Effects of Femur Position on Radiographic Assessment of Femoral Head and Neck Excision Completeness in Cats.

OBJECTIVE: The aim of this study was to determine the effect of femoral position on radiographic assessment of completeness of femoral head and neck excision (FHNE) in cats. STUDY DESIGN: The study included 20 femurs from adult cats. Complete FHNE was performed on 10 femurs and incomplete excision consisting of inadequate excision of the distal medial femoral neck was performed on 10 femurs. The lesser trochanter was maintained in all femurs. Each femur was positioned through a predetermined set of eight radiographic views about the long axis. Sensitivity (SE), specificity (SP) and accuracy were calculated for each femoral position. RESULTS: Craniocaudal views of the femur in external rotation (30° and 45°) had the highest SE, SP and accuracy (SE: 97.5% and 97.5%; SP: 92.5% and 95%; and accuracy: 95% and 96%, respectively) followed by external rotation of 15 (SE: 92.5%, SP: 87.5% and accuracy: 90%) relative to standard craniocaudal (SE: 57.5%, SP: 72.5%, accuracy: 65%) and lateromedial (SE: 2.5%, SP: 0%, accuracy: 1%) radiographic views. CONCLUSIONS: Evaluation of craniocaudal radiographic views with the femurs in external rotation can increase the ability to assess the adequacy of the FHNE in cats.

Comparison of femoral angulation measurement between radiographs and anatomic specimens across a broad range of varus conformations.

OBJECTIVE: 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. CONCLUSION: 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.