Abstract
The posterior cruciate ligament (PCL) provides important contributions to the stability and normal biomechanical function of the knee. Injury to the PCL is relatively rare in isolation, but more commonly occurs in combination with injury to other ligamentous or meniscal structures. PCL insufficiency can be detected on physical examination using a number of different maneuvers, and additional diagnostic aids include stress radiography and MRI; ultrasonography is also an emerging tool to assist with the diagnosis of PCL injury. PCL sprains are graded according to the degree of laxity in the knee and the presence of concomitant injury to other structures. Nonoperative management is typically recommended for treatment of acute, isolated, low-grade PCL sprains and for chronic, asymptomatic PCL sprains. Surgery may be advocated for acute, high-grade PCL sprains, PCL sprains that are combined with other injuries, and for chronic PCL sprains associated with persistent symptomatic laxity or pain. Several different surgical techniques are currently used for PCL reconstruction, and it remains unclear if one method is superior to the others. Nonoperative and postoperative rehabilitation protocols vary, but general principles common to most programs include progressive weight bearing, progressive range of motion, and quadriceps strengthening. After PCL injury and recovery, an adverse long-term outcome that has been reported is the development of degenerative arthritis; it remains unclear if surgical reconstruction improves this outcome. Nonetheless, many patients report good subjective outcomes, and return to activities or sports is often possible for patients managed with surgery and for those managed conservatively.
Keywords
PCL injury, PCL sprain, PCL tear, Posterior cruciate ligament (PCL)
| Synonym | |
| |
| ICD-10 Codes | |
| M23.621 | Other spontaneous disruption of posterior cruciate ligament of right knee |
| M23.622 | Other spontaneous disruption of posterior cruciate ligament of left knee |
| M23.629 | Other spontaneous disruption of posterior cruciate ligament of unspecified knee |
| S83.521 | Sprain of posterior cruciate ligament of right knee |
| S83.522 | Sprain of posterior cruciate ligament of left knee |
| S83.529 | Sprain of posterior cruciate ligament of unspecified knee |
| Add seventh character to category S83 for episode of care (A—initial encounter, D—subsequent encounter, S—sequelae) | |
Definition
The posterior cruciate ligament (PCL) is an intra-articular but extrasynovial knee structure that arises from the posterior aspect of the tibial plateau (about 1 cm distal to the joint line), crosses (“cruciate”) behind the anterior cruciate ligament (ACL), and inserts into the lateral portion of the medial femoral condyle ( Fig. 76.1 ). Its overall tensile strength is the greatest of all the knee ligaments. It is innervated by branches of the tibial nerve and derives its vascular supply from the middle genicular artery.
The main function of the PCL is to resist posterior displacement of the tibia relative to the femur, but it also acts as a secondary restraint to external tibial rotation. Together with the ACL, the PCL contributes to the “screw-home” mechanism of the knee by which the tibia glides to its exact position at terminal knee extension.
Two bundles of collagen fibers comprise the PCL: the larger and stronger anterolateral bundle is tight in flexion, whereas the posteromedial bundle is tight in extension. These two bundles have traditionally been viewed as independently acting structures, with flexion dominated by the anterolateral bundle and extension dominated by the posteromedial bundle. However, recent evidence has emerged suggesting that their actions are more cooperative than previously thought. The average distance between the center of the femoral attachments of the anterolateral and posteromedial bundles is 12.1 ± 1.3 mm; this distance on the tibial side is 8.9 ± 1.2 mm.
Two separate ligaments, the anterior meniscofemoral ligament (Humphrey) and the posterior meniscofemoral ligament (Wrisberg), form a Y-shaped sling around the PCL ; these ligaments are hypothesized to function as secondary restraints against posterior displacement of the tibia, although both ligaments may not be present in all knees.
PCL injuries are reported as occurring in a range of 1% to 44% of acute knee injuries. PCL tears (sprains) are graded according to the degree of laxity in the knee and the presence or absence of concomitant injury to other knee structures; Table 76.1 presents the general classification of PCL injuries according to grade. Isolated injury to the PCL (grades I to III) is relatively rare, as most PCL sprains occur in combination with other knee injuries, including injury to the ACL, medial collateral ligament, and posterolateral corner. A recent population-based study done in Olmsted County, Minnesota found the annual incidence of isolated, complete PCL tears to be 2 per 100,000 individuals. In contrast to ACL injuries, both isolated and combined PCL injuries appear to have a higher incidence in males.
| Grade | Definition | Laxity (mm) |
|---|---|---|
| I | PCL partially torn | <5 |
| II | PCL partially torn | 5–9 |
| III | PCL completely torn | >10 |
| IVa | PCL and LCL, posterolateral injury | >12 |
| IVb | PCL and MCL, posteromedial injury | >12 |
| IVc | PCL and ACL injury | >15 |
In general, PCL tears occur when the tibia is displaced posteriorly in a flexed knee. Common mechanisms of PCL injury include motor vehicle accident (dashboard injury) and falling on a flexed knee with the foot in plantar flexion. The PCL may also rupture from hyperextension or forced hyperflexion. If rotational forces are also present at the time of injury, combined injury to other knee structures, particularly the posterolateral corner, must also be considered.
Definition
The posterior cruciate ligament (PCL) is an intra-articular but extrasynovial knee structure that arises from the posterior aspect of the tibial plateau (about 1 cm distal to the joint line), crosses (“cruciate”) behind the anterior cruciate ligament (ACL), and inserts into the lateral portion of the medial femoral condyle ( Fig. 76.1 ). Its overall tensile strength is the greatest of all the knee ligaments. It is innervated by branches of the tibial nerve and derives its vascular supply from the middle genicular artery.
The main function of the PCL is to resist posterior displacement of the tibia relative to the femur, but it also acts as a secondary restraint to external tibial rotation. Together with the ACL, the PCL contributes to the “screw-home” mechanism of the knee by which the tibia glides to its exact position at terminal knee extension.
Two bundles of collagen fibers comprise the PCL: the larger and stronger anterolateral bundle is tight in flexion, whereas the posteromedial bundle is tight in extension. These two bundles have traditionally been viewed as independently acting structures, with flexion dominated by the anterolateral bundle and extension dominated by the posteromedial bundle. However, recent evidence has emerged suggesting that their actions are more cooperative than previously thought. The average distance between the center of the femoral attachments of the anterolateral and posteromedial bundles is 12.1 ± 1.3 mm; this distance on the tibial side is 8.9 ± 1.2 mm.
Two separate ligaments, the anterior meniscofemoral ligament (Humphrey) and the posterior meniscofemoral ligament (Wrisberg), form a Y-shaped sling around the PCL ; these ligaments are hypothesized to function as secondary restraints against posterior displacement of the tibia, although both ligaments may not be present in all knees.
PCL injuries are reported as occurring in a range of 1% to 44% of acute knee injuries. PCL tears (sprains) are graded according to the degree of laxity in the knee and the presence or absence of concomitant injury to other knee structures; Table 76.1 presents the general classification of PCL injuries according to grade. Isolated injury to the PCL (grades I to III) is relatively rare, as most PCL sprains occur in combination with other knee injuries, including injury to the ACL, medial collateral ligament, and posterolateral corner. A recent population-based study done in Olmsted County, Minnesota found the annual incidence of isolated, complete PCL tears to be 2 per 100,000 individuals. In contrast to ACL injuries, both isolated and combined PCL injuries appear to have a higher incidence in males.
| Grade | Definition | Laxity (mm) |
|---|---|---|
| I | PCL partially torn | <5 |
| II | PCL partially torn | 5–9 |
| III | PCL completely torn | >10 |
| IVa | PCL and LCL, posterolateral injury | >12 |
| IVb | PCL and MCL, posteromedial injury | >12 |
| IVc | PCL and ACL injury | >15 |
In general, PCL tears occur when the tibia is displaced posteriorly in a flexed knee. Common mechanisms of PCL injury include motor vehicle accident (dashboard injury) and falling on a flexed knee with the foot in plantar flexion. The PCL may also rupture from hyperextension or forced hyperflexion. If rotational forces are also present at the time of injury, combined injury to other knee structures, particularly the posterolateral corner, must also be considered.
Symptoms
Patients may report a history that includes common mechanisms of injury as noted above, though in some cases the mechanism of injury may be unclear. In contrast to patients who have sustained ACL injuries, it is uncommon for patients who have sustained PCL injuries to report having heard or felt a pop or tear in knee. Patients with acute PCL injuries are more likely to present with pain or discomfort in the posterior knee and a sensation of knee instability. Knee stiffness and swelling may also be reported. In the subacute or chronic setting, patients may describe knee pain that is less distinct and may be anteriorly located; they may also report pain that is most prominent as they descend stairs or ramps and when decelerating.
Physical Examination
Due to the high incidence of combined PCL injuries as noted above, it is essential to perform a thorough and complete examination of the knee to assess for injury to other ligamentous or meniscal structures. This includes a careful neurovascular examination to rule out injury to the popliteal artery, tibial nerve, and peroneal nerve.
With an acute PCL injury, contusion of the anterior tibia or popliteal ecchymosis may be evident on exam; swelling and effusion are variable and could be absent altogether. Some muscle weakness may be detected due to pain or inactivity. Range of motion testing may reveal a 10 to 20 degree flexion deficit in comparison with the intact knee. Assessment of gait may reveal varus thrust, which would raise suspicion for concomitant posterolateral corner injury.
In evaluating the PCL itself, the goal is to identify posterior subluxation of the tibia, which occurs when PCL insufficiency is present. There are a variety of exam maneuvers that may be used to assess the integrity of the PCL; among these are the posterior drawer, posterior (reverse) Lachman, posterior sag, quadriceps active, reverse pivot shift, and dynamic posterior shift tests. Each of these tests is described briefly below, and Table 76.2 presents a comparison of sensitivities and specificities for each test.
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