Written by: Dr. Frederick Buechel, Jr.

What is knee arthritis?

Osteoarthritis is the most common form of knee arthritis. Arthritis is a term that combines “arthro”- which means “joint”, and “-itis” which means “inflammation” to make the word “arthritis” that means “joint inflammation”. Knee arthritis is “knee joint inflammation”. There are many causes of joint inflammation. We define the type of joint inflammation by the term in front of the word “arthritis” like osteoarthritis.

What is knee osteoarthritis?

Knee OsteoarthritisOsteoarthritis is the most common form of arthritis. “Osteoarthritis” is joint inflammation from a degenerative condition of the joint cartilage. This condition can occur as the result of a traumatic injury to the knee or, from a genetic predisposition to cartilage degeneration. The process can begin with cartilage softening. This is followed by fraying and fissuring of the surface cartilage on the end of the bone. As the cartilage wears down, the surface can start to delaminate from the bone surface. This can progress until the surface cartilage is completely worn from the bone.

As this process progresses, the pressure on the bones increases as the shock absorbing capability of the cartilage is reduced. The bone responds by growing wider at the edges producing what are called “osteophytes”, or bone spurs. As this process occurs, the joint compartment lining called the synovium, can be activated to produce a response to the irritation, and it can start producing increased volumes of lubricating joint synovial fluid.

Arthroscopic View of Knee Osteoarthritis Stages

This increased joint fluid can fill the knee compartment causing swelling, pain, reduced range of motion and the fluid can be pressurized out the back of the knee causing popliteal cysts (Baker’s cysts) and can be pressed into the bone causing fluid cysts in the bone below the cartilage surface that are called “sub-chondral cysts”. The bone also can react to the increased pressure by getting harder, which we call sub-chondral sclerosis. These changes can be seen on x-ray and MRI.

What are the symptoms of knee osteoarthritis?

The symptoms patients experience from osteoarthritis of the knees are listed below. These symptoms occur from the breakdown and loss of cartilage that causes increased friction and irritation, the release of chemicals that stimulate pain and the further breakdown of cartilage, and fluid production from the lining of the knee joint that makes motion more difficult, increases pressure in the knee, and directs fluid to places it normally is not present. The degenerated cartilage surfaces can also lead to the tearing of the cartilage bumper between the bones called the meniscus.

Knee Arthritis Pain Symptom LocationsSymptoms can include:
• Pain when walking
• Pain getting up from seated position
• Pain walking Stairs
• Dull aching Pain
• Stiffness in knee
• Swelling of the knee Joint
• Swelling behind the knee joint called a popliteal cyst, or Baker’s Cyst.
• Loss of motion in the knee from fluid accumulation, bone spurs, cartilage loss and pain
• Decreased walking distance due to pain
• Limping due to pain and angular deformity
• Knee angular deformities due to loss of cartilage surface and bone surface with advanced wear.

What are the causes of knee osteoarthritis?

The causes of knee osteoarthritis are most commonly due to genetic predisposition, from a prior joint injury that damaged the cartilage surface, or damage to the cartilage surface protecting “meniscus” that leads to higher pressure on the knee joint surface cartilage.

How do you diagnose osteoarthritis?

There are several steps to help diagnose osteoarthritis of the knee. These include:

History & Physical Exam

Patient health history of previous injuries or pain and a brief physical and mobility examination of the problem area may help narrow the cause of discomfort or lack of mobility.


X-rays are the first line of imaging to identify and characterize knee osteoarthritis. These should be taken first before or in conjunction with any other imaging studies done. Proper X-ray views performed at the correct angles, and with weight bearing on specific views, are needed to be able to correctly diagnose the knee joint arthritic condition and properly show the joint space loss from osteoarthritis. X-rays show us the bones of the knee but not the cartilage surface. Knee osteoarthritis findings that are seen on x-ray include:

  • Joint space loss
  • Sub-chondral sclerosis (hardening of the bone, increased white appearance)
  • Bone spurs
  • Bone cysts
  • Angular deformity

Cartilage surfaces on x-ray are invisible. Therefore, cartilage thickness or thinning is identified by the height of the space seen between the bones. Bigger space, more cartilage. Smaller space, less cartilage. Sub-chondral sclerosis is the hardening of the bone (increased bone density) just below the cartilage surface seen as whiter on the x-ray film.

 Proper Diagnostic x Ray Views for Knee Osteoarthritis

Bone spurs or “osteophytes” are the extra bony growth seen at the edges of the bone surfaces in patients with osteoarthritis. These can be small or giant growths of extra bone. Some patients develop very large osteophytes that can limit motion of the knee. Some osteophytes form and are freely floating in the knee joint and they can be referred to as osteochondral “loose bodies”.

Sub-chondral Bone cysts are thought to be created by pressurized joint fluid getting into the bone below the damaged cartilage surfaces. Some cysts are small and some a quite large. These cysts can weaken the bone and/or be a source of pain. Angular deformities occur as the cartilage surfaces progressively wear away and then the bone starts to wear down. When the inside of the knee joint called the “medial side” wears down, the knee angles inward and this “bowlegged” deformity is called “varus”. When the outside of the knee joint called the “lateral side” wears down, the knee angles outward and this “knocked-kneed” deformity is called “valgus”. The actual quality of structural damage to the cartilage or the exact volume of the cartilage loss or damage cannot be seen on x-ray but can be visualized using MRI.


When to get and MRI types for Knee OsteeoarthritisWhen to order MRI’s:

  • When pain is not limited to the compartment where the x-ray disease is located
  • When X-rays are suspicious for other compartment disease or, when there is pain without x-ray explanation for the pain. 

After the diagnosis of osteoarthritis is made with proper x-rays, MRI images can further detail the damage and exact locations of cartilage disease and show all the healthy structures of the knee joint. MRI provides detailed images without the use of radiation, instead it uses magnets to create images of the bone and soft tissues of the knee. The MRI can show cartilage thickness, areas of damage, fraying and flaps and the areas of healthy cartilage. MRI can show bone reaction and inflammation in detail, which the x-rays cannot. The MRI, unlike the x-rays, shows the cartilage, ligaments, tendons, muscles, nerves, and vessels, as well as the bone.

What Dr. Buechel Looks for:

  • Meniscus Tears – When the joint line is tender or painful
  • Large Popliteal Cysts – Can cause posterior knee pain and limited motion
  • Osteonecrosis – Medial Femoral Condyle or Tibial Plateau
  • Articular Cartilage Disease – Knowing the quality of the cartilage in each compartment can help make the proper decision between partial and total knee in some cases
  • Bone bruising or stress fractures
  • Tendon and ligament injury or inflammation

What makes someone a knee osteoarthritis specialist?

A knee osteoarthritis specialist is usually an orthopaedic surgeon. These surgeons are trained in the evaluation, diagnosis, and treatment of osteoarthritis. Orthopaedics surgeons do operate on knees with osteoarthritis but they are also the doctors who are often the first line treaters of this condition with non-operative options also. A good orthopaedic surgeon should teach you about your condition and then offer you the best options based on the condition your knee is in at the time of your visit.

Sometimes patients can be treated initially with non-surgical options, but some patients present too late in the process and require surgery to provide the most pain relief and functional improvement. Orthopaedic kneesurgeon specialists are interested in all the options for treating this condition and should be knowledgeable or open to the more advanced treatments currently available for patients which include robotics and biologic solutions to osteoarthritis.

Can you leave knee osteoarthritis untreated?

Yes, you can leave knee osteoarthritis untreated. Unlike cancer or heart disease, osteoarthritis left untreated will not shorten your life. However, it will reduce your quality of life. Managing your quality of life, reducing pain and increasing function, is what treating knee osteoarthritis is all about. There are non-surgical and surgical ways to treat knee osteoarthritis.

How do treat knee osteoarthritis non-surgically?

There are many ways that patients can try to reduce the symptoms of their knee osteoarthritis. Any of the non-surgical options can be tried and used until the symptoms are no longer tolerable by the individual. Some treatments have very little risk, some have greater risk and more side effects. Patients must weigh the risk benefit ratio of each of these options when deciding if they are right for them.

There are more proven non-surgical options, and some that have not really shown much benefit in the medical literature that can be considered. Ultimately, it is the patients desire to try any of the options that determines the course of treatment. Below is a list of several of the non-surgical options for osteoarthritis of the knee:

  • NSAIDs
  • Ice
  • Physical therapy
  • Nutritional supplements
  • Glucosamine Turmeric
  • Unloader Braces
  • Electrical stimulation
  • Cortisone injections
  • PRP injections
  • Stem Cell injections
  • Acupuncture
  • Topical pain medications and anti-inflammatories

How do you treat knee osteoarthritis surgically?

There are several surgical options for knee osteoarthritis that is painful and no longer responsive to non-surgical care. These options should be discussed with your surgeon based on your particular condition.

• Partial Knee Replacement: See details below
• Total Knee Replacement: See details below
• Osteotomy
• Cartilage Repair procedures
• Arthroscopic “washout”

What is a partial knee replacement?

Partial knee replacement is a procedure that replaces the surfaces of the bones in one or two of the three compartments of the knee. This is for patients with non-inflammatory arthritis like osteoarthritis, osteonecrosis, and post-traumatic arthritis. All the ligaments of the knee are preserved with this procedure. The surfaces are replaced with metal and plastic surfaces with implant materials that are the same as total knee replacement materials.

Partial knee replacement, when done well, is a great option for osteoarthritis of the knee, and many patients say it feels more natural than total knee replacement.

The recovery is usually faster and less difficult than a total knee replacement. This is generally much less invasive than total knee replacement. The lifespan of a properly indicated and performed partial knee replacement is similar to a properly done total knee replacement. The implants can last 15-25 years or more, before the plastic part could wear down and needs replacing, or the metal parts loosen from the bone and need replacing. Sometimes just the plastic part can be changed in the future if necessary making the recovery from this procedure very fast.


Partial knee replacements can be converted to total knee replacement in the future if necessary. If only one side is replaced, this does not mean that the other side will eventually wear out also. The partial knee replacement may be the only replacement ever needed for many patients. Not all patients are candidates for this procedure, this is why interested patients should seek the advice of an experienced partial knee surgeon to get correct advice. Robotic-Arm Assisted Partial Knee replacement (Mako Partial Knee) is an advanced system that allows for highly accurate installation of partial knee replacements which has been shown to significantly reduce the risk of early failure seen in manually performed partial knee replacement. Review the Robotic Joint Center Partial Knee Replacement Page for full details.

What is a total knee replacement?

Total knee replacement is a procedure that replaces all three compartments of the knee joint, and it is also a surface replacing procedure. This is for patients with all types of arthritis, inflammatory and non-inflammatory. This can be performed on patients with moderate to severe arthritis and with patients that have significant bone loss and deformities. During total knee replacement, one or two of the middle knee ligaments are removed. (The ACL and possibly the PCL) The surfaces are replaced with metal and plastic surfaces.

Before and after complex Robotic Total Knee by Dr. Buechel

Most implants use polyethylene as the plastic and cobalt chrome and titanium alloys as the metals. In some cases, ceramics or ceramic coated surfaces are used on the femoral side. Total knee replacement is a good option for patients with global knee pain and cartilage loss in all three compartments of the knee. Patients with total knee replacements can participate in all activities of daily living. Most surgeons recommend low to moderate impact activity after total knee replacement. Some patients continue with very active and high impact lifestyles which for some is okay, but the risk is accelerated plastic wear and possibly implant loosening from the bone, which may require sooner revision surgery. Robotic-Arm Assisted Total Knee replacement (Mako Total Knee) is an advanced system that allows for highly accurate installation of total knee replacements which allows for more accurate bone preparation, implant sizing, and ligament balance which makes the knee feel more natural, move better and has been shown to causes less pain post operatively in some studies. Review the Robotic Joint Center Robotic Total Knee Replacement Page for full details.

What is an Arthroscopic “Washout/Cleanout”?

This treatment option for primary osteoarthritis of the knee has been shown to provide no long-lasting benefits. Using an arthroscope, the knee is flushed of the cartilage debris using saline solution, and some of the frayed edges of cartilage can be trimmed. Some people may feel some improvement for a few months, but the symptoms if improved generally return soon after. Some people feel worse after a knee arthroscopy and “cleanout” for just osteoarthritis. There is a benefit for some if you have an acute tear of your meniscus and the meniscal tear is the real cause of the pain, and your arthritis is not severe. However, in these cases, patients may still not have long lasting pain relief.

What is an Osteotomy?

An osteotomy is a surgical treatment that cuts the bone and changes the angle of knee bones to change the pressure on the knee joint from the worn down side to the healthier side. This is designed for younger patients with osteoarthritis on only one side of the joint. It involves a significant operation that requires the bone to be cut with a surgical saw, the position changed and then held in the new position with plates and screws, followed by a period of weight bearing reduction until the bone heals. It is generally offered to younger heavy laboring patients but has several negative aspects that should be fully discussed with the surgeon prior to considering this option.

Frederick F. Buechel, Jr. MD

Meet Frederick F. Buechel, Jr. MD

Frederick Buechel, Jr., MD is an internationally renowned orthopedic knee surgeon, an international instructor, and an expert in the field of Robotic Partial Knee Replacement and Robotic Total Knee Replacement.

Learn More

Patient Experiences

29 Total Reviews


Call us at 212-308-3089.
Or click to send an appointment request online.

Request an Appointment

Meet Frederick F. Buechel Jr. MD

Frederick F. Buechel Jr. MD is an internationally renowned Orthopaedic Surgeon who is Fellowship Trained in Knee and Hip Joint Replacement and specializes in robotic partial knee replacement, robotic total knee replacement, knee meniscus surgery, and stem cell therapy. Learn More »

Schedule Your Appointment Today