Knee arthritis is a condition that affects more than four million Americans annually, occurs when degenerative changes develop in the cartilage that lines the knee joint.
The knee joint is a complex structure with three main compartments that have individual functions and structures: the inner (medial) compartment and the outer (lateral) compartments are formed by the articulation (or joining) of the lowest part of the thighbone (femur) and the highest part of the shinbone (tibia). The third compartment of the knee is formed by the kneecap (patella) and the front part of the femur and is called the “patello-femoral joint.”
Figure 1: Diagram of knee anatomy, including the patello-femoral compartment, which is located behind the kneecap (patella). Click on image to enlarge.
While the first two compartments are the most important for the patient to walk on flat terrain, the third compartment (patello-femoral joint) is involved in activities like walking on inclined terrain, going up and down stairs, kneeling, squatting, and rising from the sitting position.
Knee arthritis frequently affects two or more compartments of the knee. However, in rare cases, arthritis may be isolated to the patellofemoral compartment. This condition, which is more commonly seen in women, is characterized by pain in the front part of the knee (behind the patella, or kneecap) that typically worsens when the patient walks on inclined terrain, goes up and down stairs, knees, squats, and rises from the sitting position (while walking on level ground is often unaffected).
“Patellofemoral arthritis is diagnosed when loss of cartilage is seen in the joint on x-rays or MRI and no other compartment of the knee is affected,” explains Friedrich Boettner, MD. (Please Note: Many patients with osteoarthritis of the knee first develop the disease in the medial compartment of the knee and subsequently develop patellofemoral arthritis; however, this article focuses on patients who develop arthritis limited to the patellofemoral joint.)
According to Beth Shubin Stein MD patellofemoral joint arthritis is more common in women than in men. Based on the radiographs and MRI studies, your physician can determine if you carry anatomical factors that further predispose you to this condition: a radiographic parameter that is frequently found to be abnormal in patients with isolated patellofemoral arthritis is the “Q angle.”
The Q angle is determined between the quadriceps muscle running down the front of the thigh and its attachment through the patellar tendon below the knee joint. The patella is imbedded in this “musculotendinous complex” that allows the patient to straighten the knee. It tracks on a perfectly matched “rail” provided by the femur, much like a train on a track.
A Q angle exceeding normal range indicates that the patella is being pulled laterally (to the side), and the joint is no longer congruent. This places abnormal stress on the patellofemoral joint, leading to progressive wear and tear of the soft cushion of the joint (cartilage). Dr. Shubin Stein notes, “Women tend to have higher Q angles than men, predisposing them to this condition that typically manifests during the third and fourth decades of life.”
Another factor predisposing patients to patellofemoral arthritis is excessive hip anteversion, a condition in which the neck of the femur rotates too far forward in the hip socket, resulting in additional lateral (sideways) pull on the patella.
In addition, patellofemoral arthritis is more common in patients with patellofemoral dysplasia. In these patients the trochlea groove (femoral side) is misshapen and no longer matches the patella surface, increasing contact stresses and therefore resulting in early cartilage deterioration.
Some patients with loose patellar ligaments and the previously mentioned anatomical abnormalities resulting in severe “maltracking” of the patella can suffer episodes of complete “derailment” (dislocation) of the patella. “This condition - known as patellar instability - also predisposes patients to early patellofemoral arthritis, as each dislocation episode further damages the cartilage coating on the patella and/or trochlea,” explains Dr Shubin Stein.
The anatomical phenomena that lead to patellofemoral arthritis usually affect both legs. Therefore, patients may develop a similar problem in both knees. The orthopedic surgeon will judge if studying both knees is necessary, even though the patient may be experiencing pain in only one knee.
According to Alejandro Gonzalez Della Valle, MD, “In the early stages, patellofemoral arthritis does not cause significant pain or disability. Many affected individuals may be able to walk on level ground for miles - although uneven terrain may cause discomfort - and maintain good flexibility and range of motion in the knee. As a result, the condition may become relatively advanced before the patient seeks treatment.”
When patellofemoral arthritis is detected, depending on the degree of cartilage damage, the orthopedist may recommend adaptive measures such as avoiding stairs and low seating or placing a pillow on a chair to make rising more comfortable. Physical therapy may also be prescribed to strengthen and stretch the quadriceps muscle and to compensate for the loss of cartilage while improving patella tracking during motion.
Most patients can initially achieve good pain relief by taking acetaminophen (Tylenol) or non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil and Motrin) or naproxen (Aleve). Patients may also experience pain relief with some oral nutritional supplements like glucosamine and chondroitin sulfate, fish oil or vitamin E. However, there is little data on the latter over-the-counter supplements.
An intraarticular steroid injection (cortisone shot) is often a useful alternative to reduce pain and intraarticular inflammation and is almost always performed before considering surgery. Another option may be injection of viscosupplements, which help to lubricate the joint and might extend the effect of the steroid injection. Non-operative treatment can be successful for quite some time, especially in patients that do not need to climb stairs. However, Dr. Boettner cautions that “once the patellofemoral arthritis results in increasing patella bone loss, surgery may be recommended to avoid excessive bone loss and difficulties with implant fixation.”
“If the surgeon feels that surgery is not yet warranted in patients with bone on bone patellofemoral arthritis,” Dr. Boettner adds, “he/she may recommend regular follow up examinations, including x-rays, to make sure the patient does not develop bone loss of the patella and notching of the anterior femur.”
Dr. Shubin Stein points out that “the age of the patient and the amount of cartilage damage often dictates the surgical treatment options.” For example, in younger patients with mild cartilage changes, the orthopedist may suggest a lateral release, a procedure in which the tight ligaments on the outer side of the kneecap are cut to achieve better alignment and tracking of the kneecap and allow a smoother, less painful motion in the joint. Most surgeons agree that a lateral release is rarely indicated in isolation and should not be performed if more advanced cartilage damage is encountered.
Alternatively a tibial tuberosity osteotomy (which refers to the part of the shinbone that the patellar tendon is attached to), a procedure to improve the Q angle and reduce the pressure on the patellofemoral joint, can improve patellofemoral symptoms in patients with significantly enlarged Q angles and a relatively well preserved patellofemoral joint space. Joint preserving procedures are usually reserved for patients less than 50 years of age and are no longer indicated once significant cartilage loss or “bone on bone” disease is present.
Figure 2: MRI Images of a 47 year old patient considered for patellofemoral knee replacement. The images show well-preserved medial and lateral compartments and severe arthritis in the patellofemoral compartment, shown behind the patella (kneecap) at the end of the white arrow. (© F. Boettner, MD) Click on image to enlarge.
Total Knee Replacement
In general, patients with “bone on bone” arthritis or absence of cartilage in the joint and severe joint pain can be candidates for total knee replacement. However, “We learned that while total knee replacement is a very good treatment option for patients with osteoarthritis throughout the knee, it may not be the only option for patients who present with isolated patellofemoral arthritis,” says Dr. Della Valle. “Often patients with patellofemoral arthritis have excellent range of motion before surgery and might lose some motion after a total knee replacement. They can also walk relatively long distances before surgery, and major surgery like a total knee replacement with a rather long recovery time may not be appealing to these patients.”
Partial Knee Replacement
Patients frequently ask their surgeon why it is necessary to replace all the compartments of the knee when only one (the patellofemoral compartment) is affected by arthritis. In patients with advanced patellofemoral arthritis and no involvement of the medial and lateral compartment of the knee, the orthopedic surgeon may recommend a patellofemoral knee replacement, which is a type of partial knee replacement. In this procedure, arthritic surfaces on the femur and patella are removed and replaced with prosthetic components, somewhat like capping a tooth, while the remaining compartments of the joint and all the knee ligaments are preserved. The components are made of metal and plastic to create a bearing surface that glides smoothly and resists wear.
Figure 3: Image of the femoral component of a patellofemoral knee replacement implant. (© F. Boettner, MD) Click on image to enlarge.
Figure 4: Radiographs of the patellofemoral joint before (L) and after (R) patellofemoral knee replacement. (© F. Boettner, MD) Click image to enlarge.
Over the past decade partial knee replacement for the medial compartment of the knee has become popular, according to Dr. Boettner. “In recent years, there has been an increased interest in the use of partial knee replacements of the patellofemoral joint as well.”
Dr. Boettner summarizes the consensus of the Hip and Knee Service at HSS:
A patellofemoral knee replacement is a treatment option for selected patients with advanced arthritis affecting only the patellofemoral compartment. In this group of patients, a partial knee replacement is a less invasive surgical option that can substantially relieve pain and improve knee function. The surgery preserves more bone, cartilage and, ligaments; and the recovery is generally faster than from a total knee replacement. For young patients any knee replacement is done with the understanding that revision surgery may be necessary later in life. Patellofemoral knee replacement has the advantage that later revision to a total knee replacement may be potentially easier than the revision of a total knee replacement.
However, the Hip and Knee Service also feels that it must be emphasized that only patients with degenerative changes in the patellofemoral joint and adequate patellar alignment are considered optimal candidates for this procedure. Arthritis involving the other compartments and those with poor patella alignment do not do well with a patellofemoral knee replacement.
“Based on an analysis of the literature, older patients are considered the ideal candidates for patellofemoral knee replacement.” explains Dr. Della Valle: “The decreased activity level in patients above age 75 makes loosening of the implants and progression of arthritis in the remaining compartments of the knee less likely and therefore reduces the most common reasons for revision surgery. Older patients also often have multiple health issues and are at increased risk for perioperative complication. Since patellofemoral knee replacement is less invasive and minimizes perioperative blood loss it seems reasonable to believe that it may involve less risk for older patients.
“A patellofemoral knee replacement is also especially appealing since revision to a total knee replacement usually does not pose a significant problem. However adherence to the indication criteria is key to avoid less optimal functional outcomes and early revisions,” states Dr. Della Valle.
For women between the ages of 60 and 75 with patellofemoral arthritis, determining optimal surgical treatment may be more difficult. Because these patients might be faced with the need for a revision of their patellofemoral knee replacement somewhere between the ages of 75 or 80 years old - depending on when the initial surgery is performed - they may elect to have a total knee replacement which is less likely to require revision surgery after 10 years. “Although a total knee replacement can be associated with more discomfort following surgery and the possibility of more restricted range of motion, it may [remove] the need for a revision surgery in this age group,” Dr. Boettner explains.
Partial knee replacement has a low risk of perioperative complications. However, the procedure does have some of the same potential post-surgical complications as total knee replacement, including deep venous thrombosis (blood clot), delayed wound healing, and implant infection, as well as implant wear and loosening. Other complications are much less common than in total knee replacement, including nerve damage or the need for blood transfusions.
“While we today try to minimize the surgical trauma during total knee replacement with minimal invasive implantation techniques, partial knee replacements are truly minimally invasive since they spare large parts of the joint and do not alter the motion pattern (kinematic) by preserving the anterior and posterior cruciate ligaments, which are usually removed during total knee replacement,” explains Dr. Shubin Stein.
As compared to total knee replacement, partial knee replacement will speed the postoperative rehabilitation and offers the potential for excellent function. At Hospital for Special Surgery we have established a partial knee replacement rehabilitation pathway that will offer patients discharge from the hospital within 1-2 days compared to 3-4 days after total knee replacement surgery. The patient will require intensive physical therapy during a period that ranges from six weeks to three months to achieve the best possible outcome.
As with many complex orthopedic procedures, Dr. Della Valle notes, it’s in the best interest of the patient to select an institution and surgeon with a high volume of experience performing the surgery.
To find out more about partial knee replacement at HSS, please visit the Physician Referral Service or call 1 (877) 606-1555.