The frontal (coronal) and sagittal planes are the standard reference planes. Radiographs that correspond with these planes are AP and lateral X-rays, respectively. If there is an angulation on both frontal and sagittal planes, it means the deformity is on the oblique plane. Deformities other than those on the frontal and sagittal planes are oblique plane deformities. These deformities were previously known as biplanar deformities. However, this description was wrong because they were uniplanar angular deformities in the oblique plane (Figs. 21.1 and 21.2).

Fig. 21.1
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An oblique plane deformity of the left tibia; clinical view (left), AP radiography (right)

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Fig. 21.2
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An oblique plane deformity of the left tibia; clinical sagittal view (left), lateral radiography (right)

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1 Apical Direction of Angulation

Angular deformities may occur on any plane. For the frontal plane, medial and lateral (varus, valgus), and for the sagittal plane, anterior and posterior (procurvatum, recurvatum) directions can be seen for each plane. For an oblique plane deformity, for each X-ray view (AP and LAT), there is an apical direction of angulation (Figs. 21.3 and 21.4) [1, 2].

Fig. 21.3
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Right tibia of a patient with an anterolateral oblique plane deformity, AP X-ray shows an apical direction of angulation to the lateral side

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Fig. 21.4
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The right tibia of a patient with an anterolateral oblique plane deformity (same patient as shown in Fig. 21.3). Lateral X-ray shows an apical direction of angulation to the anterior side

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As a combination, oblique plane deformities can be classified in four types according to the apical direction of angulation. Sagittal plane must be stated first for the classification [3, 4]:

  1. 1.

    Anteromedial deformities; a combination of varus and procurvatum deformities

  2. 2.

    Anterolateral deformities; a combination of valgus and procurvatum deformities

  3. 3.

    Posteromedial deformities; a combination of varus and recurvatum deformities

  4. 4.

    Posterolateral deformities; a combination of valgus and recurvatum deformities

2 The Magnitude of the Deformity

There is no absolute correlation between the actual angle of deformity and those measured on both AP and LAT X-rays. This angle we measured on both AP and LAT are only projections. The actual angle can only be measured if the X-ray is taken perpendicular to the deformity plane.

Before the operation, the maximum or actual angulation of the deformity must be measured and the right deformity plane must be determined. Using the angulation values on the AP and LAT X-rays, the actual value can be measured using trigonometric calculations; however, this is quite difficult. In practice, we use a similar method to that developed by D. Paley for the calculations. It is simple and can be used very quickly [5].

3 Paley’s Graphic Method

Before this practical method, we used some normograms defined by Bar and Breitfuss in 1989 and Ilizarov in 1989. Because these methods contain some trigonometric calculations, charts, and tables, we use Paley’s graphic method (1990–1992), which is simpler to use and without any miscalculations [6, 7].

Let’s analyze the deformity of the patient on the Figs. 21.1 and 21.2 and establish the actual angulation angle using Paley’s graphic method.

Step 1

CORA and the angulation on the AP and LAT X-rays must be determined with the same method, as explained in previous chapters (Chaps. 2 and 3).

For this case, on the left tibia AP X-ray, there is a 20° valgus angulation, and the apical direction of angulation is on the lateral side. On the lateral X-ray, there is a procurvatum deformity of about 35°, and the apical direction of angulation is on the anterior side (Figs. 21.1 and 21.2).

Step 2

Draw a coordinate graph with x- and y-axes on the paper. The x-axis refers to the frontal plane; the y-axis refers to the sagittal plane. The surface of the graph refers to the transverse plane. The right of the x-axis is the (+) side, and the left of the x-axis is (−) side. The upper side of the y-axis is the (+) side and the lower side of the y-axis is (−) side (Fig. 21.5).

Fig. 21.5
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Drawing of the coordinate graph with x- and y-axes and determination of the (+) and (−) sides

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The capital letters of the anterior (A), medial (M), lateral (L), and posterior (P) have to be added to the graph. When analyzing, pay attention to the extremity side especially. When the sides are positioned on the graph, look down to your own extremity. If the deformity is on the right or left extremity, position the sides according to you (Fig. 21.6).

Fig. 21.6
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Drawing of the coordinate graph with x- and y-axes and positioning of the anatomic sides

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For the right side

The (+) side of the x-axis is lateral; the (−) side is medial.

The (+) side of the y-axis is anterior; the (−) side is posterior.

For the left side

The (+) side of the x-axis is medial, the (−) side is lateral.

The (+) side of the y-axis is anterior, the (−) side is posterior (Fig. 21.5).

Step 3

Place landmarks 1 mm on the x- and y-axes. 1 mm refers to 1° of angulation. In this case, the 20° of angulation must be placed on the x-axis, and the 35° of angulation must be placed on y-axis (Fig. 21.7).

Fig. 21.7
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Placement of the angulation values. Each mm refers to 1° of angulation

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The apex of the deformity must be considered while placing the values on the chart. On the AP X-ray, the 20° varus deformity is on the lateral side. For this value, 2 cm on the (−) side of the x-axis must be marked. On the LAT X-ray, the apex of the procurvatum deformity is on the anterior side. For this value, 3.5 cm on the (+) side of the y-axis must be marked.

Step 4

Draw a perpendicular line from the marked points of the axes. The crossing point must be connected to the center. This line revealed refers to an oblique plane deformity (Fig. 21.8).

Fig. 21.8
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After connecting the perpendicular lines from the marked points, the apical direction of angulation on the oblique plane is revealed

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Step 5

After all this planning, measure the angle between the new line and the x-axis. This angle refers to the plane of deformity according to the frontal plane. In this case, the deformity plane makes an angle between the frontal plane of 55° and sagittal plane of 35° (Fig. 21.9).

Fig. 21.9
figure 9

Determining the deformity plane and angulation correction axis (ACA)

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Step 6

After determining the angulation correction axis, the deformity plane bone and soft tissue projection must be added to the chart (Fig. 21.10).

Fig. 21.10
figure 10

Addition of the bone and soft tissue reference after the determination of the deformity plane and the hinge axis

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Step 7

Positioning the hinge: After the actual deformity axis and plane has been determined, the diameter of the bone at the deformity level must be measured, which is shown in Fig. 21.11. If the hinges are positioned tangential to the farthest anterolateral cortex, this means the correction comes with lengthening as in an open-wedge osteotomy. If the hinges are positioned tangential to the posteromedial cortex, this means the correction comes with shortening, as in a closed-wedge osteotomy.

Fig. 21.11
figure 11

Hinge positioning. There are three major hinge positions for the osteotomy. Use the anterior line for the open wedge, and for the closed wedge, use the posterior line

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4 Angulation Correction Axis (ACA)

ACA is perpendicular to the deformity plane (Fig. 21.9). This means that varus–valgus deformities are corrected on the frontal plane, and recurvatum– procurvatum deformities are corrected on the sagittal plane.

The angulation correction axis of an oblique plane deformity is a line perpendicular to the deformity plane. The correction axis can be drawn from the CORA point in the radiograph. If an open-wedge osteotomy is planned, ACA must be on the convex cortex of the bone. If a closed-wedge osteotomy is planned, ACA must be on the concave cortex of the bone (Fig. 21.11). The transverse projection of the bone must be drawn on the graph for the correction osteotomy. The diameter of the bone must be measured on both lateral and AP views, and the bone shape must be drawn inside the marked points. After elongation, the lines refer to the angulation plane; a perpendicular line to this axis must be drawn (Figs. 21.12 and 21.13).

Fig. 21.12
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Clinical photos of the patient in Figs. 21.1 and 21.2 during treatment

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Fig. 21.13
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Clinical photos of the patient in Figs. 21.1 and 21.2 after the treatment

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