254 Dance Anatomy and Kinesiology
A slight amount of knee hyperextension is con-
sidered desirable in some dance aesthetics such as
classical ballet. However, excessive hyperextension
can be of concern from an injury perspective. One
approach to meet both biomechanical and aesthetic
conditions is to limit the amount of knee hyperex-
tension when the leg is weight bearing and reserve
use of a mildly hyperextended knee for the non-
weight-bearing gesture leg when aesthetics dictate
the “hyperextended line.”
For dancers, a knee that does not fully extend
and appears bent is also of concern from an
aesthetic perspective. This condition is termed
genu antecurvatum (L. genu, knee + ante-curvus, for-
ward curve) or “hyperflexed knees” (figure 5.11B).
Careful evaluation by a dance medicine physician
is essential to determine how much of this limita-
tion is structural versus soft tissue or neuromuscular
in nature, as well as whether it is azppropriate to
carefully stretch the knee to facilitate full extension.
In many cases, desired changes can be achieved
with a very careful but consistent stretching pro-
gram, combined with dance technique modifica-
tion.Tibial Torsion
When one views the knee from the front, malalign-
ment of the knee can also be seen predominantly in
the transverse plane, as evidenced by inward or out-
ward facing of the knee relative to the hip joint, ankle
joint, or both. This transverse rotation can be due to
malalignment of related joints (e.g., femoral torsion)
or rotation along the length of the bones themselves.
If the distal end of the tibia faces medially or exces-
sively laterally when the distal end of the femur faces
directly forward, the malalignment is termed tibial
torsion. One can picture outward or external tibial
torsion by imagining that the upper tibia and tibial
tuberosity stay facing front while the lower tibia is
rotated externally so that it is facing slightly toward
the side as seen in figure 5.34B (p. 290). In this situa-
tion, the foot will be pointing outward relative to the
knee. Some dancers exhibit marked external tibial
torsion, and this bony alignment offers an advantage
for achieving a more turned-out position with the
feet without creating undesired torsion at the knee.
Conversely, with inward or internal tibial torsion,
the feet point straight ahead or toward each other
when the patellae face forward. When standing,
most people exhibit a slight external tibial torsion,
which increases from approximately 5° at birth to an
average of about 15° at skeletal maturity (Luke and
Micheli, 2000). Tibial torsion has important impli-cations for ankle and foot mechanics, as well as the
knee, and will be readdressed in chapter 6.Knee Mechanics.
The mechanics of the knee joint are more complex
than is the case for other true hinge joints, primarily
due to two factors. First, flexion and extension at the
tibiofemoral joint do not involve simple movement
around one axis but rather incorporate rolling and
gliding with a shifting axis at different degrees of
flexion. Second, small amounts of transverse rotation
also accompany flexion and extension.Knee Flexion and Extension
The knee joint motions of flexion and extension
occur primarily in the sagittal plane between the
condyles of the femur and tibia. The movements of
the femoral condyles relative to a fixed tibia (closed
kinematic chain) can be compared to that of a bicycle
wheel, with the femoral condyles rolling backward
and forward upon the tibial condyles like a bicycle
wheel on the road as seen in figure 5.12A. In addi-
tion, the femoral condyles glide or slide over the
tibial condyles similarly to a bicycle wheel when it
skids. This latter sliding motion is necessary to keep
the femur positioned over the tibial condyles. For
example, when the femoral condyles roll backward
during flexion (such as during the descent of a first-
position parallel plié), the femur would roll off the
back of the tibia (figure 5.12A) without an anterior
sliding motion that occurs after about 25° of flexion
(figure 5.12B) to offset the backward motion associ-
ated with rolling (Levangie and Norkin, 2001). The
opposite occurs in extension (such as in rising from
the plié), with the femoral condyles first rolling for-
ward and then sliding backward to offset the forward
motion associated with rolling (figure 5.12C). So,
this simultaneous use of rolling and sliding allows for
the desired surfaces of the femur to stay in contact
during flexion and extension and prevents excessive
relative movement of the associated bones that could
jeopardize joint integrity.Knee Rotation
Although the primary motions at the knee joint are
flexion and extension, the fact that the two condyles
at the distal end of the femur are different in size and
shape and are not quite parallel necessitates slight
transverse rotation. The degree of rotation permitted
varies with the degree of knee flexion and is strongly