24
23
Copyright © 2008 Stryker.
Copyright © 2008 Stryker.
UNIT 5
Characterizing Deformity About the Knee
Determination of a varus/valgus deformity only tells us
that the deformity exists; details such as its location
are not revealed. Additional analyses, utilizing joint-line
orientation, allow prediction of outcomes of particular
osteotomy methods and anticipation of certain TKA
problems. Previous discussion has only considered
knee position as a center-point (i.e., centered on the
mechanical axis). Deformity can be characterized
according to 4 ‘origins’:
1. Deformity on the Femoral Side of the Joint
Due either to developmental abnormality or to attrition
of bone very close to the joint as a result of fracture,
degenerative wear, avascular necrosis, collapse, etc.
2. Deformity on the Tibial Side of the Joint
Due either to developmental abnormality,
degeneration, etc.
3. Deformity Within the Joint Itself
Due to asymmetric wear.
4. Deformity Due to Discreet
Extra-articular Angulation
Generally exemplified by new angulation after fracture
or osteotomy.
Considering these origins of deformity requires
establishing standards for normal (average) values
indicating joint line orientation, with any variation alluding
to the deformities just described. In Figure 5.1, the
normal articular cartilage space (medial vs. lateral) is
approximately equal – lines across the distal femoral
condyles and across the medial and lateral tibial
plateaus are essentially parallel.
In Figure 5.2, the overall joint line is typically slightly
different from perpendicular (2 to 3°, on average).
Figure 5.1
Joint lines added.
Figure 5.2
Representative angles for a non-deformed knee.
6°
90°
87-8°
81°
92-3°