Background
Anterior cruciate ligament (ACL) injury is a main cause of recurrent knee instability and may result in secondary damages to other structures of the knee, such as meniscal tears and articular cartilage degeneration [
1]. Currently, ACL reconstruction is the gold-standard surgical technique for ACL injury [
2]. Reconstruction can be performed by using autograft, allograft or synthetic graft [
3]. Despite the vast amount of researches, there still have a great deal of debates concentrating on the clinical outcomes of using different grafts in ACL reconstruction.
Autograft is a well-recognized and widely used material for ACL reconstruction due to a good graft stability and a well return to high-level sports [
4]. And bone-patella tendon-bone (BPTB) autograft has historically served as the gold standard for ACL reconstruction based not only on widespread global use but also as the first autograft option. Reconstruction with synthetic grafts has the advantage of eliminating both the donor-site morbidity and disease transmission with fast rehabilitation [
5]. High graft failures, no so-called ligamentization and severe synovitis have been reported as major disadvantages of synthetic grafts [
6‐
8].
A few conventional narrative reviews have addressed related issues about the graft selection for ACL reconstruction [
9‐
12]. Firm conclusions regarding the clinical outcomes with autografts or synthetic grafts cannot be drawn from those narrative reviews due to some inherent bias. Moreover, there have already been systematic reviews and meta-analysis which compared the clinical outcomes between allografts and autografts using in ACL reconstruction [
13‐
16]. Critically evaluation and summarization for the outcomes between autografts and synthetic grafts using in ACL reconstruction have not been performed currently.
Using the best available evidence, the purpose of this research is to compare synthetic grafts with autografts in ACL reconstruction by evaluation the clinical outcomes including the results of instrumented laxity, patient-oriented outcomes, complications and graft failures.
Discussion
The key findings of present meta-analysis indicated that, in general, the patient-oriented outcomes and the rate of complications of ACL reconstruction with synthetic grafts were not significantly different from those with autograft, especially for new generation synthetic grafts (LARS and PGA- Dacron). However, with regard to knee laxity, ACL reconstruction with early artificial grafts had obviously poorer knee laxity from those with autografts (95% CI: 1.03, 4.72) while new artificial grafts showed no significant difference with autografts (95% CI: 0.21, 1.93).
The LK artificial ligament was a polyester mesh-like structure intended as a scaffold for soft tissue ingrowth [
28]. The LAD, a band-like braid of polypropylene, was designed to protect the autogenous graft from excessive stresses [
29]. Murray et al. reported that 28% of the group were known to have ruptured the LK ligament and 56% had increased laxity compared to the opposite normal knee at a 10–16 year follow-up [
30]. A study conducted since 1983, included 856 patients accepted ACL reconstruction with LAD, showed 63 cases of complications and 73 cases of re-surgery [
31]. Long-term follow-up results documented both the LK artificial ligament and the LAD were not suitable as an ACL substitute [
30‐
32]. Moreover, the LAD caused effusions and reactive synovitis in the knee for provoking inflammatory reactions, and was found to delay maturation of autogenous graft [
33]. The knee laxity and the IKDC grades were significantly different from autografts and early artificial ligaments, indicating that the short-term outcomes of early artificial ligaments were worsen than autografts. The results of our research for early artificial ligaments were consistent with previous studies. It was not suggested to use early synthetic grafts including the LK artificial ligament and the LAD due to their poor follow-up outcomes.
The LARS artificial ligament was made of polyethylene terephthalate, divided in two parts (intra-articular part and extra-articular part) [
34]. Intra-articular part was composed of longitudinal external rotation fibers without transverse fibers as an imitation of ACL anatomic structure while extra-articular part was weaved by longitudinal and transverse fibers in order to avoid ligament deformation. Dericks et al. reported encouraging results in 220 cases of ACL reconstruction used LARS artificial ligament with a mean follow-up of 2.5 years [
35]. In 2013, Parchi reported no case of complications and only one case of mechanical graft rupture after using LARS artificial ligament for ACL reconstruction at a mean follow-up of eight years [
36]. In 2015, a study with a minimum follow-up of 10 years, showed almost half of the patients (8/18) were subjectively not satisfied with the surgical result using LARS artificial ligament [
7]. The clinical outcomes were appealing at short-term but controversy at long-term [
36‐
38]. In our research, 3 studies compared LARS artificial ligament with autografts, showing no significant difference in knee laxity, functions and the rate of complications [
22,
25,
27]. The outcomes of LARS artificial ligament used in ACL reconstruction were appealing at least in short-term follow-up. Another new synthetic graft called PGA-Dacron graft, consisted of synthetic braided ligament made of 75% degradable PGA filaments and 25% non-degradable Dacron thread, showed a satisfied result compared to autograft including knee laxity, range of motion, patient-oriented questionnaires, muscle performance, degenerative changes of knee, and the rate of failure and complications [
26].
Complications occurred in the autograft group were infection, patellofemoral pain, recurrent effusion and extension loss. In the synthetic graft group, complications included interference screw-related problems (pain and screw loosening), patellofemoral pain and extension loss. There were altogether 12 cases in the autograft group and 8 cases in the synthetic graft group. Extension loss was the most common complication in included studies and it might be associated with graft impingement and a formation of cyclops [
39,
40]. Graft impingement was mainly caused by malposition of femoral bone tunnel and a “cyclops” was a fibrous nodule caused by proliferation of fibrovascular tissues similar to a healing scar after ACL reconstruction [
41,
42]. The synthetic grafts were located in a non-anatomic but isometric placement while the autografts were usually located in an anatomic placement. The results of complications showed no significant difference between these two location methods.
Some studies documented that subjective outcomes were not correlated with objective outcomes including instrumented laxity test and clinical examination [
43]. Among these included studies, three of them showed difference in objective parameters but no significant difference in patient-oriented outcomes [
21,
22,
24]. Meanwhile, the opposite circumstance did not appear (similar in objective outcomes but different in subjective outcomes). Kraeutler et al. suggested that patient satisfaction is the most important measurable index for the outcomes of ACL reconstruction [
13]. Only the overall IKDC grades showed better results in the autografts than in the early synthetic grafts and the rest indicators for patient satisfaction showed no significant difference between groups. However, it was still well recognized that a KT-1000 side-to-side difference of >5 mm was defined as a clinical failure [
37]. Both objective parameters and subjective outcomes shoulder be considered for assessment of ACL reconstruction.
The limitations of this study were as follows: (1) Until now, there was still lack of high-quality RCT or large-scale multi-center retrospective comparable studies to prove the effectiveness of artificial ligaments compared to autografts. (2) The follow-up time was not sufficiently long for evaluation of ACL reconstruction. (3) In the included studies, the types of grafts used in ACL reconstruction were not the same (Hamstring tendon, BPTB, LK, LAD, LARS and PGA-Dacron). (4) The data included in the research did not cover all included studies due to the lack of relative data.