Copyright © 2007 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Frank R. Noyes, MD*,
Cincinnati Sports Medicine and Orthopaedic Center and the University of Cincinnati
Posted November 2007
Markolf et al. conducted a cadaveric investigation to
determine the effect of three different posterolateral graft reconstructions on
posterior cruciate ligament forces, posterior cruciate ligament graft forces,
and the restoration of normal external tibial rotation limits. The posterior
cruciate ligament reconstructions were done with a single bundle bone-patellar
tendon-bone graft with use of a tibial inlay technique. The grafts were
tensioned to 200 N to restore posterior tibial translation limits to within 1
mm of that seen in the intact knee at 90° of flexion. Posterior cruciate
ligament graft forces were measured under external rotation torques to
determine the ability of concurrent posterolateral reconstructions to "off-load"
or protect posterior cruciate ligament grafts from potentially deleterious
loading conditions.
I will highlight what I consider to be the most important
findings of the study:
In essence, there were four conditions studied: posterior
cruciate ligament intact; posterior cruciate ligament graft reconstruction;
posterolateral reconstruction (lateral collateral ligament alone, lateral
collateral ligament plus popliteus, or lateral collateral ligament plus
popliteofibular ligament) and level of posterolateral graft tension (10 or 30
N); and position of tibial rotation during posterolateral graft tensioning
(neutral or "unlocked," allowing internal tibial rotation at 30° of flexion).
The data provided posterior cruciate ligament intact forces,
posterior cruciate ligament graft forces, and tibial rotations under an
external tibial rotation torque (200 N) for the different posterolateral
reconstructions and under the tensions described above. There were two instances
in which data that would have been helpful were not provided. The first was the
posterior translation limits (under posterior loading conditions), which would
have determined if the posterior cruciate ligament grafts restored normal
translation limits from 0° to 120° of flexion. The second was the millimeters
of lateral joint opening (under an adduction moment) to determine if the
posterolateral grafts restored normal adduction motion limits from 0° to 120°
of flexion. It is assumed that both of these motion limits were restored by the
posterior cruciate ligament and posterolateral graft reconstructions, which is
important in the interpretation of the results.
The data showed that the sectioning of the popliteus tendon,
popliteofibular ligament, and lateral collateral ligament produced the typical
increase in external tibial rotation, which was greatest at 30° to 40° of
flexion. A decrease in external rotation limits occurred at higher knee flexion
positions due to the additional rotational restraint of the posterior cruciate
ligament.
The mean forces in the posterior cruciate ligament graft
increased with sectioning of the popliteus tendon (popliteus tendon removed
from femur, which also removed popliteofibular ligament function) and nearly
doubled when the lateral collateral ligament was sectioned (see Fig. 3 of
Markolf et al.). This finding adds support to prior studies that emphasized
the importance of the diagnosis and repair or reconstruction of associated
posterolateral insufficiency with posterior cruciate ligament reconstruction.
Even more important are the results of this study with
regard to the effect of the three posterolateral ligament reconstructions on posterior
cruciate ligament graft forces.
The lateral collateral ligament reconstruction alone
restored external tibial rotation limits to nearly normal conditions at both 10
N and 30 N of graft tension (see Fig. 4 of Markolf et al.). However, the posterior
cruciate ligament graft forces were abnormal, in fact, nearly doubled (see Fig.
6 of Markolf et al.). The data imply the necessity to restore function of both
the lateral collateral ligament and popliteus complex to unload posterior
cruciate ligament grafts.
The finding that the lateral collateral ligament reconstruction alone did not unload the posterior cruciate ligament graft has
importance in the interpretation of a number of prior biomechanical studies
that reported opposite findings—namely, that reconstruction of only one of the
posterolateral structures was sufficient to restore external tibial rotation
limits or unload the posterior cruciate ligament graft. The authors conducted a
thorough review of these prior studies and reflected that, often, the graft
tension limits and conditions of tibial rotation were not provided. It is my
experience in cadaveric studies that it is possible to tension or overtension
only one of the posterolateral structures, thereby restoring tibial rotation
limits. This type of study design may provide a false sense of security to the
surgeon that this is all that is required in posterolateral reconstructions.
From a clinical standpoint, one of the most frequent
suspected causes of failure of posterolateral reconstructions is restoration of
only one of the ligament structures1. An example would be a
reconstruction of only the popliteus tendon or popliteofibular ligament,
leaving an insufficient lateral collateral ligament (identified with a positive
lateral tibiofemoral arthroscopic gap test). An alternative example is
reconstruction of only the lateral collateral ligament, leaving an insufficient
popliteus unaddressed. Given the large external tibial rotation and adduction
torques on the posterolateral structures under in vivo loading conditions, it
is necessary to surgically restore all deficient or injured posterolateral
structures.
In this regard, many posterolateral operative procedures
have been described that are termed "femoral-fibular reconstructions" in which
a nonanatomical graft is placed to restore the lateral collateral ligament and
perhaps a portion of the popliteofibular ligament. It remains unknown from
clinical data if a femoral-fibular graft reconstruction alone is sufficient or
whether an additional popliteus graft reconstruction is necessary, which would
require more operative time and would add complexity to the procedure. Our data
show, for chronic posterolateral insufficiency involving the entire ligamentous
complex, that a femoral-fibular reconstruction has a high long-term failure
rate. This led to our decision many years ago to effect anatomic reconstruction
of all structures2, which has also been advocated by other authors3-7.
The reader should note that, with acute posterolateral
injuries, it is often possible to reconstruct the lateral collateral ligament
with a graft and repair other torn structures, including the popliteal
muscle-tendon-ligament complex, capsule, and menisci. The lateral collateral
ligament reconstruction provides the necessary protection during the initial
postoperative period of rehabilitation and knee mobilization. I also believe
that, in certain nontraumatic "interstitial" injuries to the posterolateral
structures that are due to chronic stretching over time (as with a varus
malalignment), the complex anatomical reconstructions can be avoided by
performing a proximal advancement procedure during or after correction of the
osseous malalignment8.
One fault of this study is that the popliteus tendon and the
popliteofibular ligament reconstruction produced a highly overconstrained
condition with loss of external tibial rotation (see Fig. 4 of Markolf et al.),
so that the effect of either graft reconstruction could not be determined under
normal external tibial rotation positions. This overconstrained graft condition
appeared to result in an artificial condition in which the grafts resisted any
external tibial rotation, thereby prematurely unloading the posterior cruciate
ligament graft. The knees did not reach a position of sufficient external tibial rotation
(see Fig. 4 of Markolf et al.) to study the expected interactions on the posterior
cruciate ligament graft. I would suggest that it is necessary to tension the
posterolateral grafts to restore the normal external tibial rotation limits
under the same loading conditions as the precut state, which was in fact done
with the posterior cruciate ligament grafts that were tensioned to resist
posterior tibial translation to the normal posterior motion limit at 90° of flexion.
There are a few minor anatomical points worth mentioning.
The description of the popliteofibular ligament proximal attachment as "a diffuse
connection to the posterolateral complex" is more appropriately described as a
proximal attachment to the popliteus tendon at the proximal musculotendinous
junction, which should be identified at the time of surgical exploration. The
distal popliteus graft reconstruction shown in Figure 1 of Markolf et al.
should be in a more lateral position just adjacent to the posterior aspect of
the tibiofibular joint and not in the midline adjacent to the posterior
cruciate ligament graft, which is too close to the neurovascular structures.
The proximal femoral attachment of the popliteus graft and the popliteofibular
ligament graft (the same graft location was used for both) was located "2.7 mm
proximal and 11 mm anterior to the center of the popliteus footprint." This is
a different location than that recommended in other studies and results in a
nonanatomical graft placement, which I believe is responsible for the abnormal
constraint of external tibial rotation shown in the data. Therefore, the data
from this investigation needs to be interpreted according to the graft location
in this position. The isometric points for grafts used in this study were based
only on flexion-extension data without taking into account coupled tibial
rotations. Anatomical reconstructions involve placement of the popliteus graft
at the native femoral attachment site.
In summary, this study confirms that the loss of the lateral
collateral ligament alone or along with the popliteus tendon (plus popliteofibular
ligament) resulted in increased forces on the posterior cruciate ligament
grafts. The necessity to determine the functional competence of all of the
posterolateral structures at the time of posterior cruciate ligament
reconstruction was proven. This study suggests that a graft reconstruction of
the lateral collateral ligament alone is insufficient to decrease or unload posterior
cruciate ligament graft forces. This provides added support to the concept of
restoring all of the functional components of the posterolateral ligament
structures at the time of surgery. Because the popliteus tendon and popliteofibular
ligament graft reconstructions overconstrained tibial rotation, their function
of unloading the posterior cruciate ligament graft at the normal limits of
tibial external tibial rotation could not be determined. The data show that
tensioning of posterolateral grafts at neutral tibial rotation markedly
overconstrains external tibial rotation in cadaveric knees. Insomuch as this
applies to surgical reconstruction, the recommendation is to tension
posterolateral grafts to restore normal tibial rotation limits and not
overtension the grafts, which would risk failure as the knee resumes its normal
rotation limits postoperatively. Overconstrained grafts (due either to the
tension applied or the angle of knee flexion or rotation) in any ligament
reconstruction do not restore normal joint kinematics and may be deleterious
due to increased contact loads on the joint.
This study is from a group of scientists who have
contributed greatly to our understanding of the function and surgical
reconstruction of the ligaments of the knee. All of their investigations
deserve careful reading and reflection on the data and ideas. It has been a
great professional enjoyment of mine to read and ponder the many new and novel
concepts the senior author has provided in his published works. Readers are
encouraged to read the companion paper to this investigation ("Femoral Fixation
Sites for Optimum Isometry of Posterolateral Reconstruction," by Sigward et al.
[JBJS, November 2007]).
*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. Noyes FR, Barber-Westin SD, Albright JC. An analysis of the causes of failure in 57 consecutive posterolateral operative procedures. Am J Sports Med. 2006;34:1419-30.
2. Noyes FR, Barber-Westin SD. Posterolateral knee reconstruction with an anatomical bone-patellar tendon-bone reconstruction of the fibular collateral ligament. Am J Sports Med. 2007;35:259-73.
3. LaPrade RF. Anatomic reconstruction of the posterolateral aspect of the knee. J Knee Surg. 2005;18:167-71.
4. LaPrade RF, Johansen S, Wentorf, FA, Engebretsen L, Esterberg JL, Tso A. An analysis of an anatomical posterolateral knee reconstruction: an in vitro biomechanical study and development of a surgical technique. Am J Sports Med. 2004;32:1405-14.
5. LaPrade RF, Ly TV, Wentorf FA, Engebretsen L. The posterolateral attachments of the knee: a qualitative and quantitative morphologic analysis of the fibular collateral ligament, popliteus tendon, popliteofibular ligament, and lateral gastrocnemius tendon. Am J Sports Med. 2003;31:854-60.
6. LaPrade RF, Tso A, Wentorf FA. Force measurements on the fibular collateral ligament, popliteofibular ligament, and popliteus tendon to applied loads. Am J Sports Med. 2004;32:1695-701.
7. Terry GC, LaPrade RF. The posterolateral aspect of the knee. Anatomy and surgical approach. Am J Sports Med. 1996;24:732-9.
8. Noyes FR, Barber-Westin SD. Surgical restoration to treat chronic deficiency of the posterolateral complex and cruciate ligaments of the knee joint. Am J Sports Med. 1996;24:415-26.
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