Sudden onset pain usually refers to an acute lesion of soft tissue, like ligaments or menisci. Especially if the pain persists or recurs frequently combined with chronic or recurring swelling of the knee joint a careful and precise evaluation and examination of the patient is necessary to come to the exact diagnosis. If a soft tissue lesion within the joint is then confirmed we usually perform an arthroscopy of the knee joint. That allows us to evaluate the joint by means of a small video camera that is inserted through a tiny hole in the sin. We can also perform small surgical procedures through an additional small incision.

Serious sports accidents can cause a sudden distorsion of the knee resulting in an injury of the anterior cruciate ligament (ACL) and in a (chronic) instability of the joint. Especially young and active patients will benefit from a reconstruction of the ligament by a tendon autograft (anterior cruciate ligament reconstruction), which is done arthroscopically.

In young patients with healthy soft tissue and cartilage, who suffer a meniscal rupture or a cartilage defect, it might be possible to suture the meniscus and perform osteochondral transplantation to fill the defects. The shredded parts of the menisci are removed and the menisci are smoothened.

In the older patient mostly degenerative changes are present, menisci and most of the joint cartilage are worn out and cause pain through the concomittant inflammation of the synovial tissue inside the joint. "Cleaning up" within in the joint, meaning removal of shredded or torn parts of menisci or cartilage and partial removal of synovial membrane, can reduce pain and might prolong the time until a total joint replacement will be necessary.

Certain cases require total knee replacement  to acquire painfree joint movement with sufficient stability.

Persistent knee joint problems in patients with varus- or valgus deformity might be partially solved by correction osteotomies in the distal femur or the proximal tibia.