Medial knee fold syndrome is a specific type of synovitis of the knee joint. Plica mediopatellaris is the Latin term for the fold of the synovium in the medial compartment of the knee. This structure is not a disease in itself, but it can cause persistent pain in the knee joint. The synovial fold consists of the mesenchymal tissue that forms in the knee during the embryological phase of development. During fetal life, this tissue forms connective tissue septum that divide the knee joint into three compartments, which disappear with development, and their remnant may be folds of the synovial membrane on the joint wall, commonly known as files (from the Latin word plica - fold). The synovial fold is located on the medial side of the patella and begins in the suprapatellar region, continuing diagonally to Hoffa's fat body.

The aim of conservative treatment of arthrosis is to relieve pain, improve functioning, and slow down the progression of the disease. The treatment includes weight reduction, unloading joints, rehabilitation, and pharmacotherapy. If patients do not react adequately to oral medication or if it is not advisable for health reasons, intra-articular injections are a very good treatment option. Intra-articular injections include viscosupplementation with hyaluronic acid, treatment with growth factors in platelet-rich plasma (PRP), and stem cell therapy. Oral joint supplements are only supportive - those are mainly preparations for athletes who want to take care of the health of their excessively overloaded joints.

The knee joint in the frontal plane is stabilized by ligaments:

- medial colateral ligament (MCL) - stabilizes the knee from the medial side,
- lateral colateral ligament (LCL) - stabilizes the knee from the lateral side.
The former is more likely to be damaged, usually as a result of a knee deformation when playing football or other contact sports. A ligament rupture can be successfully treated conservatively, while a complete ligament rupture causes medial instability of the knee joint and is an indication for surgical treatment.

Jumper's knee (patellar ligament enthesopathy) is one of the frequent overload injuries of the knee extension apparatus. The extension apparatus includes the quadriceps muscle of the thigh, the patella and the patella ligament which attaches to the tibial tuberosity. All structures are involved in actively extending the knee or inhibiting its bending when landing on a bent limb. Patellar ligament inflammation is a pain in the front of the knee that increases with or shortly after jumping and running training. Injury is most common among volleyball players, handball players, athletes and baseball players. Treatment depends on the degree of damage to the patella ligament and mainly consists in rehabilitation. When conservative treatment remains ineffective or there is severe damage or rupture of the ligament, surgery is required.

In the era of increased interest in a healthy lifestyle and sport, and in particular in long-distance running, an increasing number of amateur runners are exposed to various types of injuries. They most often result from overloads of the locomotor system, which are the result of a poorly selected training plan, maladjustment of loads and training volume to one's abilities, poorly selected equipment (e.g. worn-out footwear and its inadequate cushioning) or running routes or anatomical and biomechanical factors.

One of such injuries is the Iliotibial band syndrome (ITBS), commonly known as the runner's knee, associated with overloading the muscles involved in the run. This ailment affects mainly long-distance runners (accounting for as much as 12% of all running injuries), but also physically active people with increased work of extensors and hip abductors (footballers, cyclists).

The characteristic symptoms are swelling and pain on the outside of the knee or any part of the iliotibial band. It seems that the cause of the ailments lies in the knee joint, however, the history and careful diagnostics show that the cause of the injury usually lies outside the knee and is related to the anatomical structure of the band and its biomechanics of operation.

Daily activity causes forces on the kneecap, often several times greater than the human body weight. Healthy patellar articular cartilage adapts to these forces, while in the case of disturbances in the normal mechanical function of the patella, the forces acting on it are excessive and concentrated in one place. This aggregation of these factors is manifested by pain and a crunching feeling in the knee when it is straightened and bent. Such symptoms may indicate damage to the patellar cartilage, i.e. chondromalacia. Therefore, the treatment of this disease must be directed primarily not only at damaged cartilage, but also at the correction of the mechanical abnormality of the patella function, which causes its excessive overloading.

Osteoarthritis of the knee (gonarthrosis) is the most common cause of chronic knee pain. The essence of the degeneration is the degradation of the articular cartilage, leading to its gradual abrasion until the bone surface is exposed. Gonarthrosis is the result of the combination of biological factors related to the reduced quality of cartilage and mechanical factors related to acute injuries and chronic overload of the knee. Inflammatory factors in the course of systemic diseases are also important.

The degenerative process covers not only the articular cartilage, but later also the subcartilage layer of the bones, the joint capsule and ligaments, leading to deformation and painful limitation of mobility in the knee joint. The result of the disease is impaired gait and reduced quality of life. Treatment is mainly based on the elimination or reduction of risk factors accelerating the degeneration of the knee joint. In the advanced stage of the disease, it is necessary to replace the damaged joint with an artificial knee prosthesis.