The kneecap or patella articulates with a groove on the front of the femur known as the trochlea and together they form the patellofemoral joint. The end of the femur broadens to form the femoral condyles and these articulate with the end of the tibia forming the tibiofemoral joint.
The surfaces of the patella, femur and tibia that articulate with each other are covered in articular cartilage. Arthritis is the result of these surfaces being worn away.
Two c shaped rings of cartilage known as the menisci are located between the two bones and these help with load transmission effectively forming the shock absorbers of the knee.
The knee is stabilised with four major ligaments; the anterior and posterior cruciate ligaments inside which are important in resisting forward and backward movement of the tibia and the medial and lateral collateral ligaments which stabilise the knee on each side. In reality, the major function of the cruciate ligaments is resisting rotational movements of the tibia.
The large quadriceps muscles at the front of the leg insert onto the upper pole of the patella via the quadriceps tendon. The patellar tendon then runs from the lower pole of the patella to its insertion on the tibal tuberosity. Contraction of the quadriceps allows the knee to straighten or extend.
This is the most common symptom that patients report. It is important to note whether the pain began suddenly or whether it came on gradually; if it began after a minor twist or fall; the exact location of the pain i.e on the inside (medial), outside (lateral), behind the kneecap (anterior) or generalized; its duration; if it is constant or purely activity related or if certain activities exacerbate it; if it is a sharp pain or dull ache; if the pain radiates anywhere and whether it is relieved by simple analgesia.
This refers to the knee giving way. It often occurs as you go to change direction or pivot. Sometimes patients feel that they simply don't trust the knee and thus they avoid performing certain movements or go to protect it before it even gives way. Occasionally the knee can give way in response to a sudden dart of pain and this is known as "quads inhibition" rather than true instabilty.
Swelling simply refers to the build-up of fluid within the knee. Usually this is due to synovial fluid i.e the normal lubricating fluid within the joint and in this case, it is known as an effusion. Occasionally this will feel like a tightness in the back of the knee. If swelling occurs suddenly after an injury, then it may be due to blood and this is called a haemarthrosis.
Locking of the knee refers to a sudden inability to bend and / or straighten the knee. It often only lasts a few minutes although you may have some lingering discomfort afterwards. Sometimes you might feel something moving around inside the joint.
The menisci commonly tear as a result of very minor trauma and is often something as simple as a little twist getting out of bed. The pain will often settle and many tears do not require any surgery but if a persistent cause of pain or if they produce symptoms such as locking, they may require surgery. The size, location and direction of the tear are all important in deciding whether a tear can be repaired with sutures or whether it will need resection of the torn segment (a partial menisectomy).
This refers to damage to the articular surface of the knee. The size, location and depth of the defect is important and will determine the necessary traetment. Smaller defects often heal with fibrocartilage a type of scar cartilage that although different at a microscopic level to normal hyaline cartilage, can still protect the bone underneath. Larger defects may require surgery and a variety of techniques are available from simply creating some holes down to the bone underneath to stimulate healing (microfracture) to transferring some cartilage from a non-weightbearing area of the knee (mosaicplasty) to growing special cartilage cells (chondrocytes) in the laboratory and re-inserting them into the defect often embedded in a special matrix (MACI - Matrix assisted autologous chondrocyte implantation).
A plica is a synovial fold of tissue that can form a thickened band as it rubs across the medial femoral condyle with knee flexion. It is a common cause of anteromedial knee pain when inflamed but is frequently found incidentally and can be asymptomatic.
Also known as jumper's knee, this is an overuse injury characterized by repeated microscopic tears of the tendon and degeneration of the normal collagen structure. Tendonitis refers to an acute inflammation in the tendon often following an injury whereas a tendinosis is chronic and often lacks inflammation.
A similar pathology to patellar tendinosis but occurring on the other side of the patella at the quadriceps tendon. Once again it is commonly an overload issue and often co-exists with patellar tendinosis.
A piece of cartilage from a previous injury can sometimes move around the knee joint. When it gets caught between the femur and tibia it can create a sudden pain and locking of the knee. This often resolves after only a few minutes.
Bursae are small sacs that contain a tiny drop of synovial fluid and are lined by a synovial membrane. They are found where skin, muscles or tendons move across a bony prominence and normally reduce friction at these points. However, occasionally they can get inflamed and result in pain and sometimes quite significant swelling. A secondary infection can also develop in them. Inflammation in them is common in people who kneel a lot at work. In the knee the two most common are pre-patellar and infra-patellar bursitis and are known as housemaid's and clergyman's knee respectively.
This is a disease of the synovial lining characterized by the production of multiple small cartilaginous loose bodies within the joint.
A Baker's or popliteal cyst is another bursa of the knee that usually lies deep to one of the hamstrings tendons at the back. It frequently communicates with the knee joint itself and in adults usually swells up in response to some pathology within the knee joint. Patients often notices swelling, pain or pressure at the back of the joint. Mostly it settles when the cause is treated but rarely the cyst itself will require excision.
Iliotibial band friction syndrome
This refers to pain over the outside (lateral side) of the knee due to overuse. It is due to friction as the iliotibial band moves back and forth over the bony prominence of the lateral femoral condyle. It can usually be treated with a course of physiotherapy and occasionally requires a steroid injection.
This refers to a special type of localized cartilage loss under the kneecap and is an extremely common cause of anterior knee pain. The vast majority of times it can be managed with a rehabilitation programme and rarely requires surgery.
This is common in active adolescents and causes pain where the patellar tendon inserts onto the tibial tubercle. It is caused by repetitive microtrauma to the tendon insertion and usually improves with rest and activity modification.
Sinding-Larsen Johansson syndrome
This is a similar traction related disorder in the adolescent but occurs at the opposite end of the patellar tendon as it inserts onto the patella.
This is a condition of adolescents where the bone just under the articular cartilage dies due to lack of blood supply. This can allow the fragment of cartilage to come loose and in some cases detach completely. Often it can be managed by observation alone but surgery is required if the fragment detaches or if symptoms fail to improve following activity modification.
Pigmented villonodular synovitis
This is a disease that involves inflammation and overgrowth of the synovial lining of the knee leading to progressive destruction of the joint. Early in the disease process it can be treated with arthroscopic or open debridement of the synovium.
Fat pad impingement syndrome
A large lump of richly innervated fatty tissue lies deep to the patellar tendon and is known as the infrapatellar fatpad or Hoffa's fatpad. Occasionally this can get pinched with knee movement causing anterior knee pain.