Tangential Patella Settegast is a radiography positioning projection of the Lower Extremity. Prone, knee flexed 45-90 degrees, CR perpendicular to patella underside. SID 40". The centering point is located underside of patella, tangential to patellar surface.. The central ray is perpendicular to underside of patella, tangential to surface.. Image-quality criteria include patellar articular surface and facets clearly visualized., patellofemoral joint space open and uniform.. Standard exposure ranges from 60 to 70 kVp, 4 to 7 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Patellar articular surface in tangential view.
- Medial and lateral patellar facets.
- Patellofemoral articulation.
- Patellar articular cartilage.
- Femoral groove.
- Anterior femoral condyles.
Patient preparation
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the leg.
- Position patient prone on table with knee forward.
- Flex knee 45 to 90 degrees, adjusting degree as tolerated.
- Position IR under patella tangential to articular surface.
Position & centering point
Underside of patella, tangential to patellar surface.
Central ray
Perpendicular to underside of patella, tangential to surface.
Exposure / technique
- kVp
- 60–70
- mAs
- 4–7
- SID
- 40" (102 cm)
- Notes
- Tangential projection shows patellar facets and articular cartilage.
Image-quality criteria
- Patellar articular surface and facets clearly visualized.
- Patellofemoral joint space open and uniform.
- No superimposition of femur over patellar facets.
- Patellar outline complete with smooth margins.
- Articular cartilage surface visible.
- Collimation 4 x 4 inches around patella.
Common errors / ARRT traps
- 1 Insufficient knee flexion prevents tangential patella visualization.
- 2 Excessive flexion foreshortens patellar surface.
- 3 CR not perpendicular to patellar underside distorts facets.
- 4 IR not positioned tangential to patella surface.
Clinical indications
- Patellar chondromalacia and cartilage damage assessment.
- Patellar facet arthritis evaluation.
- Osteochondritis dissecans of patella.
- Patellar fracture extent and surface involvement.
Aligned to the 2025 ARRT Content Specifications.