The posterior compartment is primarily composed of the hamstring muscle group.  With the exception of the short head of the ____, all originate from the _____ tuberosity and are innervated by the tibial portion of the _____ nerve.  Recall that the “hamstring part” of the adductor magnus is also innervated by the tibial portion of sciatic nerve.

The posterior compartment is primarily composed of the hamstring muscle group.  With the exception of the short head of the biceps femoris, all originate from the ischial tuberosity and are innervated by the tibial portion of the sciatic nerve.  Recall that the “hamstring part” of the adductor magnus is also innervated by the tibial portion of sciatic nerve.

• semitendinosus
• semimembranosus
• biceps femoris

1. Origin- ischial tuberosity
2. Insertion- medial surface of proximal tibia (the most posterior contribution of the pes anserinus)
3. Innervation- tibial part of sciatic nerve; L5, S1, S2
4. Function- extend thigh, flex leg, internally rotate flexed leg; can contribute to trunk extension

1. Origin- ischial tuberosity
2. Insertion- posteromedial aspect of proximal tibia
3. Innervation- tibial part of sciatic nerve; L5, S1, S2
4. Function- extend thigh, flex leg, internally rotate flexed leg; can contribute to trunk extension

1. Origin
1. Long head- ischial tuberosity
2. Short Head- linea aspera and lateral supracondylar line of femur
2. Insertion- head of fibula (tendon is split by lateral collateral ligament)
3. Innervation
1. Long head- tibial part of sciatic nerve; L5, S1, S2
2. Short Head- common fibular part of sciatic nerve; L5, S1, S2
4. Function- Extend thigh, flex leg, external rotation of flexed leg; can contribute to trunk extension

Neurovasculature

• Four perforating branches of the _____ artery provide the main blood supply and are visualized in the posterior compartment as they emerge after piercing adductor magnus.
•   The superior end of the posterior compartment also receives some supply from branches of the _____ and _____ arteries.
•   The_____ nerve passes lateral to the ischial tuberosity and into the posterior compartment.  It lies in a plane between the adductor magnus and the hamstrings as it descends.  The _____ nerve usually divides into separate _____ and _____ branches near the superior angle of the popliteal fossa.  The _____ nerve follows the medial border of biceps femoris and its tendon along the superolateral boundary of the popliteal fossa.  The _____ nerve continues distally into the popliteal fossa. 

• Four perforating branches of the deep femoral (profunda) femoral artery provide the main blood supply and are visualized in the posterior compartment as they emerge after piercing adductor magnus.
•    The superior end of the posterior compartment also receives some supply from branches of the medial and lateral circumflex femoral arteries.
•    The sciatic nerve passes lateral to the ischial tuberosity and into the posterior compartment.  It lies in a plane between the adductor magnus and the hamstrings as it descends.  The sciatic nerve usually divides into separate tibial and common fibular (peroneal) branches near the superior angle of the popliteal fossa.  The common fibular nerve follows the medial border of biceps femoris and its tendon along the superolateral boundary of the popliteal fossa.  The tibial nerve continues distally into the popliteal fossa. 

• Superolateral – Biceps Femoris
• Superomedial – Semimembranosus, Semitendinosus
• Inferolateral – Lateral Head of Gastrocnemius
• Inferomedial – Medial Head of Gastrocnemius
• Posterior (Roof) – Skin & Fascia
• Anterior (Floor) – Femur, Oblique Popliteal Ligament (thickening of posterior knee joint capsule), Popliteus and its fascial covering.

• small saphenous vein
• popliteal artery
• popliteal vein
• tibial nerve
• common fibular nerve
• popliteal lymph nodes & vessels

1. Small Saphenous Vein 

1. Popliteal Artery 

1. Popliteal Vein 

1. Tibial Nerve

1. Common Fibular Nerve

Articular Capsule 

• Anterior – Quadriceps tendon, patella and patella ligament replace the capsule.   The patellar retinacula are lateral expansions from the quadriceps tendon, patella and patella ligament that extend to the femoral and tibial condyles.
• Posterior – The capsule is perforated by the popliteus muscle.  The arcuate popliteal ligament is a thickening of the capsule arching over the exiting popliteus.  The oblique popliteal ligament is a capsular thickening that extends from the semimembranosus muscle and runs parallel to the popliteus.
• Medial – The medial (tibial) collateral ligament blends with the capsule.
• Lateral - The iliotibial tract blends with the capsule.  The lateral (fibular) collateral ligament does not blend with the capsule.

_____ – Lines the fibrous capsule, creating an envelope for the synovial fluid that bathes the tibiofemoral and patellofemoral articular surfaces.

• The _____, although within the fibrous capsule, are not within the synovial envelope.  Rather, the outer surface of the synovial membrane attaches to the edges of the _____.  
• Posteriorly, the synovial membrane reflects inward into the intercondylar region, therefore excluding the cruciate ligaments from the synovial envelope.  A bi-layer fold of synovial membrane, the _____, is created anterior to these structures by the reflection.
• The synovial cavity has a large upward extension deep to the quadriceps tendon, _____

Synovial Membrane – Lines the fibrous capsule, creating an envelope for the synovial fluid that bathes the tibiofemoral and patellofemoral articular surfaces.

• The menisci, although within the fibrous capsule, are not within the synovial envelope.  Rather, the outer surface of the synovial membrane attaches to the edges of the menisci.  
• Posteriorly, the synovial membrane reflects inward into the intercondylar region, therefore excluding the cruciate ligaments from the synovial envelope.  A bi-layer fold of synovial membrane, the infrapatellar synovial fold, is created anterior to these structures by the reflection.
• The synovial cavity has a large upward extension deep to the quadriceps tendon, the suprapatellar bursa.

• patellar l.
• lateral (fibular) collateral l. (LCL)
• medial (tibial) collateral l. (MCL)
• oblique popliteal l. and popliteal l. 

• rounded, cordlike, strong
• inferior lateral epicondyle of femur to lateral head of fibula
• tendon of popliteus passes deep to it separating it from the lateral meniscus
• not part of the fibrous capsule

• flat band, strong (weaker then LCL)
• medial epicondyle of femur to superior medial surface of tibia
• at midpoint, attached to medial meniscus
• most frequently injured knee ligament; injury of the medial meniscus may be concurrent because of attachment

• thick, strong
• patella to tibial tuberosity
• blends with the medial and lateral patellar retinacula

 Oblique Popliteal Ligament and Popliteal Ligament (less important than other extracapsular l.)

• Oblique Popliteal Ligament- reflected/recurrent expansion of the semimembranosus tendon; reinforces posterior capsule; superolateral to inferomedial 
• Popliteal Ligament- expansion of posterolateral capsule that arches over popliteus

- these ligaments are within the knee joint; recall that they are extrasynovial (not within the synovial envelope)  

• Anterior Cruciate Ligament
• Posterior Cruciate Ligament
• Menisci (medial and lateral)

• anterior intercondylar area of tibia to posterior part of medial side of lateral femoral condyle
• slack in flexion, taut in extension; prevents anterior displacement of tibia on femur and knee hyperextension
• weaker than PCL

• posterior intercondylar area of tibia to anterior part of lateral surface of medial femoral condyle
• taut in flexion; prevents posterior displacement of tibia on femur, helps prevent knee hyperflexion

Menisci - crescent shaped plates of fibrocartilage on the articular surface of the tibia that serve to deepen the surface and attenuate compressive forces (“shock absorbers”).  _____ attach the menisci to the tibial condyles on the periphery and the _____ tethers the menisci together anteriorly.

Menisci- crescent shaped plates of fibrocartilage on the articular surface of the tibia that serve to deepen the surface and attenuate compressive forces (“shock absorbers”).  Coronary ligaments attach the menisci to the tibial condyles on the periphery and the transverse ligament of the knee tethers the menisci together anteriorly.

• C-shaped plate of fibrocartilage on the articular surface of the medial tibial plateau
• adhered to deep surface of the tibial collateral ligament

• circular shaped plate of fibrocartilage on the articular surface of the lateral tibial plateau
• smaller and more freely movable than the medial meniscus
• separated from the fibular collateral ligament by the tendon of popliteus
• a small ligamentous band, the posterior meniscofemoral ligament,  extends from the posterior aspect of the lateral meniscus to the PCL and medial femoral condyle

1. Flexion- performed principally by the hamstrings; Limited by contact between the calf and thigh.

2. Extension- Performed principally by the quadriceps; Limited by the cruciate and collateral ligaments.

3.  Internal Rotation (tibia on femur- the point of reference for rotation of the knee is the tibia!) - Performed by semitendinosus, semimembranosus, sartorius, popliteus;  checked by the cruciate ligaments.

4. Lateral Rotation (of tibia on femur) - Performed by biceps femoris; Checked by the collateral ligaments.

5. Locking/Unlocking of the Knee - With the foot on the ground, when the knee is extended the knee passively “locks” by internal rotation of the femur on the tibia (this is the same as external rotation of the knee).  In the locked position, the musculature can relax without making the joint too unstable.  To “unlock” the knee, the femur externally rotates (largely by contraction of the popliteus) so that flexion can occur. 

Innervation- the knee joint is provided by branches of the _____, _____, _____, and _____ nerves.

Blood supply- of the knee joint is from 

• the descending _____ branch of the femoral artery
• the superior (2), inferior (2) and middle _____ arteries (branches of the popliteal artery)
• the anterior and posterior recurrent branches and fibular circumflex (branches of the anterior tibial artery). 

Bursae Around the Knee (major/clinically important ones - 4)

• suprapatellar bursa
• infrapatellar (subcutaneous & deep) bursae
• subcutaneous prepatellar bursa
• anserine bursa

Lie superficial and deep to the patellar ligament.

• _____ Ligament – Damaged from blow to the lateral side of knee.  Because the medial meniscus is firmly adherent to the MCL, twisting strains of this ligament may tear or detach the medial meniscus from the fibrous capsule.

• Medial Collateral Ligament – Damaged from blow to the lateral side of knee.  Because the medial meniscus is firmly adherent to the MCL, twisting strains of this ligament may tear or detach the medial meniscus from the fibrous capsule.

• _____ Ligament – Damaged from blow to the medial side of knee (uncommon); may be associated with detachment of biceps femoris an/or injury to the common fibular nerve

• Lateral Collateral Ligament – Damaged from blow to the medial side of knee (uncommon); may be associated with detachment of biceps femoris an/or injury to the common fibular nerve

• _____ Ligament – Damaged from posteriorly directed force/blow to tibia (tibia) 

• Posterior Cruciate Ligament – Damaged from posteriorly directed force/blow to tibia (tibia) 

• “_____” – MCL, ACL and medial meniscus injury.

• “Unhappy Triad” – MCL, ACL and medial meniscus injury.

• _____ Tears – More common in medial meniscus; usually a twisting force in weight bearing

• Meniscal Tears – More common in medial meniscus; usually a twisting force in weight bearing

• ______ Syndrome – Pain deep to the patella from abnormal mechanics, direct blow to the patella or osteoarthritis; may also be inflammation of peripatellar soft tissue (e.g. medial retinaculum) from repetitive abnormal mechanics.

• Patellofemoral Syndrome – Pain deep to the patella from abnormal mechanics, direct blow to the patella or osteoarthritis; may also be inflammation of peripatellar soft tissue (e.g. medial retinaculum) from repetitive abnormal mechanics.

• _____ – Inflammation of the bursae commonly due to friction, compressive forces or wounds.  

• Bursitis – Inflammation of the bursae commonly due to friction, compressive forces or wounds.