The B QUAD Foot-Type is a mildly over-pronated foot type or Mild Pes Planus. This is the result of a Compensated Rearfoot Varus with a flexible forefoot valgus deformity. It is often to be found unilateral and is often associated with a structural leg length discrepancy.
The B QUAD Foot-Type is a rarely occurring combined foot deformity, affecting less than 10% of the population. In addition, it is often unilateral. The B QUAD Foot-Type is a mildly over-pronated foot due to a compensated rearfoot varus deformity, however that over pronation is somewhat minimized by a forefoot valgus deformity that acts like a "pronation-deterrent".
In some cases, this foot-type may be caused by an acquired plantarflexed 1st ray, functioning as a forefoot valgus. This may occur in flexible pes planus foot types as the peroneals are working overtime to try and pull the forefoot into a pronatory twist in attempt to stabilize the midtarsal joint. It is also common to see this condition occur unilaterally on a short limb. Pronating the forefoot into a valgus alignment supinates the foot and helps lengthen the limb. When this foot-type occurs on one side only, we refer to this as a "foot disparity". When foot disparities occur, each foot functions differently from one another, as so each limb functions differently as well. This has a direct affect on the hips and low back, often leading to sacral-iliac pain. Heel and lower back pain is common. The torque foot nature of this foot-type allows the valgus forefoot to offset the uncompensated inverted heel alignment that would normally lead to a toe out gait pattern (see C Quad Foot-Type). Overall, the foot progression angle for this person is such that the feet point relatively straight ahead during gait (no toe out) with a narrow base of support, much like a tight rope walker.
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B QUAD POSSIBLE CLINICAL SYMPTOMS
• 1st Ray Hypermobility
• Sacroiliac Joint Pain
• Often unilateral, may be associated with
leg length discrepancies
MOUSE OVER THE PHASE FOR DETAILS OF THE B QUAD GAIT
At initial contact, the calcaneus strikes the ground in a slightly inverted alignment relative to the floor. Since the rearfoot varus is primarily compensated, the subtalar joint immediately pronates at heel strike. In this case, unlike the compensated rearfoot varus in the Quad D foot-type, the calcaneus does not evert to a completely vertical position. This is due to the forefoot valgus alignment and the premature loading of the 1st ray at footflat, which decelerates subtalar joint pronation. It is for this reason that the midtarsal joint only partially unlocks, unlike the Quad D foot-type. One more important observation is that during gait the foot progression angle is toe-in.
As weight moves forward over the foot in midstance, the midtarsal joint remains partially unlocked. Ground reaction forces push through the forefoot valgus until the forefoot is loaded evenly on the ground. This repetitive force on the 1sr ray may lead to 1st ray hypermobility and clinical symptoms such as sesamoiditis. As the midtarsal joint remains partially unlocked, the foot is in a state of persisting mobility and the overall height of the arch is allowed to drop in a vertical direction. This drop in arch height is sometimes referred to as navicular drop; however, we alternatively refer to this motion as "midfoot sag," more clearly differentiating it from medial shelfing (i.e. medial or horizontal displacement of the arch that evident in the E and F foot types). However, unlike the Quad D foot-type, the midtarsal joint is only partially unlocked, therefore decreasing the severity of the vertical arch drop. Normally in gait co-contraction of the gastrocsoleus and the peroneals should create a pronatory twist of the forefoot to facilitate re-supination of the subtalar joint and relocking of the midtarsal joint in preparation for propulsion. This has already been facilitated by the valgus alignment of the forefoot. This foot-type is still partially unstable, but less so than the Quad D foot-type.
Propulsion Phase As the heel lifts off the ground, initiating the propulsive period of gait, you may notice the foot "bending backwards" at the level of the midtarsal joint. This can be seen by looking at the lateral side of the midfoot. This is another indicator that this foot-type is still partially unstable, but not as severely as the Quad D foot-type.
This lateral column should be straight and stable, but notice how it is bending backward and sagging. This is a sign of midfoot instability.
In this foot-type, some re-supination does occur at the subtalar joint, but not enough to avoid midtarsal joint instability. Because of this instability and abnormal pronation into propulsion, 1st ray function is still somewhat impaired, allowing the ground reaction forces to drive the 1st ray dorsally, transferring some pressure to the 2nd metatarsal head. and associated transverse metatarsal arch reversal. This leads to callus formation of the central metatarsal heads. Final propulsion is shared between the 1st and 2nd metatarsal heads.