone complexity and patient preference.
Percutaneous Nephrolithotomy (PCNL)
For large stones, typically over 1.5 to 2 cm, or for complex branching stones that fill multiple parts of the kidney’s drainage system, a more direct surgical approach is needed. Percutaneous nephrolithotomy involves making a small puncture through the back directly into the kidney. A rigid scope is passed through this channel, and the stone is broken up with ultrasonic, pneumatic, or laser energy and suctioned out in pieces.
PCNL is also used when stones haven’t responded to shock waves or ureteroscopy, for stones made of cystine (a composition that resists ESWL), and for stones in kidneys with unusual anatomy that makes other approaches impractical. It requires general or spinal anesthesia and a hospital stay, making it the most involved of the three options. General anesthesia is often preferred because patients lie face down during the procedure, and it allows better airway control.
Medication to Help Stones Pass
Not all stones need a procedure. For stones stuck in the ureter, medications that relax the smooth muscle of the ureter can help the stone pass on its own. These drugs work by blocking receptors concentrated in the lower ureter that control muscle tone. By reducing the squeezing force and frequency of the ureter’s natural contractions, they lower the pressure around the stone and widen the passage.
This approach works best for stones larger than 5 mm but still small enough to pass. In that size range, medication substantially increases the odds of clearance, translating to roughly 302 additional stone clearances per 1,000 patients treated. For stones 5 mm or smaller, the benefit is minimal because most of those stones pass on their own regardless. Side effects are generally mild but present.
How Size and Location Determine the Approach
Stone size is the single biggest factor in choosing a method. Here’s how the general decision framework breaks down:
- Under 5 mm: Most pass spontaneously. Medication may be offered but adds little benefit at this size.
- 5 to 10 mm: Medication can meaningfully improve passage rates. If intervention is needed, both ESWL and ureteroscopy are options depending on location.
- 10 to 20 mm: Ureteroscopy is often preferred, especially for lower pole kidney stones. ESWL remains an option for some stones in this range if they’re in a favorable position and aren’t too dense.
- Over 20 mm: PCNL is the standard recommendation. Shock waves lose effectiveness, and ureteroscopy alone may not be able to handle the volume of stone material.
Stone composition also plays a role. Very hard stones, like those made of calcium oxalate monohydrate or cystine, resist shock waves and often require laser treatment or PCNL. Softer stones fragment more easily with ESWL. CT scans can estimate stone density before treatment to help guide this choice. Location within the kidney matters as well: stones in the lower pole are harder to clear with shock waves because gravity works against fragment drainage from that position.