Source | (WeChat official account) Rui Lin in the cloud (ID: ruilinfly)

Rui Lin asked:

1. There are too many nouns in the sagittal analysis diagram of lower limbs, including the total length of ankle joint MOT and the level of ankle joint MOT, the total length of knee joint MOT and the level of knee joint MOT. I wonder if it is necessary to make such a detailed distinction in operation.

2. Why do you ignore the femoral shaft angle (MDA = 10) when analyzing the sagittal deformity of femur?

Overview of Rui Lin:

We should master the analysis of sagittal deformity of lower limbs.

1. Full-length sagittal pad (full-length mechanical axis of lower limbs): total flexion or hyperextension of knee joint (femoral and tibial anterior cortex method).

2. Sagittal anatomical axis plane of tibial deformity correction.

3. sagittal anatomical axis plane for correction of femoral deformity

4. Knee joint abnormalities: subluxation (center point method), flexion deformity and hyperextension deformity (the overall flexion and extension deformity obtained in step 1 excludes the anterior and posterior arch deformities of the distal femur and the proximal tibia, and the rest are simple flexion and extension deformities of the knee joint).

FFD: Fixed flexion deformity

He: joint flexion

PDFA: average 83(83.4)

aPPTA: 8 1 4

aADTA: 80 2

Fixed flexion deformity of knee joint (FFD)VS flexion contracture of knee joint (see Figure 6- 10b).

The midline of the proximal femur intersects with the distal femur in the middle of femur, and the normal midsection diaphyseal angle (MDA) is about 10.

The full-length mPDFA was measured by the straight line from the center of femoral head to 1/3aJER (improved sagittal anatomical axis of femur). If it is less than 79, it means that there is anterior arch deformity. If it is greater than 87, it means that there is posterior arch deformity.

The knee joint has no functional range of motion on the frontal plane, so MAD has no compensatory range of motion. Because the knee joint has flexion and extension activities in the sagittal plane, it will compensate for the sagittal deformity of femur and tibia (Figure 6-2).

Figure 6- 1

A. When the knee joint is in a completely straight position, the mechanical axis of the upper and lower limbs on the sagittal plane runs from the center of the femoral head to the rotation center of the ankle joint and passes in front of the rotation center of the knee joint.

B When the knee joint is in the flexion position of 5, the mechanical axis of the upper and lower limbs on the sagittal plane passes through the rotation center of the knee joint.

The straight line connecting the rotation center of hip joint (femoral head center) and ankle joint (located at the apex of lateral talus process on lateral radiograph) is the mechanical axis of lower limbs on sagittal plane. When the knee joint is in a completely straight position, under normal circumstances, the mechanical shaft of the lower limb passes through the front of the rotation center of the knee joint (on the lateral radiograph, it is located at the junction of Blumensaat line and posterior cortical bone), so that the knee joint can be locked (Rui Lin: "locking" means that a stable state can be maintained only by the static stable structure of the joint? ) In the completely straight position, you can relax the quadriceps femoris at this time. If the sagittal mechanical axis cannot be located in front of the rotation center of the knee joint due to deformity, the quadriceps femoris must continue to work to maintain the knee joint in a straight position, which will cause fatigue of the quadriceps femoris; For paralyzed patients (such as poliomyelitis and spina bifida), sagittal mechanical axis forward movement is an important compensation mechanism in gait.

The causes of poor sagittal alignment include deformity of anterior and posterior arches of femur and tibia and subluxation of knee joint. Should flexion deformity and hyperextension deformity of knee joint also be included? .

Rui Lin thinks about what is the sagittal defect of lower limbs. Refers to the abnormal relationship between the full-length mechanical axis in the sagittal plane of the lower limb and the rotation center of the knee joint?

A Under normal circumstances, when the knee joint is in a completely straight position, the midpoint of the width of the lateral femoral condyle and the midpoint of the width of the tibial plateau on the sagittal plane are located in a straight line (I). When the knee joint is subluxated, this pair of lines is interrupted (ii).

B subluxation of knee joint is the cause of sagittal abnormality. When the distance (d) between the center lines exceeds 3 mm, posterior dislocation or anterior dislocation will occur. Rui Lin: How to define the direction of the center line? Refers to the direction of the lower limb force line?

A On the X-ray film of the knee joint in the maximum extension position, when the mechanical axis of the lower limb does not pass in front of the rotation center of the knee joint, there is an abnormality of sagittal flexion alignment.

B. When the full-length mechanical axis of tibia and femur is in the hyperextension (he) position and exceeds 5, there is abnormal straightening alignment.

The focus of the sagittal pad is to determine whether there is poor alignment of flexion or extension. When the knee joint is in a completely straight position, the sagittal mechanical axis is not in front of the rotation center of the knee joint, which indicates that the sagittal buckling alignment is abnormal; When the passive hyperextension of the knee joint exceeds 5, it shows that the arrangement of sagittal extension is abnormal.

When determining whether there is flexion alignment deformity, the whole body lateral radiograph with the knee joint in a completely straight position is needed; It is necessary to photograph the femur and tibia at the position of maximum hyperextension (HE) to determine whether there is extension alignment abnormality.

Because of compensatory flexion or extension of joint motion, although there is deformity in femur or tibia, it will not show extension or flexion-alignment abnormality. Therefore, sagittal MAD is easy to mislead, and the judgment of whether there is sagittal skeletal deformity mainly depends on MOT (Abnormal Joint Orientation Test).

If the diaphysis is deformed, PDFA and PPTA may be normal with respect to the adjacent diaphysis, but abnormal with respect to the whole femur and tibia respectively, so two MOTs are independently performed for the distal femur and the proximal tibia respectively.

The full-length test mainly focuses on the trend of the joint line of the distal femur and the proximal tibia, and the relationship with the improved mechanical axis of the femur or tibia respectively.

When the knee joint is in a completely straight position, the anterior cortical bone of the distal femur and the anterior cortical bone of the proximal tibia are in a straight line under normal circumstances (Figure 6- 10a), which can be used as the best index of the complete straight knee joint. Measuring the angle between the tibial cortical line and the anterior femur can describe the fixation flexion deformity (FFD) or knee flexion (he) (Figure 6-65438+).

Draw the improved femoral mechanical axis from the center of the femoral head to 1/3aJER, and measure the PDFA relative to this axis. Judging whether there is anterior and posterior arch deformity in the distal femur according to the angle. Rui Lin: See Figure 6-6 for the drawing of the motion direction line of the distal femoral joint.

Step 1

When the knee joint is in the maximum extension position, draw the anterior cortical lines of the proximal tibia and the distal femur, and measure the angle between the two lines.

Any buckling angle greater than 0 is considered to have fixed buckling deformation (FFD).

Joint flexion (HE) is considered to exist at any extension angle greater than 5.

Second step

The PDFA is measured through the midline of the distal femoral shaft, and the absolute value of the difference from the measured PDFA is obtained according to the normal contralateral PDFA value or the normal PDFA average value of 83, so as to determine the degree of abnormal walking direction of the distal femoral joint.

Third step

PPTA is measured by the midline of the proximal tibia, and the absolute value of the difference from the measured PDFA value is obtained according to the normal contralateral PPTA value or the normal PPTA average value of 8 1, so as to determine the degree of abnormal walking direction of the proximal tibia joint.

Fourth step

Focus film distance

From the FFD obtained in step 1, the sum of the anterior arch deformity and the posterior arch deformity obtained in steps 2 and 3 are subtracted and added respectively.

If the difference is 0, the deformity of the anterior arch of bone is the cause of FFD.

B If the difference is greater than 0, the deformity of the anterior arch is not the whole cause of FFD, so there is still knee flexion contracture.

If the difference is less than 0, the deformation of the anterior arch is greater than FFD, so there is still relaxation of the knee joint.

male

Subtract and add the sum of the posterior arch deformity and the anterior arch deformity obtained in steps 2 and 3 from the he obtained in step 1, respectively.

If the difference is 0, the deformity of posterior arch is the cause of FFD.

If the difference is greater than 0, the posterior arch deformity is not the whole cause of FFD, so there is still knee joint relaxation.

F If the difference is less than 0, the deformity ratio of the posterior arch is more, so there is still knee flexion contracture.

Draw the improved tibial mechanical axis from the center of ankle joint to 1/5aJER, and measure ADTA relative to this axis.

If ADTA is less than 78, it means that there is a full-length posterior arch deformity in the proximal tibial joint line.

B If ADTA is greater than 84, it means that there is a full-length anterior arch deformity in the proximal tibial joint line.

Draw the midline of the distal tibia and measure ADTA. If ADTA is less than 78 or greater than 85, the running direction of ankle joint line relative to DAA line is abnormal.

Step 1

Draw the midline of the tibial shaft, each segment represents the anatomical axis of the bone segment, and carry out MOT between the proximal and distal midline of the tibial shaft, the knee joint line and the ankle joint line respectively.

Second step

Determine whether the joint running direction angle is normal (PPTA, ADTA).

A

1. If PPTA is normal, there is no other proximal Cora or anatomical axis.

2. If PPTA is abnormal, draw the anatomical axis with reference to the direction line of knee joint. If available, the reference point can be from the normal opposite side, or from 1/5ager. If you can get it, you can use the normal PPTA value on the opposite side as the template angle; If the opposite PPTA is unavailable or abnormal, you can use the normal average value of PPTA of 8 1.

ADTA was measured at the midline of the distal tibia.

1. If ADTA is normal, there is no other distant Cora.

2. If ADTA is abnormal, draw the anatomical axis with reference to the running direction line of ankle joint. If available, you can take the reference point from the normal contralateral side or draw a line from the center point of the adult joint. If available, the normal contralateral ADTA value can be used as the template angle. If the opposite ADTA is unavailable or abnormal, the normal average value of ADTA of 80 can be used.

Third step

Determine whether it is a single vertex or a multi-vertex angular deformity, mark CORA and measure the degree.

A If only 1 pairs of anatomical axes can be drawn, then there are only 1 CORA and 1 angles.

B For every additional 1 anatomical axis, 1 CORA and 1 angle will be added.

Step 1

Draw the midline of the femoral shaft, and each segment represents the anatomical axis of the bone segment. MOT is performed between the midline of the distal shaft and the knee joint line.

PDFA is measured relative to the midline of the distal femur.

Second step

Determine whether the joint running direction angle is normal (PDFA)

A If PDFA is normal, there is no other distal cora or anatomical axis.

B. If PDFA is abnormal, draw the anatomical axis with reference to the direction line of the knee joint. If available, the reference point can be taken from the normal contralateral side, or for adults, a straight line can be drawn from the knee running direction line 1/3aJER. If available, the normal relative PDFA value can be used as the template angle. If the contralateral PDFA is unavailable or abnormal, the normal average value of PDFA 83 can be used.

Third step

Determine whether it is a single vertex or a multi-vertex angulation deformity, mark CORA and measure the angle.

This preoperative planning method does not consider the proximal femoral deformity, because the anatomical axis can be used when the position is higher than the femoral neck. The relationship between the direction of femoral head and the direction of femoral neck will be discussed separately in chapter 19.

Rui Lin thought about how to determine the middle deformity of femoral sagittal plane. According to fig. 6-6, the anatomical axes of the proximal and distal femurs themselves have an intersection angle of10. Draw the proximal and distal anatomical axes of femur on sagittal plane. If the intersection angle between them is greater than 10, it means there is deformity.