Unicompartmental Knee Arthroplasty: A Patient's Guide to Partial Knee Replacement using Minimally-Invasive Surgery (MIS) Techniques.

Edited By: Seth S. Leopold, M.D.
Last updated Wednesday, December 29, 2004

Figure 6 - Knee arthritis can affect any of the three compartments of the knee. Medial-sided knee pain, located on the part of the knee that faces the opposite knee, is the most common location for arthritic pain.

Figure 7 - Lateral knee pain, affecting the "outside" of the knee, is sometimes the result of arthritis of the knee.

Figure 8 - Pain behind the kneecap from arthritis may occur along with arthritis elsewhere in the knee, or in isolation. Isolated patellofemoral arthritis is the least common pattern of knee arthritis.

Figure 9 - This patient had diffuse arthritis throughout his knee from an old fracture of the tibia (shinbone), which at that time was treated with the two screws that are visible. This patient was later treated with a total knee replacement, similar to the one shown in Figure 10.

Figure 10 - This patient had rheumatoid arthritis and symptoms throughout her knee, resulting in the traditional total knee replacement pictured here.

Figure 11 - This patient's arthritis was confined to the medial ("inside") compartment of her knee on x-rays, and her pain was localized to that part of the knee as well. She was a good candidate for minimally-invasive partial knee replacement.

Figure 12 - Minimally-invasive partial knee replacement may be performed for either medial ("inside" of the knee) or lateral ("outside" of the knee) arthritis patterns, provided the symptoms are limited to that one part of the knee. X-rays of two knee replacements are shown here. On the left is a lateral replacement, and on the right is a medial replacement.

Review of the condition

What are some general characteristics of arthritis of the knee? What are its usual manifestations?

Pain

Pain is the most noticeable symptom of knee arthritis. In most patients, the pain gradually gets worse over time, but sometimes has more sudden “flares” where the symptoms get acutely severe. The pain is almost always worsened by weight-bearing and activity. In some patients, the pain becomes severe enough to limit even routine daily activities.

Stiffness

Morning stiffness is present in certain types of arthritis; patients with this symptom may notice some improvement in knee flexibility over the course of the day. Rheumatoid arthritis patients may experience more frequent morning stiffness than patients with osteoarthritis.

Swelling and warmth

Patients with arthritis sometimes will notice these symptoms. If the swelling and warmth are excessive, and are associated with severe pain, inability to bend the knee, and difficulty with weight-bearing, those signs might represent an infection. Such severe symptoms require immediate medical attention. Joint infection of the knee is discussed below.

Location

The knee joint has three “compartments” that can be involved with arthritis (see figure 6). Most patients have both symptoms and findings on X-rays that suggest involvement of two or more of these compartments--for example, pain on the lateral side (see figure 7) and beneath the kneecap (see figure 8). Patients who have arthritis in two or all three compartments, and who decide to get surgery, most often will undergo total knee replacement (see figures 9 and 10).

However, some patients have arthritis limited to one compartment of the knee--most commonly the medial side (see figure 11). When patients with one-compartment arthritis (also called “unicompartmental” arthritis) decide to get surgery, they may be candidates for the mini knee (see figure 12).

What are the different types of arthritis of the knee?

Inflammatory arthritis

This broad category includes a wide variety of diagnoses, including rheumatoid arthritis, lupus, gout, and many others. It is important that patients with these conditions be followed by a qualified rheumatologist, as there are a number of exciting new treatments that may decrease the symptoms and perhaps even slow the progression of the joint damage.

Patients with inflammatory arthritis of the knee usually have joint damage in all three compartments, and therefore are not good candidates for partial knee replacement. However, inflammatory arthritis patients who decide to have total knee replacement have an extremely high likelihood of success; these patients often experience total or near-total pain relief following a well-performed joint replacement.

Osteoarthritis

Osteoarthritis is also called OA or “degenerative joint disease.” OA patients represent the large majority of arthritis sufferers. OA may affect multiple joints, or it may be localized to the involved knee. Activity limitations due to pain are the hallmarks of this disease.

OA patients who have symptoms limited to one compartment of the knee are sometimes good candidates for the mini knee.

What else might be confused with or similar to arthritis of the knee? How can these be distinguished from the condition?

Meniscus tear

Sometimes patients with knee pain don't have arthritis at all. Each knee has two rings of cartilage called "menisci" (this is the plural form of "meniscus"). The menisci work similarly to shock absorbers in a car.

Menisci may be torn acutely, in a fall or as the result of other trauma, or they may develop degenerative tears from wear-and-tear over many years. Patients with meniscus tears experience pain along the inside or outside of the knee; sometimes the pain is worse with deep squatting or twisting. Popping and locking of the knee are also occasional symptoms of meniscus tears.

Since some of these symptoms may be present with arthritis, and the treatment of arthritis is different from that of meniscus tears, it is important to make the correct diagnosis. A good orthopaedic surgeon can distinguish the two conditions by taking a thorough history, performing a careful physical examination, and by obtaining imaging tests. X-rays and Magnetic Resonance Imaging (MRI) scans may be helpful in distinguishing these two conditions.

Joint infections

Also called infectious arthritis or septic arthritis, a joint infection is a severe problem that requires emergent medical (and often surgical) attention. If not treated promptly, knee infections can cause rapid destruction of the joint; in the worst cases, they can become life-threatening.

Symptoms of a knee joint infection include:

• severe pain,
• joint swelling and warmth,
• fevers, and
• marked inability to walk, bend the knee, or bear weight.

Patients who suffer from arthritis are not more likely to develop such infections. They may occur in anyone. Arthritis patients who develop such infections would notice a significant worsening in their pain, as well as some of the other symptoms listed above.

A physician will make the diagnosis of a joint infection based on history and physical examination, blood tests, and by sampling joint fluid from the knee.

Again, a joint infection is a serious condition that requires immediate medical attention.

How common is arthritis of the knee (statistics, demographics, risk factors)?

How is arthritis of the knee diagnosed? What tests or exams may be used?

History and physical examination

An orthopaedic surgeon will begin the evaluation with a thorough history and physical exam. Based on the results of these steps, (s)he may order plain X-rays.

X-rays

If you have arthritis of the knee, it will be evident on routine X-rays of the joint. X-rays taken with you standing up are more helpful than those taken with you lying down, as the way your joint functions under load (i.e. standing) provides important treatment clues to your physician.

Also, plain X-rays will allow your orthopaedic surgeon to determine whether your arthritis pattern would be suitable for the mini knee, should you eventually decide that surgery is for you.

Can medications help arthritis of the knee?

It is important to distinguish broadly between two types of arthritis: inflammatory arthritis (including rheumatoid arthritis, lupus, and others) and non-inflammatory arthritis (such as osteoarthritis).

Although there is some level of inflammation present in all types of arthritis, conditions that fall into the category of true inflammatory arthritis are often very well managed with a variety of medications, and more treatments are coming out all the time. Individuals with rheumatoid arthritis and related conditions need to be evaluated and followed by a physician who specializes in those kinds of treatments, called a rheumatologist. Excellent non-surgical treatments (including many new and effective drugs) are available for these patients; those treatments can delay (or avoid) the need for surgery, and also help prevent the disease from affecting other joints.

So-called non-inflammatory conditions, including osteoarthritis (sometimes called degenerative joint disease), also sometimes respond to oral medications (either painkillers like Tylenol, or non-steroidal anti-inflammatory drugs like aspirin, ibuprofen, celebrex, or vioxx) but in many cases, symptoms persist despite that type of treatment.

It is important to avoid using narcotics (such as Tylenol #3, vicoden, percocet, or oxycodone) since they are have many side effects, are habit-forming, and make it harder to achieve pain-control safely and effectively after surgery, should that become necessary. Narcotics are designed for people with short-term pain (like after a car accident or surgery), or for people with chronic pain who are not surgical candidates. People who feel they need narcotics to achieve pain control should consider seeing a joint replacement surgeon (an orthopaedic surgeon with experience in knee replacements) to see whether surgery is a better option.

Can exercises help arthritis of the knee?

Specifically, how is arthritis of the knee improved by partial knee replacement surgery?

This exciting new technique is much less disruptive to the tissues (muscles, tendons, and ligaments) around the knee than traditional total knee replacement. The small size of the incision, and the less-invasive nature of the surgical approach, allows patients to recover from this operation much more quickly.

Hospital stays are shorter--down to 1 or 2 days for most patients--and the recovery period is much faster. Patients lose less blood, experience substantially less pain than traditional knee replacement, and often walk unassisted (no cane or walker) within a week or two of the operation. Even many patients who have both knees done at once with this newer technique are able to walk without the assistance of a walker or cane fairly quickly.

A recent study from England (Journal of Arthroplasty Dec 2001; 16(8): 970-6) compared the rehabilitation of minimally-invasive partial knee replacement patients with the rehab of patients who had partial knee replacements done through a longer incision, as well as with patients who had conventional total knee replacements. The patients who had the “mini” replacement recovered about twice as quickly as those who had partial replacements done with the older partial-replacement technique, and about three times faster than traditional total knee replacements (see movie 1).

Quicktime movie

• Movie 1 - Patient walking less than two weeks after having both knees replaced on the same day (0.59 MB)

Surgery for arthritis of the knee at the University of Washington

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