The chronic pain and limited mobility caused by advanced arthritis often lead people to consider knee replacement surgery. This common procedure offers two primary approaches for restoring joint function: Total Knee Replacement (TKR) and Partial Knee Replacement (PKR). TKR and PKR represent distinct surgical strategies, each with specific requirements for patient selection and different implications for recovery and long-term joint function.
Defining the Surgical Scope and Patient Eligibility
The fundamental difference between the two procedures lies in the amount of the knee joint that is replaced. The knee joint is divided into three compartments: the medial (inside), the lateral (outside), and the patellofemoral (under the kneecap). A Total Knee Replacement replaces all three of these damaged compartments with artificial components, resurfacing the entire joint.
A Partial Knee Replacement, also known as unicompartmental knee replacement, is a more focused procedure that replaces only the single compartment affected by arthritis. This approach leaves the healthy cartilage, bone, and ligaments in the other two compartments intact.
The extent of the patient’s arthritis is the primary factor determining eligibility for PKR or TKR. PKR is only an option when the joint damage is strictly confined to one compartment, typically the medial side. For a PKR to be successful, the patient must also have intact and functional anterior and posterior cruciate ligaments (ACL and PCL) to maintain knee stability.
If the arthritis is widespread, affecting two or more compartments, or if the patient has significant knee deformity, a TKR is generally required. TKR is the necessary intervention when the ligaments are compromised or the joint damage is too extensive for a partial replacement to provide lasting relief.
Comparing the Procedure and Initial Recovery
The surgical scope directly influences the invasiveness of the procedure and the patient’s initial recovery experience. A PKR is a less extensive surgery than a TKR, requiring a smaller incision and involving the removal of less bone and soft tissue.
The reduced surgical trauma associated with PKR often translates to a faster and less painful initial recovery period. Patients undergoing a partial replacement frequently report less immediate post-operative pain and are able to mobilize more quickly. The typical hospital stay for a PKR is shorter, and some patients may even qualify for an outpatient procedure, whereas a TKR generally involves a stay of a few days.
The timeline for returning to normal activities also reflects the difference in surgical burden. PKR patients often return to many daily activities within four to six weeks. In contrast, the recovery for a TKR is more prolonged, often ranging from three to six months for a more complete recovery. For both procedures, the commitment to post-operative physical therapy is a significant factor in achieving a successful outcome.
Functional Results and Implant Lifespan
In the long term, both procedures offer a high degree of patient satisfaction and substantial pain relief. However, functional outcomes and implant durability present a trade-off between the two approaches. Since PKR preserves more of the patient’s natural bone and ligaments, it often results in a knee that feels more “natural” during movement.
PKR patients often achieve a greater range of motion and report higher function, particularly younger, more active individuals. This is partially due to the retention of the anterior cruciate ligament, which is often removed during a TKR. Despite these functional benefits, the PKR has a higher long-term risk of needing a second surgery, known as revision.
Registry data suggests that the pooled 25-year survival rate for TKR implants is around 82.3%, indicating a high degree of durability. The long-term revision rate for PKR is significantly higher, with one registry reporting a revision rate of 28.4% at 20 years for osteoarthritis patients. The main reason for this higher revision rate is the progression of arthritis in the remaining unreplaced compartments of the knee.
TKR is the more comprehensive and durable solution, addressing the entire joint to prevent the arthritis from progressing in other areas. PKR offers the advantage of a less invasive procedure and a potentially more natural-feeling knee, but it carries a higher long-term risk of future revision surgery to convert it to a total knee replacement.