🦵joints

Anterior Cruciate Ligament (ACL) vs Posterior Cruciate Ligament (PCL)

The ACL and PCL are the two cruciate ligaments of the knee, named for their tibial attachments and crossing pattern. The ACL prevents anterior tibial translation and is commonly injured in sports; the PCL prevents posterior tibial translation and is injured in dashboard injuries.

Comparison Table

Feature

Anterior Cruciate Ligament (ACL)

Posterior Cruciate Ligament (PCL)

Tibial attachment

Anterior tibial plateau (between intercondylar eminences)

Posterior tibial plateau (behind intercondylar eminences)

Femoral attachment

Posterior aspect of lateral femoral condyle

Anterior aspect of medial femoral condyle

Primary function

Prevents anterior tibial translation

Prevents posterior tibial translation

Secondary function

Resists internal rotation, valgus stress

Resists external rotation, varus stress

Injury mechanism

Non-contact pivoting, deceleration, landing

Dashboard injury, fall on flexed knee

Frequency

Much more common

Less common

Associated injuries

MCL, menisci ("unhappy triad")

Often isolated, or with posterolateral corner

Clinical test

Lachman (most sensitive), anterior drawer, pivot shift

Posterior drawer, posterior sag sign

MRI finding

Disrupted fibers, bone bruise lateral condyle/posterolateral tibia

Disrupted fibers, bone bruise anterior tibia

Treatment (complete tear)

Usually surgical reconstruction (especially in athletes)

Often conservative (isolated), surgical if combined injuries

Blood supply

Middle genicular artery, poor healing

Middle genicular artery, relatively better healing

Key Differences

→Named by tibial attachment: ACL attaches to Anterior tibia, PCL to Posterior tibia
→ACL prevents anterior tibial translation; PCL prevents posterior tibial translation
→ACL injuries from pivoting sports; PCL from dashboard injuries
→ACL usually requires surgery; PCL often treated conservatively

Clinical Relevance

•Lachman test (ACL): Knee at 20-30° flexion, anterior tibial translation
•Posterior drawer test (PCL): Knee at 90° flexion, posterior tibial translation
•Posterior sag sign (PCL): Tibia sags posteriorly when knee flexed to 90°
•ACL + MCL + medial meniscus = "unhappy triad" (though lateral meniscus may be more common)

Study Tips

✓ACL: Anterior tibia to Lateral femur (posteriorly)
✓PCL: Posterior tibia to Medial femur (anteriorly)
✓ACL = Active sports injuries; PCL = Passive dashboard injuries
✓Lachman test at 20-30° is most sensitive for ACL (hamstrings relaxed)
✓Both are intra-articular with poor healing due to synovial fluid environment

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FAQs

Common questions about this comparison

The Lachman test is performed with the knee at 20-30° flexion, where the hamstrings are more relaxed. In anterior drawer (90° flexion), contracted hamstrings can mask anterior tibial translation by providing posterior force. Additionally, meniscal injuries can affect the drawer test but not Lachman.

The PCL has better blood supply and healing potential than the ACL. Additionally, the quadriceps muscle actively prevents posterior tibial translation during daily activities, compensating for PCL deficiency. The ACL is the primary restraint against anterior translation with no effective muscle compensation.

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