Two of the most important tests in the physical examination of the pes valgus deformity are next performed with the child again in their relaxed stance position.
The first of these tests, the maximum pronation test, is a maneuver designed to determine whether the foot is standing in the maximally pronated subtalar joint position.
While in their relaxed stance position, ask the child to try to lift up the lateral sides of their forefeet, but instructing them that they may not flex their knees to do so.
If the maximum pronation test is done correctly, the child will use their peroneus brevis muscle to attempt to pronate their subtalar joint, and if the subtalar joint is not already maximally pronated, the calcaneus will evert further.
The physician should observe for heel motion from behind the patient. Any further calcaneal eversion of less than two degrees during the test signifies that the child is standing in their maximally pronated position.
Sometimes it is helpful for the physician to actually use their own feet or their hands placed on the ground in front of the child to demonstrate exactly how to perform this maneuver.
It is important in both children and adults to determine whether or not a foot in the relaxed stance position is maximally pronated.
If the child's foot is not maximally pronated at the subtalar joint then there is much less chance of that foot having significant pathology in the future since the pronation moments acting on that subtalar joint are being partially counterbalanced by subtalar joint supination moments which are acting to prevent its maximal pronation.
If, however, the subtalar joint is maximally pronated during relaxed stance, then this indicates that the pronation moments acting on that subtalar joint are much greater than the subtalar joint supination moments.
The overwhelming pronation moment acting on the standing foot therefore causes the subtalar joint to hit its end range of pronation range of motion, and a maximally pronated subtalar joint results.
The level of severity of these excessive pronation moments acting on the subtalar joint can be estimated by the next test, the supination resistance test.
The supination resistance test is actually a clinical test which has been used for many years but has never had its true significance defined.
The supination resistance test is performed again while the patient is in their angle and base of gait in relaxed stance.
The child must be instructed during the test to not assist the doctor in any fashion by even the slightest extrinsic muscular contraction or by any lower extremity movement or the test will be invalid.
The test involves simple application of a superiorly directed lifting force from the physician's fingertips to the area of the patient's medial longitudinal arch just plantar to the medial half of the navicular bone.
Basically, the supination resistance test involves determining the amount of lifting force which the physician's fingertips must apply to cause supination motion at the subtalar joint.
If there is a great deal of pronation moment acting on the child's foot then it will take a large amount of manual lifting force under the navicular to produce any subtalar joint supination motion.
If there is relatively little pronation moment acting across the subtalar joint then it will take a very small amount of lifting force to produce supination.
Heavier children will obviously require more lifting force under the navicular to produce supination than lighter children.
However, the actual weight of the individual has less effect on the degree of lifting force needed to produce supination than the location of the subtalar joint axis.
In a normal foot during standing, the subtalar joint axis is in its normal lateral location in relation to the medial navicular bone.
Therefore, supination of the subtalar joint becomes relatively easy with lifting force under the navicular since there is a relatively long lever arm for the lifting force to produce supination moment on the subtalar joint axis and supination motion results with little lifting force.
If, however, the subtalar joint axis is medially deviated, such as in children with pes valgus deformity, then the much shorter lever arm will necessitate a much greater lifting force under the medial navicular to produce even small increases in supination moment across the subtalar joint axis.
As a result, the more severe pes valgus deformities are very hard to supinate with digital lifting pressure under the medial navicular.
As is obvious from this discussion, the feet which have the most medially deviated subtalar joint axes will also be the feet which have the greatest amounts of pronation moments acting on them and will also be the feet which are the hardest to supinate in the supination resistance test.
In addition, these feet are easily identifiable since the talar head is positioned well medial to the calcaneus and rest of the foot during standing.
When the foot is found to be maximally pronated in the maximum pronation test, the supination resistance test should next be employed to determine the severity of the pronation moments acting on the foot during standing.
If the examiner finds that the lifting force under the navicular is approaching a magnitude which equals about half the patient's body weight and that the lifting force is not producing any subtalar joint supination motion, then it can be assumed that the subtalar joint axis is directly over or medial to the physician's fingertips.
This observation indicates both an extremely medially deviated subtalar joint axis and extreme pronation moments acting on the subtalar joint during weightbearing activities.
If, however, it takes less than five pounds of digital lifting force to cause subtalar joint supination motion during the supination resistance test then this finding indicates that the foot has a less medially deviated subtalar joint axis, has a less medially located talar head and has less overall pronation moment acting on it.
Like any clinical test, the supination resistance test requires practice and observation on numerous patients in order for it to become a useful test within the physician's clinical armamentarium.
The test, however, is so useful in regards to establishing a valid comparison between the patient's own two feet and from one flatfoot to the next that, once learned, it becomes the one clinical test which most reliably unmasks many of the "unseen" pathologic internal forces acting within the feet of children with pes valgus deformity.
(Kirby KA, Green DR:
Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed), Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992.)
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