Patellofemoral Joint: The articulation between the articular surface of the PATELLA and the patellar surface of the FEMUR.Patellofemoral Pain Syndrome: A syndrome characterized by retropatellar or peripatellar PAIN resulting from physical and biochemical changes in the patellofemoral joint. The pain is most prominent when ascending or descending stairs, squatting, or sitting with flexed knees. There is a lack of consensus on the etiology and treatment. The syndrome is often confused with (or accompanied by) CHONDROMALACIA PATELLAE, the latter describing a pathological condition of the CARTILAGE and not a syndrome.Patella: The flat, triangular bone situated at the anterior part of the KNEE.Knee Joint: A synovial hinge connection formed between the bones of the FEMUR; TIBIA; and PATELLA.Patellar Dislocation: Displacement of the PATELLA from the femoral groove.Femur: The longest and largest bone of the skeleton, it is situated between the hip and the knee.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.Osteoarthritis, Knee: Noninflammatory degenerative disease of the knee joint consisting of three large categories: conditions that block normal synchronous movement, conditions that produce abnormal pathways of motion, and conditions that cause stress concentration resulting in changes to articular cartilage. (Crenshaw, Campbell's Operative Orthopaedics, 8th ed, p2019)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.Cartilage Diseases: Pathological processes involving the chondral tissue (CARTILAGE).Biomechanical Phenomena: The properties, processes, and behavior of biological systems under the action of mechanical forces.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.Joint DiseasesQuadriceps Muscle: The quadriceps femoris. A collective name of the four-headed skeletal muscle of the thigh, comprised of the rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis.Athletic Tape: Adhesive tape with the mechanical strength to resist stretching. It is applied to the skin to support, stabilize, and restrict movement to aid healing and/or prevent injuries of MUSCULOSKELETAL SYSTEM.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.Arthroplasty, Replacement, Knee: Replacement of the knee joint.Joints: Also known as articulations, these are points of connection between the ends of certain separate bones, or where the borders of other bones are juxtaposed.Range of Motion, Articular: The distance and direction to which a bone joint can be extended. Range of motion is a function of the condition of the joints, muscles, and connective tissues involved. Joint flexibility can be improved through appropriate MUSCLE STRETCHING EXERCISES.Weight-Bearing: The physical state of supporting an applied load. This often refers to the weight-bearing bones or joints that support the body's weight, especially those in the spine, hip, knee, and foot.Pain: An unpleasant sensation induced by noxious stimuli which are detected by NERVE ENDINGS of NOCICEPTIVE NEURONS.DislocationsMagnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Tibia: The second longest bone of the skeleton. It is located on the medial side of the lower leg, articulating with the FIBULA laterally, the TALUS distally, and the FEMUR proximally.Fluoroscopy: Production of an image when x-rays strike a fluorescent screen.Stress, Mechanical: A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area.Osteoarthritis: A progressive, degenerative joint disease, the most common form of arthritis, especially in older persons. The disease is thought to result not from the aging process but from biochemical changes and biomechanical stresses affecting articular cartilage. In the foreign literature it is often called osteoarthrosis deformans.Anterior Cruciate Ligament: A strong ligament of the knee that originates from the posteromedial portion of the lateral condyle of the femur, passes anteriorly and inferiorly between the condyles, and attaches to the depression in front of the intercondylar eminence of the tibia.Arthralgia: Pain in the joint.Finite Element Analysis: A computer based method of simulating or analyzing the behavior of structures or components.Knee Injuries: Injuries to the knee or the knee joint.Surgical Tape: A flat, flexible strip of material used to cover or fasten together damaged tissue.Knee Prosthesis: Replacement for a knee joint.Hip Joint: The joint that is formed by the articulation of the head of FEMUR and the ACETABULUM of the PELVIS.Braces: Orthopedic appliances used to support, align, or hold parts of the body in correct position. (Dorland, 28th ed)Bone Malalignment: Displacement of bones out of line in relation to joints. It may be congenital or traumatic in origin.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Finger Joint: The articulation between the head of one phalanx and the base of the one distal to it, in each finger.Arthroplasty: Surgical reconstruction of a joint to relieve pain or restore motion.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Pain Measurement: Scales, questionnaires, tests, and other methods used to assess pain severity and duration in patients or experimental animals to aid in diagnosis, therapy, and physiological studies.Orthotic Devices: Apparatus used to support, align, prevent, or correct deformities or to improve the function of movable parts of the body.Hip: The projecting part on each side of the body, formed by the side of the pelvis and the top portion of the femur.Ankle Joint: The joint that is formed by the inferior articular and malleolar articular surfaces of the TIBIA; the malleolar articular surface of the FIBULA; and the medial malleolar, lateral malleolar, and superior surfaces of the TALUS.Knee: A region of the lower extremity immediately surrounding and including the KNEE JOINT.Torso: The central part of the body to which the neck and limbs are attached.Posterior Cruciate Ligament: A strong ligament of the knee that originates from the anterolateral surface of the medial condyle of the femur, passes posteriorly and inferiorly between the condyles, and attaches to the posterior intercondylar area of the tibia.Bone Diseases, DevelopmentalSesamoid Bones: Nodular bones which lie within a tendon and slide over another bony surface. The PATELLA (kneecap) is a sesamoid bone.Gait: Manner or style of walking.Tendons: Fibrous bands or cords of CONNECTIVE TISSUE at the ends of SKELETAL MUSCLE FIBERS that serve to attach the MUSCLES to bones and other structures.