Knee replacement surgery is a common treatment for individuals suffering from severe arthritis that has damaged the joint surfaces. This procedure involves removing the damaged bone and cartilage. Artificial components are then used to replace them, restoring function and relieving pain. While both total and partial knee replacement surgeries differ fundamentally in the extent of the joint they address, understanding this distinction, surgical criteria, and the post-operative experience is important.
The Scope of Total Knee Replacement
Total Knee Replacement (TKR) is a comprehensive procedure for those whose arthritis affects multiple areas of the knee joint. The knee is divided into three compartments: the medial (inner side), the lateral (outer side), and the patellofemoral (under the kneecap). In a TKR, the surgeon resurfaces the entire ends of the thigh bone (femur) and the shin bone (tibia).
This process involves removing the damaged cartilage and underlying bone from all three compartments. Metal components are cemented onto the prepared bone surfaces. A high-density plastic spacer is placed between the metal parts to mimic the function of healthy cartilage, providing a smooth gliding surface for movement. The back of the kneecap is often resurfaced.
The Scope of Partial Knee Replacement
Partial Knee Replacement (PKR), also called unicompartmental knee replacement, is a bone-preserving procedure. This option is reserved for those whose arthritis is strictly confined to only one of the knee’s three compartments. The damage is most frequently isolated to the medial compartment, which is the inner side of the knee.
During a PKR, the surgeon only replaces the damaged cartilage and bone in that single affected area. The healthy cartilage, bone structure, and surrounding ligaments in the unaffected compartments are left intact. The implant used is significantly smaller than a total knee implant, resulting in less tissue disruption during surgery.
Determining Patient Eligibility
The primary factor differentiating patient eligibility is the location and extent of the arthritic damage. TKR is recommended for patients with widespread damage affecting two or all three compartments of the knee. It is also the choice for individuals with inflammatory arthritis, such as rheumatoid arthritis, or those presenting with significant angular deformity or ligament instability, as a TKR can correct these structural issues.
Conversely, a patient must meet criteria to be considered a candidate for a PKR. Damage must be entirely limited to one compartment, and the major ligaments, particularly the anterior cruciate ligament (ACL), must be intact and functional to ensure joint stability. PKR is not able to address significant deformities or complex instability. While age and activity level were once strict considerations, the most important factor remains the condition of the joint itself.
Post-Surgical Comparison
Because PKR is a less invasive procedure with less bone and tissue dissection, it results in a faster and less painful recovery compared to TKR. Patients undergoing PKR often return to light activities within a few weeks, while TKR patients may require three to six months for recovery due to the extensive tissue trauma.
PKR often results in a knee that feels more “natural.” This is attributed to the preservation of healthy cartilage, bone, and ligaments, which contributes to better joint mechanics and range of motion. TKR, by replacing the entire joint, sometimes results in a feeling that the knee is artificial.
When considering long-term durability, TKR implants have a lower revision rate and are associated with excellent outcomes lasting 20 years or more. PKR implants, while highly successful, have a slightly higher likelihood of needing revision surgery within ten years. This is primarily because the arthritis can progress in the two compartments that were not replaced, potentially necessitating a future conversion to a Total Knee Replacement.