Cast index
Formula: Inner diameter of cast on lateral view (m) / Inner diameter of cast on AP view (n)
Cut-off: 0.7-0.8
Padding index
Formula: Dorsal fracture site gap (h) / Maximum interosseous length in AP view (g)
Cut-off: 0.3
Cantebury index
Formula: Cast index (m/n) + Padding index (h/g)
Cut-off: 1.1
Three Point Index (TPI)
[(distal radial gap + ulnar fracture site gap + proximal radial gap) divided by the contact between fracture fragments in transverse projection] + [(distal dorsal gap + volar fracture site gap + proximal dorsal gap) divided by the contact between fracture fragments in sagittal projection]
i.e. [(a+b+c)/x] + [(d+e+f)/y]
Cut-off: 0.8
Original Three Point Index
The formula for the three-point index is [( a + b + c )/ x ] + [( d + e + f )/ y ].
(A) On the anteroposterior radiograph, ‘‘a’’ is the narrowest distal radial side gap at the level of radiocarpal or proximal carpal joint, ‘‘b’’ is the narrowest ulnar-side gap at the level of the fracture (within 1 cm of the fracture line), and ‘‘c’’ is the narrowest proximal radial side gap within the area between 3-7 cm proximal to the fracture site. ‘‘x’’ is the projection of the contact length between the proximal and distal fragments in the horizontal plane on the anteroposterior radiograph.
(B) On the lateral radiograph of an extension-type fracture, ‘‘d’’ is the narrowest distal dorsal-side gap at the level of the radiocarpal joint or proximal carpal bones, ‘‘e’’ is the narrowest volar-side gap within 1 cm of the level of the fracture line, and ‘‘f’’ is the narrowest proximal dorsal-side gap within the area between 3-7 cm of the fracture site. ‘‘y’’ is the projection of the contact length between the proximal and distal fragments in the sagittal plane on the lateral radiograph.
Gap index
Formula: [(Radial fracture site gap + Ulnar fracture site gap)/Inner diameter of cast in AP plane] + [(Dorsal fracture site gap + Volar fracture site gap)/Inner diameter of cast in lateral plane]
i.e. (a+b)/x + (c+d)/y
Cut-off: 0.15
