Notas / Notes - Active Congress.......

VIERNES / FRIDAY
216
CONSTRAINT IN REVISION TOTAL
KNEE ARTHROPLASTY
Keith R. Berend, MD
Joint Implant Surgeons, Inc., The Ohio State University,
Mount Carmel Health System
New Albany, Ohio (USA)
The goals of total knee arthroplasty (TKA) are to relieve pain,
restore function, and provide the patient with a stable joint.
In regard to types of implants, the workhorses are posterior
cruciate retaining (CR), posterior stabilized (PS), and posterior
stabilized constrained (PSC) designs. However, there is a
continuum of constraint now available that ranges from cruciate
retaining to a CR lipped device, to an anterior stabilized
(AS) device, to a posterior stabilized device, to a PS “plus”
that fits with a PS femoral component but provides a small
degree of varus-valgus constraint, to a PSC or constrained
condylar type of device, to a rotating hinge.
As the degree of deformity, bone loss, contracture, ligamentous
instability and osteopenia increases, so does the demand
for prosthetic constraint. 1-3 When compromise is minimal
and the posterior cruciate ligament (PCL) is intact and without
deformity, a cruciate retaining device is appropriate. 3,4 For
moderate compromise with deficiency or compromise of the
PCL, an anterior stabilized or posterior stabilized device is
warranted. In severe cases, with attenuation or absence of
either of the collateral ligaments, a constrained condylar device,
with options of stems, wedges and augments, is advisable.
In salvage situations, when both collaterals are compromised,
a rotating hinge should be utilized.
Prerequisites for use of a posterior cruciate retaining device
in revision TKA are an intact PCL, balanced medial and lateral
collateral ligaments, and equal flexion and extension gaps.
Possible scenarios include a polyethylene liner exchange as
part of an incision and debridement for early infection or hematoma,
a polyethylene liner exchange as part of a procedure
to resurface, realign or revise the patella in a knee, and
the revision of a failed unicompartmental knee arthroplasty.
With a CR lipped bearing, a slight posterior lip is incorporated
into the sagittal profile of the component to provide a small
amount of extra stability in the articulation. It is important for
the surgeon to be aware of the design features of the implant
system he or she is using. For example, in a system where
the CR bearing has 3 degrees of posterior slope and the CR
lipped bearing has no slope, the thickness of a CR lipped
bearing posteriorly is approximately 2 mm greater than the
standard CR bearing. A CR lipped bearing would be indicated
in a revision for instability where the flexion gap is just slightly
looser than the extension gap and the PCL is intact. This
might occur at the time of an incision and debridement for
hematoma or infection, or a patellar revision. In a scenario
where the patient’s knee is somewhat lax in flexion and stable
in extension, a CR lipped bearing may help to stabilize both
the flexion and extension gaps while still allowing the knee
to obtain full extension, whereas if a CR standard bearing in
the next thicker size is used to stabilize the flexion gap, a flexion
contracture may result.
Anterior stabilized bearings are required infrequently. An
indication in revision TKA for such a device would be when
the femoral and tibial components are well fixed, the flexion
and extension gaps are balanced, but the PCL is deficient,
and the surgeon does not want to change the well-fixed CR
femoral component.
Like the anterior stabilized bearing, the posterior stabilized
bearing is indicated when the flexion and extension gaps are
balanced, the medial and lateral collateral ligaments are
balanced, and the PCL is incompetent. If the tibial component
is well fixed and aligned, but the femoral component is loose,
the surgeon can revise to a posterior stabilized component.
If there is concern about slight asymmetry of the medial and
lateral collateral ligaments, the surgeon may wish to consider
using a posterior stabilized plus type of bearing, which will
fit in the housing of a posterior stabilized femoral component
and will add just a little more stability while allowing for approximately
2 degrees of internal and external rotation.
The posterior stabilized constrained component, which
provides varus-valgus constraint, is the workhorse for revision
total knee arthroplasties. It is indicated in cases where a
complete revision of the femoral and tibial components is
required and there is attenuation of the medial or lateral
collateral ligament. A posterior stabilized bearing will not
provide varus-valgus stability. Specific indications for a PSC
device are in knees compromised by attenuation of the medial
collateral ligament secondary to valgus malalignment with
inability to obtain satisfactory varus/valgus stability in both
flexion and extension, in knees complicated by an incompetent
PCL and inability to obtain symmetry in both
flexion and extension, in knees complicated by varus/valgus
instability with or without flexion-extension gap symmetry
and in cases of recurrent dislocation of a PS TKA.
The rotating hinge is indicated in salvage situations for gross
instability, where both the medial and lateral collateral ligaments
are compromised and incompetent.
The take-home message is that stability is critical. Don’t leave
the operating room without it.
SUGGESTED READING
1. Lombardi AV Jr, Mallory TH, Eberle RW. Constrained
Knee Arthroplasty. In: W. Norman Scott (editor). The Knee,
(Vol 2), St. Louis: Mosby-Yearbook, Inc., pp. 1305-1323,
1994.