Dr. Pomeranz's Ultimate Guide to :

MRI of the Knee

Posterior Cruciate Ligament


The posterior cruciate ligament (PCL), along with the anterior cruciate ligament, stabilises the knee joint. The PCL originates from lateral side of posteromedial femoral condyle and attaches to the extreme posterior intracondylar tibial region.8

posterior cruciate ligament  posterior cruciate




Posterior Cruciate Ligament: Proposed Function

  • Resists posterior drawer
  • Resists hyperextension
  • Limits internal rotation
  • Limits hyperextension
  • Prevents varus and valgus8




Posterior Cruciate Ligament: Bundles

  • Anterolateral - Approximately 65% of PCL, and important in flexion of the knee
  • Posteromedial - Approximately 35% of PCL, and important in extension of the knee




Posterior Cruciate Ligament: Biomechanics

  • Internal tibial rotation tightens PCL; external tibial torsion relaxes it
  • Hamstring activity decreases PCL strain from 0-75 degrees flexion
  • Varus, valgus moments only minor effects on PCL strain
  • Strain with posteromedial band least at 15 degrees flexion, 9 degrees greater at 120 degrees and 3 degrees greater at full extension3




Posterior Cruciate Ligament: Injuries

Need to determine if the injury is:

  • Complete with disruption
  • Interstitial
  • Partial

Note: Correlate with physical findings

Mechanism of injury

  • Fall on flexed knee-usually complete disruption mid substance
  • Fall on hyperflexed knee-frequently interstitial in situ failure8




Posterior Cruciate Ligament: Mechanism of Injury

  • Hyperextension: peels proximal attachment from femur
  • Hyperflexion: tears near tibial attachment
  • Hyperextension: ACL also torn
  • Varus and valgus rotation: collateral also torn Fowler, AAOS Course, 1993
  • Most from vehicular accidents [94%], Trickey, JBJS 1968
  • Athletic injury [40-76%], Kennedy et al, Orthop Digest 1979
  • Most from hyperflexion, not blows to proximal tibia Fowler & Messieh, AJSM 1980 6




Posterior Cruciate Ligament: Mechanism Suggesting Injury

  • Blow to proximal tibia: flexed knee
  • Hyperflexion of knee: foot in plantar flexion
  • Fall on flexed knee with:
    • Foot dorsiflexed: no injury to PCL, strikes patella
    • Foot plantar flexed, PCL at risk, strikes tibial tubercle
  • Often as a result of high energy trauma, though may be secondary to trivial injury 10
  • Posterolateral rotatory instability (PLRI)
  • Anteromedial rotatory instability (AMRI)




Posterior Cruciate Ligament: MRI Assessment

  • Atrophy, common with chronic injuries
  • Even with high grade tears, PCL shape is often preserved
  • The extent of signal and its cross-sectional involvement of the ligament allows grading
  • Bone contusions with PCL tear are not as consistent as with ACL tear, but meniscal injuries near the roots either medially or laterally
  • Retraction of the PCL with complete tear is rare
  • Avulsion injury, particularly off the tibial end, is uncommon, associated with flexion injury and may not be seen arthroscopically 8




Posterior Cruciate Ligament: Physical Exam

  • Straight abnormal posterolaxity 10 mm or less [range 4-10 mm], knee at 90° flexion
  • With abnormal posterior laxity decreases internal rotation of tibia, knee at 90° flexion
  • Abnormal external tibial rotation less than 5 degrees, knee at 30° flexion
  • Effusion, usually mild
  • Pretibial abrasion or contusion
  • Varying degrees of decreased range of motion, limpness, tenderness 8




Posterior Cruciate Ligament: Treatment

  • PCL injuries and associated ligamentous laxity resulting in multidirectional instability have a high probability of unsatisfactory results
  • Conservative treatment failures include: chondromalacia patellae, meniscal tears, degenerative medial condyle (Reference: Torg et al, Clin Orthop 1989)
  • 40% greater chance of unsatisfactory result in the multidirectional group if treated conservatively
  • A survey of the Herodicus Society [58 members] showed that the vast majority favored initial conservative treatment of all grades of isolated PCL tears (Reference: Bernard Bach, 1992)
  • Repair of bony avulsion of PCL results in excellent static and functional results
  • Isolated PCL interstitial tear: conservative treatment 8
  • PCL injury combined with other major ligament injuries: General consensus weighs heavily toward operative treatment 3




Posterior Cruciate Ligament: Conservative Treatment of Tears

  • Splint for comfort: 0 to 2 weeks
  • Rapid controlled mobilization
  • Weight bearing: as tolerated
  • Anti-inflammatory Rx 8
  • Quadriceps rehabilitation early Hamstrings rehabilitation later 5
  • Return to full activities following isolated PCL injury: two to eight weeks 1




Posterior Cruciate Ligament: Poor Functional Result with Injury

  • Strong consideration for surgery for those with multidirectional injuries 11
  • Patellar dislocations may be associated with PCL injury 11

Poor functional result more likely if PCL injury is associated with:

  • Meniscectomy
  • Quadriceps weakness
  • Chondromalacia patellae or patellar instability
  • LCL injury 8




Posterior Cruciate Ligament: Pearls

  • The PCL is generally 15-20 mm and is blacker, thicker, curved, and more easily visualized than the ACL
  • It is contained in a strong sheath, but is extrasynovial
  • It courses from anterosuperior to posteroinferior, appearing in the medial side of the femoral tunnel.
  • Contiguous with one major bundle, may appear excessively taut with knee flexion or buckled with hyperextension [buckling may simulate ACL tear, PCL buckling is a sign of ACL laxity]
  • Wide area of attachment
  • Attaches to the lateral side of the medial femoral condyle and into the recess in the posterior aspect of tibia
  • More hypointense than the ACL
  • Arcuate shape in extension
  • Straight shape in flexion
  • 30% thicker than the ACL [16-18 mm]
  • Two times as strong as ACL or MCL
  • Insufficiency is associated with quadriceps tendinitis, patellar grinding and premature degenerative disease
  • Intra-articular but extrasynovial location
  • Accessory ligaments of Humphrey [in front of the PCL] or Wrisberg [behind the PCL] are seen in 90% of nor­mal studies
  • Tears of the PCL are repaired by suturing +/- graft augmentation
  • Avulsions of the tibial insertion are repaired with screw fixation or pull-through procedures
  • Bone contusions with PCL tear are not as consistent as with ACL tear; however, meniscal injuries near the meniscal roots either medially or laterally may occur
  • Retraction of the PCL with complete tear is rare 8




Posterior Cruciate Ligament: Evaluations and Pitfalls of Injuries on MRI

  • Atrophy, common with chronic injuries
  • Even with high grade tears, PCL shape is often preserved
  • The extent of signal and its cross-sectional involvement of the ligament allows grading
  • Avulsion injury, particularly off the tibial end, is uncommon

Pitfalls in the Diagnosis of PCL Injury

  • Acute blood in the PCL sheath may simulate a higher grade of injury than really exists
  • Visibility is difficult with edema
  • A bone flake or avulsion injury, particularly seen in children, may be missed on MR without the plain film and is often associated with a large hemarthrosis
  • Sheath inflammation with arthritis may obscure the PCL; this is particularly profound on T1 or proton density imaging
  • High grade PCL tears still do not often retract
  • Remember that a PCL tear may be profound on MR and may be missed arthroscopically, since the tibial end of the PCL is difficult to visualize with the arthroscope when the ACL is intact, regardless of the experience of the arthroscopist 8



Posterior Cruciate Ligament: Example

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This 53-year-old male has left knee pain since a fall at work. You are shown proton density (image 1) and proton density with fat-suppression (image 2) images with abnormality labeled (green arrow).


image57  image32

  Image 1 - Sagittal PD                                            Image 2 - Sagittal PD


The diagnosis is posterior cruciate ligament (PCL) avulsion fracture with typical pretibial abrasion from impaction with the knee in flexion as mechanism of injury.

Typical mechanism of injury is a blow to the knee in flexion (“dashboard or aviator injury”), usually with contusion of the anterior prepatellar soft tissues (image 2, pink arrows).

Most posterior cruciate ligament tears are not surgically treated. Surgical treatment is indicated if there is fragment displacement, diastasis, or an accompanying posterolateral corner injury so as to prevent posterolateral rotary instability (PLRI), or posterolateral recurrent instability syndrome. Sometimes, with a posteromedial corner semimembranosus injury, the PCL may also have to be repaired.

Typically, tears of the PCL itself do not produce retraction, separation or gapping of the PCL fibers. Rather, there is bleeding and interstitial injury of the ligament even though functionally the ligament is no longer a source of tibial stability and restraint.

However, when there is a fracture at the PCL attachment to the tibia in the PCL notch, surgery may be indicated. A. The choices are immobilization or casting if the fragment is close to the main bone. This might help precipitate a union. B. On the other hand, if there is a substantive gap, rotation, or angulation, the fragment may require repositioning and external fixation from a posterior approach.





Posterior Cruciate Ligament: Appendix



  • Overextension of the knee
  • ACL laxity
  • ACL acute tear
  • ACL chronic tear
  • Oversizing of anterior cruciate ligament graft


  • Distal posterior cruciate ligament tear
  • Avulsion of the posterior cruciate ligament tibial insertion


  • Ehlers-Danlos syndrome
  • Marfan's syndrome
  • Cutis-Laxa





Specificity  [%]

Accuracy  [%]





Polly, et al.





Mink et al.




Schlesinger et al.






Bonamo, unpublished data, 1990






Fischer et al.













  • Treatment decisions for PCL injury are based on the degree of PCL laxity
  • Normal tibiofemoral relationship: tibia 1 cm anterior to the femoral condyles (90° of flexion)

Laxity Grades

Grade I

0.5 cm difference in step-off as compared with the normal knee

Grade II

1 cm difference in step-off (anterior tibia and femoral condyles are flush)

Grade III

Anterior tibia is lying posterior to the femoral condyles

Note: The majority of knees with Grade II and lower PCL laxity are treated non-operatively



Knee Instability

Structures Frequently Torn

Straight medial

Anterior cruciate

Posterior cruciate

Middle and posterior medial thirds

Straight lateral

Anterior cruciate

Posterior cruciate

Middle and posterior lateral thirds

Straight anterior

Anterior cruciate

Posterior cruciate

Middle medial and lateral thirds

Straight posterior

Posterior cruciate

Posterior medial and lateral thirds


Anterior cruciate

Middle and posterior medial thirds


Anterior cruciate

Middle lateral third ± iliotibial band


Posterior lateral third





Four entities

  • Posterolateral: Rare to be isolated
  • Posterior/posterolateral: most common
  • Anterior/posterolateral: next most common
  • Posteromedial: rare

PCL: Incidence 9

  • PCL injury in 3% of all acute hemarthroses
  • Recognition of PCL injuries has led to belief these are more common than once thought
  • MR has corroborated this


  • Clinical impression equivocal
  • Special cases
  • Research
  • Revision ligament surgery
  • Postoperative complaints


  • 201 Consecutive MRIs and knee injuries: Findings confirmed by arthroscopy
  • 190 Normal PCL
  • 13 Torn PCL

Sensitivity, Specificity, Accuracy = 100%


  • Approximately 5-8% patients with isolated PCL injuries progress to post-traumatic arthritis [much lower than ACL]
  • Higher incidence reported in patients with more than isolated PCL laxity



Posterior Cruciate Ligament: References

  1. Bergfeld, AAOS Inst Course #208, 1990
  2. Bonamo JJ, Saperstein AL. Contemporary MRI of the knee. In Fitzgerald SW, ed. MRI Clinics of N America. 2: 491, 1994.
  3. Fowler and Messieh, AJSM 1980.
  4. Gross et al. AJSM 20: 732, 1992
  5. Kannus et al. J Trauma, 12: 110, 1991
  6. McCarroll et al, Phys Sp Med. 1985.
  7. Munk PL, Helms CA. MRI of the knee. Gaithersburg, Aspen Publishers Inc. 1992: 80.
  8. Pomeranz SJ. Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
  9. Shelbourne & Johnson, "The Knee," 1994
  10. Trickey, JBJS 1968
  11. Warren R. AAOS Course 1993