(1) Static alignment of the socket

The purpose of static alignment of the socket is to determine the spatial position of the socket during prosthesis assembly. The reference line of the static alignment of the socket is determined based on the static balance of the prosthesis and the force vector of the resultant force on the socket. The method of alignment is to find the alignment reference line on the plane of the ischium, and then determine the flexion and adduction angle of the socket according to the condition of the stump. In this way, the position of the socket in space is determined. In the transverse elliptical socket, the ischial support area bears the main load. At the same time, the whole part of the ischium also plays the role of load-bearing surface, bearing part of the load. Because of this load distribution relationship, the position of the resultant force vector acting on the socket is located medial and posterior to the ischial support area under static state. The reference line of the opposite line is also biased medially and posteriorly, towards the direction of the ischial support. The line between the medial margin of the sciatic ring and the midpoint of the lateral margin was taken as the transverse axis of the ischium. The vertical line perpendicular to the horizontal axis and dividing the horizontal axis into inner 40% and outer 60% is used as the reference line (A-P line) for the front and back alignment of the socket. The transverse axis was shifted backward by 0.5-2cm according to the volume of the socket, the flexion Angle, the strength of the hip extensor, and the patient's individual stabilization needs to obtain an anterolateral reference line (M-L line). The more the medial and lateral alignment reference is translated backward, the more stable the prosthesis will be.

                                                                         The reference line of the socket alignment in the transverse ellipse in the ischium plane receives

The flexion and adduction of the socket have a great influence on the prosthesis assembly. The adduction alignment of the socket is consistent with the physiological state of femoral adduction. At the same time, the abductor muscle can play a more effective role and maintain the lateral stability of the prosthesis. In the same way, the flexion alignment of the socket must give the initial flexion angle to the socket, which is conducive to play the function of the hip extensor muscle and maintain the stability of the prosthetic knee joint. The flexion and adduction angles of the socket depend on the condition of the optic stump. For medium-length stumps, 5° of luminal flexion and 5° of adduction were accepted for alignment. The longer the stump, the longer the lever the patient has to control the prosthesis, the more muscle they have, the more strength they have, and the better their ability to control and stabilize the prosthesis. When the alignment between the socket and the prosthesis, the advantage of the patient's long stump should be taken into account to increase the flexibility of the prosthesis. For short limbs, the initial flexion angle of the socket should be increased appropriately.

(2) Static alignment of AK prosthesis

The static alignment of prosthesis refers to the determination of the relative position relationship between the socket, knee joint, ankle joint and the prosthetic foot in the three-dimensional space. The relative position relationship between them can be described by the reference line. The reference line for the AK prosthesis is an imaginary vector. It is consistent with the resultant force vector of the prosthesis under static state. This imaginary vector can be represented by the intersection of the frontal and sagittal planes. The two planes are determined with the aid of double plumb lines on the aligner. The front plumb line is called the front plumb line (or A line), and the back plumb line is called the back plumb line (or P line). Accordingly, there are medial (or M) and lateral (or L) perpendiculars. The anterior and posterior perpendicular lines determine the sagittal plane, and the medial and lateral perpendicular lines determine the frontal plane. Since the line reference does not exist, it can only be represented by a projection onto the prosthesis. We can determine its projection onto the prosthesis surface with the help of the double plumb line on the alignment meter. When you look at the frontoid line, when the front vertical line overlaps the back vertical line, their projection onto the prosthesis is called the frontoid line. When you look at the sagittal plane, the projection of the medial vertical and the lateral vertical onto the prosthesis is what we call the sagittal plane. Only by observing in this way the reference line of the prosthesis can be truly reflected. In this way, we can determine the relative position of the socket, knee joint, and prosthesis on the alignment instrument. Keep the ankle level with the knee joint, taking into account the height of the heel. Then observe the prosthetic alignment from front to back and inside. Anterior alignment line in frontal plane: the reference line passing through the middle of the big toe, the midpoint of the ankle joint, the midpoint of the knee joint, and the socket. Medial posterior alignment line in frontal plane: the reference line passing through the midpoint of the posterior malleolus, the midpoint of the ankle, the midpoint of the knee joint and the socket.

Medial and lateral alignment in sagittal plane: the reference point of alignment between the prosthetic foot and the knee joint, and the reference line of inner and outer alignment of the socket. Because of the variety of prosthetic foot and knee joint, the line regulation is also different. Specific reference points for line alignment are provided by each manufacturer. When fitting the prosthetic line, the line should be adjusted or adjusted according to the manufacturer's recommendation and the patient's actual situation. Taking uniaxial fixed friction knee joint as an example, the static alignment of prosthesis is illustrated. Among them, the position of knee joint and prosthetic foot (in sagittal plane) can also be adjusted according to the stability requirements. The forward movement of the prosthetic foot or the posterior position of the knee joint can improve the stability of the knee standing state. On the contrary, the prosthesis is less stable, but easier to swing into.