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The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study
Journal of Orthopaedic Science xxx (2016) 1e6
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Original Article
The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study Yoshio Onishi, Kazunori Hino, Seiji Watanabe, Kunihiko Watamori, Tatsuhiko Kutsuna, Hiromasa Miura* Department of Bone and Joint Surgery, Ehime University Graduate School of Medicine, Shitsukawa, Toon, Ehime 791-0295, Japan
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a b s t r a c t
Article history: Received 12 November 2015 Received in revised form 1 May 2016 Accepted 12 July 2016 Available online xxx
Background: The influence of tibial resection on the joint gap and on stability against posterior laxity in posterior cruciate ligamenteretaining total knee arthroplasty (CR-TKA) remains unclear. In addition, there are no detailed reports regarding how much of the tibial attachment of the posterior cruciate ligament (PCL) is preserved during tibial resection. Our goals were to evaluate the influence of tibial resection on the intraoperative joint gap and on postoperative anteroposterior stability in a clinical population, and to assess the preserved area of the tibial PCL attachment using cadaveric knees. Methods: In 20 consecutive patients, the joint gaps before and after tibial resection at 90 flexion and full extension were analyzed during CR-TKA, and anteroposterior stability was evaluated postoperatively. In 11 cadaveric knees, tibial resection with a thickness of 8, 10, 12, or 14 mm and a posterior slope of 3, 4, 5, 6, or 7 was simulated using computed tomography images, and the percentage of the preserved area of the attachment was calculated. Results: The flexion gaps before and after tibial resection were 18.1 ± 1.9 mm and 18.4 ± 2.2 mm, respectively, with no statistically significant difference (p ¼ 0.08). Similarly, the extension gap did not increase significantly before and after tibial resection (20.8 ± 2.5 mm and 21.0 ± 2.6 mm; p ¼ 0.45). All knees maintained anteroposterior stability at the follow-up period (32.0 ± 1.9 months). The posterior slope of the tibial resection was 5.9 ± 1.4 , and the thickness of the lateral tibial resection was 10.4 ± 1.1 mm. The cutoffs to preserve more than 50% of the attachment were 10-mm thickness and 5 slope. Conclusions: Our results showed that tibial resection did not influence the intraoperative joint gap or postoperative anteroposterior stability. However, our analysis demonstrated that increased amounts of tibial resection led to considerable damage to the attachment. © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction In posterior cruciate ligamenteretaining total knee arthroplasty (CR-TKA), a small bone block (bone island) is often preserved by inserting an osteotome anterior to the ligament in order to protect the posterior cruciate ligament (PCL) during tibial resection [1], but this procedure is troublesome and the bone island is at risk of fracture. In contrast, many surgeons, including us, resect the tibial plateau entirely and remove part of the PCL attachment from the resected tibial plateau. However, this is a concern as it has been
* Corresponding author. E-mail address: [email protected] (H. Miura).
reported that resecting the PCL results in an increased flexion gap both in normal [2] and osteoarthritic knees [3]. Several studies investigated the influence of tibial resection on the PCL [4e9], and found that during CR-TKA the tibial attachment of the PCL was often damaged or removed. Some therefore recommended retaining the PCL attachment. These studies evaluated the attachment with imaging modalities (magnetic resonance imaging [MRI] and radiography [4,8], MRI [5,7,9], or high-resolution digital photography [6]) but did not evaluate the influence of tibial resection on the joint gap. To our knowledge, no clinical reports are available regarding the joint gap after tibial resection. The influence of tibial resection on stability against posterior laxity has not been clarified either, nor is there sufficient detail on how the extent of PCL attachment during tibial resection impacts the outcomes of this procedure.
http://dx.doi.org/10.1016/j.jos.2016.07.008 0949-2658/© 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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We therefore clinically evaluated the influence of tibial resection on the intraoperative joint gap and on postoperative anteroposterior stability, and used cadaveric knees to investigate the preserved area of the tibial PCL attachment. 2. Patients and methods 2.1. Clinical assessment of the intraoperative joint gap and postoperative anteroposterior stability Between July 2012 and January 2013, we prospectively examined 20 consecutive patients (20 knees) who underwent CR-TKA for varus osteoarthritis. Those with severe deformity, severe flexion contracture, and severe instability were excluded. There were 18 women and two men with a mean age of 71.8 years (range, 62e82 years). The preoperative femorotibial angle (FTA) was 184.7 ± 3.1. Their clinical status and MRI showed no abnormalities in their PCLs. All knees displayed varus osteoarthritis of KellgreneLawrence grade 4 [10]. All operations were performed by the same senior author with a measured resection technique using a PCL-retaining prosthesis (MERA Quest Knee System, Senko Medical Instrument Manufacturing, Tokyo, Japan). This prosthesis has a shallow dish surface insert. This insert was used for all patients. All patients gave their informed consent and agreed to participate in this study. The knees were exposed using a medial parapatellar approach. The distal femur was resected perpendicularly to the mechanical axis using preoperative long-leg radiographs, and femoral external rotation was determined by preoperative computed tomography (CT). We referred to the surgical epicondylar axis. Rotational alignment was determined by measuring the angle between the surgical epicondylar axis and the posterior condylar axis as measured on CT slices. The anterior cruciate ligament (ACL) was resected when it was present. PCLs of all 20 knees were macroscopically near normal. The tibial plateau resection was made perpendicular to the mechanical axis in the frontal plane and equal to the lateral posterior slope in the sagittal plane, using an extramedullary alignment guide. We targeted 5 e6 of the posterior slope on the basis of a report that the mean posterior tibial slope in the lateral plateau was 6 in the varus knee [11] and 10-mm thickness of the lateral tibial resection. The deep medial collateral ligament was carefully liberated from the underlying osteophytes on the medial tibia. All medial and lateral osteophytes of the tibia were removed. To evaluate the influence of tibial resection, we
reproduced the states before and after the resection (i.e., the states before and after resection of the bone island). First, we made a bone island. We inserted an osteotome (with the island outlined) anterior to the PCL to protect the ligament during tibial resection, then shaped the island with a rongeur (Fig. 1A). Furthermore, osteophytes of the posterior femoral condyle were removed and the posterior capsule was released from the posterior aspect of the femur. The central joint gaps (millimeters) at 90 flexion and full extension were measured using a tensioning device [12] (Offset Repo-Tensor, Zimmer, Warsaw, IN) at a 40-lb distracting force with the capsule closed and the patella reduced. We set a 40-lb distracting force on the basis of a report that the joint gap at full extension with 40 lb of joint distraction force corresponded most closely to the insert thickness [12]. A limb holder (De Mayo Knee Positioner, Innovative Medical Products, Plainville, CT) was used to maintain the knee position. The measurements were performed three times, and the mean value was recorded. Next we resected the island with a rongeur after releasing the attachment of the PCL from the island with an electric scalpel (Fig. 1B). We measured the central joint gaps by the same method. In addition, plain radiography was used postoperatively to measure the posterior slope of the tibial resection. The thickness of the lateral tibial resection was measured by a caliper. Furthermore, we measured the total anteroposterior displacement of all knees postoperatively using a KT-1000 arthrometer (MEDmetric, San Diego, CA) to evaluate the anteroposterior stability. The follow-up ranged from 29 to 35 months (mean, 32.0 months). The displacement was recorded at 30 and 75 flexion while applying an anterior force of 133 N and a posterior force of 89 N [13]. Measurements were performed three times, and the mean value was used for evaluation. Based on the results of a knee kinematics study [14] using cadaveric knees, knees that had less laxity in total anteroposterior displacement at 75 than at 30 flexion were defined as having a functioning PCL, whereas knees with greater laxity at 75 flexion were defined as having a nonfunctioning PCL. 2.2. Cadaveric assessment of the preserved area of the tibial PCL attachment Ethical approval for this study was obtained from the ethical committee of our institution. Embalmed cadaveric knees were used
Fig. 1. A) A schema of intraoperative bone island preservation. Black solid arrows indicate the bone island. The black asterisk indicates the PCL. B) A schema of removed island. Black solid arrowheads indicate the partial detachment of the PCL.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
Y. Onishi et al. / Journal of Orthopaedic Science xxx (2016) 1e6
Fig. 2. Posterior view of the right tibia, showing the location of the tibial attachment of the PCL outlined with eight fine pins.
to evaluate tibial PCL attachment. These knees were removed after the cadavers were used in the anatomy laboratory of our institution. The cadavers were fixed with embalming fluid containing 10% formaldehyde. Eleven adult knees (eight from female donors and three from male donors), with no macroscopic degenerative or traumatic changes, were used in this study. The mean age of the donors at the time of death was 88.3 years (range, 83e92 years). Preparation began with the removal of all extra-articular soft tissue, followed by careful dissection through anterior and posterior approaches. The PCL was detached from the femoral attachment, and the synovial sleeve surrounding the PCL was carefully removed. The
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tibial PCL attachment was identified by pulling the PCL fibers in all directions, and its shape was trapezoidal as described by others [15e18]. The attachment was outlined peripherally using eight 1.2mm-diameter fine pins (Fig. 2). All tibiae were scanned at a slice thickness of 1 mm with a CT scanner (SOMATOM Spirit, Siemens Medical Solutions, Erlangen, Germany). The CT data were reconstructed with image analysis software (ZedView version 10.0, LEXI, Tokyo, Japan). To evaluate the area of the tibial PCL attachment during TKA, we simulated several tibial resection approaches. We defined the anteroposterior axis of the tibia as a line connecting the middle of the PCL and the medial one-third of the patellar tendon attachment. Both the coronal and sagittal anatomical axes of the tibia were defined as lines connecting the midpoints of the proximal and distal metaphyses, and we settled the posterior tibial slope. The mean tibial angle to anatomical axis in varus of all 11 knees was 4.7, and it was considered that there was no difference between anatomical axis and mechanical axis on the basis of a report that both axes changed significantly with that of S10 [19]. Resections were simulated perpendicular to the coronal anatomical axis with thicknesses of 8, 10, 12, or 14 mm from the lateral joint plane and with posterior slopes of 3, 4, 5, 6, or 7. We assumed a cartilage thickness of 2 mm [20] (Fig. 3A). The PCL attachment was approximated as a polygon feature. The area of the polygon (in square pixels) separated by the resection plane was measured using ImageJ software version 1.49 (National Institute of Health, Bethesda, MD) (Fig. 3B), and the percentage of the preserved area of the tibial PCL attachment was then calculated. All measurements using CT images were performed by the first author and were repeated at three-month intervals. The intraclass correlation coefficient was excellent (95% confidence interval [CI], 0.87 to 0.99). Two observers (the first author and K.W.) independently made all CT measurements. The interclass correlation coefficient was excellent (95% CI, 0.85 to 0.98).
Fig. 3. A) Coronal plane CT image showing the simulation of the tibial resection. White circles outline the location of the tibial attachment of the PCL. The white dotted line represents the coronal anatomical axis. The lower white dashed line represents the joint plane on CT image, and the upper dashed line represents the actual joint plane considering a cartilage thickness of 2 mm. The white solid line represents the resection plane. The white solid arrow indicates the amount of tibial resection from the lateral plateau. B) White solid lines represent the resection plane. Upper coronal plane CT image represents the identification of the external boundary of the tibial PCL attachment. Lower image represents the identification of the preserved area of the tibial PCL attachment.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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Fig. 4. A) Bar chart showing the mean flexion gap before and after resection. Error bars represent the standard deviation. B) Bar chart showing the mean extension gap before and after resection. Error bars represent the standard deviation.
2.3. Statistical analysis The paired t-test was performed to compare the joint gaps before and after tibial resection. We compared the postoperative total anteroposterior displacements at 30 and 75 flexion using the paired t-test. A multiple regression analysis was performed to model the concurrent effects of the thickness and the posterior slope on the preserved area. All statistical analyses were conducted using JMP software version 11.2 (SAS Institute, Cary, NC). A significant difference was defined as a p value < 0.05.
more strongly by the thickness (regression coefficient [b], 10.09; 95% CI, 10.56 to 9.62; p < 0.001) than the slope (b, 4.60; 95% CI, 5.34 to 3.85; p < 0.001). The linear regression equation was expressed as follows: Preserved area (%) ¼ 179.32e10.09 Thickness (mm) 4.60 Slope ( ).
3. Results 3.1. The clinical intraoperative joint gap and postoperative anteroposterior stability The mean (±standard deviation) flexion gaps were 18.1 ± 1.9 mm before resection and 18.4 ± 2.2 mm after resection (Fig. 4A). The flexion gap did not change significantly after resection (p ¼ 0.08). The mean extension gaps were 20.8 ± 2.5 mm before resection and 21.0 ± 2.6 mm after resection (Fig. 4B). The extension gap did not change significantly after resection (p ¼ 0.45). At the follow-up period (32.0 ± 1.9 months), the total anteroposterior displacements of all knees were larger at 30 (10.3 ± 1.5 mm) than at 75 flexion (6.2 ± 1.1 mm) (p < 0.001) (Fig. 5). All knees had a functioning PCL. The mean posterior tibial slope was 5.9 ± 1.4 , and the mean thickness was 10.4 ± 1.1 mm from the lateral tibial plane. 3.2. The preserved area of the tibial PCL attachment in cadaveric specimens The preserved area of the tibial PCL attachment decreased with increasing thickness and increasing slope (Fig. 6). The cutoffs to preserve more than 50% of the area were 10-mm thickness and 5 slope, which were the same as our target values. A multiple regression analysis showed that the preserved area was influenced
Fig. 5. The total anteroposterior displacements of all 20 knees at 30 flexion and at 75 flexion.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
Y. Onishi et al. / Journal of Orthopaedic Science xxx (2016) 1e6
Fig. 6. The percentage of the PCL attachment area that was preserved at a thickness of 8, 10, 12, and 14 mm. Boxes show the value of the preserved area. Box length represents the interquartile range. The line in the center of the boxes represents the median value. The bar represents the range of the preserved area.
4. Discussion Our study demonstrated that tibial resection did not result in a significant increase of the joint gap, and that the knees maintained anteroposterior stability postoperatively. In contrast, the results showed that increased amounts of tibial resection led to considerable damage to the PCL attachment. We found that the joint gap did not change clinically after tibial resection, and this may be anatomically plausible. The PCL is comprised of the anterolateral bundle (ALB) and the posteromedial bundle (PMB). There are several reports on the anatomical attachments of the bundles [16,21,22]. Tajima et al. [16] studied tibial PCL attachments from 21 fresh-frozen adult cadaveric knees, and the knees were evaluated with three-dimensional laser photography. They reported that the centers of the ALB and PMB attachments were 1.5 ± 0.8 mm and 6.0 ± 2.0 mm, respectively, from the tibial plane. They showed that the attachment of the PCL was trapezoid-shaped and became wider inferiorly. A separate study reported that the transverse axis of the tibial plateau was approximately 3.0 varus to the mechanical axis of the tibia in normal knees [23]. This angle becomes larger in knees with varus osteoarthritis. Therefore in our tibial resection, which was perpendicular to the mechanical axis in the frontal plane (i.e., it was extended obliquely against the tibial plane) and 10.4 ± 1.1 mm from the lateral plateau, the ALB attachment was at risk for damage but the majority of the PMB attachment was preserved and the joint gap was maintained. In this study the knees maintained anteroposterior stability after tibial resection, and several biomechanical factors are thought to contribute to this outcome. The ALB has been thought to be taut in knee flexion, and the PMB taut in knee extension [24]. Ahmad et al. [25], however, found that the PMB was taut in knee flexion as well, in a study that evaluated six fresh-frozen cadaveric knees with a digital coordinate measuring device. They reported that the ALB length increased with knee flexion, while the PMB length
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decreased with increases in knee flexion angles from 0 to 45 and increased from 60 to 120 . Their results also indicated that knee flexion orients the PMB to better resist posterior tibial translation. These findings suggest that anteroposterior stability was maintained after tibial resection in this study because the majority of the PMB attachment was preserved by our procedure. Our study examined in detail the preserved area of the PCL attachment following tibial resection, and it was larger than the areas found in a number of other studies [4e9]. Shannon et al. [4] investigated 22 knees comparing preoperative MRI images with postoperative radiographs. They reported that the attachment was removed completely in 36.4% of patients after tibial resection. However, their findings were confirmed indirectly by comparing vertical distances from the fibular head, and not by a cadaveric study. Matziolis et al. [5] investigated 182 knees on sagittal MR images using simulated tibial resections with posterior slopes of 0 and 7 and a thickness of 10 mm from the lateral joint plane. They reported that in men and women, respectively, 45 ± 28% and 46 ± 30% of the PCL attachment was removed with 0 slope, and 69 ± 24% and 67 ± 25% with 7 slope. However, they evaluated only attachment length and not area. They simulated the resection 8 mm from the medial joint plane, which seems slightly excessive compared to the usual tibial resection amount during TKA. Feyen et al. [6] investigated 20 cadaveric knees with high-resolution digital photography using simulated tibial resection with a posterior slope of 3 and a thickness of 9 mm from the lateral joint plane. They reported that 68.8 ± 15.3% of the PCL attachment was removed. However, there seem to be measurement errors due to differences in imaging conditions before and after the tibial resection. They found that the surface area of the PCL attachment was 148.9 ± 25.8 mm2, a value smaller than that of Tajima et al. [16] (243.9 ± 38.2 mm2), who measured it using a three-dimensional laser scanner. Our results suggest that tibial resection is beneficial in CR-TKA as it facilitates the surgical procedure and preserves the intraoperative joint gap and postoperative anteroposterior stability. However, as is evident from our simulation of the resection, increased resection amounts may lead to considerable damage of the PCL attachment. Several reports are available regarding the ALB, which may be at risk of damage after the resection [26e28]. Harner et al. [26] examined the ALB and PMB separately in 14 fresh-frozen cadaveric knees, and reported that the ALB had a significantly greater linear stiffness and ultimate load than the PMB. Race et al. [27] tested nine fresh-frozen cadaver knees and reported that the ALB was the primary restraint to posterior drawer as it resisted between 50 and 74% of this force in the midrange of flexion (40e120 ). Papannagari et al. [28] tested seven normal knees kinematically with MRI and dual-orthogonal fluoroscopy and suggested that the ALB might play a role in constraining the mediolateral translation of the tibia, whereas the PMB might play a role in constraining anteroposterior translation. Accordingly, it would be better to preserve the ALB attachment. Furthermore, as has been mentioned in several reports [29e32], we must consider the quality of the PCL in TKA. Kleinbart et al. [29] histologically examined 24 PCLs harvested during TKA and reported 17% normal ligaments, 20% with mild focal changes, and 63% with marked degenerative changes. Therefore, we would recommend the retention of a bone island in CR-TKA whenever possible, and the use of a posterior-stabilized (PS) prosthesis if a bone island is not made and the amount of the tibial resection is large. We should also evaluate, at different amounts of tibial resection, the ultimate load of the preserved PCL against distracting forces in flexion and against posterior drawer forces. There were several limitations to our study. First, a comparatively small number of patients and cadavers were investigated.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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However, the clinical portion of our study was a biomechanical assessment that compared the joint gaps generated by tibial resection and evaluated postoperative anteroposterior stability, while the cadaveric portion study used a CT scanner to minimize errors. Therefore, we believe that the numbers used were large enough to fulfill our purposes. Second, the measurements were performed only at a 40-lb distraction force, and stronger forces might alter the influence of the tibial resection. Third, we should strengthen the condition with 5.9 posterior slope and 10.4-mm thickness, and with the condition changed, joint gap and stability might be altered. Fourth, we used the anatomical axis to simulate the tibial resection. However, the anatomical axis is identical to the mechanical axis in most knees. Therefore, we believe the percentage of the preserved area does not change. Fifth, we approximated the attachment as a polygon feature and did not measure the surface area of the PCL attachment. However, a change of the attachment is relative, and the percentage of the preserved area does not change. In summary, we evaluated the influence of tibial resection on the PCL in CR-TKA using clinical and cadaveric assessments. Our analysis showed that tibial resection in CR-TKA did not influence the intraoperative joint gap or postoperative anteroposterior stability. However, an increase in the amount of tibial resection led to considerable damage of the PCL attachment, and the cutoffs to preserve more than 50% of the attachment were 10-mm thickness and 5 slope. Therefore, we would recommend the retention of a bone island in CR-TKA, and the use of a PS prosthesis if a bone island is not made and the amount of the tibial resection is large. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgments We thank Masami Ishimaru MD, PhD and Yasutake Iseki MD (Department of Bone and Joint Surgery, Ehime University Graduate School of Medicine) for assistance with this study. References [1] Barnes CL, Sledge CB. Total knee arthroplasty with posterior cruciate ligament retention designs. Surgery of the knee. 2nd ed. New York: Churchill-Livingstone; 1993. p. 815e27. [2] Matsui Y, Kadoya Y, Horibe S. The intact posterior cruciate ligament not only controls posterior displacement but also maintains the flexion gap. Clin Orthop Relat Res 2013 Apr;471(4):1299e304. [3] Kadoya Y, Kobayashi A, Komatsu T, Nakagawa S, Yamano Y. Effects of posterior cruciate ligament resection on the tibiofemoral joint gap. Clin Orthop Relat Res 2001 Oct;391(10):210e7. [4] Shannon FJ, Cronin JJ, Cleary MS, Eustace SJ, O'Byrne JM. The posterior cruciate ligament-preserving total knee replacement: do we 'preserve' it? A radiological study. J Bone Jt Surg Br 2007 Jun;89(6):766e71. [5] Matziolis G, Mehlhorn S, Schattat N, Diederichs G, Hube R, Perka C, Matziolis D. How much of the PCL is really preserved during the tibial cut? Knee Surg Sports Traumatol Arthrosc 2012 Jun;20(6):1083e6. [6] Feyen H, Van Opstal N, Bellemans J. Partial resection of the PCL insertion site during tibial preparation in cruciate-retaining TKA. Knee Surg Sports Traumatol Arthrosc 2013 Dec;21(12):2674e9. [7] Liabaud B, Patrick Jr DA, Geller JA. Is the posterior cruciate ligament destabilized after the tibial cut in a cruciate retaining total knee replacement? An anatomical study. Knee 2013 Dec;20(6):412e5. [8] Jawhar A, Wasnik S, Scharf HP, Roehl H. Fibula head is a useful landmark to predict the location of posterior cruciate ligament footprint prior to total knee arthroplasty. Int Orthop 2014 Feb;38(2):267e72.
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Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original Article
The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study Yoshio Onishi, Kazunori Hino, Seiji Watanabe, Kunihiko Watamori, Tatsuhiko Kutsuna, Hiromasa Miura* Department of Bone and Joint Surgery, Ehime University Graduate School of Medicine, Shitsukawa, Toon, Ehime 791-0295, Japan
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a b s t r a c t
Article history: Received 12 November 2015 Received in revised form 1 May 2016 Accepted 12 July 2016 Available online xxx
Background: The influence of tibial resection on the joint gap and on stability against posterior laxity in posterior cruciate ligamenteretaining total knee arthroplasty (CR-TKA) remains unclear. In addition, there are no detailed reports regarding how much of the tibial attachment of the posterior cruciate ligament (PCL) is preserved during tibial resection. Our goals were to evaluate the influence of tibial resection on the intraoperative joint gap and on postoperative anteroposterior stability in a clinical population, and to assess the preserved area of the tibial PCL attachment using cadaveric knees. Methods: In 20 consecutive patients, the joint gaps before and after tibial resection at 90 flexion and full extension were analyzed during CR-TKA, and anteroposterior stability was evaluated postoperatively. In 11 cadaveric knees, tibial resection with a thickness of 8, 10, 12, or 14 mm and a posterior slope of 3, 4, 5, 6, or 7 was simulated using computed tomography images, and the percentage of the preserved area of the attachment was calculated. Results: The flexion gaps before and after tibial resection were 18.1 ± 1.9 mm and 18.4 ± 2.2 mm, respectively, with no statistically significant difference (p ¼ 0.08). Similarly, the extension gap did not increase significantly before and after tibial resection (20.8 ± 2.5 mm and 21.0 ± 2.6 mm; p ¼ 0.45). All knees maintained anteroposterior stability at the follow-up period (32.0 ± 1.9 months). The posterior slope of the tibial resection was 5.9 ± 1.4 , and the thickness of the lateral tibial resection was 10.4 ± 1.1 mm. The cutoffs to preserve more than 50% of the attachment were 10-mm thickness and 5 slope. Conclusions: Our results showed that tibial resection did not influence the intraoperative joint gap or postoperative anteroposterior stability. However, our analysis demonstrated that increased amounts of tibial resection led to considerable damage to the attachment. © 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction In posterior cruciate ligamenteretaining total knee arthroplasty (CR-TKA), a small bone block (bone island) is often preserved by inserting an osteotome anterior to the ligament in order to protect the posterior cruciate ligament (PCL) during tibial resection [1], but this procedure is troublesome and the bone island is at risk of fracture. In contrast, many surgeons, including us, resect the tibial plateau entirely and remove part of the PCL attachment from the resected tibial plateau. However, this is a concern as it has been
* Corresponding author. E-mail address: [email protected] (H. Miura).
reported that resecting the PCL results in an increased flexion gap both in normal [2] and osteoarthritic knees [3]. Several studies investigated the influence of tibial resection on the PCL [4e9], and found that during CR-TKA the tibial attachment of the PCL was often damaged or removed. Some therefore recommended retaining the PCL attachment. These studies evaluated the attachment with imaging modalities (magnetic resonance imaging [MRI] and radiography [4,8], MRI [5,7,9], or high-resolution digital photography [6]) but did not evaluate the influence of tibial resection on the joint gap. To our knowledge, no clinical reports are available regarding the joint gap after tibial resection. The influence of tibial resection on stability against posterior laxity has not been clarified either, nor is there sufficient detail on how the extent of PCL attachment during tibial resection impacts the outcomes of this procedure.
http://dx.doi.org/10.1016/j.jos.2016.07.008 0949-2658/© 2016 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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We therefore clinically evaluated the influence of tibial resection on the intraoperative joint gap and on postoperative anteroposterior stability, and used cadaveric knees to investigate the preserved area of the tibial PCL attachment. 2. Patients and methods 2.1. Clinical assessment of the intraoperative joint gap and postoperative anteroposterior stability Between July 2012 and January 2013, we prospectively examined 20 consecutive patients (20 knees) who underwent CR-TKA for varus osteoarthritis. Those with severe deformity, severe flexion contracture, and severe instability were excluded. There were 18 women and two men with a mean age of 71.8 years (range, 62e82 years). The preoperative femorotibial angle (FTA) was 184.7 ± 3.1. Their clinical status and MRI showed no abnormalities in their PCLs. All knees displayed varus osteoarthritis of KellgreneLawrence grade 4 [10]. All operations were performed by the same senior author with a measured resection technique using a PCL-retaining prosthesis (MERA Quest Knee System, Senko Medical Instrument Manufacturing, Tokyo, Japan). This prosthesis has a shallow dish surface insert. This insert was used for all patients. All patients gave their informed consent and agreed to participate in this study. The knees were exposed using a medial parapatellar approach. The distal femur was resected perpendicularly to the mechanical axis using preoperative long-leg radiographs, and femoral external rotation was determined by preoperative computed tomography (CT). We referred to the surgical epicondylar axis. Rotational alignment was determined by measuring the angle between the surgical epicondylar axis and the posterior condylar axis as measured on CT slices. The anterior cruciate ligament (ACL) was resected when it was present. PCLs of all 20 knees were macroscopically near normal. The tibial plateau resection was made perpendicular to the mechanical axis in the frontal plane and equal to the lateral posterior slope in the sagittal plane, using an extramedullary alignment guide. We targeted 5 e6 of the posterior slope on the basis of a report that the mean posterior tibial slope in the lateral plateau was 6 in the varus knee [11] and 10-mm thickness of the lateral tibial resection. The deep medial collateral ligament was carefully liberated from the underlying osteophytes on the medial tibia. All medial and lateral osteophytes of the tibia were removed. To evaluate the influence of tibial resection, we
reproduced the states before and after the resection (i.e., the states before and after resection of the bone island). First, we made a bone island. We inserted an osteotome (with the island outlined) anterior to the PCL to protect the ligament during tibial resection, then shaped the island with a rongeur (Fig. 1A). Furthermore, osteophytes of the posterior femoral condyle were removed and the posterior capsule was released from the posterior aspect of the femur. The central joint gaps (millimeters) at 90 flexion and full extension were measured using a tensioning device [12] (Offset Repo-Tensor, Zimmer, Warsaw, IN) at a 40-lb distracting force with the capsule closed and the patella reduced. We set a 40-lb distracting force on the basis of a report that the joint gap at full extension with 40 lb of joint distraction force corresponded most closely to the insert thickness [12]. A limb holder (De Mayo Knee Positioner, Innovative Medical Products, Plainville, CT) was used to maintain the knee position. The measurements were performed three times, and the mean value was recorded. Next we resected the island with a rongeur after releasing the attachment of the PCL from the island with an electric scalpel (Fig. 1B). We measured the central joint gaps by the same method. In addition, plain radiography was used postoperatively to measure the posterior slope of the tibial resection. The thickness of the lateral tibial resection was measured by a caliper. Furthermore, we measured the total anteroposterior displacement of all knees postoperatively using a KT-1000 arthrometer (MEDmetric, San Diego, CA) to evaluate the anteroposterior stability. The follow-up ranged from 29 to 35 months (mean, 32.0 months). The displacement was recorded at 30 and 75 flexion while applying an anterior force of 133 N and a posterior force of 89 N [13]. Measurements were performed three times, and the mean value was used for evaluation. Based on the results of a knee kinematics study [14] using cadaveric knees, knees that had less laxity in total anteroposterior displacement at 75 than at 30 flexion were defined as having a functioning PCL, whereas knees with greater laxity at 75 flexion were defined as having a nonfunctioning PCL. 2.2. Cadaveric assessment of the preserved area of the tibial PCL attachment Ethical approval for this study was obtained from the ethical committee of our institution. Embalmed cadaveric knees were used
Fig. 1. A) A schema of intraoperative bone island preservation. Black solid arrows indicate the bone island. The black asterisk indicates the PCL. B) A schema of removed island. Black solid arrowheads indicate the partial detachment of the PCL.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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Fig. 2. Posterior view of the right tibia, showing the location of the tibial attachment of the PCL outlined with eight fine pins.
to evaluate tibial PCL attachment. These knees were removed after the cadavers were used in the anatomy laboratory of our institution. The cadavers were fixed with embalming fluid containing 10% formaldehyde. Eleven adult knees (eight from female donors and three from male donors), with no macroscopic degenerative or traumatic changes, were used in this study. The mean age of the donors at the time of death was 88.3 years (range, 83e92 years). Preparation began with the removal of all extra-articular soft tissue, followed by careful dissection through anterior and posterior approaches. The PCL was detached from the femoral attachment, and the synovial sleeve surrounding the PCL was carefully removed. The
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tibial PCL attachment was identified by pulling the PCL fibers in all directions, and its shape was trapezoidal as described by others [15e18]. The attachment was outlined peripherally using eight 1.2mm-diameter fine pins (Fig. 2). All tibiae were scanned at a slice thickness of 1 mm with a CT scanner (SOMATOM Spirit, Siemens Medical Solutions, Erlangen, Germany). The CT data were reconstructed with image analysis software (ZedView version 10.0, LEXI, Tokyo, Japan). To evaluate the area of the tibial PCL attachment during TKA, we simulated several tibial resection approaches. We defined the anteroposterior axis of the tibia as a line connecting the middle of the PCL and the medial one-third of the patellar tendon attachment. Both the coronal and sagittal anatomical axes of the tibia were defined as lines connecting the midpoints of the proximal and distal metaphyses, and we settled the posterior tibial slope. The mean tibial angle to anatomical axis in varus of all 11 knees was 4.7, and it was considered that there was no difference between anatomical axis and mechanical axis on the basis of a report that both axes changed significantly with that of S10 [19]. Resections were simulated perpendicular to the coronal anatomical axis with thicknesses of 8, 10, 12, or 14 mm from the lateral joint plane and with posterior slopes of 3, 4, 5, 6, or 7. We assumed a cartilage thickness of 2 mm [20] (Fig. 3A). The PCL attachment was approximated as a polygon feature. The area of the polygon (in square pixels) separated by the resection plane was measured using ImageJ software version 1.49 (National Institute of Health, Bethesda, MD) (Fig. 3B), and the percentage of the preserved area of the tibial PCL attachment was then calculated. All measurements using CT images were performed by the first author and were repeated at three-month intervals. The intraclass correlation coefficient was excellent (95% confidence interval [CI], 0.87 to 0.99). Two observers (the first author and K.W.) independently made all CT measurements. The interclass correlation coefficient was excellent (95% CI, 0.85 to 0.98).
Fig. 3. A) Coronal plane CT image showing the simulation of the tibial resection. White circles outline the location of the tibial attachment of the PCL. The white dotted line represents the coronal anatomical axis. The lower white dashed line represents the joint plane on CT image, and the upper dashed line represents the actual joint plane considering a cartilage thickness of 2 mm. The white solid line represents the resection plane. The white solid arrow indicates the amount of tibial resection from the lateral plateau. B) White solid lines represent the resection plane. Upper coronal plane CT image represents the identification of the external boundary of the tibial PCL attachment. Lower image represents the identification of the preserved area of the tibial PCL attachment.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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Fig. 4. A) Bar chart showing the mean flexion gap before and after resection. Error bars represent the standard deviation. B) Bar chart showing the mean extension gap before and after resection. Error bars represent the standard deviation.
2.3. Statistical analysis The paired t-test was performed to compare the joint gaps before and after tibial resection. We compared the postoperative total anteroposterior displacements at 30 and 75 flexion using the paired t-test. A multiple regression analysis was performed to model the concurrent effects of the thickness and the posterior slope on the preserved area. All statistical analyses were conducted using JMP software version 11.2 (SAS Institute, Cary, NC). A significant difference was defined as a p value < 0.05.
more strongly by the thickness (regression coefficient [b], 10.09; 95% CI, 10.56 to 9.62; p < 0.001) than the slope (b, 4.60; 95% CI, 5.34 to 3.85; p < 0.001). The linear regression equation was expressed as follows: Preserved area (%) ¼ 179.32e10.09 Thickness (mm) 4.60 Slope ( ).
3. Results 3.1. The clinical intraoperative joint gap and postoperative anteroposterior stability The mean (±standard deviation) flexion gaps were 18.1 ± 1.9 mm before resection and 18.4 ± 2.2 mm after resection (Fig. 4A). The flexion gap did not change significantly after resection (p ¼ 0.08). The mean extension gaps were 20.8 ± 2.5 mm before resection and 21.0 ± 2.6 mm after resection (Fig. 4B). The extension gap did not change significantly after resection (p ¼ 0.45). At the follow-up period (32.0 ± 1.9 months), the total anteroposterior displacements of all knees were larger at 30 (10.3 ± 1.5 mm) than at 75 flexion (6.2 ± 1.1 mm) (p < 0.001) (Fig. 5). All knees had a functioning PCL. The mean posterior tibial slope was 5.9 ± 1.4 , and the mean thickness was 10.4 ± 1.1 mm from the lateral tibial plane. 3.2. The preserved area of the tibial PCL attachment in cadaveric specimens The preserved area of the tibial PCL attachment decreased with increasing thickness and increasing slope (Fig. 6). The cutoffs to preserve more than 50% of the area were 10-mm thickness and 5 slope, which were the same as our target values. A multiple regression analysis showed that the preserved area was influenced
Fig. 5. The total anteroposterior displacements of all 20 knees at 30 flexion and at 75 flexion.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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Fig. 6. The percentage of the PCL attachment area that was preserved at a thickness of 8, 10, 12, and 14 mm. Boxes show the value of the preserved area. Box length represents the interquartile range. The line in the center of the boxes represents the median value. The bar represents the range of the preserved area.
4. Discussion Our study demonstrated that tibial resection did not result in a significant increase of the joint gap, and that the knees maintained anteroposterior stability postoperatively. In contrast, the results showed that increased amounts of tibial resection led to considerable damage to the PCL attachment. We found that the joint gap did not change clinically after tibial resection, and this may be anatomically plausible. The PCL is comprised of the anterolateral bundle (ALB) and the posteromedial bundle (PMB). There are several reports on the anatomical attachments of the bundles [16,21,22]. Tajima et al. [16] studied tibial PCL attachments from 21 fresh-frozen adult cadaveric knees, and the knees were evaluated with three-dimensional laser photography. They reported that the centers of the ALB and PMB attachments were 1.5 ± 0.8 mm and 6.0 ± 2.0 mm, respectively, from the tibial plane. They showed that the attachment of the PCL was trapezoid-shaped and became wider inferiorly. A separate study reported that the transverse axis of the tibial plateau was approximately 3.0 varus to the mechanical axis of the tibia in normal knees [23]. This angle becomes larger in knees with varus osteoarthritis. Therefore in our tibial resection, which was perpendicular to the mechanical axis in the frontal plane (i.e., it was extended obliquely against the tibial plane) and 10.4 ± 1.1 mm from the lateral plateau, the ALB attachment was at risk for damage but the majority of the PMB attachment was preserved and the joint gap was maintained. In this study the knees maintained anteroposterior stability after tibial resection, and several biomechanical factors are thought to contribute to this outcome. The ALB has been thought to be taut in knee flexion, and the PMB taut in knee extension [24]. Ahmad et al. [25], however, found that the PMB was taut in knee flexion as well, in a study that evaluated six fresh-frozen cadaveric knees with a digital coordinate measuring device. They reported that the ALB length increased with knee flexion, while the PMB length
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decreased with increases in knee flexion angles from 0 to 45 and increased from 60 to 120 . Their results also indicated that knee flexion orients the PMB to better resist posterior tibial translation. These findings suggest that anteroposterior stability was maintained after tibial resection in this study because the majority of the PMB attachment was preserved by our procedure. Our study examined in detail the preserved area of the PCL attachment following tibial resection, and it was larger than the areas found in a number of other studies [4e9]. Shannon et al. [4] investigated 22 knees comparing preoperative MRI images with postoperative radiographs. They reported that the attachment was removed completely in 36.4% of patients after tibial resection. However, their findings were confirmed indirectly by comparing vertical distances from the fibular head, and not by a cadaveric study. Matziolis et al. [5] investigated 182 knees on sagittal MR images using simulated tibial resections with posterior slopes of 0 and 7 and a thickness of 10 mm from the lateral joint plane. They reported that in men and women, respectively, 45 ± 28% and 46 ± 30% of the PCL attachment was removed with 0 slope, and 69 ± 24% and 67 ± 25% with 7 slope. However, they evaluated only attachment length and not area. They simulated the resection 8 mm from the medial joint plane, which seems slightly excessive compared to the usual tibial resection amount during TKA. Feyen et al. [6] investigated 20 cadaveric knees with high-resolution digital photography using simulated tibial resection with a posterior slope of 3 and a thickness of 9 mm from the lateral joint plane. They reported that 68.8 ± 15.3% of the PCL attachment was removed. However, there seem to be measurement errors due to differences in imaging conditions before and after the tibial resection. They found that the surface area of the PCL attachment was 148.9 ± 25.8 mm2, a value smaller than that of Tajima et al. [16] (243.9 ± 38.2 mm2), who measured it using a three-dimensional laser scanner. Our results suggest that tibial resection is beneficial in CR-TKA as it facilitates the surgical procedure and preserves the intraoperative joint gap and postoperative anteroposterior stability. However, as is evident from our simulation of the resection, increased resection amounts may lead to considerable damage of the PCL attachment. Several reports are available regarding the ALB, which may be at risk of damage after the resection [26e28]. Harner et al. [26] examined the ALB and PMB separately in 14 fresh-frozen cadaveric knees, and reported that the ALB had a significantly greater linear stiffness and ultimate load than the PMB. Race et al. [27] tested nine fresh-frozen cadaver knees and reported that the ALB was the primary restraint to posterior drawer as it resisted between 50 and 74% of this force in the midrange of flexion (40e120 ). Papannagari et al. [28] tested seven normal knees kinematically with MRI and dual-orthogonal fluoroscopy and suggested that the ALB might play a role in constraining the mediolateral translation of the tibia, whereas the PMB might play a role in constraining anteroposterior translation. Accordingly, it would be better to preserve the ALB attachment. Furthermore, as has been mentioned in several reports [29e32], we must consider the quality of the PCL in TKA. Kleinbart et al. [29] histologically examined 24 PCLs harvested during TKA and reported 17% normal ligaments, 20% with mild focal changes, and 63% with marked degenerative changes. Therefore, we would recommend the retention of a bone island in CR-TKA whenever possible, and the use of a posterior-stabilized (PS) prosthesis if a bone island is not made and the amount of the tibial resection is large. We should also evaluate, at different amounts of tibial resection, the ultimate load of the preserved PCL against distracting forces in flexion and against posterior drawer forces. There were several limitations to our study. First, a comparatively small number of patients and cadavers were investigated.
Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008
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However, the clinical portion of our study was a biomechanical assessment that compared the joint gaps generated by tibial resection and evaluated postoperative anteroposterior stability, while the cadaveric portion study used a CT scanner to minimize errors. Therefore, we believe that the numbers used were large enough to fulfill our purposes. Second, the measurements were performed only at a 40-lb distraction force, and stronger forces might alter the influence of the tibial resection. Third, we should strengthen the condition with 5.9 posterior slope and 10.4-mm thickness, and with the condition changed, joint gap and stability might be altered. Fourth, we used the anatomical axis to simulate the tibial resection. However, the anatomical axis is identical to the mechanical axis in most knees. Therefore, we believe the percentage of the preserved area does not change. Fifth, we approximated the attachment as a polygon feature and did not measure the surface area of the PCL attachment. However, a change of the attachment is relative, and the percentage of the preserved area does not change. In summary, we evaluated the influence of tibial resection on the PCL in CR-TKA using clinical and cadaveric assessments. Our analysis showed that tibial resection in CR-TKA did not influence the intraoperative joint gap or postoperative anteroposterior stability. However, an increase in the amount of tibial resection led to considerable damage of the PCL attachment, and the cutoffs to preserve more than 50% of the attachment were 10-mm thickness and 5 slope. Therefore, we would recommend the retention of a bone island in CR-TKA, and the use of a PS prosthesis if a bone island is not made and the amount of the tibial resection is large. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgments We thank Masami Ishimaru MD, PhD and Yasutake Iseki MD (Department of Bone and Joint Surgery, Ehime University Graduate School of Medicine) for assistance with this study. References [1] Barnes CL, Sledge CB. Total knee arthroplasty with posterior cruciate ligament retention designs. Surgery of the knee. 2nd ed. New York: Churchill-Livingstone; 1993. p. 815e27. [2] Matsui Y, Kadoya Y, Horibe S. The intact posterior cruciate ligament not only controls posterior displacement but also maintains the flexion gap. Clin Orthop Relat Res 2013 Apr;471(4):1299e304. [3] Kadoya Y, Kobayashi A, Komatsu T, Nakagawa S, Yamano Y. Effects of posterior cruciate ligament resection on the tibiofemoral joint gap. Clin Orthop Relat Res 2001 Oct;391(10):210e7. [4] Shannon FJ, Cronin JJ, Cleary MS, Eustace SJ, O'Byrne JM. The posterior cruciate ligament-preserving total knee replacement: do we 'preserve' it? A radiological study. J Bone Jt Surg Br 2007 Jun;89(6):766e71. [5] Matziolis G, Mehlhorn S, Schattat N, Diederichs G, Hube R, Perka C, Matziolis D. How much of the PCL is really preserved during the tibial cut? Knee Surg Sports Traumatol Arthrosc 2012 Jun;20(6):1083e6. [6] Feyen H, Van Opstal N, Bellemans J. Partial resection of the PCL insertion site during tibial preparation in cruciate-retaining TKA. Knee Surg Sports Traumatol Arthrosc 2013 Dec;21(12):2674e9. [7] Liabaud B, Patrick Jr DA, Geller JA. Is the posterior cruciate ligament destabilized after the tibial cut in a cruciate retaining total knee replacement? An anatomical study. Knee 2013 Dec;20(6):412e5. [8] Jawhar A, Wasnik S, Scharf HP, Roehl H. Fibula head is a useful landmark to predict the location of posterior cruciate ligament footprint prior to total knee arthroplasty. Int Orthop 2014 Feb;38(2):267e72.
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Please cite this article in press as: Onishi Y, et al., The influence of tibial resection on the PCL in PCL-retaining total knee arthroplasty: A clinical and cadaveric study, Journal of Orthopaedic Science (2016), http://dx.doi.org/10.1016/j.jos.2016.07.008