What White Lines Mean on a Knee X-ray
White lines on a knee radiograph represent areas of increased density, most commonly indicating bone (cortical margins, trabecular patterns, osteophytes), calcifications (such as chondrocalcinosis or vascular calcification), or sclerotic changes in the subchondral bone.
Normal White Lines
On a standard knee X-ray, white (radiopaque) structures include:
- Cortical bone margins: The dense outer shell of the femur, tibia, patella, and fibula appears as bright white lines
- Trabecular bone pattern: The internal bone architecture creates a network of white lines within the bone
- Joint surfaces: The subchondral bone plate at the articular surfaces appears as a thin white line
Pathological White Lines
White lines can also indicate disease processes:
Sclerosis and Osteoarthritis
- Subchondral sclerosis: Increased bone density beneath the cartilage surface appears as thickened white lines, commonly seen in osteoarthritis 1
- Osteophytes: Bony spurs at joint margins appear as white projections
Calcifications
- Chondrocalcinosis: Calcium deposits in cartilage (CPPD disease) create white lines within the menisci or articular cartilage 1
- Vascular calcifications: Atherosclerotic vessels may appear as linear white densities
Fracture Lines
- Healing fractures: Callus formation and sclerotic bone around fracture sites appear white
- Stress fractures: May show as white sclerotic lines before becoming visible as dark fracture lines
Important Clinical Context
The interpretation of white lines depends entirely on their location, pattern, and clinical context. When evaluating chronic knee pain, radiography is the appropriate initial imaging study 1. If white lines suggest specific pathology (such as chondrocalcinosis or osteochondritis dissecans), further imaging with MRI may be indicated to assess soft tissue structures, cartilage, and bone marrow changes that are not visible on plain radiographs 1.
Key Pitfall
Do not confuse white (radiopaque) lines with radiolucent lines (dark lines), which represent gaps or areas of decreased density. Radiolucent lines are particularly relevant in the context of total knee arthroplasty, where they may indicate issues at the bone-cement or cement-implant interface 2, 3, 4.
For any concerning white lines on knee radiographs—particularly if associated with joint space narrowing, effusion, or persistent pain—MRI without contrast is the next appropriate imaging study to fully characterize the underlying pathology 1.