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 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).

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

PCL: BUCKLING IN THE SAGITTAL PLANE ⁸

Common

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

Uncommon

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

Rare

Ehlers-Danlos syndrome
Marfan's syndrome
Cutis-Laxa

RELIABILITY OF MAGNETIC RESONANCE IMAGING OF THE PCL ²

	Sensitivity [%]	Specificity [%]	Accuracy [%]	NPV [%]	PPV [%]
Polly, et al.	–	100	100	100	100
Mink et al.	92	95	95	–	–
Schlesinger et al.	50	97	95	97	50
Bonamo, unpublished data, 1990	73	100	99	99	100
Fischer et al.	80	99	99	99	57
Mean	74	98	98	99	77

TIBIOFEMORAL RELATIONSHIP ⁸

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

CLASSIFICATION OF KNEE INSTABILITY ⁷

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
Anteromedial	Anterior cruciate Middle and posterior medial thirds
Anterolateral	Anterior cruciate Middle lateral third ± iliotibial band
Posterolateral	Posterior lateral third
Combined	Variable

ASSOCIATED CAPSULOLIGAMENTOUS ABNORMAL LAXITY AND PCL ⁸

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

MR INDICATIONS: PCL INJURY 1995 ⁸

Clinical impression equivocal
Special cases
Research
Revision ligament surgery
Postoperative complaints

MR INVESTIGATION: PCL ⁴

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

Sensitivity, Specificity, Accuracy = 100%

PCL ARTHRITIS ⁸

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

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