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Posterior Cruciate Ligament Tibial Insertion Anatomy and Implications for Tibial Tunnel Placement
Posterior Cruciate Ligament Tibial Insertion Anatomy and Implications for Tibial Tunnel Placement Yong Seuk Lee, M.D., Ho Jong Ra, M.D., Jin Hwan Ahn, M.D., Jeong Ku Ha, M.D., and Jin Goo Kim, M.D.
Purpose: The purposes of this study were (1) to predict the tibial insertion of the posterior cruciate ligament (PCL) and posterior cortex that aligned with the tibial tunnel (PCTT) by use of 2-dimensional plain radiographs by evaluating the relation between plain radiograph and computed tomography (CT) images and (2) to determine the safe angle of the tibial guide for preventing breakage of the posterior cortex. Methods: In 10 fresh cadaveric tibias, the soft tissues were dissected and the tibial footprint of the PCL was identified. The insertion of the PCL, the longest distance from the PCTT to the posterior cortex that aligned with the tibial plateau (PCTP), and the possible maximum angle of the tibial guide to the most posteriorly positioned cortical line were measured from simple anteroposterior (AP) and lateral radiographs, as well as CT. Results: The mean tibial insertion of the PCL from the joint line was located between 5.9 ⫾ 1.1 and 17.4 ⫾ 2.4 mm on the simple AP radiographs and between 2.2 ⫾ 1.2 and 12.3 ⫾ 1.5 mm on the simple lateral radiographs (P ⫽ .005). The PCL insertion was from the posterior 48% of the area of the posterior intercondylar fossa to the posterior cortex. The longest distance from the PCTT to the PCTP was 10.8 ⫾ 2.2 mm. The maximum angle of the tibial guide to the PCTT possible on CT and the PCTP on lateral radiographs was 52° ⫾ 5° and 62° ⫾ 4.5°, respectively (P ⫽ .005). Conclusions: The mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the PCL fovea to the posterior cortex. The maximum possible angle of the tibial guide to the PCTT based on CT was 52°. Therefore the angle of the tibial guide pin must be limited for tibial footprint reconstruction to prevent posterior wall breakage. Clinical Relevance: Increasing the tibial guide angle may have some advantages, but there is a limit because of posterior wall breakage.
A
s we have seen in anterior cruciate ligament reconstruction, re-creation of the normal anatomy gives superior results.1-3 Less attention has been
From the Department of Orthopedic Surgery, Ajou University School of Medicine (Y.S.L.), Suwon; Department of Orthopedic Surgery, Barun Hospital (H.J.R.), Jinju; Department of Orthopedic Surgery, Inje University, Seoul Paik Hospital (J.K.H., J.G.K.), Seoul; and Department of Orthopedic Surgery, SungKunkwan University, Samsung Medical Center (J.H.A.), Seoul, South Korea. The authors report no conflict of interest. Received November 10, 2009; accepted June 23, 2010. Address correspondence and reprint requests to Jin Goo Kim, M.D., Ph.D., Department of Orthopedic Surgery, Inje University, Seoul Paik Hospital, Jeo Dong 2 Ga, Gung Gu, Seoul, South Korea. E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/9667/$36.00 doi:10.1016/j.arthro.2010.06.024
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paid to the placement of the tibial tunnel during posterior cruciate ligament (PCL) reconstruction than to the femoral tunnel.4 Furthermore, for the tibial tunnel in the PCL, the focus has been to prevent the killerturn effect and neurovascular injury.5-8 The posterior aspect of the proximal tibia has a unique 3-dimensional anatomy compared with the mid or distal tibia, because multiple structures change abruptly, including the tibial plateau, posterior intercondylar fossa, and posterior cortex. The PCL inserts to the sloping central depression between the medial and lateral portions of the tibial plateau, and this insertion is distinct from the vertical cortex of the tibia (Fig 1A and 1B).4 For transtibial PCL reconstruction, plain radiographs or C-arm images are frequently used during the creation of the tibial tunnel. On the lateral plain ra-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 27, No 2 (February), 2011: pp 182-187
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FIGURE 1. (A) Posteroanterior and (B) oblique views. The black arrows indicate the 4 corners of the PCL insertion, and the open arrow marks the transition from the fossa to the posterior tibia. (C) The breakage of the posterior cortex could occur if the angle of the tibial guide increases. (D) Real arthroscopic view from anterior orifice of tibial tunnel.
diograph, the images of the medial and lateral tibial condyles overlap. Consequently, the posterior cortex that aligned with the tibial tunnel (PCTT) appears to be more anterior than the posterior cortex that aligned with the tibial plateau (PCTP). Therefore there is a limit to the increase in the tibial guide angle for tibial footprint reconstruction because of posterior wall breakage. We found some breakage of the posterior cortex in another cadaveric study (Fig 1C) and during a real operation (Fig 1D). In our opinion the possible causes of this breakage may be a posterior orifice that is too low to prevent a too anteriorly positioned tibial tunnel or too large of a tibial guide pin angle to prevent the killer-turn effect. However, there is little information on the radiographic anatomy of the PCL insertion and the relation between the PCTT and the PCTP. The purposes of this study were (1) to predict the tibial insertional point of the PCL and PCTT by use of 2-dimensional plain radiographs by evaluating the relation between plain radiographs and computed to-
mography (CT) images and (2) to determine the safe angle of tibial guide pin for the prevention of breakage of the posterior cortex. The hypothesis of this study was that there would be a limit in increasing the angle of the tibial guide pin in anatomic PCL reconstruction because of breakage of the posterior cortex. METHODS We studied 10 cadaveric knees (5 paired knees [3 from male cadavers and 2 from female cadavers]), with no gross degenerative changes or traumatic changes. The mean age was 51.3 years (range, 34 to 61 years). After the disarticulation of knee joint, the soft tissues were removed except for the tibial footprint of the PCL. Four corners were marked with a drill tip. A screw (industrial use of 4 mm in diameter with an 8-mm head) was inserted at each of the 4 corners of the PCL insertion and at 1-cm intervals in the posterior cortex aligned with the tibial tunnel. The screws were tightened until the screw head was flush
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Y. S. LEE ET AL. graph, the distance was measured from reference lines (Amis and Jakob’s line9: this base line is parallel to the medial tibial plateau and passes through the posterior corner of the tibial shelf) to the central portion of the screw heads of 4 screws that were inserted at each of the 4 corners of the PCL insertion. On the AP radiograph, the reference line was drawn from the edge of the medial tibial plateau to the edge of the lateral tibial plateau. By use of sagittal CT of the posterior intercondylar fossa at 1-mm slices, the ratio of the sagittal insertional length of the PCL to the total length of the entire posterior intercondylar fossa was calculated (Fig 3).4 The distance of the sagittal PCL insertion was measured from the anteriorly positioned screw to the posteriorly positioned screw that was inserted at the corner of the PCL insertion. The longest distance parallel to the reference line (Amis and Jakob’s line) between the PCTT and the PCTP was measured from the lateral radiograph (Fig 4). The maximum tibial guide angles to the PCTP and to the PCTT were assessed with a lateral radiograph and a sagittal CT image of the posterior intercondylar fossa, respectively (Fig 5). We used sagittal CT images for the measurement of maximum guide angle to the PCTT instead of lateral radiographs because CT images were taken from the posterior intercondylar fossa that was aligned to the tibial tunnel, and these
FIGURE 2. The distance from the joint line to the proximal aspect (solid arrow) and distal aspect (open arrow) of the PCL were measured from (A) AP and (B) lateral radiographs. Transverse red lines are reference lines, and longitudinal red lines are distances between the reference line and the central portion of the screw head.
with the surface of the cortex (Fig 1A). In total, 8 screws were inserted. One sports medicine surgeon performed the main procedure, and two assistants helped. Regarding the PCL tibial attachment measurements, simple anteroposterior (AP) and lateral radiographs were taken as shown in Fig 2. The specimens were laid down to the X-ray tube or floor of CT for the AP radiograph and CT images (MDCT; Siemens, Erlangen, Germany). The CT images were taken from the lateral end of the medial tibial plateau to the medial end of the lateral tibial plateau at 1-mm slices. The lateral radiograph was taken perpendicular to the sagittal-plane alignment of the tibia. On the lateral radio-
FIGURE 3. By use of sagittal CT of the posterior intercondylar fossa [long arrow indicates its length], the ratio of the PCL length to the entire length of the PCL facet was calculated. The distance of the sagittal PCL insertion [short arrow indicates its length] was measured from the anteriorly positioned screw to the posteriorly positioned screw that was inserted at the corner of the PCL insertion.
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FIGURE 4. (A) Pre-marked and (B) post-marked lateral radiographs show the position of the PCTT (screw insertion area) and the longest distance parallel to the reference line (Amis and Jakob’s line) from the PCTT (dotted line) to the PCTP (solid line) as measured by use of the lateral radiograph.
were supposed to be more accurate than lateral radiographs. A first transverse line was drawn from the central portion of the PCL insertion, perpendicular to the tibial shaft. A second line was drawn from the central portion of the PCL insertion to a point 5 mm anterior from the first (transition point from the fossa to the posterior tibia) and second cortical screws. We used half of the diameter (5 mm) from the posterior cortex because we usually use a 10-mm-diameter tibial tunnel. All measurements were obtained by use of a picture archiving and communication system (PACS) monitor (General Electric, Chicago, IL) with a mouse point cursor and automated computer calculation of the distance and angle.10 The measurements were taken twice by 2 orthopaedic surgeons to reduce the intraobserver and interobserver bias. A power analysis was performed. We believed that a difference in the angle of more than 5° would be clinically significant because we usually changed the guide angle with 5° intervals. Measurements were assessed by examining the intrarater and inter-rater reliability by use of the intraclass correlation coefficient. The Wilcoxon signed rank test was used with SPSS software (version 15.0; SPSS, Chicago, IL); P ⬍ .05 was deemed to be statistically significant. RESULTS The inter-rater and intrarater reliability ranged from 0.75 to 0.88. If the ␣ was 0.05, the power was 75% with 10 cadavers. The mean tibial insertion of the PCL from the joint line as measured on the AP radiographs (Fig 2A) was 5.9 ⫾ 1.1 mm to the proximal aspect of the PCL and 17.4 ⫾ 2.4 mm to the distal aspect of the PCL. The mean tibial insertion of the PCL from the
joint line as measured on the lateral radiographs (Fig 2B) was 2.2 ⫾ 1.2 mm to the proximal aspect of the PCL and 12.3 ⫾ 1.5 mm to the distal aspect of the PCL. There was a significant difference between the AP and lateral radiographs (P ⫽ .005). The PCL insertion was in the posterior 48% of the area of the posterior intercondylar fossa (Fig 3). The longest distance from the PCTT to the PCTP was 10.8 ⫾ 2.2 mm (Fig 4B). The maximum possible angle of the tibial guide to the PCTT based on CT (Fig 5B) and the PCTP from the lateral radiograph (Fig 5A) was 52° ⫾ 5° and 62° ⫾ 4.5°, respectively. There was a significant difference between the 2 angles (P ⫽ .005). DISCUSSION The principal finding of this study was that the mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the posterior intercondylar fossa, to the posterior cortex. The posterior cortical line can overlap because of the anatomic characteristics of the knee. Therefore the PCTT is different from the PCTP seen on simple lateral radiographs. This indicates that the posterior cortex can break if the tibial tunnel is based on the PCTP seen on simple radiographs. The general orthopaedic principle of surgery replicating the normal anatomy suggests that placement too far from the true anatomic insertion could compromise the function of the graft.4 Several studies have examined the anatomy of the PCL insertion.4,11-13 Girgis et al.14 reported that it was 2 to 3 mm distal to the articular plane, and Takahashi et al.13
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FIGURE 5. (A) The maximum possible angle of the tibial guide to the PCTP (dotted line) was measured from lateral radiographs, and (B) the maximum possible angle of the tibial guide to the PCTT was measured from sagittal CT images of the posterior intercondylar fossa. The first transverse line was drawn from the central portion of the PCL insertion, and this line was perpendicular to the tibial shaft. The second line was drawn from the central portion of the PCL insertion to a point positioned 5 mm anterior to the first and second cortical screws after the tunnel diameter was taken into consideration.
reported that the anterolateral bundle insertion was located virtually on the articular plane (close to 0 mm) and the posteromedial bundle insertion was located a mean of 4.6 mm distal to the articular plane. Moorman et al.4 reported that the more posterior fibers, which insert up to 20 mm down the posterior cortex of the tibia, posterior and inferior to the posterior intercondylar fossa, are 0.5 mm thick. They emphasized that in
the sagittal plane, the center of the working fibers of the PCL lies 7 mm anterior to the posterior cortex of the tibia, as measured along the posterior intercondylar fossa. In our study the insertional point was similar to that of Moorman et al., although the evaluation method was different. Therefore we only marked with the screws at the corner of working thick fibers. The sloping central depression between the medial and lateral portions of the tibial plateau has been called the PCL fovea, facet, or fossa.4,14 Anatomically, this insertion is distinct from the vertical cortex of the tibia and can serve as a consistent radiographic landmark for pin placement in PCL reconstruction.4 We found that the PCL insertion was in the posterior 48% of the area of the PCL fovea, to the posterior cortex, consistent with Moorman et al.4 (posterior half of posterior intercondylar fossa). This implies that the guidewire should be placed more anteriorly, approximately half the diameter of the tibial tunnel from the posterior cortex as measured along the posterior intercondylar fossa, to preserve the remnant fibers and achieve an anatomic insertion during PCL reconstruction. However, 1 important issue should be mentioned. The posterior cortex of the plateau area curves posteriorly to the tibial plateau, whereas the posterior cortex of the posterior intercondylar fossa area is depressed anteriorly. Thus this area overlaps on lateral radiographs. The distance between the PCTT and the PCTP is determined from the 2-dimensional lateral radiographs because the unique 3-dimensional anatomy of the posterior aspect of the proximal tibia is converted to a 2-dimensional image. Consequently, to prevent breakage of the posterior cortex, it is important to identify the posterior intercondylar fossa and the PCTT during transtibial PCL reconstruction. It is also helpful to determine the PCTT by rotating the tibia internally and externally. However, this is not perfect, and all possible considerations must be given to determine the exact location of the PCTT. Our study has several limitations. First, the sample size was relatively small, and the power was not strong. Second, we could not prove the negative aspects of minimal breakage of the posterior cortex, because the fixation is performed at the anterior orifice when aperture fixation is performed. Furthermore, expansion or suspensory fixation is possible on the posterior side of proximal tibia.5,15 Third, this study evaluated only the sagittal angle of the tibial tunnel. Fourth, taking the radiographs in a standard position is very difficult, and small changes in the angle of the X-ray beam or rotation of the specimen will influence
PCL TIBIAL INSERTION ANATOMY some of the measurements. Fifth, the screws that were used in this study were relatively large, and identifying the center of the screw could be imprecise. CONCLUSIONS The mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the PCL fovea to the posterior cortex. The maximum possible angle of the tibial guide to the PCTT based on CT was 52°. Therefore the angle of the tibial guide pin must be limited for tibial footprint reconstruction to prevent posterior wall breakage. REFERENCES 1. Forsythe B, Kopf S, Wong AK, et al. The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models. J Bone Joint Surg Am 92:14181426. 2. Kopf S, Martin DE, Tashman S, Fu FH. Effect of tibial drill angles on bone tunnel aperture during anterior cruciate ligament reconstruction. J Bone Joint Surg Am 92:871-881. 3. van Eck CF, Lesniak BP, Schreiber VM, Fu FH. Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart. Arthroscopy 26:258-268. 4. Moorman CT III, Murphy Zane MS, Bansai S, et al. Tibial insertion of the posterior cruciate ligament: A sagittal plane analysis using gross, histologic, and radiographic methods. Arthroscopy 2008;24:269-275.
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5. Lee YS, Ahn JH, Jung YB, et al. Transtibial double bundle posterior cruciate ligament reconstruction using TransFix tibial fixation. Knee Surg Sports Traumatol Arthrosc 2007;15: 973-977. 6. Ahn JH, Chung YS, Oh I. Arthroscopic posterior cruciate ligament reconstruction using the posterior trans-septal portal. Arthroscopy 2003;19:101-107. 7. Berg EE. Posterior cruciate ligament tibial inlay reconstruction. Arthroscopy 1995;11:69-76. 8. Kim SJ, Choi CH, Kim HS. Arthroscopic posterior cruciate ligament tibial inlay reconstruction. Arthroscopy 2004;20:149154 (Suppl 2). 9. Amis AA, Jakob RP. Anterior cruciate ligament graft positioning, tensioning and twisting. Knee Surg Sports Traumatol Arthrosc 1998;6:S2-S12 (Suppl 1). 10. Yoo JC, Ahn JH, Lee YS, Koh KH. Magnetic resonance arthrographic findings of presumed stage-2 adhesive capsulitis: Focus on combined rotator cuff pathology. Orthopedics 2009;32:22. 11. Edwards A, Bull AM, Amis AA. The attachments of the fiber bundles of the posterior cruciate ligament: An anatomic study. Arthroscopy 2007;23:284-290. 12. Tajima G, Nozaki M, Iriuchishima T, et al. Morphology of the tibial insertion of the posterior cruciate ligament. J Bone Joint Surg Am 2009;91:859-866. 13. 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. 14. Girgis FG, Marshall JL, Monajem A. The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis. Clin Orthop Relat Res 1975:216-231. 15. Ahn JH, Bae JH, Lee YS, Choi K, Bae TS, Wang JH. An anatomical and biomechanical comparison of anteromedial and anterolateral approaches for tibial tunnel of posterior cruciate ligament reconstruction: Evaluation of the widening effect of the anterolateral approach. Am J Sports Med 2009;37: 1777-1783.
Purpose: The purposes of this study were (1) to predict the tibial insertion of the posterior cruciate ligament (PCL) and posterior cortex that aligned with the tibial tunnel (PCTT) by use of 2-dimensional plain radiographs by evaluating the relation between plain radiograph and computed tomography (CT) images and (2) to determine the safe angle of the tibial guide for preventing breakage of the posterior cortex. Methods: In 10 fresh cadaveric tibias, the soft tissues were dissected and the tibial footprint of the PCL was identified. The insertion of the PCL, the longest distance from the PCTT to the posterior cortex that aligned with the tibial plateau (PCTP), and the possible maximum angle of the tibial guide to the most posteriorly positioned cortical line were measured from simple anteroposterior (AP) and lateral radiographs, as well as CT. Results: The mean tibial insertion of the PCL from the joint line was located between 5.9 ⫾ 1.1 and 17.4 ⫾ 2.4 mm on the simple AP radiographs and between 2.2 ⫾ 1.2 and 12.3 ⫾ 1.5 mm on the simple lateral radiographs (P ⫽ .005). The PCL insertion was from the posterior 48% of the area of the posterior intercondylar fossa to the posterior cortex. The longest distance from the PCTT to the PCTP was 10.8 ⫾ 2.2 mm. The maximum angle of the tibial guide to the PCTT possible on CT and the PCTP on lateral radiographs was 52° ⫾ 5° and 62° ⫾ 4.5°, respectively (P ⫽ .005). Conclusions: The mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the PCL fovea to the posterior cortex. The maximum possible angle of the tibial guide to the PCTT based on CT was 52°. Therefore the angle of the tibial guide pin must be limited for tibial footprint reconstruction to prevent posterior wall breakage. Clinical Relevance: Increasing the tibial guide angle may have some advantages, but there is a limit because of posterior wall breakage.
A
s we have seen in anterior cruciate ligament reconstruction, re-creation of the normal anatomy gives superior results.1-3 Less attention has been
From the Department of Orthopedic Surgery, Ajou University School of Medicine (Y.S.L.), Suwon; Department of Orthopedic Surgery, Barun Hospital (H.J.R.), Jinju; Department of Orthopedic Surgery, Inje University, Seoul Paik Hospital (J.K.H., J.G.K.), Seoul; and Department of Orthopedic Surgery, SungKunkwan University, Samsung Medical Center (J.H.A.), Seoul, South Korea. The authors report no conflict of interest. Received November 10, 2009; accepted June 23, 2010. Address correspondence and reprint requests to Jin Goo Kim, M.D., Ph.D., Department of Orthopedic Surgery, Inje University, Seoul Paik Hospital, Jeo Dong 2 Ga, Gung Gu, Seoul, South Korea. E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/9667/$36.00 doi:10.1016/j.arthro.2010.06.024
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paid to the placement of the tibial tunnel during posterior cruciate ligament (PCL) reconstruction than to the femoral tunnel.4 Furthermore, for the tibial tunnel in the PCL, the focus has been to prevent the killerturn effect and neurovascular injury.5-8 The posterior aspect of the proximal tibia has a unique 3-dimensional anatomy compared with the mid or distal tibia, because multiple structures change abruptly, including the tibial plateau, posterior intercondylar fossa, and posterior cortex. The PCL inserts to the sloping central depression between the medial and lateral portions of the tibial plateau, and this insertion is distinct from the vertical cortex of the tibia (Fig 1A and 1B).4 For transtibial PCL reconstruction, plain radiographs or C-arm images are frequently used during the creation of the tibial tunnel. On the lateral plain ra-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 27, No 2 (February), 2011: pp 182-187
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FIGURE 1. (A) Posteroanterior and (B) oblique views. The black arrows indicate the 4 corners of the PCL insertion, and the open arrow marks the transition from the fossa to the posterior tibia. (C) The breakage of the posterior cortex could occur if the angle of the tibial guide increases. (D) Real arthroscopic view from anterior orifice of tibial tunnel.
diograph, the images of the medial and lateral tibial condyles overlap. Consequently, the posterior cortex that aligned with the tibial tunnel (PCTT) appears to be more anterior than the posterior cortex that aligned with the tibial plateau (PCTP). Therefore there is a limit to the increase in the tibial guide angle for tibial footprint reconstruction because of posterior wall breakage. We found some breakage of the posterior cortex in another cadaveric study (Fig 1C) and during a real operation (Fig 1D). In our opinion the possible causes of this breakage may be a posterior orifice that is too low to prevent a too anteriorly positioned tibial tunnel or too large of a tibial guide pin angle to prevent the killer-turn effect. However, there is little information on the radiographic anatomy of the PCL insertion and the relation between the PCTT and the PCTP. The purposes of this study were (1) to predict the tibial insertional point of the PCL and PCTT by use of 2-dimensional plain radiographs by evaluating the relation between plain radiographs and computed to-
mography (CT) images and (2) to determine the safe angle of tibial guide pin for the prevention of breakage of the posterior cortex. The hypothesis of this study was that there would be a limit in increasing the angle of the tibial guide pin in anatomic PCL reconstruction because of breakage of the posterior cortex. METHODS We studied 10 cadaveric knees (5 paired knees [3 from male cadavers and 2 from female cadavers]), with no gross degenerative changes or traumatic changes. The mean age was 51.3 years (range, 34 to 61 years). After the disarticulation of knee joint, the soft tissues were removed except for the tibial footprint of the PCL. Four corners were marked with a drill tip. A screw (industrial use of 4 mm in diameter with an 8-mm head) was inserted at each of the 4 corners of the PCL insertion and at 1-cm intervals in the posterior cortex aligned with the tibial tunnel. The screws were tightened until the screw head was flush
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Y. S. LEE ET AL. graph, the distance was measured from reference lines (Amis and Jakob’s line9: this base line is parallel to the medial tibial plateau and passes through the posterior corner of the tibial shelf) to the central portion of the screw heads of 4 screws that were inserted at each of the 4 corners of the PCL insertion. On the AP radiograph, the reference line was drawn from the edge of the medial tibial plateau to the edge of the lateral tibial plateau. By use of sagittal CT of the posterior intercondylar fossa at 1-mm slices, the ratio of the sagittal insertional length of the PCL to the total length of the entire posterior intercondylar fossa was calculated (Fig 3).4 The distance of the sagittal PCL insertion was measured from the anteriorly positioned screw to the posteriorly positioned screw that was inserted at the corner of the PCL insertion. The longest distance parallel to the reference line (Amis and Jakob’s line) between the PCTT and the PCTP was measured from the lateral radiograph (Fig 4). The maximum tibial guide angles to the PCTP and to the PCTT were assessed with a lateral radiograph and a sagittal CT image of the posterior intercondylar fossa, respectively (Fig 5). We used sagittal CT images for the measurement of maximum guide angle to the PCTT instead of lateral radiographs because CT images were taken from the posterior intercondylar fossa that was aligned to the tibial tunnel, and these
FIGURE 2. The distance from the joint line to the proximal aspect (solid arrow) and distal aspect (open arrow) of the PCL were measured from (A) AP and (B) lateral radiographs. Transverse red lines are reference lines, and longitudinal red lines are distances between the reference line and the central portion of the screw head.
with the surface of the cortex (Fig 1A). In total, 8 screws were inserted. One sports medicine surgeon performed the main procedure, and two assistants helped. Regarding the PCL tibial attachment measurements, simple anteroposterior (AP) and lateral radiographs were taken as shown in Fig 2. The specimens were laid down to the X-ray tube or floor of CT for the AP radiograph and CT images (MDCT; Siemens, Erlangen, Germany). The CT images were taken from the lateral end of the medial tibial plateau to the medial end of the lateral tibial plateau at 1-mm slices. The lateral radiograph was taken perpendicular to the sagittal-plane alignment of the tibia. On the lateral radio-
FIGURE 3. By use of sagittal CT of the posterior intercondylar fossa [long arrow indicates its length], the ratio of the PCL length to the entire length of the PCL facet was calculated. The distance of the sagittal PCL insertion [short arrow indicates its length] was measured from the anteriorly positioned screw to the posteriorly positioned screw that was inserted at the corner of the PCL insertion.
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FIGURE 4. (A) Pre-marked and (B) post-marked lateral radiographs show the position of the PCTT (screw insertion area) and the longest distance parallel to the reference line (Amis and Jakob’s line) from the PCTT (dotted line) to the PCTP (solid line) as measured by use of the lateral radiograph.
were supposed to be more accurate than lateral radiographs. A first transverse line was drawn from the central portion of the PCL insertion, perpendicular to the tibial shaft. A second line was drawn from the central portion of the PCL insertion to a point 5 mm anterior from the first (transition point from the fossa to the posterior tibia) and second cortical screws. We used half of the diameter (5 mm) from the posterior cortex because we usually use a 10-mm-diameter tibial tunnel. All measurements were obtained by use of a picture archiving and communication system (PACS) monitor (General Electric, Chicago, IL) with a mouse point cursor and automated computer calculation of the distance and angle.10 The measurements were taken twice by 2 orthopaedic surgeons to reduce the intraobserver and interobserver bias. A power analysis was performed. We believed that a difference in the angle of more than 5° would be clinically significant because we usually changed the guide angle with 5° intervals. Measurements were assessed by examining the intrarater and inter-rater reliability by use of the intraclass correlation coefficient. The Wilcoxon signed rank test was used with SPSS software (version 15.0; SPSS, Chicago, IL); P ⬍ .05 was deemed to be statistically significant. RESULTS The inter-rater and intrarater reliability ranged from 0.75 to 0.88. If the ␣ was 0.05, the power was 75% with 10 cadavers. The mean tibial insertion of the PCL from the joint line as measured on the AP radiographs (Fig 2A) was 5.9 ⫾ 1.1 mm to the proximal aspect of the PCL and 17.4 ⫾ 2.4 mm to the distal aspect of the PCL. The mean tibial insertion of the PCL from the
joint line as measured on the lateral radiographs (Fig 2B) was 2.2 ⫾ 1.2 mm to the proximal aspect of the PCL and 12.3 ⫾ 1.5 mm to the distal aspect of the PCL. There was a significant difference between the AP and lateral radiographs (P ⫽ .005). The PCL insertion was in the posterior 48% of the area of the posterior intercondylar fossa (Fig 3). The longest distance from the PCTT to the PCTP was 10.8 ⫾ 2.2 mm (Fig 4B). The maximum possible angle of the tibial guide to the PCTT based on CT (Fig 5B) and the PCTP from the lateral radiograph (Fig 5A) was 52° ⫾ 5° and 62° ⫾ 4.5°, respectively. There was a significant difference between the 2 angles (P ⫽ .005). DISCUSSION The principal finding of this study was that the mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the posterior intercondylar fossa, to the posterior cortex. The posterior cortical line can overlap because of the anatomic characteristics of the knee. Therefore the PCTT is different from the PCTP seen on simple lateral radiographs. This indicates that the posterior cortex can break if the tibial tunnel is based on the PCTP seen on simple radiographs. The general orthopaedic principle of surgery replicating the normal anatomy suggests that placement too far from the true anatomic insertion could compromise the function of the graft.4 Several studies have examined the anatomy of the PCL insertion.4,11-13 Girgis et al.14 reported that it was 2 to 3 mm distal to the articular plane, and Takahashi et al.13
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FIGURE 5. (A) The maximum possible angle of the tibial guide to the PCTP (dotted line) was measured from lateral radiographs, and (B) the maximum possible angle of the tibial guide to the PCTT was measured from sagittal CT images of the posterior intercondylar fossa. The first transverse line was drawn from the central portion of the PCL insertion, and this line was perpendicular to the tibial shaft. The second line was drawn from the central portion of the PCL insertion to a point positioned 5 mm anterior to the first and second cortical screws after the tunnel diameter was taken into consideration.
reported that the anterolateral bundle insertion was located virtually on the articular plane (close to 0 mm) and the posteromedial bundle insertion was located a mean of 4.6 mm distal to the articular plane. Moorman et al.4 reported that the more posterior fibers, which insert up to 20 mm down the posterior cortex of the tibia, posterior and inferior to the posterior intercondylar fossa, are 0.5 mm thick. They emphasized that in
the sagittal plane, the center of the working fibers of the PCL lies 7 mm anterior to the posterior cortex of the tibia, as measured along the posterior intercondylar fossa. In our study the insertional point was similar to that of Moorman et al., although the evaluation method was different. Therefore we only marked with the screws at the corner of working thick fibers. The sloping central depression between the medial and lateral portions of the tibial plateau has been called the PCL fovea, facet, or fossa.4,14 Anatomically, this insertion is distinct from the vertical cortex of the tibia and can serve as a consistent radiographic landmark for pin placement in PCL reconstruction.4 We found that the PCL insertion was in the posterior 48% of the area of the PCL fovea, to the posterior cortex, consistent with Moorman et al.4 (posterior half of posterior intercondylar fossa). This implies that the guidewire should be placed more anteriorly, approximately half the diameter of the tibial tunnel from the posterior cortex as measured along the posterior intercondylar fossa, to preserve the remnant fibers and achieve an anatomic insertion during PCL reconstruction. However, 1 important issue should be mentioned. The posterior cortex of the plateau area curves posteriorly to the tibial plateau, whereas the posterior cortex of the posterior intercondylar fossa area is depressed anteriorly. Thus this area overlaps on lateral radiographs. The distance between the PCTT and the PCTP is determined from the 2-dimensional lateral radiographs because the unique 3-dimensional anatomy of the posterior aspect of the proximal tibia is converted to a 2-dimensional image. Consequently, to prevent breakage of the posterior cortex, it is important to identify the posterior intercondylar fossa and the PCTT during transtibial PCL reconstruction. It is also helpful to determine the PCTT by rotating the tibia internally and externally. However, this is not perfect, and all possible considerations must be given to determine the exact location of the PCTT. Our study has several limitations. First, the sample size was relatively small, and the power was not strong. Second, we could not prove the negative aspects of minimal breakage of the posterior cortex, because the fixation is performed at the anterior orifice when aperture fixation is performed. Furthermore, expansion or suspensory fixation is possible on the posterior side of proximal tibia.5,15 Third, this study evaluated only the sagittal angle of the tibial tunnel. Fourth, taking the radiographs in a standard position is very difficult, and small changes in the angle of the X-ray beam or rotation of the specimen will influence
PCL TIBIAL INSERTION ANATOMY some of the measurements. Fifth, the screws that were used in this study were relatively large, and identifying the center of the screw could be imprecise. CONCLUSIONS The mean tibial insertion of the PCL from the joint line was located higher on the lateral radiographs than on the AP radiographs, and the PCL insertion was in the posterior 48% of the area of the PCL fovea to the posterior cortex. The maximum possible angle of the tibial guide to the PCTT based on CT was 52°. Therefore the angle of the tibial guide pin must be limited for tibial footprint reconstruction to prevent posterior wall breakage. REFERENCES 1. Forsythe B, Kopf S, Wong AK, et al. The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models. J Bone Joint Surg Am 92:14181426. 2. Kopf S, Martin DE, Tashman S, Fu FH. Effect of tibial drill angles on bone tunnel aperture during anterior cruciate ligament reconstruction. J Bone Joint Surg Am 92:871-881. 3. van Eck CF, Lesniak BP, Schreiber VM, Fu FH. Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart. Arthroscopy 26:258-268. 4. Moorman CT III, Murphy Zane MS, Bansai S, et al. Tibial insertion of the posterior cruciate ligament: A sagittal plane analysis using gross, histologic, and radiographic methods. Arthroscopy 2008;24:269-275.
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