Isolated Single-Bundle Reconstruction

Introduction

Restoration of the native anatomy and performing individualized anterior cruciate ligament (ACL) surgery are critical to a successful outcome after ACL reconstruction. The surgeon needs to consider multiple anatomic factors, such as size and shape of the tibial and femoral insertion sites, notch characteristics, and the rupture pattern of the ligament. The ultimate goal is to restore the patient’s native anatomy to that prior to injury. In 10-40% of cases of ACL injuries, an isolated single-bundle tear of either the anteromedial (AM) or posterolateral bundle (PL) is present. As each bundle has its own unique biomechanical properties, reconstructing both bundles when only one is torn would not optimize the patient’s native knee kinematics. Depending on the degree of injury involvement of the remaining bundle, an isolated augmentation of the injured bundle may be considered. This chapter outlines techniques for isolated AM- or PL-bundle augmentation surgery for two scenarios: (1) traumatic single-bundle injury and (2) patholaxity after prior ACL reconstruction in the setting of a healed, well-placed ACL graft. The reader is referred to other chapters within this book for a more detailed description of the ACL anatomy and double-bundle reconstruction technique.

Background

Anatomic studies demonstrate that the AM bundle becomes tight in knee flexion while the PL bundle becomes tight with knee extension. Under a combined rotatory load of 10-Nm valgus and 5-Nm internal tibial torque, the in situ force of the PL bundle is higher at 15 degrees of flexion and lower at 30 degrees of flexion. The in situ force in the AM bundle is similar at 15 degrees and 30 degrees of knee flexion. These biomechanical properties correlate with varying contributions to knee stability depending on the degree of knee flexion. Furthermore, the likelihood of single-bundle ACL ruptures also varies depending on the position of the knee at time of injury.

Despite some early healing after injury, the majority of patients never return to their preinjury level of activity or sport. More than 30% of patients have fair or poor results at final follow-up. Seventy-two percent of partial ACL tears have activity-related symptoms at early follow-up. Noyes et al. followed 32 patients with partial ACL tears and found that 12 went on to complete rupture. Given these disappointing results, augmentation surgery may offer a more definitive solution.

History

The patient history from a partial disruption of the ACL or from a patient who continues to have laxity despite prior reconstruction can be vague. In some instances of partial ACL disruption, a traumatic event may occur, however, in many cases, patients may report a minor event in which the knee may have felt as though it “shifted” or “rolled.” Patients may even return to play the same day or within a week of the initial injury. In rare cases, there may be a minor complaint of pain with certain activity, with no specific injury reported. Conversely, within the setting of prior ACL reconstruction, patients are usually able to describe their symptoms more concretely. The patient may state that the knee continues to feel unstable or has no strength. Oftentimes, coaches or the training staff may note the patient lacks the confidence in his or her knee due to subtle differences from the noninjured leg. Determining the exact degree of morbidity from these symptoms can be challenging but is very important in deciding whether surgical intervention is necessary.