Overview
Not all knee arthritis involves the entire knee. In some patients, the arthritis is limited primarily to one compartment while the remainder of the knee remains relatively healthy. In carefully selected patients, partial knee arthroplasty allows me to replace only the damaged portion of the knee while preserving healthy cartilage, ligaments, and bone throughout the rest of the joint.
The concept is different from total knee arthroplasty. Rather than replacing all of the major joint surfaces, we identify the portion of the knee that has worn out and replace only that compartment. Because more of the patient's normal knee is preserved, a partial knee replacement can often feel more natural than a total knee replacement in appropriately selected patients. There are two types of partial knee arthroplasty that I perform: medial unicompartmental knee arthroplasty and patellofemoral arthroplasty.
When Is Partial Knee Arthroplasty Recommended?
Partial knee arthroplasty is designed for specific patterns of arthritis in which the remaining portions of the knee are sufficiently preserved. As with other forms of joint replacement, surgery is generally considered when appropriate conservative treatment no longer provides adequate relief and arthritis is significantly affecting quality of life.
Medial Unicompartmental Knee Arthroplasty
The medial compartment, or inside portion of the knee, is one of the most common areas for arthritis to develop. A medial unicompartmental knee arthroplasty replaces only the damaged medial compartment while preserving the healthy cartilage, ligaments, and bone throughout the remainder of the knee.
For this procedure, it is essential that the lateral compartment is essentially normal. Mild to moderate patellofemoral arthritis may still be acceptable in selected patients and does not necessarily eliminate partial knee arthroplasty as an option. Because the unaffected portions of the knee remain intact, the goal is to replace only the worn medial compartment while preserving as much of the patient's natural knee as possible.
Patellofemoral Arthroplasty
Patellofemoral arthroplasty is used when arthritis is isolated to the joint between the patella and the trochlear groove at the end of the femur. Rather than replacing the entire knee, only the damaged patellofemoral joint is resurfaced while the healthy medial and lateral compartments are preserved. This operation is reserved for carefully selected patients with isolated patellofemoral arthritis.
MAKO Robotic-Assisted Partial Knee Arthroplasty
As with my total knee replacements, every patient undergoes a preoperative CT scan that creates a three-dimensional model of the knee. I use the MAKO robotic-assisted system, one of the most advanced technologies available for knee arthroplasty. It combines detailed preoperative planning with real-time information during the operation. This is particularly valuable in partial knee replacement because the goal is to replace the damaged compartment while preserving and appropriately balancing the remainder of the patient's natural knee.
During surgery, the MAKO system allows highly accurate adjustments based on the patient's individual anatomy and knee mechanics. The robot does not perform the operation. I perform the surgery, while MAKO provides sophisticated information and guidance that helps me individualize the reconstruction.
Recovery
Patients begin walking immediately after surgery using a walker or crutches and transition to a cane as soon as they are comfortable. Most patients discontinue walking aids within approximately 4-6 weeks. Physical therapy typically begins at home. The first postoperative visit is approximately three weeks after surgery, at which point most patients transition to outpatient physical therapy.
Knee Extension
Regaining the ability to get the knee completely straight is one of the most important priorities during the early recovery period. I tell patients that the knee does not need to remain straight throughout the day. What matters is that it can get completely straight. Check it in the morning. If the knee gets completely straight, move on to the other aspects of rehabilitation. If it does not, spend time working on extension during the day and check it again that evening. Until full extension can be reliably achieved, it should remain a daily focus.
Blood Clot Prevention
Patients receive postoperative anticoagulation to decrease the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE). Most patients receive one full-strength 325 mg aspirin twice daily for approximately 30 days. Patients with a previous history of DVT or pulmonary embolism may require a stronger anticoagulant and a different postoperative anticoagulation plan.
Potential Complications
Partial knee arthroplasty carries many of the same potential complications as total knee arthroplasty, including implant loosening, stiffness, blood clot or pulmonary embolism, and infection. Infection is fortunately uncommon. Prosthetic joint infections usually occur months or even years after surgery when bacteria circulating in the bloodstream attach to the prosthesis. Treatment requires additional surgery and usually involves removal of the prosthesis, placement of a temporary antibiotic spacer, IV antibiotics, and eventual revision arthroplasty. Fortunately, the overwhelming majority of appropriately selected patients experience significant improvements in pain, function, and quality of life.