INSTRUCTIONAL LECTURE: 8:5 231–244 GENERAL ORTHOPAEDICS Anterior cruciate ligament failure and management Juan Carlos Monllau 1,2 , Simone Perelli1,2 and Giuseppe Gianluca Costa3 1 Department of Orthopaedic Surgery, Hospital del Mar, Universitat Autònoma de Barcelona (UAB), Barcelona, Spain Correspondence 2 ICATKnee, Institut Catalá de Traumatologia i Medicina de l’Esport (ICATME), Hospital Universitari Dexeus, UAB, should be addressed Barcelona, Spain to J C Monllau 3 Orthopaedic Surgery Department, Ospedale Umberto I, Enna, Italy Email jmonllau@psmar.cat • Anterior cruciate ligament (ACL) reconstruction failure can be defined as abnormal knee Keywords function due to graft insufficiency with abnormal laxity or failure to recreate a functional f anterior cruciate knee according to the expected outcome. ligament failure • Traumatic ruptures have been reported as the most common reason for failure. They are f anterior cruciate followed by technical errors, missed concomitant knee injuries, and biological failures. ligament revision • An in-depth preoperative examination that includes a medical history, clinical examinations, advanced imaging, and other appropriate methods is of utmost importance. f preoperative planning • There is still no consensus as to the ideal graft, but autografts are the favorite choice even in f graft choice ACL revision. f posterior tibial slope • Concomitant meniscal treatment, ligamentous reconstruction, and osteotomies can be f osteotomy performed in the same surgical session to remove anatomical or biomechanical risk factors for the failure. f outcomes • Patient expectations should be managed since outcomes after ACL revision are not as good f instructional lecture as those following primary ACL reconstruction. EFORT Open Reviews (2023) 8, 231–244 Introduction Surgical reconstruction of the anterior cruciate ligament outcomes have been reported in one-third of all cases (5). (ACL) is supported in the international literature as the Beyond that instability, Johnson and Fu proposed a more treatment of choice in sports-active patients due to the inclusive definition of failure considering also pain and fundamental role of the ACL in joint kinematics and in the stiffness (8). Such objective criteria do not consider the preservation of the intra-articular knee structures (1, 2). patients’ functional demands that could not be met due to The last two decades have seen significant advancements a dysfunctional knee. Finally, the 2022 European Society in surgical techniques, our understanding of knee of Sport Traumatology, Knee Surgery and Arthroscopy biomechanics and injury prevention expertise. Despite (ESSKA) consensus defined ACL reconstruction failure as this, the risk of failure is still substantial. It ranges from abnormal knee function due to graft failure itself with 1.8 to 11.1% (3, 4) at midterm follow-up and up to 10.4– abnormal laxity or failure to recreate a functional knee 16.7% at long-term follow-up (5). according to the expected outcome (9). The unambiguous and universally accepted definition When an ACL reconstruction fails, revision surgery of failure after ACL reconstruction is yet to be determined. is indicated to improve knee function. The number of Historically, a failed ACL reconstruction was defined by the these procedures has risen over the years (10), as the presence of abnormal anteroposterior or rotatory knee natural result of the increasing participation in sports. instability (6). However, a recent meta-analysis reported However, ACL revision is still a demanding surgery and 34% of patients undergoing ACL reconstruction had a provides inferior outcomes (in terms of both patient- positive Lachman test and 24% of those patients had reported outcomes and objective function scores) when a positive pivot-shift test in spite of having satisfactory compared to primary ACL reconstruction (11, 12, 13). subjective outcomes (7). Conversely, in another meta- Several issues are still a matter of debate. They include analysis evaluating long-term ACL reconstruction results, a the preoperative evaluation, the ideal graft choice, when positive Lachman and pivot shift test were found in 9.4 and a one-step approach can be performed or a two-step 9.3% of cases, respectively. However, abnormal objective approach is required, the need for concomitant surgeries www.efortopenreviews.org © 2023 the author(s) This work is licensed under a Creative Commons https://doi.org/10.1530/EOR-23-0037 Attribution-NonCommercial 4.0 International License. INSTRUCTIONAL LECTURE: 8:5 232 GENERAL ORTHOPAEDICS as well as indications for bony deformities correction. The most common causes of recurrent instability identified available literature does not provide clear evidence-based after ACL reconstruction is vertical femoral tunnel knowledge on these topics. As a result, the management placement high in the intercondylar notch, which is not of failed ACL reconstructions is still too often based on the able to constrain the knee under rotatory forces (26, 27). surgeons’ personal experience. On the other hand, a graft that is placed too posterior and This article aims at providing an evidence-base as well low in the femoral condyle edge is exposed to high strain as an expert opinion about the etiology, preoperative during knee extension (25). Tibial tunnel placement planning, and management of patients with a failed ACL plays an important role in knee stability and graft failure reconstruction. Furthermore, outcomes after ACL revision risk. An excessively posterior tibial tunnel may result in will be discussed with the aim of providing a friendly- a vertical ACL graft, thus affecting both anteroposterior reader review of the currently available literature. and rotatory knee stability (31). However, an anterior tibial tunnel also leads to greater graft impingement in Reasons for failure extension and excessive strain in knee flexion (32, 33). Technical errors also include fixation failures even though The identification of the causes of failure is the first step for they seem to be a very uncommon cause of failure. It a successful ACL revision. However, this can be challenging has only been reported in about 2–5% of cases (15, 34). because several factors may lead to ACL reconstruction For instance, interference screw divergence has been failure (14). Sometimes, the main cause can be unclear, proven to affect graft pullout strength (35, 36, 37). or a combination of more reasons may be found (14, 15). Similarly, cortical buttons deployed in the substance of The causes of failure may be temporally distinguished the quadriceps can cause underlying muscle necrosis and between early and late, although an exact cut-off has not eventual graft slippage before full graft incorporation. been determined (9). Early failure is usually related to the Otherwise, secondary graft slippage through relatively failure of graft incorporation because of fixation errors soft cancellous bone may be responsible for failure if the or biological factors, aggressive rehabilitation or poor button is deployed in the femoral tunnel’s cancellous compliance, a premature return to high-demand activities, bone (38). and a new traumatic event (16). Late failures may be due Missed concomitant knee injuries constitute another to technical errors, recurrent trauma, or missed associated substantial theme in this topic. The available literature injuries (17). reports that nearly 15% of ACL failures are a result of a Knee trauma has been reported as the most common missed diagnosis of concomitant ligament, meniscus, reason for failure. It accounts for 29–70% of revision or cartilage lesions (16, 39). The most commonly cases (15, 16, 18, 19). Although not predictable, some unrecognized instability is secondary to a posterolateral predisposing factors have been called into question. They corner (PLC) injury (17). Several biomechanical studies have comprise a younger age, the male gender, and high- demonstrated that PLC injuries significantly contribute to impact activities (14, 20). Early aggressive rehabilitation anteroposterior knee stability (40) and increase loads on and a premature return to sport may also lead to reinjury the ACL when applying a varus moment or a combined (17, 21). Improper neuromuscular control exposes the ACL varus-internal rotation moment to the knee joint (41, 42). graft to increased loads, thus increasing the risk of failure. It also happens during simulated gait and squatting testing A large body of research done over the last 25 years that (43). In such settings, an isolated ACL reconstruction is not focused on this issue has demonstrated that prevention enough to restore native knee stability (42). Similarly, the programs can effectively decrease the number of ACL tears posteromedial aspect of the knee greatly contributes to (22, 23, 24). anteromedial knee stability. ACL strain was found to be Technical errors seem to play a major or contributing increased after medial collateral ligament (MCL) sectioning role in 22–79% of reported ACL failures (16, 19), with in some cadaveric studies, exposing the ACL to the risk of tunnel malposition being the leading cause of failure rupture when applying a valgus stress or an intra-rotation (18, 19). Positioning errors in tunnel placement can movement of the tibia (44, 45). Furthermore, combined involve both the femoral tunnel and the tibial tunnel MCL and ACL deficiency generates increased anterior tibial that may result in excessive graft strain (25), persistent translation when compared to isolated ACL-deficient knee instability (26, 27), graft impingement (28, 29), and (44). Meniscus integrity loss has also been advocated as a loss of motion (19, 30). While inadequate stability and potential cause of ACL reconstruction failure. Then again, excessive strain may predispose to mechanical failure, conflicting outcomes have been described in the literature graft impingement can cause an attritional rupture (14, 46). Nonetheless, there is abundant evidence in the or interfere with biological healing. Femoral tunnel literature about the contribution of the menisci to knee positioning errors are found to be more common than stability as they act as secondary restraints for anterior and tibial tunnel ones (18, 19). Unsurprisingly, one of the rotatory tibial displacement (47, 48, 49). Meniscus repair www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 233 GENERAL ORTHOPAEDICS would seem to restore knee stability comparable to ACL- status. Varus malalignment has been demonstrated to have reconstructed knees with intact menisci (49). a two-fold incidence r in the revision setting with respect to Biological failure is another unsolved question. The real primary ACL reconstruction (57). On the other hand, valgus incidence of this reason for graft failure is unclear since an malalignment led to an increase in the in situ forces on the unambiguous definition has not yet been determined (17). ACL graft, with particular regard to the posterolateral bundle Several pathways have been debated to explain the reasons (58). Gait analysis may reveal the presence of a valgus/varus for biological failure. The reasons encompass a disturbance thrust or hyperextension, which may be indicative of a more in revascularization, inhibited cellular proliferation, or complex structural problem that should be addressed prior deficiency in the ligamentization process (50). Graft choice to any revision. Likewise, extensor mechanism dysfunction plays a great role in explaining biological failures since graft should be identified if present. incorporation is strictly related to graft type, the bone-to- Careful inspection of the skin should be performed to graft interface as well as patient immune response. It is not plan the skin incision with the aim of preventing wound surprising that biological failure is found more pronounced healing difficulties and skin necrosis. Active and passive in allografts (51). Among the autografts, hamstring range-of-motion (ROM) should be assessed and compared tendons showed a significantly higher biological failure with the uninjured side. Knee extension or flexion deficits rate in comparison to bone-patellar tendon-bone (BPTB) represent a contraindication for ACL revision surgery grafts (19). Infection can be counted among the causes of (9) unless they are the result of a malpositioned graft. biological failure. Although uncommon, this complication Knee hyperextension is a well-recognized risk factor for may lead to devasting sequelae for the knee joint (52). Early failure (59, 60, 61) and may require concomitant surgical diagnosis and prompt treatment are crucial to minimize procedures (62). Furthermore, basic knee examination consequences of sepsis (52, 53, 54). Graft preservation should assess the presence of intra-articular effusion, protocols have been reported with mixed results. However, patellar tracking, patellar tendon discomfort, quadriceps the risk of graft removal or secondary graft failure remains strength, and patellar facet tenderness. high (52, 54, 55). The prevention of infection by adopting The mainstay of ligament assessment is the manual appropriate measures (for instance, autograft soaking in evaluation of anteroposterior (with the Lachman test and vancomycin) remains the trump card (56). the anterior drawer test) and rotatory knee laxity (with the pivot-shift test). The Lachman test has the greatest Preoperative assessment sensitivity and is the most accurate test for ruling out ACL injury (63). In patients with large thigh girth, this An in-depth preoperative examination that includes the maneuver can present difficulties. Modified versions of medical history, clinical examinations, and advanced the original Lachman’s test in the prone position (64) as imaging methods is a crucial element for the successful well as alternative tests like the Lever test can be used management of ACL reconstruction failures. (65). The pivot-shift test better correlates with patients’ Patients’ demographic characteristics (age, gender, clinical symptoms and subjective instability but can body mass index) as well as patient-specific modifiable show low diagnostic performance in patients that are features (type of sport resumed, timing of returning awake (66). Laxity-detection devices can be helpful to to sport after ACL reconstruction) deserve particular better evaluate knee laxity, but they cannot replace a consideration due to their role as predisposing factors to careful manual evaluation (9). A side-to-side difference ACL failure (14). The level of activity, pain, swelling, and greater than 5 mm is widely accepted as evidence of ACL instability symptoms should also be assessed. Recurrent insufficiency (9). Due to the high incidence of missed synovitis and persistent pain should induce suspicion of concomitant injuries, physical evaluation needs to be a low-grade infection. The surgical details of the previous supplemented by evaluation of the entire ligamentous ACL reconstruction need to be collected before performing apparatus of the knee. The presence of a positive the revision procedure. Knowledge of the previously used posterior drawer or sag sign should be documented as graft, the drilling technique, and the fixation methods help it suggests an associated posterior cruciate ligament the surgeons to properly make the graft choice and plan (PCL) insufficiency. Valgus and varus tests at 0° and the surgical technique. The rehabilitation protocol and 30° of knee flexion may reveal concomitant medial and postoperative complications also need to be investigated. lateral collateral ligament insufficiency, respectively. The external rotation recurvatum and dial test at 30° and Physical examination 90° of knee flexion should be performed to test the PLC. Further diagnostic tests (joint line tenderness, Mc Murray A meticulous physical examination must include standing test, Apley test, etc.) should be included to diagnose and gait assessment of the lower limbs to evaluate coronal potential concomitant intra-articular pathologies like and sagittal limb alignment and the muscular/neurological meniscal tears or cartilage defects. www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 234 GENERAL ORTHOPAEDICS Radiologic evaluation MRIs provide critical information about the primary graft, location and orientation, and diameter of the existing Preoperative imaging is a crucial part of surgical bone tunnels, as well as information about patellar tendon planning in patients who are candidates for ACL revision. length and quadriceps tendon thickness (9, 73). However, Radiographic evaluation represents the first-line test and computed tomography (CT) scans are more reliable to helps surgeons to evaluate some fundamental parameters evaluate bone tunnels (74, 75). They provide fundamental like joint narrowing, patellar height, posterior tibial slope information when choosing a one-step or a two-step (PTS), tunnel placement and widening, and retained surgical approach (72). Some authors even support three- hardware (9). An accurate radiological assessment should dimensional CT scan reconstruction to get much more include the following views: accurate information on tunnel size and location (76). • Bilateral anteroposterior full-length weight-bearing view: It can be used to define the presence of coronal Surgical management malalignment and plan concomitant corrective Surgical management of an ACL failure can be highly osteotomies if indicated. demanding for even the most experienced surgeons. • Posteroanterior weight-bearing view at 45° of flexion Several controversies remain in clinical practice and there (Rosenberg view): This view increases the sensitivity are numerous potential pitfalls during surgery. The ideal of the standard anteroposterior view to document the graft choice, when to perform a one-stage or a two-stage extent of cartilage wear (9). Additionally, it can be used surgery, and the need for concomitant procedures are to evaluate bony morphology and detect predisposing just some of the open questions with no easy solution. factors to failures such as the femoral notch shape and Although there is a growing interest in these main the lateral femoral condyle width (14, 67). topics, the literature on them is still sparce. An evidence- • Lateral view at 30° of flexion: This view allows for the based approach remains the most appropriate to guide measurement of the static anterior tibial translation, surgeons in this complex topic. the patellar height (thus approximately determining the length of the patellar tendon), and the PTS, provided Graft choice that the first 15 cm of the proximal tibia is visible (9). An increased PTS has been shown to be associated with a The selection of the optimal graft in ACL revision surgery greater risk of graft failure following ACL reconstruction has always been a matter of debate. It is well known that (68). A concomitant PTS-reducing osteotomy (tibial the ACL graft plays a significant role in clinical outcomes deflexion osteotomy) can be indicated in selected (77), the development of osteoarthritis (78), and the risk of failure after primary reconstruction (79). Hence, the cases. Similarly, increased anterior tibial translation is a choice of the graft can also have a great influence on ACL common finding in multiple ACL reconstruction failures revision outcomes. and can be used as red flag in high-risk patients (69, 70). To date, there is no standard graft for ACL revision. • Axial weight-bearing radiographic view (Baldini view The graft used in primary ACL reconstruction, the (71)): It is useful for evaluating patellar tracking and presence of severe tunnel widening, and concomitant degenerative patellofemoral changes. This is essential ligament deficiency are three fundamental determinants when planning to use BPTB or quadriceps tendon as an when choosing the new graft (9). However, other autograft. This axial weight-bearing view can provide clinical considerations like patellofemoral joint disorder, additional information over standard unloaded axial anthropometric measures, the surgeons’ skills, and which radiographic views (71). kind of sport the patient plans to resume should be considered. Secondary radiographic views may be requested in the Autografts remain the most preferred choice even suspicion of multiligament knee injuries. These include in revision ACL reconstructions (11, 13, 80, 81, 82). varus or valgus stress views to evaluate the integrity of Despite its donor site morbidity and the lesser versatility the lateral and medial ligaments, respectively. Kneeling in comparison to allografts, autografts have indisputable or Telos posterior stress views to quantify posterior laxity advantages. These include faster and more reliable due to PCL and accessory ligaments insufficiency may biological integration (83), no risk of disease transmission also be called for (72). or immunological rejection, and better objective stability Magnetic resonance imaging (MRI) is mandatory to (80, 84). BPTB is used more frequently in revision settings evaluate the integrity of the other knee ligaments and than in primary reconstructions since hamstrings remain the status of articular cartilage and menisci. Furthermore, the most popular choice in the latter setting (11, 13, 80, www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 235 GENERAL ORTHOPAEDICS 81, 82). Proponents argue that bone-to-bone integration modulus, and maximum stress as well as the maximum may be particularly convenient in a biologically impaired force up to 46% (96). This may explain why allografts scenario such as failed ACL reconstruction (85, 86, 87). provide inferior objective outcomes and greater failure Ipsilateral BPTB reharvesting has been proposed by rates than autografts in clinical studies (80, 84). Indeed, if some authors, but a higher rate of complications and an allograft irradiated with higher doses is excluded, there poorer functional scores have been reported in contrast is no difference between autografts and allografts relative to contralateral BPTB harvesting (88, 89). The quadriceps to outcomes (80, 97). Various chemical sterilization tendon with or without a bone block is increasingly being measures have been proposed as alternatives, but those used as an alternative to BPTB. The low complication rate techniques have also been associated with negative effects prolonged freezing at −80°C has been shown to decrease and the good midterm outcomes support this choice, on the biomechanical properties of allografts (93). Even but the long-term benefits are yet to be demonstrated (90, 91). Hamstring tendons remain a valuable option load to failure, ultimate stress, and ultimate strain (93). even in revision procedures. One significant advantage In addition to this, some issues persist concerning to using the hamstring graft is the lower risk of donor the healing and biological incorporation of allografts. site morbidity, especially anterior knee pain and patellar Although the healing process is the same as in autografts, fracture (92). This may be particularly important in the replacement of the donor tissue with host synovial patients involved in kneeling or squatting activities or in cells has proven to be significantly slower (98, 99). It may patients who are predisposed to patellofemoral pain. Some require 3 years or more for complete incorporation (98). authors even recommend harvesting the contralateral For those reasons, allografts should be used prudently hamstring tendon, but the high risk of contralateral ACL in patients with a high risk of failure, especially pediatric tear should not be disregarded (4). The most reported and adolescent athletes, as existing studies have revealed disadvantage is related to graft size, which may represent a significantly higher failure rate for the allograft than the a major limitation in challenging cases with severe tunnel autograft in those patient populations (79). enlargement. Furthermore, soft tissue-to-bone healing Synthetic grafts represent a further option but should requires a slower process of fibrovascular scar tissue be considered with circumspection because of their maturation at the graft-tunnel interface than bone-to- inferior middle and long-term results (100). At present, bone healing with direct contact (85, 86, 87). However, synthetic grafts are indicated as an alternative to the there is currently no evidence of the superiority of BPTB above-mentioned graft options in the older, less active over the hamstring tendons graft in revision ACL surgery population among whom the risk of graft rupture is in terms of knee stability and failure rates (80). comparatively less (14, 100). Allografts are another appealing option in ACL revision due to the lack of potential complications related to One- or two- stage surgery autograft harvesting. Types of allografts include BPTB, Achilles tendon, the tendons of tibialis anterior or The decision for a one- or two-stage revision depends posterior, and tendons of peroneus longus or brevis. All on multiple factors that must be considered as there is have different biomechanical properties (15, 80, 93). The currently no consensus regarding the indication of one or versatility of allografts can be convenient when facing another procedure (101, 102). challenging cases, and customized bone blocks can Even though it is not frequent, a two-stage revision is be used to fill enlarged tunnels during a single-stage mandatory if an infection is suspected. procedure (50). On the other hand, allografts have some Planning a one-stage ACL revision in the case of inherent drawbacks. They include availability, increased a significant extension or flexion deficit requires an cost, and the theoretical risk of disease transmission. exhaustive analysis of the causes. When the cause Nevertheless, the reported incidence of infection is less of the deficit in mobility can be resolved at the same than 1% (94) and the risk of viral disease transmission time as that of instability, the functional results have is estimated to be less than 1 in 1,600,000 cases (95). proven to be satisfactory. It is mostly true in the case Another source of concern is the biomechanical properties of completely incorrect positioning of the tunnels or of allografts. Those properties may be affected by several displaced meniscal or osteochondral tissues within the factors like the age of the donor, sterilization process, tibio-femoral joint (103). and preservation methods (93). Donors older than 65 When the cause of the ROM deficit is not detectable years of age provide allogenic tissue with significantly or is due to severe arthrofibrosis, a two-stage surgery is lower ultimate stress values than younger donors (93). recommended. The sterilization process was an important topic in the Rarely does the presence of metallic material interfere last decade. Gamma irradiation has been demonstrated, with a one-step surgery, but it may. Either way, the with a dose-dependent effect, to reduce strain energy, presence, position, and bone integration of interferential www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 236 GENERAL ORTHOPAEDICS screws, plate, or nail should be evaluated properly to be compromised both if the tunnels are partially anatomic decide the surgical approach. In the case of multiple and when they are anatomic but present with severe previous surgeries, the scars should also be taken into osteolysis (111). (Fig. 1) account. When possible, a skin approach located at For these cases, a two-stage procedure is more previous scars is suggested to avoid vascular impairment recommendable even though some rescue procedures that and skin necrosis. allow for a one-stage revision have been described. They The location, dimension, and morphology of the described the different uses of bone impaction grafting previous bone tunnels is probably the most important to support the new bone tunnels circumferentially even factor to be considered for a proper decision as to the in the case of mispositioning or severe osteolysis of the technique to be used in the revision ACL reconstruction. former tunnels (112, 113). When the position of the previous tunnels is correct Finally, it might be possible to approach complex cases (anatomic), only the diameter should be considered. A in which both the tibial and femoral tunnels are dilatated high level of evidence is still lacking, but most authors or mispositioned using an Achilles tendon allograft. consider that a diameter around 12 mm is the cut-off to Following the steps of the over-the-top technique or consider a revision in two stages (104, 105). Anyway, no drilling an out-in femoral tunnel, the femoral part of the absolute threshold exists for the critical tunnel diameter, reconstruction is resolved. Furthermore, the problem of and some authors suggest 15 mm as the limit for a one- the tibial tunnel is solved by sculpting a truncated cone stage revision (106). Possibly, a universal threshold can block of the desired dimension from the calcaneus bone be proposed given that it varies when it comes to graft block to fill the gap of the former tunnel (114). choice, drilling technique, fixation technique, and knee In the case in which there is no collision but the size (104, 105, 106). distance between the two tunnels is less than 2 mm, the Nevertheless, some authors consider that the clinical risk of this bone bridge rupture is high during maneuvers results at 5–15 years postoperatively are the same in like reaming, impacting, or screwing in the new tunnel. patients with a more or less 12 mm tunnel diameter when For these reasons, the previous tunnel can be filled with a one-stage ACL revision is performed (107). structural bone or an interference screw to improve the Even in the case of a diameter larger than 15 mm, some resistance of the bone bridge (115). (Fig. 2) techniques have been described to bypass the problem of In the case of a two-stage revision, the bone grafting of a precarious fixation of the new graft in the former tunnel the previous tunnel can be achieved with an autologous if a one-stage revision is required or suggested for clinical graft (both from the iliac crest and from the proximal tibia) or personal reasons. Haidar et al. (108) proposed the use or with an allograft (either preformed cylinders or bone of an out-in technique for femoral tunnel drilling. They chips or tailored bone blocks) (101). stated that this technique makes for a different obliquity of the tunnel and thereby allows for a solid fixation and good integration of the graft even in the case of a previous femoral tunnel of greater diameter. Pioger et al. (109) subsequently presented promising results using this even when a one-stage revision surgery was performed in patients with large femoral tunnel diameter. Another approach to solve the problem of a dilated femoral tunnel is the over-the-top technique (110). In this case, the graft does not need a femoral tunnel. It is passed behind the lateral femoral condyle (over the top position) and fixed on the posterolateral cortex of the femur by means of staples. More complex is the analysis of the cases without dilation but with mispositioning of the tunnels. Precise preoperative planning should make clear whether the previous tunnels are completely out of the way (completely non-anatomic) for the creation of the new ones or if any kind of interference is expected (partially Figure 1 anatomic or previous anatomic tunnels). In the first case, Preoperative CT scan axial view showing three different tunnels a one-stage procedure is an available option. In the latter for previous ACL reconstruction. In this case, a two-stage case, the stability and the integration of the new graft may revision is recommended. www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 237 GENERAL ORTHOPAEDICS so when facing multiple failed ACL reconstructions. If the PTS is greater than 12º and the patient does not present preoperative hyperextension, an anterior closing-wedge osteotomy to reduce the tibial slope should be considered (119, 120, 121, 122) (Fig. 3). In the case of medial meniscus insufficiency, the indication for this kind of osteotomy is even more supported from a biomechanical point of view. The goal of the correction is not clearly described since a range of values from 3 to 10° has been described (123, 124). The use of the anterolateral tenodesis in the setting of an ACL revision has been described as beneficial. Therefore, it Figure 2 should be considered in almost all cases if there are no The previous tunnel was filled with an interference screw before contraindications for this procedure (e.g. concomitant the drilling of the new femoral tunnel to avoid the breakage of PLC lesion) (125, 126). the bone bridge between the two tunnels. In the case of two-stage revision, an anterolateral tenodesis should be performed in the first stage to reduce Allograft bone matrix and calcium phosphate have also subjective and objective stability in the interim between been described as useful for tunnel grafting, but solid the two stages (127). clinical results for these techniques are lacking (106, 116). Peripheral knee instability can be a cause of failure of When a two-stage procedure is adopted, the time the ACL revision or a risk factor for poorer outcomes (128). between the two stages of the revision should be Therefore, both medial and lateral clinically evident sufficient to allow for the correct integration of the instability should be addressed at the same time as an graft. Most of the authors suggest a period of between ACL revision. Indications for the thresholds of peripheral 3 and 6 months, with there being a difference between instability are lacking but the general recommendation is autologous or allogenic bone. A CT scan can be used to to address grade 2 and 3 instability (129, 130). evaluate bone integration before the second stage of the Meniscal transplantation is usually reserved only for revision (117, 118). patients who present with the so-called postmeniscectomy syndrome, pain and swelling associated or not to cartilage lesions after a meniscectomy. Considering the Concomitant procedures stabilization properties of the menisci in the setting of When a revision ACL surgery is performed, several an ACL revision surgery, meniscal transplantation may be other procedures may be required to resolve both the indicated even without pain or repetitive swelling. The anatomical predisposing factor for the ACL failure and reason behind that is that a total or subtotal meniscectomy other symptoms like compartmental pain. can contribute to knee instability that, if not addressed, More than 4º of varus or valgus is considered a coronal can lead to a failure of the ACL revision (131, 132). deformity suitable for correction. The osteotomy is mostly indicated in the case of symptomatic cartilage or meniscal Outcomes insufficiency, when a varus or valgus thrust is present or if a meniscal transplantation or cartilage procedure Although evidence on ACL revision outcomes remains is performed at the same time as the ACL revision (119, sparse, an increasing body of research has been made 120, 121). Moreover, any sagittal malalignment should be available over recent years. Several systematic reviews and addressed in the setting of an ACL revision, and even more meta-analyses have focused on this issue and investigated Figure 3 From left to right are described all the phases of a concomitant slope-decreasing osteotomy in the context of an ACL revision surgery. www.efortopenreviews.org INSTRUCTIONAL LECTURE: 8:5 238 GENERAL ORTHOPAEDICS the different aspects of ACL revision surgery and the 4 years to 41% after 6 years (105). Patients who underwent related results. ACL revision are exposed to twice the risk of having Patient-reported outcome measures (PROMs) have radiographic evidence of osteoarthritis when compared been shown to have increased from their preoperative to patients who had had primary ACL reconstruction (11). status in three recent systematic reviews (12, 81, 102). The progression of osteoarthritis was more pronounced However, ACL revision PROMs were reported significantly in the medial tibiofemoral compartment, followed by the inferior to primary ACL reconstruction subjective scores patellofemoral compartment and lateral compartment (11). According to the objective International Knee (137). This finding matches with the higher prevalence of Documentation Committee classification, a normal or concomitant meniscal lesions in the medial compartment nearly normal knee function is reported in between 62 and at the time of revision surgery (13, 137). 91% of cases (11, 12, 13, 133, 134, 135). Again, this finding was significantly inferior to the results after primary ACL reconstruction (11, 12, 13). Conversely, anteroposterior Conclusion knee laxity evaluated manually by performing the The management of ACL reconstruction failure has Lachman test or using an arthrometric test does not become an increasingly common challenge in recent significantly differentiate between primary and revision decades. Correct identification of the reasons for failure ACL reconstruction (11, 12), but a higher rate of abnormal and accurate preoperative planning are essential for rotatory knee laxity is described in the ACL revision group successful ACL revision. Although clinical research has (11, 12). increased over the years, several issues are still debated. Return to sports activity after revision ACL reconstruction They include the ideal graft choice and indications for was addressed in five meta-analyses, with mixed results associated surgical procedures. There remains a great (11, 12, 81, 133, 134, 135). In two of them (11, 12), there need to perform more high-quality studies with the goal was no difference between the primary and the revision of developing evidence-based knowledge in this field and groups on the Tegner activity scale. In an additional meta- providing better outcomes to the growing demand for analysis including 59 studies (102), the pooled Tegner solutions. score at the last follow-up was found to be significantly lower than the preinjury Tegner score. Three patients out of four were able to return to sport at any level, with ICMJE conflict of interest statement no difference in patients who underwent primary ACL The authors declare that there is no conflict of interest that could be perceived reconstruction. However, this finding radically changed as prejudicing the impartiality of the research reported. when addressing the return to sports at the same level, since only 43% of patients were reported against 63% in Funding statement the primary ACL reconstruction (102). These results match No funding was received for this manuscript. with those published in another 2 meta-analyses (81, 135), in which almost 8 patients out of 10 were able to return to sports after revision ACL reconstruction, but only half References of them returned to the same pre-injury sport level. The 1. Kessler MA, Behrend H, Henz S, Stutz G, Rukavina A & Kuster MS. Function, average time to return to sports was reported as between osteoarthritis and activity after ACL-rupture: 11 years follow-up results of conservative 5 and 12 months after surgery (81, 135). The main reason versus reconstructive treatment. 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