Kneecap (Patellofemoral) Replacement

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is a kneecap (patellofemoral) replacement?

A patellofemoral joint replacement is a type of partial knee replacement or unicompartmental knee replacement. Unlike a total knee replacement, kneecap replacement doesn’t entail removing the entire knee joint. Instead, it only involves one part or compartment of the knee.

The knee has three compartments—the medial (inside) compartment, the lateral (outside) compartment, and the patellofemoral compartment. The patellofemoral compartment encompasses the area between the patella—or kneecap—and the femur—or thighbone. A patellofemoral knee replacement is surgery on this specific compartment.

Normally, the kneecap sits in a groove on the thigh bone called the trochlea. As you bend and extend your knee, the kneecap slides along this channel. Cartilage lines the trochlea and covers the back of the kneecap. This reduces friction and allows the bones to glide smoothly as you move. Diseased cartilage can cause pain and other symptoms when you move your knee.

In kneecap replacement surgery, doctors remove damaged cartilage and resurface the trochlear groove and the back of the kneecap with implants (man-made materials). The goal is to restore pain-free motion and full function of the knee joint.

Why is a kneecap replacement performed?

A kneecap replacement is an alternative to total knee replacement for people who meet certain criteria. Doctors may recommend this surgery if you have osteoarthritis that only affects the patellofemoral compartment. People with this type of limited knee arthritis tend to be female and relatively young.

Doctors will usually only consider this surgery if other nonsurgical treatments have failed to relieve pain or are no longer working. Other treatments may include weight loss, medications, joint injections, bracing, physical therapy, and activity modification.

Kneecap replacement may not be the right option for you if you have any of the following:

  • Deformity of the leg or malalignment of the tibia (shin bone) and femur
  • Knee stiffness
  • Ligament damage
  • Problems with patellar tracking, which can allow the kneecap to slide sideways

Before deciding on a kneecap replacement, talk with your doctor about all risks and benefits of the procedure specific to your knee anatomy and overall health.

What is the benefit of patellofemoral knee replacement vs. total knee replacement?

One of the main benefits of patellofemoral joint replacement over total knee replacement is that the knee ligaments are not cut to access the compartment to be replaced. This can make the knee joint move more naturally with better range of motion. The quadriceps tendon is also not cut. Compared to replacing the entire knee, patellofemoral joint replacement has a shorter recovery time, involves less blood loss and pain, and better knee function.

There is some evidence from a 2018 review that long-term function with patellofemoral knee joint replacement is less than a total knee replacement. However, there are a variety of possible factors underlying the difference, including patient characteristics, surgical expertise, and type of implant, among others.

Ask your doctor what makes you a good candidate for kneecap replacement.

Who performs a kneecap replacement?

An orthopedic surgeon performs a kneecap replacement. Orthopedic surgeons specialize in the management of diseases, disorders and conditions of the bones, muscles, and connective tissues.

A kneecap replacement is a relatively new procedure compared to a total knee replacement. Not all hospitals or specialists offer it as an option. If you are considering a kneecap replacement, find an orthopedic surgeon with experience performing the procedure.

How does the surgeon replace the kneecap?

Kneecap replacements usually take place in a hospital. In some cases, doctors replace the kneecap as an outpatient procedure. It involves making an incision down the front of the knee. The first step after the incision is an inspection of the knee joint. The doctor will check to make sure there is no ligament damage or damage to the other two compartments. If the doctor finds a problem, a total knee replacement may be necessary instead. (You and your surgeon should discuss this possibility before you schedule surgery.)

Once your doctor has verified that a kneecap replacement is appropriate, the surgery can proceed. The surgery involves two steps. The first step is to prepare the bones. Your doctor will remove the damaged cartilage and some bone from the trochlear groove and the back of the kneecap. The second step is attaching a metal implant over the trochlea and a plastic cover on the back of the kneecap. These implants provide new surfaces that can glide smoothly. Resurfacing is another name for this process.

Kneecap replacement is major surgery that requires anesthesia. Your doctor will use either general anesthesia or regional anesthesia. General anesthesia is a mixture of IV (intravenous) medicines and gases that put you in a deep sleep. Regional anesthesia is known as a nerve block. It involves injecting an anesthetic around certain nerves to numb a large area around the surgical site. You may also have sedation in addition to regional anesthesia to keep you comfortable.

Some orthopedic surgery centers have expertise in performing minimally invasive partial knee replacements. Discuss this option with your surgeon at your initial surgery consultation appointment.

What to expect the day of your kneecap replacement

In general, the day of your surgery you can expect to:

  • Talk with a preoperative nurse. The nurse will perform an exam, ensure all necessary tests are in order, start an IV, and answer questions. You’ll also sign medical consent forms.
  • Remove all clothing and jewelry and dress in a hospital gown. It is a good idea to leave all jewelry and valuables at home or with a family member. The surgical team will give you blankets for modesty and warmth.
  • Talk with the anesthesiologist or nurse anesthetist about your medical history and the type of anesthesia you will have.

You will likely have sedative medication before the team takes you to the operating room (OR). The anesthesiologist or nurse anesthetist will start your anesthesia once you’re in the OR. The surgical team will monitor your vital signs throughout the procedure and during your recovery. The surgery takes about an hour.

What are the risks and potential complications of a kneecap replacement?

All surgeries carry risk and the potential for complications. In some cases, these complications can be serious and even life-threatening. It’s possible to experience complications during the surgery itself or throughout recovery. Ask your doctor how you can reduce the risk of complications with your treatment and recovery plan.

General risks of surgery

The general risks of surgery include:

  • Bleeding, which can lead to shock
  • Infection

Potential complications of patellofemoral joint replacement

Most kneecap replacements are successful, but potential complications include:

  • Continued pain
  • Nerve, muscle, blood vessel, or knee structure damage
  • Patellar instability, which can lead to chronic kneecap dislocations
  • Wear and tear, which may eventually lead to the need for additional surgery

Reducing your risk of complications

You can reduce your risk of certain complications by:

  • Choosing a surgeon with a good track record of patellofemoral joint replacement surgeries
  • Following activity, dietary and lifestyle restrictions and recommendations before your surgery and during recovery
  • For females, informing your doctor if you are nursing or if there is any possibility of pregnancy
  • Notifying your doctor immediately of any concerns, such as bleeding, fever, or increase in pain
  • Taking your medications exactly as directed
  • Telling all members of your care team if you have allergies

How do I prepare for a kneecap replacement?

You can take steps before surgery that can improve comfort and outcome during recovery. You can prepare for a kneecap replacement by:

  • Answering all questions about your medical history and medications. This includes prescription medications, over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.
  • Arranging for a ride home after surgery or hospital discharge. It is also a good idea to have someone stay with you for the first 24 hours.
  • Getting preoperative testing as directed. Testing will vary depending on your age, health, and specific procedure. Preoperative testing may include a chest X-ray, electrocardiography (ECG), blood tests, and other tests as needed.
  • Following dietary guidelines as directed.
  • Losing excess weight before the surgery through a healthy diet and exercise plan.
  • Not eating or drinking before surgery as directed. Your surgery may be cancelled if you eat or drink too close to the start of surgery because you can choke on stomach contents during anesthesia.
  • Stop smoking as soon as possible. Even quitting for a few days can be beneficial and can help the healing process.
  • Taking or stopping medications exactly as directed. For kneecap replacement, this may include not taking aspirin, ibuprofen (Advil, Motrin), and blood thinners.

Questions to ask your doctor

Facing surgery can be stressful. Consider making a list of questions to help you remember everything you want to ask your doctor. Questions you may want to ask include:

  • Why do I need kneecap replacement? Are there any other options for treating my condition?
  • Do you perform minimally invasive kneecap replacements? Am I a candidate for this procedure?
  • How long will the surgery take? When can I go home?
  • What restrictions will I have after the surgery? When can I expect to return to work and other activities?
  • When will I start physical therapy and where do I go for it?
  • What kind of assistance will I need at home?
  • What medication plan should I follow before and after the surgery?
  • How will I manage my pain? Will you prescribe pain medication? Can I use over-the-counter pain relievers?
  • How should I contact you if I have problems? Ask for numbers to call during and after regular hours.
  • When should I see you in follow-up after the surgery?

What can I expect after a kneecap replacement?

The road to recovery can be smoother when you know what to expect and can plan and prepare.

How long will it take to recover?

You will stay in the recovery room after surgery until you are alert and your vital signs are stable. In some cases, doctors plan an outpatient procedure and you can go home after your recovery room stay. Otherwise, you will have a brief hospital stay, usually a night or two.

Recovery after a kneecap replacement is a gradual process. The time it takes to recover varies depending on your age, general health, and other factors. You may need to use crutches, a cane, or a walker for a few days after your surgery. These devices will help you bear weight on the knee.

Physical therapy will be an important part of your recovery. It typically starts about a week after surgery. The outcome of your recovery depends on regaining strength in your quadriceps muscles. Physical therapy can help you do this safely and successfully.

You will likely be able to return to work and daily activity in 2 to 6 weeks. This part of the recovery is usually faster than with a total knee replacement. Full kneecap replacement recovery time can take 6 to 12 months.

Will I feel pain?

There will be pain after a kneecap replacement. Controlling pain is important for healing and a smooth recovery. It allows you to fully participate in physical therapy and rehabilitation. Contact your doctor if you are in pain despite following your pain control plan or if your pain gets worse or changes in any way. It could be a sign of a complication.

When should I call my doctor?

For questions between appointments, contact your doctor’s office. However, you should call your doctor right away or seek immediate medical care if you have any of the following:

  • Drainage of pus, redness or swelling around your incision
  • Fever. It’s common to have a fever right after surgery. Your doctor will give you instructions about when to call for a fever.
  • In ability to urinate or move your bowels
  • Leg pain, redness or swelling, which could mean you have a blood clot
  • Unexpected bleeding

How might a kneecap replacement affect my everyday life?

Kneecap replacement can reduce pain and improve function so you can lead a more active, normal life. Compared to a total knee replacement, a kneecap replacement preserves ligaments and other bones and cartilage in the knee. This gives the knee a more normal feel than a total knee replacement. It also allows the knee to move more naturally, which can help you return to a broader range of activities.

With current kneecap implants, a kneecap replacement can last for up to 20 years. However, it is possible to develop osteoarthritis in the other two knee compartments. Eventually, this may require a total knee replacement.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Mar 11
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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  3. Patellofemoral Joint Replacement. Hospital for Special Surgery. https://www.hss.edu/conditions_patellofemoral-joint-replacement.asp
  4. Patellofemoral Replacement. American Academy of Orthopaedic Surgeons. https://orthoinfo.aaos.org/en/treatment/patellofemoral-replacement/
  5. Strickland SM, Bird ML, Christ AB. Advances in patellofemoral arthroplasty. Curr Rev Musculoskelet Med. 2018;11(2):221-230.
  6. Unicompartmental Knee Replacement. American Academy of Orthopaedic Surgeons. https://orthoinfo.aaos.org/en/treatment/unicompartmental-knee-replacement