CHAPTER 25 Double-Bundle Posterior Cruciate Ligament Reconstruction
Injuries to the posterior cruciate ligament (PCL), although infrequent, often present as complex problems that can result in severe disability because of the relationship between posterior instability and rotatory instability, combined with other ligamentous injury and cartilage degeneration. It is rare that PCL injuries occur in isolation; they frequently present in conjunction with anterior cruciate ligament (ACL) or posterolateral corner injuries.1 Both the rare isolated and concomitant PCL lesions are often misdiagnosed or overlooked altogether because PCL-specific symptoms can be difficult to distinguish or can be confounding when presenting with additional injuries.2
Joint function impairment in PCL-deficient knees correlates positively with chronicity.3–6 A PCL failure over time imposes additional medial compartment forces, resulting in increased pain and joint effusion. Functional limitations become increasingly frequent, especially with coexisting ligament injuries.7,8 Better understanding of PCL biomechanics has led to improvements in clinical evaluation and resulted in earlier recognition of PCL insufficiency. With earlier diagnoses and improvements in PCL reconstruction techniques, surgical indications for this type of injury have expanded markedly.9–13
Anatomic descriptions of the PCL vary by degree of detail. The ligament is commonly described as consisting of two fiber bundles, the anterolateral (AL) and posteromedial (PM), with each defined by their relative femorotibial insertion sites, respectively. The anterior section comprises the bulk of the fibers, with the cross-sectional mass almost four times larger than the posterior section. The AL bundle is taut in flexion and becomes lax when approaching extension, whereas the significantly smaller PM bundle is tight in extension (Figs. 25-1 and 25-2) and relaxes toward flexion.14
FIGURE 25-1 In this posterior image, the PCL is visualized and the PM bundle is seen crossing posteriorly to the AL bundle as it travels diagonally and superior from the tibial attachment on the posterior aspect of the femoral insertion with the knee in extension.
FIGURE 25-2 This lateral x-ray view of the previous image shows the relative position of the guide wires used to identify the positional anatomy in the photograph. In this knee angle, the PL bundle is almost vertical.
In close conjunction with the PCL, two meniscofemoral ligaments can be present in some knees. Although their presence can vary, their attachments are uniform. Both ligaments attach distally to the posteromedial aspect of the lateral meniscus. The anterior meniscofemoral ligament (ligament of Humphry) passes diagonally anterior to the PCL and inserts on the lateral aspect of the medial femoral condyle in the roof of the intercondylar notch. The posterior meniscofemoral ligament (ligament of Wrisberg) passes at almost the same angle posterior to the PCL to the femur, blending with the attachment of the posterior longitudinal group of PCL fibers. Literature reviews15–17 have shown that Humphry ligaments are present alone in 25% to 38%, Wrisberg ligaments present alone 39% to 50%, both present in 17% to 20%, and neither in 3% to 8% of knees. Both meniscofemoral ligaments have roles as secondary restraints to posterior tibial translation, which has been noted subsequent to complete transection of the PCL.18,19 With their cross-sectional area at about 10 mm2 and each ligament comprising an estimated 22% of the PCL cross section, the extent of any ligament function potential will vary by the comparative size of the PCL and the presence or absence of either meniscofemoral ligament.
When the knee is flexed and approaches 45 degrees, the AL bundle fibers tighten and are aligned to resist posterior tibial force. In contrast, the PM bundles exhibit reciprocal behavior, are tight in extension and, when the knee is flexed, begin to slacken. The angle of the PM bundle is not suitable to resist posterior tibial force while tight during knee extension and only provides secondary restraint to resist hyperextension. Once flexion meets or exceeds 120 degrees, the PM bundle femoral attachment moves anteriorly in relation to the tibia so that it is tight and aligned to resist posterior tibial forces, which illustrates its function in deep knee flexion. As complete knee flexion is approached, the AL fibers wrap against the intercondylar notch roof, becoming almost vertical to the tibial plateau, and are thus poorly aligned to control posterior tibial translation. In the presence of collateral ligament and posterolateral corner pathology, PCL injuries have additional rotatory laxity, valgus instability, and posterior tibial translation.20,21
The posterior drawer test is a reliable clinical assessment tool and should be performed at both 30 and 90 degrees for PCL assessment. Begin by defining the distance (usually 1 cm) of the medial tibial plateau from the medial femoral condyle at 90 degrees of flexion. Grade I injuries are not associated with significantly abnormal joint motion and have a palpable but diminished step-off (0 to 5 mm). Grade II injuries are indicated with slight to moderate joint motion and have lost their step-off, but the medial tibial plateau cannot be pushed beyond the medial femoral condyle (5 to 10 mm). Grade III injuries are usually associated with markedly abnormal joint motion and an absent medial step-off, and the tibia can be moved posterior to the medial femoral condyle (>10 mm). Obvious positive posterior sag is present in these cases. To perform the posterior sag test, the hip and knee are flexed to 90 degrees; with complete tears, the tibia sags and becomes obviously posteriorly subluxed relative to the femur and by comparison to the other knee.
Note that some normal laxity is seen in patients with physiologic genu recurvatum. If posterior translation is normal at 90 degrees but slightly increased at 30 degrees, a PLC injury is likely. Not all patients with PCL tears have a positive posterior drawer test on physical examination.22 Although the PCL is commonly evaluated by performing the posterior drawer test at 90 degrees,23–26 it can also be assessed by other methods, including the dynamic posterior shift test,27 the quadriceps active test, the posterior sag sign, the prone posterior drawer test, and the reverse pivot-shift test.28 Using the quadriceps active test in the presence of a PCL tear, the active contraction of the quadriceps muscle with the knee from 60 to 90 degrees of flexion produces anterior tibial movement and a posterior tibial sag is eliminated.
Plain radiography with five views—anteroposterior (AP), lateral, sunrise notch, weighted AP, and Merchant views—is preferred for knee assessments. The identification of any insertion site avulsion fractures, fragments, or small tibial plateau fractures are additional signs of combined ligament injuries. A lateral view may demonstrate posterior subluxation of the tibia and, when obvious, is pathognomonic for a PCL lesion.
To characterize PCL injury by magnetic resonance imaging (MRI), three planes should be used—axial, coronal, and sagittal. The use of a dedicated knee coil improves signal-to-noise ratio and a small field of view (10 to 14 cm) helps improve spatial resolution.29 The most sensitive views for evaluating the PCL are obtained with the sagittal oblique plane. With MRI, evaluations of PCL tears can be delineated into intrasubstance, partial, complete, or avulsion. Hemorrhage and edema are evident interstitially in intrasubstance tears. Partial tears are evident by interruption of a portion of one of the margins of the ligament and may present a circumferential ring of hemorrhage or edema (halo sign) around the margins. Complete tears have portions of the ligament that are completely absent and may include hemorrhage and edema blurring the margins or in focal areas in lieu of the ligament at tibial or femoral attachments. Avulsions are usually at the tibial insertion and the PCL will retract away with its bone fragment.
When precise physical examination is complicated by pain, MRI is helpful for diagnosing acute lesions and also contributes to the diagnosis of concomitant injuries. Diagnostic arthroscopy is usually not required to evaluate PCL tears with the advent of MRI, which has excellent specificity and sensitivity for soft tissue diagnoses. However, in some cases, the presence of metallic foreign bodies, intracranial surgical clips, pacemaker wires, patient size, or motion limitations may preclude the use of MRI.
In the past, it was assumed that patients with an isolated PCL rupture did well with nonoperative treatment.30,31 Shelbourne and colleagues32 have studied chronic PCL injury nonoperated patients; 170 patients were untreated for their grade II or lower acute isolated PCL injuries. They stated that “…their conditions didn’t deteriorate over time as a group.” However, 20% reported giving way with activities of daily living, 26% reported giving way with strenuous activity, and 54% reported that they did not experience any instability. It is important to note that isolated PCL grade II or lower injuries are atypical. Nonoperative management for isolated PCL injuries (rarely occurring) is not a standard that should be applied universally to multiple ligament injuries.
Most single-strand techniques attempt to reconstruct the larger anterolateral bundle.33,34 The posteromedial bundle, and the stability it provides in extension, is ignored. Double-bundle techniques have arisen in an attempt to address both the anterolateral and posteromedial bundles.35–37 In vitro research36,38 has suggested that these double-bundle reconstructions can eliminate joint laxity in flexion and extension.
A tibial tunnel drill guide used in the present technique for the PCL known as the Tundra system (Smith & Nephew Endoscopy; Andover, Mass) uses coring reamers (trephines) that are externally guided instead of using internal cannulation with a guide wire. A guide wire is not required for the placement of the tibial tunnel with this system. The point of contact on the guide arm by the trephine is a small plate (backsplash). In the lateral view, it looks like a triangular wedge. It is round, 11 mm in diameter; it prevents the trephine from passing beyond it and protects the posterior structures from injury. When used in conjunction with an Achilles graft in the present double-bundle technique, difficulty with graft passage around the “killer turn” is obviated.
This arthroscopic technique for double-bundle PCL reconstruction uses an Achilles tendon allograft. This graft source anatomically mimics the PCL insertion and, when prepared into two bundles, can be used to reconstruct the AL and PM ligament components of the PCL. This arthroscopic reconstruction is secured with anatomic fixation by three bioabsorbable interference screws using a single-incision, five-portal technique.