Copyright © 2008 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Thomas J. Gill, MD*,
Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
Posted August 2008
Historically, the clinical outcomes of surgical
reconstructions for injuries to the posterior cruciate ligament have not been
as good as those achieved after reconstruction of the anterior cruciate
ligament. This is particularly true on objective physical examination during
longer-term follow-up, in which posterior drawer testing often reveals residual
posterior laxity, if not frank instability.
A variety of explanations have been offered for this
finding. From a surgical perspective, transtibial tunnel reconstructions have
been criticized as being subjected to the "killer angle," in which the posterior
cruciate ligament graft makes an acute turn around the posterior aspect of the
tibia and is subject to undue strain. With time, it has been suggested that
this leads to fraying and/or stretching of the graft.
DeFrate et al.1 offered another explanation for
the inability to reconstruct the native posterior stability of the knee joint with
use of transtibial tunnel reconstruction. In their study, the site of fixation
of the posterior cruciate ligament graft was investigated, particularly with
respect to the length of the graft between the fixation sites. Three different
lengths were chosen to approximate the length of the graft used for cortical
fixation with transtibial tunnel techniques, tibial inlay techniques, and
"aperture fixation." The investigators found that shorter graft lengths
resulted in stiffer grafts and less residual posterior laxity on posterior
drawer testing.
One of the most frequently cited reasons for residual laxity
and/or instability following isolated reconstruction of the posterior cruciate
ligament is failure to recognize associated posterolateral corner injuries. The
posterolateral corner is commonly used to describe the lateral collateral
ligament, the popliteus tendon, the popliteofibular ligament, and the arcuate ligaments
located at the posterolateral aspect of the joint capsule. Failure to address
concomitant posterolateral instability has been indicated as a cause of failure
of anterior as well as posterior cruciate ligament reconstructions.
The paper by Sekiya et al. attempts to offer a clinical
means of recognizing posterolateral corner injuries when they occur in
conjunction with posterior cruciate ligament tears. In their study, they
evaluated ten pairs of cadaver knees with posterior drawer testing, dial
testing, and stress radiography. The knees were tested while intact and then
retested after the sequential cutting of the posterior cruciate ligament,
followed by resection of the posterolateral corner structures. They concluded
that a grade of 3 on posterior drawer testing and >10 mm of posterior tibial
translation on stress radiography correlate with disruption of the
posterolateral corner in addition to complete disruption of the posterior
cruciate ligament.
While I would agree with the basic premise and conclusions
of this study, there are several important issues that must be kept in mind.
First and foremost, this study was performed on cadaver knees, with no
physiologic muscle loads applied during the testing. Gill et al.2 have previously shown that the kinematics of cadaveric posterior cruciate
ligament reconstructions with and without the application of muscle loads are
very different, with increased external rotation and posterior laxity once the
muscle loads themselves have been added. Sekiya et al. mention this limitation,
but they state that since patients often have pain and guarding during the clinical
examination, surgeons usually rely on intraoperative examinations, done with
use of dial testing and posterior drawer testing and with the patient under
anesthesia, to determine whether or not there is a posterolateral corner
injury. Furthermore, they state that surgical decisions are made on this basis.
I disagree with this premise. Posterior cruciate ligament
reconstructions, and particularly posterolateral corner reconstructions, are
technically demanding procedures. The surgical plan should almost always be
decided preoperatively. In my experience, posterior drawer testing is far less likely
to elicit muscle-guarding than anterior drawer testing is, and both the drawer
test and dial test are not typically painful for the patient. Moreover, since posterior
cruciate ligament and posterolateral corner reconstructions are very rarely
done on an acute basis, the examination that is done in the office on a
subacute basis, on a knee which usually has very little swelling, is seldom
painful for the patient. Thus, muscle guarding is much less of a problem during
posterior drawer testing than it is during anterior cruciate ligament
examination, which is often associated with knee joint effusions and pain. I perform
an examination under anesthesia only to confirm my surgical plans, not to make
them.
Another important fact to keep in mind is that patients do
not always present with complete injuries to the posterolateral corner. In
fact, it has been my experience that posterolateral corner "sprains" are far
more common than complete disruption of the lateral collateral ligament,
popliteus tendon, and posterolateral capsule. This is where "semantics" and
definitions of knee injuries become so critical. It is often stated that
"isolated" tears of the posterior cruciate ligament are very rare, and
therefore isolated reconstructions of the posterior cruciate ligament should
be rare as well. I think that these types of statements can lead to substantial
confusion in the treatment of posterior cruciate ligament tears. In my opinion,
we should be discussing whether there is "isolated instability" of the
posterior cruciate ligament or associated "instability" of the posterolateral
corner.
I often see patients with a complete tear of the posterior
cruciate ligament as well as a sprain injury to the posterolateral corner as
defined by magnetic resonance imaging standards. However, on dial testing,
there is no increased external rotation. Although I typically start by treating
many of these injuries nonoperatively, it is not uncommon to have to do a
subsequent "isolated" posterior cruciate ligament reconstruction due to
persistent knee pain or instability. While the study by Sekiya et al. may serve
as a useful guide for complete tears of the lateral collateral ligament and
popliteus, it is not generally difficult on physical examination and magnetic
resonance imaging to identify varus instability due to a torn lateral
collateral ligament or to identify truly pathologic posterolateral corner
disruption with a dial test that shows an increase in external rotation of more
than 20°. Although the following statement is a bit oversimplified, I would
suggest that the single biggest factor in determining whether an associated
procedure "needs" to be done to the posterolateral corner is simply whether the
lateral collateral ligament is competent in the setting of a complete tear to
the posterior cruciate ligament.
Sekiya et al. bring much needed continued attention to the
need to identify and treat complete disruption of the posterolateral corner
when reconstructing a torn posterior cruciate ligament. However, it must be
kept in mind that the term posterolateral
corner injury is very complex, and includes both subtle sprains and
complete tears. The statement made in this study—that a finding of >10 mm on
posterior drawer testing should alert the examiner to a complete disruption of
the posterolateral corner—is a good place to start. However, the conclusion
must be validated with the application of in vitro muscle loads or, more
importantly, by studying such patients in vivo under the application of true
physiologic muscle loads. Posterolateral corner injuries can encompass a broad
spectrum from simple sprain injury to complete disruption.
Despite all of these guidelines, the surgeon must ultimately
use his or her clinical judgment to assess the degree of associated injuries,
the amount of increased external rotation as seen on physical examination, and the
age, occupation, and activity level of the patient prior to going to the
operating room, at which point a careful examination with the patient under
anesthesia should be done to confirm the carefully made preoperative plan, not to make it.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.
References
1. DeFrate LE, van der Ven A, Gill TJ, Li G. The effect of length on the structural properties of an Achilles tendon graft as used in posterior cruciate ligament reconstruction. Am J Sports Med. 2004;32:993-7.
2. Gill TJ, DeFrate LE, Wang C, Carey CT, Zayontz S, Zarins B, Li G. The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads. Am J Sports Med. 2003;31:530-6.
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