The PCL has been considered by some to be the strongest knee ligament (7). More recent studies indicate that the ACL and PCL are of approximately equal strength (8,9,10). The PCL is the primary restraint to posterior tibial translation at the knee, and plays an integral part in knee joint stability.

The PCL is named because of its posterior insertion on the tibia (11,12). PCL fibers are more vertically aligned than those of the oblique ACL fibers. The PCL originates on the posterior lateral aspect of the medial femoral condyle where its attachment is in the form of a segment of a circle. The tibial attachment of the PCL is situated in a depression between the two tibial plateaus. This attachment in the PCL fossa extends for a few millimeters below the tibial articular surface (13).

Synovial tissue reflected from the posterior capsule covers the ligament on its medial, lateral, and anterior surfaces. Distally, the posterior portion of the PCL blends with the posterior capsule and periosteum. Strictly anatomically speaking, the PCL is extra-articular while lying within its own synovial sheath (12).

Girgis et al. (13) found in cadaver and fresh knee dissections that the PCL averaged 38 mm in length and 13 mm in width, whereas the ACL averaged 38 mm in length and 11 mm in width.

The PCL has been shown to consist of two major inseparable bundles. The anterior bundle makes up the bulk of the ligament and is tight in flexion and lax in extension. The posterior bundle is much thinner, and these fibers are tight in extension and lax in flexion. In reality, there is a gradually changing pattern of fiber tension going from anterior to posterior as the knee is extended (11,12,13,14). Recent studies suggest that the PCL consists of four fiber regions: anterior, central, posterior longitudinal and posterior oblique. These fiber regions are based on fiber orientation and osseous attachment sites with the anterior and central groups comprising approximately 85% of the PCL bulk (15).

The fiber regions should not be confused with the meniscofemoral ligaments, which are distinct and separate structures. In approximately 70% of knees, an accessory meniscofemoral ligament is present (13,16). The anterior meniscofemoral ligament of Humphry lies anterior to the PCL, arising from the posterior horn of the lateral meniscus and inserting on the femur with the PCL. It is approximately one third the diameter of the PCL. The posterior meniscofemoral ligament of Wrisberg arises as a continuation of the posterior horn of the lateral meniscus and is closely associated with the PCL. It has been measured to be up to one half the diameter of the PCL (16). There are no attachments between the PCL and the medial meniscus.

The majority of the blood supply to the PCL stems from the middle genicular artery, a branch of the popliteal artery (17). The middle genicular artery also supplies the synovial sheath which itself is a major contributor of nourishment to the PCL (18,19). Capsular vessels also supply the base of the PCL via branches from the popliteal and inferior genicular arteries (19). Katonis et al. (20) observed three types of nerve endings in the PCL in a histologic study (20). They observed Ruffini corpuscles (Type I, pressure receptors), Vater-Pacini corpuscles (Type II, velocity receptors), and free nerve endings (Type IV, pain receptors). They further postulated that damage to the PCL not only creates a mechanical disturbance, but a central neurologic one as well. This is most likely secondary to lack of feedback mechanisms.

The PCL is the primary restraint to posterior tibial translation at all flexion angles >30 degrees (21,22). It provides 95% of the total restraining force for the straight posterior drawer (21). Gollehon et al. (22) found in a biomechanical study of cadaveric knees that isolated sectioning of the PCL did not affect varus or external rotation of the tibia at any position of knee flexion. As expected, isolated sectioning of the PCL increased posterior tibial translation with a posteriorly directed force at all angles of flexion (maximum at 90 degrees). Sectioning of the lateral collateral ligament and the posterolateral complex, leaving the PCL intact, resulted in small but significant increases in posterior translation at all angles of flexion (maximal at 30 degrees).

As the knee progresses from flexion to extension, the tibia externally rotates relative to the femur. This has been
traditionally called the “screw home” mechanism of the knee. Possible hypotheses of this mechanism include bony anatomy and relative lengths of the cruciates (23). Van Dommelen and Fowler (12) suggested that the PCL plays an important role in the screw home mechanism because of variable region tautness at different flexion angles.

Covey and Sapega (24) have conducted a biomechanical study of cadavers to determine the effects of normal knee joint motion and loading on end to end fiber length behavior of the four fiber regions. They found obvious differences in tautness of the region when comparing passive joint motion with simulated quadriceps force. This data may help in determining optimum graft placement and post PCL reconstruction rehabilitation programs.

The posterior lateral corner consists of the lateral collateral ligament, the acucuate ligament, the popliteus tendon, the popliteofibular ligament, the short lateral ligament, the fabellofibular ligament, and the posterior lateral capsule. The fibular attachment of the popliteus tendon, the popliteofibular ligament, is a common supporting structure of the posterolateral corner of the knee. This structure reinforces the posterolateral capsule. Its oblique anatomical orientation indicates that it may act as a static restraint to varus and external rotation movements (25).

The posterolateral corner structures serve to resist varus stress, posterior tibial translation near full extension, and external rotation of the tibia relative to the femur. Sectioning of the posterolateral corner structures results in small increases in posterior tibial translation, but major increases in varus rotation and external tibial rotation (25).

The incidence of PCL injuries has been reported to be in the range of 1% to 40% of acute knee injuries (2,26,27,28,29,30,31). This appears to be patient population dependent, and PCL injury occurs more frequently in trauma patients than athletic injury patients (28,29). We have reported the incidence of PCL injuries in acute knee injuries from our tertiary care regional trauma center (32). We have shown a 38% incidence of PCL tears in acute knee injuries from our center. The two most frequent combined PCL injuries were ACL/PCL (45.9%), and PCL/posterolateral corner injuries (41.2%). PCL/posterolateral corner injuries are the second most frequently encountered multiple ligament injuries of the knee involving the PCL (2,28,29,32).

PCL and posterolateral corner tears may result from a variety of injuries. Isolated PCL tears most likely result from a direct blow to the proximal tibia, causing a posteriorly directed force. This occurs with the so-called dashboard knee in motor vehicle accidents, or when the proximal tibia contacts an immovable object. A fall on a flexed knee with the foot in plantar flexion may also induce an isolated PCL tear (13). Forced flexion plus internal rotation has also been reported to cause isolated PCL tears (33). Hyperextension, forced varus, forced tibial external rotation have been associated with PCL/posterolateral corner injuries (28,29,32). The most frequent PCL/posterolateral corner injury mechanism seen in our clinic is a direct blow to the proximal medial tibia causing forced posterolateral tibial translation.