Search and study selection
Initially, 262 documents were yielded in the electronic databases after screening the core terms. 129 duplicates were eliminated, then 115 of 129 records were removed based on their titles and abstracts. Subsequently, after downloading and identifying the full text, 9 articles without access to the inclusion criteria were excluded. Ultimately, this meta-analysis contained a total of 9 eligible studies[17-20, 25-29] published between 1999 and 2018. The specific process of literature identification and selection is shown in Figure 1.
Nine retrospective studies with 1043 patients were enrolled in our meta-analysis and the characteristics and the general demographics of the identified studies were listed in Table 2 and Table 3. The sample size of the included studies ranged from 16 to 186, and the studies were published between 2008 and 2019. The 1043 patients all underwent MIS-TLIF, 412 obese patients, and 631 nonobese patients (Table 2). The duration of surgery was reported in 6 studies, estimated blood loss was reported for 3 studies, the length of hospital stay was reported in 5 studies, and ODI and LP-VAS scores were reported in 2 studies, BP-VAS score was shown in 2 studies. The number of complications was reported in 6 studies (Table 4). According to the data extracted, ODI, LP-VAS, and BP-VAS scores were divided into early (≤6 months after MIS-TLIF) and late (≥24 months after MIS-TLIF) period. The NOS score as the aspect of methodological quality for each selected study were all over six points, revealing the high quality (Table 1).
Results of Meta-Analysis
Primary Outcomes. Complications were the primary adverse events to evaluate the safety and efficacy of MIS-TLIF for obese patients and nonobese patients. In our study, major complications included durotomy, epidural hematoma, genitourinary, neurologic, cardiac, pulmonary, and any medical condition. The data of the complications in 6 studies[18, 19, 27, 29-31] was pooled and there was a higher risk of adverse events in obese patients (OR, 1.89; 95% CI 1.10 to 3.23; n = 471; p =0.02; I2=38%; Figure 2a). Besides, 4 trials[18, 19, 25, 29] had compared the intraoperative complications between the obese group and normal group undergoing MIS-TLIF, and no difference was found between obese and nonobese groups for intraoperative complications(OR: 0.57; 95% CI 0.14 to 2.30; n = 251; p =0.43; I2=0%; Figure 2b), however, based on a comprehensive analysis of data of postoperative complication from five studies[18, 19, 27, 29, 30], the fixed-effect model was used and obese patients had the increasing risk of complication than nonobese patients and the difference was significant (OR, 2.26; 95% CI 1.26 to 4.05; n = 455; p =0.006; I2=50%; Figure 2c).
Estimated blood loss. Three studies compared the estimated blood loss of the obese and normal groups[20, 26, 27]. Using a fixed-effect model shows no difference was found in estimated blood loss between obese and normal groups after MIS-TLIF (MD, -2.02; 95% CI -13.64 to 9.59; n = 406; p = 0.73; I2=0% Figure 3a).
Duration of surgery. There were 6 studies related to the duration of surgery[17, 20, 26-29]. The random-effect model was used in this analysis and no significant difference was found in the duration of surgery between patients who were obese and nonobese (MD, 15.26; 95% CI -0.77 to 31.28; n = 695; p = 0.06; I2=73%; Figure 3b).
length of hospital stay (LOS). Five studies reported the LOS[18, 20, 26, 28, 29]. The pooled results using random-effects model indicated that obese patients have similar length of hospital stay with nonobese patients after surgery (MD, 0.37; 95% CI -0.16 to 0.90; n = 709; p = 0.18; I2=72%; Figure 3c).
Oswestry disability index (ODI). Two studies[18, 28] reported data on early (≤6 months after MIS-TLIF) and late ODI scores (≥24 months after MIS-TLIF). The random-effects forest plot indicated no significant difference on ODI scores between two groups whether in early postoperative period (MD, 5.1; 95% CI -2.42 to 12.63; n = 248; p=0.18 I2=63%; Figure 4a) or late postoperative period (MD, 0.45; 95% CI -4.72 to 5.62; n = 224; p=0.87 I2=29%; Figure 5a).
Visual analog scale (VAS). Two studies[18, 28] investigated the outcome of the VAS score in the early postoperative period (≤6 months after MIS-TLIF). The fixed-effects model was used when no significant heterogeneity occurred, there was no difference between obese and nonobese patients concerning BP-VAS and LP-VAS. The specific statistics were shown in Figure 4(MD, -0.08; 95% CI -0.75 to 0.59; n = 362; p=0.81 I2=0%; Figure 4b) and (MD, 0.29; 95% CI -0.65 to 1.23; n = 247; p =0.55 I2=0%; Figure 4c), respectively. Additionally, 3 studies[18, 28, 29] reported the outcome of late BP-VAS scores (≥24 months after MIS-TLIF). The random-effects forest plot shows no statistical difference was observed in late BP-VAS (MD, 1.43; 95% CI -0.73 to 3.60; n = 249; p=0.19 I2=74%; Figure 5b). Additionally, the late LP-VAS score was reported in two studies[18, 28]. The forest plot using the fixed-effected model shows no significant difference in LP-VAS score in the late period after MIS-TLIF between patients who were obese and nonobese (MD, -0.26; 95% CI -0.82 to 0.31; n = 228; p=0.37 I2=5%; Figure 5c).