topography of the femoral attachment of the posterior ... · topography of the femoral attachment...

Topography of the Femoral Attachment of thePosterior Cruciate Ligament

By Osmar V. Lopes Jr., MD, Mario Ferretti, MD, Wei Shen, MD, PhD, Max Ekdahl, MD,Patrick Smolinski, PhD, and Freddie H. Fu, MD

Investigation performed at the Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania

Background: The success of posterior cruciate ligament reconstruction has varied. The objective of this study was todetermine quantitatively and qualitatively the topography and osseous landmarks of the femoral footprints of theanterolateral and posteromedial bundles of the posterior cruciate ligament in order to enhance repair.

Methods: Twenty unpaired knees from twenty human cadavers were evaluated. The surface features of the femoralfootprints of the anterolateral and posteromedial bundles of the posterior cruciate ligament were studied by means ofmacroscopic observation and three-dimensional laser photography.

Results: We observed, both visually and with three-dimensional laser photography, an osseous prominence locatedproximal to the femoral footprint of the posterior cruciate ligament in eighteen of the twenty human knees. Thisosseous landmark, denominated the ‘‘medial intercondylar ridge,’’ determined the proximal border of the posteriorcruciate ligament footprint. In eight of the twenty knees, we observed a small osseous prominence between the an-terolateral and posteromedial bundles of the posterior cruciate ligament. A clear change in the slope of the femoralfootprint of the posterior cruciate ligament was seen between the anterolateral and posteromedial bundles. Theaverage area of the posterior cruciate ligament footprint (and standard deviation) was 209 ± 33.82 mm2, the averagearea of the anterolateral bundle was 118 ± 23.95 mm2, and the average area of the posteromedial bundle was 90 ±16.13 mm2.

Conclusions: The femoral footprint of the posterior cruciate ligament has a unique surface anatomy, with a medialintercondylar ridge being frequently present and a medial bifurcate ridge being less frequently present.

Clinical Relevance: These anatomical findings may assist surgeons in performing posterior cruciate ligament recon-struction in a more anatomical fashion.

The posterior cruciate ligament is considered to be theprimary restraint to posterior knee translation and asecondary restraint to varus, valgus, and external rota-

tion of the knee joint1. It is composed of two functionalbundles: the anterolateral bundle and the posteromedialbundle2,3. It has been demonstrated that these two bundleshave distinct patterns of tension during the range of motion ofthe knee joint. The anterolateral bundle is taut near 90� offlexion, and the posteromedial bundle is taut at nearly fullextension2,4.

The success of posterior cruciate ligament reconstruc-tion has been variable5,6. Some recent studies have shown thatdouble-bundle posterior cruciate ligament reconstruction can

restore knee kinematics better than can single-bundle poste-rior cruciate ligament reconstruction7-9. Previous studies havedemonstrated that the placement of the femoral tunnel for theposterior cruciate ligament reconstruction is more importantthan the placement of the tibial tunnel in terms of restoringgraft forces10,11.

Knowledge of the anatomy of the posterior cruciateligament is crucial to understanding the function of its twobundles as well as to improving the outcome of reconstructionsurgery. Although many studies have provided important in-formation about the femoral footprint of the posterior cruciateligament2,12-17, we are not aware of any published detailed an-atomical evaluations of the bone landmarks and topography of

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor amember of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercialentity. 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 authors, or a member of their immediate families, are affiliated or associated.

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COPYRIGHT � 2008 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED

J Bone Joint Surg Am. 2008;90:249-55 d doi:10.2106/JBJS.G.00448

the femoral footprint of the posterior cruciate ligament. In ouropinion, a description of these osseous landmarks may assistsurgeons in selecting the anatomical placement of femoraltunnels during single or double-bundle reconstruction of theposterior cruciate ligament. Thus, the main objective of thisstudy was to evaluate qualitatively and quantitatively the bonelandmarks and topography of the femoral footprints of the

anterolateral and posteromedial bundles of the posterior cruciateligament.

Materials and Methods

Twenty unpaired fresh-frozen human cadaveric knees fromtwenty adults (fifteen men and five women) were used in

this study. The average age at the time of death was seventy-

Fig. 1

Anterior view of the left knee in 90� of flexion, showing the two bundles of the

posterior cruciate ligament: the anterolateral bundle (white arrow) and the

posteromedial bundle (black arrow). All soft tissue, except the posterior and

anterior cruciate ligaments, was stripped off.

Fig. 2

A: Gross appearance of the location of the femoral attachment of the posterior cruciate ligament onto the medial intercondylar wall (sagittal view

of a left knee). The white arrow indicates the attachment site of the anterolateral bundle, and the black arrow indicates the attachment site of the

posteromedial bundle. B: Gross appearance of the medial intercondylar ridge (black arrows) and the medial bifurcate ridge (white arrows).

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TH E J O U R N A L O F B O N E & JO I N T SU R G E RY d J B J S . O R G

VO LU M E 90-A d NU M B E R 2 d F E B RUA RY 2008TO P O G R A P H Y O F T H E F E M O R A L AT TAC H M E N T O F T H E

PO S T E R I O R CRU C I AT E LI G A M E N T

four years (range, fifty-seven to ninety-three years). Cadavericknees that showed severe degenerative changes, signs of frac-tures, or evidence of ligament injury had been excluded fromthe study. The knees were completely dissected to expose theposterior cruciate ligament and the medial femoral condyle(Fig. 1). The synovial covering of the posterior cruciate liga-ment was removed, along with the meniscofemoral ligaments.The femoral footprints of the anterolateral and posteromedialbundles of the posterior cruciate ligament could be identifiedon the basis of the different tension pattern of each bundleduring the range of motion of the knee, with the anterolateralbundle being taut in flexion and the posteromedial bundlebeing taut in full extension. The bundles were separatedcarefully with use of blunt dissection. The footprints of theanterolateral and posteromedial bundles were carefully definedwith ink before all soft tissue was removed to expose the medialwall of the intercondylar notch.

At first, gross observation of the bone topography, withspecial attention to the femoral footprints of the anterolateraland posteromedial bundles, was performed in all knees (Fig.2). Second, the knees were photographed with a laser three-dimensional digitizer camera (VIVID 910 3D Digitizer; KonicaMinolta Sensing, Osaka, Japan), and the images were analyzedwith specific software (Geomagic Studio 9; Geomagic, Re-search Triangle Park, North Carolina) (Fig. 3). This noncon-tact method allows three-dimensional visualization and digitalmeasurements of the observed surface through the analysisof 307,000 triangulation blocks. The precision of the three-dimensional images is approximately 0.0008 mm. The accuracy

is 0.22 mm for the x axis, 0.16 mm for the y axis, and 0.10 mmfor the z axis18. Thus, it serves as an accurate means of mea-suring the area of the femoral footprint of the posterior cru-ciate ligament as well as the distance and length of all observedfeatures. The central point of each area was located visuallyon the digital images. The distance between the centers of theanterolateral and posteromedial footprints was measured, andthe shortest distance from the center of each bundle’s footprintto the edge of the articular cartilage and to the medial inter-condylar ridge was identified. The surface anatomy of themedial wall of the intercondylar notch was also observed withthis method, with measurements made of defined osseouslandmarks. We use the terms ‘‘proximal/distal’’ and ‘‘anterior/posterior’’ throughout this article to describe the location ofthe structures on the medial intercondylar wall when the kneewas in the anatomical position.

Results

The femoral footprints of the posterior cruciate ligamentsvaried in shape and size. The shape was a semicircle in

fifteen of the twenty knees and an oval in five. The femoralattachment of the posterior cruciate ligament was concave innineteen knees and flat in one. The three-dimensional laserdigital measurement showed the average area (and standarddeviation) of the femoral posterior cruciate ligament footprintto be 209 ± 33.82 mm2, with the average area of the antero-lateral bundle measuring 118 ± 23.95 mm2 and the averagearea of the posteromedial bundle measuring 90 ± 16.13 mm2.The average distance between the central points of the bundles

Fig. 3

Image made with three-dimensional laser photography, showing the attachment of the anterolateral (AL) and posteromedial (PM) bundles of the

posterior cruciate ligament onto the medial femoral condyle in a left knee. Similar to a lateral portal view of the medial condyle, this view shows the

medial intercondylar wall when the knee is in 90� of flexion. The small picture of the femur in the middle shows the orientation of the specimen.

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Fig. 4

Image made with three-dimensional laser photography, showing the medial inter-

condylar ridge (black arrows) and the medial bifurcate ridge (white arrows). This image

simulates a lateral portal view of the left knee when the knee is near 90� of flexion.

The small picture of the femur in the left corner shows the orientation of the specimen.

Fig. 5

Left: Image made with three-dimensional laser photography, showing the medial intercondylar wall of the left knee. To emphasize the osseous

features on the medial intercondylar wall, the femoral shaft is omitted. Note a small ridge (the medial bifurcate ridge, black arrow) between the

anterolateral and posteromedial bundles. Right: A cross section through the entire posterior cruciate ligament footprint with a schematic diagram

of the angle formed between the anterolateral (AL) and posteromedial (PM) bundle attachments. The small picture of the femur in the middle shows

the orientation of the specimen.

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was 11 ± 1.18 mm. With the knee at 90� of flexion, the averageshortest distances from the centers of the anterolateral andposteromedial bundles to the articular cartilage edge were 7 ±1.02 mm and 8 ± 0.99 mm, respectively.

An osseous prominence located proximal to the fem-oral attachment of the posterior cruciate ligament was grosslyand digitally identified in eighteen of the twenty knees. Thisosseous prominence was named the ‘‘medial intercondylarridge’’ by the senior author (F.H.F.). With the knee in theanatomical position, the medial intercondylar ridge runsobliquely through the entire femoral footprint of the poste-rior cruciate ligament from proximal to distal and from an-terior to posterior (Fig. 4). Its average length was 14.24 ±2.3 mm. The average distances between the medial inter-condylar ridge and the center point of the posterior cruciateligament, the anterolateral bundle, and the posteromedial bun-dle were 4.36 ± 0.61 mm, 3.63 ± 0.4 mm, and 3.13 ± 0.4 mm,respectively.

In addition to the medial intercondylar ridge, we alsoobserved a subtle osseous prominence located between thefemoral footprints of the anterolateral and posteromedialbundles (Fig. 4). It was identified in eight of the twenty kneesas a discrete osseous ridge on the bone. We propose that it becalled the ‘‘medial bifurcate ridge.’’ The average length of themedial bifurcate ridge was 5.8 ± 1.38 mm. In addition, achange of slope was observed between the femoral footprintsof the anterolateral and posteromedial bundles (Fig. 5). Withuse of the medial bifurcate ridge as the pivot, the averageangle formed by the anterolateral and posteromedial femoral

footprints was 140� ± 12.8�. All quantitative data are given inTable I.

Discussion

The anatomy of the posterior cruciate ligament has beendescribed in several studies2,3,12-17,19. The footprint area and

the locations of the two bundles have been reported. However,the details of the bone anatomy related to the femoral footprintof the posterior cruciate ligament have not been described, toour knowledge. A detailed description of the femoral foot-prints of the anterolateral and posteromedial bundles is neededto enable surgeons to accurately place femoral tunnels inposterior cruciate ligament surgery.

Girgis et al.2 reported the anatomical measurements ofthe total posterior cruciate ligament footprint, but they did notevaluate the anatomical measurements of each bundle’s foot-print separately. Harner et al.15 and Morgan et al.20 reportedthat the femoral attachment of the posterior cruciate ligamentspans, on the average, a distance of 32 mm in anterior-to-posterior depth. Single-bundle reconstruction may not coverall of the femoral footprint of the posterior cruciate ligamentand does not reproduce the anatomy of the anterolateral andposteromedial bundles or their functional patterns20. Harneret al.13 used a digitizing system (accurate to within 0.8 mm) torecord the coordinates of the periphery of the attachment ofthe posterior cruciate ligament and its bundles. They usedthirty equally spaced points to collect the data. The averagearea of the femoral footprint of the posterior cruciate ligamentwas reported to be 128 ± 22 mm2, and they did not findsignificant differences between the areas of the anterolateraland posteromedial bundles13. In another anatomic study,Takahashi et al.17 used photographs with a measurement scale(one scale for each photograph of each femur) to evaluate thefemoral attachment of the posterior cruciate ligament. Theyreported that the area of the anterolateral femoral footprintaveraged 58 ± 25.4 mm2 and that of the posteromedial femoralfootprint averaged 64.6 ± 24.7 mm2. These differences in theliterature may be due to the different methods used for mea-surement as well as to ethnic and gender differences in thehuman subjects that were studied. Our study confirmed thatthe anterolateral and posteromedial bundles have distinctivefemoral footprints. Our measurements of the average areas ofthe anterolateral and posteromedial footprints are larger thanthose previously described in the literature. This discrepancymay be due to the reasons mentioned above and mainly to thefact that the three-dimensional analysis used in this study maycover the total area of the concave attachment of the posteriorcruciate ligament more accurately. Also, it is important to notethat we included all peripheral fibers of the posterior cruciateligament attachment in our measurements. We believe thatthese additional factors may have contributed to the largerareas that we observed.

The location of the femoral footprint of the posteriorcruciate ligament has been described in many differentways16,17,19-21. Wind et al.21 reported that the center of thefootprint is located 1 cm proximal to the articular cartilage.

TABLE I Quantitative Analysis of the Femoral Attachment of the

Posterior Cruciate Ligament and Its Landmarks

Mean and StandardDeviation

Footprint area (mm2)

Posterior cruciate ligament 209 ± 33.82

Anterolateral bundle 118 ± 23.95

Posteromedial bundle 90 ± 16.13

Length of medial intercondylar ridge (mm) 14.24 ± 2.3

Change of slope (deg) 140 ± 12.8

Shortest distance (mm) between articularcartilage edge and center of:

Anterolateral bundle 7 ± 1.02

Posteromedial bundle 8 ± 0.99

Distance between centers of anterolateraland posteromedial bundles (mm)

11 ± 1.18

Length of medial bifurcate ridge (mm) 5.8 ± 1.38

Distance (mm) from medial intercondylarridge to center of:

Posterior cruciate ligament 4.36 ± 0.61

Anterolateral bundle 3.63 ± 0.4

Posteromedial bundle 3.13 ± 0.4

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Mejia et al.16 used the ‘‘o’clock’’ method and suggested that theposterior cruciate ligament may extend from 12 to 4 o’clockin the right knee and from 12 to 8 o’clock in the left knee.Takahashi et al.17 measured the distances between the centers ofthe anterolateral and posteromedial bundle footprints and theanterior border of the articular cartilage using a line parallel tothe Blumensaat line. The average distances were 9.6 mm and10.6 mm for the anterolateral and posteromedial bundles,respectively. Morgan et al.20 defined the centers of the anter-olateral and posteromedial bundles by using three differentaxes in reference to the articular cartilage. Their results showedthat the center of the anterolateral bundle originated 13 mmposterior and 13 mm inferior to the border of the articularcartilage whereas the center of the posteromedial bundleoriginated 8 mm posterior and 20 mm inferior to the border ofthe articular cartilage. In a recent study, Edwards et al.19 usedthe ‘‘o’clock’’ method and the center of a circle outlining theposterior aspect of the medial femoral condyle as a reference.The centers of the footprints of the posterior cruciate ligamentbundles were found to be at a variety of o’clock positions whenmeasured parallel to the femoral intercondylar notch roof orthe femoral shaft. On the femoral side, the center of the an-terolateral bundle was, on the average, 7 ± 2 mm from thearticular cartilage at 10:20 ± 00:30 o’clock, and the center ofthe posteromedial bundle was 10 ± 3 mm from the articularcartilage at 08:30 ± 00:30 o’clock.

These previous studies were conducted with use of dif-ferent methods, and the results were reported in different ways.Thus, it may be somewhat confusing for surgeons attemptingto choose the appropriate site for placement of the femoraltunnel in a reconstruction of the posterior cruciate ligament.Our findings suggest a different approach for determining thefootprints of the anterolateral and posteromedial bundles. Themedial intercondylar ridge was found to define the proximallimit of the posterior cruciate ligament, whereas the medialbifurcate ridge was found to separate the femoral footprints ofthe anterolateral and posteromedial bundles. We believe thatthese two ridges may be used to assist the surgeon in deter-mining the placement of the anterolateral and posteromedialtunnels on the femoral side. During the surgery, both tunnelsshould be placed more distally than the medial intercondylarridge, and they should be separated by the medial bifurcateridge.

Previous investigators have reported that the femoralattachment of the posterior cruciate ligament is relativelyplanar and approximates a half-moon shape2,13. In this study,we found that the femoral attachment site of the posteriorcruciate ligament was concave in nineteen of twenty knees andwas relatively planar in only one specimen. The shape of thefemoral attachment site was approximately semicircular infifteen femora and oval in five. We found that the two bundleswere located in different planes and there was a change of slopebetween the femoral footprints of the anterolateral and pos-teromedial bundles. This finding may also be used to assist inthe anatomical placement of femoral tunnels in reconstruc-tions of the posterior cruciate ligament. However, it is im-portant to note that the bone topography reported heredescribes subtle features related to the femoral footprint of theposterior cruciate ligament. Careful probing and removal ofthe residual posterior cruciate ligament soft tissue are neces-sary to identify these structures.

This study had at least two limitations. First, a relativelysmall number of knees was examined considering the greatpossibility of anatomical variations. Second, despite the ac-curacy of the three-dimensional laser measurement systems,the measurements relied on human judgment (i.e., deter-mining the center of a footprint), which may have introducedbias.

We demonstrated that the femoral footprint of theposterior cruciate ligament has a unique surface anatomy, witha medial intercondylar ridge being frequently present and asecond osseous landmark, the medial bifurcate ridge, beingidentified less frequently. These osseous landmarks may beused as a guide for placement of anatomical femoral tunnelsduring reconstructions of the posterior cruciate ligament. n

Osmar V. Lopes Jr., MDMario Ferretti, MDWei Shen, MD, PhDMax Ekdahl, MDPatrick Smolinski, PhDFreddie H. Fu, MDDepartment of Orthopaedic Surgery, University of Pittsburgh, 3471 FifthAvenue, Suite 1011, Pittsburgh, PA 15213. E-mail address for F.H. Fu:[email protected]

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