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
This study was designed to determine the most isometric
femoral attachment sites for lateral collateral ligament, popliteus tendon, and
popliteofibular ligament grafts that are used to reconstruct the posterolateral
structures of the knee. I agree on the importance of this study because, as the
authors indicate, there is no consensus on which graft-attachment site or method
of tensioning is best and the described operative techniques have varied
greatly.
The study involved three phases: identification of the
anatomic attachment sites of the posterolateral structures, suture placement at
the distal attachment of the posterolateral structures and identification of
the most ideal isometric femoral center, and graft placement at this ideal femoral
location to determine if graft-length changes were similar to the suture
placement. The results showed that the graft placement was indeed similar to
the isometric site identified by the ideal suture location.
The authors acknowledge the difficulty in controlling tibial
rotation as the measurements of suture and graft-length change were made at 0°,
10°, 30°, 45°, 70° and 90° of flexion. The unconstrained tibia was allowed to
seek its own axis of rotation. Tibial rotation was measured with a goniometer,
and the authors manually reproduced these knee positions for the conditions of
the experiment. Unfortunately, information was not given concerning the
rotation position of the tibia with regard to the external and internal range
of rotation of the tibia. These conditions indicate that the suture-length and
graft-length changes are made at different rotation positions at the respective
knee-flexion positions. The addition of a three-dimensional goniometer fixed to
the specimen would have provided exact rotation conditions, tibial rotation
limits, and accurate repositioning. This point has further bearing on the
conclusions of graft placement on external tibial rotation, which will be
discussed later.
A coordinate grid was located at the center of the femoral
popliteus tendon attachment, permitting the placement of twenty-one holes in
the femur, 5 mm apart, for measurement of suture length changes with knee
flexion. The suture was placed at the anatomical distal attachment and at
varying positions in the femoral grid. The anatomical attachments of the lateral
collateral ligament, popliteus tendon, and popliteofibular ligament were
similar to those described in the literature, representing important data to be
used to identify attachment sites at surgery. The mean location of the center
of the footprint of the lateral collateral ligament was described as being
approximately 3 mm posterior and slightly proximal (0.85 mm) to the mean
epicondyle center, which is in agreement with the findings of LaPrade et al.1 (3.1 mm posterior,
1.4 mm proximal to the femoral epicondyle), with the main attachment at a small
osseous depression just posterior to the lateral femoral epicondyle.
The authors describe the lateral collateral ligament femoral
attachment as being 11.5 mm proximal to the popliteus tendon attachment.
LaPrade and associates1 measured this distance as 18.5 mm, indicating that there may be anatomic
variability and size differences in specimens and that these attachment
distances therefore need to be determined at the time of surgery.
The reader should note that the suture isometry graft
changes shown in the figures have a positive value when the graft slackens
(relative graft lengthening, or less graft tension, or decrease in graft
attachment separation distance) and a negative value under the opposite
conditions. This is different from the usual description of published isometric
data, such as for anterior and posterior cruciate ligaments, where a positive
value represents an increase in millimeters of graft attachment separation
distance (graft elongation or increasing graft tension). Of interest, the
greatest length change in the isometric suture data occurred between 0° and 30°
of flexion for the popliteus tendon and popliteofibular ligament grafts (see Figs.
4 and 5 of Sigward et al.), which was not true for the lateral collateral
ligament graft (see Fig. 4).
The reader should carefully analyze Figures 3-A and 3-B in
the paper by Sigward et al., which show the femoral isometric points for each
specimen and note the major difference in the isometric points between
specimens. For example, for the lateral collateral ligament (see Fig. 3-A), the
optimum isometric points in reference to the anatomic attachment of the lateral
collateral ligament varied greatly: the point was 5 mm distal in six specimens,
5 mm anterior in four specimens, and 5 mm anterior and 5 mm distal to the lateral
collateral ligament attachment in four specimens. A similar difference between
specimens was shown for the popliteus tendon and popliteofibular isometric
points. In each of the figures, the mean location (shown by the square) was
used for the conclusions and recommendations for ideal graft placement.
In my opinion, given this variability in isometric points
between specimens, it is probable that a mean value for the ideal isometric
value for graft placement would be incorrect (in a knee undergoing surgery) by
a number of millimeters in a proximal-distal or anterior-posterior direction.
It is suspect if a single mean value is truly representative of this wide
variation in the isometric points. This problem is reflected in the rather
large standard deviations in graft-length changes (see Figs. 4, 5, and 6 in
Sigward et al.) with increasing knee flexion, even though the mean values
themselves varied by 1 mm or so from the ideal isometric position reported. The
authors do emphasize the importance of the surgeon going through the same
analysis in terms of using a suture at selected graft attachment locations to
determine that the graft sites chosen are realistic. A problem arises, however,
in that the conditions at surgery are far from ideal and that it is still
unknown if truly accurate values can be obtained.
In my opinion, the data from the ideal attachment location
recommended for the popliteus tendon and popliteofibular ligament grafts are
incorrect for a number of reasons. The authors state that the anatomical femoral
location for the popliteus tendon "is not the best choice" and recommend a
graft location 11 mm anterior and 2.7 mm proximal to the femoral footprint of
the popliteus tendon. This is markedly different from the anatomical footprint
chosen for anatomical posterolateral reconstructions that I2 and others3 have recommended. In
the companion paper to this study ("Effects of Posterolateral Reconstructions
on External Tibial Rotation and Forces in a Posterior Cruciate Ligament Graft,"
by Markolf et al. [JBJS, November 2007]), the degrees of external tibial
rotation were provided after graft reconstruction. A popliteus tendon or popliteofibular
ligament graft placed in the position recommended by those investigators
produced a major overconstraint of external tibial rotation at all angles of knee
flexion (5 N-M external tibial torque, see Fig. 4 in Markolf et al.). Under
passive knee flexion-extension, the knee joint assumed a position of internal
tibial rotation. This indicates that the graft location is too anterior in
terms of allowing normal external tibial rotation.
I believe that recommendations for graft isometry must take
into account tibial rotation positions and that the graft should not be
overtensioned to limit external tibial rotation. The goal is to restore the
normal limits of external tibial rotation with an appropriately placed graft that
resists external tibial rotation at the normal limit as well as during varus
rotation. In my experience, this goal can be achieved with anatomic
reconstruction2. The primary issues are the
flexion and tibial rotation position and the amount of tension placed on the
graft so that the joint is not overconstrained for tibial rotation or adduction
rotation4. Therefore I encourage the authors to add tibial rotation
measurements to their protocol as they continue their work, as these
measurements will provide the additional information required to be more
precise in graft placement and tensioning recommendations.
The recommendations that I would provide for tensioning a
posterolateral graft are to place the knee in 30° of flexion and in neutral
tibial rotation and apply a small tension load. The knee should be taken to
full extension. As the authors indicate, the graft may be under greater tension
and full extension should not be blocked. The knee should also be externally
rotated 15° to avoid overconstraining tibial rotation. I prefer placement of
grafts at anatomic attachment sites, believing that this is the most ideal
method we have at present to replicate normal anatomy.
In summary, the authors have provided important information
on the effect that changes in the femoral location of grafts have on graft
elongation properties. There appears to be major variability in the measurement
of the single isometric point for lateral collateral ligament, popliteus tendon,
and popliteofibular ligament grafts from specimen to specimen under the
specific conditions in this experiment. Unfortunately, the tibial rotation
positions and limits were not measured and the effect of the graft isometric
placement recommended on tibial rotation was not determined. For this reason, I
do not believe that the recommendations for the popliteus and popliteal grafts
placed substantially anterior to their normal anatomical attachment can be
accepted, as this may produce substantial blocking of normal external tibial
rotation. The data and the questions raised allow for more studies to be
performed which will, I am sure, improve the still largely empiric
recommendations in the literature for posterolateral graft reconstruction
techniques. Readers are encouraged to read the companion paper to this
investigation ("Effects of Posterolateral Reconstructions on External Tibial
Rotation and Forces in a Posterior Cruciate Ligament Graft," by Markolf 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. 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.
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. Grood ES, Stowers SF, Noyes FR. Limits of movement in the human knee. Effect of sectioning the posterior cruciate ligament and posterolateral structures. J Bone Joint Surg Am. 1988;70:88-97.
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