Classification Levels

Question 1

Lawson’s classification:

Answer 1

differentiates the various forms of accessory navicular

Question 2

Lawson Type 1

Answer 2

accessory navicular (*os tibiale externum):

• smallest in size
• round in shape
• located w/in posterior tibial tendon
• positioned most proximal of the 3 types

Question 3

Lawson Type 2

Answer 3

• larger accessory navicular
• semi-circular in shape (“D” shaped)
• lies immediately next to navicular tuberosity
  
  • considered accessory ossification center that remains attached to tuberosity by cartilage or fibrous tissue

Question 4

Lawson Type 3

Answer 4

accessory navicular that appears like a very large navicular that wraps around the talar head

• also called cornuate navicular
• also has accessory ossification center
• OSSEOUS union b/w tuberosity and the accessory bone