KINETICS AND KINEMATICS DURING GAIT 1,2 KNEE OA BIOMECHANICS • During walking the ground reaction force passes medial to the knee, which produces an adduction moment determining the load in the knee. • When varus knee alignment comes on top of this inherent loading pattern, the peak adduction moment increases, resulting in increased medial compartment loads. • Increased medial compartment load can cause cartilage damage and knee pain.
ADDUCTION MOMENT
M MF MD = X
F
F
GROUND REACTION FORCE DISTANCE
F D
Ground reaction forces during gait in the normal knee (left) and varus aligned knee (right). In a knee with an increased varus alignment, the Knee Adduction Moment is bigger as the distance between the center of the knee joint and Ground Reaction Force has increased. (figure with courtesy of Jim Richards 1 )
D
M
D
M
NORMAL ALIGNMENT
VARUS ALIGNMENT
Shifting the ground reaction force to the center of the knee reduces medial compartment loading. A: Varus alignment with GRF excessively loading the medial compartment B: Reduced varus alignment shifts the GRF to the center of the knee and reduces the load on the medial compartment
A
B
1. The Comprehensive Textbook of Clinical Biomechanics, 2nd Edition. Elsevier 2018. ISBN 9780702054891. 2. Andriacchi TP. Dynamics of knee malalignment. Orthop Clin North Am. 1994 Jul;25(3):395-403.
DONJOY OFFLOADING BRACES BIOMECHANICS EXPLAINED The DonJoy 3-POINT FORCE SYSTEM offloads the affected compartment: A correcting moment around the knee joint can be obtained by dial-in of a telescopic hinge or a BOA ® . The correcting forces of this leverage system act proximal, distal and opposite to the affected compartment to produce comfortable offloading. The resultant moment at the affected side widens (or offloads) the affected joint space. The offload can be fine-tuned to a comfortable setting by increasing or decreasing the dial-in of the hinge or the BOA ® . Cushioned condyle pads and cuffs avoid pressure points from the leverage arms.
SEMI-RIGID BRACE with BOA ® dial, example: DONJOY OA GO ® for medial knee OA 1. BOA ® mechanisms are tightened creating tension within the BOA ® cables (dotted lines) above and below the knee. 2. BOA ® tension in the cables (orange arrows) changes the angulation of the lateral plates. 3.As a result of this, corrective forces are produced on the medial plates. 4. Consequently, a push effect is created on the condyle pad on the lateral side of the knee through tension. 5.This produces a corrective moment which offloads the affected compartment.
DUAL UPRIGHT BRACE with telescopic hinge, example: OA NANO ™ for medial knee OA. 1. Dial-in of the telescopic hinge . 2. This produces a translation of the condyle pad towards the lateral side of the knee, thereby producing a push force on the unaffected compartment of the knee. 3.This force creates a reaction force on the rigid cuffs proximal and distal to the affected compartment. 4.The resultant correcting moment offloads the affected compartment.
SINGLE UPRIGHT BRACE , example: ROAM ™ OA for medial knee OA 1. Dial in the BOA ® dials. 2. This creates a tension in the oblique straps (green arrows). 3.This produces a pull force on the harness opposite to the affected compartment of the knee 4. This creates a leverage system through the rigid thigh and calf cuffs. 5.This leverage system offloads the affected compartment.
Individual results may vary. Neither Enovis, DJO, LLC or any of their subsidiaries dispense medical advice. The contents of this document do not constitute medical, legal, or any other type of professional advice. Rather, please consult your healthcare professional for information on the courses of treatment, if any, which may be appropriate for you. BOA® is a registered trademark of BOA® Technology Inc.
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