Knee arthritis is a degenerative condition that can severely limit mobility and cause persistent pain, often requiring surgical intervention. This procedure, known as knee arthroplasty or knee replacement, is highly effective in relieving discomfort and restoring function. The term “knee replacement” encompasses two distinct surgical approaches: partial (PKR) and total (TKR), each tailored to the specific extent of the joint damage. The decision between PKR and TKR is determined by the location of the arthritis, the integrity of the knee’s supporting structures, and the patient’s overall health profile. Understanding the differences between these two procedures is helpful when discussing treatment options with a surgeon.
Anatomical Extent of the Procedure
The fundamental distinction between the two replacement types lies in how much of the joint surface is resurfaced with artificial components. The knee joint is divided into three compartments: the medial (inside), the lateral (outside), and the patellofemoral (beneath the kneecap).
A partial knee replacement, also termed unicompartmental arthroplasty, is a targeted procedure that addresses damage in only one of these three compartments. The procedure involves removing the damaged cartilage and a small amount of underlying bone solely from the affected area, such as the medial compartment, which is most frequently afflicted by osteoarthritis. This approach preserves the healthy cartilage, bone, and supporting ligaments in the remaining two compartments, resulting in a smaller implant.
Conversely, a total knee replacement is a comprehensive procedure that replaces the load-bearing surfaces of all three compartments. The ends of the thigh bone (femur) and shin bone (tibia), as well as the back surface of the kneecap (patella), are resurfaced with metal and plastic components. Due to the broader scope of the procedure, TKR requires a larger surgical incision and more extensive soft tissue and bone dissection compared to the less invasive PKR.
Criteria for Patient Selection
The eligibility requirements for each procedure are governed by the localized condition of the knee joint, confirmed through imaging and physical examination. Partial knee replacement is an option only for patients whose arthritis is confined exclusively to one compartment. This localized damage often occurs following a prior injury, causing isolated deterioration.
A non-negotiable requirement for PKR candidacy is the presence of intact and functional anterior and posterior cruciate ligaments (ACL and PCL). These ligaments are typically left untouched during a partial replacement. Patients must also have minimal pre-existing stiffness or significant angular deformity in the joint, as these issues cannot be reliably corrected with a partial resurfacing. Younger, more active patients with isolated damage are frequently considered ideal candidates for this more conservative approach.
Total knee replacement becomes the necessary intervention when the arthritic damage is widespread, affecting two or all three compartments of the joint. TKR is also required if the patient’s knee has lost structural support due to compromised or non-functional ligaments. Furthermore, TKR is the standard treatment when the patient presents with a severe pre-existing deformity, as the procedure allows the surgeon to correct the alignment and balance the ligaments. Rheumatoid arthritis, an inflammatory condition that typically affects the entire joint, also necessitates a total replacement.
Post-Surgical Recovery and Implant Lifespan
The reduced anatomical extent of the partial replacement translates into a distinctly different post-surgical experience. Because PKR is less invasive, it involves less blood loss and trauma to the surrounding tissues, leading to a shorter hospital stay, often just one to two days, and sometimes even an outpatient procedure. Patients undergoing PKR typically report lower immediate postoperative pain and a faster return to daily activities, often within four to six weeks.
The preservation of native bone and ligaments in PKR often allows the knee to feel more “natural” after recovery, and patients may achieve a greater range of motion compared to TKR. Conversely, TKR is a more extensive procedure that requires a longer recovery and rehabilitation period, often taking three to six months for a complete return to function.
Total knee replacements have a well-established track record, showing survival rates of approximately 98% at ten years and over 80% at 20 years. While modern partial knee implants have excellent long-term outcomes, with up to a 95% survival rate at ten years, they carry a higher long-term risk of requiring revision surgery. This is primarily because the preserved compartments remain susceptible to the progression of arthritis over time. If arthritis develops or progresses in the previously healthy areas, the PKR must be converted to a TKR to address the new damage.