III. Indications of the Associated Joint Kinetics
One of the more common problems experienced in ambulatory patients with myelomeningocele at the L4 or L5 functional level is a knee valgus thrust during the initial weight-bearing phase of the gait cycle. It is believed that this motion must compromise the medial soft tissue structures of the knee over time. The most common treatment for this problem is the knee-ankle-foot orthosis (KAFO) which is meant to protect the medial knee.
The body's response to the valgus thrust at the knee is a net knee adductor moment (Figure 13). Joint kinetic data, specifically the net knee coronal plane moment in stance, would substantiate the presence of a knee valgus thrust; that is, the net internal knee moment would be an adductor moment.
Illustration of the net internal knee joint moment in the coronal plane for a person with a knee valgus thrust. The lateral trunk lean positions the body center of gravity lateral to the knee joint center so that there is a valgus thrust on the knee. The body's response to this thrust is a net knee adductor moment.
In Video 8, a child with L4 myelomeningocele is ambulating independently. In early stance (front view), during loading response (weight acceptance) for each step, there is a visual valgus thrust of the knee. At this point in the gait cycle, one can also observe greater than normal knee flexion (in the side view) and an excessive lateral trunk lean (in the front view). Left knee moment data for the coronal plane (Figure 14), however, show a net knee abductor moment in stance within the normal range. This indicates that there is no actual valgus thrust at the left knee in stance.
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Video 8. Side and front views of an 8-year-old-boy with L4 myelomeningocele. Front view demonstrates a visual valgus thrust during loading response, bilaterally. There is also a large lateral trunk lean, greater than normal pelvic rotation, knee flexion and ankle dorsiflexion, bilaterally.
The coronal plane knee moment for the left side (red) of a patient with myelomeningocele (Video 8). The magnitude of the stance phase knee moment is less than the normal abductor moment (Point A). Blue band on plot indicates first standard deviation of the mean normal reference in Newton-meters/kg.
This inconsistency between "visual" and gait data can be explained by the three-dimensional joint kinematic data, which reveal a complicated sequence of movements, all occurring simultaneously (Figure 15). During loading response, the pelvis and hip are internally rotated and continue to rotate more internally. The knee is flexed and continues to flex, the ankle is dorsiflexed and continues to dorsiflex, and the foot progression remains constant. There is also a substantial lateral trunk lean. The combination of these movements result in a rapid medial motion of the knee center with a fixed foot and give the appearance of a knee valgus thrust.
Coronal (first column), sagittal (second column) and transverse (third column) plane motion (degrees) for upper body, pelvis, hip, knee and ankle motion for right (red) and left (green) sides of a patient with myelomeningocele (Video 8). The plots document greater than normal internal rotation of the pelvis (Point A), rapid internal rotation of the hips (Point B), knee flexion (Point C), asymmetrical normal foot progression (Point D), which is more external on the right side during weight-acceptance phase of the gait cycle. This combination of movement during weight-acceptance contributes to the "visual" valgus thrust observed at the knees. Blue band on each plot indicates first standard deviation of the mean normal reference in degrees.
These data do not suggest that this patient will always have normal knee moments in the coronal plane. However, they do suggest that, at this time, a KAFO prescribed to protect the medial knee is not warranted.
Cite this: Clinical Gait Analysis and Its Role in Treatment Decision-Making - Medscape - Sep 01, 1999.