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Knee
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Knee

Knee
Superficial structures of the anterior knee:
Patella
Kneecap, the largest sesamoid bone in the body; is encased in connective tissue.
Ligaments and connective tissues:
  • Superiorly, the patellar tendon (aka tendon of quadriceps femoris) envelops and attaches the patella to the muscles of the thigh.
  • Inferiorly, the patellar ligament extends inferiorly from the patella to the tibial tuberosity.
  • Laterally, the iliotibial band (aka IT band, iliotibial tract) extends inferiorly along the femur and attaches to the lateral aspect of the tibia to provide structural support to the knee.
  • Medially, the pes anserinus is the collective tendinous insertion of semitendinosus, gracilis, and sartorius on the tibia; they provide additional stabilization to the medial aspect of the knee.
Extracapsular collateral ligaments:
Arise from the fibrous layer of the articular capsule and maintain alignment between the upper and lower leg bones.
  • Medial collateral ligament (aka MCL, aka tibial) from the medial aspect of the femur to the medial aspect of the tibia.
  • Lateral collateral ligament (aka LCL, aka fibular) from the lateral aspect of the femur to the lateral aspect of the fibula.
5 major patellar bursae
Fluid-filled sacs that provide cushioning and allow for smooth movement of the bones
  • Suprapatellar bursa - located deep to the patellar tendon. It is clinically important to realize that this large bursa is continuous with the knee joint, because this anatomical continuity allows spread of infection from the bursa to the joint.
  • Prepatellar bursa - lies superficial to the patella.
  • Subcutaneous infrapatellar bursa - overlies the patellar ligament.
  • Deep infrapatellar bursa - lies deep to the patellar ligament.
  • Anserine bursa - lies between the tibial collateral ligament and the pes anserinus.
Deep structures anterior knee:
  • Transverse ligament - its precise function is uncertain, and its presence is variable.
  • Medial and lateral menisci - plates of fibrocartilage that attach to the articular surfaces of the tibia, which aid in shock absorption and lubricate the joint. They lie outside the synovial cavity but within the joint capsule.
  • Medial and lateral collateral ligaments extend vertically over medial (tibial) and lateral (fibular) sides of the knee.
The medial meniscus attaches to the medial collateral ligament, which makes it more vulnerable to injury than the lateral meniscus.
  • Anterior and posterior cruciate ligaments - lie outside the synovial cavity, but inside the knee joint capsule, and prevent anterior/posterior sliding between the femur and tibia.
The posterior cruciate ligament (aka PCL) extends from the posterior intercondylar area of the tibia and passes superiorly, anteriorly, and medially to attach to the lateral surface of the medial femoral condyle. The anterior cruciate ligament (aka ACL) extends from the anterior intercondylar area of the tibia and passes superiorly and posteriorly to insert on the medial surface of the lateral femoral condyle.
Features of the superficial posterior knee:
  • Tendon of popliteus – extends from the lateral condyle of the femur and inserts on the medial aspect of the proximal tibia.
  • Arcuate popliteal ligament – extends from the fibular head, arches over popliteus, and then merges with the posterior articular capsule.
  • Oblique popliteal ligament - an extension of the semimembranosus tendon that blends with the posterior joint capsule.
Clinical correlations:
  • Patellar reflex involves a tap of the patellar ligament, which elicits knee extension.
  • Genu valgum (aka knock-knee) is when the tibia is angled laterally; it may result from collapse of the lateral aspect of the knee and tearing of the medial collateral ligament.
  • Genu varum (aka bowleg) is when the tibia is angled medially; it may result from collapse of the medial aspect of the knee and tearing of the lateral collateral ligament.
  • Bursitis, a common clinical condition, involves inflammation and swelling of the joint bursa.
  • Cruciate ligament rupture is indicated by posterior and anterior drawer signs:
Posterior drawer sign occurs in the setting of PCL rupture; the tibia slides backwards on the femur. Anterior drawer sign occurs in the setting of ACL rupture; the tibia slides forwards on the femur. A segment of the patellar ligament can be used to repair the anterior cruciate ligament.
  • The unhappy triad (aka O'Donoghue's triad of the knee joint) involves injury to the: tibial collateral ligament, anterior cruciate ligament, and medial meniscus.
  • Popliteal (Baker's) cyst is a common cause of painful swelling behind the knee, which results from knee arthritis, meniscus injury, or tear of the joint capsule.
Related Anatomy
Muscles
Vastus intermedius (of quadriceps femoris) Biceps femoris (long head) (of hamstrings) Gracilis Popliteus Semitendinosus (of hamstrings) Rectus femoris (of quadriceps femoris) Semimembranosus (of hamstrings) Vastus lateralis (of quadriceps femoris) Vastus medialis (of quadriceps femoris) Biceps femoris (short head) (of hamstrings)

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