Figure 5.

Example of estimation of the true angular deformity and the position of the plane of the deformity, using the rectangle rule. In this example, the angles measured on radiographs were 19° in AP view and 14° in lateral view. A rectangle was constructed such that one side represented the Ap plane and the other, the lateral plane. The angles measured on radiographs were transformed into units of length (in this example, one degree corresponded to 1 cm). The diagonal was measured with a ruler (in this case, 24 cm) and this measurement was transformed into degrees, using the same conversion rule (24 cm corresponded to 24°). This angle was the true angular deformity, which when projected in the AP plane was 19° and in the lateral plane, 14°. By measuring the angles formed between the diagonal and the AL and lateral planes (43° with the AP plane and 47° with the lateral plane), the position of the plane of the deformity relative to the AP and lateral planes was obtained.