Anterior Cruciate Ligament Reconstruction of Partial Tears: Reconstructing One Bundle

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Chapter 60 Anterior Cruciate Ligament Reconstruction of Partial Tears

Reconstructing One Bundle

Fotios Paul Tjoumakaris, Anthony Buoncristiani, James S. Starman, Freddie H. Fu

Introduction

It has been estimated that approximately 60,000 to 75,000 anterior cruciate ligament (ACL) reconstructions are performed annually in the United States.¹ This number is likely higher, as larger segments of the population have become active and participate in year-round sporting activities within the past several years. Outcomes of ACL reconstructions have been exhaustively studied, with many reports demonstrating successful return to sport and returning stability to the previously injured knee, particularly when compared with conservative management.^2,³ Despite tremendous advances within the field of ACL reconstruction, success rates of primary reconstruction continue to hover between 70% to 95% within the best centers.⁴^–⁶ With the increasing numbers of ACL being performed come the requisite number of cases that fail due to any variety of mechanisms: arthrofibrosis, extensor mechanism failure, recurrent patholaxity, and traumatic arthrosis.⁷ Several studies have demonstrated inferior results of revision surgery when compared with primary reconstruction, with many of these studies citing recurrent laxity as the primary mechanism of failure.⁸^–¹²

The concept of recurrent laxity following a partial ACL injury or of a failed ACL reconstruction (with an intact, well-placed graft) can be treated within the same context. Both scenarios represent the same underlying anatomical defect: an isolated injury or absence of one of the bundles of the ACL that compromises the ability of the knee to achieve stability and normal kinematics. Most ACL injuries are currently treated with reconstruction of the anteromedial (AM) bundle of the ACL. Recurrent laxity within this situation can be classified as recurrent tear of the graft, continued instability despite graft incorporation and healing with proper graft placement, and improper placement of the graft leading to continued laxity. Recurrent laxity after isolated partial ACL tears can be from isolated injury to the posterolateral (PL) or AM bundles that results in the inability of the knee to resist either rotatory or translational forces.¹³ Our technique of isolated PL or AM augmentation surgery has evolved from this foundation of applying anatomical principles of the ACL with the anatomical injury or failure pattern. This chapter outlines our technique for isolated PL bundle augmentation surgery within the setting of recurrent patholaxity after prior ACL reconstruction (and a healed, well-placed ACL graft) as well as after partial ACL disruption (isolated PL bundle injury). Please see Chapter 25 for a more detailed description of the ACL anatomy and double-bundle reconstruction technique.

Preoperative Considerations

History

ACL injuries typically occur in patients who participate in activities that require running, jumping, or cutting. The classic scenario is often a young female athlete who sustains an injury while her foot is planted and slightly flexed, with a pivot moment applied to the knee. The ensuing injury is often characterized as a “pop” or other traumatic event, and swelling from a hemarthrosis is often present within minutes to hours after this insult. The patient history from a partial disruption of the ACL or from a patient who continues to have laxity despite having undergone prior reconstruction can be more vague. In some instances of partial ACL disruption, a traumatic event may occur, as is the case with a complete tear; 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 have even gone back to competitive play the same day or within a week of the initial injury. In rare cases, there may be the minor complaint of pain with certain activity, with no specific injury reported. Within the setting of prior ACL reconstruction, patients are usually good historians with regard to their symptoms due to their prior experience. The patient in this setting may state that the knee continues to feel unstable or has no strength, or the patient may be observed by coaches and the training staff to lack this confidence on the knee due to subtle differences from the noninjured leg. Determining the exact amount of morbidity from these symptoms can be challenging but is very important in deciding whether surgical intervention is warranted.

Physical Examination

The physical examination is very similar to that for most knee injuries. The knee is first inspected for any bruising or contusion that may indicate a more serious injury. The knee is checked for an effusion; if one is present and causing significant discomfort that impedes the physical examination, we will aspirate it from a superolateral portal. The range of motion is assessed; if limited, it may indicate concomitant meniscal pathology, although this is rarely seen with partial tears of the ACL. The knee is then examined for any tenderness along the joint line or joint line swelling, which also could represent the presence of meniscus pathology. The ligamentous evaluation is performed and compared with the contralateral extremity. The knee is checked first for valgus or varus instability at both 0 and 30 degrees. The Lachman and pivot-shift exams are then performed. The presence of a 2+ or 3+ Lachman with minimal shift may indicate involvement of the AM bundle with minimal involvement of the PL bundle. It is important to ascertain whether the patient is guarding or contracting the hamstrings, as these actions will impair the clinician’s ability to detect pathologic translations. The patient who has a large pivot shift with very minimal translation on the Lachman examination may have an isolated injury to the PL bundle. Rarely will patients have a positive anterior drawer sign, as the secondary stabilizers (medial meniscus/posteromedial corner) are usually preserved within this injury pattern. The exam concludes with determination of the KT-1000 and its comparison with the contralateral extremity. A normal KT does not preclude the presence of injury to a portion of the ACL and is no substitute for a good physical examination.

Imaging

We obtain plain radiographs in all patients to look for associated pathology. These radiographs include bilateral anteroposterior (AP) flexion weight-bearing views, a lateral view of the involved knee, and bilateral merchant or sunrise views. The radiographs are inspected for soft tissue swelling, an effusion, the presence of any fractures, physeal closure (for younger patients), and overall alignment. In patients who have undergone prior ACL reconstruction, the prior tunnel placement is evaluated as well as prior hardware placement and presence of tunnel expansion. Determination of joint space narrowing is paramount in determining prognosis, and any patient who demonstrates any evidence of arthrosis on the knee series is further evaluated with a long cassette to determine alignment. If significant side-to-side difference exists (greater than 3–5 degrees) on the alignment series, consideration is given to a realignment procedure to unload the affected compartment. We obtain a magnetic resonance imaging (MRI) scan in any patient suspected of having a partial ACL tear or continued laxity after prior single-bundle ACL reconstruction. The MRI is also useful to inspect for the presence of any meniscal or chondral pathology. Reviewing the MRI with an experienced radiologist is often necessary to accurately make the diagnosis and properly plan for surgical intervention. Studies have shown that MRI diagnosis of partial ACL tears can be challenging.^14,¹⁵ In one series, nine of nine complete tears were accurately diagnosed by MRI, whereas only 1 of 9 partial tears were correctly identified.¹⁴ Findings that were suggestive of partial ACL tears in this series were the presence of some intact fibers, thinning of the ligament, a mass posterolateral to the ACL, and a wavy or curved ligament. The MRI is inspected for the presence of a bone contusion, as this usually indicates a more severe injury. One study demonstrated that only 12% of patients with a partial tear of the ACL had a bone contusion in comparison to 72% with complete tears.¹⁶

Additional coronal imaging may help to better delineate injury to the PL bundle, whereas the sagittal images are usually sufficient to visualize the AM fibers.

Indications

The indications for PL bundle augmentation surgery are not solely based on the preoperative evaluation. A patient who has undergone a prior single-bundle reconstruction with adequate graft placement and incorporation but who continues to experience patholaxity is perhaps the optimal candidate for this procedure. Patients who have suspected partial tears of the ACL with a positive pivot-shift examination, minimal translation with the Lachman maneuver, and an MRI that confirms the presence of the AM bundle are also qualified candidates for this procedure; however, these patients should demonstrate that they have recurrent laxity after a rehabilitation program and functional bracing regimen. These parameters are further defined arthroscopically once the entire injury pattern to the ACL is delineated and the presence of an intact AM bundle and disrupted PL bundle is found at surgery. Contraindications to surgical intervention include a patient who is unwilling to cooperate with the rehabilitation program and a patient who lacks a full or near-full range of motion on physical examination. The presence of open physes is not an absolute contraindication to using this technique; however, we do advise that younger patients be braced until they have reached skeletal maturity.

Surgical Technique

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