Knee joint disorders. Illustration of a sagittal section through a human knee joint, showing five disorders. The first two are a bone tumour (cancer, pink, upper left) and a fracture of the knee-cap (patella, centre left). Below this, from left to right, are: prepatellar bursitis (purple stripes); chondromalacia patellae (green); and osteochondritis causing a lesion and an inflamed bone (brown) and cartilage (blue) fragment at the base of the femur. Prepatellar bursitis (housemaid's knee) is an inflammation of the prepatellar bursa at the front of the knee. Chondromalacia patellae is the inflammation of the underside of the patella and softening of the cartilage.