Posterior Cruciate Ligament

Introduction

The posterior cruciate ligament (PCL) is the largest and strongest ligament in the knee, with a unique innate healing capacity. Therefore, as opposed to other ligaments such as the anterior cruciate ligament (ACL), injuries to the PCL less commonly require surgical intervention. Nevertheless, when PCL tears are suspected, a conscientious clinical approach must be taken to not only diagnose these injuries, but to accurately discriminate between those that can be managed conservatively versus those that require surgery. The foundations of the diagnosis begin with a history and physical examination and are augmented by increasingly specific imaging techniques including stress radiography and magnetic resonance imaging (MRI). Once diagnosed, PCL tears are categorised into those amenable to nonoperative management and those requiring reconstruction. Evidence has demonstrated that grade I and II injuries can be successfully treated with dynamic PCL bracing, whereas acute grade III PCL injuries and combined ligament injuries are optimally addressed with double bundle PCL reconstruction (DB-PCLR) to restore native biomechanics of the knee. The goal of this chapter is to provide detailed descriptions of the surgically relevant anatomy; the biomechanical properties of the PCL and its bundles; the diagnostic approach, including physical examination and imaging; the operative and nonoperative options with corresponding indications; and the updated literature on clinical outcomes after PCL injuries.

Demographic Characteristics

Injuries to the PCL can occur both in isolation or in the context of multiligament and meniscal injuries. Isolated injuries are usually the result of forced posterior translation of the tibia that can occur with the knee flexed, such as in the classic dashboard injury pattern, or with forced hyperextension of the knee. ^, Epidemiological data have reported the incidence of isolated injuries to be approximately 2 in 100,000 annually, with more tears occurring in men than women in the general population. Among all knee ligament injuries, PCL injuries are relatively uncommon. Data published from the Danish Knee Ligament Reconstruction registry reported that of 23,253 knee ligament reconstructions from 2005 to 2015, only 581 were registered as PCL reconstructions. It must be acknowledged that this does not account for PCL injuries managed nonoperatively; nonetheless, the relative rarity of isolated PCL injuries makes the natural history and epidemiology difficult to study. Furthermore, isolated injuries may in fact comprise a minority of all PCL injuries, with reported rates of multiligament PCL injuries approaching 60% or higher. These injury mechanisms often include additional rotational or varus/valgus stress resulting in multiligament and concurrent meniscal injuries. ^,

Whether in the context of isolated injury or multidirectional instability, PCL deficiency contributes to altered kinematics and increased contact pressures, specifically in the medial compartment and patellofemoral joint. In the long term, patients with isolated PCL tears have a significantly increased risk (hazard ratio (HR) 6.2) of symptomatic arthritis and the subsequent need for total knee arthroplasty (HR 3.2). This is corroborated by others who have reported on arthroscopic evaluation of chronic PCL-deficient knees (≥5 years from index injury) documenting frequencies of degenerative cartilage lesions of 77.8% and 46.7% for the medial femoral condyle and patella, respectively. Incompetence of the PCL also increases risk to posterolateral knee structures, placing them at risk of subsequent injury. Because of these long-term consequences, it is imperative that these injuries are accurately diagnosed and adequately treated in a timely manner.

Anatomy

The PCL originates from the lateral aspect of the medial femoral condyle, along the medial roof and wall of the notch. It courses posteriorly and laterally to its attachment nestled between the posterior aspects of the medial and lateral tibial plateaus. The surgically relevant anatomy of the PCL is fundamentally centred on a discussion of the two-bundle structure and the detailed qualitative and quantitative descriptions of the femoral and tibial attachments. The two distinct bundles of the PCL are the anterolateral bundle (ALB) and posteromedial bundle (PMB), named for the relationship of their attachment sites to one another. The two bundles serve distinct and codominant functions as a consequence of these attachment sites, which have been described in exquisite detail in relationship to reproducibly identifiable bony landmarks and neighbouring attachments.

In regards to the femoral origin of the PCL, several bony landmarks have been identified to describe the location of the footprints, including the trochlear point, medial arch point, medial intercondylar ridge and posterior point ( Figs 7.1 and 7.2 ). ^, These landmarks have been described in great detail both graphically and descriptively to facilitate the accurate and reproducible identification of the PCL bundle footprints during reconstruction. The trochlear point references the point of intersection of the distalmost aspect of the trochlear cartilage, the medial arch articular cartilage along the lateral wall of the medial condyle and the medial aspect of the apex notch. Moving medially down the intercondylar notch, the medial arch point represents the transition from the notch roof to the wall. Continuing to follow the arch of articular cartilage distally down the notch and then posteriorly along the lateral aspect of the medial condyle, the next point encountered is the posterior point, which has been aptly defined as the most posterior point of the articular cartilage margin.

Using these landmarks, the femoral attachments of the ALB and PMB have been quantitatively defined. The centre of the femoral attachment of the ALB is 7.4 mm from the trochlear point, 11.0 mm from the medial arch point and 7.9 mm from the distal margin of the femoral articular cartilage. The PMB centre is located 12.1 mm from the ALB centre, bordered by the medial intercondylar ridge, which runs directly in the anteroposterior direction, passing through the posterior point ( Fig. 7.3 ).

The tibial attachment in the PCL facet has been similarly defined using reproducible bony and soft tissue landmarks. ^, Within the facet, the ALB bundle centre has been described in relation to the shiny white fibres of the medial meniscal posterior root, residing 6.1 mm from the point at which these fibres pass closest to the PCL tibial attachment ( Fig. 7.4 ). The fibres of the PMB can be qualitatively divided into thick and thin portions, the former of which has been deemed to be the anatomical centre because of its robust attachment and biomechanical importance. The centre of the thick portion of the PMB is located 8.9 mm from the centre of the ALB, 11.1 from the shiny white fibre point, 12.6 mm from the lateral articular margin and 3.1 mm from the medial groove. These footprint locations are subsequently used as the basis for anatomical PCL reconstruction.