Posterior Cruciate Ligament Injury

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Original Editors - Sigrid Bortels as part of the Vrije Universiteit Brussel's Evidence-based Practice project

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Definition/Description

A posterior cruciate ligament (PCL) injury can appear in different forms and degrees. They are less common than anterior cruciate ligament (ACL) injuries because the PCL is much broader and much stronger. A PCL injury can be isolated or combined with other ligamentous injuries. The severity of the injury determines the treatment protocol. The severity can range from a stretch of the ligament to a total rupture of the ligament in the transverse direction. A rupture varies in degrees of disability, from no impairment to severe impairment. [1] In a first degree PCL-injury the damage is limited, there are only microscopic tears. In a second degree there is a partial tear of the ligament and the patient will experience a small feeling of instability. In a third degree the ligament is completely torn. [10] In part 5, Characteristics, these criteria are discussed.

Clinically Relevant Anatomy

The posterior cruciate ligament (PCL) is found in the knee joint and runs from the internal surface of the medial femoral condyle [2] to the centre of the posterior aspect of the tibia plateau (area intercondylaris posterior), 1 cm below the articular surface of the tibia [3]. The PCL and the anterior cruciate ligament (ACL) run in opposite direction to form an ‘X’.
The PCL is twice as thick as the ACL, which means that it is much stronger. Therefore PCL injuries are less common than ACL injuries.

A PCL consists of two inseparable bundles: the wide [3] anterolateral bundle (AL) and the smaller posteromedial (PM) bundle.
The AL bundle is most tight in midflexion of the knee and inward rotation, while the PM bundle is most tight in knee extension and deep flexion. [2][3]

The orientation of the fibers varies between bundles. The AL bundle is more horizontally orientated in extension and becomes more vertical as the knee is flexed beyond 30°. The PM bundle is vertically orientated in knee extension and becomes more horizontal through a similar range of motion. 

The PCL is the major stabilizing ligament of the knee. Its primary function is resisting the posterior displacement of the tibia in relation to the femur. Its secondary function is preventing hyperextension and limiting internal rotation, adduction (varus rotation) and abduction (valgus rotation). [3]

Epidemiology /Etiology

The most frequent mechanism of PCL injury is a direct blow to the anterior aspect of the proximal tibia when the knee is flexed, resulting in posterior translation of the tibia platform. Hyperextension and rotational or varus/valgus stress mechanisms may also be responsible for PCL tears. [1][7]

This occurs mostly during sports, such as football, soccer and skiing. In the study of Fowler and Messieh[8], isolated PCL injuries were commonly reported in athletes and hyperflexion was the most frequent mechanism of injury. [7]

A PCL injury can also result from a car accident in which a posterior force is applied to the tibia when the flexed knee hits the dashboard ('Dashboard injury'). This can be combined with posterolateral ligament injuries if the anteromedial aspect of the knee strikes the dashboard with a varus force applied.[9] Also a bad landing from a jump, a simple misstep or fast changes of direction can result in a PCL injury. [6][7]

The study of Peterson et al. says the incidence of PCL injury in the United States is unknown. They did, however, find a 2% incidence of isolated, asymptomatic and unknown PCL injuries in National Football League predraft physical examinations. An incidence of 3,5-20% was reported for operated, isolated and combined PCL injuries. [1]

Characteristics/Clinical Presentation

Characteristics 



PCL injuries present themselves in several degrees according to the severity.

Grade 1: The ligament has limited damage. There are only microscopic tears in the ligament. It is still able to fulfill its function and stabilize the knee joint even though it has been slightly streched.[10]Grade 2: In contrast to grade I there is a small feeling of instability. The ligament is partially torn and becomes loose.[10]


Grade 3: At this point the ligament is completely torn or removed from the bone. This type of injury is mostly accompanied by a sprain of the ACL and/or collateral ligaments.[10][11]



Clinical Presentation 







A distinction can be made between the symptoms of an acute PCL injury and a chronic injury. [14][15]

Acute PCL injury:
Clinical presentation of an acute PCL injury appears in different ways of which the extent depends on the severity of the injury.

In an isolated acute PCL injury the symptoms will often be vague and minimal[1][12][15], sometimes so that the person doesn’t notice or feel the sprain.[15] This means there is minimal pain, swelling, instability and a full range of motion.[12][15] Also a near-normal gait pattern can be observed.[1]

In a PCL injury combined with other ligamentous injuries it is possible that the following symptoms appear in different extents: swelling[13][14], pain which can be experienced in the anterior and posterior part of the knee[13], a feeling of instability or looseness in the knee[13], limited range of motion[14], difficulty in walking and the knee may be bruised or lacerated.

Chronic PCL injury:
Patients with a chronic PCL injury may or may not have a history of injury.[14] Common complaints in chronic PCL injuries are discomfort in the knee during weight bearing in a semi flexed position (like as- and descending stairs or squatting) and aching in the knee when walking a long distance. There are also complaints about instability and a sense of instability when walking on an uneven surface.[15] Retropatellar pain and pain in de medial compartment of the knee could occur as well.[14][15] Potential swelling and stiffness depend on the degree of associated chondral damage.[15]

Differential Treatments

Acute PCL injury:
The treatment used for an acute, isolated grade I or II sprain is most commonly non-operative.[9][11] The conditions for this treatment are: a posterior drawer less than 10 mm, a decrease in posterior drawer excursion with internal rotation on the femur, less than 5° abnormal rotary laxity and/or no significant increased valgus-varus laxity.[9] [16]
It is usually adequate to relatively immobilize the knee and to use crutches during a two week period for protected weightbearing. Subsequently physical therapy, which mainly includes protective quadriceps muscle rehabilitation, will be a determining factor for further rehabilitation.[9][11]



A 3rd grade injury can also be cured in a non-operative manner. Because of the high probability of injuries to other posterolateral structures, an immobilization period of two to four weeks in full extension is recommended. Because of this the posterior tibial sag is minimalized, which means that less force is applied to the damaged PCL and posterolateral structures. Subsequently physical therapy will mainly consist of quadriceps rehabilitation and straight-leg raise exercises.

If the patient is a young athlete, they will sooner decide to treat the injury operatively. Thay way the athlete will be able to reach his level again. 



A grade III injury is most of the time a combined injury. In this case there will be a surgical intervention (reconstruction of the ligaments). 


Chronic PCL injury:
If the patient has a chronic isolated PCL injury grade I or II, the treatment comprises physical therapy. When the patient develops recurrent pain and swelling a bone scan is recommended. The results of this treatment are controversial. Wind et al[9] recommend surgical intervention when the scan is positive and the patient is unable to modify his activities. Harner et al[11] recommends a reduction in activities until the pain and swelling subside. They do not recommend a surgical intervention. Both articles recommend a surgical intervention in case of a grade III sprain.
A chronic PCL injury can also be a combined injury. Just as in the acute injuries surgery is indispensable.

 

Diagnostic Procedures

There are four different ways of imaging used to diagnose a PCL injury: radiographic imaging (Xrays), magnetic resonance imaging (MRI), bone scans and ultrasound.[9][18] (Diagnostic Imaging for Physical Therapists)
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Radiographic imaging
Standard Xrays include antero-posterior image, tunnel view, sunrise view and a lateral view. This last one is to detect posterior sag and to measure the slope of the proximal tibia. The images are taken in different positions such as bilateral standing and 45° knee flexion weightbearing. 



If an Xray is taken in the early stage post-injury, it can help with the diagnosis of a PCL avulsion fracture. These fractures heal well when operated early. 
In case of a chronic PCL injury plain radiographs can help assess the joint space narrowing, preferably including weightbearing and sunrise view. [9][18]

Stress Xrays are used in addition to the standard radiographs. These images are taken while kneeling, during active hamstring contraction in 90° knee flexion and/or with an instrumented stress device. They allow a noninvasive and objective comparison of the sagittal translation between the injured and intact knee. They also eliminate errors from compliance of soft tissues by measuring skeletal displacement alone. Stress Xrays are superior to plain Xrays when it comes to assessing the magnitude of posterior tibial translation in the injured knee. [9][18]

Magnetic resonance imaging (MRI)
MRI is used to identify whether the tear is complete or incomplete and whether the PCL injury is isolated or other ligamentous, meniscal and/or cartilage structures in the knee are affected as well. Examples of these other injuries are meniscal tears (medial or lateral), osteochondral injury involving the anterior tibia plateau and anterior-lateral femur condyle and ligamentous injuries (ACL, MCL, LCL). The sensitivity and specificity of MRI in acute PCL injury is high.
In case of a chronic PCL tear, MRI scans may appear normal when grade I and II tears are present. [9]

Bone scans
These can be useful in the evaluation of patients with chronic PCL injury who experience pain and instability. The scans can show early arthritic changes before MRI or Xray. These patients have a higher risk of developing articular cartilage degenerative changes, shown by areas of increased radiotracer uptake, most commonly in the medial and patellofemoral compartments. [9][18]

Ultrasound imaging
According to Cho et al[19] ultrasound imaging can be used in the evaluation of suspected PCL injuries, as it is more cost effective than MRI. There are numerous limitations noted in the study and further research is necessary. [18]

Finally a neurovascular examination is necessary, especially when the injuries are combined with damage to other structures. An arteriogram is used to evaluate the vascular status in the limb, pulses are to be documented and a motor/sensory examination must be done. [9]

Outcome Measures

Following instruments could be used to determine the baseline function of the patients knee. The comparison between the results before and after treatment determines the efficacy or progress of the specific given treatment.

K1-1000 arthrometer


Posterior laxity from the resting position and the active anterior translation starting from the resting period can be measured with the K1-1000 arthrometer.[26] Shelbourne et al[26] say there is no statistical relationship between the grade of laxity and the function.[26][28] The posterior drawer test, posterior Lachman test, posterior sag sign en quadriceps active test are physical examination tests used to evaluate the posterior laxity. [27][28][30]

Boyer et al their results of sensitivy and reproducibility demonstrated the reliability of the K1-1000 arthrometer. Ballantyne et al said that the K1-1000 arthrometer has a good reliability, but that the interrater reliability is influenced by the experience of the of the therapist. They recommend that repeated measurements should be taken by the same examiners.

Boyer P, Djian P, Christel P, Paoletti X, Degeorges R. [Reliability of the KT-1000 arthrometer (Medmetric) for measuring anterior knee laxity: comparison with Telos in 147 knees]. Revue de chirurgie orthopédique et réparatrice de l'appareil moteur.  2004 Dec;90(8):757-64.
Level of evidence: 2B

Ballantyne BT, French AK, Heimsoth SL, Kachingwe AF, Lee JB, Soderberg GL. Influence of Examiner Experience and Gender on Interrater Reliability of KT- 1000 Arthrometer Measurements. Physical Therapy. 1995; 75:898-906.
Level of evidence: 3B

Cybex II dynamometer 

Strength testing of the quadriceps muscle can be measured by the Cybex II dynamometer.[26][28] Shelbourne et al[26] confirm there’s no correlation between the grade of laxity and quadriceps muscle strength testing.
The study of Molczyk et al shows intraobserver reliability coefficients of 0.89 to 0.98 for tester one and 0.72 to 0.97 for tester two. The interobserver reliability coefficients ranged from 0.69 tot 0.95 across speeds and movements. No evidence based articles with a higher level of evidence were found.

Molczyk L, Thigpen LK, Eickhoff J, Goldgar D, Gallagher JC. Reliability of Testing the Knee Extensors and Flexors in Healthy Adult Women Using a Cybex II Isokinetic Dynamometer. The Journal of orthopaedic and sports physical therapy. 1991 Jul; 14(1):37-41
Level of evidence: 3B

Subjective assessment 

The two instruments above are objective measurements. Subjective assessment of the knee function is possible with the Noyes knee score Questionnaire and International Knee Documentation Committee (IKDC). Shelbourne et al[29] claim that subjective scores of patients with acute, isolated PCL injuries were independent of grade of PCL laxity and mean scores did not decrease with time from injury.[29]
Noyes et al their results showed a high test-retest reliability of the items of the Noyes knee score Questionnaire (ICC coefficients >0.70) [1]. According to Higgins et al the IKDC is a reliable instrument [2]. 

[1]Barber-Westin SD, Noyes FR, McCloskey JW. Rigorous statistical reliability, validity, and responsiveness testing of the Cincinnati knee rating system in 350 subjects with uninjured, injured, or anterior cruciate ligament-reconstructed knees. The American journal of sports medicine. 1999 Jul-Aug;27(4):402-16.
Level of evidence: 2B

[2]Higgins LD, Taylor MK, Park D, Ghodadra N, Marchant M, Pietrobon R, Cook C. Reliability and validity of the International Knee Documentation Committee (IKDC) Subjective Knee Form. Joint Bone Spine. 2007 Dec;74(6):594-9.
Level of evidence: 1B

Examination

Examination is important to ascertain the grade of injury to determine which treatment should be used.[7] There are two general manners to identify a posterior cruciate ligament injury: physical examination, which is mainly performed by physical therapists and radiological evaluation, which is performed by radiologists.

Physical examination 


1. The posterior drawer test (PDT) is one of the most accurate tests for PCL injury.[7][31] The sensitivity for this test is high, whereas the specificity is low.[32] The test can only be executed when there is no swelling in the knee joint.[7]
   Technique:
   
In normal conditions the medial tibial plateau is approximately one cm anterior to the adjacent medial femoral condyle.[31] The hip is placed in 45° flexion, the knee in 90° flexion and the tibia in 15° external rotation. The foot position is fixed while the examiner pushes the tibia posteriorly to the femur with his thumbs near the anteromedial and anterolateral joint line.[27]
   Results:
   If the examiner cannot palpate this one cm step-off or if the end point is soft when pushing the tibia posteriorly, a PCL injury is suspected.[31] With this test a differentiation between the grades can be made.[31] More than 10 mm posterior translation can indicate a posterolateral ligament complex (PLC) injury.[31][7]
   
   
2. When there is an acute PCL injury, it is not always possible to execute the PDT because of the swelling. In this case the posterior Lachman testis a good alternative, because only 30° knee flexion is required.[27][32]
   
Technique: 
The patient’s knee is flexed in 30° with the tibia in a neutral position. In a deficient knee a posterior sag of the tibia could already be noticed at the beginning of the test. Next the examiner exerts a posteriorly directed force on the tibia.[27]
   Results: 

   A slight increase in posterior translation with the knee at 30° but not at 90° indicates a PLC injury. Whereas increased translation at both position indicates a PCL injury.[27]
   
   
3. Theposterior sag signis the most sensitive physical examination test.[32] The knee is flexed in 90° and the foot is resting on the examination table.[7][31] When the PCL is torn, the examiner can see a “sagging” of the tibia.
   
4. The quadriceps active test has a high specificity compared to other evaluation tests.[32] 

   Technique:

   The knee is flexed in 90° and the foot is resting on the examination table (same starting position as the posterior sag sign). The examiner stabilizes the foot and then asks the patient to slide that foot down the examination table.[31]
   
Results:
   Because of the contraction of the quadriceps muscle group, the examiner observes a reduction of the posteriorly subluxated tibia.[31] This test is easier to interpret in higher-grade and chronic PCL injuries.[27][31]
   
5. The dial test or tibial external rotation test
   Technique:
   The patient lies on his back with both knees flexed in 30° and next in 90° to differentiate PCL from PLC injury. The examiner places both hands on the feet and applied a maximal external rotation force.[27] 

   Results:
   The test is positive if the medial border of the foot (thigh-foot angle) or the tibial tubercle externally rotates 10°-15° more than the not affected side.
   If this occurs in 30° knee flexion but not in 90°, the diagnosis is an isolated PLC injury with an intact PCL. If it occurs at both 30° and 90° a combination of PCL and PLC injury is suggested.[7][27][31]

All tests above are used to detect a PCL injury. Other test exist to evaluate global functions of the knee that could also be damaged in a PCL injury. Examples are the varus/valgus test at 0° and 30° knee flexion, the external rotation recurvatum test [7][27][32] and the reverse pivot shift test.[7][27][31][32]
Apart from these tests, it is also important to evaluate the gait for instability. An indication for instability could be a varus thruststand.[7][31] Static weightbearing alignment should also be checked, because there can be a varus malalignment when the patient has a PCL injury.[7][31]

Medical Management

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Physical Therapy Management

1. RICE- method: Rest, Ice, Compression, Elevation → helps to speed the recovery.

2. Physical therapy: it is a careful rehabilitation program, with specific exercises to stretch and strengthen the leg muscles and to restore function in the knee. Strengthening the quadriceps is the key factor in a successful recovery, because the quadriceps can take the place of the PCL to a certain extent, helping to prevent the femur from moving too far forward over the tibia.
Some therapists recommend the use of a knee brace to support the knee during movement or when the patient is engaged in athletic activity. The use of a brace has not yet been shown effective during exercises.

These are some typically exercises for a PCL injury.

• "Closed chain" exercises (minisquats, gentle stretching, leg press, bicycling, stair-stepper exercises).- Proprioceptive exercises such as balance-board therapy, mini-trampoline balancing.
• Full range of motion should be achieved 4-6 weeks after injury.
• Functional training (for sporters), beginning with forward and backward running and progressing to lateral movements, and sport-specific activities.

Key Research

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Resources

1. http://www.wheelessonline.com/ortho/anatomy_of_the_posterior_cruciate_ligament
2. http://www.arthroscopy.com/sp05001.htm
3.Gerard B. Rondhuis (1196). Knierevalidatie, Elsevier/De Tijdstroom
4.http://orthoinfo.aaos.org/topic.cfm?topic=a00420
5. http://www.hughston.com/hha/a.pcl.htm
6. R. Timothy, M.D. Stapleton (1996). The posterior cruciate ligament, Hughston Health Alert, 8, nr. 1, 2-3.
7. E. Brown David, D. Neumann randall (2004). Orthopedic secrets, 3, Philadelphia, Pennsylvania 
8. http://www.healthcentral.com/encyclopedia/408/264.html

Clinical Bottom Line

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Recent Related Research (from Pubmed)

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