Classification of Anterior Cruciate Ligament Failures

There are a multitude of contributing factors to the rupture of an ACL graft. However, a general rule of thumb is that if the failure occurs in the first 6 months, it is most likely a result of a technical error, although failure of graft incorporation (especially with allografts), excessive rehabilitation, and premature return to full activities can also play a role. If the failure occurs after 1 year postoperatively, it is most likely a result of a traumatic event.

The most common cause of failure in primary ACL reconstruction is technical error in tunnel placement, typically involving vertical placement of the femoral tunnel (Fig. 76-1). Historically, concern for ACL-roof impingement in extension led some surgeons to place their tibial tunnels too posteriorly. If the femoral tunnel is then drilled transtibially through the posterior tibial tunnel, a subsequent high (anteromedial [AM]) graft position will result from the orientation of the drill guide. The ACL graft is then malpositioned between a posterior tibial tunnel and a high or vertical femoral position. It should also be noted that even with an independent femoral tunnel in an “anatomic” position on the femoral wall, a posterior tibial tunnel will create a vertical graft in the sagittal plane and may not adequately address rotational stability.

This mismatched graft position may diminish impingement and improve anteroposterior (AP) stability; however, it fails to restore normal rotational stability of the knee. Abnormal biomechanics are observed, and patients may report subjective instability even though they have a normal Lachman test result and minimal KT1000 side-to-side difference.5,21 Their rotational instability, however, manifests with a positive pivot glide or 1+ pivot shift even though the Lachman and anterior drawer test results may remain normal. It is important to keep in mind that range of motion may provide important clues regarding the presence of notch impingement and, most important, accurate tunnel placement.² Regardless, to restore more normal knee kinematics, patients may require a revision ACL reconstruction.

History

Patients who experience recurrent instability may benefit from a revision reconstruction to stabilize the knee and restore function. Preoperative data collection and planning are important to ensure success of the reconstruction. If available, previous operative notes, arthroscopic images, and imaging are reviewed to determine previous surgical tunnels, graft location, meniscal status, and cartilage defects. In the setting of a previous significant meniscectomy, staged or concomitant meniscal transplantation may be required.

Physical Examination

A thorough physical examination is performed to assess knee stability not only anteriorly but also posteriorly, medially, and laterally. It is critical to exclude a subtle posterolateral or posteromedial laxity that may be contributing to graft attenuation. All test results should be compared with those of the opposite knee. The affected knee’s range of motion should be recorded, with particular attention to subtle knee flexion contractures. Patellofemoral crepitation and mobility should be assessed. If it is available, a KT1000 measurement should be performed on both knees to provide objective anterior-posterior translation parameters.

Imaging

If no previous radiographs are available, we recommend obtaining at least four views to determine tunnel orientation and to help decide whether hardware will need to be removed during revision surgery (AP in extension, posteroanterior [PA] Rosenberg, lateral, and skyline). The radiographs will also help assess the slope of the tibial plateau because this can contribute to a failure mechanism. Magnetic resonance imaging can help evaluate concomitant pathologic changes, such as meniscal tears and posterior cruciate ligament (PCL) or posterolateral corner injuries. If there is any suggestion of tunnel widening on conventional radiographs, we routinely obtain a computed tomographic scan to better delineate tunnel expansion.

Graft Choice

Several graft options are available for revision ACL reconstruction. Autografts include hamstring tendon, quadriceps tendon, and patellar tendon from the ipsilateral or contralateral knee. Allograft options include Achilles, patellar, hamstring, quadriceps, and tibialis anterior tendons. Our preference is to use allograft tissue if a patellar tendon autograft has been harvested previously. Although some surgeons prefer the use of a contralateral patellar tendon graft, we have noted that most patients do not want to have their “normal” knee surgically violated. Although biomechanical characteristics of quadrupled hamstring grafts are more than adequate for revision reconstruction, secure fixation in the expanded tunnels can be difficult, especially when soft tissue grafts had been used primarily. Patellar tendon allograft provides bone for supplemental grafting, and extra-large bone blocks can be customized to provide improved tunnel fill for primary interference fixation. In our institution we have historically used nonirradiated patellar tendon allograft for revision procedures, with excellent results.³

Indications and Contraindications

Revision ACL reconstruction is indicated after a failed primary reconstruction, defined as a symptomatic, unstable knee that interferes with the activity level desired by the individual patient. Contraindications include significant medical comorbidities and current or recent infection. Uncorrected malalignment, decreased range of motion, and degenerative changes are relative contraindications that can frequently be addressed in staged or concomitant procedures.

Furthermore, a staged procedure should be considered in the following circumstances:

Anesthesia and Positioning

Most patients undergo general anesthesia. A femoral nerve block can be useful in controlling postoperative pain, although we rarely use nerve blocks or regional anesthesia. Patients are positioned supine on the operating room table. The foot of the bed is flexed; a tourniquet is applied to the operative thigh, which is then secured in a leg holder. The contralateral leg rests in a gynecologic leg holder with both the hip and the knee flexed no more than approximately 60 degrees to prevent traction on the femoral or peroneal nerves. To prevent lumbar spine extension and traction on the femoral nerve, we reflex the operating bed slightly and place it in Trendelenburg position. It is important to be able to flex the operative knee to approximately 110 degrees of flexion to allow proper placement of the femoral tunnel and screw if a single-incision endoscopic technique is to be used.

Examination Under Anesthesia and Diagnostic Arthroscopy

A thorough examination under anesthesia is performed before the thigh is secured in the leg holder, to reassess ACL incompetency as well as to rule out any other injuries to the PCL, medial collateral ligament, and posterolateral corner complex. Diagnostic arthroscopy is performed to evaluate all potential concomitant pathology. All necessary repairs or debridement are performed before the ACL revision. One should be particularly attentive of partial-thickness meniscal tears, which appear more commonly on the undersurface medially and on the superior surface laterally. Any arthritic changes or articular surface wear should be well documented.

Specific Steps

Box 76-1 outlines the specific steps of this procedure.

3 Removal of Old Hardware

It is critical to consider whether former hardware will require removal or whether it may be bypassed at revision surgery. Various interference screws are commercially available with differing morphologic appearances radiographically. Most can be removed with a standard 3.5-mm screwdriver, but every effort should be made to determine the specific brand of the screw to prepare necessary specialized equipment. This is the first decision point; if previous tunnels are nonanatomic and nonoverlapping, the hardware can generally be left in place (Figs. 76-2 and 76-3). If the tunnels will overlap, the hardware may require initial removal for the new tunnel to be made, but it may have to be subsequently reinserted to provide construct fixation stability. In our experience, bioabsorbable screws are generally not resorbed at the time of revision surgery and frequently fracture on attempted removal secondary to softening. The surgeon may therefore have to ream through these screws to properly position the new tunnel.

Figure 76-2 Graft 1 represents a nonanatomic tunnel with a revision procedure completed without removal of any old hardware.

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