The most important findings of this study were that after revision of ACL reconstruction satisfactory improvement was noted for patient-reported functional outcomes (Lysholm knee score, Tegner activity level and VAS for pain score) in all the groups. No difference was found in functional outcomes between the three groups at the final follow-up. All the patients returned to the pre-injury activity level. A tendency for higher graft failure was noted with HT (19.2%) than QT (10%) or BPTB (10%) grafts. To the best of the author’s knowledge, this is the first study comparing all three autografts; QT, HT and BPTB for revision ACL reconstruction.

The incidence of ACL reconstruction is increasing over the past few decades. Excellent results after primary ACL reconstruction allow the patients to participate in highly demanding activities such as jumping, cutting, deceleration, and pivoting sports [5]. These activities substantially increased the risk of retear, therefore, the need for revision surgery has also increased over time [7].

In the present study, the Lysholm, Tegner activity levels and VAS for pain scores improved and reached pre-injury levels in all three groups. No significant difference was noted in patient-reported outcomes between the three groups at a 2-year follow-up. Mouarbes et al. [19] noted no significant difference in functional outcomes at the final follow-up between the three groups. Runner et al. [24] found comparable patient-reported outcomes in the primary QT and HT groups. Similarly, in another study, no significant difference was noted in patient-reported outcomes between the primary HT and QT ACL reconstruction group [25]. Lind et al. [15] in their randomized control trial noted no difference in subjective patient outcomes between HT and QT graft groups but they reported significantly less donor site pain in the QT group. Functional outcomes are also comparable between QT and HT autograft in revision ACL reconstruction. In their revision ACL reconstruction, Barié et al. found comparable functional outcomes with QT and HT autograft [1]. Similarly, in another revision study, Häner et al. [12] also found comparable results with QT and HT autograft. Improvements in patient-reported outcomes are comparable to previous studies.

Interestingly, a significant improvement from pre-injury to final follow-up was seen in the BPTB group. In their recent study, Yumashev et al. [29] also found a significantly higher Lysholm score in the BPTB group than HT group for revision ACL reconstruction. One of the possible reasons for significant improvement in Lysholm and VAS score from pre-injury level to final follow-up in the BPTB group was comparatively younger age patients in the BPTB (32.6 ± 8.3) compared to QT (37.6 ± 10.5) and HT group (36.2 ± 10.5).

The choice of graft in revision ACL reconstruction may be limited based on previously used grafts and it depends on various factors such as age, level of sports activities, previous tunnel position, tunnel enlargement, graft used in primary ACL surgery and surgeon’s preference [2, 21]. Graft choice is especially relevant in type C revision ACL, considering the fact that a single-stage revision procedure is possible with a thicker graft diameter [9]. BPTB and QT autografts provide a thicker diameter than HT autografts, therefore, in this situation use of QT and BPTB is preferable.

Graft choice influences graft failure [11]. Multicentre ACL revision study (MARS) found that in revision ACL reconstruction re-rupture is 2.78 times less likely with autografts than with allografts [17]. Similarly, various meta-analyses also reported lower graft failure with autografts than with allografts [4, 8, 22]. Therefore, the use of autografts is especially recommended in young highly demanding patients. Considering these facts, the present study used only autografts for revision ACL reconstruction. However, the graft choice between QT, HT and BPTB autografts remains widely debated in surgical practice.

The current study found a higher tendency of graft failure with HT than with QT and BPTB autograft, although the graft failure rate was not significant between the 3 groups. Both QT and BPTB have a higher graft diameter and strength compared to an HT graft which may explain the higher failure rate of HT grafts [22]. In their systematic review, Conte et al. [3] found that if the size of HT graft is equal to or less than 8 mm, then the relative risk of failure increase by 6.8 times. A recent systematic review of registry data including Danish, Norwegian and Kaiser Permanente (KP) registries found a higher failure of HT grafts compared with BPTB grafts [22]. Similarly in another large cohort meta-analysis graft failure was higher in the HT group [26]. Eggeling et al. [6] in their recent revision ACL study, compared graft failure between QT and HT and found higher graft failure in HT (17.4%) than in QT (2.3%). These findings are in accordance with the current study.

QT autografts are used far less commonly than HT and BPTB grafts [18]. One of the major factors responsible for its lesser use is historical harvesting techniques, where extensive dissection of extensor apparatus leads to quadriceps weakness, moreover, graft harvested by older techniques was biomechanically weaker and associated with residual rotatory knee laxity [27]. But, improvements in harvest techniques, allow the surgeon to reliably yield a robust volume of QT graft without hampering the quadriceps strength and very less donor site morbidity. Recent studies compared the biomechanical properties of QT and BPTB autograft and found superior results with QT compared to BPTB [16, 20, 28]. Therefore, in recent times QT autograft increasing in popularity for revision ACL reconstruction. Winkler et al. found that the use of QT autograft for revision ACL increased significantly (49% vs. 18%, p < 0.001) in 2015–2020 compared to 2010–2014.

In the current study, graft failure was similar in QT and BPTB groups. In their meta-analysis, Riaz et al. [23] reported comparable graft survival and joint stability with QT and BPTB grafts but lower donor site morbidity with QT graft. Mouarbes et al. [20] confirmed these findings in their recent meta-analysis with 2856 patients and found that graft survival is comparable with QT and BPTB grafts with lesser pain at the graft harvest site in the QT group than in the BPTB group. These meta-analyses with a large patient cohort suggest that QT and BPTB autografts are comparable for graft failure. However, both meta-analyses included studies with primary ACL reconstruction. To the best of the author’s knowledge, no study is available for revision ACL reconstruction comparing QT and BPTB graft, therefore, comparison of QT and BPTB autograft for revision ACL reconstruction with previous studies is not possible.

There are a few limitations of the present study. The first and the most important limitation is the small sample size, that underpowered to identify any difference in functional outcomes and graft failure. Revision ACL reconstruction is a less frequently performed procedure than primary reconstruction. Second, this was a retrospective analysis of patient-reported subjective outcome measures; however, all data were collected prospectively. A prospective study considering objective scores along with subjective scores should be conducted.

The clinical relevance of the present study lies in the fact that the incidence of revision ACL reconstruction is increasing and surgeons should be aware of all the available graft options. QT autograft is the least studied and least used graft compared to other grafts, especially for revision ACL reconstruction. Many surgeons do not even consider the QT as a possible graft option when discussing with the patients. Promising clinical results continues to emerge concerning the viability of QT autograft in revision ACL reconstruction. Based upon the findings of this study surgeon can counsel and advise the patient regarding the graft choice for revision ACL reconstruction.