Knee Osteoarthritis
What is it?
Knee osteoarthritis is a degenerative process in the tibiofemoral and patellofemoral joints, which leads to loss of cartilage and pain. It’s a bit like when a tire loses its tread.
How does it get hurt/damaged?
A healthy knee has a host of factors that help the knee functioning normally, the major factors being:
Ligaments, providing stability and helping the knee move the way it should
An inside (medial) and outside (lateral) meniscus, helping disperse forces between the tibia and femur
Synovial fluid, providing nutrients and lubrication for the cartilage/knee
Cartilage, providing smooth minimal friction movement
When one of these things gets out of whack, it can start the process of arthritis. Loss of meniscus leads to an inability to cushion the knee, causing irregular wear on the cartilage. Injury to a ligament leads to abnormal motion which causes abnormal force and subsequent wear. A traumatic injury from impact to cartilage can lead to a pothole or roughened area on the cartilage surface which affects the motion and wear of the surround cartilage. Lastly, changes to the synovial fluid in the knee, from infection, autoimmune disorders, or trauma, can all lead to damage to cartilage wear and arthritis.
What are the risk factors?
You will start to sense a trend in regards to risk factors for knee injury. They are always lumped into modifiable and non-modifiable, and many of these risk factors are consistent across many different injuries/pathologies of the knee.
Modifiable:
Bodyweight: 1 pound of bodyweight = 7 pounds of force through the knee. For example: 15 pounds one way or the other changes forces on your knee by over 100 (105) pounds.
Muscle strength and tone: the reason physical therapy works is not because it reverses the disease, but instead helps to strengthen the dynamic stabilizers of the knee, aka, your surrounding muscles. This helps to improve your overall gait (walking) biomechanics. This helps you to walk normally, without a limp, and in so doing helps your muscles to absorb more of the forces that your knee experiences when walking. Strong, well-balanced muscles protect the knee.
Intra-articular inflammatory state: simply put, swelling and inflammation hurts, and is caused by cells in the knee in response to an injury or in the case of arthritis in response to the chronic degeneration. We can’t undo the cause of the swelling, but we can help to diminish the swelling with oral (by mouth), topical (skin based) and intra-articular (shot) medications. Things like corticosteroids, non-steroidal anti-inflammatories (Advil, Aleve, Mobic, etc) and natural anti-inflammatories (omega-3, turmeric, ginger, etc) can all act to reduce inflammation.
Bony alignment: patients who are knock kneed or bow-legged end up loading their knee in a pathologic way which can lead to earlier wear and degeneration. This can be addressed with bracing to help offload the area of the knee that is overloaded. The brace in essence acts like a car jack, to “jack” open the area of the knee that is experiencing too much force and therefore pain. Surgery can also correct the issue.
Nonmodifiable:
Post-traumatic development of osteoarthritis: patients who have sustained a major knee injury in their life are at a significantly elevated risk of developing osteoarthritis later in life.
How common is knee osteoarthritis?
13% of women over 60 and 10% of men over 60 have symptomatic knee osteoarthritis.
When should you be worried about knee osteoarthritis and what should you do initially?
Knee osteoarthritis can manifest in a number of ways, however commonly presents as progressive knee pain, first noticeable with high-demand activities. This can then progress to knee pain with stairs, shorter walks and eventually aching and pain at night.
When the symptoms are bothersome enough and affecting your quality of life, you should present to your primary care provider to discuss symptoms and next steps of care.
What is the severity of the injury and the treatment options?
Knee osteoarthritis is commonly “graded” on xrays and MRI, however what matters the most is the patient. We treat patients, not images, which means some patients have debilitating pain with moderate X-ray reads, while others have end stage arthritis on xrays but very little pain or disability. Because any kind of treatment comes with risks, the patient and the physician should always weigh the risks and the potential reward of the proposed treatment to know what is the best option.
There are numerous treatment options, but the three main pathways are:
Conservative (nonoperative) management: this includes if applicable: bracing, injections, physical therapy, weight loss, medical management. From an injection standpoint, there are numerous but three common types: a) Corticosteroid injections which aim to decrease inflammatory response, b) Hyaluronic acid injections which also can decrease inflammation and concurrently increase lubrication in the joint, and c) Biologics which include stem cell injections, platelet rich plasma (PRP) injections as well as others. In the setting of arthritis, the biologic agents are not acting so much to “regenerate” or regrow cartilage/reverse the arthritis, they are more acting to decrease the inflammatory state and improve pain.
Surgical management, aka “joint preserving”: these types of procedures are aimed to address malalignment. If a patient is severely knock kneed or bow-legged and their arthritis is isolated to one area of the knee, a surgery called an osteotomy can be performed. In an osteotomy, the bone is cut and realigned to straighten out the knee joint and thereby offload the area of the knee that is painful. The osteotomy is more powerful and definitive than an unloader brace but acts by a similar principle, like a car jack that can open up the damaged space. This option allows the patient to maintain their native joint. The two main kinds of osteotomies are a distal femoral osteotomy (cutting the lowest part of the femur) and proximal tibial osteotomy (cutting the highest or top part of the tibia).
Arthroplasty or joint replacement: this option includes replacing either a portion or the entirety of the knee joint with metal and plastic. In doing so, the damaged cartilage surfaces of the knee and the arthritis are removed, thus removing the pain causing agents. However, it’s a big procedure which requires extensive soft tissue manipulation, so the surgery itself does cause pain at least for a period of time following the operation. The main kinds of arthroplasty are: a) patellofemoral arthroplasty, replacing the trochlea and the patella, b) medial or lateral unicompartmental arthroplasty, just replacing the inside or the outside portion of the knee, and c) a total knee arthroplasty, replacing all three compartments.
