To determine if measurement of anatomic lateral distal femoral angle (aLDFA) from radiographs is valid across a broad range of femoral varus conformations.Study Design:
Radiographic and anatomic study.Sample Population:
Large breed canine cadavers (n = 5) and femora (n = 10).Methods:
Cadavers were held in dorsal recumbency and 8 craniocaudal radiographic projections made of each femur: 1 image pre- and postosteotomy and at each of 6 progressive levels of induced distal varus deformity. Femurs were collected. Three blinded examiners independently measured varus on each radiograph (R-aLDFA) and femoral specimen (S-aLDFA) on 3 separate occasions. Intra- and interobserver variance in R-aLDFA and S-aLDFA measurements were determined. The strength of relationship between R-aLDFA and S-aLDFA and positive and negative predictive values for R-aLDFA were calculated.Results:
Intra- and interobserver variance in R-aLDFA (mean, 0.54% and 0.40%, respectively) and S-aLDFA (mean, 0.43% and 0.41%, respectively) were acceptable. The strength of relationship between R-aLDFA and S-aLDFA (adjusted R2 = 78.2%) was marginally below the acceptance criterion of 80%. Using aLDFA ≥ 102° as an indication for corrective femoral osteotomy, radiography was successful in correctly identifying corrective femoral osteotomy candidates (positive predictive value) and noncandidates (negative predictive value) 72% and 96% of the time, respectively.Conclusion:
R-aLDFA did not reach the desired accuracy for femoral varus measurement across the range of conformations evaluated.