- Email: [email protected]
Movement of the posterior cruciate ligament during knee flexion––MRI analysis
ELSEVIER
Journal of Orthopaedic Research
Journal of Orthopaedic Research 23 (2005)334339
www.elsevier.comnocate/orthres
Movement of the posterior cruciate ligament during knee flexion-MRI analysis Takeshi Komatsu Yoshinori Kadoya b, Shigeru Nakagawa Gen Yoshida ', Kunio Takaoka a
b,
Department of Orthopaedic Surgery, Dynamic Sports Medicine Institute, 2-6-10 Kozu, Chuo-ku. Osaka City 542-0072, Japan Department of Orrhopaedic Surgery. Osaka Rosai Hospital, Japan Department of Orrhopuedic Surgery, Osaka City University Graduate School of Medicine, Japan
Received 29 January 2004
Abstract
The movement of the posterior cruciate ligament (PCL) during flexion of the living knee is unknown. The purpose of the present study was to analyze the movement of the PCL using magnetic resonance imaging (MRI). The posterior cruciate ligaments in 20 normal knees were visualized using MRI from extension to deep flexion. Sagittal inclination relative to the longitudinal axis of the tibia was measured and analyzed with reference to the patellar tendon (PT) and the anterior cruciate ligament (ACL). Although the PCL was slack in extension, it straightened with anterior inclination (24.1 k 5.1") at 90" flexion. At active maximum flexion (129.2 k 8.1°), the ligament was almost parallel (3.9 f 7.4" inclination) to the longitudinal axis of the tibia. At passive maximum flexion ( 1 58.8 f 5.8"), the inclination was reversed anteroposteriorly. measuring -23.0 k 6.7". The PCL and PT moved in a corresponding manner within 20" of discrepancy. The results of this in vivo study of the PCL have clinical relevance to conservative therapy for PCL knee injuries. The results of this study could also be useful in PCL reconstruction surgery to determine the optimum graft position to allow maximum postoperative motion. 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. Keywords: Knee kinematics; Magnetic resonance imaging; Posterior cruciate ligament: Anterior cruciate ligament; Patellar tendon
Introduction The treatment of posterior cruciate ligament (PCL) tears in young athletes is controversial because of the diverse nature of PCL injuries, limitations of the clinical studies performed, and insufficient understanding of the biomechanics involved [4,5,9,22]. The role of PCL retention in total knee arthroplasty (TKA) is also controversial [15,20] and the restoration of the knee flexion angle has been a challenge in both TKA and PCL reconstruction surgery. Recently, the force applied to the PCL Corresponding author. Tel.: +81 6 6211 3996; fax: +81 6 6211
3994. E-mail address: [email protected] (T. Komatsu).
in deep flexion has been a subject of interest, but results obtained have been contradictory [14,16,17]. These controversies, at least in part, arose from technical difficulties in visualizing the living normal knee in deep flexion, which is essential to determine the position of the PCL and calculation of the applied force. Such difficulties can now be overcome by magnetic resonance imaging (MRI), which allows accurate visualization of the living knee joint at various angles of flexion. Another advantage of MRI is that studies can be performed on living subjects without irradiation. The authors have previously reported MRI analysis of femorotibial movement over the arc between 15" and deep flexion [18,23]. The purpose of this study was to analyze the movement of the PCL with reference to
0736-0266/$- see front matter 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. doi: 10.1016/j.orthres.2004.08.001
T. Koiiiutsir et al. I Journul of Orrliopuedic Reseurcli 23 (2005) 334-339
the patellar tendon (PT) and the anterior cruciate ligament (ACL) throughout the flexion arc. It was hypothesized that the position of the PCL relative to the PT and ACL determines its functional role in the context of knee kinematics. Materials and methods The subjects were 20 Japanese male volunteers who worked at the authors' institutions, who had no symptoms of knee injury, and whose MR images showed no abnormalities. They gave informed consent and agreed to participate in this study without payment, which was approved by our institutional review board. Their mean age was 29.7 years (range: 26-40 years). Each subject was scanned in an open MRI unit (AIRIS, HITACHI, Tokyo, Japan). Consecutive 5 m m thickness scans traversing the entire knee were obtained in the sagittal plane. Imaging parameters were 0.3T using the spin echo (TR: 500ms, TE: 38ms) imaging method, with a 256 x 256 scan matrix (scanning time: 2min and 30s). Scans were performed to view the knees at neutral rotation through the following steps of knee flexion: full extension, 15". 90°, active maximum flexion and passive maximum flexion. The position of neutral rotation was defined as the position in which the subject spontaneously placed his knee without any specific instructions. The subject was scanned while lying on the left side with the knee to be scanned in contact with the table. The position of active maximum flexion was obtained by instructing the subject to maximally flex his knee, and this position was maintained using an elastic bandage. The position of passive maximum flexion was obtained and maintained by the subject's body weight as in our previous study (Fig. 1) [18]. Measurement method
Measurements were performed separately by two independent observers (T.K. and S.N.), and the mean value of each subject was used for analysis. From each sequence of scans, images were selected in which the femoral and tibial attachments of the FCL and ACL could be detected at the observer's discretion (Fig. 2A and B). Lines were drawn to connect the central position of the femoral and the tibial attachments of the cruciate ligaments, and the angles relative to the longitudinal axis of the tibia were measured at each flexion angle. The direction of the patellar tendon was determined in the same manner using the most suitable image (Fig. 2C). The measured angle was expressed as a positive value when the ligament or tendon was anteriorly inclined relative to the tibia (e.g. the ACL exhibited a negative value and the PCL exhibited a positive value in extension). The actual measured degree of flexion was measured in the MRI images in which
335
the femoral and tibial longitudinal axes could be detected at each flexion angle. Interobserver error was calculated using a commercially available software package (Excel 2002, Microsoft Corp., USA).
Results
The actual measured degrees of knee flexion from neutral to passive maximum flexion in the 20 subjects were -2.5 f 3.3", 14.7 f 9.9", 82.5 f 7.9", 129.2 k 8.1" and 158.8 f 5.8" respectively (mean f SD). Interobserver error was 6.6 f 1.1" (mean f 95% confidence interval) for the measurement of the PCL, 6.8 f 1.1" for the ACL, and 5.4 f 0.9" for the PT. The PCL was usually visualized at full length in a slice traversing the medial intercondylar notch of the femur, whereas the ACL and PT were simultaneously identified in a slice traversing the lateral intercondylar notch. Representative images of the PCL, ACL and PT at each flexion angle are shown in Fig. 3A and B. In extension, the PCL was curved over the intercondylar eminence (Fig. 3A). At 90" flexion, the PCL appeared as a straight bundle with an average inclination of 24.1 f 5.1" to the longitudinal axis of the tibia (Fig. 3B). The PT was essentially parallel (2.9 f 6.9") and the ACL exhibited -55.5 5 6.1" inclination to the longitudinal axis of the tibia (Fig. 4B). At active maximum flexion, the PCL became parallel (3.9 k 7.4") to the longitudinal axis of the tibia (Fig. 3C). When the knee was passively flexed, the angle between the PCL and the longitudinal axis of the tibia continued to decrease and reached an angle that was negative (-23.0 f 6.7") by the standard established for this study. The PCL at passive maximum flexion was curved over the intercondylar notch of the femur (Fig. 3D) and the ACL was almost horizontal over the tibial intercondylar eminence (-80.4 f 4.5") (Fig. 4D). The averaged inclinations observed in the PCL, ACL and PT at each flexion angle are summarized in Table 1 and illustrated in Fig. 5. The PCL and PT moved in a corresponding manner within 20" of discrepancy throughout the flexion arc.
Discussion
Fig. 1. The scanning position at passive maximum flexion.
The PCL has been believed to be the primary resistance to posterior tibial translation [2,3,8,13]. The biomechanics of the PCL, however, have been investigated mainly in cadaver knees [2,6,10,13] and there has been a paucity of data on the normal living knee. PCL injuries are usually a result of sporting activity, and patients with an acute isolated PCL tear can be treated with a brief period of splinting followed by an early quadriceps strengthening rehabilitation regime [21,22]. It has been intuitively accepted that quadriceps
T. Komatsu et al. I Journal of' Orthopaedic Research 23 (2005) 334-339
336
Fig. 2. The methods of measurement of inclination of the PCL (A), ACL (B) and PT (C) on selected MRI images. The proximal and distal attachments of the ligamentdtendon are identified (white square) and connected (white line). The angles relative to the longitudinal axis of the tibia were measured (arrow).
(A)
@I
(C)
(D)
Fig. 3. Representative MRI images of the PCL and PT at each flexion angle (A: extension, B: 90" flexion, C: active maximum flexion, D: passive maximum flexion). The longitudinal axis of the tibia is indicated by the black line.
T. Komatsu et al. I Journul of Orthopaedic Rescarch 23 (2005) 334-339
(A)
(B)
(C)
331
(D)
Fig. 4. Representative MRI images of the ACL and PT at each flexion angle (A: extension, B: 90" flexion, C: active maximum flexion, D: passive maximum flexion). The longitudinal axis of the tibia is indicated by the black line.
Table 1 The averaged inclinations of PCL, ACL and PT at each flexion angle Knee flexion angle (degrees), mean f SD 0
PT PCL ACL a
21.5 f 4.3
39.4 f 3.9 -32.6 f 6.5
15
90
129"
I 59b
24.1 f 4.6 41.4 f 5.0 -36.0 f 6.5
2.9 f 6.9 24.1 & 5.1 -55.5 f 6.1
-14.5 f 6.6 3.9 f 1.4 -61.1 f 6.8
-21.5 f 4.0 -23.0 f 6.1 -80.4 f 4.5
The angle of active maximum flexion. The angle of passive maximum flexion.
+ ACL -1 O
0
20
O 40 60
T
I
80 100 120 140 160 Kaeeflaionangle (degnes)
Fig. 5. The averaged inclinations of PCL, ACL and PT at each flexion angle.
contraction brings the tibia forward [l 11 and compensates for the posterior instability caused by PCL insufficiency. The present study does lend anatomic support to this theory, when the knee is in the extended position, based on the anterior inclination of the PT relative to the tibial longitudinal axis. However, the present study T is parallel to the tibial longitualso indicates that the F dinal axis when the knee is flexed 90" and it would provide less anterior posterior stabilization (Fig. 4B). Based on the parallel alignment of the PT, quadriceps contraction appears to primarily maintain the anterior aspect of the joint gap when the knee is flexed. In addition, the
change in inclination of the PT with knee flexion was similar to that of the PCL and the upright position of the PT at 90" may act to provide anteroposterior stability in the same manner as the PCL. Anatomically this would imply that the PT functions as an anterior analogue of the PCL. The PCL was rather upright at 90" of flexion (24.1 k 5.1" inclination) and then became parallel to the longitudinal axis of the tibia in active maximum flexion. This observation provides grounds for our hypothesis that the main function of the PCL over 90" flexion is to maintain the joint gap between the femur and the
338
T. Komatsu et al. I Journal of Orthopaedic Research 23 (2005) 334-339
tibia rather than to provide anteroposterior stability in isolation. The knee flexed over 90" is thus posteriorly stabilized by the maintained distance between the femorotibial articular surface exerted by the PCL and the concave tibial articular surface on the medial side. This consideration is supported by our intraoperative observation that sacrificing the PCL results in a significant increase in the flexion gap, with little corresponding increase in the extension gap [12]. As regards the kinematics of deep knee flexion, we have previously reported subluxation of the lateral femoral condyle over the tibial articular surface [18]. The present study showed that in this extreme position, the PCL became inclined posteriorly relative to the tibia. The ACL was virtually horizontal to the tibial articular surface and appeared to be pressed over the tibia. Taking these findings together, passive maximum flexion (approximately 160" flexion) appears to be an anatomically abnormal position and could be regarded as a subluxation. A possible limitation in this study is that the ligament directions were estimated based on the center of attachments. The PCL can be described as having multiple bundles and areas of fiber attachment with different functional roles [6]. Biomechanical studies have shown that very little of the PCL is truly isometric throughout the knee flexion arc [6]. For example, it has been reported that the anterolateral band tightens during knee flexion, while the posteromedial band plays a relatively greater role in stabilizing the knee during extension [1,7]. The authors admit oversimplification of the complexity of the PCL structure, but interobserver errors were approximately 6" when identifying the average area of attachments of the PCL. The changes in the inclination of the PCL, however, amounted to 60", which is much larger than the estimated error. Thus the authors believe that the main findings and conclusion drawn from this study are valid. A potential weakness of the study was the lack of muscular activity and weight-bearing, but our recent results have shown that the kinematics of the PCL was not affected by weight-bearing [19]. In conclusion, the present study visualized and analyzed the movement of the PCL, ACL and PT in normal living subjects throughout the flexion range. Based on the upright position of the PCL in a flexion arc over go", the PCL plays an important role for the maintenance of the joint gap during flexion. The close resemblance of the PCL and PT in inclination to the tibia could explain the mechanism of compensation by the quadriceps for PCL insufficiency, because the upright position of the PT at 90" may act to provide anteroposterior stability in the same manner as the PCL. The results of this in vivo study of the PCL have clinical relevance to conservative therapy for PCL knee injuries. The results of this study could also be useful in PCL reconstruction surgery to determine the optimum graft position that allows maximum postoperative motion.
Acknowledgement
The authors thank H. Sakamoto, MD, PhD (Sakamot0 Clinic, Sakai City, Osaka, Japan), for his help in providing the MRI unit.
References Abbot LC, Saunders JB, Bost FC, et al. Injuries to the ligaments of the knee joint. J Bone Joint Surg 1944;26503-21. Bergfeld JA, McAllister DR, Parker RD, et al. The effects of tibial rotation on posterior translation in knees in which the posterior cruciate ligament has been cut. J Bone Joint Surg 200 1;83A:133943. Butler DL, Noyes FR, Grood ES. Ligamentous restraints to the antero-posterior drawer in the human knee: a biomechanical study. J Bone Joint Surg 1980;62A:259-70. Clancy Jr WG, Shelbourne KD, Zoellner GB, et al. Treatment of knee joint instability secondary to rupture of the posterior cruciate ligament: report of a new procedure. J Bone Joint Surg 1983; 65Az310-22. Cosgarea AJ, Jay PR. Posterior cruciate ligament injuries: evaluation and management. J Am Acad Orthop Surgeons 2001;9:297-307. Fuss FK. Anatomy of the cruciate ligaments and their function in extension and flexion of the human knee joint. Am J Anat 1989;184165-76. Girgis FG, Marshall JL, Al Mondjem ARS. The cruciate ligaments of the knee joint: anatomical, functional and experimental analysis. Clin Orthop 1975;10621&31. Gollehon DL, Torzilli PA, Warren RF. The role of the posterolateral and cruciate ligaments in the stability of the human knee: a biomechanical study. J Bone Joint Surg 1987;69A:23342. Harner CD, Hoher J. Evaluation and treatment of posterior cruciate ligament injuries. Am J Sports Med 1998;26:471-82. Hoher J, Vogrin TM, Woo SL-Y, et al. In situ forces in the human posterior cruciate ligament in response to muscle loads: a cadaveric study. J Orthop Res 1999;17:763-8. [l 11 Howell SM. Anterior tibial translation during a maximum quadriceps contraction: is it clinically significant? Am J Sports Med 1990;18573-8. [I21 Kadoya Y, Kobayashi A, Komatsu T, et al. Effects of posterior cruciate ligament resection on the tibiofemoral joint gap. Clin Orthop 200 1;391:2 1@7. [13] Li G, Gill TJ, DeFrate LE, et al. Biomechanical consequences of PCL deficiency in the knee under simulated muscle loads-an in vitro experimental study. J Orthop Res 2002;20:887-92. [14] Li G, Zayonts S, Most E, et al. In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation. J Orthop Res 2004;22:293-7. [IS] Li M, Ritter MA, Moilanen T, et al. Pointcounter-point: total knee arthroplasty. J Arthroplasty 1995;10:560-70. [I61 Nagra T, Dyrby CO, Alexander EJ, et al. Mechanical loads at the knee joint during deep flexion. J Orthop Res 2002;20:8814. [I71 Nagra T, Andriacchi TP, Alexander E, et al. Muscle co-contraction increases the load on the posterior cruciate ligament during deep knee flexion. Trans Orthop Res SOC, New Orleans, LA 2003:843. [I81 Nakagawa S, Kadoya Y, Todo S, et al. Tibiofemoral movement 3: full flexion in the living knee studied by MRI. J Bone Joint Surg 2000;82B:1199-200. [I91 Nakagawa S, Johal P, Pinskerova V. The posterior cruciate ligament during flexion of the normal knee. J Bone Joint Surg 2004;86B:450-6.
T. Komatsu et at. I Journal of Orthopaedic Research 23 (2005) 334-339 [20] Pagnano MW, Cushner FD, Scott WN. Role of the posterior cruciate ligament in total knee arthroplasty. J Am Acad Orthop Surgeons 1998;6:176-87. [21] Shelboume KD, Jennings RW, Vahey TN. Magnetic resonance imaging of posterior cruciate ligament injuries. Am J Knee Surg 1999;12:209-13.
339
[22] Shelbourne KD, Davis TJ, Patel DV. The natural history of acute, isolated, nonoperatively treated posterior cruciate ligament injuries: a prospective study. Am J Sports Med 1999;27:27683. [23] Todo S, Kadoya Y, Moilanen T, et al. Anteroposterior and rotational movement of femur during knee flexion. Clin Orthop 1999;362:162-70.
Journal of Orthopaedic Research
Journal of Orthopaedic Research 23 (2005)334339
www.elsevier.comnocate/orthres
Movement of the posterior cruciate ligament during knee flexion-MRI analysis Takeshi Komatsu Yoshinori Kadoya b, Shigeru Nakagawa Gen Yoshida ', Kunio Takaoka a
b,
Department of Orthopaedic Surgery, Dynamic Sports Medicine Institute, 2-6-10 Kozu, Chuo-ku. Osaka City 542-0072, Japan Department of Orrhopaedic Surgery. Osaka Rosai Hospital, Japan Department of Orrhopuedic Surgery, Osaka City University Graduate School of Medicine, Japan
Received 29 January 2004
Abstract
The movement of the posterior cruciate ligament (PCL) during flexion of the living knee is unknown. The purpose of the present study was to analyze the movement of the PCL using magnetic resonance imaging (MRI). The posterior cruciate ligaments in 20 normal knees were visualized using MRI from extension to deep flexion. Sagittal inclination relative to the longitudinal axis of the tibia was measured and analyzed with reference to the patellar tendon (PT) and the anterior cruciate ligament (ACL). Although the PCL was slack in extension, it straightened with anterior inclination (24.1 k 5.1") at 90" flexion. At active maximum flexion (129.2 k 8.1°), the ligament was almost parallel (3.9 f 7.4" inclination) to the longitudinal axis of the tibia. At passive maximum flexion ( 1 58.8 f 5.8"), the inclination was reversed anteroposteriorly. measuring -23.0 k 6.7". The PCL and PT moved in a corresponding manner within 20" of discrepancy. The results of this in vivo study of the PCL have clinical relevance to conservative therapy for PCL knee injuries. The results of this study could also be useful in PCL reconstruction surgery to determine the optimum graft position to allow maximum postoperative motion. 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. Keywords: Knee kinematics; Magnetic resonance imaging; Posterior cruciate ligament: Anterior cruciate ligament; Patellar tendon
Introduction The treatment of posterior cruciate ligament (PCL) tears in young athletes is controversial because of the diverse nature of PCL injuries, limitations of the clinical studies performed, and insufficient understanding of the biomechanics involved [4,5,9,22]. The role of PCL retention in total knee arthroplasty (TKA) is also controversial [15,20] and the restoration of the knee flexion angle has been a challenge in both TKA and PCL reconstruction surgery. Recently, the force applied to the PCL Corresponding author. Tel.: +81 6 6211 3996; fax: +81 6 6211
3994. E-mail address: [email protected] (T. Komatsu).
in deep flexion has been a subject of interest, but results obtained have been contradictory [14,16,17]. These controversies, at least in part, arose from technical difficulties in visualizing the living normal knee in deep flexion, which is essential to determine the position of the PCL and calculation of the applied force. Such difficulties can now be overcome by magnetic resonance imaging (MRI), which allows accurate visualization of the living knee joint at various angles of flexion. Another advantage of MRI is that studies can be performed on living subjects without irradiation. The authors have previously reported MRI analysis of femorotibial movement over the arc between 15" and deep flexion [18,23]. The purpose of this study was to analyze the movement of the PCL with reference to
0736-0266/$- see front matter 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. doi: 10.1016/j.orthres.2004.08.001
T. Koiiiutsir et al. I Journul of Orrliopuedic Reseurcli 23 (2005) 334-339
the patellar tendon (PT) and the anterior cruciate ligament (ACL) throughout the flexion arc. It was hypothesized that the position of the PCL relative to the PT and ACL determines its functional role in the context of knee kinematics. Materials and methods The subjects were 20 Japanese male volunteers who worked at the authors' institutions, who had no symptoms of knee injury, and whose MR images showed no abnormalities. They gave informed consent and agreed to participate in this study without payment, which was approved by our institutional review board. Their mean age was 29.7 years (range: 26-40 years). Each subject was scanned in an open MRI unit (AIRIS, HITACHI, Tokyo, Japan). Consecutive 5 m m thickness scans traversing the entire knee were obtained in the sagittal plane. Imaging parameters were 0.3T using the spin echo (TR: 500ms, TE: 38ms) imaging method, with a 256 x 256 scan matrix (scanning time: 2min and 30s). Scans were performed to view the knees at neutral rotation through the following steps of knee flexion: full extension, 15". 90°, active maximum flexion and passive maximum flexion. The position of neutral rotation was defined as the position in which the subject spontaneously placed his knee without any specific instructions. The subject was scanned while lying on the left side with the knee to be scanned in contact with the table. The position of active maximum flexion was obtained by instructing the subject to maximally flex his knee, and this position was maintained using an elastic bandage. The position of passive maximum flexion was obtained and maintained by the subject's body weight as in our previous study (Fig. 1) [18]. Measurement method
Measurements were performed separately by two independent observers (T.K. and S.N.), and the mean value of each subject was used for analysis. From each sequence of scans, images were selected in which the femoral and tibial attachments of the FCL and ACL could be detected at the observer's discretion (Fig. 2A and B). Lines were drawn to connect the central position of the femoral and the tibial attachments of the cruciate ligaments, and the angles relative to the longitudinal axis of the tibia were measured at each flexion angle. The direction of the patellar tendon was determined in the same manner using the most suitable image (Fig. 2C). The measured angle was expressed as a positive value when the ligament or tendon was anteriorly inclined relative to the tibia (e.g. the ACL exhibited a negative value and the PCL exhibited a positive value in extension). The actual measured degree of flexion was measured in the MRI images in which
335
the femoral and tibial longitudinal axes could be detected at each flexion angle. Interobserver error was calculated using a commercially available software package (Excel 2002, Microsoft Corp., USA).
Results
The actual measured degrees of knee flexion from neutral to passive maximum flexion in the 20 subjects were -2.5 f 3.3", 14.7 f 9.9", 82.5 f 7.9", 129.2 k 8.1" and 158.8 f 5.8" respectively (mean f SD). Interobserver error was 6.6 f 1.1" (mean f 95% confidence interval) for the measurement of the PCL, 6.8 f 1.1" for the ACL, and 5.4 f 0.9" for the PT. The PCL was usually visualized at full length in a slice traversing the medial intercondylar notch of the femur, whereas the ACL and PT were simultaneously identified in a slice traversing the lateral intercondylar notch. Representative images of the PCL, ACL and PT at each flexion angle are shown in Fig. 3A and B. In extension, the PCL was curved over the intercondylar eminence (Fig. 3A). At 90" flexion, the PCL appeared as a straight bundle with an average inclination of 24.1 f 5.1" to the longitudinal axis of the tibia (Fig. 3B). The PT was essentially parallel (2.9 f 6.9") and the ACL exhibited -55.5 5 6.1" inclination to the longitudinal axis of the tibia (Fig. 4B). At active maximum flexion, the PCL became parallel (3.9 k 7.4") to the longitudinal axis of the tibia (Fig. 3C). When the knee was passively flexed, the angle between the PCL and the longitudinal axis of the tibia continued to decrease and reached an angle that was negative (-23.0 f 6.7") by the standard established for this study. The PCL at passive maximum flexion was curved over the intercondylar notch of the femur (Fig. 3D) and the ACL was almost horizontal over the tibial intercondylar eminence (-80.4 f 4.5") (Fig. 4D). The averaged inclinations observed in the PCL, ACL and PT at each flexion angle are summarized in Table 1 and illustrated in Fig. 5. The PCL and PT moved in a corresponding manner within 20" of discrepancy throughout the flexion arc.
Discussion
Fig. 1. The scanning position at passive maximum flexion.
The PCL has been believed to be the primary resistance to posterior tibial translation [2,3,8,13]. The biomechanics of the PCL, however, have been investigated mainly in cadaver knees [2,6,10,13] and there has been a paucity of data on the normal living knee. PCL injuries are usually a result of sporting activity, and patients with an acute isolated PCL tear can be treated with a brief period of splinting followed by an early quadriceps strengthening rehabilitation regime [21,22]. It has been intuitively accepted that quadriceps
T. Komatsu et al. I Journal of' Orthopaedic Research 23 (2005) 334-339
336
Fig. 2. The methods of measurement of inclination of the PCL (A), ACL (B) and PT (C) on selected MRI images. The proximal and distal attachments of the ligamentdtendon are identified (white square) and connected (white line). The angles relative to the longitudinal axis of the tibia were measured (arrow).
(A)
@I
(C)
(D)
Fig. 3. Representative MRI images of the PCL and PT at each flexion angle (A: extension, B: 90" flexion, C: active maximum flexion, D: passive maximum flexion). The longitudinal axis of the tibia is indicated by the black line.
T. Komatsu et al. I Journul of Orthopaedic Rescarch 23 (2005) 334-339
(A)
(B)
(C)
331
(D)
Fig. 4. Representative MRI images of the ACL and PT at each flexion angle (A: extension, B: 90" flexion, C: active maximum flexion, D: passive maximum flexion). The longitudinal axis of the tibia is indicated by the black line.
Table 1 The averaged inclinations of PCL, ACL and PT at each flexion angle Knee flexion angle (degrees), mean f SD 0
PT PCL ACL a
21.5 f 4.3
39.4 f 3.9 -32.6 f 6.5
15
90
129"
I 59b
24.1 f 4.6 41.4 f 5.0 -36.0 f 6.5
2.9 f 6.9 24.1 & 5.1 -55.5 f 6.1
-14.5 f 6.6 3.9 f 1.4 -61.1 f 6.8
-21.5 f 4.0 -23.0 f 6.1 -80.4 f 4.5
The angle of active maximum flexion. The angle of passive maximum flexion.
+ ACL -1 O
0
20
O 40 60
T
I
80 100 120 140 160 Kaeeflaionangle (degnes)
Fig. 5. The averaged inclinations of PCL, ACL and PT at each flexion angle.
contraction brings the tibia forward [l 11 and compensates for the posterior instability caused by PCL insufficiency. The present study does lend anatomic support to this theory, when the knee is in the extended position, based on the anterior inclination of the PT relative to the tibial longitudinal axis. However, the present study T is parallel to the tibial longitualso indicates that the F dinal axis when the knee is flexed 90" and it would provide less anterior posterior stabilization (Fig. 4B). Based on the parallel alignment of the PT, quadriceps contraction appears to primarily maintain the anterior aspect of the joint gap when the knee is flexed. In addition, the
change in inclination of the PT with knee flexion was similar to that of the PCL and the upright position of the PT at 90" may act to provide anteroposterior stability in the same manner as the PCL. Anatomically this would imply that the PT functions as an anterior analogue of the PCL. The PCL was rather upright at 90" of flexion (24.1 k 5.1" inclination) and then became parallel to the longitudinal axis of the tibia in active maximum flexion. This observation provides grounds for our hypothesis that the main function of the PCL over 90" flexion is to maintain the joint gap between the femur and the
338
T. Komatsu et al. I Journal of Orthopaedic Research 23 (2005) 334-339
tibia rather than to provide anteroposterior stability in isolation. The knee flexed over 90" is thus posteriorly stabilized by the maintained distance between the femorotibial articular surface exerted by the PCL and the concave tibial articular surface on the medial side. This consideration is supported by our intraoperative observation that sacrificing the PCL results in a significant increase in the flexion gap, with little corresponding increase in the extension gap [12]. As regards the kinematics of deep knee flexion, we have previously reported subluxation of the lateral femoral condyle over the tibial articular surface [18]. The present study showed that in this extreme position, the PCL became inclined posteriorly relative to the tibia. The ACL was virtually horizontal to the tibial articular surface and appeared to be pressed over the tibia. Taking these findings together, passive maximum flexion (approximately 160" flexion) appears to be an anatomically abnormal position and could be regarded as a subluxation. A possible limitation in this study is that the ligament directions were estimated based on the center of attachments. The PCL can be described as having multiple bundles and areas of fiber attachment with different functional roles [6]. Biomechanical studies have shown that very little of the PCL is truly isometric throughout the knee flexion arc [6]. For example, it has been reported that the anterolateral band tightens during knee flexion, while the posteromedial band plays a relatively greater role in stabilizing the knee during extension [1,7]. The authors admit oversimplification of the complexity of the PCL structure, but interobserver errors were approximately 6" when identifying the average area of attachments of the PCL. The changes in the inclination of the PCL, however, amounted to 60", which is much larger than the estimated error. Thus the authors believe that the main findings and conclusion drawn from this study are valid. A potential weakness of the study was the lack of muscular activity and weight-bearing, but our recent results have shown that the kinematics of the PCL was not affected by weight-bearing [19]. In conclusion, the present study visualized and analyzed the movement of the PCL, ACL and PT in normal living subjects throughout the flexion range. Based on the upright position of the PCL in a flexion arc over go", the PCL plays an important role for the maintenance of the joint gap during flexion. The close resemblance of the PCL and PT in inclination to the tibia could explain the mechanism of compensation by the quadriceps for PCL insufficiency, because the upright position of the PT at 90" may act to provide anteroposterior stability in the same manner as the PCL. The results of this in vivo study of the PCL have clinical relevance to conservative therapy for PCL knee injuries. The results of this study could also be useful in PCL reconstruction surgery to determine the optimum graft position that allows maximum postoperative motion.
Acknowledgement
The authors thank H. Sakamoto, MD, PhD (Sakamot0 Clinic, Sakai City, Osaka, Japan), for his help in providing the MRI unit.
References Abbot LC, Saunders JB, Bost FC, et al. Injuries to the ligaments of the knee joint. J Bone Joint Surg 1944;26503-21. Bergfeld JA, McAllister DR, Parker RD, et al. The effects of tibial rotation on posterior translation in knees in which the posterior cruciate ligament has been cut. J Bone Joint Surg 200 1;83A:133943. Butler DL, Noyes FR, Grood ES. Ligamentous restraints to the antero-posterior drawer in the human knee: a biomechanical study. J Bone Joint Surg 1980;62A:259-70. Clancy Jr WG, Shelbourne KD, Zoellner GB, et al. Treatment of knee joint instability secondary to rupture of the posterior cruciate ligament: report of a new procedure. J Bone Joint Surg 1983; 65Az310-22. Cosgarea AJ, Jay PR. Posterior cruciate ligament injuries: evaluation and management. J Am Acad Orthop Surgeons 2001;9:297-307. Fuss FK. Anatomy of the cruciate ligaments and their function in extension and flexion of the human knee joint. Am J Anat 1989;184165-76. Girgis FG, Marshall JL, Al Mondjem ARS. The cruciate ligaments of the knee joint: anatomical, functional and experimental analysis. Clin Orthop 1975;10621&31. Gollehon DL, Torzilli PA, Warren RF. The role of the posterolateral and cruciate ligaments in the stability of the human knee: a biomechanical study. J Bone Joint Surg 1987;69A:23342. Harner CD, Hoher J. Evaluation and treatment of posterior cruciate ligament injuries. Am J Sports Med 1998;26:471-82. Hoher J, Vogrin TM, Woo SL-Y, et al. In situ forces in the human posterior cruciate ligament in response to muscle loads: a cadaveric study. J Orthop Res 1999;17:763-8. [l 11 Howell SM. Anterior tibial translation during a maximum quadriceps contraction: is it clinically significant? Am J Sports Med 1990;18573-8. [I21 Kadoya Y, Kobayashi A, Komatsu T, et al. Effects of posterior cruciate ligament resection on the tibiofemoral joint gap. Clin Orthop 200 1;391:2 1@7. [13] Li G, Gill TJ, DeFrate LE, et al. Biomechanical consequences of PCL deficiency in the knee under simulated muscle loads-an in vitro experimental study. J Orthop Res 2002;20:887-92. [14] Li G, Zayonts S, Most E, et al. In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation. J Orthop Res 2004;22:293-7. [IS] Li M, Ritter MA, Moilanen T, et al. Pointcounter-point: total knee arthroplasty. J Arthroplasty 1995;10:560-70. [I61 Nagra T, Dyrby CO, Alexander EJ, et al. Mechanical loads at the knee joint during deep flexion. J Orthop Res 2002;20:8814. [I71 Nagra T, Andriacchi TP, Alexander E, et al. Muscle co-contraction increases the load on the posterior cruciate ligament during deep knee flexion. Trans Orthop Res SOC, New Orleans, LA 2003:843. [I81 Nakagawa S, Kadoya Y, Todo S, et al. Tibiofemoral movement 3: full flexion in the living knee studied by MRI. J Bone Joint Surg 2000;82B:1199-200. [I91 Nakagawa S, Johal P, Pinskerova V. The posterior cruciate ligament during flexion of the normal knee. J Bone Joint Surg 2004;86B:450-6.
T. Komatsu et at. I Journal of Orthopaedic Research 23 (2005) 334-339 [20] Pagnano MW, Cushner FD, Scott WN. Role of the posterior cruciate ligament in total knee arthroplasty. J Am Acad Orthop Surgeons 1998;6:176-87. [21] Shelboume KD, Jennings RW, Vahey TN. Magnetic resonance imaging of posterior cruciate ligament injuries. Am J Knee Surg 1999;12:209-13.
339
[22] Shelbourne KD, Davis TJ, Patel DV. The natural history of acute, isolated, nonoperatively treated posterior cruciate ligament injuries: a prospective study. Am J Sports Med 1999;27:27683. [23] Todo S, Kadoya Y, Moilanen T, et al. Anteroposterior and rotational movement of femur during knee flexion. Clin Orthop 1999;362:162-70.