Knee joint is the largest joint in human body. Body weight passes through knee joint during standing, walking and jogging. Knee joint is used consistently during daily activities. Knee joint deteriorates following excessive use of knee joint, trauma, infection or inflammation. Wear and tear of knee joint causes arthritis and ligamental sprain in later part of life. Knee joint is also known as hinge joint because of the movement like hinge of the door. Knee joint links upper leg (femur bone) with the lower leg (tibia and fibula bone). The knee joint is formed by femur, tibia, fibula and patella (knee cap). Knee joint controls movement of lower leg resulting in flexion and extension. Knee joint also achieves minimum external and internal rotation. Knee joint is a synovial joint since the joint is enclosed within capsule of synovial membrane. The cartilages line the joint surface of the femur, tibia and patella. Knee joint is supported by several tendon, ligament, muscle and bursa.
Bones of Knee Joint
Four bones participate in knee joint: Femur, Tibia, Fibula and Patella.
- Longest and strongest bone in the human body.
- Proximal end forms a hip joint
- Proximal end (upper end) is the head of femur, which is like ball in shape
- Distal end (lower end) is made up of medial (inner) and lateral (outer) condyle
- The bottom flat articulating surface forms a link with tibia to form a knee joint
- The front surface of the femur links with patella to form a Patello-Femoral joint.
- The tibia is one of the two bones of lower leg that links upper leg (thigh) and foot.
- The tibia forms a knee joint by getting linked with femur at the upper end.
- The tibia links with fibula at upper end to form a part of knee joint and links at the lower end to form a part of ankle joint.
- The flat surface of proximal end (upper end) of tibia is divided in to medial (inner) and lateral (outer) epicondyle.
- The medial and lateral epicondyle of tibia forms a link to form a knee joint with medial and lateral condyle of femur.
- The fibula lies along the lateral side of tibia.
- The fibula is shorter bone than tibia.
- The fibula does not articulate with the femur or patella.
- Most of the weight is transmitted through the tibia and occasionally during walking or standing partial weight is transmitted through fibula.
- The patella is uneven oblong bone also known as kneecap.
- The patella is largest sesamoid bone in the human body.
- The back (posterior) articulating surface of patella links with femur to form patella-femoral joint.
- The patella is enclosed and covered by the tendon of the quadriceps femoris muscle.
Knee joint has two divisions as follows-
- Minor Knee Joint- also known as Femoro-Patellar articulation. The joint is a link or articulation between femur and patella.
- Major Knee Joint- also known as Femoro-Tibial articulation. Joint is a link or articulation between femur and tibia.
Minor Knee Joint: Femoro-Patellar Articulation
The patella is also known as kneecap. The inner surface of patella is in contact with anterior (front) surface of lower end of femur known as patellar groove. Patella slides over patellar groove of femur during flexion and extension. Inner surface of Patella is lined by a smooth cartilage, which allows smooth movement of patella over the anterior surface of femur.
Major Knee Joint: Femoro-Tibial Articulation
Femur is linked with tibia at medial and lateral side. The medial and lateral articulating end of femur and tibia bone are known as medial and lateral condyles. Lateral condyle of femur is larger in size than medial condyle. Articulating surface is covered with smooth cartilages. Lateral condyle is wider in front and medial condyle is uniform in width from anterior to posterior surface. The smooth plane and variable width of articulating surface permits rolling movement to achieve flexion and extension of the knee joint as well as sliding movements.
Knee joint is also known as synovial joint. Joint is covered from outside by a thin synovial membrane forming a capsule.
- Synovial membrane is attached to circumference of the femur and tibial cartilage within the knee joint.
- Synovial membrane protrudes anteriorly as supra-patellar bursa and posteriorly as medial and lateral femur condyle extension.
- The synovial membranes secretes viscous fluid known as synovial fluid.
Knee Joint Capsule
Knee joint capsule is formed by synovial membrane and thin fibrous layers.
- Knee joint capsule encloses knee joint.
- Capsule protects internal structure of the knee joint from infection and trauma.
- Capsule acts as a barrier between internal and external structure of knee joint.
- The fibrous layer continues laterally and medially as thick band of fibrous tissue and become the intrinsic ligaments of the knee joint.
Cartilages of Knee Joint
- Cartilages of the knee joint are either fibrous cartilage or hyaline cartilage.
- Fibrous cartilage covers articulating surface of femur and tibia.
- Fibrous cartilages have higher tensile strength and durability.
- Knee joint cartilage covers the articulating surface of femur and tibia.
Medial and lateral meniscuses are made up of fibrous cartilage. Surface of meniscus are covered by hyaline cartilage. Hyaline cartilage provides smooth surface for sliding and rolling movements of knee joint. Hyaline cartilages do not self-restore and are prone to wear and tear. Newly formed cartilages are mostly fibrous cartilages. Fibrous cartilages often build cracks and uneven surface causing osteoarthritis.
Anatomy of Menisci-
- Menisci are crescent medial (inner) and lateral (outer) cartilages.
- Menisci are wedge or "C" shaped.
- Menisci links femur and tibia to form a knee joint.
- The medial and lateral menisci lies between medial and lateral condyle of femur and tibia.
- Menisci are hyaline cartilages that consist of connective tissue, extensive collagen fibers and cartilage cells.
- Menisci also functions as shock absorber.
- Surface of menisci facing tibia and femur are shaped to optimize joint movements.
- Synovial membrane is attached to outer surface of menisci.
- The outer surface (circumference) of menisci is thick and convex in shape and middle or central portion of menisci are thin and concave in shape.
- The outer layer is well vascularized and inner layer is avascularized (no blood supply).
- Lateral menisci is wider or thicker and occasionally gets caught between femur and tibia resulting in "clucking".
- The medial meniscus firmly adheres to the deep surface of the MCL medially, the ACL anteriorly, and the PCL posteriorly.
Functions of Menisci-
- Protects End of the Bone
- Shock Absorber
- Smooth Joint Movement
- Presence of cartilage widens and deepens the articulating surface between the femoral condyles and the tibia.
- Menisci often are cracked in the center, which has least blood supply and healing is slow or none.
- Menisci are often torn with twist or turn of the knee joint.
Cause of Complication-
- Twist and turn of the knee joint- forceful rotation of knee joint
- Abnormal bend of knee joint while coming down the staircase or slope.
- Automobile Accident
- Work Accident
- Fall on Slippery Surface
Ligaments of Knee Joint
Ligaments are bundle of thick and tough fibrous tissue. Ligament links the bones to form a joint.
Function of Ligament-
- Provides stability by limiting movements
- Links joint together
- Prevents joint subluxation and dislocation
- Protects articulating capsules and synovial membrane
Ligaments of knee joint are divided in to following 2 groups-
A. Intra-Capsular Ligament
B. Extra-Capsular Ligament
A. Intra-Capsular Ligaments are as Follows-
- Cruciate Ligament
- Anterior Cruciate Ligament (ACL)
- Posterior Cruciate Ligaments
- Transverse Ligament
- Menisco-Femoral Ligament
- Anterior Menisco-Femoral Ligament
- Posterior Menisco-Femoral Ligament
- Menisco-Tibial Ligament
B. Extra-Capsular Ligaments are as Follows-
- Lateral Collateral Ligament
- Medial Collateral Ligament
- Patellar Ligament
Anterior Cruciate Ligament (ACL)-
- Ligament is also known as ACL.
- ACL prevents anterior slippage or subluxation of tibia.
- ACL is attached to medial meniscus and intercondylar (between medial and lateral condyle) surface of tibia anteriorly (front).
- ACL is attached to lateral condyle of the femur posteriorly.
- ACL passes from front to back of the joint.
- ACL holds femur and tibia together.
Posterior Cruciate Ligament (PCL)-
- Ligament also known as PCL
- Stretches from medial condyle of femur to back of the inter-condylar (between medial and lateral condyle) area.
- The ligament prevents posterior displacement of the tibia over femur bone.
- PCL is attached to back of intercondylar surface of tibia and front of femur.
- Links medial (inner) and lateral (outer) meniscus anteriorly (in front).
- Ligament is either single strip or several strip depends on individuals.
Anterior Menisco-Femoral Ligament-
- Ligament is attached anteriorly to menisci and femoral condyle.
- Ligament lies anterior to meniscus
- Ligament prevents sliding of femur over meniscus.
- Ligament may be absent in majority of the individuals.
Posterior Menisco-Femoral Ligament-
- Ligament is attached posteriorly to menisci and femoral condyle.
- Ligament lies posterior to meniscus
- Ligament prevents sliding of femur over meniscus.
- Ligament is stretched from posterior horn of the lateral meniscus to medial femoral condyle.
- Ligament passes posteriorly behind the posterior cruciate ligament.
- Ligament is often absent in 60 to 70% individuals.
Menisco-Tibial Ligament (MCL)-
- Ligament is attached to lower surface of the menisci and articulating surface of the tibia.
- Ligament prevents slippage of the tibia over meniscus.
Lateral Collateral Ligament (LCL)-
- Ligament is attached to lateral epicondyle of femur and lateral head of fibula.
- LCL splits biceps femoris muscle tendon in to anterior and posterior head of tendon.
- Ligament anchors knee joint and prevents slippage laterally.
Medial Collateral Ligament (MCL)
The MCL extends from the medial epicondyle of the femur to the medial condyle and superior part of the medial surface of the tibia. The MCL is firmly attached to the medial meniscus, which is why these are commonly torn at the same time in contact sports.
- Ligament lies anterior to knee joint
- Ligament is continuation of quadriceps muscles.
- Lower end of Ligament passes over patella and attaches to tibial tuberosity.
- Medial and lateral section of the patellar ligament is known as medial and lateral retinacula.
- Medial and lateral retinacula are extension of vastus medialis and vastus lateralis muscles.
- Retinacula ligament prevent slippage of patella laterally and medially.
- Retinacula ligament maintains patellar contact with anterior surface of femur.
Oblique Popliteal Ligament
- Ligament is attached to medial tibial condyle and lateral femoral condyle.
- Reinforces knee joint capsule posteriorly.
- Ligament originates from tendon of semi-membranous muscles.
Arcuate Popliteal Ligament
- Ligament is attached to head of back of fibula.
- Reinforces knee joint capsule posteriorly.
- Spreads over posterior (back) surface of knee joint.
Watch The Video Of Ligaments Of The Knee
Bursa Of The Knee Joint
Knee joint is surrounded by several bursae. List of bursa are as follows-
- Anterior Group Bursae
- Medial Bursa
- Posterior Bursa
A. Anterior Group of Bursa
a. Suprapatellar Bursa
- Bursa lies between patella and quadriceps femoris muscle
- Presents as single or multi-segmental sacs
- Painful condition with knee joint movements
- The bursa is next to articularis genus muscle, which protects bursa from injury.
b. Patellar Bursa
- Patellar bursa is a superficial bursa that lies between skin and patella.
- The sac is a continuation of knee joint synovial membrane.
- Bursa has a three extension described as follows-
- Anterior- Subcutaneous Pre-Patellar Bursa
- Superior- Subcutaneous Supra-Patellar Bursa
- Inferior- Subcutaneous Infra-Patellar Bursa
B. Medial Bursa-
The Anserine Bursa
- Lies anteriorly on medial side
- Located deep to the tendon pes anserinus.
- Pes anserinus is the conjoint tendon formed by the sartorius, gracilis, and semitendinosus tendons.
C. Posterior Bursa
The Semimembranosus Bursa
- Bursa lies in the popliteal fossa
- Inflammation of the bursa causes posterior swelling of the knee joint
Tendons And Muscles Of The Knee Joint
Following muscles and tendons support knee joint.
- Gracilis Sartorius
- Biceps Femoris