Knee Arthritis: Causes, Diagnosis and Complex Replacement

Knee arthritis has four main causes: osteoarthritis, the most common, which comes with age; rheumatoid arthritis, an inflammatory disease that can strike young patients; post-traumatic arthritis after a fracture or injury; and gout. Diagnosis rests on blood tests, inflammatory markers and a standing X-ray. Early disease can sometimes be treated with physiotherapy and, in selected cases, injections; a destroyed or deformed knee needs replacement, often with computer navigation or a robot.

Every surgeon sees arthritic knees. What separates the routine case from the difficult one is the cause behind the damage and the shape of the bone around it. Dr. Rohit Lamba, an orthopaedic and joint replacement surgeon, built this part of his masterclass around the difficult end of the range: knees bent by old fractures, frozen by gunshot injury, weakened by steroids or eroded by severe arthritis in a heavy patient. This article covers the causes of knee arthritis, how each is identified, what can be done before surgery, and how navigation and robotics change what is possible when replacement is needed. The wider spectrum of disorders in the session is in the complete guide to orthopaedic disorders.

The four causes of knee arthritis

Knee arthritis is not one disease. Dr. Lamba distinguishes four causes, and each leaves a different pattern of damage.

Osteoarthritis

Osteoarthritis is the most common cause and comes with age. The cartilage that lines the ends of the thigh bone and shin bone wears away over years, the joint space narrows, and bone begins to rub on bone. It usually affects older patients and progresses slowly.

Rheumatoid arthritis

Rheumatoid arthritis is an inflammatory arthritis in which the knee is damaged by the patient's own immune system. Unlike osteoarthritis, it can affect very young patients, and in advanced cases the whole cartilage is lost. Dr. Lamba noted that even very young patients sometimes need surgery as a result.

Treatment of rheumatoid arthritis carries a second problem for the surgeon: steroids. Long-term steroid use weakens bone, and a standard implant may not hold in it. One of his patients, a young woman, needed a knee implant with a rod running down into the bone on both sides of the joint, because her bone was too weak to support a standard component. She went home, in his words, very happy.

Post-traumatic arthritis

The third cause is arthritis that develops after a fracture or other injury around the knee. A fracture that heals in the wrong position changes how load passes through the joint, and the cartilage wears unevenly until arthritis sets in. These knees are often stiff as well as painful, and the bone around them is deformed, which is what makes surgery difficult.

Gout

The fourth cause is gout, a condition in which high levels of uric acid in the blood cause inflammation in the joints. Uric acid crystals deposited in the joint trigger attacks of inflammation, and repeated attacks damage the cartilage over time.

How knee arthritis is diagnosed

Knee arthritis is diagnosed with blood tests and inflammatory markers followed by a standing X-ray, and the aim is to name the cause, because the cause decides the treatment. Dr. Lamba's work-up has two parts.

Blood tests. He starts with routine blood tests and inflammatory markers:

• ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein), general markers that rise when there is inflammation in the body.
• Anti-CCP (anti-cyclic citrullinated peptide antibodies), a blood test that points specifically to rheumatoid arthritis.

Imaging. The X-ray is taken with the patient standing. Under body weight the joint space closes to its true width, so a standing X-ray shows the condition of the cartilage better than any view taken lying down. Dr. Lamba repeated the point for emphasis: X-rays of the knee in the standing position.

Together, the markers separate inflammatory from degenerative disease, and the standing X-ray grades how much cartilage is left.

Knee arthritis treatment before surgery

Early cases can sometimes be treated with exercises and physiotherapy. Strengthening the muscles around the knee reduces the load on the damaged cartilage and improves function.

In certain cases, Dr. Lamba uses what he described as cartilage restoration procedures given as an injection into the joint:

• Viscosupplementation, an injection of a gel that lubricates the joint.
• Platelet-rich plasma (PRP), an injection of a concentrate prepared from the patient's own blood.

The evidence for both injections in knee osteoarthritis is mixed, and major guidelines do not recommend either routinely. They are an option in selected patients, not a substitute for replacement once the joint has failed. Rheumatoid arthritis has its own medical treatment, covered in the complete guide.

Computer navigation and robotic knee replacement

When the cartilage is gone, the answer is knee replacement. For the hardest knees, Dr. Lamba uses two technologies.

Computer navigation

A computer navigation system gives the surgeon live information during the operation: how the joint is aligned, how much bone has to be cut, and how the implant should be placed. At the start of the procedure the surgeon registers specific landmarks on the knee, and the system works from them. From then on, the numbers on screen guide the surgeon to the best alignment of the knee and the best position of the implant.

The robotic system

The robotic system provides the same information and goes further in two ways. First, the plan is made before the operation begins: a CT scan of the knee is loaded into the system, which works out in advance how the bone should be cut and where the implant should sit. Second, a robotic arm carries out the major part of the bone cutting itself, within the boundaries of that plan.

When the technology matters

For a straightforward knee, conventional instruments work well. The technology earns its place when the bone itself is abnormal. Conventional knee replacement relies on guide rods passed inside the thigh bone to set alignment. When the bone is bent by an old fracture, those rods cannot be used, and the surgeon needs another way to know where the true axis of the leg lies. Navigation and robotics provide it, because they work from landmarks and scans rather than from the inside of the bone.

Complex knee replacement: four difficult cases

Dr. Lamba presented a series of cases that show where these tools make the difference.

A knee with a badly healed fracture

The first patient had severe arthritis and an old fracture slightly above the knee that had united in the wrong position, leaving the bone crooked. The deformity meant normal instruments could not be used. With the robotic system, Dr. Lamba completed the reconstruction using basic implants, with no special implants at all. After surgery the X-ray showed a knee that was totally straight and well balanced.

A knee frozen after a gunshot injury

A young man had a gunshot injury that left his knee crooked, severely arthritic and completely stiff: it did not bend at all. He needed special implants as well as computer navigation. Three weeks after surgery he was walking comfortably without any support.

A stiff knee after a fracture that did not unite

Another patient had a stiff knee that would not bend, with severe arthritis that had developed because a fracture had not united well. This knee needed special techniques and implants, and with the help of the robot the operation went smoothly. He went on to walk and bend his knee comfortably.

Severe deformity with bone loss

A very heavy patient had a badly deformed knee with severe arthritis, and her X-rays showed that almost 30% of the bone had been lost to the damage. After reconstruction her legs were straight and she was able to stand and walk.

Dr. Lamba also showed a man walking comfortably without a stick two weeks after knee replacement.

When to refer a knee for complex replacement

Three practical lessons follow from these cases.

1. Investigate the cause before planning treatment. Inflammatory markers and anti-CCP identify rheumatoid arthritis, which may still respond to medicines if the cartilage is intact. Uric acid points to gout.
2. Get a standing X-ray. It is the single most useful image of cartilage loss and the baseline for every later decision.
3. Refer deformed, stiff or post-traumatic knees to a surgeon with navigation or robotic experience. Old fractures, gunshot injuries, steroid-weakened bone and large bone loss are exactly the knees in which conventional instruments struggle and navigation or robotics can help.

Costs are on the total knee replacement cost page and, for both knees at once, the bilateral knee replacement cost page. Hip conditions from the same session, including avascular necrosis and sickle cell disease, are covered in the article on when hip replacement is needed. For a different surgeon's approach to osteoarthritis before replacement, see Dr. Ramkinkar Jha's article on osteoarthritis diagnosis and treatment.