Knee Anatomy Joint Capsule
Another important part of knee anatomy is the joint capsule. This is like a bag that surrounds the joint containing synovial fluid to nourishand lubricate the knee allowing it to move smoothly and freely.
Any swelling that occurs in the joint is contained inside the capsule, which is why injuries can cause the knee to “balloon”. If the joint capsule is damaged, swelling is no longer confined to the joint so tends to actually be less obvious.
You can find out more in the knee swelling section.
Joint Capsule And Lining
The synovium is the lining of the joint space. The synovium is a layer of tissue that defines the joint space.
The synovial cells produce a slippery, viscous fluid called synovial fluid within the joint. In conditions that cause inflammation of the joint, there can be an abundance of synovial fluid produced, which leads to swelling of the knee joint.
Anatomy Of The Knee Joint
Figure 1. External Ligaments of the Knee A. Anterior B. Posterior
Figure 2. Internal Ligaments of the Knee A. Anterior B. Superior C. Posterior
Figure 3. Communicating Bursae A. Anterior B. Posterior
Figure 5. Non Communicating Bursae A. Sagittal
Figure 5. Blood Supply of the Knee Joint A. Anterior B. Posterior
Figure 6. Nerves Supply the Knee Joint A. Anterior B. Posterior
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Anatomical Features Of The Knee
The main features of the knee anatomy include bones, cartilages, ligaments, tendons and muscles. In the knee joint, the femur articulates with the tibia and the patella. The knee joint is a synovial joint this means it contains a fluid that lubricates it. This fluid is known as the synovial fluid. Consult the diagrams provided to better digest the descriptions of the features below.
Diagram of the anatomy of the knee
Brian0918 via wikimedia commons
The Knee In Static Load And During Ambulation
The knee joint is subjected to forces both in static load both during ambulation. In the first case on the femoral and tibial articular surfaces are concentrated the reaction forces determined by the lower limb contact with the ground. The optimal condition in which there is a uniform distribution of these forces occurs when the mechanical and anatomical axis fall within normal limits.
The first is defined as the line traced between the centre of the femoral head and of the ankle and normally passes through the centre of the knee in both anterior-posterior and latero-lateral views. Instead, the anatomical axis originates in the centre of the knee from the union between the axis of the femoral and the tibial shaft. This line delimitates an obtuse angle externally orientated of 172-177° .
Weightbearing full-length hip-to-ankle X-ray of the lower limbs with normal mechanical and anatomical axis
When this angle increases the knee has a varus conformation in this situation the lower limb mechanical axis moves medially.
A genu varus with mechanical axis medialized and anatomical axis that determines a valgus knee angle > 172-175°. B genu valgus with mechanical axis lateralized and anatomical axis that determines a valgus knee angle < 172-175°. C: genu recurvatum with mechanical axis anteriorized
Left valgus knee. A preoperative clinical and x-ray views. B intraoperative images with deterioration of the cartilage. C postoperative radiographs
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Positions Of Anatomical Features Of Knee
It is easy to understand the anatomy of the knee if you know how the names of its features were derived.
Terms used to describe the position of anatomical features of the knee are in relation to an imaginary line drawn through the whole length of the body. This line separates the body into two equal halves such that parts of the body that occur in pairs will be on opposite sites of this midline.
In knee anatomy, a term with medial as part of its name refers to a position closer to the midline. In this case, it will be a position closest to the other knee. A term with ‘lateral’ as part of its name refers to a position of the knee away from the midline. In this case, it will be a position farthest away from the other knee. A term with ‘anterior’ or ‘posterior’ in its name refers to the front or the back of the body respectively.
Diagram to Illustrate the positions of medial and lateral features of the knee
The Muscles In The Back Of The Knee
Hamstring Muscle diagram
- Gastrocs: A group of 2 muscles that sit in on the lower leg backside that works in tandem with the hamstrings to cause the knee to bend. The gastroc or calf muscle can be strained and torn during sports like tennis or basketball. The athlete will feel a “pop’ in the calf.
Calf Muscle Diagram
- Tendons attach the knee muscles to the bone. The two patellar tendons can also be prone to overuse and the development of patellar tendonitis. Jumper’s knee is common in the knee with athletics.
All of these muscles also have functions at different joints such as the hip and the ankle. Injuries to these structures, such as a pull or strain, will cause pain when activating the muscle and, if severe enough, will cause significant weakness.
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The Ligaments And Their Functions
Collateral ligaments
The MCL is composed of two layers: superficial and deep. During flexion of the knee, the superficial vertical fibres are taut, while the posterior and deep are unstretched. The opposite happens during the extension. The primary function of the MCL is to prevent a deviation of the knee during valgus stress. The dissection of its superficial component determines a significant increase of the deviation in valgus between 0° and 45° of flexion, as well as external rotation. On the other hand, the dissection of deep fibres or deep oblique ligaments or the posterior capsule do not increase joint instability during these movements. This means that the superficial component of the MCL is the main structure that counteracts to the stresses in valgus and external rotation and it offers a weak resistance to anterior translation of the tibia. The posterior oblique and deep fibres seem to play a secondary role as stabilizers.
The lateral collateral ligament origin on the lateral femoral epicondyle anteriorly to the origin of the gastrocnemius muscle. It has a structure similar to a cord that passes under the lateral retinaculum to insert on the head of the fibula, merging at this level with the insertion of the biceps femoris tendon. It prevents the deviation in varus as well as the excessive internal rotation of the knee. The LCL is taut when the knee is extended as consequence varus laxity increases when this joint is flexed.
Cruciate ligaments
Ial Knee Arthroplasty Of The Patellofemoral Joint
Isolated patellofemoral joint pathologies accounts for approximately 10% of knee problems, and is most common in younger females . A variety of surgical treatment options are available if nonoperative measures fail to achieve satisfying results , with the aim of delaying the necessity for arthroplasty. Joint replacement procedures are considered once both the patellar and femoral sides of the PFJ are involved .
The first patellar prosthesis was described by McKeever in 1955, followed by the first femoral component 24 years later, as described separately by Lubinus and Blazina . Enhanced second-generation prostheses with a broad symmetrical trochlear flange evolved in the 1990s, and the design has been refined and updated continually in the intervening years.
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Vascular Supply Of The Knee
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Anterior view of the vascular supply of the knee joint
Image by BioDigital, edited by Lecturio
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Posterior view of the vascular supply of the knee joint
Image by BioDigital, edited by Lecturio
Cartilage Of The Knee
There are two types of the cartilage of the knee joint:
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Synovial Bursa In The Knee: Cushioning For Bones Muscles And Tendons
The knee also contains bursae that protect the joint from rubbing and from pressure during movements of the knee. They are found above the kneecap, in front of and behind the patellar tendon. Bursae are slidable, elastic, fluid-filled “pads” that can become inflamed. An inflamed bursa or bursitis can be very painful.
Anterior Cruciate Ligament Injury
The anterior cruciate ligament is the most commonly injured ligament of the knee. The injury is common during sports. Twisting of the knee is a common cause of over-stretching or tearing the ACL. When the ACL is injured a popping sound may be heard, and the leg may suddenly give out. Besides swelling and pain, walking may be painful and the knee will feel unstable. Minor tears of the anterior cruciate ligament may heal over time, but a torn ACL requires surgery. After surgery, recovery is prolonged and low impact exercises are recommended to strengthen the joint.
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Bones Around The Knee
There are three important bones that come together at the knee joint:
A fourth bone, the fibula, is located just next to the tibia and knee joint, and can play an important role in some knee conditions.
The tibia, femur, and patella, all are covered with a smooth layer of cartilage where they contact each other at the knee joint. There is also a small bone called a fabella, that is often located behind the knee joint.
A type of bone called a sesamoid bone , the fabella is of little consequence to the function of the knee joint. It is only found in about 25% of the population.
How Do The Anatomy Of Knee And Lower Leg Affect Movement
The knee is a hinge joint that sits between the thigh and the shin. It functions the same as a hinge on a door and sometimes gets a creaky as a hinge can. This joint allows the legs to bend and straighten, necessary for walking, going up and downstairs, going from sitting to standing, running, and jumping. The knee’s anatomy consists of many structures from the bones, tendons, and ligaments to the cartilage and muscles to help the knee function.
If you want to learn more about knee anatomy, please watch this knee anatomy video or this article Knee JOINT Anatomy.
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Knee Doctors In Jacksonville
Many types of knee injuries can occur. Muscles, tendons, ligaments, and cartilage can be strained and sprained. It is really important to have your knee pain properly diagnosed by an orthopedic physician. JOI Rehab also has 12 Physical Therapy locations, which can certainly help you on the road to recovery. With over 90 Rehab Clinicians trained in providing you with the highest quality of orthopedic care. For an appointment, please call 904-858-7045.
If you want to learn more about a torn ACL, go to Torn ACL or go to Knee Ligaments Article.
To schedule an appointment for physical therapy at one of the 12 JOI Rehab Centers, please call
JOI MD’s now offer quick fracture care. Make an appointment by calling , schedule online, or click the link below…
Impact Of Arthritis On The Joint
Osteoarthritis is wear and tear of the cartilage layer on the ends of the bones. The space between the two bones see on x-ray is not space, instead, it is cartilage that cannot be seen by the x-ray. As this cartilage wears down the space between the two joints narrow. This can increase pain, swelling, and stiffness.
Located at Community Hospital EasteCommunity.com/FixKnee
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Lower Leg & Knee Joint Anatomy
There are eight different components of knee joint anatomy:
A really important part of knee joint anatomy is the cartilage. There are two different types of knee cartilage:
- Articular Cartilage: a thin layer of cartilage whichlines the surfaces of the knee joints
- Knee Meniscus: a special extra thick layer of cartilage that sits on the top of the tibia
The knee meniscus is particularly important as it acts as a shock absorber to reduce theforces going through the bones and reduces friction, allowing the bonesto move smoothly.
The back of the patella is also lined with cartilage, the thickest in the whole body due to the immense forces that go through the kneecap.
You can find out all about the different types of knee cartilage, how they work, and cartilage injuries and how to treat them in the knee joint cartilage anatomy section.
A Rather Special Bone: The Kneecap The Largest Human Sesamoid Bone
The kneecap also known as the patella is the largest human sesamoid bone. It is fused with the tendon structure that runs from the thigh muscle to the shin bone. The section above the kneecap is called the quadriceps tendon, and the section below the kneecap is called the patellar tendon.
In a sense, the patella acts as a “spacer” between the tendon and the joint, allowing greater leverage and less effort to extend the knee. Moreover, the patella like all sesamoid bones prevents the tendons from being damaged by compressive stress when moving back and forth over the joints.
If we had no kneecaps, incidentally, our thigh muscles would probably be much bigger and we would probably not be able to walk.
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Knee Stability And Its Movements
The overall stability of the knee depends on the interaction of the capsule, menisci, ligaments and muscles, the geometry of the articular surfaces and the femoro-tibial modifications during loading. These are all interdependent between them, thus allowing a normal motility and, at the same time, an effective stability.
The knee is a modified hinge joint where the lack of congruence between the bone surfaces permits six degrees of movement, three translational and three rotational . The movements are determined by the sliding of the articular surfaces of the tibia and femur and the orientation of the four major ligaments of the knee.
In particular, the movement of flexion and extension is the broadest and more important. The first is defined as a posterior approaching movement of the leg to the thigh, which can be active or passive and dependent on the hip position. During the active flexion, the knee can reach 120°-140° with the hip flexed, while passively reach up to 160°.
The medial compartment has a contact 1.6 times greater than the lateral. Flexion is ensured by a combination of rotation and sliding of the femur over the tibia. The movements of the articular surfaces mainly depend on the conformation and orientation of the articular surfaces and of ACL, PCL, MCL and LCL.
Diseases And Afflictions Of The Knee Joint
Falls or accidents often cause injuries to the knee joint. These can occur singly, but also in combination.
- Meniscus lesion
- Inner ligament tear
- Patellar dislocation
The application of strong force, for example an impact with a hard surface, can cause fractures of the bony components of the knee, such as a patella fracture.
Wear and inflammation in the knee can lead to pain. A few examples:
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Functional Anatomy Of Knee Joint
The specific design of knee joint anatomy allows a number of functions:
Supporting The Knee Joint: Ligaments Tendons And Muscles
The knee joint is held in place by a prominent ligamentous apparatus. The ligaments prevent the bony structures from rubbing against each other too much.
- Collateral ligaments: The collateral ligaments stabilise the knee mainly against bending stresses in the frontal plane. The ligaments therefore prevent the knee from twisting sideways.
- Cruciate ligaments: The anterior and posterior cruciate ligaments are found inside the knee joint. These two ligaments stabilise the knee against various movements of the tibia in the sagittal plane: The anterior cruciate ligament prevents the tibia from sliding forward . Similarly, the posterior cruciate ligament prevents the tibia from sliding backwards .
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Design Criteria Of Knee Arthroplasty
The history of total knee arthroplasty began in the 1860s, when Fergusson reported the first resection for knee osteoarthritis . Interpositional arthroplasties, using materials such as joint capsules, muscle, fascia and free fascial grafts, were attempted over subsequent years, but were ultimately unsuccessful . The first reports of total joint replacement were made by Thermestocles Gluck in the 1880s, who used an ivory hinged design fixed with a cement made from plaster of Paris, pumice and colophony . Condylar knee designs, in which the femoral and tibial load-bearing surfaces are replaced with unconnected artificial components, were first investigated in the late 1960s .
The majority of the knee prosthesis that are currently used are based on the evolution of these systems developed in the 1960s.
The objective of the knee replacement is twofold:
1) function and kinematics as much as possible equal to the normal knee
2) long-term survival of the implant.
Also the prothesized knee is subjected to compression and shear forces in static load and during every movement and walking.
The comprehension of the entity and direction of these forces is very important. The choice of adequate prosthetic surfaces, a precise capsular-ligamentous balance, also through accurate bone resections, have the aim of minimizing them, thus preserving the bone-prosthesis interface.
The final long-term result should be a stable, well-functioning and asymptomatic prosthetic implant.