Deformity Correction of Lower Limb Bones/Basic Principles/Mechanical Axis Deviation (MAD) and Hip-Knee-Ankle angle (HKA)

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Annotations:

• 0:14 Mechanical Axis of the leg
• 1:15 Varus and Valgus
• 1:40 Mechanical Axis Deviation (MAD)

The mechanical axis of the lower limb or the leg is different from the mechanical axis of femur and tibia bones. It is defined as a line drawn from femoral head center to the ankle center.

The distance between the leg mechanical axis line and the center of the knee in the frontal plane is called the Mechanical Axis Deviation (MAD). The normal range of MAD is 8+/-7 mm medially

The MAD is described as either medial or lateral. Medial and lateral MADs are also referred to as varus or valgus malalignments, respectively (Fig. 6b)

The HKA angle is the medial angle between the mechanical axis line of femur and mechanical axis line of tibia in the frontal plane.

The normal range of HKA is 180 +/- 3°. If HKA < 177°, leg is known as to be in varus malalignment and if HKA > 183°, leg is in valgus malalignment (Fig. 6b)