2. Definition of fit and alignment
Alignment :
it deals with the angular relationship of the
orthotic components to each other and to a reference line relating the
orthoses to the body as a whole.
Fit :
It deals with the relationship between the orthoses anatomical
landmarks and body contours.
3. The objectives of proper fit and
alignment are :
1. Flat heel and sole contact of the shoe with the ground.
2. Anatomical- mechanical joint congruency.
3. Horizontal orientation of joint axes.
4. Conformity to landmark contours and landmarks.
Joint characteristics related to
orthotic fit and alignment :
Hip joint : The hip joint is a ball and socket joint which
permits universal motion of the lower limb : Abduction -
adduction, flexion - extension and transverse rotation.
Knee joint :
In normal standing
The axes of both knee joints lies in the same plane and are
perpendicular to the line of progression
4. The knee joint is considered a polycentric joint.
Polycentric joint :
“It is a polycentric prosthetic
knee joint, which mimics the movement of a
normal knee joint while walking. At the same
time, it provides stability during the weight-
bearing phase to ensure the person can walk
with their artificial limb
5. Without fall in walking:
During the normal range of motion the
knee joint are not only exhibits a rotary but also a translatory
component ;the femur not only flexes with respect to the tibia but also
translate forward from an extended to a flexed position.
Transverse rotation :
There is transverse rotation of
approximately 10° of the femur with respect to the tibia with the
femur rotating internally as the knee joint moves from flexion to
extension.
Ankle joint :
Due to the natural torsion of the tibia the axis of the
ankle joint is rotated externally 20° to 30° with respect to the knee
axis. Tibial torsion is a developmental phenomenon which increases
from a minimal amount of about 2°. In a new born to a parameter
value of 20° to 30° by the age of seven years.
This developmental adaptation places the ankle joint in the best
position for upright walking.
6. The line of progression
The term is used to denote the direction in which
we walk. Though it is a straight line the center of
gravity oscillates from side to side as it moves
forward.
“The line of progression is represented a
summation of the excursions of the center of
gravity during locomotion.”
7. The externally rotated ankle - joint axis is not
perpendicular to the progression during the first half of
the stance phase shown in diagram :
It is approximately perpendicular to a tangent of the path
of the center of gravity of the body which permits the
ankle joint to bend freely in the direction of movement of
the center of gravity from the heel-strike to the midstance
phase of walking.
8. Subtalar joint:
The Subtalar joint performs especially important functions :
1. In standing it permits mediolateral shifting of the center of gravity while the foot
retains flat heel and sole contact with the floor.
2. It permits the foot to adapt to uneven ground.
3. During walking it regulate the tension of the planter Apo neurosis as weight is
transferred from the heel forward.
4. It absorb shock.
5. During flexion of the knee as in squatting it help to compensate for the difference in
alignment of the ankle joint and knee joint as projected in the transverse plane.
