Balancing the Varus Knee
Paul R. Kim, M.D.,
F.R.C.S.(C) Active Staff, Ottawa Hospital General
Campus Clinical Lecturer, University of Ottawa Ottawa, Ontario Introduction The
varus knee is the most common deformity presenting for total knee arthroplasty. The goal of TKA in this patient group is
to obtain a well-balanced and well functioning knee. To achieve this, release of contracted
tissues and removal of peripheral osteophytes is necessary in order to obtain
correction of the deformity. Technique Through
an initial medial parapatellar exposure the patella is everted laterally and
the knee flexed. If difficulty is
encountered here, other maneuvers such as lateral release, rectus snip,
quadriceps turndown or tibial tubercle osteotomy may be employed for
exposure. In knees with a mild varus
deformity (up to 10 degrees of varus) the dissection is carried
subperiosteally over the proximal one centimeter of the medial tibia. This can be increased distally depending
upon the amount of varus deformity present.
Dissection must continue posteriorly to at least the midportion of the
medial tibial plateau in order to obtain adequate exposure when flexing the
knee. All peripheral osteophytes are
removed from the distal femur and proximal tibia, especially those in the
posteromedial aspect of the tibial plateau.
For most patients this provides adequate enough exposure/release to
obtain a well-balanced knee. If
further medial release is needed the capsular sleeve is dissected
subperiosteally to the level of the posteromedial corner of the joint. Varus/valgus balance is assessed
intraoperatively with the use of spacer blocks and/or with the trial
components in place. If necessary,
further release of the superficial MCL is carried out distally along the
proximal medial tibia to obtain sufficient soft tissue balancing. Care must be taken not to overstrip
leading to excess medial laxity. The
superficial MCL attaches over a 4 to 5 centimeter distance distal to the
joint line. Dissection of this structure
can be safely completed distally to this point. In
those knees with more severe deformity (10 to 20 degrees of varus) further
measures are necessary to obtain adequate balancing4 with
significant long-standing varus deformity the medial structures become
fibrosed. As well, the PCL and
posteromedial capsule also act as deforming structures. In these patients, release is afforded by
stripping the pes anserinus, joint capsule and tibial collateral ligament
from the proximal medial tibia. In
addition, release of the tight posteromedial portion of the joint capsule and
PCL is usually necessary to complete correction of the deformity. Release of the PCL necessitates use of a
posterior stabilized prosthesis.
Because the medial soft tissues are stripped from the bone as a
sleeve, they remain as an intact soft tissue structure providing medial
support and do not require fixation back to bone. In
knees with severe medial bone loss and a significant varus deformity (>20 degrees),
augments may be necessary to restore the tibial plateau to anatomic
alignment.5 Release of the
medial side proceeds in a fashion similar to that described above for the
moderate varus knee. Usually complete
release of soft tissue from the medial tibial face is necessary in these
situations.3 In many
severe fixed varus deformities there will be associated lateral subluxation
of the tibia. This is due in part to
contracture of the popliteus and is corrected by release of the popliteus
tendon. This may also help to improve
knee flexion. The
medial epicondylar osteotomy is another option for balancing the varus knee
in both primary and revision situations.2 This was described by Dr. G.A. Engh and
involves osteotomizing and subsequently reattaching the medial epicondyle
after final component implantation.
According to the author it allows excellent exposure and is a means of
correcting varus deformity without damaging ligamentous structures. It also avoids disruption of the extensor
mechanism for exposure in knees with limited flexion. The osteotomized fragment is reattached
with sutures to the distal medial femoral condyle in a position that allows
for optimal balance of the knee. In
revision knee arthroplasty the medial structures are usually scarred from
previous surgery and are best dealt with as a sleeve of tissue as described
above for the moderate to severe varus knee.
For the revision procedure ligamentous balancing is just as important
as in the primary procedure. Measures that may not have been performed in the
primary procedure need to be addressed.
Removal of peripheral osteophytes from the femoral and tibial sides
again need to be completed in addition to a medial release. I suggest to always use a posterior
stabilized prosthesis for revisions in order to avoid problems with joint
line elevation and instability.
Having a constrained insert available as an alternative is also a must
for revision knee arthroplasty. An
incompetent MCL either from an old injury or intraoperative damage is a
difficult problem for any surgeon.
Primary repair or imbrication with supplemental postoperative bracing
can be used to correct the problem.
Another option involves the use of a highly constrained or hinged knee
arthroplasty if repair is unsuccessful or if the patient is elderly. Conclusion Balancing
the varus knee is accomplished through a step-wise fashion as outlined
above. In those patients with severe
deformity it is necessary to perform a significant medial release in order to
balance the knee. It has also been
shown that “too loose” is probably better than “too tight” in terms of
collateral ligament laxity.1
Attention to these details intraoperativley should lead to improved
results for patients undergoing total knee arthroplasty. References: 1. Edwards, E. The effect of postoperative
collateral ligament laxity in total knee arthroplasty. Clin. Orthop.
236,p.44, 1988. 2. Engh, G. A. Medial epicondylar osteotomy: a
technique used with primary and revision total knee arthroplasty to improve
surgical exposure and correct varus deformity. Instr. Course. Lect. 48:153-6.
Review.153, 1999. 3. Karachalios, T. Severe varus and valgus
deformities treated by total knee arthroplasty. J. Bone Joint Surg. Br.
76:938, 1994. 4. Laskin, R. S. Medial capsular recession for
severe varus deformities. J. Arthroplasty. 2:313, 1987. 5. Teeny, S. M. Primary total knee arthroplasty in
patients with severe varus deformity. A comparative study. Clin. Orthop.
273,p.19, 1991.  Previous Lecture
|
