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Posterior cruciate ligament injury

Posterior cruciate ligament injury
Literature review current through: Jan 2024.
This topic last updated: Oct 31, 2023.

INTRODUCTION — The posterior cruciate ligament (PCL) is the primary restraint to posterior translation of the tibia at the knee joint [1-4]. The bulk of injuries to this ligament occur in combination with other internal derangements of the knee in association with multi-ligament trauma; isolated PCL injuries are uncommon [5,6]. The PCL is the knee ligament least frequently injured during sports [5-7]. Over time, increasing knowledge of the anatomy and biomechanics of this ligament has highlighted its importance with regard to knee stability and function. As isolated injury is uncommon, the natural history of injury has yet to be elucidated fully.

The presentation, evaluation, diagnosis, and nonoperative management of PCL injuries are reviewed here. Other knee injuries and an overall approach to knee complaints in active adults are discussed separately. (See "Anterior cruciate ligament injury" and "Medial (tibial) collateral ligament injury of the knee" and "Lateral collateral ligament injury and related posterolateral corner injuries of the knee" and "Approach to the adult with knee pain likely of musculoskeletal origin" and "Approach to the adult with unspecified knee pain".)

ANATOMY AND BIOMECHANICS — The posterior cruciate ligament (PCL) is the largest and strongest of the intra-articular ligaments of the knee, originating at the lateral border of the medial femoral condyle and inserting at the posterior tibia in a depression called the PCL facet (fovea centralis) that lies between the medial and lateral tibial plateaus (picture 1 and figure 1 and figure 2) [1,2,8-10]. The PCL is considered an intra-articular but extrasynovial structure because of the synovial sheath that lines the ligament [4]. The extrasynovial location accounts for the limited swelling seen with isolated PCL injuries. Due to its association with the posterior capsule, blood supply to the PCL is not permanently lost with an intrasubstance tear. This permits primary surgical repair in some cases of PCL injury [9].

The PCL is structurally divided into two distinct yet inseparable bundles identified as the larger anterolateral (AL) and the smaller posteromedial (PM) bundles (figure 3). Classically, it was taught that, in addition to location, these bundles could be distinguished by their function, with each bundle exhibiting different patterns of tension and relaxation depending upon the degree of knee flexion [1,2,8,9]. However, subsequent biomechanical studies have demonstrated a more synergistic "codominant relationship" between the AL and PM bundles, with both contributing to knee stability throughout a full range of flexion (0 to 120 degrees) [11].

The PCL works in concert with the meniscofemoral ligaments, which together make up the PCL complex. The meniscofemoral ligaments originate from the posterior horn of the lateral meniscus and insert on the medial femoral condyle anterior to the PCL (ligament of Humphrey inserts anteriorly) and posteriorly to the PCL (ligament of Wrisberg inserts posteriorly). While anchoring the lateral meniscus, these ligaments also act as a secondary restraint to posterior tibial translation [2,4,8,9].

The primary role of the PCL complex is to restrict posterior translation of the tibia with respect to the femur, while also acting as a secondary restraint to external rotation [2,8,10]. In addition, the PCL protects the extended knee from varus and valgus stress. The role of the PCL in providing posterior knee stability increases as the knee is brought into flexion. The PCL provides 95 percent of posterior stability when the knee is flexed between 30 and 90 degrees [8]. Each bundle of the PCL contributes to joint stability based upon its distinctive fiber orientation in relation to the degree of knee flexion [1,2,8]. Essentially, tension in each bundle develops in a reciprocal fashion during knee flexion and extension: The AL bundle becomes slack in extension but progressively more taut with knee flexion; the PM bundle is tight in extension but becomes progressively more slack with knee flexion [1,8]. Therefore, it may be more useful to consider the PCL as a single, complex structure with a continuum of fibers of different lengths and varying tensions depending on the degree of knee flexion [8].

The posterolateral complex, or PLC, (also referred to as the posterolateral corner) consists of the lateral collateral ligament (LCL), iliotibial band, popliteus tendon, popliteofibular ligament, arcuate ligament, and posterolateral joint capsule. The PLC is an important secondary constraint against posterior tibial translation, with a primary function of resisting varus and external rotational forces. The amount of posterior tibial translation increases significantly when both the PCL and PLC are injured. The clinician must be aware of this intimate anatomical relationship as an injury to both structures suggests a need for prompt surgical treatment [1,2]. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee".)

EPIDEMIOLOGY — The incidence of posterior cruciate ligament (PCL) injury is reported to range from 1 to 44 percent of all knee injuries [3,5,6,12]. This wide variability in incidence probably exists because of the subtlety with which isolated injuries can present. One report supports the notion that isolated PCL injury is rare, comprising only 3.5 to 7.5 percent of trauma-related injury [5,6]. Common associated knee injuries involve the posterior lateral corner, anterior cruciate ligament (ACL), and medial collateral ligament (MCL).

Many individuals who have sustained a PCL injury continue to function at a high level in sports and so may not present to clinicians, thus lowering the reported incidence. One study found a 2 percent incidence of asymptomatic PCL injury among college American football players presenting for examination prior to the National Football League (NFL) draft [2,3,13]. Another found that 3 percent of individuals participating in the NFL Combine between 2009 and 2015 had sustained a PCL injury, with 15.9 percent having had surgical reconstruction [14].

The main cause of PCL injury is high-energy trauma, most often involving motor vehicle collisions (MVCs) [5,6,15]. Sporting activities are the second most common cause of injury and are less likely to result in combined ligament injury. According to a retrospective study of 19,530 sports-related injuries, the PCL is among the least likely of structures to be injured in athletics, comprising up to 0.65 percent of all athletic-related knee injuries [7]. Another large retrospective analysis found that 45 percent of PCL injuries were due to MVCs, while 40 percent were related to athletic injury [15]. In this study, motorcycle accidents made up 28 percent of the motor vehicle injuries, while football (soccer) was the sport most often associated with PCL injury (25 percent). MVCs accounted for up to 63.8 percent of cases involving combined ligamentous injuries of the knee, compared with athletic injury, which accounted for 47.5 percent of such cases.

Playing surface is a potential risk factor for knee ligament injuries among athletes. A study performed using the United States' National Collegiate Athletic Association (NCAA) Injury Surveillance System found an association between artificial turf and PCL tears sustained by American football players [16]. PCL tear rates for players at the most elite level (ie, Division I) were three times greater during games played on artificial turf compared with natural grass (rate ratio [RR] 2.99; 95% CI 1.39-6.99). Among Division II and III players, the risk was higher (RR 3.13; 95% CI 1.14-10.69).

MECHANISM OF INJURY — Posterior cruciate ligament (PCL) injuries may be sustained from high- or low-energy trauma. High-energy mechanisms, primarily motor vehicle collisions (MVCs), may cause PCL injury when a posteriorly directed sheer force is applied to a flexed knee (figure 4). One example is the classic "dashboard injury" in which the anterior knee, including the proximal tibia, of the driver or a front seat passenger collides with the car's dashboard. When such a force is combined with varus rotation, the lateral or posterolateral structures of the knee may be injured in addition to the PCL [2,3,15].

PCL injuries sustained during athletics typically occur when an athlete falls on their flexed knee while the foot is plantarflexed or from a direct blow to the anterior knee. In addition, the PCL and posterior capsule can be torn by a hyperflexion or hyperextension mechanism, with or without a posterior-directed force [2,3,15]. Valgus and varus forces applied to the knee can cause a PCL injury, but such mechanisms typically involve injuries to multiple knee structures [15].

CLINICAL PRESENTATION — The presentation of patients with a posterior cruciate ligament (PCL) injury varies depending upon the nature of the trauma involved (high- versus low-energy) and associated injuries and comorbidities. PCL injuries sustained from high-energy trauma are frequently associated with additional knee injuries, including damage to the posterolateral corner (PLC), anterior cruciate ligament (ACL), and medial collateral ligament (MCL) [6]. Particularly in cases of low-energy trauma, a careful history detailing the mechanism of injury is important for identifying PCL injury. PCL injury can be classified further based on the timing of injury (acute versus chronic) and severity (isolated versus multiligamentous). These variables affect treatment and prognosis [15].

As the large majority of PCL injuries are sustained during motor vehicle collisions (MVCs), the clinician must maintain a high index of suspicion for ligamentous knee injury, including complete knee (tibiofemoral) dislocation, for any patient complaining of knee pain or dysfunction following high-energy trauma [1,3]. Knee dislocation can cause severe morbidity from vascular disruption if not recognized and treated immediately. Knee injuries associated with high-velocity trauma often present with severe hemarthrosis, inability to bear weight, gross instability, and decreased range of motion. Assessments of knee dislocation and of the patient involved in major trauma are discussed separately. (See "Knee (tibiofemoral) dislocation and reduction" and "Initial management of trauma in adults" and "Trauma management: Approach to the unstable child".)

PCL injuries sustained from low-energy trauma (eg, sporting injuries) may present with gross instability, particularly if associated with injuries to posterolateral knee structures or with more subtle symptoms that can make diagnosis difficult. The presentation of an isolated PCL injury is often subtle and quite different from that of an injury to the ACL, which often involves an acute popping sensation perceived by the athlete at the time of injury, typically while performing a quick pivoting maneuver or landing from a jump, followed by the development of a large knee effusion. Patients with an isolated PCL injury generally do not report feeling or hearing such a "pop." They may have a mild to moderate knee effusion, a slight limp, pain in the back of the knee (especially with squatting or kneeling), and loss of terminal knee flexion (final 10 to 20 degrees). Complaints of joint instability are more common with multiple knee ligament injuries than an isolated PCL injury [1-3,12]. Acutely, many of these athletes may continue to play sports and not seek medical attention [3,12]. An athlete's only complaint may be a sensation that "something's not right" in the knee or of generalized knee pain; the patient may have difficulty being more precise [12].

Patients suffering from a chronically injured PCL-deficient knee present more often with generalized anterior knee pain that may localize to the medial compartment or patellofemoral joint. According to an observational study of tibiofemoral motion involving open-access magnetic resonance imaging of patients with a PCL-deficient knee, altered kinematics related to PCL deficiency cause a fixed anterior subluxation of the medial femoral condyle in relation to the medial tibial plateau [17]. This appears to increase the risk for degenerative changes in the medial knee. In this study, imaging was performed while patients performed several weightbearing movements. The lateral compartment of the knee appears to be unaffected by the compressive forces created by PCL deficiency.

Patients with a chronic PCL-deficient knee may complain more of disability than instability that is most noticeable when negotiating inclines such as stairs or ramps [2,3,12]. Athletes presenting with a chronic injury may complain of pain when sprinting or decelerating and mild instability [3]. Many individuals with chronic PCL insufficiency are found to have been injured in a previous MVC [15]. Such patients often sustained life-threatening injuries that caused the knee injury to be overlooked.

EXAMINATION FINDINGS

General knee examination — For patients presenting immediately following a motor vehicle collision (MVC) or other high-energy trauma, a precise knee examination may not be possible due to severe pain and swelling, or the need to perform urgent diagnostic imaging (eg, assessment of the popliteal artery from suspected knee dislocation) or more urgent interventions. Whenever possible, the knee is thoroughly examined as part of the secondary trauma survey. Of crucial importance is assessing for major vascular injury of the injured extremity. (See "Knee (tibiofemoral) dislocation and reduction" and "Initial management of trauma in adults".)

For patients presenting with knee pain following low-energy trauma or with chronic complaints, it is important to perform a careful knee examination paying close attention to joint stability and function. The knee examination is reviewed in detail separately; elements of the examination of particular importance to the assessment of posterior cruciate ligament (PCL) injury are discussed below. (See "Physical examination of the knee".)

The knee examination begins with careful inspection, using the uninjured lower extremity for comparison. Asymmetries can be appreciated by watching the patient's stance and gait. Findings may include swelling, joint effusion, muscle atrophy, malalignment (eg, varus or valgus), and ecchymosis or other skin changes. In patients with a PCL injury, general inspection and palpation of the knee while the patient is supine may reveal a mild to moderate effusion, or possibly no effusion in case of chronic injury [1-3].

With acute isolated PCL injury, the patient may manifest an antalgic gait [18]. Depending upon the patient's anatomy and concomitant injuries, any of several gait abnormalities may be present. Loss of restraints against external rotation of the tibia (best evaluated by the dial test (picture 2)) in combination with tibia vara or genu recurvatum can produce a varus thrust gait or knee hyperextension in combination with a varus thrust gait, best noted during the stance phase of the gait cycle [19,20]. The varus thrust pattern consists of a dynamic lateral bowing of the knee during the weightbearing phase of gait, which places a greater load on the medial knee. Other patients may walk with a slightly flexed knee in order to avoid the pain and instability associated with a varus thrust or varus hyperextension gait pattern [19,20]. These abnormal gait patterns are typically more pronounced with combined PCL and posterolateral corner (PLC) injury [1,20-22]. (See "Clinical assessment of walking and running gait".)

Examination findings in the patient with a chronically PCL-deficient knee are generally more subtle. Suggestive findings may include tibia vara (bow legged) or genu recurvatum (hyperextended knee) [1,18,19,21,23]. Comparison with the uninjured extremity is often useful. Tibia vara, which may stem from progressive incompetence of posterolateral knee structures injured at the same time as the PCL, is best seen while inspecting the weightbearing patient from behind. Genu recurvatum, which may develop from abnormal alignment due to posterior subluxation of the tibia, is best evaluated by observing sagittal knee alignment while the patient is weightbearing.

Following inspection, the knee is palpated for signs of injury, although with acute PCL injuries, findings other than effusion may be scant. It is difficult to differentiate using palpation the structures of the posterolateral complex (PLC), which is commonly injured in association with the PCL. Few structures are palpable in the posterior fossa, the space between the medial and lateral hamstring tendons, but the area may be tender. The lateral collateral (LCL) and medial collateral (MCL) ligaments should be palpated, and focal tenderness at these ligaments suggests injury [1,2]. As it can be difficult to distinguish the LCL from the biceps femoris tendon and iliotibial band at the joint line (picture 3), the examiner should begin palpation at the lateral femoral condyle and follow the cordlike LCL distally as it crosses over the joint line towards the fibular head (picture 4).

Following palpation, active knee flexion is assessed by having the supine patient flex the knee maximally, bringing the heel as close as possible to the gluteal fold. Flexion can be measured in degrees using a goniometer or by the minimum distance between the heels and the closest gluteal surface. Normal flexion is approximately 130 degrees. If an effusion is present, as seen in acute PCL injury, it is likely that active terminal flexion will be reduced by 10 to 20 degrees [1,2].

The clinician should determine the position of the tibia in relation to the femur with the knee flexed to 90 degrees. This enables detection of asymmetries and allows for correction of posterior subluxation of the tibia in the PCL-injured knee. In the normal knee, the medial tibial plateau lies approximately 1 cm anterior to the medial femoral condyle when the knee is flexed to 90 degrees. PCL injury should be suspected if this step-off is absent [1,3,4]. As described below, it is important to avoid confusing a PCL injury for an anterior cruciate ligament (ACL) injury when performing an anterior drawer or Lachman test with the knee in this position [1,3].

As other knee ligaments are commonly injured along with the PCL, it is important to test the joint for laxity. The ACL is best assessed using the Lachman and anterior drawer maneuvers, while the MCL or LCL are assessed with the valgus and varus stress tests respectively, at 0 and 30 degrees of flexion. (See "Physical examination of the knee", section on 'Assessing joint stability'.)

Special tests for PCL injury — The primary tests used to assess the integrity of the PCL and posterior knee include the posterior drawer test, posterior sag sign, and quadriceps active test. The performance of these examination maneuvers is described in detail separately. (See "Physical examination of the knee", section on 'Tests for PCL injury and posterior stability'.)

Posterior drawer test – The posterior drawer test (figure 5) is generally considered the most accurate examination maneuver for detecting PCL injury [24]. Prior to performing the posterior drawer test, the clinician must ascertain the position of the tibia relative to the femur. Posterior subluxation of the tibia due to a loss of PCL integrity can compromise test results.

Posterior sag sign (Godfrey test) – If a PCL injury is present, the tibia sags below the level of the uninjured side (picture 5). This finding can be appreciated in patients with acute or chronic PCL insufficiency [1,3].

Quadriceps active test – In the PCL-deficient knee, the tibia starts in a posteriorly subluxed position (as seen with the posterior sag sign), but with contraction of the quadriceps the tibia translates anteriorly (movie 1 and figure 6).

Criteria for isolated PCL injury — When evaluating a patient for PCL injury, it is important to rule out multiligamentous knee injury. An isolated PCL injury is likely if the following criteria are met [12,25]:

Posterior drawer test shows less than 10 mm laxity. In rare instances, an isolated PCL injury can manifest >10 mm of laxity on posterior drawer testing. In all cases, such a finding necessitates assessment of other knee structures, particularly the PLC.

Rotatory laxity of less than 5 to 10 degrees, performed with the knee in 30 degrees and 90 degrees of flexion (ie, negative dial test). (See "Physical examination of the knee", section on 'Tests for PCL injury and posterior stability'.)

No sign of associated ligamentous injury (ie, negative testing for MCL, LCL, and ACL injury).

The Lachman test and varus and valgus stress testing at 0 and 30 degrees of knee flexion are effective examination maneuvers for diagnosing concomitant ligament injury, but they may be ineffective immediately following acute injury due to patient guarding. In these cases, magnetic resonance imaging (MRI) is effective at ruling out concomitant ligament or cartilage injury when an immediate, definitive diagnosis is required. (See 'Diagnostic imaging' below.)

Classification of PCL injury — The magnitude of posterior knee translation as measured during the posterior drawer test allows the examiner to grade a PCL injury by comparing findings with the uninjured, contralateral knee [1-4,12]. Standard grading is as follows:

Grade 1 – The anterior border of the medial tibial plateau can be displaced posteriorly but remains anterior to the medial femoral condyle (0 to 5 mm posterior displacement).

Grade 2 – The anterior border of the medial tibia plateau can be displaced posteriorly until it is flush with the medial femoral condyle (posterior displacement of 5 to 10 mm).

Grade 3 – The anterior border of the medial tibial plateau can be displaced posteriorly beyond the anterior border of the medial femoral condyle (posterior displacement >10 mm).

Grade 1 and Grade 2 injuries are considered partial PCL tears; Grade 3 injuries represent complete PCL tears [1].

Associated injuries — When a Grade 3 injury is identified clinically, the clinician must maintain a high index of suspicion for combined injury involving other capsuloligamentous knee structures, primarily those of the PLC. It is important to recognize these combined PCL and PLC injuries as management is more likely to require surgery [1-3]. Assessment of the PLC includes four examination maneuvers: the external rotation recurvatum test, posterolateral drawer test, reverse pivot shift test, and dial test at 30 and 90 degrees. Examination of the PLC is described in detail separately. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Clinical presentation and examination'.)

DIAGNOSTIC IMAGING

Approach to diagnostic imaging

Suspected acute PCL injury — With any acute knee injury presenting after moderate or severe trauma in which a posterior cruciate ligament (PCL) injury is suspected and that is accompanied by concerning physical findings, such as joint effusion, focal bony tenderness, decreased range of motion, or limp, we obtain plain radiographs of the knee as part of the initial diagnostic imaging. Plain radiographs may reveal fractures and avulsion injuries (image 1). If trauma is relatively minor and concerning physical findings are absent, the Ottawa knee rules can be used to guide decisions about plain radiographs. (See "Approach to the adult with knee pain likely of musculoskeletal origin", section on 'Imaging in the evaluation of acute knee pain'.)

We suggest obtaining magnetic resonance imaging (MRI) for all patients in whom a PCL injury is suspected on clinical grounds (eg, blow to flexed knee with positive posterior drawer test) following acute trauma involving the knee. (See 'Magnetic resonance imaging' below.)

Suspected subacute or chronic PCL injury — Following a subacute or chronic knee injury (time since injury greater than six weeks) in which a PCL tear is suspected, we use the Ottawa knee rules to help determine whether plain radiographs of the knee are needed as part of the initial diagnostic imaging in adults. Although validated in children, the Ottawa knee rules were designed with acute injuries such as fractures in mind [26]. Many pediatric and adolescent patients present with subacute or chronic knee pain, and the authors generally obtain plain knee radiographs in these cases to assess for conditions such as avulsed apophyses or osteochondritis dissecans that may account for such symptoms. If plain radiographs identify such conditions, workup proceeds as indicated.

If plain radiographs are unrevealing or not indicated but chronic PCL injury is suspected on clinical grounds, we suggest obtaining an MRI to assess both the PCL and possible associated injury, although the sensitivity of MRI for chronic PCL tears is limited. (See 'Magnetic resonance imaging' below.)

Plain radiography — Plain radiographs are the initial studies obtained in most patients with an acute knee injury and suspected PCL tear. Anteroposterior (AP) and lateral views are used to rule out fracture of the tibial plateau, femoral condyles, and patella. The lateral view should be examined carefully looking for bony avulsion of the tibial PCL insertion (image 1) and posterior sag of the tibia, which suggest a PCL injury (image 2) [1-3,12]. A cortical avulsion off the medial tibial plateau has been described as a medial "Segond-type" fracture that may be associated with tears of the PCL and medial meniscus, but further research is needed [27].

In the patient with a suspected chronic PCL-deficient knee, weightbearing AP views of the knee should be obtained, as well as a lateral view and sunrise views of the patella (image 3). These images should be examined for posterior sag of the tibia, avulsion fracture of the PCL insertion, and degenerative changes in the medial and patellofemoral compartments [1-3,12]. Posterolateral or posteromedial subluxation may be apparent if the posterolateral or posteromedial compartments have been disrupted [12].

Stress radiographs — More clinicians are using stress radiographs to diagnose and grade PCL injuries [3,11,15]. Stress radiographs enable the clinician to obtain objective measurements of tibial translation in the sagittal plane noninvasively and to compare measurements in injured and uninjured knees [2]. Stress radiographs can be performed manually or with the aid of a mechanical device, which may allow for more consistent measurements.

Some experts endorse the single-leg kneeling technique, obtaining a view of the injured and uninjured knees to compare posterior tibial translation [11]. This technique is thought to be more cost effective and accessible, although the position can be uncomfortable and proper performance depends on voluntary bodyweight loading of the affected joint. A weighted-gravity stress radiograph may be used instead of the kneeling technique to improve patient comfort while obtaining the necessary stress to demonstrate pathological posterior tibial translation [28].

A retrospective study comparing findings from stress radiographs of 1041 consecutive patients with PCL tears to findings from cadaveric dissection studies found that posterior translation of the tibia in excess of 8 mm was associated with complete insufficiency of the PCL, while translation exceeding 12 mm was indicative of additional injury to secondary restraining structures, such as those of the posterolateral complex (PLC) [29]. Similar results have been reported in cadaver studies [30].

Magnetic resonance imaging — In most cases of suspected PCL injury, magnetic resonance imaging (MRI) is obtained to assess both the PCL and other soft tissue knee structures. MRI is highly sensitive and specific for acute PCL tears but much less accurate for detecting chronic tears.

Studies using arthroscopy as the gold standard have found the sensitivity and specificity of MRI for diagnosing acute PCL injury to approach 100 percent [31-33]. The PCL is best seen on the sagittal view with a normal ligament appearing as a dark, curvilinear structure on T1 and T2 sequences (image 4 and image 1) [2,12]. The clinician must be mindful that a clinical Grade 3 injury significantly raises the likelihood for more severe damage involving other capsuloligamentous knee structures, primarily those of the PLC.

In many instances of chronic injury, the PCL appears relatively normal due to the ability of the ligament to heal [34,35]. A systematic review of follow-up studies of posttraumatic PCL injuries revealed that 77 to 93 percent of partial or complete PCL tears regained continuity [35]. Thus, the accuracy of MRI in diagnosing chronic PCL injury is relatively low, with one small retrospective study reporting 57 percent [34]. Of note, the MRI appearance of the PCL following chronic injury has not been shown to correlate with clinical stability; in other words, a continuous ligament does not imply a stable knee [3,34,35].

Radionuclide imaging (bone scan) — For a patient with chronic PCL deficiency associated with pain and instability, bone scan may be able to identify early degenerative changes in the patellofemoral or medial compartments of the knee [1,2]. The decision about whether to obtain a bone scan in the setting of possible chronic PCL injury is best left to an orthopedic specialist. Results of the study can help to determine whether reconstruction of the PCL will be undertaken. Bone scan is not used in the assessment of suspected acute PCL injury.

Ultrasound — Ultrasound can assess the PCL only to a limited extent, but it may reveal changes consistent with PCL injury, such as enlargement of the ligament compared with the contralateral knee or in some cases a focal disruption in ligament continuity [36,37]. MRI is superior for evaluation of acute PCL injury and for identifying concomitant injury of menisci, ligaments, and articular cartilage. More research is needed to determine the capacities of ultrasound for identifying PCL injury. Ultrasound may offer a viable alternative for diagnosing suspected chronic PCL injuries not appreciated on MRI due to elongated healing.

DIAGNOSIS — Definitive diagnosis of an acute or subacute posterior cruciate ligament (PCL) injury can be made with magnetic resonance imaging (MRI) or arthroscopy (although arthroscopy is not performed for the purpose of diagnosis). A presumptive clinical diagnosis can often be made based upon the mechanism of injury and examination findings. A direct blow to the anterior portion of a flexed knee from a car dashboard, an opponent, or the ground is the most common mechanism, while a positive posterior drawer test, posterior sag sign, and quadriceps active test are highly suggestive findings. (See 'Mechanism of injury' above and 'Clinical presentation' above and 'Examination findings' above.)

Establishing a definitive diagnosis of chronic PCL injury can be difficult as both MRI and direct visualization using arthroscopy have limitations. As PCL tears can heal over time, MRI studies of chronic injuries may fail to identify such injuries, although degenerative changes found in the medial and patellofemoral compartments of the knee are suggestive. A PCL tear may be difficult to detect using arthroscopy because the PCL is partially obscured by the anterior cruciate ligament (ACL) and may appear intact despite clinical laxity and the existence of a partial tear [24,38].

INDICATIONS FOR ORTHOPEDIC CONSULT OR REFERRAL — Based upon our clinical experience and that of our surgical colleagues, and the limited available published evidence, we suggest that the following injuries be referred to a knowledgeable orthopedic surgeon:

Grade 3 posterior cruciate ligament (PCL) injuries – Anterior border of medial tibial plateau can be displaced posteriorly beyond the anterior border of the medial femoral condyle (posterior displacement >10 mm [39] ).

PCL injuries associated with any fracture or any additional soft tissue injuries of significance (eg, injury of the posterolateral complex [PLC], anterior cruciate ligament [ACL] injury, meniscal tear).

PCL disruption involving avulsion of the ligamentous insertion at the tibia [39,40].

In addition, if the clinical picture is unclear or the patient is a high-level athlete, it is reasonable to obtain orthopedic consultation. We suggest that acute isolated PCL injuries (ie, Grade 1 and 2 injuries) be managed nonoperatively, as outlined below. Should appropriate nonoperative management of a Grade 1 or Grade 2 PCL injury be unsuccessful (eg, patient experiences persistent pain or instability), orthopedic consultation should be obtained. However, given the limitations of surgical interventions, we adhere to a course of physical therapy and nonoperative management for as long as possible, and we generally wait up to 12 months before referring patients with lower grade PCL injuries. We refer patients with a chronic, isolated PCL injury to a knowledgeable orthopedic surgeon if they have developed functional instability or symptoms such as recurrent effusions or worsening pain [40]. Otherwise, we begin treatment with an appropriate physical therapy program. (See 'Follow-up care' below.)

It is vitally important that the treating clinician has, by examination and imaging, confirmed the diagnosis of isolated PCL injury, and determined its grade, before making a determination about the need for consultation. A multiligamentous knee injury is vastly different than an isolated PCL injury, with far greater associated morbidity, and surgical consultation is required for all these injuries.

DIFFERENTIAL DIAGNOSIS — Posterior cruciate ligament (PCL) injuries, particularly those sustained in high-energy trauma, are often associated with other injuries of the knee and elsewhere. Important injuries to consider when PCL tear is suspected include the following:

ACL injuries — The mechanisms of injury associated with PCL trauma may also injure the anterior cruciate ligament (ACL). However, the history and examination findings associated with ACL tears are generally distinct from those of PCL tears. Athletes who sustain an ACL injury often hear or feel an acute "pop" at the time of injury, and the mechanism generally involves a quick pivoting maneuver or landing from a jump, followed acutely by the development of a large knee effusion. The knee often feels unstable and a Lachman test is positive. It is important that the Lachman maneuver be performed correctly to avoid a false positive result. Should a definitive diagnosis be required, magnetic resonance imaging (MRI) readily distinguishes between these two acute injuries. (See 'General knee examination' above and "Anterior cruciate ligament injury".)

LCL and PLC injuries — Lateral collateral ligament (LCL) and posterolateral corner (PLC) injuries are often sustained in combination with PCL injury, particularly following high-energy trauma, and must be distinguished from isolated PCL injuries as multi-ligament trauma typically requires surgical intervention. In the presence of an LCL injury, a varus stress maneuver reveals abnormal widening and pain at the lateral joint line; the maneuver does not provoke such widening or pain with an isolated PCL injury. Likewise, the examination maneuvers commonly used to assess the PLC (ie, external rotation recurvatum test, posterolateral drawer test, reverse pivot shift test, and dial test at 30 and 90 degrees) are unlikely to be positive in the setting of an isolated PCL injury. MRI is highly accurate for identifying injury to the LCL and PLC in addition to the PCL, but the radiologist must be consulted to ensure that the appropriate imaging protocol is used. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Clinical presentation and examination' and "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Imaging' and "Physical examination of the knee", section on 'Tests for PCL injury and posterior stability'.)

Meniscal injuries (lateral and medial) — There can be significant overlap in the clinical presentation of PCL and meniscal injuries, and these injuries may be sustained simultaneously [41]. Meniscal injuries often present with nonspecific mechanical symptoms, such as popping, locking, or catching of the knee joint, and functional instability, which may also be present with PCL injuries. Pain and disability are comparable, and signs such as mild to moderate effusions may be similar. Differences in the physical examination include joint line tenderness and positive McMurray and Thessaly maneuvers, which are often present with meniscal injury, and the posterior sag and posterior drawer tests, which are positive in the presence of PCL injury but not with isolated meniscal injuries. Diagnostic imaging may be needed to distinguish these two injuries. (See "Meniscal injury of the knee".)

Proximal tibia fractures — Fracture of the proximal tibia can occur in the same setting where one might see a PCL injury. Motor vehicle collisions (MVCs) causing direct trauma to the knee or hyperextension injuries sustained on the athletic field are common mechanisms for both types of injury. Typically, a tibial fracture presents with a hemarthrosis, which manifests as a larger effusion than is typically seen with PCL injury, and substantial pain, which is also uncharacteristic of an isolated PCL injury. Pain and guarding from a tibial fracture are likely to prevent the clinician from performing examination maneuvers that can distinguish between the two injuries. Plain radiographs usually reveal a tibial fracture. (See "Proximal tibial fractures in adults".)

Knee (tibiofemoral) dislocation — A knee (tibiofemoral) dislocation is a limb-threatening injury requiring emergent evaluation. The clinician must maintain a high index of suspicion for such injury in any patient complaining of knee pain or dysfunction following significant knee trauma. Knee dislocation is typically sustained through high-energy trauma (eg, MVC) and causes severe pain and gross instability of the knee. Swelling is generally severe, and there may be obvious deformity, assuming the dislocation does not reduce spontaneously. (See "Knee (tibiofemoral) dislocation and reduction".)

Bone contusion — The mechanisms commonly associated with many PCL injuries, such as direct knee trauma and knee hyperextension, can also cause a bone contusion of the tibia, and the two injuries may coexist [42]. Bone contusions can cause significant pain and disability, causing restrictions in knee motion and possibly an effusion. However, the posterior sag and posterior drawer tests are negative in the patient with an isolated bone contusion. In difficult cases where the examination is limited and a definitive diagnosis is required, MRI readily distinguishes between these two acute injuries.

Patellar and quadriceps tendon tears — Both tendon tears and PCL injuries can occur with a fall onto a flexed knee. However, when such trauma causes a patellar or quadriceps tendon tear, the patient often reports feeling a "pop" in their knee along with some degree of immediate disability and a knee effusion. These presenting symptoms and signs are highly atypical of a PCL injury. Patients with tendon tears are generally unable to bear weight on the injured leg or to perform a straight leg raise, whereas patients with a PCL injury are usually able to do both, although posterior sag of the tibia may be noted during the straight leg raise. Often, there is a palpable defect and reproducible tenderness when examining a torn patellar or quadriceps tendon, while such findings are not found with PCL injuries. On plain radiographs, the height of the patella may be altered (patella alta or baja) or signs of a patellar avulsion injury may be present in patients with tendon tears. If obtained, an MRI clearly distinguishes between these two injury types. (See "Quadriceps muscle and tendon injuries", section on 'Quadriceps and patellar tendon tears'.)

INITIAL TREATMENT — Once the treating clinician has established that there is no need for referral, initial treatment of an isolated posterior cruciate ligament (PCL) injury involves standard management of pain and functional disability if present. The basic principles of protection, rest, ice, compression, elevation, and medications (PRICE-M) apply.

We suggest maintaining the affected knee in hinged knee brace locked in full extension for approximately two weeks in order to reduce posterior lag in the acutely injured knee. Alternatively, a standard knee immobilizer may be used. After two weeks, the brace is unlocked to allow progressive range of motion exercises. There is no high-quality evidence supporting this approach, but we and some others consider immobilization in extension to be an important part of initial treatment [12]. Chronic PCL-deficient knees do not require bracing unless the patient reports a high degree of functional instability; if a brace is used in this setting, it should be unlocked.

PCL injuries themselves generally do not cause significant pain or joint effusion, but these may develop due to associated bone contusions. Therefore, appropriate rest may require a period of limited weightbearing using crutches. The use of crutches is intended for pain control and is not mandatory. Ice applied to the knee, elastic compression wraps (eg, ACE wraps), and elevation of the affected extremity above heart level may be needed to reduce swelling and discomfort. Analgesic medications may be needed for pain. Options may include a short course of acetaminophen or nonsteroidal antiinflammatory drugs (NSAIDs). Opioids are typically unnecessary. Usually, patients are able to resume school or desk-type work soon after an isolated PCL injury.

FOLLOW-UP CARE — There is a dearth of high-quality evidence and currently no consensus about what constitutes optimal nonoperative rehabilitation and management of an isolated posterior cruciate ligament (PCL) injury [25,39]. Rehabilitation of the conservatively treated, isolated PCL injury can resemble that of the surgically reconstructed PCL, for which there is better evidence [43]. The approach described below is based upon our experience and our interpretation of the available literature. Rehabilitation of a PCL injury can be difficult and the authors strongly prefer that rehabilitation be supervised by a knowledgeable physical therapist.

Early rehabilitation — Rehabilitation may begin when swelling has diminished and pain is well controlled; practically, for many patients that means immediately after presentation. Early rehabilitation following an acute, isolated PCL injury consists primarily of general mobility and open-chain quadriceps exercises. These include ankle pumps (active dorsiflexion and plantarflexion of the ankles) and quad sets (active contraction of the quad with the knee in extension). The goal of early rehabilitation is to prevent joint stiffness and encourage recruitment of the quadriceps, which the patient may have difficulty activating due to pain or joint effusion. Full strength and function of the quadriceps are needed for full recovery, and thus addressing this muscle group early in the course of treatment is important. The authors avoid open-chain hamstring exercises (eg, heel slides) to prevent unopposed hamstring activation, which may accentuate posterior sag of the tibia, contribute to joint irritation, and delay recovery.

Supervision by a knowledgeable physical therapist, athletic trainer, or comparable professional during this early stage of recovery is not mandatory but can be helpful to ensure that pain and swelling (if present) are manageable and the prescribed exercises are being performed correctly. Modalities often available through physical therapy, such as neuromuscular electrical stimulation, can help with quadriceps activation even if the patient is unable to perform simple open-chain exercises [44,45].

During rehabilitation, some patients may benefit from additional support of the posterior knee, which can be provided by the taping method pictured in the following graphic (picture 6). Note that the support provided by this method would not be adequate for a patient returning to full sport. Ideally, such patients should have developed sufficient strength of the muscles supporting the knee that extraneous support is unnecessary, or barring that should use a robust functional PCL brace.

Later rehabilitation — The advanced stage of rehabilitation typically commences four to six weeks after the initial injury, when pain and disability have subsided. Although several rehabilitation protocols for surgically treated PCL injuries have been published, there is relatively little evidence available to guide the rehabilitation of PCL injuries managed nonoperatively [3,12,46-48]. An example of a properly designed, nonoperative PCL rehabilitation protocol for an isolated, uncomplicated, acute PCL injury can be found in the attached table and reference (table 1) [25]. Initially, the goals of this stage of rehabilitation are to continue to protect the knee, regain full knee motion, and strengthen the muscles primarily responsible for supporting the PCL-deficient knee (ie, quadriceps). Depending on patient goals, more challenging exercises are gradually introduced that enable the patient ultimately to regain full function.

Typically, rehabilitation for PCL injuries takes longer than that for ACL injuries [49]. Rehabilitation protocols following PCL reconstruction range from 26 to 52 weeks [47,50], whereas rehabilitation of the nonoperatively treated PCL-deficient knee is typically completed in half that time. It is important to note that rehabilitation protocols are function based and not time based.

RETURN TO SPORT OR WORK — Decisions concerning return to sport or heavy labor are necessarily multifactorial and entail balancing patient preference, subjective assessments of persistent pain and functional limitations, and objective evaluations of strength and performance. There is no single "gold standard" for determining return to sport [48].

The authors make their determination in concert with the physical therapists who have been conducting the patient's rehabilitation. The athlete is expected to demonstrate symmetric strength and proprioception in the affected and the uninvolved extremities. Strength can be assessed with single leg presses using resistance machines; proprioception may be determined by standing on one leg and maintaining balance and a level pelvis for 30 seconds. Plyometric and other functional tests are commonly used by physical therapists for these assessments, especially in athletes, and these may include timed single-leg hops for distance, shuttle runs, single-leg vertical jumps for height, and the Star Excursion Balance Test (picture 7) [51]. As a general rule of thumb, performance of the injured leg should be within 10 percent of that of the uninjured leg prior to return to sport [48].

For patients who do desk work or do not engage in vigorous activity, return to work can typically be achieved as soon as pain and functional disability have abated sufficiently. The time needed for a return to this sort of work is generally within two to four weeks and can commence while the patient is still undergoing rehabilitation.

Beyond the period of early rehabilitation, there is no evidence to support functional knee bracing in patients with isolated posterior cruciate ligament (PCL) injuries. When returning patients to sport, the authors do not routinely use functional knee braces, although these may be used for activities that are considered high-risk (eg, American football linemen). Following surgical reconstruction, such knee bracing may be used during sport for up to 18 months postoperatively [48].

COMPLICATIONS AND PROGNOSIS — The natural history of isolated, nonoperatively treated posterior cruciate ligament (PCL) tears continues to be a source of debate. Some authors believe that the natural history of PCL tears entails inevitable degenerative changes and have argued that this supports the need for surgical intervention [40]. Others have noted that the prevalence of knee osteoarthritis after PCL reconstruction appears to be similar or worse than that seen in knees treated conservatively [52,53]. There is insufficient high-quality evidence to determine the true prognosis or the best approach to treatment.

Based on limited evidence, it appears that most patients can expect to have good subjective and functional results with nonoperative management of isolated PCL tears. One prospective study of 133 patients reported that the majority had good subjective results at five-year follow-up, with half able to return to sport at the same or a higher level [54]. Smaller studies of similar design report comparable results [53,55]. However, premature osteoarthritis is a long-term concern, as it is with any internal derangement of the knee. According to a case series of 44 patients managed nonoperatively and followed for a mean of 14.3 years, the prevalence of moderate to severe knee osteoarthritis was 11 percent [52].

No factors have been identified that accurately predict which patients will develop complications, such as osteoarthritis, instability, or chronic pain. As an example, the grade of PCL injury does not correlate with the development of degenerative joint disease [3].

Historically, the results of surgical repair of isolated PCL injuries have been less satisfactory than comparable repairs of anterior cruciate ligament (ACL) reconstructions [56]. In addition, the PCL has greater natural healing ability than the ACL, with one study demonstrating continuity of the disrupted PCL in 20 of 21 patients six months after injury with conservative treatment [57].

Nevertheless, PCL repair and reconstruction are becoming more common, although high-quality evidence pertaining to the surgical treatment of isolated PCL injuries is lacking, and controversy exists about appropriate management [40,52,54,58]. The sources of controversy encompass a number of issues related to PCL surgery, including: repair versus reconstruction, single-bundle versus double-bundle reconstruction techniques, preferred graft options (eg, Achilles allograft versus hamstring autograft), whether any PCL remnant should be preserved in reconstruction, and the best surgical approach (eg, tibial tunnel versus tibial inlay) [56]. In the United States, many if not most Grade 3 injuries are currently managed nonoperatively, with surgery primarily reserved for acute, multiligamentous knee injuries [59].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Meniscal injury" and "Society guideline links: Knee pain".)

SUMMARY AND RECOMMENDATIONS

Anatomy and epidemiology – The posterior cruciate ligament (PCL) is the largest and strongest of the intra-articular ligaments of the knee, and the primary restraint to posterior translation of the tibia at the knee joint. PCL injuries are usually sustained from high-energy trauma (eg, motor vehicle collision [MVC]) in association with damage to other knee structures. Sporting activities are the second most common cause of PCL injury. Isolated PCL injuries are relatively uncommon, and athletes with such injuries may continue to function at a high level. (See 'Anatomy and biomechanics' above and 'Epidemiology' above.)

Mechanism of injury – High-energy mechanisms of PCL injury typically involve a posteriorly directed sheer force applied to a flexed knee, as might occur when a knee strikes a dashboard during a MVC. PCL injuries sustained during athletics typically occur when an athlete falls on their flexed knee while the foot is plantar-flexed or from a direct blow to the anterior knee.

Clinical presentation: High energy trauma – The presentation of patients with a PCL injury varies depending upon the type of trauma, associated injuries, and comorbidities. Injuries sustained from high-energy trauma are frequently associated with damage to the posterolateral corner (PLC), anterior cruciate ligament (ACL), medial collateral ligament (MCL), or a combination of these. (See 'Clinical presentation' above.)

The possibility of a complete knee (tibiofemoral) dislocation, a limb-threatening injury, must be considered for any patient complaining of knee pain or dysfunction following high-energy trauma. (See "Knee (tibiofemoral) dislocation and reduction".)

Clinical presentation: Low energy trauma – PCL injuries sustained from low-energy trauma (eg, sporting injuries) may present with gross instability, particularly if associated with injuries to posterolateral knee structures, but typically present with more subtle symptoms, particularly in the case of an isolated PCL injury. Patients may present with a mild to moderate knee effusion, a slight limp, pain in the back of the knee (especially with squatting or kneeling), and loss of terminal knee flexion (final 10 to 20 degrees). Patients suffering from a chronically injured PCL-deficient knee present more often with generalized anterior knee pain that may localize to the medial compartment or patellofemoral joint.

Physical examination – Following high-energy trauma, the knee examination may be limited by pain, swelling, or the need to perform more urgent interventions. Gross instability due to multiple ligament disruptions (eg, knee dislocation) can damage the popliteal artery, putting the limb at risk.

For patients assessed following low-energy trauma or with chronic complaints, perform a careful knee examination paying close attention to joint stability and function. Findings often include gait abnormalities, joint effusion, tenderness in the posterior fossa, and loss of terminal knee flexion. The most useful tests for detecting PCL injury are the posterior drawer test (figure 5), posterior sag sign (picture 5), and quadriceps active test (movie 1 and figure 6). Given the frequency of injury to other knee ligaments in patients with PCL damage, the stability of the ACL, MCL, and lateral collateral ligament (LCL) should be assessed. (See 'Examination findings' above.)

Imaging – For any acute knee injury presenting after moderate or severe trauma in which a PCL injury is suspected and that is accompanied by concerning physical findings (eg, joint effusion, focal bony tenderness, decreased range of motion, limp), we obtain plain radiographs of the knee as part of the initial diagnostic imaging.

If trauma is relatively minor and concerning physical findings are absent, the Ottawa knee rules can be used to guide decisions about plain radiographs. The Ottawa knee rules are reviewed separately. (See "Approach to the adult with knee pain likely of musculoskeletal origin", section on 'Imaging in the evaluation of acute knee pain'.)

We suggest obtaining magnetic resonance imaging (MRI) for all patients in whom a PCL injury is suspected on clinical grounds (eg, blow to flexed knee with positive posterior drawer test) following acute trauma involving the knee. In addition, we suggest obtaining an MRI for patients with a chronic PCL injury suspected on clinical grounds and unrevealing plain radiographs. The accuracy of MRI is limited with chronic PCL injuries. (See 'Approach to diagnostic imaging' above and 'Magnetic resonance imaging' above.)

Indications for orthopedic referral – PCL injuries that meet any of the following criterial should be referred to a knowledgeable orthopedic surgeon:

Grade 3 PCL injuries: Anterior border of medial tibial plateau can be displaced posteriorly beyond the anterior border of the medial femoral condyle (posterior displacement >10 mm)

PCL injuries associated with any fracture or any additional soft tissue injuries of significance (eg, injury of the PLC, ACL, or meniscus)

PCL disruption involving avulsion of the ligamentous insertion at the tibia (see 'Indications for orthopedic consult or referral' above)

Differential diagnosis – When evaluating the patient with a possible PCL injury, other conditions to consider include: ACL injury, PLC and LCL injury, meniscal injury, proximal tibia fracture, knee (tibiofemoral) dislocation, bone contusion, and patellar and quadriceps tendon tear. (See 'Differential diagnosis' above.)

Management – Initial treatment of a PCL injury involves standard management of pain and functional disability, if present. The basic principles of protection, rest, ice, compression, elevation, and medications (PRICE-M) apply. The management of isolated PCL injuries consists primarily of a progressive physical therapy program. For isolated acute PCL injuries, we suggest maintaining the affected knee in full extension for approximately two weeks initially in order to reduce posterior lag. (See 'Initial treatment' above and 'Follow-up care' above and 'Return to sport or work' above and 'Complications and prognosis' above.)

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Topic 94717 Version 22.0

References

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