Canal Flare Index in the Canine Femur Is Influenced by the Measurement Method

We evaluated whether differences exist among the canal flare index (CFI) values obtained by different calculation methods in the veterinary literature.

The endosteal widths were measured from radiographic images of canine cadaveric femora. Three different formulae were used to calculate the CFI. The CFI_LT-M was the ratio of endosteal width at the medial aspect of the lesser trochanter (LT) to the midshaft (M), while the CFI_LT-I was the ratio of LT to the isthmus (I). The CFI_PLT-I was the ratio of endosteal width at the proximal aspect of the lesser trochanter (PLT) and the I. The widths at each level and the CFI calculation methods were compared. Using Rashmir-Raven's method, the femora were typed as stovepipe, normal and champagne fluted. The limits of agreement were also evaluated.

The endosteal width at the proximal aspect of the lesser trochanter was 12% wider than at the medial aspect and 8% wider at the midshaft than at the isthmus. The CFI_LT-M was less than CFI_LT-I and CFI_PLT-I by 9 and 20%, respectively. By Rashmir-Raven's classification, the CFI_LT-M method provided 18% stovepipe, 79% normal and 3% champagne fluted femora. The CFI_LT-I method showed the stovepipe, the normal and the champagne fluted as 6, 82 and 12%, respectively. The CFI_PLT-I method classified the femora either normal (55%) or champagne fluted (45%). The comparison of CFI_LT-M with the other methods using Bland-Altman analysis showed lower mean difference for the CFI_LT-I than the CFI_PLT-I.

The level of width measurements at proximal femora might have an impact on the CFI values, likewise, preoperative planning procedures and the selection of a stem type in total hip arthroplasty.