Knee Complex Study Notes

The knee complex is composed of two distinct articulations located within a hinge joint capsule:
- Tibiofemoral Joint
- Patellofemoral Joint
It plays a major role in supporting the body during dynamic and static activities, by facilitating the transmission of forces from the ground to the body.

The knee is responsible for moving the body during:
- Sitting and squatting activities (eccentric control as one sits down)
- Locomotor activities, controlling and transferring body weight.
In an Open Kinematic Chain (OKC), the knee provides mobility for the foot in space.

The primary bones involved in the knee complex include the fibrillator and tibial structures:

Distal Articular Surface
- Medial Condyle: Distal enlarged portion that articulates with the tibia medially.
- Lateral Condyle: Distal enlarged portion that articulates with the tibia laterally.
- Lateral Epicondyle and Medial Epicondyle: Rough surfaces for muscle attachment.
- Patellar Surface: Anterior union of the two condyles; makes contact with the patella.
- Intercondylar Fossa: Separates the two condyles posteriorly and serves as a boundary for the popliteal fossa.

Proximal Articular Surface:
- Medial Condyle: Expanded medial surface located proximally.
- Lateral Condyle: Expanded lateral surface located proximally.
- Intercondylar Tubercle: Non-articular area that separates the two tibial condyles, into which internal ligaments attach.
- Tibial Tuberosity: Roughened area on the anterior border that receives the patellar ligament.

Head of Fibula: Upper slender end that articulates with the lower surface of the lateral tibial condyle, but does not enter the knee joint.

Functions mainly as an anatomical pulley and reduces friction between the quadriceps tendon and the femoral condyle.
The ability of the patella to slide on the femoral condyle is crucial for maintaining knee motion.
This joint is classified as a modified plane joint, which is the least congruent joint in the body.
An important function of the patella is to improve the efficiency of knee extension by holding the quadriceps tendon farther forward.

Meniscus: Asymmetric C-shaped fibrocartilaginous joint disks that help deepen the tibial articular surfaces and facilitate better adaptation with the femoral condyles.
- Primarily attached to the tibia via the meniscotibial ligament (coronary ligament), is avascular in its inner two-thirds and partly vascular in the outer one-third, which limits its regeneration potential.
- Functions:
- Shock absorption by directing the femoral articular condyles.
- Lubrication through distribution of synovial fluid.
- Improve weight distribution by increasing contact between the condyles.
- Participate in locking mechanism of the joint by directing the femoral articular condyles.

Menisci are most prone to being torn during rotation of the femur over a fixed tibia when the knee is flexed, leading to pain and swelling in the knee joint.

The joint capsule consists of interlacing fibers reinforced by structures such as the oblique popliteal ligament and is associated with the semimembranosus tendon.
The cavity is extensive and is supported by ligaments that control excessive knee extension, varus/valgus stresses, and help stabilize the knee joint during motion.

Medial Collateral Ligament (Tibial): Resists valgus stress, is attached to the medial aspect of the femur and tibia, consists of two layers (superficial and deep).
Lateral Collateral Ligament (Fibular): Resists varus stress, does not blend with the joint capsule but stabilizes the knee.

Anterior Cruciate Ligament (ACL): Prevents anterior displacement of the tibia on the femur and restricts external rotation of the tibia in flexion.
Posterior Cruciate Ligament (PCL): Prevents posterior displacement of the tibia beneath the femur and checks extension/hyperextension.

Formed from the tensor fasciae latae muscle, it reinforces the anterolateral aspect of the knee.

Assists in checking valgus stresses, passes from the medial tibial condyle to the posterior aspect of the joint capsule.

The motions of the knee joint include:
- Flexion-Extension
- Axial Rotation:
- Occurs when the knee is flexed.
- External rotation is about twice as large as internal rotation.
Q Angle: The angle formed between a line from the anterior superior iliac spine (ASIS) to the mid-point of the patella and a line from the tibial tuberosity to the mid-point of the patella, with a normal angle being 10 to 15 degrees measured in full extension or slightly flexed.

The femoral condyle surfaces are convex while the tibial surfaces are relatively flat, limiting bone stability.
Pathologies include genu valgum (knock-knee) and genu varum (bow-leg).

Include Rectus Femoris, Vastus Medialis Oblique, Vastus Lateralis, and Vastus Intermedius.

Include Biceps Femoris (both heads), Semitendinosus, Semimembranosus, Gastrocnemius, Plantaris, Popliteus, Adductor Gracilis, and Sartorius.

Defined as a loss of mechanical advantage of the quadriceps muscle caused by muscle atrophy, diminishing power, adhesion formation, or effusion related to meniscal injury.