**2. Biomechanics and templating**

The most important surgical technique that affects patient satisfaction and functional outcomes is the correct positioning and alignment of the components. Despite the introduction of computer assisted surgery, patient-specific designs, and kinematic knee alignment, the concept of optimal restoration of alignment still has added controversy on the best approach of planning TKA [3–5].

Most surgeons still agree, and it is traditionally accepted that the alignment of the lower limb should be within 0° ± 3° of the mechanical axis after surgery (measured by the angle formed by the center of the femoral head, the center of the knee, and the center of ankle) [6] (**Figure 1**). By positioning the femoral and tibial components perpendicular to its mechanical axis, there is a balanced distribution of mediolateral forces, not overloading the bone implant interface as well as the bone itself which could lead to loosening of the implant. Furthermore, malalignment causes increased polyethylene wear, leading to osteolysis.

In order to plan a TKA, a preoperative image exam that evidences all reference points is necessary to estimate the anatomical and mechanical axis of the femur and tibia. Since short-leg X-rays do not expose the whole lower limb references, they are not suitable for planning TKA when it is used alone. Long-leg radiograph (LLR) is traditionally used to estimate alignment of the lower limb. It is acquired on weight-bearing films, including the hip, knee, and ankle, with the patella facing forwards. The X-ray beam should be parallel to the articular surface [7]. Although the LLR acquisition is quite standardized, has long track records and it is fairly available, there are concerns about its use, since flexion contractures and rotational malposition could distort the interpretation of the native anatomy [8].

**2.1. Manual templating**

should be within 0° ± 3°.

For this instance, we propose a step-by-step methodology for planning TKA based on mechanical alignment, using LLR. We suggest the use of a parchment paper as it avoids scratching the LLR. First, the mechanical axis of the femur (MAF) is defined by connecting a line from the center of the femoral head to the femoral intercondylar notch. Then, the anatomical axis of the femur (AAF) is estimated by connecting a line from the center of the intramedullary femoral canal to the femoral intercondylar notch. The angle formed by the mechanical and anatomical axis of the femur (MAFÂ) is measured, using a protractor. This part of planning has particular importance for those who intend to use intramedullary distal femoral cut guides. Since the femoral stem follows the path of the AAF, the surgeon would know how to accomplish a

**Figure 1.** Alignment angle. Measured by the center of the femoral head to center of the knee and center of the ankle. It

Planning Primary Total Knee Arthroplasties http://dx.doi.org/10.5772/intechopen.72775 3

Besides the fact that LLR is quite standardized, has a long track record, and is fairly available, there have been reported concerns about the accuracy when there are flexion contractures and when the position of image acquisition is not neutral, since rotation of the limb could distort the interpretation of native anatomy.

#### Planning Primary Total Knee Arthroplasties http://dx.doi.org/10.5772/intechopen.72775 3

**Figure 1.** Alignment angle. Measured by the center of the femoral head to center of the knee and center of the ankle. It should be within 0° ± 3°.

#### **2.1. Manual templating**

minimal debris production; not leaving dead spaces; avoiding long intramedullary stem and intramedullary cement; a standard insertion procedure; minimal range of motion (5–90°); resist-

During the early 1970s, a range of prostheses such as unicondylar, bicondylar, and hinged were used with respect to the patient's preoperative condition and deformity. Since then, a lot of different kinds of implants have been developed following the tendency of maximizing flexion, minimizing wear, and better accommodation of gender and racial anatomic variation. Nowadays, a resurrection of old strategies such as uncemented fixation and partial knee replacement has been noted and minimally invasive approaches are growing respecting the

This chapter introduces a TKA preoperative planning method based on mechanical alignment and the modified GAP balancing principles. Kinematic alignment (KA) principle, anterolateral approach, and strategies for soft tissue balancing in special situations are cited as well.

The most important surgical technique that affects patient satisfaction and functional outcomes is the correct positioning and alignment of the components. Despite the introduction of computer assisted surgery, patient-specific designs, and kinematic knee alignment, the concept of optimal restoration of alignment still has added controversy on the best approach of

Most surgeons still agree, and it is traditionally accepted that the alignment of the lower limb should be within 0° ± 3° of the mechanical axis after surgery (measured by the angle formed by the center of the femoral head, the center of the knee, and the center of ankle) [6] (**Figure 1**). By positioning the femoral and tibial components perpendicular to its mechanical axis, there is a balanced distribution of mediolateral forces, not overloading the bone implant interface as well as the bone itself which could lead to loosening of the implant. Furthermore, malalign-

In order to plan a TKA, a preoperative image exam that evidences all reference points is necessary to estimate the anatomical and mechanical axis of the femur and tibia. Since short-leg X-rays do not expose the whole lower limb references, they are not suitable for planning TKA when it is used alone. Long-leg radiograph (LLR) is traditionally used to estimate alignment of the lower limb. It is acquired on weight-bearing films, including the hip, knee, and ankle, with the patella facing forwards. The X-ray beam should be parallel to the articular surface [7]. Although the LLR acquisition is quite standardized, has long track records and it is fairly available, there are concerns about its use, since flexion contractures and rotational malposi-

Besides the fact that LLR is quite standardized, has a long track record, and is fairly available, there have been reported concerns about the accuracy when there are flexion contractures and when the position of image acquisition is not neutral, since rotation of the limb could distort

ing rotation; and resisting excessive movements in any direction.

patient's desire of shortening postoperative recovery [1, 2].

ment causes increased polyethylene wear, leading to osteolysis.

tion could distort the interpretation of the native anatomy [8].

the interpretation of native anatomy.

**2. Biomechanics and templating**

planning TKA [3–5].

2 Primary Total Knee Arthroplasty

For this instance, we propose a step-by-step methodology for planning TKA based on mechanical alignment, using LLR. We suggest the use of a parchment paper as it avoids scratching the LLR. First, the mechanical axis of the femur (MAF) is defined by connecting a line from the center of the femoral head to the femoral intercondylar notch. Then, the anatomical axis of the femur (AAF) is estimated by connecting a line from the center of the intramedullary femoral canal to the femoral intercondylar notch. The angle formed by the mechanical and anatomical axis of the femur (MAFÂ) is measured, using a protractor. This part of planning has particular importance for those who intend to use intramedullary distal femoral cut guides. Since the femoral stem follows the path of the AAF, the surgeon would know how to accomplish a perpendicular cut to the MAF, by positioning the distal femoral cut guide in a valgus angle to the AAF, referenced by MAFÂ.

After knowing the inclination of the distal femoral cut, the surgeon should evaluate the level of bone resection, anticipating the amount of bone resection. Usually, in a primary TKA, the level of bone resection corresponds to the femoral component thickness (e.g*.,* 9 mm). This step simulates the surgical moment when the surgeon places the distal femoral cut guide onto the distal femoral bone. Using a protractor, the surgeon draws a line perpendicular to the MAF above the first point of the distal femoral bone contact (e.g., 9 mm), from distal to proximal. By doing it, the surgeon could simulate the level and inclination of the distal femoral cut. One should notice that the LLR film does not correspond to real size, being reduced to fit on the film frame. Typically, the amount of reduction in size is reported on the printed film and should be used to make a conversion between film size and actual size.

The same rationality is applied to the tibial bone. The mechanical and anatomical axes are coincident on the tibia, so the mechanical axis of the tibia (MAT) can be defined as a line drawn from the center of the tibial spines to the center of the talus. Mechanical and anatomical axes are usually coincident on the tibia. The mechanical axis of the tibia (MAT) can be defined as a line drawn from the center of the tibial spines to the center of the talus. After defining MAT, tibial cut is planned perpendicular to the MAT. Usually, surgeons plan to cut 8–10 mm below the unworn side of the tibial plateau, but it can be adjusted to best fit the components and balance the knee. So, the surgeon places a line from proximal to distal, at the level desired below the unworn side of the plateau. Still, conversion between LLR size and real size should be adjusted using a mathematical calculation. The whole process of manual templating technique is illustrated in **Figure 2**.

The more parallel the bone cut planes, the less ligament release is necessary. The less parallel the bone cut planes, the more ligament release is necessary. One must note that there is a limit for releasing ligaments. When a great amount of releasing is necessary, the surgeon should consider a more constrained implant, since it could get into a situation called "over resection looseness," when the ligament function capacity is exceeded.

The size of the components can be also estimated during the planning of a TKA. To do it so, the surgeon must have the specific prosthesis templates and should order a short-leg X-ray in an actual size (1:1).
