Study selection
We initially identified 969 studies and included 7 randomized controlled trials with 600 participants in the meta-analysis after screening for eligibility[18-20, 28-31]. The PRISMA study flow diagram was shown in Fig. 1.
Study characteristics
A total of 7 randomized controlled trials with 600 participants were included. One study showed statistically significant differences between genders[28], and one study did not provide BMI data[19]. None of the studies included learning cases. The demographic characteristics of the patients were shown in Table 1.
Risk of bias
All the studies included in the meta-analysis were randomized controlled trials of high quality. It is difficult to blind the doctors performing surgeries to the patient groups, but we think that the absence of blinding did not contribute to detection bias, at least in some outcome parameters. The risk of bias graph for each study and the risk of bias summary were shown in Fig. 2 and Fig. 3.
Clinical outcomes
Length of the incision
Five studies[18-20, 28, 31] with a total of 503 patients were included in the comparison of the length of the incision between the DAA and PA in primary THA. We failed to find a significant difference between the DAA group and PA group, and there was statistically significant heterogeneity among the studies (MD=-2.79 cm, 95% CI -5.77 to 0.18, p = 0.07, I2=100%, Fig. 4).
Surgery duration
Six studies[18-20, 28, 30, 31] with a total of 549 patients were included in the comparison of the surgery duration between the DAA and PA in primary THA. The DAA required a significantly longer surgery duration (13.74 min, 6.88 to 20.61, p<0.0001, Fig. 5), but there was statistically significant heterogeneity among the studies (I2=93%).
Blood loss
Four studies[20, 28, 30, 31] with a total of 357 patients were included in the comparison of perioperative blood loss between the DAA and PA in primary THA. We failed to find a significant difference between the DAA group and PA group, and there was statistically significant heterogeneity among the studies (MD=58.96 ml, 95% CI -4.46 to 122.38, p = 0.07, I2=97%, Fig. 6).
Transfusion rates
Three studies[19, 20, 31] with a total of 344 patients were included in the comparison of the transfusion rates between the DAA and PA in primary THA. We failed to find a significant difference between the DAA group and PA group, and there was statistically significant heterogeneity among the studies (OR=0.35, 95% CI 0.04 to 3.15, p = 0.35, I2=87%, Fig. 7).
Length of hospital stay (LOS)
Six studies[18, 19, 28-31] with a total of 496 patients were included in the comparison of the LOS between the DAA and PA in primary THA. There was no significant difference between the DAA group and PA group in terms of the LOS (MD=-1.52 day, 95% CI -3.75 to 0.71, p = 0.18, Fig. 8). There was statistically significant heterogeneity among the studies (I2=100%).
Complications
Five studies[18-20, 28, 31] were included in the comparison of the complications between the DAA and PA in primary THA. Three studies[18, 20, 28] reported the occurrence of postoperative dislocation. There was no significant difference between the two groups in terms of the number of cases of dislocation (OR=0.52, 95% CI 0.09 to 3.08, p = 0.48, I2=0%, Fig. 9). Three studies[18, 28, 31] reported the occurrence of postoperative fractures. There was no significant difference between the two groups in terms of the number of fractures (OR=1.45, 95% CI 0.27 to 7.66, p = 0.67, I2=0%, Fig. 10). Three studies[18-20] reported the occurrence of postoperative DVT. There was no significant difference between the two groups in terms of the number of cases of DVT (OR=0.43, 95% CI 0.08 to 2.45, p = 0.34, I2=0%, Fig. 11). Two studies[18, 20] reported the occurrence of postoperative LCNT neuropraxia. There was no significant difference between the two groups in terms of the number of cases of LCNT neuropraxia (OR=43.20, 95% CI 0.70 to 2654.71, p = 0.07, I2=74%, Fig. 12). Four studies[18-20, 28] reported overall number of postoperative complications. There was no significant difference between the two groups in terms of the number of overall postoperative complications (OR=1.39, 95% CI 0.72 to 2.66, p = 0.32, I2=0%, Fig. 13).
Functional outcomes
VAS score
Three studies[20, 28, 31] with a total of 311 patients were included in the comparison of the VAS score between the DAA and PA in primary THA. There was no significant difference between the two groups in terms of the preoperative VAS score (MD=-0.08, 95% CI -0.41 to 0.25, p = 0.62, I2=42%, Fig. 14). Two studies[28, 31] reported the VAS score on 1st and 2nd day postoperatively. The DAA yield a significantly higher VAS score at 1st day postoperatively (MD=-0.65, -0.91 to -0.38, p<0.00001, I2=0%, Fig. 15). The DAA showed a significantly higher VAS score at 2nd days postoperatively (MD=-0.67, -1.34 to -0.01, p=0.05, I2=88%, Fig. 16), but there was statistically significant heterogeneity among the studies (I2=88%). Two studies[20, 28] reported the VAS score at 12 months postoperatively. There was no significant difference between the two groups in terms of the VAS score at 12 months postoperatively (MD=-0.01, 95% CI -0.47 to 0.50, p = 0.96, I2=72%, Fig. 17).
Harris Hip Score (HHS)
Five studies[19, 20, 28, 30, 31] with a total of 477 patients were included in the comparison of the HHS score between the DAA and PA in primary THA. There was no significant difference between the two groups in terms of the preoperative HHS score (MD=-0.61, 95% CI -2.15 to 0.93, p = 0.44, I2=12%, Fig. 18). Two studies[28, 30] reported the HHS score at 6 weeks postoperatively. The DAA yield a significantly higher HHS score at 6 weeks postoperatively (MD=6.05, 1.14 to 10.95, p=0.02, I2=52%, Fig. 19). Three studies[19, 28, 31] reported the HHS score at 3 months postoperatively. There was no significant difference between the two groups in terms of the HHS score at 3 months postoperatively (MD=6.30, 95% CI -1.70 to 14.31, p = 0.12, I2=89%, Fig. 20). Two studies[28, 31] reported the HHS score at 6 months postoperatively. There was no significant difference between the two groups in terms of the HHS score at 6 months postoperatively (MD=0.67, 95% CI -1.87 to 3.21, p = 0.60, I2=0%, Fig. 21). Two studies[20, 28] reported the HHS score at 12 months postoperatively. There was no significant difference between the two groups in terms of the HHS score at 12 months postoperatively (MD=0.65, 95% CI -1.16 to 2.46, p = 0.48, I2=0%, Fig. 22).
Radiographic outcomes
According to the Lewinnek safe zone (anteversion angle of 15°±10° and abduction angle of 40°±10°)[32], we estimated the radiographic outcomes of the DAA and PA. Five studies[18-20, 28, 31] with a total of 503 patients were included in the comparison of the radiographic outcomes between the DAA and PA in primary THA. There was no significant difference between the two groups in the postoperative anteversion angle (MD=-0.01, 95% CI -4.21 to 4.20, p = 1.00, I2=96%, Fig. 23). Besides, there was no significant difference between the two groups in the postoperative abduction angle (MD=1.06, 95% CI -0.95 to 3.07, p = 0.30, I2=82%, Fig. 24).