Chondromalacia Patellae: A degeneration of the ARTICULAR CARTILAGE of the PATELLA, caused by a decrease in sulfated MUCOPOLYSACCHARIDES in the ground substance. When accompanied by pain, it is sometimes considered part of or confused with PATELLOFEMORAL PAIN SYNDROME.Patella: The flat, triangular bone situated at the anterior part of the KNEE.Cartilage Diseases: Pathological processes involving the chondral tissue (CARTILAGE).Joint DiseasesFlatfoot: A condition in which one or more of the arches of the foot have flattened out.Knee Joint: A synovial hinge connection formed between the bones of the FEMUR; TIBIA; and PATELLA.Cartilage, Articular: A protective layer of firm, flexible cartilage over the articulating ends of bones. It provides a smooth surface for joint movement, protecting the ends of long bones from wear at points of contact.Integrin-Binding Sialoprotein: A highly glycosylated and sulfated phosphoprotein that is found almost exclusively in mineralized connective tissues. It is an extracellular matrix protein that binds to hydroxyapatite through polyglutamic acid sequences and mediates cell attachment through an RGD sequence.Femur: The longest and largest bone of the skeleton, it is situated between the hip and the knee.Joint Instability: Lack of stability of a joint or joint prosthesis. Factors involved are intra-articular disease and integrity of extra-articular structures such as joint capsule, ligaments, and muscles.Collateral Ligaments: A number of ligaments on either side of, and serving as a radius of movement of, a joint having a hingelike movement. They occur at the elbow, knee, wrist, metacarpo- and metatarsophalangeal, proximal interphalangeal, and distal interphalangeal joints of the hands and feet. (Stedman, 25th ed)Tracheobronchomalacia: A congenital or acquired condition of underdeveloped or degeneration of CARTILAGE in the TRACHEA and the BRONCHI. This results in a floppy non-rigid airway making patency difficult to maintain.Arthroplasty, Subchondral: Surgical techniques used to correct or augment healing of chondral defects in the joints (CARTILAGE, ARTICULAR). These include abrasion, drilling, and microfracture of the subchondral bone to enhance chondral resurfacing via autografts, allografts, or cell transplantation.Baseball: A competitive nine-member team sport including softball.Arthroscopy: Endoscopic examination, therapy and surgery of the joint.Knee Injuries: Injuries to the knee or the knee joint.Patellar Ligament: A band of fibrous tissue that attaches the apex of the PATELLA to the lower part of the tubercle of the TIBIA. The ligament is actually the caudal continuation of the common tendon of the QUADRICEPS FEMORIS. The patella is embedded in that tendon. As such, the patellar ligament can be thought of as connecting the quadriceps femoris tendon to the tibia, and therefore it is sometimes called the patellar tendon.