Knee arthritis is a degenerative condition that causes pain and limits mobility as the smooth cartilage cushioning the joint wears away. When non-surgical treatments like medication or physical therapy no longer provide adequate relief, surgical intervention becomes necessary to restore function. The two primary surgical options for resurfacing the damaged joint are Total Knee Replacement and Partial Knee Replacement. Understanding the differences between these procedures, from their scope to long-term outcomes, is the first step toward making an informed decision about treatment.
Total Knee Replacement Defined
Total Knee Replacement (TKR), also known as Total Knee Arthroplasty, resurfaces the entire joint. The knee is divided into three compartments: the medial (inner), lateral (outer), and patellofemoral (under the kneecap). During TKR, the surgeon removes damaged cartilage and a small amount of underlying bone from the ends of the femur and tibia across all three compartments.
These damaged surfaces are capped with metal components, and a durable plastic spacer is inserted between them to recreate a smooth gliding surface. TKR is recommended for patients with severe or widespread arthritis affecting multiple compartments or those with significant knee deformities. It is the most common form of knee replacement due to its reliability in providing long-term pain relief and improved function.
Partial Knee Replacement Defined
Partial Knee Replacement (PKR), also called Unicompartmental Knee Arthroplasty (UKA), replaces only the arthritic or damaged compartment of the knee. This procedure leaves the remaining healthy cartilage and bone intact. PKR most frequently addresses damage confined to the medial (inner) compartment of the knee.
By focusing only on the diseased area, the surgeon preserves the patient’s native tissue and ligaments in the lateral and patellofemoral compartments. Ideal candidates for PKR have isolated, single-compartment arthritis, strong functioning ligaments, and relatively good overall knee alignment. Because the procedure is less invasive, it offers advantages when the arthritis is localized.
Criteria for Choosing the Procedure
The decision between partial and total knee replacement depends on a clinical assessment of the knee’s internal condition and the patient’s overall health. The primary factor is the extent and location of arthritic damage within the three knee compartments. If diagnostic imaging confirms the damage is strictly confined to one area, PKR is considered.
If the arthritis has spread to involve the lateral or patellofemoral compartments, Total Knee Replacement is the appropriate surgical choice. Ligament stability is also crucial for PKR, specifically the integrity of the anterior cruciate ligament (ACL). A functional and intact ACL is required because the PKR implant relies on this natural structure to provide stability and normal motion.
The degree of knee deformity or misalignment is also considered. TKR is often necessary to correct significant bowing or knock-knee deformities that accompany advanced, multi-compartment arthritis. While patient age and activity level are secondary, the primary rationale remains the pattern of the disease and the stability of the joint’s soft tissues.
Differences in Recovery and Longevity
The less extensive nature of Partial Knee Replacement (PKR) results in a faster and less painful recovery. PKR involves a smaller incision (three to five inches) compared to the larger incision required for TKR. This reduction in surgical trauma results in less blood loss and a shorter hospital stay, with some PKR procedures performed on an outpatient basis.
Patients undergoing PKR begin rehabilitation sooner and report a quicker return to normal daily activities, sometimes within four to six weeks. The recovery period for TKR is longer, requiring several months of intensive physical therapy to regain full function. Many PKR patients also report that the knee feels more “natural” because much of the native joint structure is preserved.
In terms of longevity, both implants offer excellent long-term outcomes, with most TKR prostheses expected to last 15 to 20 years or more. While PKR implants have a high success rate (around 90% at ten years), they carry a greater risk of requiring revision surgery later. Revision is needed if arthritis develops in the remaining native compartments or if the initial implant wears out, necessitating conversion to a Total Knee Replacement.