The fourth-fifth intermetatarsal angle is used to assess for a bunionette deformity. It should not be confused with the first intermetatarsal angle, used to assess for hallux valgus deformity.
Measurement
The fourth-fifth intermetatarsal angle is formed between the long axis of the fourth and fifth metatarsals on AP weight-bearing foot radiographs 1,2.
Interpretation
The normal fourth-fifth intermetatarsal angle is proposed to be <6.5-8° 1,2. In normal feet, the average fourth-fifth intermetatarsal angle is 6.5° (range 3-11°) whereas it is >9.6° in feet with symptomatic bunionette 1,2.