Detailed Anatomy of the Knee Joint

In our latest blog post we take a closer look at our favourite joint in the body; the knee joint. The knee is what is known as a synovial joint whereby two or more bones connect via a cavity consisting of cartilage, a joint cavity, synovial fluid, ligaments, tendons, Bursa's and Articular discs. There are six different types of synovial joints found in the body with the knee being a hinge joint as it only allows movement across one axis in flexion and extension. Although this has been adapted to a modified hinge joint as the joint does allow for a small amount of rotation and lateral movement.



Bones and Cartilage (Meniscus)


The knee joins the two largest bones in the body, the Femur and Tibia, and is therefore the largest joint in the body. The end of the femur contains two condyles (medial and lateral). Condyles are found at all major joints and provide a rounded surface for ligaments and tendons to form a strong attachment point to. Each bone is lined with a shiny white surface referred to as the articular cartilage or meniscus. This layer of cartilage ensure bones are not grinding together, it allows for a smooth movement of each bones around the joint and acts as a shock absorber when pressure is applied through the femur, tibia and fibula. The final bone to make up the knee joint is the kneecap or patella. This is what is known as a sesamoid bone as it is an independent bone developed in a tendon. The kneecap sits in what is called the trochlear grove of the femur and is primarily there to protect the anterior part of the knee, however it also allows for a greater extension of the knee by increasing the pulling angle of the quadriceps muscles and tendon.


Ligaments


There are more major ligaments in the knee, each is there to connect the femur to the tibia and fibula, whilst stabilising the knee joint and preventing too much forward, backward and rotational movement.

  • The Anterior Cruciate Ligament (ACL) is located in the centre of the knee and prevents the tibia sliding forward and rotation.

  • The Posterior Cruciate Ligament sits just behind the ACL and prevents backward movement of the tibia.

  • The Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL) give stability to the knee with the MCL on the inside knee connecting the Femur to the Tibia (the larger shin bone), and the LCL on the outside of the knee connecting the Femur to the Fibula (the smaller shin bone).

Ligaments are an incredibly strong connective tissue made up of collagen fibres. The main role of the ligaments at the knee are to stabilise the knee ensuring it only moves in the way it is designed to (flexion, extension and a small degree of medial and lateral rotation).


Tendon


There are 2 tendons in the knee, the Quadriceps Tendon and Patellar Tendon (sometimes referred to as a ligament). These are the strong, elastic, connective bands of tissue that run over the front of the knee. The quadriceps tendon attaches the four quad muscles to the kneecap and patella ligament which sits just below the patella and onto the Tibia. When the quadriceps contract and shorten this pulls the Quad tendon, patella and patella ligament causing extension of the knee.




Muscles


The two main muscles at the knee are the Quadriceps (Rectus Femoris, Vastus Lateralis, Vastus Medialis and Vastus Intermedius) and Hamstrings (Bicep femoris, semitendinosus and semimembranosus). The quadriceps main function is to extend the knee joint when they contract, therefore the main function of the hamstring is to flex the knee. Muscles use the Antagonistic effect whereby they work in pairs to facilitate movement, as an example for the knee to flex the quadriceps must relax to allow the hamstrings to contract and move the knee.

There are also deeper muscles in and around the knee, a lot smaller than the quads and hamstrings and produce less movement but are just as important.


  • The Gracilis is a long, thin muscle that runs from the pubic bone down to the medial side of the tibia, this muscle produces adduction at the hip and assists in knee flexion.

  • The Sartorius is the longest muscle in the body. It originates from the Anterior Superior Iliac spine and attaches at the medial side of the Tibia. Sartorius is a synergist in that it is not solely responsible for a movement but assists in a number of movements at the hip (flexion, abduct, and lateral rotation) and knee (flexion and medial rotation).

  • The popliteus muscle is triangular shaped and located at the back of the knee originating from the Lateral condyle of the femur and the posterior horn of the lateral meniscus, it inserts into the posterior side of the Tibia. This muscle is the key to unlocking the knee, when the knee is locked it slightly medially rotates, the popliteus laterally rotates the knee allowing it to flex.

  • Tensor Fascia Latae (TFL) is actually located at the hip, however together with the gluteus maximus it inserts into the Iliotibial Tract (IT Band) which runs laterally over the hip and knee. The TFL muscle works to flex, medial rotate and abduct the hip, laterally rotate the knee and stabilise the torso. The IT Band inserts onto the lateral condyle of the Tibia which stabilises the knee and is hugely important when running/walking.

  • Plantaris is the final deep muscle of the knee, its runs behind the knee with a long tendon (the longest in the body) attaching to the medial side of the calcaneus (heel bone) It assists in knee flexion and ankle plantarflexion but more importantly give proprioceptive feedback on the position of the foot and achillies tendon.



Injuries of the knee


We see a range of injuries that occur at the knee, both chronic and acute. Here is a list of some of the most common ones:

Patella Femoral Syndrome (Also known as Runners Knee):

This is one of the most common knee injuries we see in the clinic, although it can be very painful and debilitating, it is very easy to fix. The pain comes from underneath the kneecap and can be especially painful when walking up and down stairs. The cartilage that sits below the patella becomes inflamed and irritated, often due to misalignment because of a muscle imbalance or tightness from the quadriceps. Kinesiology taping is very effective here to allow an athlete to continue to complete whilst going through treatment and rehab.

Patella Tendonitis (Jumpers Knee)

The patella tendon connects the kneecap (patella) to the tibial tuberosity (top of the shin. It works with the quadricep tendon and quadriceps to extend the knee joint. Athletes who extend the leg rapidly (running, kicking, jumping) are at higher risk of developing patella tendonitis. The patella tendon is also put under high stress when the quadriceps perform an eccentric contraction, lengthening whilst under load. Examples of this type of muscle contraction include walking/running downhill, landing from a jump, slowing down when running. Pain here can be similar to patella femoral syndrome; pain is felt just below the kneecap along the tendon and at the attachment site at the top of the shin. Runners knee can also be painful to palpate along the patella tendon.

Iliotibial Band Syndrome

Also, a very common overuse injury we see, ITB pain presents as pain down the outside of the knee, especially when running and cycling. Similarly, to Runners Knee this injury is caused from muscle issues further up, from the hip and glutes in this case. Tightness from the Tensor Fasciae Latae and Glute max muscle pull on the Iliotibial tract which in turn causing increased tension and friction on the attachment site on the lateral side of the knee.

Torn Meniscus

This acute injury is caused by forceful twisting or hyperflexion of the knee joint. Pain presents from deep inside the knee, either laterally or medially and often when twisting motions of the knee are performed. The meniscus can tear in different ways and in different locations, intrasubstance/incomplete tears on the outer portion of the meniscus are common and don’t always cause problems. The richer blood supply in the outer part of the meniscus means these types of tears often heal by themselves. Complex or bucket-handle tears are more severe and will often require more physical therapy and surgery. We are able to assess the knee joint to establish if the meniscus is torn and what actions need to be taken to resolve the issue.

Ligament injuries

Ligament injuries mostly occur acutely from sudden twisting or changing of direction. For that reason, athletes who compete in games sports such as Football and Hockey are at higher risk. The four ligaments create a strong, stable structure between the femur and Tibia and fibular, although incredibly strong they can rupture or tear if put under excessive load. ACL is the most common ligament to rupture or strain, a classic example of this is when the boot or studs of a player gets stuck in the ground and the body tries to twist, this creates excessive rotation at the knee joint and too much load through the ACL. We asses the knee to establish what ligaments are damaged, how badly and then can prescribe a rehabilitation programme as required. Cruciate ligament injuries rarely cause pain, rather an instability in the knee and a locking, popping or giving way of the knee.

Collateral ligaments, the two then run down the inside and outside of the knee are also damaged acutely and more so from a direct impact or trauma as oppose to movements alone. The medial ligament is more commonly damaged from a direct blow to the outside of the knee. Collateral ligaments can also cause a pop or lock within the knee but are accompanied by pain and swelling.




Thank you for reading this blog, we hope you enjoyed it and found it useful. We'd love to hear your thoughts so feel free to leave us a comment.


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