The present meta-analysis focused on an outcome comparison between ACLR using the all-inside technique with suspensory cortical button graft fixation and ACLR using the full tibial tunnel technique. It included five RCTs and four retrospective cohort studies comparing these two types of surgical methods. With both femur and tibial side suspensory cortical button graft fixation use, the greater graft thickness of quadrupled semitendinosus tendon was available for ligament reconstruction. Less tibial tunnel widening in the further follow-up was observed in those patients with suspensory cortical button graft fixation. The present analysis showed that the all-inside ACLR technique was not critically superior to the full tibial tunnel technique in functional outcomes, knee laxity measured with arthrometer, or tendon rerupture rate.
A previous systematic review by de Sa et al in 2018 had reported a low graft failure rate and ideal clinical improvement using the all-inside ACLR technique. However, the review focused on compiling the reported outcomes from individual studies rather than the comparison between different surgical methods (5).
Since the last review of de Sa et al, several studies have directly compared the all-inside ACLR with the full tibial tunnel technique. Thus, we hypothesized that an analysis of the comparison studies would provide some valuable insights into the ongoing debate. Browning et al had systematically reviewed ACLR using suspensory or aperture fixation and found that the suspensory device engendered better knee stability and less graft failure (21). Recently, with the evolution of surgical instruments and techniques, suspensory devices are used in most all-inside ACLRs. Thus, both the bone tunnel preparation technique and the fixation device might affect the clinical outcome of ACLR.
The difference in functional outcome between the two methods was not significant in the individual studies or in our pooled data. First, according to most of the studies, we noted that ACLR is a surgery with high patient satisfaction, and most patients felt clear improvement postoperatively. Second, the follow-up time in the selected studies was relatively short, which might not have been sufficient to reveal fixation failure because of the screw degradation process or the tunnel widening phenomenon (22). In regard to postoperative pain, three studies had mentioned this outcome measurement. However, the data could not be pooled, given it was assessed in different ways and at different times. The individual studies reported comparable postoperative pain and analgesic consumption for both the all-inside and full tibial tunnel groups at all follow-up times (12, 14, 19). Return to sports was investigated by two studies (15, 16); however, the data were recorded in a different time frame. Baldassarri et al stated that the patients who underwent full tibial tunnel ACLR showed slightly better performance in the postoperative 6–8 months’ follow-up, but this difference became insignificant in further follow-up. Desai et al found that the mean time for return to sports was longer in the patients with all-inside ACLR (12.5 vs 9.9 months). Although the return to sports is an important parameter to measure graft maturation of the ACLR, it varies between the types of sports and rehabilitation protocols. More studies comparing the rate and level of return to sports are warranted.
With suspensory cortical button fixation, the necessity of harvested graft length was approximately 28 cm, and could be achieved with only semitendinosus tendon harvesting most of the time (23). The previous systemic reviews stated that tendon graft thickness of 8 mm had lower failure rates in ACLR, and this lower limit diameter could also be achieved by using quadrupled semitendinosus tendon (ST4) graft in most cases, regarded as inherent property of the all-inside ACLR with suspensory cortical button fixation technique (24). However, there are many factors that might influence the thickness of the tendon graft such as age, gender, and body height. Thus, it must be noted that every patient cannot not achieve the ideal graft length and thickness by using the semitendinosus tendon only, and the gracilis must be secondarily harvested.
Some studies have shown that this gracilis-sparing technique could achieve more minimal surgical incision and less donor site morbidity (1, 25). Since both the semitendinosus and gracilis tendon function both as knee flexors and tibial internal rotators, harvest causes weakness of internal tibial rotation. Both Kouloumentus et al and Monaco et al had stated that the improved flexion strength in the group of patients who underwent all-inside ACLR could be attributed to the gracilis-sparing technique (3, 4), and it is beneficial to functional activity or sports with high demands on hamstring muscle strength (25).
Tunnel widening is always a concern in ACL reconstruction surgery. In the biomechanical aspect, synovial fluid penetration and micromovements at the graft to bone interface (bungee and windshield wiper effect) might enlarge the tunnel. The inflammatory response or foreign body reaction to the bioabsorbable screw could be the biological cause for tunnel widening. Using advanced imaging, the current studies have shown significant increases in tunnel volume in the group of patients with bioabsorbable interference screws or even cyst formation at follow-up (13, 17). Although the current evidence could not prove a correlation between tunnel widening and poor clinical outcomes or graft failure, the concern is that bone loss of the tunnel might be an obstacle for revision surgery, given the graft failure rate in young athletes was high (26). Further, we found that two of the studies (12, 17) measured the bone tunnel diameter of postoperative radiography as the reference point to determine the tunnel widening, however two of the studies (13, 18) use the initial drill diameter as the reference point. The inconsistency in tunnel measurement might have raised potential bias since the bone tunnel diameter could easily be altered by drilling or tightening the interference screw during the surgery. Thus, standardized volume measurement might help us shed light on the change in tunnel volume.
In our review, the pooled data showed that graft failure was similar between the all-inside and full tibial tunnel ACLR. However, the all-inside technique of ACLR exhibited a trend toward longer operation time (12, 17). Furthermore, care must be taken with regard to surgical complications related to suspensory cortical button use, such as a dislodged button or suture breakage, as reported in a previous study. The selected studies reported that the study period included the surgeon’s learning curve on the newly developed all-inside technique. The unfamiliarity with the surgical instrument and fixation device might be the cause of all these complications (3, 14, 16, 17, 19). Finally, the all-inside technique is dependent on the retrograde drilling technique, which requires specific surgical instruments, such as a retrograde reaming device and suspensory fixation device, which are sold by certain companies as listed in Table 2. The relation between these factors and the potential conflict of interests declared by the selected studies must be considered (12–14, 16, 18).
Limitations
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 five 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.
Conclusion
In this systematic review and meta-analysis, with a limited follow-up period, we found that the all-inside ACLR technique with suspensory cortical button fixation was not clinically superior to the full tibial tunnel technique with interference screw fixation in functional outcome and knee laxity as measured with an arthrometer. However, the advantages of using suspensory cortical button fixation included the use of a thicker ST4 graft for reconstruction, and brought less tibia tunnel widening compared with bioabsorbable interference screw fixation.