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    Revision ACL Reconstruction: Current Concepts

    Revision of a failed anterior cruciate ligament reconstruction is a complex procedure. In this article, the authors review key points in evaluating and managing patients who present with a failure, including identifying the etiology of failure, recognizing concomitant pathology, and understanding operative considerations for the revision procedure.

    Authors

    Abigail Campbell, MD, MSc; Michael Zacchilli, MD; and Michael Alaia, MD

    Background

    Primary reconstruction of the anterior cruciate ligament (ACL) is performed more than 100,000 times per year in the US. Reported failure rates for ACL reconstruction (ACLR) are between 3% and 7%. [1-3] Causes of failure include:

    • Infection
    • Hardware complication
    • Motion loss
    • Recurrent instability

    Recurrent instability can present with either a torn or intact graft and can be classified as early failure (less than 6 months after surgery) or late failure (more than 6 months after surgery). Patients can also have subjective laxity without measured laxity due to pain, stiffness, or poor muscular control. Daniel et al [4] demonstrated that a side-to-side difference greater than 3 mm in anteroposterior (AP) laxity with the knee at 30° is correlated with structural failure of the ACL graft.

    Outcomes of revision ACLR are poorer than those of primary reconstruction:

    • The likelihood of failure is 3 to 4 times higher for revision ACLR. [5]
    • The rate of return to sport is reported at 43% for revision ACLR, compared with 87% for primary ACLR. [6-8]
    • Revision ACLR has higher rates of associated chondral or meniscal injury than primary ACLR. [9]

    ACLR Failure Etiology

    There are several reasons for ACLR failure. Some can be directly prevented by proper operative technique, while others, such as arthrofibrosis and infection, may relate to patient factors or inherent risks that cannot be mitigated by the operating surgeon.

    Most ACLR failures occur after non-contact injuries. Chen et al [10] reported that 55% of re-rupture following ACLR were from traumatic non-contact injury, 25% were atraumatic, and 11% were from traumatic contact injury.

    Surgically, tunnel malposition is the cause of about 50% of ACLR failures. Femoral tunnel position is often too anterior and/or too vertical. [11] Vertical femoral tunnels are associated with rotational laxity, resulting in functional failure. Anterior tunnels can lead to increased tension in flexion with subsequent failure or loss of flexion. Graft impingement and failure can be a result of anterior, medial, or lateral malposition of the tibial tunnel, and posterior cruciate ligament impingement can be an effect of a posterior tibial tunnel.

    Tunnel malposition has been directly associated with operative technique. Jaecker et al [12] recently reported no increased rate of femoral or tibial tunnel malposition with transtibial compared with anteromedial technique. However, numerous anatomic studies have demonstrated poorer tunnel placement with the transtibial technique than with independent femoral drilling. High-volume Swedish registry data have demonstrated a higher risk of revision ACLR with transtibial drilling of the femoral tunnel. [13]

    Concomitant pathology, such as meniscal deficiency (Figure 1) or collateral ligament insufficiency, can also complicate ACLR. The status of the meniscus is of critical importance given its role as a secondary stabilizer. Revision ACLR procedures have a significantly higher incidence of medial compartment injuries compared with primary ACLR procedures. [10] Partial menisectomy not only decreases contact area and increases the contact pressure of the tibiofemoral joint, [14, 15] but it also increases strain on the ACL graft by 30% to 50%. [16, 17]

    Figure 1. Meniscal deficiency on coronal and sagittal MRI.

    Shelbourne et al [18] demonstrated greater laxity after ACLR in patients with previous partial medial menisectomy compared with those who had an intact medial meniscus, and Robb et al [19] reported up to a 5 times greater failure rates with deficiency of either the medial or lateral meniscus. This important stabilizing force has been shown to improve with meniscus repair. [20]

    The “hidden lesion” of the posterior horn medial meniscus has been a subject of abundant recent study. Also referred to as a “ramp” lesion, [21] this often-missed concomitant injury has a reported incidence of 24%, with significantly higher rates in patients with direct contact injuries. [22] DiPhillipo et al [23] recently published a review of 301 ACLRs and reported a ramp lesion incidence of 16.6%, with an MRI sensitivity of 48%. They identified posteromedial bone bruising as a secondary finding associated with ramp lesions; it was present 72% of the time.

    Native varus malalignment was shown to be associated with increased forces on the ACL graft. A cadaver model representing both 6.5° and 12° of varus yielded a 25% and 70% increase in ACL strain, respectively, compared with neutrally aligned knees. [24] Native posterior slope can also affect ACL mechanics. Christensen et al [25] associated increased posterior tibial slope with increased rates of early revision, with increasing risk with increasing slope. Specifically, they reported an odds ratio of 1.6 for a 2° increase in slope, 2.4 for 4° of slope, and 3.6 for a 6° increase in slope. [25] Brandon et al [26] demonstrated a greater magnitude of pivot shift with increased tibial slope. A recent study by Sabzevari et al [27] associated tibial tunnel widening with increased lateral tibial posterior slope.

    Graft type can also contribute to failure:

    • In autograft, bone-tendon-bone graft has the benefit of providing bone-to-bone healing, while quadrupled hamstring graft has the highest load to failure at time zero. Although overall autograft ACLR has a low failure rate, [28, 29] Persson et al [30] demonstrated a higher failure rate for hamstring tendon fixation than with patellar tendon fixation.
    • Allograft has been shown to be associated with risk of re-rupture in young athletes. [31] Hybrid autograft-allograft reconstruction may be associated with higher failure rates than autograft reconstruction. Burris found a 40% failure rate in hybrid grafts, compared with 7% in autograft. [32] Tunnel diameter less than 8 mm has also been associated with increased failure rates of allografts. [32]

    Osteochondral injury has been associated with delayed failure of an ACLR, and significantly higher rates of cartilage degeneration were found in revision ACLR than in primary ACLR by Ohly et al. [33] A combined analysis of MOON (Multicenter Orthopaedic Outcomes Network) and MARS (Multicenter ACL Revision Study) data demonstrated an increased odds ratio for significant lateral and patellofemoral compartment chondral damage, but not for medial compartment chondral damage, in revision ACLR versus primary ACLR. [34]

    Patient Assessment

    History and Physical Exam

    A thorough history and physical examination are imperative when a patient presents with a suspected failed primary ACLR. The surgeon needs to evaluate:

    Mechanism of injury and functional status. Did the failure occur with an athletic re-injury or a low-energy mechanism (such as stepping off a curb)? Or is this simply chronic failure over time? Understanding the patient’s level of function, occupation, and athletic level is also important.  

    Pain versus instability. Is the patient’s main complaint pain or instability? Pain may indicate the presence of a meniscal or chondral injury, prompting consideration of concomitant procedures.  

    Surgical history. When did the initial injury occur and when was the reconstruction done? Is this an early or a late failure? What graft type and fixation method were used in the primary procedure? The authors always attempt to obtain the initial operative report, if available.  

    Gait and alignment. This evaluation will alert the surgeon to the presence of malalignment or thrust (particularly varus). Examination of active footwear may provide clues to subtle functional malalignment.

    Extremity exam. Assess for the presence of an effusion, point tenderness, range of motion, and location of the prior incisions. Muscle tone should be assessed for thigh atrophy.

    Specific ligamentous testing, with a focus on rotational laxity and the corner. Concomitant ligamentous injuries are ruled out with stress examinations or stress radiographs, if uncertain. Because instability can be evident without actual graft rupture, KT-1000 testing may be useful not only for the surgeon, but also to provide objective proof to the patient that the graft is incompetent. KT testing may also be helpful in the apprehensive patient, a common trait in patients with recurrent injuries.

    Imaging

    Imaging should include plain radiographs and standing limb alignment radiographs to evaluate overall alignment and posterior tibial slope.

    Plain radiographs. Radiographs are paramount for assessing tunnel and implant position, type of fixation used, and the presence of tunnel widening. Our patients are assessed radiographically with weight-bearing AP, posteroanterior (PA) flexion, lateral, and sunrise views (Figure 2).

    Posterior tibial slope can be measured on the lateral radiograph or on a sagittal MRI:

    • On a lateral radiograph, 2 transverse lines are drawn at 10 cm and 20 cm distal to the tibial plateau, and then a third line is drawn perpendicular to these lines, representing the longitudinal axis of the tibia. A line perpendicular to the longitudinal axis is drawn and the posterior slope is measured between this line and the lateral tibial plateau.
    • Sagittal MRI measurement was described by Hudek in 2009 in a similar fashion, [35] as demonstrated in Figure 2.

     

    Figure 2. Posterior tibial slope measurement on a plain radiograph and MRI. The measurement on the radiograph is done as described above. The MRI images shows the MRI longitudinal axis (MRI-LA) measured from the central sagittal cut and the lateral plateau cut comparing tangent to lateral tibial plateau and orthogonal line to MRI-LA. The angle between these 2 lines represents the lateral tibial plateau posterior slope. [35]

    Standing radiographs. Full leg-length weight-bearing alignment radiographs (Figure 3) are always obtained to rule out malalignment as a source of failure and to plan concomitant realignment procedures.

    Figure 3. Standing limb alignment radiographs measure the mechanical axis of near-normally aligned right postoperative knee.

    Advanced imaging. MRI is essential for evaluating cartilage and ligamentous integrity. Volumetric MRI or, ideally, low-dose CT scan is necessary for assessing tunnel position and osteolysis. Tunnel widening is best assessed on CT scan (Figure 4), and we obtain a CT scan with 3-dimensional reformatting in all patients with tunnel expansion or unclear tunnel position. When button fixation was used, tibial tunnel volume was significantly underestimated on MRI scanning compared with CT scan. [37] One study reported higher inter- and intra-observer reliability with CT scans than with MRI in quantifying bone tunnel widening. [38]

    Patient Expectations

    Once the diagnosis is confirmed, it is imperative for the surgeon to have an in-depth conversation with the patient about a revision ACLR. Goals, outcomes, and expectations should be realistic, especially in the context of concomitant meniscal or chondral pathology.

    In some cases, an “ideal” revision procedure may require an osteotomy and additional extra-articular ligamentous reconstruction (such as the posterolateral corner). These procedures carry significantly increased morbidity and patient investment, and they simply may be “too much surgery” for the patient. Some patients may be perfectly content living with subtle instability, may not wish to pursue higher-level activities, or may not wish to undergo the intensive rehabilitation process associated with revision ACLR without a guarantee of success. They may be unwilling to pursue small proportional decreases in the projected failure rate at the cost of increased pain, invasive procedures, and additional postoperative functional limitation.

    In these cases, we will certainly attempt a non-operative protocol.

    Operative Considerations

    If the patient agrees to surgery, we first assess the bone tunnels, as tunnel malposition is the most common cause of ACLR failure. This must be taken into account when evaluating the patient and planning the revision procedure. New tunnels may need to be created out of plane with existing tunnels, and existing tunnels may require addressing. Prior tunnels that are “close but not good enough” to the footprint and drilled at an ideal angle pose particular difficulty: They frequently mandate a challenging confluence between revision and initial tunnels, with tunnel and aperture widening, and issues with fixation strategy. A surgeon familiar with multiple femoral drilling techniques can often utilize the opposite technique to minimize this effect.

    In many cases, the femoral tunnel is malpositioned anteriorly such that a completely separate femoral tunnel can be created. Tunnels that are slightly malpositioned can be used if there is no significant widening. In these cases, we can perform a 1-stage revision: We create a well-positioned tunnel, place the graft in a more anatomic position, and supplement with a larger interference screw or bone graft to fill any voids.

    Even with such techniques, an ACLR cannot always be revised in a 1-stage approach – specifically, a single-stage revision may not adequately address tunnel position, graft fixation, or tendon-bone healing. Two-stage procedures are often required when tunnel widening exceeds 14 mm. [39] Other relative indications for 2-stage procedure include concomitant meniscal transplant, cartilage restoration procedures, and realignment osteotomies.

    Removal of existing hardware during revision ACLR may be required and may necessitate additional instrumentation. Not only should the appropriate screwdriver set be on hand, but a broken screw removal set should also be available. If screws cannot be extracted by traditional means, coring reamers and even large barrel reamers from a revision total hip arthroplasty set may be required.

    Graft fixation has been linked to outcomes in revision ACLR. A recent MARS study found that the use of metal interference screws, absence of notchplasty, and the use of anteromedial portal or transtibial exposure are associated with superior 2-year functional outcomes. [40]

    In the case of tunnel widening, bone grafting may be necessary. Common indications for bone grafting can include converged tunnels or significant tunnel osteolysis (Figure 4). Multiple options for graft material have been identified, including:

    • Iliac crest autograft
    • Demineralized bone matrix (Figure 5)
    • Allograft dowels (Figure 6)

    If a 2-stage revision ACLR is necessary, the old tunnels are reamed and packed with bone graft in the first stage. The second stage is performed when radiographic healing is evident, typically 3 to 6 months after the initial grafting procedure. Uchida et al [41] published a series that follow 2-stage revision ACLR patients at 3, 12, and 24 weeks postoperatively. Using CT scan, they found significantly higher healing parameters (occupying ratio, union ratio, and bone mineral density) at 24 weeks than at 12 weeks, supporting an interval between stages of the procedure closer to 6 months than to 3 months. [41] Recently, Mitchell et al [42] compared 1-stage to 2-stage revisions and found significantly improved functional outcome scores in both groups, with no significant difference in failure rate.

    After first-stage bone grafting, the patient may be made partial weight-bearing on crutches with a functional ACL brace and range of motion as tolerated, advancing to low-impact exercise around 6 weeks. [43]

    Figure 4. Significant femoral tunnel osteolysis in a patient with a failed ACLR performed with an “all-inside” technique.

    Figure 5. Demineralized bone matrix grafting of a widened tunnel. The graft is shuttled into the defect with the use of a flexible cannulated system and subsequently impacted further into place with an elevator or tamp.

    Figure 6. Allograft dowel insertion into tibial tunnel. Pre-shaped dowels can be passed directly over a guide wire and tamped into place.

    Authors’ Preferred Revision Technique

    As mentioned above, the first stage of a 2-stage procedure consists of hardware and graft removal followed by bone grafting. The second stage is completed 4 to 6 months later to allow time for bony healing.

    We prefer to fill cylindrical defects with press-fit allografts soaked either in protein rich plasma (PRP) or bone marrow aspirate concentrate (BMAC). Large, non-cylindrical defects are filled with a mixture of demineralized bone matrix and corticocancellous chips, again soaked in PRP or BMAC. We attempt to remove the sclerotic borders of the old tunnels using curettage or over-reaming of the prior tunnels. We find that reamers for revision total hip arthroplasty can be quite helpful for over-reaming if the defects are very large.

    Our preferred grafts are bone-patella tendon-bone (BTB), contralateral BTB, and quadriceps tendon autograft, as these produce robust grafts with bony attachments. When autograft is unavailable, we prefer BTB or Achille’s tendon allograft, as again, the bone in these grafts reliably fills pre-existing defects.

    We prefer not to use hamstring autograft as the graft size is unpredictable and healing is less reliable than with a bony substitute. In addition, bony grafts can be contoured to the surgeon’s preferred size and can sometimes mitigate the need to perform a 2-stage revision.

    Fixation for bone grafts can be undertaken with metal, biocomposite, or PEEK interference screws, and we routinely back up revision tibial fixation with a screw and washer or knotless anchor, especially in cases in which the old tibial tunnel is used or when large tunnels are obtained. With bone fixation, it is important to tap before placing either biocomposite or PEEK screws.

    We recommend an opening wedge high tibial osteotomy (HTO) to centralize the weight-bearing axis in cases of concomitant varus malalignment, with the weight-bearing line falling in the middle of the medial compartment. Many hardware configurations are available, and we prefer systems that allow us to drill the tibial tunnel independent of the osteotomy position.

    Concomitant ligamentous pathology is preferably addressed simultaneously during the revision procedure, keeping in mind patient input in the shared decision-making process. In the case of posterolateral corner (PLC) reconstruction, however, it is critical for the PLC tunnels to be placed anatomically and angled anterior and proximal to avoid convergence with the new ACL tunnel. Fluoroscopy can be helpful to confirm the tunnel position prior to commitment.

    Medial or lateral meniscus deficiency is addressed with concomitant meniscus transplant. For a medial transplant, we use a bone plug technique to avoid iatrogenic injury to the ACL graft. In patients who would benefit from combined HTO, medial meniscus transplant, and revision ACLR, we typically performed a staged procedure beginning with combined HTO/ACLR and returning 3 to 6 months later for the meniscus transplant, plus or minus any cartilage restoration procedure.

    On the day of surgery, it is helpful to work with an experienced operative team and to have on hand multiple solutions in case the original plan is changed intraoperatively, as can be the case with revision ACLR. Typically, we have the following readily available:

    • Staples
    • Screw-and-washer systems
    • Transtibial, anteromedial, and retrograde drilling sets
    • Knotless suture anchors
    • Bone graft substitute
    • Large interference screws
    • Fluoroscopic imaging

    A well-prepared operative team and surgeon will greatly improve the chances of a successful outcome

    Conclusion

    Revision ACLR is a complex procedure. Identifying the etiology of failure, as well as being cognizant of potentially missed concomitant pathology, is essential. Discussion of patient goals and expectations will assist the surgeon in operative planning.

    Although there is much literature on pathology-specific revision ACLR techniques and outcomes, there is still a significant area of unknown regarding risk for failure and optimal revision protocols. Prospective randomized trials are needed in the field of revision ACLR, specifically:

    • Following patients with preoperative malalignment to determine if the malalignment makes them more likely to experience a failed ACLR, and if so, what kind of malalignment is associated with failure (ie, how much varus is too much to change the likelihood of failure?)
    • Following patients with a failed ACLR (now ACL-deficient) who also had an HTO to determine if the HTO protects the patient from developing medial compartment osteoarthritis
    • Comparing different types of bone graft for 2-stage revisions
    • Examining time to healing and outcomes of 2-stage revision ACLR
    • Assessing biologic augmentation of primary and revision ACLR

    Key Points

    • Revision ACLR has a lower return-to-play and higher failure rate than primary ACLR.
    • Tunnel malposition is the most common reason for ACLR failure, although alignment, posterior tibial slope, tunnel widening, meniscus pathology, and unrecognized multi-ligamentous instability must also be evaluated.
    • Graft type and graft size also play a role in failure, influencing incorporation and rerupture rate, particularly in younger patients.
    • One- or 2-stage reconstruction procedures may be used. Bone grafting and a 2-stage procedure may be indicated if there is critical tunnel overlap or tunnel size greater than 14 mm.
    • Further studies are needed regarding the natural history of malaligned patients undergoing ACLR, as well as comparisons between bone grafting techniques

    Author Information

    Abigail Campbell, MD, MSc, and Michael Alaia, MD, are from NYU Langone Orthopaedic Hospital, New York, New York. Michael Zacchilli, MD, is from the Orthopaedic Institute at Lenox Health, New York, New York.

    Disclosures

    The authors have no disclosures relevant to this article.

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