One of my mentors once said, “If I only did what I did in residency, I wouldn’t be doing any surgery anymore.” Having finished my fellowship more than 12 years ago, I never would have guessed at the evolution that would occur in my surgical practice or predicted a practice profile such as I have today.

One specific example is the use of patellofemoral arthroplasty. Clearly, the problem of patella arthritis is not new, and many patients were diagnosed with isolated patellofemoral arthritis 12 years ago. These patients were treated primarily with physical therapy and activity modification until their arthritis became intolerable, at which point they were offered a total knee arthroplasty (TKA) because first-generation patellofemoral replacements were fraught with mechanical complications due to poor design.

The advent of second-generation patellofemoral replacements has increased the use of this surgical intervention. Compared to the patient population for total joint arthroplasty, patients undergoing patellofemoral arthroplasty are younger, largely female, and quite active.

My first exposure to this procedure was at an industry-sponsored cadaver course. Since then, I have worked with several implants both on sawbones as well as in the lab. I approached this “new operation” cautiously and have been very conservative in my indications, which meant that I only performed five surgeries my first year and now perform about 30 to 40 of these procedures a year. These strict indications have led to a highly satisfied patient group (Fig. 1). Expectations and satisfaction are very closely linked and presurgical education and careful discussion of realistic outcome are important.

Indications and patient considerations
Isolated pain in the front of the knee is the primary indication for a patellofemoral replacement. The ideal candidate should be fairly asymptomatic while walking on flat ground, but experience an increase in pain when climbing or descending stairs, sitting for prolonged periods, and transitioning from a sitting to a standing position.

Most female patients will report that they stopped wearing high heels years before, secondary to their knee pain. Furthermore, these patients report years of activity modifications, including minimizing impact sports, avoiding hills when running, and, in some cases, avoiding stairs. Although many patients can gain acceptable relief by optimizing quadriceps and hip abductor strength, receiving hyaluronic acid and cortisone injections, and losing weight, patients seeking a patellofemoral arthroplasty have exhausted all conservative measures.

Contraindications are similar to those stated for unicompartmental knee arthroplasty and include inflammatory arthritis. In addition, before embarking on a patellofemoral replacement, I recommend stabilizing the patella as well as correcting significant deformity in the tibial tubercle trochlear groove distance (Q-angle). I believe that it is unwise to perform a tibial tubercle osteotomy (TTO) at the same time as a patellofemoral arthroplasty. In addition, many patients who plan to undergo a staged procedure have sufficient reduction in pain and improvement in function after the TTO that they have been able to delay the arthroplasty. Some data indicate that significant valgus or varus knee alignment portends a premature failure, making that a relative contraindication as well.

Surgery
As with a TKA, hoods and laminar air flow are used in the operating room. I use a midvastus approach through a midline incision under tourniquet control. Typical tourniquet time is 25 to 35 minutes and hospital stay ranges from 1 to 2 days. A protracted course of physical therapy is required to strengthen the quadriceps and normalize gait because most of these patients have used a quad-avoidance gait for years.

Although robotic surgery, customized patient-specific implants, and computer-assisted surgery have been used to a limited degree, no data thus far support the use or any increased cost associated with these technologies.

Return to activities
These patients are able to resume normal activities, including a return to the gym, to low-impact sports (including playing tennis), and to kneeling. After surgery, many patients can use an exercise bike or elliptical machine. None of my patients have returned to running, and I strongly discourage this type of activity. Similar to recovery after TKA, some patients continue to have anterior knee pain despite good component alignment, no effusion, and good return of strength.

Mode of failure
Although the literature is limited, the primary mode of failure is progression of arthritis within the femorotibial joint. If patellofemoral replacement is limited to patients with posttraumatic arthritis (due to either postpatellar fracture or dislocation), the longevity of the operation will be optimized. In some studies, patients with malalignment and trochlear dysplasia exhibit improved survival rates of patellofemoral replacement.

Our current studies are aimed at aiding surgeons and patients in their decision making. We also have started a critical look at outcomes of patients whose patellofemoral replacements have failed and of those patients who continue to have pain with activities after surgery. If these patients later have a TKA, what are their results?

Reasons for resurgence
Second-generation implants have led to a more reproducible surgical procedure and outcomes data on these implants show promise. A recent meta-analysis showed that second-generation patellofemoral arthroplasty has the same complication and revision rate as TKA. The increased interest in unicompartmental arthroplasty by both patients and surgeons is another reason for the resurgence of patellofemoral arthroplasty. Finally, although most of these procedures are performed with traditional jigs, the popularization of robotic surgery has increased interest in this procedure.

Sabrina Strickland, MD, is a member of the AAOS Communications Cabinet, who specializes in surgery of the knee and shoulder at the Women’s Sports Medicine Center at Hospital for Special Surgery in New York City. Dr. Strickland’s disclosure information, including any potential conflicts of interest, can be accessed at www.aaos.org/disclosure. She can be reached at stricklands@hss.edu

Bottom Line

• The advent of second-generation patellofemoral replacements, the increased interest in unicompartmental arthroplasty, and the popularization of robotic surgery have increased interest in patellofemoral arthroplasty as a surgical intervention for isolated patellofemoral arthritis.
• Compared to total knee arthroplasty patients, patients undergoing patellofemoral arthroplasty are younger, largely female, and quite active.
• Contraindications are similar to those stated for unicompartmental knee arthroplasty and include inflammatory arthritis.
• The primary mode of failure is progression of arthritis within the femorotibial joint.