Arthritis is a general term covering numerous conditions where the joint surface or cartilage wears out. The joint surface is covered by a smooth articular surface that allows pain free movement in the joint. This surface can wear out for a number of reasons; often the definite cause is not known.
When the articular cartilage wears out the bone ends rub on one another and cause pain. This condition is referred to as Osteoarthritis or “wear and tear” arthritis as it occurs with aging and use. It is the most common type of arthritis.
When arthritis affects the knee joint, it commonly occurs in two compartments, usually the medial and patellofemoral compartment. It is not common for a patient to have arthritis isolated to the patellofemoral compartment, but it does occur and is more commonly seen in women. Patellofemoral arthritis is diagnosed when the arthritic damage is only located in the patellofemoral compartment, affecting the back of the knee cap.
Patellofemoral Arthritis or knee cap arthritis causes pain and decreased mobility that is usually localized to the front of the knee joint. The patellofemoral compartment is involved in activities such as walking up and down hills or stairs, kneeling or squatting and standing back up. These activities can be become almost impossible to do when the pain from the arthritic damage is severe enough. Patients with this type of arthritis usually have no pain when walking on flat surfaces even when walking long distances.
Patellofemoral Knee Replacement surgery may be recommended by your surgeon if you have osteoarthritis contained to the patellofemoral compartment and you have not obtained adequate relief with conservative treatment options.
Traditionally, a patient with only one compartment of knee arthritis would undergo a Total Knee Replacement surgery. Patellofemoral Knee Replacement is a minimally invasive surgical option that preserves the knee parts not damaged by arthritis as well as the stabilizing anterior and posterior cruciate ligaments, ACL and PCL. This less invasive bone and ligament preserving surgery is especially useful for younger, more active patients as the implant placed more closely mimics actual knee mechanics than does a total knee surgery. Importantly, Patellofemoral Knee Arthroplasty surgery will not alter the ability of the patient to eventually move to a Total Knee Replacement in the future should that become necessary.
Partial Knee Replacement surgery is performed in an operating room under sterile conditions with the patient under general anesthesia or spinal anesthesia with sedation. It is usually performed on an outpatient basis as day surgery but the patient can stay one night in the hospital if preferred.
- The surgeon makes a small incision, about 3-4 inches long over the knee.
- The patellofemoral compartment is prepared for the artificial components by removing the damaged part of the patella and trochlea, the groove at the end of the femur.
- The new artificial components are fixed in place with the use of bone cement.
- The femoral component is made of polished metal and the patellar component looks like a plastic button which will glide smoothly in a groove located on the femoral component.
- With the new components in place, the knee is taken through a range of movements and it is crucial to balance the soft tissue components of the knee at this time.
- Once the surgeon is satisfied with the results, the incisions covered with a sterile dressing.
Risks and Complications
As with any major surgery there are potential risks involved. Specific complications related to Patellofemoral Knee Replacement surgery include:
- Infection: Infection can occur with any operation. In the knee this can be superficial or deep. Infection rates are approximately 1%. If it occurs, it can be treated with antibiotics but may require further surgery.
- Deep Vein Thrombosis: DVT are blood clots that can form in the calf muscles and travel to the lung (Pulmonary embolism). These can occasionally be serious and even life threatening. If you get calf pain or shortness of breath at any stage, you should notify your surgeon.
- Ligament Injuries: There are many ligaments surrounding the knee. These ligaments can be torn during surgery or break or stretch out any time afterwards. Surgery may be required to correct this problem.
- Injury to Blood Vessels or Nerves: Rare but can lead to weakness and loss of sensation in part of the leg. Damage to blood vessels may require further surgery if bleeding is ongoing.
- Arthrofibrosis: This is the development of thick, fibrous material around the joint that often occurs after joint injury or surgery and can lead to joint stiffness and decreased movement.
- Wear: The components eventually wear out over time, usually 10 to 15 years, and may need to be changed.
- Dislocation: An extremely rare condition where the ends of the knee joint lose contact with each other.
- Fractures or Breaks: Can occur during surgery or afterwards if you fall. To fix these, you may require surgery.
A Patient’s Guide to Partial Knee Resurfacing
The normal knee joint consists of the femur, the patella, and the tibia bones, all of which are all held together securely with soft tissue structures including ligaments and tendons. The bones are separated by shock-absorbing cartilage and lubricating synovial fluid. All of these structures move naturally through an arcing, hinge-like range-of-motion during daily activity. The knee can be divided into three main compartments or areas: the medial or inner compartment, the lateral or outer compartment, and the patellofemoral compartment under the kneecap.
For more information, please visit The Patellofemoral Center website.
