The Ankle and Foot 325In relaxed standing (static stability), these arches
are supported by the shapes of the bones, the plantar
fascia, and the ligaments that help hold these bones
together, without assistance from the muscles of the
feet (Basmajian and DeLuca, 1985; Smith, Weiss,
and Lehmkuhl, 1996). However, during movement
(dynamic stability), various extrinsic and intrinsic
muscles add active support and serve as a second
line of stability for the arches of the feet, called into
play as demands increase (figure 6.28B).
Presence of these arches allows the feet to with-
stand greater forces while still maintaining their
integrity, to better absorb shock, and to have greater
mobility and stability. When bearing weight, the
foot tends to spread slightly, which helps to absorb
the impact of the force; but the strong arches with
their springlike quality from associated ligaments
and fascia resist excessive spreading and provide an
elastic recoil that assists in locomotion (Hamill and
Knutzen, 1995).
Pes Planus (Flatfoot)
When the foot demonstrates a decrease or loss of
the medial longitudinal arch, it is called a flatfoot,
FIGURE 6.28 Arches of the foot. (A) Normal bony arches, (B) key ligaments and muscles that can help support the
medial longitudinal arch, (C) pes cavus, (D) pes planus.
or pes planus (L. pes, foot + planus, flat). A footprint
of this type will show much greater area of contact
than a normal foot (figure 6.29B). A flatfoot can be
further classified as a flexible flatfoot or a rigid flat-
foot or pes planus. With a rigid pes planus, there is
a decreased arch both when bearing weight and not.
This type of flatfoot is often secondary to structural or
pathological factors and is relatively rare. In contrast,
with a flexible or functional pes planus, an arch is
present when not bearing weight or when on demi-
pointe, but when the dancer stands, the medial lon-
gitudinal arch flattens; the head of the talus moves
inferomedially and causes the foot to pronate (figure
6.28D). This movement of the talus also brings the
adjacent navicular with it, a landmark readily used for
evaluation of the arches. It has been postulated that
congenital ligamentous laxity or excessive pronation
over time may cause stretching of the soft tissues,
such as the spring ligament and tibialis posterior
tendon, with resultant loss of height in the medial
longitudinal arch of the foot during weight bearing
(Hamilton and Luttgens, 2002; Smith, Weiss, and
Lehmkuhl, 1996; Soderberg, 1986). The flexible
flatfoot has been reported to occur in about 15% of