Casting technique related Radiographic indices

casting related indices
Source: Asadollahi S, Pourali M, Heidari K. Predictive factors for re-displacement in diaphyseal forearm fractures in children-role of radiographic indices. Acta Orthop. 2017 Feb;88(1):101-108. doi: 10.1080/17453674.2016.1255784. Epub 2016 Nov 14. PMID: 27841692; PMCID: PMC5251255. [CC-BY NC]

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

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, β€˜β€˜a’’ is the narrowest distal radial side gap at the level of radiocarpal or proximal carpal joint, β€˜β€˜b’’ is the narrowest ulnar-side gap at the level of the fracture (within 1 cm of the fracture line), and β€˜β€˜c’’ is the narrowest proximal radial side gap within the area between 3-7 cm proximal to the fracture site. β€˜β€˜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, β€˜β€˜d’’ is the narrowest distal dorsal-side gap at the level of the radiocarpal joint or proximal carpal bones, β€˜β€˜e’’ is the narrowest volar-side gap within 1 cm of the level of the fracture line, and β€˜β€˜f’’ is the narrowest proximal dorsal-side gap within the area between 3-7 cm of the fracture site. β€˜β€˜y’’ is the projection of the contact length between the proximal and distal fragments in the sagittal plane on the lateral radiograph.

gap index
Source: Shalabh K, Ajai S, Vineet K, Sabir A. Are Gap and Cast Indices Predictors of Efficacy of Reduction in Fractures of Both Bones of the Leg? A Cohort Study. Malays Orthop J. 2018 Jul;12(2):15-19. doi: 10.5704/MOJ.1807.003. PMID: 30112123; PMCID: PMC6092537.

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


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