Systematic Review
Anatomy of the Femoral Footprint of the Posterior Cruciate Ligament: A Systematic Review Steven J. Narvy, M.D., Matthew Pearl, B.S., Michael Vrla, B.S., Anthony Yi, B.S., and George F. Rick Hatch III, M.D.
Purpose: The purpose of this study was to summarize the past 10 years of orthopaedic literature to better delineate the femoral origin of the posterior cruciate ligament (PCL). Methods: A PubMed search was conducted by 2 independent reviewers (M.P., M.V.) using the search terms “posterior cruciate ligament” or “PCL,” “femur” or “femoral,” and “anatomy” or “origin” or “footprint.” Cadaveric and radiographic studies performed between January 1, 2003, and November 30, 2013, were analyzed. Results: Aggregate data from radiographic parameters indicate that the anatomic origin of the anterolateral bundle lies 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch. The origin of the posteromedial bundle lies 56% from the anterior surface and 36.5% of the tangent distance toward the notch. On the basis of cadaveric data, the center of the anterolateral bundle is 8 mm from the anterior surface (27.5% of the Blumensaat line), 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and 3.6 mm from the medial intercondylar ridge; the center of the posteromedial bundle is 11.9 mm from the anterior articular surface (42.5%), 10.9 mm along the tangent line (57.5%), and 3.1 mm from the medial intercondylar ridge. Conclusions: We were able to precisely delineate the femoral origin of the PCL through our systematic review. Clinical Relevance: Our systematic review may assist arthroscopic knee surgeons in placing anatomic tunnels during reconstruction of the PCL.
T
he posterior cruciate ligament (PCL) provides the primary restraint to posterior tibial translation and acts as a secondary restraint to tibial valgus, varus, and external rotation.1-3 The ligament consists of 2 functional bundles, a larger anterolateral bundle (ALB) and a smaller posteromedial bundle (PMB).4 The ALB has greater cross-sectional area and strength relative to the PMB. The ALB maintains nearly double the ultimate load of the PMB.5,6 Each bundle has a different tensioning pattern depending on the degree of knee flexion. The ALB is taut in knee flexion and loose in knee extension, whereas the PMB is taut in knee extension and loose in knee flexion.4,7 Recent
From the Department of Orthopaedic Surgery, University of Southern California Keck School of Medicine, Los Angeles, California, U.S.A. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received April 22, 2014; accepted July 3, 2014. Address correspondence to George F. Rick Hatch III, M.D., Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, 1520 San Pablo St, Ste 2000, Los Angeles, CA 90089, U.S.A. E-mail: [email protected] Ó 2014 by the Arthroscopy Association of North America 0749-8063/14342/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.07.004
biomechanical studies suggest that the 2 bundles of the PCL may have a co-dominant relation, functioning in a synergistic fashion throughout the range of motion.8 Injuries to the PCL are far less common than injuries to other knee structures, such as the anterior cruciate ligament (ACL) or the menisci. The incidence of PCL injuries has varied dramatically in the literature, ranging from 3% in the general population9 to as high as 38% in the trauma setting in patients with acute knee hemarthrosis.10,11 Although many isolated PCL injuries are successfully treated nonoperatively, instability, pain, arthrosis, and compromised knee function develop in some patients with PCL-deficient knees.12,13 In addition, it has been found that the clinical outcomes of PCL reconstruction are less satisfactory and less predictable relative to those of ACL reconstruction.13,14 Consequently, increasing attention has been directed toward PCL reconstruction with respect to PCL anatomy and graft placement. Data indicating improved clinical outcomes with anatomic reconstruction of the cruciate ligaments are becoming increasingly commonplace in the literature.15,16 Although evidence may be stronger for anatomic reconstruction of the ACL, data are mounting for PCL reconstruction as well.17-22 Biomechanically, it
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has been shown that the tibial-inlay technique eliminates graft abrasion and decreases graft laxity14; however, this has not translated into improved clinical outcomes in patients undergoing the tibial-inlay versus transtibial technique of PCL reconstruction.23,24 One possible explanation for the persistent posterior tibial laxity is femoral tunnel positioning.5,8,25 Anatomic reconstruction on the femoral side requires an accurate and reproducible method to guide tunnel placement. The “clock-face” method has been frequently reported as a guide for femoral tunnel placement; however, poor reproducibility has been noted among surgeons who use this method.26-28 Numerous basic science studies have sought to characterize the location of the femoral footprint of the PCL. There remains, however, significant disagreement regarding the exact location of the PCL femoral footprint in the published literature. The purpose of this study was to examine recent literature in an effort to better characterize the precise location of the femoral origin of the PCL.
Methods Before conducting the literature search, we established our specific study objective of characterizing the femoral origin of the PCL. A PubMed search was conducted by 2 independent reviewers (M.P., M.V.) using the search terms “posterior cruciate ligament” or “PCL,” “femur” or “femoral,” and “anatomy” or “origin” or “footprint.” General search terms were chosen to prevent the possibility of missing potential studies. The inclusion criteria were cadaveric and radiographic studies on human subjects published between January 1, 2003, and November 30, 2013. Studies written in a language other than English, studies focused on surgical treatment or clinical outcomes, and review articles were excluded from analysis. References from identified studies were manually searched to identify additional articles that may have been missed by our search. Data were abstracted from each study that met the inclusion criteria by 2 independent reviewers (M.P., M.V.). Data were then compiled and categorized based on study design.
Results Our initial search produced 188 articles. The abstracts were reviewed, and the search was narrowed to 108 articles. After full review of these articles and citations from these articles, 10 studies met our final inclusion criteria. Four studies evaluated the PCL’s femoral origin on the basis of radiographic findings alone. Five studies described the femoral origin of the PCL on the basis of cadaveric dissection only. One study included both radiographic and cadaveric data. Of the radiographic studies, 3 were based on plain radiography and 2 were based on computed
Fig 1. Radiographic anteroposterior femur view. Using a measurement axis generated based on the distal condyle line, Johannsen et al.29 found that the centers of the ALB and PMB were 34.1 and 29.2 mm lateral to the most medial border of the medial femoral condyle, respectively. Relative to the medial intercondylar ridge, the ALB was 6.1 mm away and the PMB was 5.2 mm away. Reprinted by Permission of SAGE Publications.29
tomography (CT). A brief synopsis of these articles is presented in this article. Radiographic Findings Johannsen et al.29 obtained fluoroscopic images of 20 cadaveric knees in which the ALB and PMB had been dissected and marked. On the anteroposterior view, the centers of the ALB and PMB were 34.1 and 29.2 mm lateral to the most medial border of the medial femoral condyle, respectively (Fig 1). Relative to the medial intercondylar ridge, the ALB was 6.1 mm away and the PMB was 5.2 mm away. On the lateral view, the ALB center and PMB center were 17.4 mm and 23.9 mm posteroproximal to the anterior cortex line of the femoral condyles along a reference line parallel with the Blumensaat line, respectively (Fig 2). In addition, the ALB and PMB were 6.1 mm and 5.5 mm away from the medial intercondylar ridge, respectively. Two studies evaluated the femoral origin of the separate bundles of the PCL using a different radiographic metric. Lorenz et al.30 dissected out the femoral origin of the PCL in 16 cadaveric specimens, separately marking the ALB and the PMB with copper wire, and standard anteroposterior and lateral knee radiographs
ANATOMY OF FEMORAL FOOTPRINT OF PCL
Fig 2. Radiographic lateral femur view. Johannsen et al.29 found that the ALB and PMB centers were 17.4 mm and 23.9 mm posteroproximal to the anterior cortex line of the femoral condyles along a reference line parallel with the Blumensaat line, respectively. Reprinted by Permission of SAGE Publications.29
were taken. On the lateral radiographs, the center of the ALB was 62% of the way from posterior to anterior along an extended Blumensaat line that intersected the posterior cortex of the femur and 16% of the tangent distance from the Blumensaat line to the most posterior point of the medial femoral condyle (Fig 3). The center of the PMB was 51% from posterior to anterior along the Blumensaat line and 35% more posterior along the tangent line (Fig 3). Osti et al.31 used the same radiographic grid method to measure the ALB and PMB femoral footprints but reported measurements in the opposite orientation (anterior to posterior). They found the ALB to be 42% of the way along the extended Blumensaat line, from anterior to posterior, and 13% of the tangent distance, whereas the PMB was 63% of the way along the extended Blumensaat line, from anterior to posterior, and 38% of the way along the tangent line based on the lateral radiographs. Two additional studies used CT imaging to describe the femoral origin of the PCL overall, without defining
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Fig 3. Average geometric midpoint of the ALB (white) (x ¼ 62% 3%/y ¼ 16% 6%) and PMB (black) (x ¼ 51% 5%/y ¼ 35% 7%) as determined by Lorenz et al.,30 who used the modified quadrant method. Using lateral radiographic images, Lorenz et al. found that the center of the ALB (white) was 62% of the way from posterior to anterior along an extended Blumensaat line that intersected the posterior cortex of the femur and 16% of the tangent distance from the Blumensaat line to the most posterior point of the medial femoral condyle. The center of the PMB (black) was 51% from posterior to anterior along the Blumensaat line and 35% more posterior along the tangent line. Reprinted from with kind permission from Springer Science and Business Media.30
the bundles separately. Greiner et al.32 dissected out the femoral origin of the PCL in 10 cadaveric knees, placed pins around the femoral origin, and then obtained CT scans of the specimens. The mean surface area of the femoral origin of the PCL was 232.2 mm2. The mean distance from the center of attachment to the roof of the notch was 8.9 mm, which corresponds to 34.7% of the total length of the Blumensaat line (Fig 4). The mean distance from the center of insertion onto the anterior articular cartilage surface was 18.7 mm, which corresponds to 73.3% of the length of the Blumensaat line. Westermann et al.33 dissected out the PCL origin on the medial femoral condyle in 7 cadavers, marked the femoral footprint with K-wires, and then used CT imaging to create a 3-dimensional (3D) surface reconstruction of the distal femur. Although the individual ALB and PMB of the PCL
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Fig 4. Blumensaat line (gold line) and measurements taken from the center of the PCL origin toward the roof of the notch (blue line) and toward the anterior articular margin (red line). Using these relations, Greiner et al.32 found that the mean surface area of the femoral origin of the PCL was 232.2 mm2 (oval). The mean distance from the center of attachment to the roof of the notch was 8.9 mm (blue line). The mean distance from the center of insertion to the anterior articular cartilage surface was 18.7 mm (red line). Reprinted from with kind permission from Springer Science and Business Media.32
were not defined, the authors determined the center point of the PCL overall to be 38% from anterior to posterior from the anterior condyle (parallel to the Blumensaat line) and 25% of the way down from the roof of the notch (distance from notch roof to distal-most aspect of medial femoral condyle, perpendicular to notch axis/Blumensaat line) (Fig 5). Table 1 and Figure 6 summarize the data from the aforementioned studies that evaluated the femoral origin of the PCL using similar measurement techniques. Taken as a whole, these data pinpoint the anatomic center of the ALB to be 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch and the PMB to be 56% from the anterior surface and 36.5% of the tangent distance. When the individual bundles are not considered, the overall center of the PCL is 67.5% from
Fig 5. Relations used by Westermann et al.33 in assessing the position of the PCL in relation to the size of the medial femoral condyle, with specimens oriented along the axis of the intercondylar notch. (c, distance from posterior femoral condyle border of PCL; C, total anteroposterior distance of condyle parallel to axis of notch; n, distance from notch roof to boundary; N, distance from notch roof to distal-most aspect of condyle, perpendicular to axis of notch.) Reprinted from Arthroscopy, Volume 29, Westermann R.W., Sybrowsky C., Ramme A.J., Amendola A., Wolf B.R., Three-dimensional characterization of the femoral footprint of the posterior cruciate ligament, 1811-1816, Ó 2014, with permission from the Arthroscopy Association of North America.33
the anterior surface of the femur and 30% of the tangent distance. Cadaveric Dissections Edwards et al.34 defined the centers of the ALB and PMB on a low/high axis and a shallow/deep axis relative to the diameter of a circle outlining the posterior medial femoral condyle, as well as by the distance from the cartilage edge relative to lines parallel to the long axis of the femur and parallel to the Blumensaat line (Fig 7). The ALB center was 11 mm from the “low” posterior, medial condyle margin along the low/high axis (29% of the femoral condyle diameter); 6 mm from the “deep” posterior, medial condyle margin along the shallow/deep axis (17% of the femoral condyle diameter); 7 mm from the cartilage edge parallel to the long axis of the femur; and 6 mm tangent from the cartilage edge parallel to the Blumensaat line (Fig 7). The PMB center was 2 mm from the low posterior, medial condyle margin along the low/high axis (6% of the femoral condyle diameter); 4 mm from the deep posterior, medial condyle margin
18.7 mm (73%) Distance not measured (62%)
Distance From Anterior Articular Surface
8.9 mm (35%) Distance not measured (25%)
Tangent Distance From Blumensaat Line Toward Notch
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Tangent Distance From Blumensaat Line Toward Notch Distance not measured (35%) 9.3 mm (38%) Type of Study Radiographs
Radiographs CT scans CT scans
Lorenz et al.30
Osti et al.31 Greiner et al.32 Westermann et al.33
Center of PMB
Distance From Anterior Articular Surface Distance not measured (49%) 30.9 mm (63%) Tangent Distance From Blumensaat Line Toward Notch Distance not measured (16%) 3.3 mm (13%)
Center of ALB
Table 1. Results of Radiographic Studies
Distance From Anterior Articular Surface Distance not measured (38%) 20.7 mm (42%)
Center of PCL Bundle
ANATOMY OF FEMORAL FOOTPRINT OF PCL
Fig 6. Summary depiction of aggregate radiographic data. The first percentage listed for each point represents the percentage of the distance from the anterior to posterior articular surface of the femur. The second percentage listed represents the percentage of the tangent distance from the Blumensaat line toward the intercondylar notch. The ALB lies 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch. The origin of the PMB lies 56% of the distance from the anterior surface and 36.5% of the tangent distance toward the notch. The overall center of the PCL is 67.5% from the anterior surface of the femur and 30% of the tangent distance.
along the shallow/deep axis (10% of the femoral condyle diameter); 10 mm from the cartilage edge parallel to the long axis of the femur; and 12 mm tangent from the cartilage edge parallel to the Blumensaat line. Takahashi et al.35 performed similar anatomic measurements on the femoral origin of the ALB and PMB based on dissection of 32 cadaveric specimens. The distance to the center of insertion of each bundle was measured from the anterior border of the articular cartilage and relative to the roof of the intercondylar notch (perpendicular to the Blumensaat line) (Fig 8) The ALB was 9.6 mm from the anterior border (29% of the length of the Blumensaat line) and 4.8 mm from the notch (25% of the longest length between the distal border of the articular cartilage and the Blumensaat line). The PMB was 10.6 mm from the
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Fig 7. Measurement systems used by Edwards et al.34 on medial femoral condyle. Edwards et al. defined the center of the ALB and PMB on a low/ high axis and a shallow/deep axis relative to the diameter of a circle outlining the posterior medial femoral condyle (left). They also measured the distance of the bundles from the cartilage edge relative to lines parallel to the long axis of the femur and parallel to the Blumensaat line (right). Reprinted from Arthroscopy, Volume 23, Edwards A., Bull A.M.J., Amis A.A., The attachments of the fiber bundles of the posterior cruciate ligament: An anatomic study, 284-290, Ó 2007, with permission from the Arthroscopy Association of North America.34
anterior border (32% of the length of the Blumensaat line) and 11.4 mm above the notch (60% of the longest length between the distal border of the articular cartilage and the Blumensaat line). Similarly, the cadaveric dissection arm of the study by Osti et al.31 noted the ALB to be 7.5 mm from the anterior articular surface (26% of an extended Blumensaat line that intersected the posterior cortex of the femur) and 3.43 mm from the notch (20% of the way along a line tangent to the Blumensaat line directed toward the distal femur); the PMB was 15.1 mm from the anterior border (53%) and 9.4 mm from the notch (55%). Anderson et al.36 determined the femoral attachment of the bundles based on 20 cadaveric dissection specimens. Three distinct anatomic points along the distal articular cartilage margin of the intercondylar notch were defined: the “trochlear point,” medial to the apex of the notch, where the articular cartilage abruptly turned medially; the “medial arch point,”
where the cartilage orientation became straight posterior after a smooth arch from the trochlear point; and the “posterior point,” which marked the most posterior extent of the articular cartilage of the medial femoral condyle (Fig 9). The ALB center was 7.9 mm from the articular cartilage distally and was triangulated at 7.4 mm from the trochlear point, 11.0 mm from the medial arch point, and 21.3 mm from the posterior point. The PMB was 8.6 mm from the articular cartilage edge distally and was triangulated at 18.8 mm from the trochlear point, 11.1 mm from the medial arch point, and 10.8 mm from the posterior point. The bundle centers were found to be 12.1 mm apart (Fig 10). Lopes et al.37 used a 3D digitizer camera to create a 3D model of the PCL in 20 cadaveric knees and evaluated the location of the femoral origin of the PCL. Relative to the medial intercondylar ridge (Fig 11), the center of the PCL was found to be 4.36 mm away, the center of the ALB was 3.63 mm away, and the PMB
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ANATOMY OF FEMORAL FOOTPRINT OF PCL
Fig 8. Method of determining the distance between the femoral insertion center and the anterior articular cartilage and the notch used by Takahashi et al.35 The distance from the anterior articular surface is parallel to the Blumensaat line. The distance from the notch is perpendicular to the Blumensaat line. Reprinted from with kind permission from Springer Science and Business Media.35
was 3.13 mm away. Relative to the articular cartilage edge, the ALB was 7 mm away and the PMB was 8 mm away; however, the study did not specify which articular cartilage edge was being referenced. In addition, the center of the ALB and the center of the PMB were found to be 11 mm apart. In another modeling study, Raphael et al.38 created 2-dimensional and 3D computer-generated reconstructions of the distal femur based on 7 cadaveric dissections. On the 2dimensional reconstruction, the ALB and PMB were 8.3 mm and 8.5 mm, respectively, from the border of the articular cartilage along the ridge formed by the medial femoral condyle and the notch wall. On the 3D reconstruction, the ALB and PMB were 9.2 mm and 8.9 mm, respectively, from the cartilage border. In addition, use of the 3D reconstruction showed that the ALB originated from the roof of the intercondylar notch in 5 of 7 specimens whereas the PMB originated in the transition between the roof and the wall of the medial femoral condyle. However, similar to the study by Lopes et al., which cartilage border was being referenced was not specified exactly for any of these measurements. Table 2 summarizes the data from the aforementioned cadaveric studies that evaluated the femoral
Fig 9. Anterior view of a left knee flexed to 90 showing the trochlear point, medial arch point, and posterior point.
origin of the PCL using similar measurement techniques. Taken together, the data place the center of the ALB 8 mm from the anterior surface (27.5% of the Blumensaat line) and 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and they place the center of the PMB 11.9 mm from the anterior articular surface (42.5%) and 10.9 mm along the tangent line (57.5%). Relative to the medial intercondylar ridge, the only available cadaveric data show the ALB to be 3.63 mm away and the PMB to be 3.13 mm away. These numbers are compared with 6.1 mm and 5.5 mm for the ALB and PMB, respectively, based on the fluoroscopic data of Johannsen et al.29
Discussion The results of our review summarize the radiographic and cadaveric descriptions of the femoral
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S. J. NARVY ET AL. Fig 10. (A) Anterolateral portal view of a right knee flexed to 90 in a supine patient. The ligamentous structures have been removed to clearly depict the femoral attachment of the PCL in a right knee and show the pertinent landmarks. (aMFL, anterior meniscofemoral ligament; pMFL, posterior meniscofemoral ligament.) (B) Quantitative measurements for the femoral attachment of the PCL. The distances of the ALB and PMB from the trochlear point, medial arch point, and posterior point are shown in millimeters. Reprinted with permission.36 Available at http:// jbjs.org/content/94/21/1936.long.
footprint of the PCL. These studies used various methods for describing the anatomy. However, the most commonly reported reference points in both the cadaveric and radiographic studies were the anterior cortical edge of the femur and the distance from the intercondylar notch (tangent to the Blumensaat line). Footprint anatomy relative to osseous landmarks seen on open dissection (e.g., the trochlear point, the medial arch point, the posterior point, and the medial epicondylar ridge) may be useful clinically in the setting of arthroscopically assisted PCL reconstruction.
Fig 11. Lateral portal view of left femur with knee flexed to 90 . The asterisks mark the border of the intercondylar ridge.
As shown in Tables 1 and 2, there is no clear overall consensus in the literature regarding the exact location of the ALB or PMB of the PCL when the data are grouped as a whole. As such, our findings parallel similar work by Apsingi et al.,28 who performed a systematic review of the femoral attachment of the PCL with a focus on clock-face values around the notch. They noted considerable variability in the height and depth of the bundle attachments to the notch and recommended that a reproducible system for describing the femoral footprint anatomy be established to help with proper tunnel placement. When grouped individually by study type (radiographically by radiographs, radiographically by CT scans, or cadaveric), the data in this study are far more concordant and may offer more reliable guidance in the clinical setting. Because many knee surgeons already use fluoroscopy to assist with drilling of the PCL’s tibial tunnel, fluoroscopic guidance could also be used to direct placement of the femoral tunnel of a double-bundle reconstruction. Our data indicate the native footprint of the ALB to be 40% from the anterior articular surface and 14.5% of the tangent; 56% and 36.5%, respectively, for the PMB; and 67.5% and 30%, respectively, for a single-bundle reconstruction. For those surgeons who wish to place their femoral tunnels without fluoroscopy, cadaveric data place the center of the ALB 8 mm from the anterior surface (27.5% of the Blumensaat line) and 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance) and place the PMB 11.9 mm from the anterior articular surface (42.5%) and 10.9 mm along the tangent line (57.5%). For single-bundle reconstructions of the PCL, there are, unfortunately, no cadaveric data available to help guide femoral tunnel placement. Finally, we posit that the 3 anatomic points along the distal articular cartilage margin (trochlear point, medial arch point, and posterior point) described by Anderson
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ANATOMY OF FEMORAL FOOTPRINT OF PCL Table 2. Results From Cadaveric Dissection Studies Center of ALB
Edwards et al.34 Takahashi et al.35 Osti et al.31
Distance From Anterior Articular Surface 7 mm 9.6 mm (29%) 7.48 mm (26%)
Center of PMB
Tangent Distance From Blumensaat Line Toward Notch 6 mm 4.8 mm (25%) 3.43 mm (20%)
et al.36 can be used as reference points for femoral tunnel reconstruction (Fig 9). These reference points are best appreciated with the knee flexed to 90 and can be used for single- or double-bundle reconstruction. Limitations This study does have limitations. First, this review was limited to studies published in the past 10 years to provide a more up-to-date evaluation of the current literature and therefore excluded older studies that may have provided different information regarding the femoral attachment of the PCL. The fairly small number of studies that compared the PCL femoral anatomy with sufficiently similar measurement methods also further limited our data points. In addition, the cadaveric dissections were often from older donors, whose anatomy could theoretically differ from that of younger patients who are more likely to have sustained a PCL injury. Nonetheless, we believe that the information derived from this study will assist arthroscopic knee surgeons in placing anatomic tunnels when reconstructing the PCL.
Conclusions This systematic review indicates that the anatomic origin of the ALB, on the basis of radiographic parameters, lies 40% of the distance from the anterior surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch and that the origin of the PMB lies 56% from the anterior surface and 36.5% of the tangent distance. On the basis of cadaveric data, the center of the ALB is 8 mm from the anterior articular surface (27.5% of the Blumensaat line), 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and 3.6 mm from the medial intercondylar ridge; the center of the PMB is 11.9 mm from the anterior articular surface (42.5%), 10.9 mm along the tangent line (57.5%), and 3.1 mm from the medial intercondylar ridge. These data may aid arthroscopic knee surgeons in placing anatomic tunnels during reconstruction of the PCL.
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Tangent Distance From Blumensaat Line Toward Notch 12 mm 11.4 mm (60%) 9.43 mm (55%)
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28.
S. J. NARVY ET AL. double-bundled “anatomic” grafts. J Bone Joint Surg Br 1998;80:173-179. Galloway M, Grood E, Mehalik J, Levy M, Saddler S, Noyes F. Posterior cruciate ligament reconstruction. An in vitro study of femoral and tibial graft placement. Am J Sport Med 1996;24:437-445. McGuire DA, Hendricks SD. Comparison of anatomic versus nonanatomic placement of femoral tunnels in Achilles double-bundle posterior cruciate ligament reconstruction. Arthroscopy 2010;26:658-666. Ziegler CG, Pietrini SD, Westerhaus BD, et al. Arthroscopically pertinent landmarks for tunnel positioning in single-bundle and double-bundle anterior cruciate ligament reconstructions. Am J Sports Med 2011;39:743-752. Garofalo R, Jolles BM, Moretti B, Siegrist O. Doublebundle transtibial posterior cruciate ligament reconstruction with a tendon-patellar bone-semitendinosus tendon autograft: Clinical results with a minimum of 2 years’ follow-up. Arthroscopy 2006;22:1331-1338.e1. Lipscomb AJ, Anderson A, Norwin E, Hovis W, Brown D. Isolated posterior cruciate ligament reconstruction. Longterm results. Am J Sport Med 1993;21:490-496. May JH, Gillette BP, Morgan JA, Krych AJ, Stuart MJ, Levy BA. Transtibial versus inlay posterior cruciate ligament reconstruction: An evidence-based systematic review. J Knee Surg 2010;23:73-79. Panchal HB, Sekiya JK. Open tibial inlay versus arthroscopic transtibial posterior cruciate ligament reconstructions. Arthroscopy 2011;27:1289-1295. Sidles JA, Larson RV, Garbini JL, Downey DJ, Matsen FA. Ligament length relationships in the moving knee. J Orthop Res 1988;6:593-610. Azzam MG, Lenarz CJ, Farrow LD, Israel HA, Kieffer DA, Kaar SG. Inter- and intraobserver reliability of the clock face representation as used to describe the femoral intercondylar notch. Knee Surg Sports Traumatol Arthrosc 2011;19:1265-1270. Colvin AC, Shen W, Musahl V, Fu FH. Avoiding pitfalls in anatomic ACL reconstruction. Knee Surg Sports Traumatol Arthrosc 2009;17:956-963. Apsingi S, Bull AMJ, Deehan DJ, Amis AA. Review: Femoral tunnel placement for PCL reconstruction in relation to the PCL fibre bundle attachments. Knee Surg Sports Traumatol Arthrosc 2009;17:652-659.
29. Johannsen A, Anderson C, Wijdicks C, Engebretsen L, LaPrade R. Radiographic landmarks for tunnel positioning in posterior cruciate ligament reconstructions. Am J Sport Med 2013;41:35-42. 30. Lorenz S, Elser F, Brucker PU, Obst T, Imhoff AB. Radiological evaluation of the anterolateral and posteromedial bundle insertion sites of the posterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc 2009;17: 683-690. 31. Osti M, Tschann P, Kunzel KH, Benedetto KP. Anatomic characteristics and radiographic references of the anterolateral and posteromedial bundles of the posterior cruciate ligament. Am J Sports Med 2012;40: 1558-1563. 32. Greiner P, Magnussen RA, Lustig S, Demey G, Neyret P, Servien E. Computed tomography evaluation of the femoral and tibial attachments of the posterior cruciate ligament in vitro. Knee Surg Sport Traumatol Arthrosc 2011;19:1876-1883. 33. Westermann RW, Sybrowsky C, Ramme AJ, Amendola A, Wolf BR. Three-dimensional characterization of the femoral footprint of the posterior cruciate ligament. Arthroscopy 2013;29:1811-1816. 34. Edwards A, Bull AMJ, Amis AA. The attachments of the fiber bundles of the posterior cruciate ligament: An anatomic study. Arthroscopy 2007;23:284-290. 35. Takahashi M, Matsubara T, Doi M, Suzuki D, Nagano A. Anatomical study of the femoral and tibial insertions of the anterolateral and posteromedial bundles of human posterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc 2006;14:1055-1059. 36. Anderson CJ, Ziegler CG, Wijdicks CA, Engebretsen L, LaPrade RF. Arthroscopically pertinent anatomy of the anterolateral and posteromedial bundles of the posterior cruciate ligament. J Bone Joint Surg Am 2012;94: 1936-1945. 37. Lopes OJ, Feretti M, Shen W, Ekdahl M, Smolinski P, Fu F. Topography of the femoral attachment of the posterior cruciate ligament. J Bone Joint Surg Am 2008;90: 249-255. 38. Raphael BS, Maak T, Cross MB, et al. From wall graft to roof graft: Reassessment of femoral posterior cruciate ligament positioning. Am J Orthop (Belle Mead NJ) 2011;40: 479-484.
Anatomy of the Femoral Footprint of the Posterior Cruciate Ligament: A Systematic Review Steven J. Narvy, M.D., Matthew Pearl, B.S., Michael Vrla, B.S., Anthony Yi, B.S., and George F. Rick Hatch III, M.D.
Purpose: The purpose of this study was to summarize the past 10 years of orthopaedic literature to better delineate the femoral origin of the posterior cruciate ligament (PCL). Methods: A PubMed search was conducted by 2 independent reviewers (M.P., M.V.) using the search terms “posterior cruciate ligament” or “PCL,” “femur” or “femoral,” and “anatomy” or “origin” or “footprint.” Cadaveric and radiographic studies performed between January 1, 2003, and November 30, 2013, were analyzed. Results: Aggregate data from radiographic parameters indicate that the anatomic origin of the anterolateral bundle lies 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch. The origin of the posteromedial bundle lies 56% from the anterior surface and 36.5% of the tangent distance toward the notch. On the basis of cadaveric data, the center of the anterolateral bundle is 8 mm from the anterior surface (27.5% of the Blumensaat line), 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and 3.6 mm from the medial intercondylar ridge; the center of the posteromedial bundle is 11.9 mm from the anterior articular surface (42.5%), 10.9 mm along the tangent line (57.5%), and 3.1 mm from the medial intercondylar ridge. Conclusions: We were able to precisely delineate the femoral origin of the PCL through our systematic review. Clinical Relevance: Our systematic review may assist arthroscopic knee surgeons in placing anatomic tunnels during reconstruction of the PCL.
T
he posterior cruciate ligament (PCL) provides the primary restraint to posterior tibial translation and acts as a secondary restraint to tibial valgus, varus, and external rotation.1-3 The ligament consists of 2 functional bundles, a larger anterolateral bundle (ALB) and a smaller posteromedial bundle (PMB).4 The ALB has greater cross-sectional area and strength relative to the PMB. The ALB maintains nearly double the ultimate load of the PMB.5,6 Each bundle has a different tensioning pattern depending on the degree of knee flexion. The ALB is taut in knee flexion and loose in knee extension, whereas the PMB is taut in knee extension and loose in knee flexion.4,7 Recent
From the Department of Orthopaedic Surgery, University of Southern California Keck School of Medicine, Los Angeles, California, U.S.A. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received April 22, 2014; accepted July 3, 2014. Address correspondence to George F. Rick Hatch III, M.D., Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, 1520 San Pablo St, Ste 2000, Los Angeles, CA 90089, U.S.A. E-mail: [email protected] Ó 2014 by the Arthroscopy Association of North America 0749-8063/14342/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.07.004
biomechanical studies suggest that the 2 bundles of the PCL may have a co-dominant relation, functioning in a synergistic fashion throughout the range of motion.8 Injuries to the PCL are far less common than injuries to other knee structures, such as the anterior cruciate ligament (ACL) or the menisci. The incidence of PCL injuries has varied dramatically in the literature, ranging from 3% in the general population9 to as high as 38% in the trauma setting in patients with acute knee hemarthrosis.10,11 Although many isolated PCL injuries are successfully treated nonoperatively, instability, pain, arthrosis, and compromised knee function develop in some patients with PCL-deficient knees.12,13 In addition, it has been found that the clinical outcomes of PCL reconstruction are less satisfactory and less predictable relative to those of ACL reconstruction.13,14 Consequently, increasing attention has been directed toward PCL reconstruction with respect to PCL anatomy and graft placement. Data indicating improved clinical outcomes with anatomic reconstruction of the cruciate ligaments are becoming increasingly commonplace in the literature.15,16 Although evidence may be stronger for anatomic reconstruction of the ACL, data are mounting for PCL reconstruction as well.17-22 Biomechanically, it
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has been shown that the tibial-inlay technique eliminates graft abrasion and decreases graft laxity14; however, this has not translated into improved clinical outcomes in patients undergoing the tibial-inlay versus transtibial technique of PCL reconstruction.23,24 One possible explanation for the persistent posterior tibial laxity is femoral tunnel positioning.5,8,25 Anatomic reconstruction on the femoral side requires an accurate and reproducible method to guide tunnel placement. The “clock-face” method has been frequently reported as a guide for femoral tunnel placement; however, poor reproducibility has been noted among surgeons who use this method.26-28 Numerous basic science studies have sought to characterize the location of the femoral footprint of the PCL. There remains, however, significant disagreement regarding the exact location of the PCL femoral footprint in the published literature. The purpose of this study was to examine recent literature in an effort to better characterize the precise location of the femoral origin of the PCL.
Methods Before conducting the literature search, we established our specific study objective of characterizing the femoral origin of the PCL. A PubMed search was conducted by 2 independent reviewers (M.P., M.V.) using the search terms “posterior cruciate ligament” or “PCL,” “femur” or “femoral,” and “anatomy” or “origin” or “footprint.” General search terms were chosen to prevent the possibility of missing potential studies. The inclusion criteria were cadaveric and radiographic studies on human subjects published between January 1, 2003, and November 30, 2013. Studies written in a language other than English, studies focused on surgical treatment or clinical outcomes, and review articles were excluded from analysis. References from identified studies were manually searched to identify additional articles that may have been missed by our search. Data were abstracted from each study that met the inclusion criteria by 2 independent reviewers (M.P., M.V.). Data were then compiled and categorized based on study design.
Results Our initial search produced 188 articles. The abstracts were reviewed, and the search was narrowed to 108 articles. After full review of these articles and citations from these articles, 10 studies met our final inclusion criteria. Four studies evaluated the PCL’s femoral origin on the basis of radiographic findings alone. Five studies described the femoral origin of the PCL on the basis of cadaveric dissection only. One study included both radiographic and cadaveric data. Of the radiographic studies, 3 were based on plain radiography and 2 were based on computed
Fig 1. Radiographic anteroposterior femur view. Using a measurement axis generated based on the distal condyle line, Johannsen et al.29 found that the centers of the ALB and PMB were 34.1 and 29.2 mm lateral to the most medial border of the medial femoral condyle, respectively. Relative to the medial intercondylar ridge, the ALB was 6.1 mm away and the PMB was 5.2 mm away. Reprinted by Permission of SAGE Publications.29
tomography (CT). A brief synopsis of these articles is presented in this article. Radiographic Findings Johannsen et al.29 obtained fluoroscopic images of 20 cadaveric knees in which the ALB and PMB had been dissected and marked. On the anteroposterior view, the centers of the ALB and PMB were 34.1 and 29.2 mm lateral to the most medial border of the medial femoral condyle, respectively (Fig 1). Relative to the medial intercondylar ridge, the ALB was 6.1 mm away and the PMB was 5.2 mm away. On the lateral view, the ALB center and PMB center were 17.4 mm and 23.9 mm posteroproximal to the anterior cortex line of the femoral condyles along a reference line parallel with the Blumensaat line, respectively (Fig 2). In addition, the ALB and PMB were 6.1 mm and 5.5 mm away from the medial intercondylar ridge, respectively. Two studies evaluated the femoral origin of the separate bundles of the PCL using a different radiographic metric. Lorenz et al.30 dissected out the femoral origin of the PCL in 16 cadaveric specimens, separately marking the ALB and the PMB with copper wire, and standard anteroposterior and lateral knee radiographs
ANATOMY OF FEMORAL FOOTPRINT OF PCL
Fig 2. Radiographic lateral femur view. Johannsen et al.29 found that the ALB and PMB centers were 17.4 mm and 23.9 mm posteroproximal to the anterior cortex line of the femoral condyles along a reference line parallel with the Blumensaat line, respectively. Reprinted by Permission of SAGE Publications.29
were taken. On the lateral radiographs, the center of the ALB was 62% of the way from posterior to anterior along an extended Blumensaat line that intersected the posterior cortex of the femur and 16% of the tangent distance from the Blumensaat line to the most posterior point of the medial femoral condyle (Fig 3). The center of the PMB was 51% from posterior to anterior along the Blumensaat line and 35% more posterior along the tangent line (Fig 3). Osti et al.31 used the same radiographic grid method to measure the ALB and PMB femoral footprints but reported measurements in the opposite orientation (anterior to posterior). They found the ALB to be 42% of the way along the extended Blumensaat line, from anterior to posterior, and 13% of the tangent distance, whereas the PMB was 63% of the way along the extended Blumensaat line, from anterior to posterior, and 38% of the way along the tangent line based on the lateral radiographs. Two additional studies used CT imaging to describe the femoral origin of the PCL overall, without defining
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Fig 3. Average geometric midpoint of the ALB (white) (x ¼ 62% 3%/y ¼ 16% 6%) and PMB (black) (x ¼ 51% 5%/y ¼ 35% 7%) as determined by Lorenz et al.,30 who used the modified quadrant method. Using lateral radiographic images, Lorenz et al. found that the center of the ALB (white) was 62% of the way from posterior to anterior along an extended Blumensaat line that intersected the posterior cortex of the femur and 16% of the tangent distance from the Blumensaat line to the most posterior point of the medial femoral condyle. The center of the PMB (black) was 51% from posterior to anterior along the Blumensaat line and 35% more posterior along the tangent line. Reprinted from with kind permission from Springer Science and Business Media.30
the bundles separately. Greiner et al.32 dissected out the femoral origin of the PCL in 10 cadaveric knees, placed pins around the femoral origin, and then obtained CT scans of the specimens. The mean surface area of the femoral origin of the PCL was 232.2 mm2. The mean distance from the center of attachment to the roof of the notch was 8.9 mm, which corresponds to 34.7% of the total length of the Blumensaat line (Fig 4). The mean distance from the center of insertion onto the anterior articular cartilage surface was 18.7 mm, which corresponds to 73.3% of the length of the Blumensaat line. Westermann et al.33 dissected out the PCL origin on the medial femoral condyle in 7 cadavers, marked the femoral footprint with K-wires, and then used CT imaging to create a 3-dimensional (3D) surface reconstruction of the distal femur. Although the individual ALB and PMB of the PCL
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Fig 4. Blumensaat line (gold line) and measurements taken from the center of the PCL origin toward the roof of the notch (blue line) and toward the anterior articular margin (red line). Using these relations, Greiner et al.32 found that the mean surface area of the femoral origin of the PCL was 232.2 mm2 (oval). The mean distance from the center of attachment to the roof of the notch was 8.9 mm (blue line). The mean distance from the center of insertion to the anterior articular cartilage surface was 18.7 mm (red line). Reprinted from with kind permission from Springer Science and Business Media.32
were not defined, the authors determined the center point of the PCL overall to be 38% from anterior to posterior from the anterior condyle (parallel to the Blumensaat line) and 25% of the way down from the roof of the notch (distance from notch roof to distal-most aspect of medial femoral condyle, perpendicular to notch axis/Blumensaat line) (Fig 5). Table 1 and Figure 6 summarize the data from the aforementioned studies that evaluated the femoral origin of the PCL using similar measurement techniques. Taken as a whole, these data pinpoint the anatomic center of the ALB to be 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch and the PMB to be 56% from the anterior surface and 36.5% of the tangent distance. When the individual bundles are not considered, the overall center of the PCL is 67.5% from
Fig 5. Relations used by Westermann et al.33 in assessing the position of the PCL in relation to the size of the medial femoral condyle, with specimens oriented along the axis of the intercondylar notch. (c, distance from posterior femoral condyle border of PCL; C, total anteroposterior distance of condyle parallel to axis of notch; n, distance from notch roof to boundary; N, distance from notch roof to distal-most aspect of condyle, perpendicular to axis of notch.) Reprinted from Arthroscopy, Volume 29, Westermann R.W., Sybrowsky C., Ramme A.J., Amendola A., Wolf B.R., Three-dimensional characterization of the femoral footprint of the posterior cruciate ligament, 1811-1816, Ó 2014, with permission from the Arthroscopy Association of North America.33
the anterior surface of the femur and 30% of the tangent distance. Cadaveric Dissections Edwards et al.34 defined the centers of the ALB and PMB on a low/high axis and a shallow/deep axis relative to the diameter of a circle outlining the posterior medial femoral condyle, as well as by the distance from the cartilage edge relative to lines parallel to the long axis of the femur and parallel to the Blumensaat line (Fig 7). The ALB center was 11 mm from the “low” posterior, medial condyle margin along the low/high axis (29% of the femoral condyle diameter); 6 mm from the “deep” posterior, medial condyle margin along the shallow/deep axis (17% of the femoral condyle diameter); 7 mm from the cartilage edge parallel to the long axis of the femur; and 6 mm tangent from the cartilage edge parallel to the Blumensaat line (Fig 7). The PMB center was 2 mm from the low posterior, medial condyle margin along the low/high axis (6% of the femoral condyle diameter); 4 mm from the deep posterior, medial condyle margin
18.7 mm (73%) Distance not measured (62%)
Distance From Anterior Articular Surface
8.9 mm (35%) Distance not measured (25%)
Tangent Distance From Blumensaat Line Toward Notch
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Tangent Distance From Blumensaat Line Toward Notch Distance not measured (35%) 9.3 mm (38%) Type of Study Radiographs
Radiographs CT scans CT scans
Lorenz et al.30
Osti et al.31 Greiner et al.32 Westermann et al.33
Center of PMB
Distance From Anterior Articular Surface Distance not measured (49%) 30.9 mm (63%) Tangent Distance From Blumensaat Line Toward Notch Distance not measured (16%) 3.3 mm (13%)
Center of ALB
Table 1. Results of Radiographic Studies
Distance From Anterior Articular Surface Distance not measured (38%) 20.7 mm (42%)
Center of PCL Bundle
ANATOMY OF FEMORAL FOOTPRINT OF PCL
Fig 6. Summary depiction of aggregate radiographic data. The first percentage listed for each point represents the percentage of the distance from the anterior to posterior articular surface of the femur. The second percentage listed represents the percentage of the tangent distance from the Blumensaat line toward the intercondylar notch. The ALB lies 40% of the distance from the anterior articular surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch. The origin of the PMB lies 56% of the distance from the anterior surface and 36.5% of the tangent distance toward the notch. The overall center of the PCL is 67.5% from the anterior surface of the femur and 30% of the tangent distance.
along the shallow/deep axis (10% of the femoral condyle diameter); 10 mm from the cartilage edge parallel to the long axis of the femur; and 12 mm tangent from the cartilage edge parallel to the Blumensaat line. Takahashi et al.35 performed similar anatomic measurements on the femoral origin of the ALB and PMB based on dissection of 32 cadaveric specimens. The distance to the center of insertion of each bundle was measured from the anterior border of the articular cartilage and relative to the roof of the intercondylar notch (perpendicular to the Blumensaat line) (Fig 8) The ALB was 9.6 mm from the anterior border (29% of the length of the Blumensaat line) and 4.8 mm from the notch (25% of the longest length between the distal border of the articular cartilage and the Blumensaat line). The PMB was 10.6 mm from the
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Fig 7. Measurement systems used by Edwards et al.34 on medial femoral condyle. Edwards et al. defined the center of the ALB and PMB on a low/ high axis and a shallow/deep axis relative to the diameter of a circle outlining the posterior medial femoral condyle (left). They also measured the distance of the bundles from the cartilage edge relative to lines parallel to the long axis of the femur and parallel to the Blumensaat line (right). Reprinted from Arthroscopy, Volume 23, Edwards A., Bull A.M.J., Amis A.A., The attachments of the fiber bundles of the posterior cruciate ligament: An anatomic study, 284-290, Ó 2007, with permission from the Arthroscopy Association of North America.34
anterior border (32% of the length of the Blumensaat line) and 11.4 mm above the notch (60% of the longest length between the distal border of the articular cartilage and the Blumensaat line). Similarly, the cadaveric dissection arm of the study by Osti et al.31 noted the ALB to be 7.5 mm from the anterior articular surface (26% of an extended Blumensaat line that intersected the posterior cortex of the femur) and 3.43 mm from the notch (20% of the way along a line tangent to the Blumensaat line directed toward the distal femur); the PMB was 15.1 mm from the anterior border (53%) and 9.4 mm from the notch (55%). Anderson et al.36 determined the femoral attachment of the bundles based on 20 cadaveric dissection specimens. Three distinct anatomic points along the distal articular cartilage margin of the intercondylar notch were defined: the “trochlear point,” medial to the apex of the notch, where the articular cartilage abruptly turned medially; the “medial arch point,”
where the cartilage orientation became straight posterior after a smooth arch from the trochlear point; and the “posterior point,” which marked the most posterior extent of the articular cartilage of the medial femoral condyle (Fig 9). The ALB center was 7.9 mm from the articular cartilage distally and was triangulated at 7.4 mm from the trochlear point, 11.0 mm from the medial arch point, and 21.3 mm from the posterior point. The PMB was 8.6 mm from the articular cartilage edge distally and was triangulated at 18.8 mm from the trochlear point, 11.1 mm from the medial arch point, and 10.8 mm from the posterior point. The bundle centers were found to be 12.1 mm apart (Fig 10). Lopes et al.37 used a 3D digitizer camera to create a 3D model of the PCL in 20 cadaveric knees and evaluated the location of the femoral origin of the PCL. Relative to the medial intercondylar ridge (Fig 11), the center of the PCL was found to be 4.36 mm away, the center of the ALB was 3.63 mm away, and the PMB
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Fig 8. Method of determining the distance between the femoral insertion center and the anterior articular cartilage and the notch used by Takahashi et al.35 The distance from the anterior articular surface is parallel to the Blumensaat line. The distance from the notch is perpendicular to the Blumensaat line. Reprinted from with kind permission from Springer Science and Business Media.35
was 3.13 mm away. Relative to the articular cartilage edge, the ALB was 7 mm away and the PMB was 8 mm away; however, the study did not specify which articular cartilage edge was being referenced. In addition, the center of the ALB and the center of the PMB were found to be 11 mm apart. In another modeling study, Raphael et al.38 created 2-dimensional and 3D computer-generated reconstructions of the distal femur based on 7 cadaveric dissections. On the 2dimensional reconstruction, the ALB and PMB were 8.3 mm and 8.5 mm, respectively, from the border of the articular cartilage along the ridge formed by the medial femoral condyle and the notch wall. On the 3D reconstruction, the ALB and PMB were 9.2 mm and 8.9 mm, respectively, from the cartilage border. In addition, use of the 3D reconstruction showed that the ALB originated from the roof of the intercondylar notch in 5 of 7 specimens whereas the PMB originated in the transition between the roof and the wall of the medial femoral condyle. However, similar to the study by Lopes et al., which cartilage border was being referenced was not specified exactly for any of these measurements. Table 2 summarizes the data from the aforementioned cadaveric studies that evaluated the femoral
Fig 9. Anterior view of a left knee flexed to 90 showing the trochlear point, medial arch point, and posterior point.
origin of the PCL using similar measurement techniques. Taken together, the data place the center of the ALB 8 mm from the anterior surface (27.5% of the Blumensaat line) and 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and they place the center of the PMB 11.9 mm from the anterior articular surface (42.5%) and 10.9 mm along the tangent line (57.5%). Relative to the medial intercondylar ridge, the only available cadaveric data show the ALB to be 3.63 mm away and the PMB to be 3.13 mm away. These numbers are compared with 6.1 mm and 5.5 mm for the ALB and PMB, respectively, based on the fluoroscopic data of Johannsen et al.29
Discussion The results of our review summarize the radiographic and cadaveric descriptions of the femoral
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S. J. NARVY ET AL. Fig 10. (A) Anterolateral portal view of a right knee flexed to 90 in a supine patient. The ligamentous structures have been removed to clearly depict the femoral attachment of the PCL in a right knee and show the pertinent landmarks. (aMFL, anterior meniscofemoral ligament; pMFL, posterior meniscofemoral ligament.) (B) Quantitative measurements for the femoral attachment of the PCL. The distances of the ALB and PMB from the trochlear point, medial arch point, and posterior point are shown in millimeters. Reprinted with permission.36 Available at http:// jbjs.org/content/94/21/1936.long.
footprint of the PCL. These studies used various methods for describing the anatomy. However, the most commonly reported reference points in both the cadaveric and radiographic studies were the anterior cortical edge of the femur and the distance from the intercondylar notch (tangent to the Blumensaat line). Footprint anatomy relative to osseous landmarks seen on open dissection (e.g., the trochlear point, the medial arch point, the posterior point, and the medial epicondylar ridge) may be useful clinically in the setting of arthroscopically assisted PCL reconstruction.
Fig 11. Lateral portal view of left femur with knee flexed to 90 . The asterisks mark the border of the intercondylar ridge.
As shown in Tables 1 and 2, there is no clear overall consensus in the literature regarding the exact location of the ALB or PMB of the PCL when the data are grouped as a whole. As such, our findings parallel similar work by Apsingi et al.,28 who performed a systematic review of the femoral attachment of the PCL with a focus on clock-face values around the notch. They noted considerable variability in the height and depth of the bundle attachments to the notch and recommended that a reproducible system for describing the femoral footprint anatomy be established to help with proper tunnel placement. When grouped individually by study type (radiographically by radiographs, radiographically by CT scans, or cadaveric), the data in this study are far more concordant and may offer more reliable guidance in the clinical setting. Because many knee surgeons already use fluoroscopy to assist with drilling of the PCL’s tibial tunnel, fluoroscopic guidance could also be used to direct placement of the femoral tunnel of a double-bundle reconstruction. Our data indicate the native footprint of the ALB to be 40% from the anterior articular surface and 14.5% of the tangent; 56% and 36.5%, respectively, for the PMB; and 67.5% and 30%, respectively, for a single-bundle reconstruction. For those surgeons who wish to place their femoral tunnels without fluoroscopy, cadaveric data place the center of the ALB 8 mm from the anterior surface (27.5% of the Blumensaat line) and 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance) and place the PMB 11.9 mm from the anterior articular surface (42.5%) and 10.9 mm along the tangent line (57.5%). For single-bundle reconstructions of the PCL, there are, unfortunately, no cadaveric data available to help guide femoral tunnel placement. Finally, we posit that the 3 anatomic points along the distal articular cartilage margin (trochlear point, medial arch point, and posterior point) described by Anderson
9
ANATOMY OF FEMORAL FOOTPRINT OF PCL Table 2. Results From Cadaveric Dissection Studies Center of ALB
Edwards et al.34 Takahashi et al.35 Osti et al.31
Distance From Anterior Articular Surface 7 mm 9.6 mm (29%) 7.48 mm (26%)
Center of PMB
Tangent Distance From Blumensaat Line Toward Notch 6 mm 4.8 mm (25%) 3.43 mm (20%)
et al.36 can be used as reference points for femoral tunnel reconstruction (Fig 9). These reference points are best appreciated with the knee flexed to 90 and can be used for single- or double-bundle reconstruction. Limitations This study does have limitations. First, this review was limited to studies published in the past 10 years to provide a more up-to-date evaluation of the current literature and therefore excluded older studies that may have provided different information regarding the femoral attachment of the PCL. The fairly small number of studies that compared the PCL femoral anatomy with sufficiently similar measurement methods also further limited our data points. In addition, the cadaveric dissections were often from older donors, whose anatomy could theoretically differ from that of younger patients who are more likely to have sustained a PCL injury. Nonetheless, we believe that the information derived from this study will assist arthroscopic knee surgeons in placing anatomic tunnels when reconstructing the PCL.
Conclusions This systematic review indicates that the anatomic origin of the ALB, on the basis of radiographic parameters, lies 40% of the distance from the anterior surface of the femur and 14.5% of the tangent distance from the Blumensaat line toward the intercondylar notch and that the origin of the PMB lies 56% from the anterior surface and 36.5% of the tangent distance. On the basis of cadaveric data, the center of the ALB is 8 mm from the anterior articular surface (27.5% of the Blumensaat line), 4.7 mm tangent from the Blumensaat line toward the notch (22.5% of the tangent distance), and 3.6 mm from the medial intercondylar ridge; the center of the PMB is 11.9 mm from the anterior articular surface (42.5%), 10.9 mm along the tangent line (57.5%), and 3.1 mm from the medial intercondylar ridge. These data may aid arthroscopic knee surgeons in placing anatomic tunnels during reconstruction of the PCL.
References 1. Butler DL, Noyes FR, Grood ES. Ligamentous restraints to anterior-posterior drawer in the human knee. A biomechanical study. J Bone Joint Surg Am 1980;62:259-270.
Distance From Anterior Articular Surface 10 mm 10.6 mm (32%) 15.1 mm (53%)
Tangent Distance From Blumensaat Line Toward Notch 12 mm 11.4 mm (60%) 9.43 mm (55%)
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