What does lucency of the patellar (kneecap) articular surface indicate and how is it managed?

From the Guidelines

Lucency of the patellar articular surface is a significant indicator of potential loosening or osteolysis, particularly in the context of total knee arthroplasty, and requires thorough evaluation and management to prevent further complications. This condition can be associated with aseptic loosening, which is a common cause of total knee arthroplasty (TKA) failure, as noted in studies such as 1. The presence of lucency may suggest areas of osteolysis, which can occur due to particle debris from polyethylene, cement, or metal, leading to a cell-mediated inflammatory response and bone resorption.

Key Considerations

• Lucency of the patellar articular surface may indicate cartilage damage or degeneration, ranging from chondromalacia patellae to osteoarthritis.
• In the context of TKA, lucency is more specifically related to complications such as aseptic loosening or osteolysis.
• Management should focus on identifying and addressing the underlying cause, whether it be loosening, osteolysis, or another mechanical issue.

Management Approach

• Initial steps involve excluding infection and evaluating the extent of lucency and its implications on joint stability and function.
• Conservative management may include activity modification, physical therapy, and pain management with NSAIDs like ibuprofen or naproxen, as well as considering weight loss for overweight patients.
• Surgical options, such as arthroscopic debridement, microfracture, autologous chondrocyte implantation, or patellofemoral arthroplasty, may be necessary for cases where conservative treatment fails or for severe defects, as guided by the most recent and highest quality evidence available, such as 1.

Underlying Pathophysiology

• The breakdown of articular cartilage, which has limited healing capacity, disrupts the smooth gliding surface of the patellofemoral joint, causing pain, crepitus, and functional limitations.
• In TKA, the introduction of foreign materials and the surgical alteration of joint mechanics can lead to unique complications, including aseptic loosening and osteolysis, as discussed in 1.

From the Research

Definition and Indication of Lucency

• Lucency of the patellar articular surface refers to an area of abnormal radiolucency (darkness) on radiographic images, which can indicate a variety of conditions, including osteochondritis dissecans (OCD) 2, 3, 4, 5.
• OCD is a condition characterized by a fragment of cartilage and bone that becomes detached from the surrounding bone, often due to repetitive microtrauma or other factors 3, 5.

Management of Lucency

• The management of lucency of the patellar articular surface depends on the underlying condition and its severity 3, 4, 5.
• For OCD, treatment options include conservative management with restriction of sports activities, drilling of the subchondral bone to stimulate healing, and surgical fixation or replacement of the osteochondral fragment 3, 5.
• The choice of treatment is tailored to the patient's skeletal maturity, size and location of the lesion, and presence of instability signs on MRI 4, 5.

Diagnostic Imaging

• Radiographic imaging, including anteroposterior, tunnel, and skyline views, may not always demonstrate the lesion, and additional views such as the Merchant view or fluoroscopic spot films may be necessary 2.
• MRI is a valuable tool for diagnosing and staging OCD, and can help identify signs of instability, such as cartilage defects, fluid around the fragment, and dislodged fragments 3, 4, 5.
• Accessory views, such as those described by 6, can be used to better visualize specific anatomic features of the patella and assess malreduction in fracture cases.