Posterior Cruciate Ligament   

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- Discussion:
    - anatomy of PCL:
    - function and natural history:
           - provides 95% of total restraining force to straight posterior translation of the tibia
             relative to femur;
           - secondary restraints to posterior displacement of the tibia include posterolateral
             capsule, popliteuss, MCL, and POL;
           - secondary action includes resistance to varus, valgus, and external rotation;
           - PCL is more verticle in extension and more horizontal in flexion;
           - hyperflexion mechanism: most common mechanism for an isolated PCL injury:
                  - hyperflexion causes the large anterolateral component to fail but spares the posteromedial
                    band (which is loose in flexion);
                  - this type injury does not involve the secondary restraints and does well with
                     non operative treatment;
                  - dashboard injury (from MVA): may result in severe combined injuries;
           - left untreated PCL ruptures may lead to chronic patello femoral as well as
             medial compartment arthrosis; 
           - references::
                  - Epidemiology of posterior cruciate ligament injuries. 
                  - Effect of PCL Deficiency on In Vivo Translation and Rotation of the Knee During Weightbearing
                    Flexion
                  - A Clinically Relevant Assessment of PCL and Posterolateral Corner Injuries. Evaluation of
                    Isolated and Combined Deficiency
    - associated injuries:
           - ACL and collateral ligament injury (knee dislocation);
           - when PCL injury occurs w/ MCL injury, expect large increase in valgus instability when the knee is
             in full extension;
           - tibial plateau rim fractures:
                  - when these occur with PCL injuries, there is often a severe combined ligament injury or
                    dislocation;
           - posterolateral knee instability;
                  - it is important to distinguish this type of instability from one plane posterior instability;
                  - isolated PCL reconstruction will not correct the rotatory instability and will only partially
                    correct the the one plane instability (since the tendency to externally rotate results in relative
                    shortening of PCL origin and insertion causing ligament laxity);
           - chondral injuries of the knee

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PCL Tears:

   - Examination of the PCLL 
   - Radiographs:
        - Accuracy of Stress Radiography Techniques in Grading Isolated and
          Combined Posterior Knee Injuries
        - Stress radiography for quantifying posterior cruciate ligament deficiency. 
   - MRI Findings:
        - references:
              - The accuracy of selective magnetic resonance imaging compared with the findings of
                arthroscopy of the knee.
              - Medial Segond-type fracture: cortical avulsion off the medial tibial plateau associated with
                tears of PCL and medial meniscus.

- Prognosis / Non Operative Treatment:
    - w/ isolated tear prognosis is generally considered to be favorable except for the long term possibility
      of patellofemoral arthrosis;
    - indications for non op treatment include chronic injury in older less active patients, or an isolated
      grade 2 injury (tibial surface flush w/ surface of femoral condyle;
    - remember that PCL tears from a hyperflexion mechanism will most commonly cause a tear of the
      larger anterolateral where as the posteromedial band remains intact (which is loose in flexion);
                  - this type injury does not involve the secondary restraints and does well with non operative
                    treatment;
    - references:
           - Natural history of the posterior cruciate ligament-deficient knee.
           - The cruciate ligaments of the knee. Girgis FG, Marshall JL, St Monajem ARS: Clin
             Orthop 1975;106:216-231.
           - Natural history of the posterior cruciate ligament-deficient knee.
           - Conservative treatment of isolated injuries to the posterior cruciate ligament in athletes.
           - Arthroscopic evaluation of articular cartilage lesions in posterior cruciate ligament—Deficient knees.
           - Subjective results of nonoperatively treated, acute, isolated posterior cruciate ligament injuries. 
           - Biomechanical verification that PCL reconstruction is unnecessary in the muscle-stabilized knee.

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- Operative Treatment of PCL Tear: 
    - indications for operative treatment: 
           - acute injuries; 
           - active young patient;
           - either isolated grade 3 tears (anterior border of tibia is posterior
              to femoral condyles) or combined injury such as grade 2 injury
              (tibial surface and the femoral condyles are flush) along with
              posterolateral instability;
    - treatment of avulsion frx:
    - PCL reconstruction: