Figure 1. Anteroposterior radiograph of right knee showing medial compartment knee arthritis
Figure 2. Sunrise view of both knees
Figure 3. MRI of right knee showing significant edema and cystic changes within the femoral condyle and proximal tibia
A 55-year-old man presents to the office with a 1-year history of right knee pain. The patient reports a history of medial compartment knee arthritis. He has tried conservative treatments including oral nonsteroidal anti-inflammatory drugs (NSAIDs), physical therapy, and cortisone injections with minimal relief. Eight months ago the patient underwent a medial meniscectomy, which made the knee pain worse. Radiographs and magnetic resonance imaging (Figure 1-3) show significant edema and cystic changes within the femoral condyle and proximal tibia. The articular cartilage of the lateral and patellofemoral components is preserved. The patient would like to discuss whether medial unicompartmental knee arthroplasty (UKA) is an appropriate option for his condition.
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Unicompartmental knee arthroplasty refers to a replacement of either the medial, lateral, or patellofemoral compartment of the knee. These procedures represent approximately 5% of knee arthroplasty procedures (4.1% medial and lateral and 0.4% patellofemoral).1 Unicompartmental knee arthroplasties are most frequently performed in the medial compartment, where arthritis most commonly develops.1
Medial UKA preserves the lateral and patellofemoral compartment, as well as the anterior and posterior cruciate ligaments, as compared with TKA. This results in a more natural feeling knee and better range of motion as compared with TKA. The most common cause of medial UKA failure is knee pain from arthritis that develops in the lateral or patellofemoral compartment.2-3 Robotic-assisted UKA has helped with component positioning and ligament balancing and there is some evidence suggesting that this technique will increase implant survivorship, although long-term studies are lacking.3
Contraindications for medial UKA include rheumatoid arthritis (which affects all compartments of the knee), anterior cruciate ligament insufficiency, history of lateral meniscectomy, and flexion contraction >10 degrees.2,3
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.
1. American Joint Replacement Registry. The seventh annual report of the AJRR and hip and knee arthroplasty. American Academy of Orthopedic Surgeons; 2020:69.
2. Jennings JM, Kleeman-Forsthuber LT, Bolognesi MP. Medial unicompartmental arthroplasty of the knee. J Am Acad Orthop Surg. 2019;27(5):166-176. doi:10.5435/JAAOS-D-17-00690
3. Lonner JH, Klement MR. Robotic-assisted medial unicompartmental knee arthroplasty: options and outcomes. J Am Acad Orthop Surg. 2019;27(5):e207-e214. doi:10.5435/JAAOS-D-17-00710