Posterior cruciate ligament injuries: causes, symptoms, diagnosis, treatment

Damage to the posterior cruciate ligament (PCL) is one of the most serious injuries to the capsular ligament apparatus of the knee joint. They are much less common than ruptures of the anterior cruciate ligament (ACL), accounting for 3-20% of all knee joint injuries.

Ruptures of the posterior cruciate ligament can be isolated or combined with injuries to other ligaments and structures of the knee joint (e.g. menisci, anterior cruciate ligament, collateral ligaments, joint capsule, popliteal tendon, arcuate ligament). Isolated ruptures of the posterior cruciate ligament account for 40% of all posterior cruciate ligament injuries and 3.3-6.5% of all knee joint injuries.

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What causes a posterior cruciate ligament injury?

There are several mechanisms of injury to the posterior cruciate ligament described in the literature. The most common is the direct mechanism of injury - a blow to the anterior surface of the proximal third of the tibia bent at the knee joint. This mechanism is most often encountered in road traffic accidents (impact on the dashboard). Injuries to the posterior cruciate ligament have become increasingly common during sports, especially in such sports as football, rugby, hockey, alpine skiing, and wrestling. A rarer mechanism of injury to the posterior cruciate ligament is the indirect mechanism of injury - a fall on the knee joint and forced hyperextension of the tibia in the joint. This leads to a rupture of the posterior part of the joint capsule and the posterior cruciate ligament. Simultaneous injury to the posterior cruciate ligament and anterior cruciate ligament usually occurs when the force of the traumatic agent is applied in several planes. This is a rotational moment with a fixed foot with the simultaneous application of force from the outside inward and from front to back. An injury of this nature is possible with falls from a height and car accidents. Knowledge and understanding of the mechanisms of injury to the posterior cruciate ligament make it possible to promptly diagnose a rupture of the posterior cruciate ligament.

Symptoms of Posterior Cruciate Ligament Injury

Due to the difficulty of differentiating between anterior cruciate ligament and posterior cruciate ligament injuries, posterior cruciate ligament injuries are often missed when making a diagnosis, leading to the development of posterior instability and secondary changes in the knee joint. Without treatment, deforming arthrosis of the knee joint progresses in 8-36% of cases.

Ruptures of the posterior cruciate ligament may be combined with damage to the postero-medial and/or postero-lateral capsular-ligamentous structures of the knee joint, depending on the mechanism of injury.

There is considerable controversy in the literature regarding the treatment of posterior instability of the knee joint. Some authors try to reconstruct the posterior cruciate ligament at all costs. Others, given the technical difficulties associated with restoring the central axis, perform plastic surgery of the active and passive structures of the knee joint that provide a stable position during abduction or adduction, as well as controlled internal or external rotation of the tibia. Reconstruction methods include plastic surgery with local tissues, plastic surgery using synthetic tissues, single-channel and dual-channel methods, open and arthroscopic methods.

All existing methods and techniques of surgical treatment of injuries of the posterior cruciate ligament of the knee joint can be divided into intra-articular and extra-articular. Extra-articular operations are based on limiting the posterior subluxation of the tibia. The meaning of extra-articular stabilization is the location of tendon structures in front of the rotation center of the knee joint, which creates an obstacle to the posterior subluxation of the tibia during movements in the joint. Currently, extra-articular reconstructions, as an isolated method of stabilization, are rarely used; more often they become an addition to intra-articular stabilization. Extra-articular stabilization is more appropriate for significant degrees of deforming arthrosis of the knee joint.

Classical examination methods are used to assess the condition of the knee joint: anamnesis, identification of the mechanism of injury, examination, palpation, measurement of the circumference of the joint and periarticular segments of the lower limb to identify muscle hypotrophy, the amplitude of passive and active movements, special tests that identify damage to the meniscus, ligament structures, instability, etc. Special additional examination methods include ultrasound, MRI, plain radiography, functional radiographs with load.

Complaints

Patient complaints vary and do not always indicate posterior instability of the knee joint. Patients may complain of:

• discomfort in the knee joint when the limb is semi-bent, when going up and down stairs, and also when walking long distances;
• pain under the patella, caused by backward bending of the tibia;
• instability in the joint when walking on uneven terrain;
• pain in the inner part of the joint, which is associated with degenerative changes in the joint.

Inspection and physical examination

During the examination, attention is paid to the nature of the gait, the presence of lameness. For all types of instability of the knee joint, attention is paid to the axis of the lower limb (varus or valgus deviation, recurvation). The examination continues with the patient lying down for comparison with the healthy limb.

Chronic posterior instability is much easier to diagnose than acute rupture of the posterior cruciate ligament. The most common complaint of patients with acute injury is knee pain. Significant joint effusion is rarely observed, since blood from a rupture of the posterior capsule (the tightness of the joint is disrupted) can spread through the interfascial spaces of the leg. Most patients with ruptures of the posterior cruciate ligament do not report a click at the time of injury, which is often heard with ruptures of the anterior cruciate ligament. Pain and hematoma in the popliteal fossa should alert the clinician to a rupture of the posterior cruciate ligament. In this case, a detailed understanding of the mechanism of injury can help in establishing the correct diagnosis (for example, a direct blow to the anterior surface of the leg on the dashboard in car accidents is the most common mechanism of injury). Patients with a ruptured posterior cruciate ligament can move independently with full weight on the limb, but the shin is slightly bent at the knee joint, the victim avoids full extension of the shin and its external rotation. During examination, special attention should be paid to bruises and abrasions of the skin on the anterior surface of the knee joint due to a direct blow, the presence of a bruise in the popliteal fossa. It is important to remember that the absence of effusion in the joint does not exclude serious injury to the capsular-ligamentous structures of the knee joint.

If the posterior cruciate ligament injuries are combined with injuries to other ligaments of the knee joint, the effusion in the joint will be much greater. With multiple ligament ruptures, there is a risk of damage to neurovascular structures. This occurs especially often with dislocations of the lower leg in the knee joint. Approximately 50% of lower leg dislocations are spontaneously reduced during the injury, so they are not detected during a medical examination, which leads to incorrect diagnosis and inappropriate treatment. Therefore, in all cases, careful monitoring of the blood circulation and sensitivity of the lower limb is necessary. In doubtful cases, Doppler scanning of the vessels of the lower limb and EMG can be performed.

Tests Used to Diagnose Posterior Cruciate Ligament Injury

The first step in the clinical examination of a damaged knee joint is to differentiate between pathological anterior and posterior displacement of the tibia. Normally, at 90° of flexion, the tibial plateau protrudes anteriorly from the femoral condyles by approximately 10 mm. In posterior instability, the tibia is displaced posteriorly by gravity. The anterior drawer sign detected from this position will be false positive, which can lead to misinterpretation of the pathology and an incorrect diagnosis.

• The posterior drawer test with the knee flexed to 90° is the most accurate test for diagnosing a posterior cruciate ligament tear. The degree of displacement is determined by changing the distance between the anterior surface of the medial tibial plateau and the medial femoral condyle. Normally, the plateau is located 1 cm in front of the femoral condyles. The posterior drawer is classified as grade I (+) with 3-5 mm of tibial displacement, with the tibial plateau located in front of the femoral condyles; grade II (++) - with 6-10 mm, the tibial plateau is at the level of the femoral condyles, grade III (+++) - with 11 mm or more, the tibial plateau is behind the femoral condyles.

The degree of sagittal displacement is assessed with the knee flexed to 30°. A slight increase in displacement at 30° rather than 90° of flexion may indicate damage to the posterior non-lateral complex (PLC). The posterior drawer test is difficult to perform in the acute period due to swelling and limitation of knee flexion. In acute injuries, the posterior Lachman test can be used.

• Reverse Lachman test (posterior Lachman test). As in the normal Lachman test, the knee is held in the same manner at 30° flexion, and the tibia is displaced posteriorly. Posterior displacement of the tibia relative to the femur indicates a rupture of the posterior cruciate ligament.
• Trillat test - posterior displacement of the tibia when bending the knee joint to an angle of 20°.
• The posterior deflection test (sag, Godfrey test) is a decrease in the convexity of the tuberosity of the tibia compared to the healthy limb. To perform this test, the patient lies on his back with the knee and hip joints bent to an angle of 90°. The doctor holds the patient's foot by the toes. Under the action of gravity, the tibia shifts.
• Active test of the quadriceps femoris - when the knee joint is bent to an angle of 90° and the foot is fixed, during tension of the quadriceps femoris, the lower leg comes out of the position of posterior subluxation (reduction).
• Active elimination test of posterior subluxation. The limb being examined is bent at the knee joint to an angle of 15°, with active lifting of the limb by 2-3 cm from the surface, the elimination of posterior subluxation of the tibia in the knee joint occurs.
• Passive reduction test for posterior subluxation of the tibia. Similar to the previous test, with the only difference being that when the lower limb is lifted by the heel, the proximal part of the tibia is displaced forward.
• Dynamic test of posterior fulcrum shift. Hip flexion 30° with small knee flexion angles. At full extension, posterior subluxation of the tibia is eliminated with a click.
• The posterior "drawer" symptom is seen in the patient's prone position with 90° knee flexion. With passive posterior displacement of the tibia, its posterior subluxation occurs. The foot is displaced toward the associated injury.
• The external rotation test of the tibia is performed with the patient in the prone position at 30° and 90 ^° of knee flexion. Isolated damage to the posterolateral structures gives the maximum increase in external rotation at 30°, and combined damage to the posterior cruciate ligament and the lateral femur increases the degree of excessive external rotation at 90 ^° of flexion. The degree of rotation is measured by the angle formed by the medial border of the tibia and the axis of the femur. Comparison with the contralateral side is mandatory. A difference of more than 10 ^D is considered pathological.

Since posterior cruciate ligament injuries are rarely isolated, all patients require clinical examination of other ligaments of the knee joint. Abduction and adduction tests are used to detect insufficiency of the fibular and tibial collateral ligaments. The examination is performed in a position of full extension of the leg and at 30° of flexion in the knee joint. The degree of abduction of the leg in the sagittal plane can be used to judge the degree of damage to the capsular-ligamentous structures. An increase in varus deviation at 30° of flexion in the knee joint indicates damage to the fibular collateral ligament. An additional small increase in varus deviation at full extension is compatible with damage to both of these structures. If there is a large degree of varus deviation at full extension, then combined injuries to the PCL, PCL, and ACL are possible.

Diagnosis of posterior cruciate ligament injury

X-ray examination

Radiographic examination is the most reliable method of examining the knee joint. Evaluation of radiographic images is very important. Calcifications and osteophytes in the posterior intercondylar region not only indicate an old injury to the posterior cruciate ligament, but can also prevent surgical intervention. Degenerative changes are often present in the medial compartment and the femoro-patellar joint. Functional radiographs with a load are performed to determine the posterior displacement of the tibia relative to the femur. Various devices are used to displace the tibia. The lower limb is placed on a special support, with an angle of flexion in the knee joint of up to 90 °, the foot is fixed, the tibia is displaced backwards using special traction to the maximum position.

Magnetic resonance imaging

The most informative of the non-invasive instrumental research methods is magnetic resonance imaging (MRI), which allows visualization of both bone and soft tissue structures of the knee joint.

The diagnostic accuracy of MRI, according to various authors, is 78-82%. MRI reveals a rupture of the posterior cruciate ligament better than that of the anterior cruciate ligament. The anterior cruciate ligament is brighter than the posterior cruciate ligament. The fibers of the posterior cruciate ligament run parallel, while the fibers of the anterior cruciate ligament are twisted. The absence of continuity of the fibers or their chaotic orientation indicate a rupture of the ligament. The intact posterior cruciate ligament is defined posteriorly as a convex, homogeneous structure of low signal intensity. A rupture increases the signal intensity. Zones of bleeding and edema (in case of an acute rupture) appear as limited areas of increased signal intensity. MRI is 100% informative in case of complete ruptures of the posterior cruciate ligament. Partial ruptures and injuries along the ligament are more difficult to recognize. With leg extension, the posterior cruciate ligament has a slight posterior slope in the sagittal plane.

Often, next to the posterior cruciate ligament, a fibrous band can be seen connecting the posterior horn of the lateral meniscus to the femoral condyle. This is the anterior or posterior meniscofemoral ligament (Wrisberg or Hemphrey).

MRI can be used to evaluate the menisci, articular surfaces, and ligaments of the knee that are not visible on plain radiographs and cannot be seen on CT scans. However, standard MRI is generally not useful for evaluating the LCL.

Ultrasound examination

Ultrasound examination allows us to study the condition of the soft tissues of the knee joint, the surface of the bone and cartilage based on the echogenicity of the structure, and also to determine tissue edema, fluid accumulation in the joint cavity or periarticular formations based on a decrease in echogenicity.

The most accessible and convenient place to examine the cruciate ligaments is the popliteal fossa. This is the attachment site of the distal parts of the ligament. Both cruciate ligaments are visible on sonograms as hypoechoic bands in the sagittal section. The anterior cruciate ligament is best examined transversely in the popliteal fossa. A comparative study of the contralateral joint is mandatory.

A complete ligament injury appears as a hypo- or anechoic mass at the femoral or tibial attachment. A partial or complete ligament injury appears as a global thickening of the ligament.

Ultrasound diagnostics can be used to detect damage to the cruciate ligaments, menisci of the knee joint, collateral ligaments, soft tissue structures surrounding the knee joint.

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Treatment of posterior cruciate ligament injury

In the acute period of injury (up to 2 weeks), when the posterior cruciate ligament is torn from the medial femoral condyle, it is possible to refix the ligament stump to the site of anatomical attachment using arthroscopic techniques.

In the case of development of chronic posterior instability of the knee joint in the compensated form, conservative treatment is carried out, including therapeutic exercises aimed at strengthening the muscles that prevent pathological posterior displacement of the tibia, massage, and electrical stimulation of the quadriceps femoris.

Subcompensated or decompensated posterior instability of the knee joint can only be eliminated surgically. For this purpose, intra-articular autoplastic or alloplastic (for example, lavsanoplasty) and extra-articular (aimed at activating the activity of periarticular muscles) stabilizing operations are performed.

In the department of sports and ballet trauma of the Federal State Institution 1 DITO, in case of damage to the posterior cruciate ligament, arthroscopic intra-articular stabilizing operations are performed using a single-bundle or double-bundle autograft from the patellar ligament.

Posterior static stabilization using a single-bundle patellar ligament autograft

This type of surgical intervention is used in patients with injuries to the posterior cruciate ligament and meniscus, one of the collateral ligaments, and also in cases of anteroposterior instability (i.e., with simultaneous restoration of the anterior cruciate ligament and posterior cruciate ligament).

At the first stage, arthroscopic diagnostics of the knee joint cavity is performed, all necessary manipulations are performed (for example, meniscus resection, excision of the anterior cruciate ligament stump, treatment of chondromalacia zones and cartilage defects, removal of free intra-articular bodies), a graft is taken from the patellar ligament. From an additional posteromedial approach, the posterior edge of the tibia is examined and freed from scar tissue. By analogy with the location of the native posterior cruciate ligament, the exit site of the intraosseous canal is determined - 1-1.5 cm below the posterior edge of the tibia in its middle. A pin is inserted into the calculated place for the tibial canal using a stereoscopic system. To determine the correct location of the pin, intraoperative radiographs are taken in the lateral projection.

A cannulated drill is inserted along the guide pin, the size of which depends on the size of the bone blocks of the transplant. A special protector is used to avoid damage to neurovascular structures.

The position of the shin at this moment is maximum forward extension.

Next, the medial femoral condyle is examined and a location for the intraosseous canal is selected, using the natural location of the posterior cruciate ligament as a reference point. A guide pin is inserted into the calculated location. When performing the femoral canal, it is necessary to maintain a constant flexion angle in the knee joint (110-120°) for the correct location and ease of drilling the canal, as well as to reduce the likelihood of damage to the cartilage on the lateral femoral condyle. A drill is inserted along the pin and the intraosseous canal is drilled.

The next stage of the operation involves inserting the transplant into the knee joint cavity. The transplant is fixed with an interference titanium or bioresorbable screw. When inserting the screw, it is necessary to stretch the transplant as much as possible to avoid it from twisting around the screw.

Then the transplant is fixed in the tibial canal with an interference screw with the tibia flexed at the knee joint to 90° and maximally removed from the posterior subluxation position. After fixing the transplant on the operating table, control radiographs are taken in direct and lateral projections. After the operation is completed, the limb is fixed with a splint. The angle of flexion of the tibia at the knee joint in the splint is 20°.

Posterior static stabilization of the knee joint using a double-bundle graft

The indication for this operation is considered to be total instability of the knee joint (damage to the posterior cruciate ligament, anterior cruciate ligament and collateral ligaments). The use of a two-bundle transplant for this type of instability allows for sufficient elimination of tibia rotation.

At stage I, arthroscopic diagnostics of the knee joint and necessary surgical manipulations regarding concomitant intra-articular pathology are similarly performed. A 13 mm wide autograft is taken from the patellar ligament with two bone blocks from the lower pole of the patella and the tibial tuberosity. The tendon part of the graft and one bone block are cut into two parts.

The next stage of the operation (selection of the attachment site of the posterior cruciate ligament on the tibia, formation of the tibial canal) is carried out in the same way as when using a single-bundle graft. Then they proceed to making the femoral canals. The center of the canal for the anterolateral bundle is localized at a distance of 7 mm from the edge of the articular cartilage and 7 mm from the roof of the intercondylar fossa, and the center of the canal for the posteromedial bundle is at a distance of 4 mm from the edge of the articular cartilage and 15 mm from the roof of the intercondylar fossa. Guide pins are inserted into the designated points one by one, and canals are drilled along them, first the posteromedial one, and then the anterolateral one. Then the graft is inserted. The posteromedial bundle is inserted and fixed first. Then, with the lower leg fully extended in the knee joint, the distal end of the graft is fixed in the tibial canal. After this, the lower leg is bent at the knee joint to 90°, the anteromedial bundle is stretched and, when the lower leg is maximally removed from the position of posterior subluxation, it is fixed.

Arthroscopic treatment of popliteal cysts (Baker's cysts)

Cysts formed in the popliteal region are very common consequences of intra-articular injuries and diseases of the knee joint, significantly disrupting its functions and tolerance to physical activity. According to various authors, the probability of popliteal cysts occurring in various pathological processes in the knee joint ranges from 4 to 20%.

Popliteal cysts, or Baker's cysts, are not true cysts. They are fluid-filled, synovial-lined masses in the popliteal fossa that are usually associated with the knee joint.

The widespread introduction of arthroscopic techniques in recent years for the diagnosis and treatment of injuries and diseases of the knee joint, as well as information about the anatomical and functional features of the joint obtained during endoscopic examination of the knee joint, formed the basis for a new direction in the treatment of popliteal cysts. The use of arthroscopy has made it possible to prove that cysts of the popliteal region develop as secondary pathological changes against the background of damage to intra-articular structures and degenerative diseases of the knee joint.

Popliteal cysts originate from the mucous bags of the knee joint - closed cavities, in some cases isolated, in others communicating with the joint cavity or with an adjacent cyst. The substrate for the occurrence of these cysts is the stretching of the bags of the popliteal region communicating with the cavity of the knee joint (in particular, the bag located between the tendons of the medial head of the gastrocnemius and semimembranosus muscles). An increase in the volume of fluid in the cavity of the knee joint leads to the accumulation of fluid in the bag and the occurrence of a popliteal cyst.

Arthroscopy allows us to detect the popliteal cyst anastomosis. It has the appearance of a capsule defect in the posterior part of the knee joint, is localized more often in its medial part at the level or above the joint space, usually has a rounded shape and sizes from 3 to 10 mm, less often - the appearance of a slit-like capsule defect up to 12-15 mm long.

Restoration of normal relationships of intra-articular structures in the knee joint helps to stop the cyst. In order to prevent the development of a cyst relapse and achieve a more reliable treatment result when a cyst anastomosis is detected, coagulation of the cyst anastomosis is performed in addition to sanitation.