Anterior Cruciate Ligament reconstruction is a complex process, although the success rate of ACL reconstruction surgery is generally 85 – 95%. Therefore, a significant number of patients who undergo ACL reconstruction may have a less than satisfactory outcome, leading to a revision ACL surgery. In general, the success rates in the literature for ACL revision surgery are approximately 75%. Revision surgery is a procedure, in which the expected clinical outcome is inferior to that which can be expected from primary reconstruction. Patients have a 5.4% risk of undergoing a second revision after five years.
Failure of an ACL reconstruction is often hard to describe. Patient dissatisfaction following primary ACL reconstruction can be divided into 3 general categories:
failure is the most common cause for failed ACL surgery. The etiology of ACL graft failure is varied and often more than one cause exists. In general, the etiology of graft failure can be dividing into 3 categories:
Early failures (< 3 months) are usually related to loss of fixation and infection. Mid‐term failures (3 – 12 months) are often due to errors in surgical technique, aggressive physical therapy and unrecognized loss of secondary restraints. Late failures (> 12 months) are usually related to trauma.
A detailed history, including a patient’s age, activity level prior to the index procedure, inciting trauma, operative technique, and postoperative course, is needed to effectively treat recurrent instability. It is essential to identify whether the patient is primarily experiencing symptoms of stiffness, pain, or true instability, as well as which activities cause these symptoms. It is also important to gain an understanding of a patient’s postoperative therapy program and course of progression, including any traumatic incidents.
A thorough physical examination is needed to identify objective findings to explain the patient’s symptomatology and treatment course.
A neurovascular exam can be helpful in identifying a vascular injury, indicating possible initial knee dislocation.
Prior skin incisions should be assessed for healing and positioning.
The Range Of Motion (ROM) should be documented, as should hamstrings and quadriceps strength. These values should be compared to the contralateral extremity.
Anterior and posterior drawer tests are helpful in evaluating the competency of the ACL and PCL. Lachman’s testing has been noted to be a very sensitive test for ACL deficiency. Varus and valgus stress testing at 30 degrees of flexion is used to evaluate the competency of collateral ligaments and opening with these stresses applied in full extension, usually suggests injury to collateral ligaments as well as other structures, such as the cruciate ligaments or joint capsule. The presence of a pivot shift is a highly sensitive test for detecting ACL deficiency. However, its utility is limited by the patient’s ability to relax and is often most useful when the patient is anesthetized.
Assessment of tibial external rotation (dial test) can be used to detect PCL or posterolateral corner (PLC) injuries. In addition to these ligamentous examination maneuvers, a thorough meniscal and cartilage examination should be performed including, McMurray’s test and evaluation of joint line tenderness.
Plain radiographs of the knees, including weight-bearing anteroposterior and lateral views, allow for assessment of:
45º posteroanterior flexion weight-bearing radiographs provide a view of the femoral condylar notch and are also sensitive for joint space narrowing. A common cause of graft failure related to surgical technique is anterior placement of the femoral tunnel, and this is often detected on lateral radiograph. An anteriorly placed femoral tunnel can lead to tightening of the grafts in knee flexion, resulting in irreversible graft stretching or loss of knee flexion. Full-length alignment films are critical in patients with varus deformity or chronic posterolateral rotatory instability.
CT scan is considered for a more extensive evaluation of bone loss and more precise evaluation of tunnel morphology. MRI is also useful to further characterize tunnel size, as well as a thorough evaluation of ligamentous structures and concomitant intra-articular pathology. Specifically, the extensor mechanism, PLC structures, MCL, and PCL should be identified. Loose bodies, meniscal injury, cartilage injuries, and osteochondral injuries are also assessed. The utility of MRI images can be impaired in patients with retained metallic implants, which can create significant imaging artifacts.
The first step in pre-operative planning is to choose a graft for the reconstruction. This is similar to graft selection in a primary ACL; however the coexisting pathology and previous procedures must be taken into account. The ideal graft is one that retains strength at least equivalent to that of the normal ACL, allows for secure fixation, has minimal morbidity, and allows for postoperative rehabilitation. The options for available grafts can be broken down into two general categories, autograft and allograft.
The surgical techniques for a revision ACL are both varied and based on the etiology of failure.
The first subset is the failed ACL with non-anatomic tunnels secondary to technical error. It is estimated that this is the etiology of failure in 70-80% of failed ACL reconstructions. Misplacement of the initial tunnels can lead to graft impingement, ligamentous laxity, improper tensioning, and eventual graft failure. In these cases, pre-operative planning is essential. Complete radiographs should be ordered. A CT scan or MRI allows further evaluation of tunnel position, tissue integrity, and any concomitant knee pathology that may need to be addressed at the time of revision.
After complete evaluation, the surgeon must determine the next course of action. If there has been significant expansion of the existing tunnels, a two-stage procedure with bone grafting of the tunnels can be utilized. This two-stage bone grafting technique is also useful in the setting of anticipated convergence between the old and new tunnels. If previous tunnels are clear of the anticipated new path, the surgery can proceed in one step without bone grafting. The other issue that the surgeon faces is the hardware that was used to fix the original graft. If this hardware will be in the way, then it must be removed intraoperatively.
The basic technique for a two-stage bone grafting procedure involves clearing and identifying the ACL footprints and previous hardware on both tibia and femur, removing hardware as necessary, and bone grafting the previous tunnels using either allograft or autograft harvested from the iliac crest (stage 1). The patient is then given 4-6 months to allow incorporation of the bone graft. After this time the second stage can be completed in the same fashion as a primary ACL reconstruction.
Currently, goals of rehabilitation following revision ACL reconstruction are similar to primary surgery but at a slower pace and more individualized. A return to preinjury level of function may be unrealistic though. Rehabilitation following primary ACL surgery emphasizes immediate postoperative weight bearing and ROM exercises, obtaining full passive knee extension, restoration of neuromuscular control, and utilizing perturbation exercises with the goal of improving overall outcome.
Postoperative rehabilitation for patients following revision ACL should be individualized and take into account a multitude of factors. Factors to consider revolve primarily around surgical techniques and graft selection, physical performance factors, occupational demands, patient characteristics and goals/expectations. The presence of concomitant procedures in revision ACL is another key component that will impact postoperative rehabilitation. Reports say that less than 10% of patients undergoing revision ACL surgery have normal meniscal or articular cartilage at the time of surgery. Therefore, reconstruction of secondary stabilizers and articular cartilage serve as the most common factors necessitating individualization and modifications beyond a standard primary ACL reconstruction.