Total knee replacement

Overview

Front view of the knee showing the femur, tibia, patella, cruciate and collateral ligaments, and the medial and lateral menisci. — **Knee anatomy.** The knee is the meeting point of the thigh bone (femur), shin bone (tibia), and kneecap (patella). Four ligaments hold it together — the ACL and PCL inside the joint and the MCL and LCL on the sides — and two C-shaped menisci cushion the joint surfaces.

The knee is a hinge joint where the femur, tibia, and patella articulate through three compartments of cartilage. When that cartilage wears through across multiple compartments — the hallmark of tricompartmental osteoarthritis — standing, walking, and stairs become painful and the leg can bow or buckle. Total knee replacement resurfaces the damaged ends of the bones.

How the Procedure Works

Standing long-leg X-ray showing a well-aligned total knee prosthesis with the hip-knee-ankle mechanical axis passing through the center of the knee replacement. — **Post-op knee replacement.** The femoral, tibial, and (usually) patellar components resurface the three worn compartments. Alignment matters as much as the implants — the mechanical axis from hip through knee to ankle should pass through the center of the new joint, as shown here.

We remove the damaged cartilage and a measured layer of bone from the femur, tibia, and typically the back of the patella — no more than necessary, because bone removal is permanent. Metal components are cemented or press-fit onto the femur and tibia, with a polyethylene spacer between them. The part of the procedure that most affects the outcome isn't implant selection; it's gap balancing and alignment. We check flexion and extension gaps with trial components in place: if the knee is tighter in flexion than extension, or vice versa, we adjust the tibial cut and soft-tissue releases until both gaps match. A knee that is well-balanced and properly aligned will track smoothly, bear load evenly, and feel stable through the full arc of motion. One that is not will hurt and wear asymmetrically regardless of implant brand.

When to Consider Total Knee Replacement

Total knee replacement is generally offered when symptoms, imaging, and a trial of non-operative care together point to surgery as the next step. The typical picture includes:

Advanced tricompartmental arthritis
Cartilage loss across multiple compartments on weight-bearing X-rays, with daily pain and functional loss.
Exhausted non-operative care
Failed extended course of anti-inflammatories, physical therapy, weight loss, bracing, and intra-articular injections.
Deformity or instability
Progressive varus or valgus deformity, or a knee that buckles — both signal that the joint is no longer supporting the limb.