- Email: [email protected]
The dynamic relations of the posterior cruciate ligament
The Knee 7 Ž2000. 39]44
The dynamic relations of the posterior cruciate ligament D.G. DunlopU , C.R.C. Walker, R.W. Nutton Princess Margaret Rose Orthopaedic Hospital, 41]43 Frogston Road West, Edinburgh, EH10 7ED, UK Accepted 9 November 1999
Abstract This study attempts to identify the immediate relations of the posterior cruciate ligament ŽPCL. during different degrees of knee flexion. Cadaveric dissection and magnetic resonance imaging of living subjects found that the popliteal artery is tethered to the oblique popliteal ligament behind the knee, but is free to move above and below this level. Movement of the neurovascular structures as a whole occurs during motion of the knee. These factors have implications for surgical practice, not only for PCL reconstruction, but also for any procedure requiring instrumentation to the back of the knee, such as total knee arthroplasty. Q 2000 Elsevier Science B.V. All rights reserved. Keywords: Cadaveric dissection; Knee
1. Introduction The anatomy of the posterior cruciate ligament ŽPCL. has been described as consisting of ‘functional bands’, in much the same way as the anterior cruciate ligament w1x. This arrangement allows tension to be varied among the fibres in these ligaments during different degrees of flexion and extension of the knee. This concept of examining the dynamic anatomy of the ligaments has been applied in our study, where we have examined the dynamic relations of the PCL with range of motion of the knee, in cadaveric dissections and in magnetic resonance imaging ŽMRI. of living subjects.
2. Cadaveric dissection Four formalin-preserved human cadavers were dis-
Abbre¨ iations: Posterior cruciate ligament, PCL; Magnetic resonance imaging, MRI U Corresponding author. Tel.: q44-131-5361000. E-mail address: [email protected] ŽD.G. Dunlop.
sected and the PCL, with its immediate relations, was identified. Change in the relative positions of the immediate relations during a range of motion of the knee, from full extension to 908 of flexion, was noted. Two knees were then cut in the mid-line sagittal plane and the other two in the coronal plane, at the level of the knee joint. PCL drill guides were then placed, to simulate drilling the tibial tunnel during a PCL reconstruction ŽFigs. 1 and 2.. Structures at risk during this procedure were identified. The static anatomy of the PCL comprised two major bands as previously described in recent journals w1x, but yet to filter down to most anatomy textbooks w2,3x. The anterolateral and posteromedial bands thicken as they move superiorly to their broad femoral origin, nestled between the thin, curved meniscofemoral ligaments of Wrisberg and Humphrey w4,5x ŽFig. 3.. The larger anterolateral fibres became taut in flexion, whereas the thinner posteromedial fibres became taut in extension. These bands have been variously named as AL and PM or as aPC and pPC although some authors do not split the structure but consider the ligament as a single fibre continuum w6,7x.
0968-0160r00r$ - see front matter Q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 8 - 0 1 6 0 Ž 9 9 . 0 0 0 4 0 - X
40
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 1. Coronal section through the knee joint, viewed from above. Drill guide positioned at the tibial PCL origin.
The popliteal artery was found to be closely adherent to the oblique popliteal ligament anteriorly, due to the origin of the middle geniculate vessels w8x, with relative freedom of movement above and below. Below the popliteal ligament there is little attachment to the popliteus muscle, but below the popliteus muscle, the artery becomes tethered once more at its bifurcation.
Fig. 2. Mid-line sagittal section with the knee at 30 and 608 flexion, respectively. Drill in position to show the tibial tunnel during a PCL reconstruction. Neurovascular bundle less likely to be damaged due to inadvertent drill advancement during flexion.
Fig. 3. Posterior aspect of two right knees viewed from behind, after sequential removal of superficial structures. The meniscofemoral ligament of Wrisberg is clearly seen curving behind the PCL from its lateral meniscal origin.
Above the popliteal ligament there is only loose aeriolar tissue between the popliteal surface of the femur and the popliteal artery, until the artery passes through the adductor hiatus medially. We noted during flexion and extension of the cadaveric knees, that the pull from the adductor hiatus on the popliteal
Fig. 4. Knee viewed from the postero-lateral aspect with a PCL guide and drill in situ, in 0 and 908 of knee flexion. Note the posterior capsule in the intercondylar region of the femur.
D.G. Dunlop et al. r The Knee 7 (2000) 39]44 41
Fig. 5. Coronal MRI scans of subject 1 at the level of the tibial PCL origin, with increasing degrees of knee flexion.
42
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 6. Coronal MRI scan showing the middle geniculate artery passing forwards to invest the cruciate ligaments, from its popliteal artery origin.
artery became increasingly more pronounced during extension. This medial pull during extension caused the un-tethered section of the popliteal artery to move medially. The posterior capsule above the oblique popliteal ligament was seen to stretch across the intercondylar femoral notch superiorly. During flexion of the knee it remained taught over the intercondylar region, sliding up and down, preventing the neurovascular bundle from subluxing into the notch ŽFig. 4..
Fig. 8. Digitised line-drawings from sequential aligned MRI scans.
3. Magnetic resonance imaging Magnetic resonance imaging ŽMRI. of two morphologically dissimilar living adult human subjects was performed. The knee scans were performed through a range of motion of the knee, from full extension to 908 of flexion ŽFig. 5., similar to the cadaveric work. Standardised alignment of the limbs allowed comparison between the two subjects. Coronal and sagittal reconstructions were performed and the immediate relations of the PCL were identified, together with
Fig. 7. Digitised line-drawings from sequential aligned MRI scans.
Fig. 9. Graph representing lateral movement of the neurovascular structures from the mid-line, with increasing degrees of knee flexion.
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
any change in their relative positions during the range of motion. The middle geniculate vessels were seen originating at the level of the popliteal ligament ŽFig. 6., with the artery closely apposed to this ligament. Below this level, at the tibial origin of the PCL, the popliteal vessels were seen to move laterally during flexion of the knee ŽFigs. 7 and 8.. The amount of movement has been quantified by measuring the distance the centre of the neurovascular bundle moves relative to the PCL in the mid-line, after alignment and standardisation of the MRI scans. This showed progressive lateral movement of the neurovascular bundle relative to the PCL of up to 6 mm with 908 of knee flexion ŽFig. 9.. The distance between the centre of the popliteal artery and the centre of the PCL ligament in the two subjects, changed during full extension to 908 of flexion, by 5]8.5 mm and 7]11 mm, respectively } an increase of approximately 150%.
4. Discussion Anatomic textbooks are slowly being replaced by ‘interactive’ electronic versions w9]11x, which allow
43
unparalleled visualisation during layer-by-layer cyber-dissection. Many of these purport to show the dynamic anatomy, but are actually based on static observation, which are then animated to enhance the visual effect. Further study is required before the standards are set for future software texts in anatomy or surgery. We have found that the neurovascular bundle in the popliteal fossa, moves laterally during flexion of the knee. It seems likely that this is due to the artery receiving a traction effect during extension, due to its medial origin ŽFig. 10. This occurred at or above the region of the oblique popliteal ligament and the middle genicular vessels, as they originate to invest the cruciate ligaments, which due to their embryological development, remain extrasynovial. Certainly in vivo, this movement occurs at the level of the PCL tibial origin, but below this, it remains closely adherent to the back of the tibia as it overlies the popliteus muscle ŽFigs. 11 and 12.. Surgeons undertaking instrumentation of the back of the knee, may find this useful information when planning their surgery. Tibial tunnels are often angled laterally, not least because the medial aspect of the tibia is more accessible. A guidewire that were to inadvertently miss the protec-
Fig. 11. Mid-line sagittal MRI scan in extension and 908 of flexion Žsee Fig. 12..
44
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 10. MRI of a right distal femur in the transverse plane, showing the popliteal vessels passing laterally from its medial origin at the adductor hiatus.
Fig. 12. Digitised line-drawings from sagittal MRI scans Žsee Fig. 11..
tive shoe of the drill guide in the back of the knee may perforate the neurovascular bundle. Flexing the knee and angling the drill medially Žor extending the knee and angling the drill laterally . may reduce this risk. Flexion of the knee additionally protects the neurovascular bundle due to the action of the posterior capsule above the oblique popliteal ligament, which holds the vessels away from the intercondylar region of the femur posteriorly. The assertion that it is safer to flex the knee during tibial osteotomy with an oscillating saw may be incorrect. The popliteal vessels are always closely adherent to the popliteus muscle at the level of the tibial cut, posteriorly and do not move on knee flexion.
w2x Last RJ. Anatomy } regional and applied, 10th ed. Churchill Livingston. w3x Grant’s Method of Anatomy, 11th ed. Williams and Wilkins. w4x Seebacher JR, Inglis AE, Marshall JL, Warren RF. The structure of the posterolateral aspect of the knee. J Bone Jt Surg 1982;64A:536]541. w5x Cho JM, Suh JS, Na JB et al. Variations in meniscofemoral ligaments at anatomical study and MR imaging. Skelet Radiol 1999;28Ž4.:189]195. w6x Covey DC, Sapega AA. Anatomy and function of the posterior cruciate ligament. Clin Sports Med 1994;13Ž3.:509]518. w7x Girgis FG, Marshall JL, Al Monajem ARS. The cruciate ligaments of the knee joint: anatomical, functional and experimental analysis. Clin Orthop 1975;106:216]231. w8x Scapinelli R. Vascular anatomy of the human cruciate ligaments and surrounding structures. Clin Anat 1997;10Ž3.: 151]162. w9x Aichroth PM, Cannon WD, Amis AA, Mahadevan V. The interactive knee CD-ROM. Primal. w10x Bentley G, Windsor RE, Williams A. The virtual surgeon } elective knee surgery CD-ROM. TVF Multimedia. w11x Hadlington S. Picture of perfect knee aids treatment of joints. Financial Times, Wed. 20 January 1999.
References w1x Morgan CD, Kalman VR, Grawl DM. The anatomic origin of the posterior cruciate ligament: where is it? Reference landmarks for PCL reconstruction. Arthroscopy 1997;13Ž3.: 325]331.
The dynamic relations of the posterior cruciate ligament D.G. DunlopU , C.R.C. Walker, R.W. Nutton Princess Margaret Rose Orthopaedic Hospital, 41]43 Frogston Road West, Edinburgh, EH10 7ED, UK Accepted 9 November 1999
Abstract This study attempts to identify the immediate relations of the posterior cruciate ligament ŽPCL. during different degrees of knee flexion. Cadaveric dissection and magnetic resonance imaging of living subjects found that the popliteal artery is tethered to the oblique popliteal ligament behind the knee, but is free to move above and below this level. Movement of the neurovascular structures as a whole occurs during motion of the knee. These factors have implications for surgical practice, not only for PCL reconstruction, but also for any procedure requiring instrumentation to the back of the knee, such as total knee arthroplasty. Q 2000 Elsevier Science B.V. All rights reserved. Keywords: Cadaveric dissection; Knee
1. Introduction The anatomy of the posterior cruciate ligament ŽPCL. has been described as consisting of ‘functional bands’, in much the same way as the anterior cruciate ligament w1x. This arrangement allows tension to be varied among the fibres in these ligaments during different degrees of flexion and extension of the knee. This concept of examining the dynamic anatomy of the ligaments has been applied in our study, where we have examined the dynamic relations of the PCL with range of motion of the knee, in cadaveric dissections and in magnetic resonance imaging ŽMRI. of living subjects.
2. Cadaveric dissection Four formalin-preserved human cadavers were dis-
Abbre¨ iations: Posterior cruciate ligament, PCL; Magnetic resonance imaging, MRI U Corresponding author. Tel.: q44-131-5361000. E-mail address: [email protected] ŽD.G. Dunlop.
sected and the PCL, with its immediate relations, was identified. Change in the relative positions of the immediate relations during a range of motion of the knee, from full extension to 908 of flexion, was noted. Two knees were then cut in the mid-line sagittal plane and the other two in the coronal plane, at the level of the knee joint. PCL drill guides were then placed, to simulate drilling the tibial tunnel during a PCL reconstruction ŽFigs. 1 and 2.. Structures at risk during this procedure were identified. The static anatomy of the PCL comprised two major bands as previously described in recent journals w1x, but yet to filter down to most anatomy textbooks w2,3x. The anterolateral and posteromedial bands thicken as they move superiorly to their broad femoral origin, nestled between the thin, curved meniscofemoral ligaments of Wrisberg and Humphrey w4,5x ŽFig. 3.. The larger anterolateral fibres became taut in flexion, whereas the thinner posteromedial fibres became taut in extension. These bands have been variously named as AL and PM or as aPC and pPC although some authors do not split the structure but consider the ligament as a single fibre continuum w6,7x.
0968-0160r00r$ - see front matter Q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 8 - 0 1 6 0 Ž 9 9 . 0 0 0 4 0 - X
40
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 1. Coronal section through the knee joint, viewed from above. Drill guide positioned at the tibial PCL origin.
The popliteal artery was found to be closely adherent to the oblique popliteal ligament anteriorly, due to the origin of the middle geniculate vessels w8x, with relative freedom of movement above and below. Below the popliteal ligament there is little attachment to the popliteus muscle, but below the popliteus muscle, the artery becomes tethered once more at its bifurcation.
Fig. 2. Mid-line sagittal section with the knee at 30 and 608 flexion, respectively. Drill in position to show the tibial tunnel during a PCL reconstruction. Neurovascular bundle less likely to be damaged due to inadvertent drill advancement during flexion.
Fig. 3. Posterior aspect of two right knees viewed from behind, after sequential removal of superficial structures. The meniscofemoral ligament of Wrisberg is clearly seen curving behind the PCL from its lateral meniscal origin.
Above the popliteal ligament there is only loose aeriolar tissue between the popliteal surface of the femur and the popliteal artery, until the artery passes through the adductor hiatus medially. We noted during flexion and extension of the cadaveric knees, that the pull from the adductor hiatus on the popliteal
Fig. 4. Knee viewed from the postero-lateral aspect with a PCL guide and drill in situ, in 0 and 908 of knee flexion. Note the posterior capsule in the intercondylar region of the femur.
D.G. Dunlop et al. r The Knee 7 (2000) 39]44 41
Fig. 5. Coronal MRI scans of subject 1 at the level of the tibial PCL origin, with increasing degrees of knee flexion.
42
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 6. Coronal MRI scan showing the middle geniculate artery passing forwards to invest the cruciate ligaments, from its popliteal artery origin.
artery became increasingly more pronounced during extension. This medial pull during extension caused the un-tethered section of the popliteal artery to move medially. The posterior capsule above the oblique popliteal ligament was seen to stretch across the intercondylar femoral notch superiorly. During flexion of the knee it remained taught over the intercondylar region, sliding up and down, preventing the neurovascular bundle from subluxing into the notch ŽFig. 4..
Fig. 8. Digitised line-drawings from sequential aligned MRI scans.
3. Magnetic resonance imaging Magnetic resonance imaging ŽMRI. of two morphologically dissimilar living adult human subjects was performed. The knee scans were performed through a range of motion of the knee, from full extension to 908 of flexion ŽFig. 5., similar to the cadaveric work. Standardised alignment of the limbs allowed comparison between the two subjects. Coronal and sagittal reconstructions were performed and the immediate relations of the PCL were identified, together with
Fig. 7. Digitised line-drawings from sequential aligned MRI scans.
Fig. 9. Graph representing lateral movement of the neurovascular structures from the mid-line, with increasing degrees of knee flexion.
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
any change in their relative positions during the range of motion. The middle geniculate vessels were seen originating at the level of the popliteal ligament ŽFig. 6., with the artery closely apposed to this ligament. Below this level, at the tibial origin of the PCL, the popliteal vessels were seen to move laterally during flexion of the knee ŽFigs. 7 and 8.. The amount of movement has been quantified by measuring the distance the centre of the neurovascular bundle moves relative to the PCL in the mid-line, after alignment and standardisation of the MRI scans. This showed progressive lateral movement of the neurovascular bundle relative to the PCL of up to 6 mm with 908 of knee flexion ŽFig. 9.. The distance between the centre of the popliteal artery and the centre of the PCL ligament in the two subjects, changed during full extension to 908 of flexion, by 5]8.5 mm and 7]11 mm, respectively } an increase of approximately 150%.
4. Discussion Anatomic textbooks are slowly being replaced by ‘interactive’ electronic versions w9]11x, which allow
43
unparalleled visualisation during layer-by-layer cyber-dissection. Many of these purport to show the dynamic anatomy, but are actually based on static observation, which are then animated to enhance the visual effect. Further study is required before the standards are set for future software texts in anatomy or surgery. We have found that the neurovascular bundle in the popliteal fossa, moves laterally during flexion of the knee. It seems likely that this is due to the artery receiving a traction effect during extension, due to its medial origin ŽFig. 10. This occurred at or above the region of the oblique popliteal ligament and the middle genicular vessels, as they originate to invest the cruciate ligaments, which due to their embryological development, remain extrasynovial. Certainly in vivo, this movement occurs at the level of the PCL tibial origin, but below this, it remains closely adherent to the back of the tibia as it overlies the popliteus muscle ŽFigs. 11 and 12.. Surgeons undertaking instrumentation of the back of the knee, may find this useful information when planning their surgery. Tibial tunnels are often angled laterally, not least because the medial aspect of the tibia is more accessible. A guidewire that were to inadvertently miss the protec-
Fig. 11. Mid-line sagittal MRI scan in extension and 908 of flexion Žsee Fig. 12..
44
D.G. Dunlop et al. r The Knee 7 (2000) 39]44
Fig. 10. MRI of a right distal femur in the transverse plane, showing the popliteal vessels passing laterally from its medial origin at the adductor hiatus.
Fig. 12. Digitised line-drawings from sagittal MRI scans Žsee Fig. 11..
tive shoe of the drill guide in the back of the knee may perforate the neurovascular bundle. Flexing the knee and angling the drill medially Žor extending the knee and angling the drill laterally . may reduce this risk. Flexion of the knee additionally protects the neurovascular bundle due to the action of the posterior capsule above the oblique popliteal ligament, which holds the vessels away from the intercondylar region of the femur posteriorly. The assertion that it is safer to flex the knee during tibial osteotomy with an oscillating saw may be incorrect. The popliteal vessels are always closely adherent to the popliteus muscle at the level of the tibial cut, posteriorly and do not move on knee flexion.
w2x Last RJ. Anatomy } regional and applied, 10th ed. Churchill Livingston. w3x Grant’s Method of Anatomy, 11th ed. Williams and Wilkins. w4x Seebacher JR, Inglis AE, Marshall JL, Warren RF. The structure of the posterolateral aspect of the knee. J Bone Jt Surg 1982;64A:536]541. w5x Cho JM, Suh JS, Na JB et al. Variations in meniscofemoral ligaments at anatomical study and MR imaging. Skelet Radiol 1999;28Ž4.:189]195. w6x Covey DC, Sapega AA. Anatomy and function of the posterior cruciate ligament. Clin Sports Med 1994;13Ž3.:509]518. w7x Girgis FG, Marshall JL, Al Monajem ARS. The cruciate ligaments of the knee joint: anatomical, functional and experimental analysis. Clin Orthop 1975;106:216]231. w8x Scapinelli R. Vascular anatomy of the human cruciate ligaments and surrounding structures. Clin Anat 1997;10Ž3.: 151]162. w9x Aichroth PM, Cannon WD, Amis AA, Mahadevan V. The interactive knee CD-ROM. Primal. w10x Bentley G, Windsor RE, Williams A. The virtual surgeon } elective knee surgery CD-ROM. TVF Multimedia. w11x Hadlington S. Picture of perfect knee aids treatment of joints. Financial Times, Wed. 20 January 1999.
References w1x Morgan CD, Kalman VR, Grawl DM. The anatomic origin of the posterior cruciate ligament: where is it? Reference landmarks for PCL reconstruction. Arthroscopy 1997;13Ž3.: 325]331.