Arthritis is the physical wearing away of the protective cartilage surface covering the ends of our bones at a joint. When functioning appropriately, this cartilage surface allows smooth and painless motion at our joints. As the cartilage wears out over time or after injury, the worn ends of the bones contact causing pain and sometimes crepitus (audible or palpable grinding of the bony surfaces). Arthritis symptoms generally progress over time at an unpredictable rate (months, years, decades) and can have periods of decreased or increased pain and symptoms. Arthritis is often associated with pain and stiffness with the initiation of movement after a period of prolonged rest, particularly in the morning (morning stiffness).
Unicompartmental (single compartment) knee replacement can be performed to resurface damaged and arthritic joint surfaces in any of the three different compartments of the knee. There is the medial tibiofemoral compartment (between the thigh bone and shin bone on the inside of the knee), the lateral tibiofemoral compartment (between the thigh bone and the shin bone on the outside of the knee), and the patellofemoral compartment (between the kneecap and the thighbone). A less invasive procedure can resurface a single compartment of the knee if the others are still in good condition. The advantage is less surgery, but the disadvantage is that unicompartment knee replacement may need revision surgery to a total knee surgery. Recent data shows that unicompartment replacement results with regard to outcomes and survival are approaching that for total knee arthroplasty. Robotic and computer navigation are improving the technical ability to accurately position of the unicompartment implants and theoretically improving the survivorship.