Is all-inside with suspensory cortical button fixation a superior technique for anterior cruciate ligament reconstruction surgery? A systematic review and meta-analysis

We performed the literature search on November 7, 2019 in the PubMed, Embase, and Cochrane databases, using the keywords “(Anterior cruciate ligament or ACL) and (All-inside, suture button, cortical button, or suspensory),” without a limitation for year of publication. The search was not restricted to randomized controlled trials due to the anticipated scarcity of published literature. Eligibility criteria for review inclusion were comparison studies of the all-inside ACLR technique with suspensory cortical button fixation and the full tibial tunnel ACLR technique, which use interference screw fixation on both the femur and tibia side or only on the tibia side. Cadaver or animal studies, biomechanical studies, literature reviews, and publication types unlikely to contain relevant information (news, comments, letters to the editor, and editorials) were excluded. Two independent reviewers (Chen and Fu) evaluated the eligibility of the selected studies. When necessary, we obtained full-text articles to determine eligibility for inclusion. Disagreements were resolved by discussion.

The methodological quality of the enrolled studies was evaluated by two reviewers independently, using Jadad scoring for the randomized controlled trials (RCTs) and the Newcastle–Ottawa Quality Assessment Scale for the nonrandomized comparative trials. The Jadad score evaluates RCT methodology according to three aspects: randomization (2 points), blinding (2 points), and an account of all patients (1 point). The range of potential scores is 0 to 5; a higher score indicates better methodological quality [6]. The Newcastle–Ottawa Quality Assessment Scale contains eight items in three categories: participant selection (four items), comparability (one item), and exposure (three items). A study can be scored a maximum of one point for items in the Selection and Exposure domains and a maximum of two points for the comparability domain [7].

All the relevant data were extracted from the selected studies by two independent reviewers. Any disagreement or data inconsistency were resolved by discussion. Information about the first author, year of publication, study design, type of treatment arm, number of patients enrolled, mean age, follow-up time, graft type and thickness, fixation technique, and material used are shown in Table 1.

The outcome measures, functional outcomes (Lysholm score, subjective and objective International Knee Documentation Committee [IKDC] score, Tegner activity scale, and Knee Society Score [KSS]), knee stability (measured using the KT-1000 instrumented knee laxity device), change of bone tunnel width, and tendon rerupture were extracted and analyzed.

In the outcome data analysis, we synthesized the continuous outcome data by using the mean difference and standard deviation (SD). If only a range was reported, the estimated SD was calculated by range/4 in moderately sized samples (15 < n ≤ 70) and by range/6 in large samples (n > 70) [16]. For the objective IKDC score evaluation, the extracted data were added and a chi-squared test with Fisher’s correction was used for between-group difference analyses. The standardized mean differences (SMDs) of the extracted data were indicated to represent a favorable treatment option. For dichotomous outcome data, we used the odds ratio (OR) for synthesis. A random-effects model was used to pool individual SMDs and ORs. The 95% confidence intervals (CI) were calculated for each outcome. Between-trial heterogeneity was determined by performing the I² test; values > 50% were regarded as indicating considerable heterogeneity. All analyses were performed using Comprehensive Meta-Analysis software (Version 3.3.070).

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 (Fig. 2). Three studies [4, 17, 18] 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 [19]. 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 [15]. 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 [14]. 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 [13, 15] scored 3 points with all randomization, blinding, and withdrawals documented; however, the detailed method of randomization and blinding was not mentioned. Two studies [11, 17] 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.

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.

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) (Fig. 4).

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) (Fig. 5). Comparison of the postoperative objective IKDC scores also showed no significant differences (p = 0.189) (Table 3).

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) (Fig. 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.

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) (Fig. 7).

Two studies investigated the anteroposterior knee stability of the operative knee using the KT-1000 arthrometer (MedMetric Corporation, San Diego, CA, USA) [9, 10], and one study [13] 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) (Fig. 8) was comparable between the groups.

The phenomenon of drill tunnel widening had been investigated by several studies [9, 10, 14, 15, 17] 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 [14, 15]. Lubowitz et al. had found no between-group difference in tunnel diameter as measured with plain film radiography. In Mayr’s study [17], 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 [9]. 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) (Fig. 9) or the follow-up tunnel width (95% CI − 1.763 to 0.299; p = 0.164) (Fig. 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) (Fig. 11).

Rerupture was described in three studies. There was no significant difference between groups within any study or after pooling of data (OR 0.758; 95% CI 0.194 to 2.961; p = 0.691) (Fig. 12).

There are several limitations of the present meta-analysis. First, the quality of the available studies is low. The five RCTs and four comparative studies described only 613 patients, which is low, considering the high incidence of ACL injury. Variations in study design, patient characteristics, sample size, reporting of outcome, and postoperative protocol resulted in high heterogeneity between the studies. The identification of an anatomical landmark for tunnel positioning varied between surgeons and was rarely mentioned in these studies. Second, we did not serially investigate outcome measurement; instead, we used the data of the last follow-up, which were commonly documented to represent the final postoperative status. Besides, the follow-up period in the selected studies were short-term to mid-term (from 6 months to 48 months) (Table 1), which may raise a concern that some complications such as graft loosening, implant breakage, or revision surgery might occur after 5 years. More studies investigating the long-term follow-up were needed to prove the reliability of this new technique and implants. Third, although the bioabsorbable interference screw has been frequently used in ACLR [27, 28] and was selected as a control technique in our selected studies, other graft fixation methods are still available, such as metallic interference screw, cross-pin, and staple fixation, which have played roles in current ACLR surgery. However, there is a lack of evidence to compare these techniques or implant fixation to the all-inside technique, and thus, it is hard to determine the optimal method.