Transtibial Alignment, Biomechanics, and Gait Analysis

goal of sagittal plane alignment

• normal gait - joint flexion through loading response allows for shock absorption and less forces transmitted proximally

• 5-10° of flexion at initial contact

• up to 20° of flexion through loading response

• allows for smooth knee flexion during initial contact through heel-off

goal of coronal plane alignment

½” varus moment at the knee to activate the screw-home
mechanism for knee stability as in normal gait
▪ Pylon should be vertical in midstance (match adduction of residual
limb)
Stance width that is neither excessively wide nor narrow for a
balance between energy expenditure and stability
▪ Too inset or outset may cause instability or excessive trunk motion

goal of transverse plane alignment

▪Smooth heel off prior to initial contact on the contralateral side
▪ No drop-off
▪Knee flexion that begins immediately after heel off
▪Smooth transfer of weight to the sound side
▪Rotation of the foot can lead to varus/valgus moments at the knee

dynamic alignment

▪First look at ML motion of the knee during midstance
▪ If coming from IR/ER of the foot, correct this first
▪ A slight varus moment should occur at the knee during midstance
▪ Fix any thrust that is present using translation or angular change
▪ If the socket is adducted or abducted, check the foot position
(equal and opposite changes = translation). Foot should be flat

▪View the patient from the Sagittal plane:
▪ Check the foot motion from heel strike through toe-off.
Motion should be smooth without hesitation or
rotation. You can DF/PF the foot or slide the foot
linearly
▪ Check the knee motion from heel strike through toe-off
▪ Does the patient have control of their knee
▪ Knee joint should move in a forward direction with no stops or
changes in speed
▪ Monitor step lengths
▪ If uneven, possibly slide the foot anterior or posterior

biomechanics of transtibial gait

• during ambulation, GRFs are applied through the socket, onto the residual limb

• forces must be managed in order to achieve appropriate comfort and prevent skin breakdown

antero-posterior forces

▪A large knee flexion moment occurs from heel strike to
foot-flat
▪Knee stability is maintained by the contraction of the
quadriceps
▪ Resulting forces are concentrated on the anterior distal tibia
and posterior proximal soft tissue
▪In order to reduce pressure, the socket must:
▪ Provide even pressure distribution in the popliteal area
▪ Provide anterior distal relief to prevent excessive pressure over
the distal tibia

medio-lateral forces

▪During single-limb-support on the prosthetic side:
▪ Ground reaction forces are medial to the knee, causing a varus moment at the knee
▪ Forces are concentrated at the proximal medial and distal lateral residual limb
▪Proximal medial forces are usually not a problem (femoral condyle and medial
tibial flare)
▪Distal lateral forces may impinge on the cut end of the fibula. Socket
modifications should:
▪ Provide relief for distal lateral fibula
▪ Provide Lateral stabilizing pressure along the shaft of the fibula
▪ Provide pressure in the pretibial muscle group region

torque

socket rotation may cause discomfort, skin breakdown, or gait deviations

shear

occurs when the socket moves in an opposite direction of the residual limb

drop-off gait deviation

▪Noticed during terminal stance and
pre-swing
▪ Heel-off occurs too early and the
patient “Drops off” too quickly onto
the sound side
▪Prosthetic Cause
▪ Short Toe Lever
▪ Foot is excessively dorsiflexed
▪ Socket is in too much flexion
▪Patient Cause
▪ Gait habit
▪ Internal rotation of hip at toe-off

delayed heel-off gait deviation

The patient’s
knee may tend to hyperextend. The
Patient may feel like they are,
“walking uphill”.
▪Prosthetic Cause
▪ Toe Lever is too long
▪ Foot may be too plantarflexed
▪ Insufficient socket flexion
▪Patient Cause
▪ Gait habit
▪ New shoes with lower heel height

vaulting gait deviation

▪Compensatory motion, characterized by
sound side plantarflexion during single limb
support on the prosthesis
▪Prosthetic Cause
▪ Long Prosthesis
▪ Poor suspension
▪ Excessive plantarflexion of foot
▪Patient Cause
▪ Gait habit, fear of catching toe
▪ Weak hip flexors on the residual limb side
▪ Improper initiation of hip flexors on residual
limb

circumduction gait deviation

▪Swing phase deviation, where the prosthesis
follows a lateral curved line as it swings
through
▪Prosthetic Cause
▪ Long prosthesis
▪ Excessive plantar flexion
▪ Functionally long
▪ Ineffective suspension
▪Patient Cause
▪ Lack of confidence in flexing knee
▪ Abduction contracture
▪ Weak hip flexors
▪ Habit, using the entire hip and pelvis to initiate
gait

trendelenberg gait deviation

▪Characterized by lateral trunk bending at
midstance on the prosthetic side
▪Prosthetic Cause
▪ Prosthesis too short
▪ Foot too outset
▪ Socket fit issues
▪Patient Cause
▪ Weak hip musculature (Gluteus Medius)
▪ Poor gait habits

uneven step length gait deviation

▪Characterized by a short step on the sound
side
▪Prosthetic Cause
▪ Pain in socket
▪ Excessive planter flexion
▪ Insufficient socket flexion
▪ Toe lever too long
▪Patient Cause
▪ Patient lacks confidence
▪ Hip contractures

varus moment gait deviation

▪Characterized by a lateral thrust at the
knee on the prosthetic side, during
midstance
▪Prosthetic Cause
▪ Foot too far inset
▪ Insufficient socket adduction
▪ Short prosthesis
▪Patient Cause
▪ Inadequate balance
▪ Weak knee
▪ Narrow gait base

valgus moment gait deviation

▪Characterized by a medial thrust at the
knee on the prosthetic side, during
midstance
▪Prosthetic Cause
▪ Prosthetic foot too far outset
▪ Excessive socket adduction
▪Patient Cause
▪ Insecurity, wants to widen base in attempt
to increase stability
▪ Weak ML knee control

toe drag gait deviation

▪Characterized by catching the
prosthetic toe on the ground during
swing phase
▪Prosthetic Cause
▪ Long prosthesis
▪ Inadequate Suspension
▪ Excessive plantarflexion
▪ Insufficient socket flexion
▪Patient Cause
▪ Weak hip extensors on sound side
▪ Weak hip abductors on sound side
▪ Poor posture
▪ Poor gait habits

wide base of support gait deviation

▪Characterized by a wider stance width
while ambulating (greater than 4”)
▪Prosthetic Cause
▪ Prosthetic foot too far outset
▪ Excessive socket adduction
▪Patient Cause
▪ Insecurity, wants to widen base in an
attempt to increase stability
▪ Weak ML knee control
▪ Hip Abductor contracture

narrow base of support gait deviation

▪Characterized by a narrow stance
width while ambulating (less than 2”)
▪Prosthetic Cause
▪ Prosthetic foot too far inset
▪ Excessive socket abduction
▪Patient Cause
▪ Poor gait habit
▪ Hip adductor contracture

knee instability (excessive knee flexion) gait deviation

▪Characterized knee flexion of greater than
10 degrees during stance phase
▪Prosthetic Cause
▪ Prosthetic foot too dorsiflexed
▪ Heel bumper too stiff
▪ Heel lever too long
▪Patient Cause
▪ Knee flexion contracture
▪ Weak quadriceps

medial whip gait deviation

▪Characterized by medial tracking of the
heel at initial swing phase
▪Prosthetic Cause
▪ Foot too externally rotated
▪Patient Cause
▪ Improper donning of prosthesis
▪ External rotation of knee at toe-off

lateral whip gait deviation

▪Characterized by lateral tracking of
the heel at initial swing phase
▪Prosthetic Cause
▪ Foot too internally rotated
▪Patient Cause
▪ Improper donning of prosthesis
▪ Internal rotation of knee at toe-off