Knee osteoarthritis and replacement

Knee osteoarthritis is the wearing away of articular cartilage due to aging. It is the most common joint disease after age 60. But age is not the only cause: it can also result from the after-effects of trauma (joint fractures, ligament ruptures particularly of the ACL, old meniscal tears, especially after meniscus removal), inflammatory diseases, or limb axis disorders (knock knees or bow legs). Osteoarthritis causes pain, stiffness and swelling, with a progressive impact on walking and quality of life.

The severity of osteoarthritis is assessed on a scale of four grades corresponding to the state of the cartilage:

• Grade I: the cartilage is softened.
• Grade II: fissures appear in the cartilage.
• Grade III: the cartilage is badly damaged, fraying like worn fabric.
• Grade IV: complete disappearance of cartilage, the bone is bare and rubs directly against bone.

This classification guides treatment: early grades are managed medically (including PRP injections), while grade IV, very advanced, often leads to knee replacement.

For grade IV osteoarthritis, disabling and resistant to medical treatment, total knee replacement (TKR) is generally proposed. The principle: resurface the destroyed joint surfaces, like relining worn surfaces. The femoral component is metallic, the tibial component combines a metal baseplate with a polyethylene insert (a special, highly resistant plastic that recreates the gliding surface), and the kneecap can be resurfaced with a polyethylene button. The prosthesis restores a pain-free, mobile joint.

To position the prosthesis with the greatest precision, Dr Charousset uses a computer-assisted surgery system. A distinction must be made between robots (where the procedure is performed by the machine according to a plan) and navigation systems (where the computer guides and informs the surgeon who performs the procedure). Dr Charousset has chosen an optical tracking navigation system: sensors fixed on the femur and tibia are tracked by a camera connected to a computer, as are the surgical instruments. Everything is done during the procedure, with no special preoperative imaging required. The computer calculates in real time the positioning of the implants in three planes, the overall axis of the lower limb, and the range of motion obtained, allowing optimal alignment.

Dr Charousset prospectively follows patients who have undergone computer-navigated knee replacement. In a series of 91 knees operated on in 87 patients (58 women, 29 men, average age 71), with an average preoperative angular deviation of 8.5°, the results confirm the reliability of the technique: average postoperative angular deviation reduced to 1.9°, very close to perfect alignment. No early surgical revision for hematoma or infection, no return to conventional instrumentation. Computer navigation proves to be a reliable tool for precise, reproducible positioning of the prosthesis.

After the operation, the patient remains under observation in the recovery room (PACU) for one to two hours. A knee X-ray is taken to check the result of the procedure. Back in the room, the pain management protocol prescribed by Dr Charousset is administered. The dressing is redone by the nurse on the second postoperative day. Pain management, anticipated from the preoperative period as part of the ERAS protocol, is a key element of comfort and recovery.

Rehabilitation begins the day after the procedure. The physiotherapist gets the patient standing and into a chair, then starts mobilizing the knee on a continuous passive motion machine (Kinetec), a device that passively mobilizes the knee to quickly regain range of motion. The physiotherapist also teaches the muscle-strengthening exercises needed to regain good tone. Rehabilitation, continued over several weeks, is decisive for the final functional result.

When osteoarthritis affects only one compartment of the knee (most often the medial one), it is not always necessary to replace the entire joint. Dr Charousset can then propose a unicompartmental knee replacement (UKR), which resurfaces only the worn compartment while preserving the rest of the knee. This less invasive procedure offers faster recovery and a knee that feels more 'natural', provided the other compartments and ligaments are healthy. The choice between total and unicompartmental replacement is discussed based on each patient's workup.