Study Selection and Critical Appraisal
The study’s search criteria, exclusion criteria, and final selection of studies are presented in a flow diagram from the Preferred Reporting Items for Systemic Reviews and Meta-Analysis (PRISMA) guidelines (Figure 2). Three studies (4, 9, 10) were published repeatedly with different lengths of follow-up; thus, we extracted the data from the most recent of them. We did not include Lubowitz's RCTs published in 2013 comparing outcomes between the all-inside and full tibial tunnel ACLR methods, with both groups using aperture fixation on the femur and tibia side instead of the suspensory cortical button fixation device (11). However, in order to reveal whether the fixation device was associated with widening of the drill tunnel, we included two studies that partially met the inclusion criteria for analysis. The first study is Lubowitz's RCT published in 2015, comparing the outcome between adjustable suspensory cortical button fixation and aperture fixation, with both groups using the all-inside drilling technique; we extracted only the data regarding the postoperative follow-up tunnel diameter (12). The second study is Colombet's prospective cohort study published in 2016 comparing tunnel diameter changes between patients who had undergone full tibial tunnel ACLR using suspensory cortical button fixation or bioabsorbable screw fixation, and we collected the tunnel diameter change data for further analysis (13). We included 5 RCTs and four comparative cohort studies published between 2013 and 2019 for the final meta-analysis. All the selected studies compared the all-inside ACLR technique (both femoral and tibial side bone socket) to the full tibial tunnel ACLR approach (femoral socket and full-length transtibial tunnel). The methodological quality of the RCTs was evaluated with the Jadad score. One study (3), clearly mentioning the method for randomization, appropriate blinding, and the withdrawal of patients from follow-up, scored five points. Two studies (12, 14) scored 3 points with all randomization, blinding, and withdrawals documented; however, the detailed method of randomization and blinding was not mentioned. Two studies (9, 15) that only mentioned the randomization and withdrawals scored 2 points. The three comparative studies were measured using the Newcastle–Ottawa scale. The study characteristics are presented in Table 1. Various outcome measures, detailed graft type, and fixation materials between the studies are listed in Table 2.
Results of Individual Studies
Graft harvest and fixation device
In autologous graft selection, six studies (3, 14, 16-19) used quadrupled semitendinosus tendon (ST4) in the all-inside group and double gracilis and semitendinosus tendon (DGST) in the full tibial tunnel group; one study did not clearly mention the autologous tendon graft donor site (15). All the studies mentioned the suspensory cortical button graft fixation device was used on both the femoral and tibial side in the all-inside group of patients. However, for the full tibial tunnel ACLR groups, three studies (3, 16, 18) used femoral side cortical button fixation with tibial side interference screw fixation, and the other four studies mentioned interference screw graft fixation on both sides. The details of fixation device choice are shown in Table 1.
Graft size and flexion strength
Given quadrupled semitendinosus tendon is an inherent property of the all-inside with suspensory cortical button fixation technique, it is the only method that could achieve adequate graft length and thickness. Three studies had documented the autograft thickness. Desai et al and Kouloumentas et al had reported that graft size in the all-inside group (mostly using ST4) was significantly thicker than in the full tibial tunnel group (mostly use DGST); a similar result was also noted in our pooled data (95% CI −1.190 to −0.668; p < 0.001) (Figure 3).
Flexion strength was investigated by Kouloumentas et al and Monaco et al. Both these studies stated that better flexion strength was noted in the group of patients treated with all-inside ACLR (3, 4). Although the data from the two studies could not be pooled due to different evaluation methods of flexion strength, the studies stated that preservation of the gracilis tendon might be associated with minor donor site morbidity and better flexion strength recovery.
Functional outcomes
The studies investigated the functional outcome with several types of parameters at various times. We have extracted the available data on the last clinical follow-up, and the following score measurements include Lysholm score, subjective and objective IKDC, Tegner activity score, and KSS.
Lysholm score
Five studies measured the Lysholm score; no significant differences were found between the two groups. The pooled data also found no significant between-group differences (95% CI −0.283 to −0.553; p = 0.526) (Figure 4).
Subjective and objective IKDC score
Both the subjective and objective IKDC scores were measured by five studies. Significant postoperative improvement was noted in both the all-inside and full tibial tunnel groups; however, no significant between-group difference was found in postoperative score measurement. The pooled data of the subjective IKDC found no significant between-group differences (95% CI −0.283 to 0.553; p = 0.526) (Figure 5). Comparison of the postoperative objective IKDC scores also showed no significant differences (p = 0.189) (Table 3).
Tegner activity score
The Tegner activity score data were extracted from four studies. A significantly higher Tegner activity score in the full tibial tunnel group (6.4 VS 6.8, p = 0.48) was noted in Desai's study. The pooled data also showed a significantly higher score in the full tibial tunnel group (95% CI 0.079 to 0.591; p = 0.01) (Figure 6). However, Desai et al had stated that both groups of patients could reach the preinjury level of activity (preinjury score, 6.6 in the all-inside group and 7.0 in the full tibial tunnel group); thus, the between-group difference was not clinically significant.
KSS
Two studies measured the KSS. There was no significant difference between the groups in any study, or after pooling of the data (95% CI −2.441 to 1.441; p = 0.614) (Figure 7).
Laxity measured by arthrometer
Two studies investigated the anteroposterior knee stability of the operative knee using the KT-1000 arthrometer (MedMetric Corporation, San Diego, CA, USA) (17, 18), and one study (14) used the Rolimeter (Aircast, Europe). All the studies stated that knee stability improved significantly postoperatively, but no significant difference between groups was noted. Given both the KT-1000 and Rolimeter provided a valid measure of knee laxity of the patients with ACL injury(20), we pooled the postoperative data measured using both types of arthrometer. We found that postoperative knee stability (95% CI −0.399 to 0.729; p = 0.567) (Figure 8) was comparable between the groups.
Tunnel widening
The phenomenon of drill tunnel widening had been investigated by several studies (9, 12, 13, 17, 18) and was considered to be associated with not only the method of tunnel prepared but also by the graft fixation device. Thus, we included two more comparative studies investigating the difference between tunnel widening by suspensory cortical button fixation and by interference screws (12, 13). Lubowitz et al had found no between-group difference in tunnel diameter as measured with plain film radiography. In Mayr’s study (9), with computed tomography as a main tool for measurement, a significant femoral tunnel volume increase was noted in the all-inside group at 6 months’ follow-up; however, in the other study with longer follow-up times (24 months) for the same groups of patients, significantly increased tibia volumes and diameters were found in the full tibial tunnel group (17). Studies by Monaco et al and Colombet et al had found significant tibia tunnel widening in the group with interference screw fixation. Due to the different type of imaging study for evaluating the diameter or volume of the drilling tunnel, we could only compile the data of tibia tunnel diameter from three studies. The pooled data showed no significant between-group differences in the direct postoperative tunnel width (95% CI −3.124 to 1.446; p = 0.472) (Figure 9) or the follow-up tunnel width (95% CI −1.763 to 0.299; p = 0.164) (Figure 10). However, when analyzing the tunnel diameter change, individual studies and the pooled data showed significantly increased tunnel diameter in the patients with interference screw fixation (95% CI −1.592 to −0.897; p < 0.001) (Figure 11).