There are four bursae around the knee joint. They are all prone to inflammation, or bursitis. However, the bursa in between the skin and the kneecap (the prepatellar bursa) is most commonly affected. The prepatellar bursa is located as shown in the diagram. Housemaid's knee is the name given to inflammation of the prepatellar bursa, hence, prepatellar bursitis.
This is a companion discussion topic for the original article at https://patient.info/bones-joints-muscles/knee-pain-patellofemoral-pain/housemaids-knee-prepatellar-bursitis