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JUEVES / THURSDAY
236
consequently accentuated wear 5 . Overrelease
of the collateral structures may result in symptomatic
instability 6 . Mild to moderate increased
varus-valgus laxity in extension has been reported
to be of no clinical importance 7 . However,
major instability may be an important cause for
total knee arthroplasty failure 8 and accounted
for 21% of 212 revision total knee arthroplasties
in the series by Sharkey et al .9 . Fehring et al. 10
reported on 27% instability cases in their total
knee revision population of 440 patients who
had to be revised after a follow-up of less than
5 years after primary TKA.
Increased varus or valgus laxity in fl exion
due to femoral component malrotation has
extensively been examined in cadaveric studies
under loaded 11 and unloaded conditions 12 .
Although femoral component malrotation is
considered the major cause for fl exion gap
imbalance 12,13 little is known on the clinical
consequences. Laskin 14 reported on patients
with medial tibial pain if the femoral
component was not externally rotated to
allow rectangularization of the fl exion gap.
Varus and valgus laxity in fl exion might be
diffi cult to quantify by clinical examination.
In a cadaver study, Grood et al. 15 compared
manually assessed medial and lateral
joint opening with varus and valgus laxity
determined by means of an Instron testing
system. They proved that erroneous laxity
assessment in fl exion is likely to occur by
clinical examination even when the primary
restraint is missing and the testing system
demonstrates a large joint opening. The application
of fl uoroscopic stress radiography on
a patient lying relaxed on a designated radiolucent
bench is a feasible, inexpensive, fast,
safe, and reproducible method for detecting
increased varus-valgus laxity of the knee in
fl exion on a routine base 16 . The moment applied
to the tibia has to be pain free avoiding
quadriceps and hamstrings cocontraction,
which increases tibiofemoral joint reaction
force and decreases joint opening 17 .
A recent study using a three-dimensional
interactive model-fi tting technique for twodimensional
fluoroscopic dynamic images
confi rms that increased femorotibial separation
(“condylar lift-off”) under weight-bearing
conditions in fl exion was more pronounced
on the lateral side, and was associated with
femoral component malrotation 18 . A study
by Stiehl et al. confi rms that condylar lift-off
occurs in clinically successful total knee
replacements 19 , but it is not known to what
extend this condition may be clinically tolerated.
An exaggerated condylar-lift off due to
increased lateral fl exion laxity because of a
malrotated femoral component may disturb
knee kinematics and ultimately accentuate
edge loading, which has been implicated as
a cause of premature polyethylene failure 20 .
A study using the WOMAC score as clinical
outcome measurement revealed that there are
specifi c symptoms associated with increased
fl exion gap imbalance due to internal femoral
component malrotation 21 . The predominant
patient complaints were pain on stair climbing,
reduced function on descending stairs and
raising from a chair, and diffi culties getting in
and out of a car or getting in and out of bath.
Attfi eld et al. 22 reported also on knees which
were not balanced in fl exion but fully balanced
in extension. Proprioception was reduced in
such knees compared to knees which were
properly balanced in fl exion and extension.
An important goal during surgey must be a
well balanced knee not only in extension but
also in fl exion. Proper femoral component
rotation reduces fl exion gap imbalance.
Bibliography
1. Freeman MAR: Anonymous Arthritis of the knee:
Clinical features and surgical management.
Springer-Verlag, New York, 1980
2. Insall JN: Choices and compromises in total knee
arthroplasty. Clin Orthop 226:43, 1988
3. Insall JN: Surgical techniques and instrumentation
in total knee arthroplasty. In Insall JN, Windsor
RE, Kelly MA, Scott WN, Aglietti P (eds): Surgery
of the knee. Churchill Livingstone, New York,
Edinburgh, London, Madrid, Melbourne, Tokyo,