Table 2 Comparison between reference standard methods used in everyday orthopedic clinical practice and ChatGPT. For each numbered angle or axis, clinical importance is provided along with reference standard methods to mark axes and angles of the lower limbs. The analysis of the ChatGPT output includes the reasons why the ChatGPT output is accurate or inaccurate

1.

Center of femoral head

The entire lower limb rotates around this very important landmark. The center of the femoral head is also the center of the hip joint.

Draw the best fitting circle over the femoral head.

The location of the femoral head is defined by this circle and its center.

Identify the center of the femoral neck and the center of the femoral head.

Draw a line from the center of the femoral neck to the center of the femoral head.

Measure the distance between the center of the femoral head and the line you drew.

ChatGPT is entirely wrong.

The center of the femoral head is a single point. Since the normal femoral head is almost spherical, this point becomes an essential landmark. ChatGPT defines and suggests drawing a line.

2.

Mechanical axis

The mechanical axis is a line from the center of the femoral head to the center of the ankle joint; it is the direction of the force vector for weight bearing. Disturbances of mechanical axis are very undesirable because the abnormal forces will be distributed on the lower limb bones and joints.

Mechanical axis is a straight line between center of the femoral head and the center of the ankle joint.

Identify the center of the hip joint, the center of the knee joint, and the center of the ankle joint.

Draw a line through the center of the hip joint and the center of the knee joint.

Draw a second line through the center of the knee joint and the center of the ankle joint.

Measure the angle between these two lines.

ChatGPT is partially correct.

While the mechanical axis does pass through the center of hip and ankle joint, it does not pass through the center of knee joint if there is any bone or joint deformity. Therefore, Chat GPT is only partially correct.

3

Anatomical axis

These axes are the geometric long axes of bone. The normal difference between the anatomical and mechanical axis of the femur is about 6 degrees. This relationship is disturbed by fractures or deformities. One goal of surgery is to restore these angular relationships.

Anatomical axis is the axis of the femoral shaft and the tibial shaft. In femur, there is a difference between anatomical and mechanical axis of a few degrees, but there is no difference among these axes in tibia.

Identify the center of the femoral head and neck, the center of the knee joint, and the center of the ankle joint.

Draw a line through the center of the femoral head and neck.

Draw a second line through the center of the knee joint and the center of the ankle joint.

Measure the angle between these two lines.

ChatGPT is entirely wrong.

There are two problems. First, anatomic axis does not involve the femoral neck, as ChatGPT describes. Second, ChatGPT instructs how to draw an angle. This is not relevant.

4

Mechanical Lateral Proximal Femoral Angle (mLPFA)

This angle is used to define the bony deformity of the femur.

Draw a horizontal line between the center of the femoral head and the mechanical axis on the lateral aspect.

Draw Mechanical axis.

The angle is between the two lines

Identify the center of the femoral head and neck and the center of the femoral shaft.

Draw a line through the center of the femoral head and neck.

Draw a second line through the center of the femoral shaft.

Measure the angle between these two lines using a goniometer.

ChatGPT is entirely wrong. It incorrectly provides instruction regarding how to draw a neck shaft angle.

The angle between femoral neck and shaft is called neck shaft angle; it is completely different than the mLPFA.

5

Mechanical Lateral Distal Femoral Angle (mLDFA)

This angle is used to characterize deformities of the knee and the inferior part of femur.

Draw Mechanical axis.

Draw a line between the distal ends of medial and lateral femoral condyles.

mLDFA is the angle between the two lines.

Identify the center of the femoral shaft and the center of the tibial plateau.

Draw a line through the center of the femoral shaft.

Draw a second line through the center of the tibial plateau.

Measure the angle between these two lines using a goniometer.

ChatGPT is entirely wrong.

The tibial plateau (the upper broad part of tibia) is not used to determine the mLDFA.

6

Medial Proximal Tibial Angle (MPTA)

This angle is used to characterize deformities of the knee and the superior part of the tibia.

Draw mechanical axis.

Draw a line parallel to the articular surface of tibia.

The angle between the two lines in MPTA.

Identify the center of the tibial plateau and the tibial shaft.

Draw a line through the center of the tibial plateau.

Draw a second line through the tibial shaft.

Measure the angle between these two lines using a goniometer

ChatGPT is entirely wrong.

The horizontal line must be parallel to the surface of the upper end of tibia. ChatGPT is inaccurately describing the angle.

7

Lateral Distal Tibial Angle (LDTA)

This angle is used to characterize a deformity near the inferior tibia and the ankle joint.

Draw the mechanical axis.

Draw a line parallel to distal tibial articular surface.

The angle between the two lines is LDTA.

Identify the center of the tibial plateau and the ankle joint.

Draw a line through the center of the tibial plateau.

Draw a second line through the ankle joint.

Measure the angle between these two lines using a goniometer.

ChatGPT is entirely wrong.

ChatGPT fails to mention the vertical line that is the mechanical axis of tibia used to determine LDTA.