Bony Anatomy
- The patella is a complex three-dimensional bone.
- The anterior, nonarticular surface is shield shaped with distal taper at inferior pole.
- The posterior (articular surface) is elliptical shaped with three facets with thickened cartilage (Fig. 22-1).
- Lateral facet—largest facet, concave, and plateaus laterally
- Medial facet—convex, smaller than lateral facet
- Odd facet—most medial aspect of the patella
- Central articular ridge separates lateral and medial facet.
- Lateral facet—largest facet, concave, and plateaus laterally
- The blood supply is provided by dorsal vessels and also ascending vessels via the fat pad inferomedially into nonarticular portions of patella.1
- Critical soft tissue attachments:
- All soft tissues attach at nonarticular portions of the patella.
- Soft tissue attachments are critical to extensor mechanism function.
- Patella tendon inserts at inferior pole of the patella and can be affected by inferior pole comminution, leading to unrecognized displacement and extensor mechanism incompetence if not treated appropriately.
- Quadriceps tendon inserts at superior pole of the patella.
- Lateral retinaculum and medial retinaculum (including medial patellofemoral ligament) insert along the respective medial and lateral portions of the patella and frequently disrupted in patella fractures.
- All soft tissues attach at nonarticular portions of the patella.
Figure 22-1 Bony anatomy of patella.
Radiographic Anatomy
Radiographic views2
- True lateral of the patella: obtained with limb in neutral rotation (Fig. 22-2)
- Salient features
- Articular tangent; correlates with articular ridge between medial and lateral facets
- Secondary articular density; created by confluence of edge of the lateral facet with variable contributions from the edge of the medial facet or intersection of the medial and odd facet
- Anterior cortical density
- Articular tangent; correlates with articular ridge between medial and lateral facets
- Salient features
- Accessory view of the lateral facet: obtained with patella in approximately 20 degrees (range 12 to 35 degrees) of external rotation (Fig. 22-3)
- Salient features
- Tangent to the lateral facet.
- Best view to visualize displacement at the lateral facet articular surface.
- Articular surface will appear as a straight line.
- Proximal beaking visualized.
- Tangent to the lateral facet.
- Salient features
- Accessory view of the medial facet: obtained with patella in approximately 30 degrees (range 15 to 45 degrees) of internal rotation (Fig. 22-4)
- Salient features
- Tangent to the medial facet
- Best view to visualize displacement at the medial facet articular surface
- Hexagonal or sail shape
- Tangent to the medial facet
- Salient features
Figure 22-2 A and B:True lateral view of the patella.
Figure 22-3 A and B:Accessory view of lateral facet.
Figure 22-4 Accessory view of medical facet.
Preoperative Imaging
AP and lateral views of the knee are usually adequate to determine if surgical or nonsurgical treatment is indicated (Fig. 22-5).
Figure 22-5 A and B: AP and lateral views of the patella.
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