PCNL has been widely used for renal stones since 1970[17]. Its high SFR is accompanied by more complications, such as blood loss and pain, which can be reduced by reducing the diameter of the percutaneous tract[18–20]. Miniperc and Microperc have both been used effectively for treating kidney stones with no clearly which one is better. Our meta-analysis showed that Microperc could obtain comparable SFR with Miniperc, but the complications such as hemoglobin drop and urinary infection associated with Microperc was lower. Besides, we found that Microperc needs shorter hospital stay time and operative time compared to Miniperc, although this difference was not statistically significant. The advantage of Miniperc compared to Microperc is that flexible or rigid nephroscope can be moved through the sheath, and lithotripsy can be continued when fragments move into other calyces[19]. To our knowledge, this is the first meta-analysis comparing the safety and effectiveness of Microperc versus Miniperc.
Miniperc was initially used for pediatric urinary stones in 1997[21]. Then Jackman et al. developed it for adults[22]. Miniperc usually refers to a percutaneous nephroscope with a nephrostomy tract less than 20 F[5]. Previous studies confirmed that complications of PCNL could reduce by reducing the diameter of the percutaneous tract[23]. Miniperc can obtain comparable SFR with standard PCNL, but complications such as blood loss and pain are reduced[19, 20]. Retrograde intrarenal surgery (RIRS) is another procedure for the treatment of upper urinary calculi. A high-quality meta-analysis showed that Miniperc provided significantly higher SFR compared with RIRS; however, Miniperc was accompanied with a higher incidence of postoperative complications[24].
In 2011, Desai et al. firstly used Microperc to fragment stones[25]. The tract of Microperc is smaller than Miniperc and standard PCNL, and the puncture and lithotripsy were completed in one step[25]. The see-through needle helps the surgeon puncture into the desired calyx. Microperc is widely used for medium-sized renal stones, which can get a SFR of 93%[26]. For lower-pole stones, the SFR of Microperc also can reach 85.7%[27]. Microperc can get as high SFR as Miniperc; however, Microperc is accompanied with lower blood loss and hospitalization time[14]. Compared with RIRS, Microperc provided significantly higher SFR; however, it is accompanied with a more significant drop in hemoglobin and more extended hospital stay[28]. For pediatric renal stones, the SFR of Microperc is 93.8%, hemoglobin drop is 0.79 ± 0.49 g/dL, no patient needs blood transfusion[15]. This indicated that Microperc can be used in children with kidney stones. The disadvantage of Microperc is the need to pay attention to the large intrapelvic pressure. In addition, micro can't exclude fragments, so it is necessary to ensure that the stones are dusted rather than fragmented[19].
SFR is a key indicator to evaluate the effectiveness of lithotripsy. Different studies have different standards for the definition of clear stone. The imaging follow-up methods are different after surgery. Three studies were followed by Kidney-Ureter-Bladder or Ultrasound[14–16], and one study was reexamination by CT[13]. The review time was one month after surgery, and one study conducted a review 48 hours after surgery[15]. The standard for SFR is no residual stone or asymptomatic fragments < 4 mm. Our pooled results showed that Microperc and Miniperc were statistically similar concerning SFR. This result indicates that Microperc does not reduce SFR when the tract size is reduced. In subgroup analyses, we divided the meta-analysis into adult kidney stones and pediatric kidney stones. The SFR of Microperc is similar to Miniperc in both adult and pediatric group. These demonstrated there is no difference between the two surgical methods in children and adults stones. We found the overall SFR of Microperc is 86.05% (148/172), and the SFR of Miniperc is 87.65% (142/162). These results show that both Microperc and Miniperc are very effective in treating moderately sized kidney stones. For lower pole stones, the SFR of Miniperc and Microperc were also similar[14].
Three studies showed that Microperc was accompanied with shorter operative time[14–16], but one study demonstrated a opposite result[13]. Our pooled result showed that Microperc and Miniperc were statistically similar concerning operative time. In subgroup analyses, our pooled results also showed that Microperc was accompanied with shorter operative time for pediatric kidney stones. This shows that Microperc is more efficient, especially for pediatric stones. Different definitions of operative time resulted in greater heterogeneity among the studies. The variations among studies during the operation such as energy source (laser or ultrasonic lithotripsy), diameter of the laser fiber, the optics (flexible), irrigation through the pump, ureteral double J stent inserted, and nephrostomy catheter placement also cause the different operation time among studies[19].
Complications are important indicators to evaluate the safety of a surgery. Our pooled results indicated that the two techniques were statistically similar concerning urinary infection (OR: 0.38; P = 0.18). However, we found that D-J stent insertion ratio is higher in Microperc. (OR: 3.49; P = 0.01). It can be explained that Microperc is done to dust the stone and leave the fragments to be spontaneously passed, and stones fragments are generally removed in Miniperc. So, Microperc needs more D-J stent insertion.
The tract size of PCNL is significantly associated with blood loss[23]. Our pooled results showed that hemoglobin drop is larger in Miniperc group (WMD: -0.98; P = 0.03).The reason may be that the enlargement of the nephrostomy tract increases the damage to the renal parenchyma and renal vascular system[20]. In the four studies we included, all patients in the Microperc group did not require blood transfusions. However, in the Miniperc group, Karatag et al. found 7.9% (5/63) patients needed blood transfusions[16]. Dundar et al. also calculated 7.4% (2/27) patients needed blood transfusions[15].
We demonstrated that the hospital stay time of Microperc is shorter, although not statistically significant. The possible reason is that Microperc has less damage and less postoperative discomfort[24]. Besides, it carries a lower urinary tract infection rate and hemoglobin drop. Furthermore, Microperc is more likely not to use percutaneous nephrostomy tube.
There are several limitations in our meta-analysis. Above all, only four retrospective case controls trails were included and analyzed, and the quality of the literature is relatively low. In addition, the heterogeneity is high among the important indicators such as operation time, hospital stay time, and hemoglobin drop. Although the random effect model is used, the results may be biased. Besides, the definition of SFR and the follow-up time are different in different studies. Moreover, many studies do not specify specific complications. Finally, the limited studies included and the limited number of patients in the study may lead to reduced confidence in the results.