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Femoral component placement changes soft tissue balance in posterior-stabilized total knee arthroplasty
Clinical Biomechanics 25 (2010) 926–930
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Clinical Biomechanics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l i n b i o m e c h
Femoral component placement changes soft tissue balance in posterior-stabilized total knee arthroplasty Hirotsugu Muratsu a,⁎, Tomoyuki Matsumoto b, Seiji Kubo b, Akihiro Maruo a, Hidetoshi Miya a, Masahiro Kurosaka b, Ryosuke Kuroda b a b
Department of Orthopaedic Surgery, Nippon Steel Hirohata Hospital, Japan Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Japan
a r t i c l e
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Article history: Received 11 March 2010 Accepted 29 June 2010 Keywords: Soft tissue balance Total knee arthroplasty Femoral component Joint gap Ligament balance
a b s t r a c t Background: We developed a new tensor for total knee arthroplasty enabling the soft tissue balance measurement after femoral trial placement with the patello-femoral joint reduced. The purpose of the present study is to compare the measurements of joint gap and ligament balance between osteotomized femoral and tibial surfaces in posterior-stabilized total knee arthroplasty with that between surfaces of femoral trial component and tibial osteotomy. Methods: Using this tensor, the effect of femoral trial placement on the soft tissue balance was analyzed in 80 posterior-stabilized total knee arthroplasties for varus osteoarthritic knees. Both joint gap and varus ligament imbalance were measured with 40 lb of joint distraction force at extension and flexion, and compared between before and after femoral trial placement. Findings: In assessing the joint gap, there was significant decrease as much as 5.3 mm at extension, not flexion, after femoral trial prosthesis placement. Varus ligament imbalances were significantly reduced with 3.1° at extension and increased with 1.2° in average at flexion after femoral trial placement. Interpretation: These changes at extension were caused by tensed posterior structures of the knee with the posterior condyle of the externally rotated aligned femoral trial. At the knee flexion, medial tension in the extensor mechanisms might be increased after femoral trial placement with patello-femoral joint repaired, and increased varus imbalance. Accordingly, we conclude that intensive medial release before femoral component placement to obtain rectangular joint gap depending on the conventional osteotomy gap measurement has a possible risk of medial looseness after total knee arthroplasty. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction Acquisition of successful long-term outcomes in total knee arthroplasties (TKAs), to achieve stable tibiofemoral and patellofemoral (PF) joints, relies on accurately aligning these joint components and balancing the soft tissues. In order to achieve these criteria, it is important to utilize the appropriate surgical techniques and welldesigned implants.(Dorr and Boiardo, 1986; Insall et al., 1979, 1985) To this end successfully, accurate femoral and tibial osteotomies and implantations in TKA have recently become relatively easily, because of the improvement of surgical instruments such as computerassisted navigation system.(Bathis et al., 2004; Jenny and Boeri, 2001; Lutzner et al., 2008; Mizu-uchi et al., 2008; Saragaglia et al., 2001; Sparmann et al., 2003; Stulberg et al., 2002) We have similarly reported the accuracy of osteotomies and implantation using CT-free
⁎ Corresponding author. Department of Orthopaedic Surgery, Nippon Steel Hirohata Hospital, 3-1 Yumesaki-cho, Hirohata-ku, Himeji city, Hyogo, Japan 671-1122. E-mail address: [email protected] (H. Muratsu). 0268-0033/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2010.06.020
navigation system and its early clinical outcome. (Matsumoto et al., 2004, 2006b) On the other hand, evaluation of soft tissue balance during TKAs remains difficult, and management is left much to the surgeon's subjective feel and experience. Although several methods and devices for assessing soft tissue balance such as manual distraction, (Griffin et al., 2000) tensors/balancer, (Insall and Easley, 2001; Laskin and Rieger, 1989; Sambatakakis et al., 1993; Unitt et al., 2008; Winemaker, 2002) and electric instruments (Attfield et al., 1994; Kaufman et al., 1996; Morris et al., 2001; Wallace et al., 1998) have been previously described, they can only be used for measurement between osteotomized bone surfaces without components with an everted or shifted patellar orientation. These joint conditions for assessing soft tissue balance were unphysiological and have poor relevancy with post-operative joint condition. In order to permit soft tissue balancing under more physiological conditions, we developed a new tensor to obtain soft tissue balancing throughout the range of motion with reduced PF and aligned tibiofemoral joints, as previously described. (Muratsu et al., 2003) We have reported our experience using this device for intra-operative measurement with the posterior-stabilized
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(PS) TKA and further discussed the clinical relevance of this tensor. (Matsumoto et al., 2007, 2006a, 2009b) At first, we reported that the joint gap increased with knee flexion to mid-range but decreased to deep flexion when acquired physiological and reproducible conditions with reduced PF joint.(Matsumoto et al., 2006a) Second, we reported that the intra-operative joint gap kinematic assessment with reduced PF joint has the possibility to predict the post-operative flexion angle and thus allows evaluation of surgical technique throughout the range of knee motion.(Matsumoto et al., 2007) Third, we demonstrated that the correlations between the soft tissue balance assessed by the tensor and the navigation system were higher with reduced PF joint than everted PF joint, suggesting that surgeons had better assess soft tissue balance during PS TKA with the PF joint reduced condition when using a navigation system. (Matsumoto et al., 2009b) Furthermore, we reported that joint gap and ligament balance in cruciate-retaining (CR) TKA demonstrated relative constant kinematic pattern compared with PS TKA (Matsumoto et al., 2009a, in press). In addition to our reports, some studies are emphasizing the importance of physiological post-operative knee condition in assessing soft tissue balance; PF joint reduction and femoral trial replacement in place (Gejo et al., 2008; Yoshino et al., 2009). The previous series of our studies were mainly focused on the effect and importance of reduced PF joint during TKA procedures. The main concepts of measurement using the new tensor are, different from the conventional tensioning devise, with femoral trial component in place as well as reduced PF joint. In the present study, accordingly, we focused on the difference in soft tissue balancing between with femoral trial component in place and with conventional osteotomized condition. The purpose of the present study is to compare the measurements of joint gap and ligament balance between osteotomized femoral and tibial surfaces in PS TKA with that between surfaces of femoral trial component and tibial osteotomy. 2. Methods Eighty consecutive osteoarthritic knees implanted with the PS TKA (NexGen LPS Flex, Zimmer, Inc,. Warsaw, IN) were subjected to the intra-operative soft tissue balance evaluation. Sixty-three females and 17 males were involved and the age at surgery was 74.5 ± 6.2 (mean ± standard deviation) years. Preoperative range of motion averaged −11.2 ± 8.4° for extension and 112.4 ± 16.1° for flexion. After excluding patients with valgus deformity and severe bony de-
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fects, remaining patient had a varus deformity with an average preoperative coronal plane alignment of 9.7 ± 4.8° in varus. Each surgery was performed by the first author (H.M) with a standardized surgical technique. 2.1. TKA tensor As previously described, our TKA tensor consists of three parts: an upper seesaw plate, a lower platform plate with a spike and an extraarticular main body. (Matsumoto et al., 2009a, 2007, 2006a, 2009b, in press); Muratsu et al., 2003) The offset connection arms from the main body connecting two independent plates at the anteromedial corner of the tibia are passed through the medial parapatellar arthrotomy. The seesaw plate is attached to the offset connection arm of the main body via a single shaft providing a central pivot in the coronal plane. In addition, the seesaw plate can move in a proximal– distal direction by means of a rack and pinion mechanism within the main body. Following both tibial and femoral osteotomies, two flat plates are placed at the center of the knee, and the tensor can be firmly fixed to the osteotomized tibia by spikes and additional pins on the platform plate. The seesaw plate has a post at the center proximally to fit the inter-condylar space and the cam of the femoral trial prosthesis of PS TKA. This post and cam mechanism controls the tibiofemoral position in both the coronal and sagittal planes, reproducing the joint constraint and alignment after the prostheses are implanted (Fig. 1). This device is ultimately designed to permit surgeons to measure the ligament balance and center joint gap both before and after femoral trial prosthesis placement, while applying a constant joint distraction force. Joint distraction forces ranging from 30 lb (13.6 kg) to 80 lb (36.3 kg) can be exerted between the seesaw and platform plates using a specially made torque driver which can change maximum torque value. After sterilization, this torque driver is placed on a rack that contains a pinion mechanism along the extra-articular main body, and the appropriate torque is applied to generate the designated distraction force; in preliminary in-vitro experiments, we obtained an error for joint distraction within ±3%. Once appropriately distracted, attention is focused on two scales that correspond to the tensor: the angle (°, positive value in varus imbalance) between the seesaw and platform plates, and the distance (mm) between the center midpoints of upper surface of the seesaw plate and the proximal tibial cut. By measuring these angular deviations and
Fig. 1. New PS TKA tensor. The new tensor consists of three parts: upper seesaw plate (a); lower platform plate (b) and extra-articular main body (c). Two plates are connected to the extra-articular main body by the offset connection arm (d) through a medial parapatellar arthrotomy, which permits reduction of the PF joint while performing measurements. The seesaw plate has a post (e) at the center proximally to fit the inter-condylar space and the cam of the femoral trial prosthesis of PS TKA. With reduced PF joint, soft tissue balance including center joint gap and ligament balance are measured with joint distraction forces using torque driver (f).
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distances under a constant joint distraction force, we are able to measure the ligament balance and center joint gaps respectively. 2.2. Intra-operative measurement We performed all TKAs using measured resection technique with a conventional resection block. After inflating the air tourniquet with 280 mm Hg at the outset of each procedure, we performed a medial parapatellar arthrotomy. The ACL and PCL were both resected. We performed distal femoral osteotomy perpendicular to the mechanical axis of the femur according to the long standing X-ray film. Femoral external rotation was preset at 3° relative to the posterior condylar axis in all patients. After this, we performed a proximal tibial osteotomy, ensuring that each cut was made perpendicular to the mechanical axis in the coronal plane and with 7° of posterior inclination along the sagittal plane; there were no bony defects noted along the eroded medial tibial plateau in any of these cases. Following each osteotomy, we removed osteophytes, released the posterior capsule along the femur, and corrected any ligament imbalances that occurred in the coronal plane by appropriately releasing soft tissues along the medial structures of the knee. We performed soft tissue release depending on the soft tissue balance with a spacer block. Following each bony resection and soft tissue release, we fixed the tensor to the proximal tibia, fitted the flat upper plate to the femoral osteotomized surface, and applied a joint distraction force of 40 lb between osteotomized surfaces in all patients. The measurements were performed at extension and flexion of the knee with opposite bone surfaces in parallel orientation as usually done with conventional gap measurement. All measurements were done in the condition with the PF joint reduced. After soft tissue balance evaluation between osteotomy surfaces, the femoral trial component was placed with tensor on the tibial bone cut, and PF joint was temporally reduced by applying stitches both proximally and distally to the connection arm of the tensor. We also loaded 40 lb of distraction force in all patients with knee at 0°and 90° of flexion. The joint distraction force was also set at 40 lb, because it re-created a joint gap at full extension with femoral trial in place which corresponded to the insert thickness of our preliminary clinical studies. We loaded this joint distraction force several times until the joint component gap remained constant; this was done to reduce the error which can result from creep elongation of the surrounding soft tissues. During each measurement, the thigh was held and knee was aligned in the sagittal plane so as to eliminate the external load on the knee at 90° of knee flexion. 2.3. Data analysis
Fig. 2. Joint gap before and after femoral component placement. With femoral trial in place with a reduced patella, the average joint gap value at extension is significantly decreased and shows significant difference between that at flexion. (*: P b 0.01 vs. before femoral trial placement, †: P b 0.01 vs. at extension).
extension and flexion each respectively. The mean varus ligament imbalances were 5.4 (SE 0.4), 3.4 (SE 0.5) and 2.3 (SE 0.3), 4.6 (SE 0.5)° before and after femoral trial placement at extension and flexion each respectively. In assessing the joint gap, there was significant decrease as much as 5.3 mm at extension after femoral trial prosthesis placement. On the other hand, joint gap at flexion showed no significant changes after femoral trial placement (Fig. 2). Varus ligament imbalances were significantly reduced with 3.1° at extension and increased with 1.2° in average at flexion after femoral trial placement (Fig. 3). 4. Discussion Conventionally, after osteotomy, an identical extension and flexion gap with no inclination between the medial and the lateral gap has been generally advocated as the most appropriate for soft tissue balance in the TKA procedure. (Insall and Easley, 2001) However, some experienced surgeons have noted difficulties in matching these balances and have begun to suggest that the flexion gap may not be rectangular as previously thought. (Griffin et al., 2000; Incavo et al., 2004) Furthermore, our original questions were whether soft tissue balance measured by conventional method between osteotomized surfaces without femoral component with everted PF joint alignment was relevancy to that after TKA procedures.
At this point, we measured the joint gap (mm) and varus ligament imbalance (°) with the knee at extension and flexion either before or after femoral trial prosthesis in place. Joint gap value before femoral trial placement was subtracted from conventional osteotomy gap by the thickness of femoral component at extension (9 mm) and flexion (11 mm), and compared with those after femoral trial placement. After expressing each measurement as a mean ± standard error of the mean (SE), we utilized a statistical software package (Statview 5.0, Abacus Concepts Inc, Berkeley, CA) to analyze the data. We performed the paired Student's t-test to compare the joint gap and varus ligament imbalance before and after femoral trial prosthesis placement and to compare those between extension and flexion. P b 0.05 was considered statistically significant. 3. Results The mean conventional osteotomy gaps were 24.8 (SE 0.4) and 27.9 (SE 0.4) mm at extension and flexion respectively. The mean joint gaps were 15.8 (SE 0.4), 16.9 (SE 0.4) and 10.5 (SE 0.2), 17.1 (SE 0.4) mm before and after femoral trial prosthesis placement at
Fig. 3. Varus ligament imbalance before and after femoral component placement. With femoral trial in place with a reduced patella, the average varus ligament imbalance at extension is significantly decreased and increased at flexion. (*: P b 0.01 vs. before femoral trial placement,).
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We have previously reported studies using this new TKA tensor, in which we discuss the importance of maintaining a reduced and anatomically oriented PF joint with femoral trial component in place, in order to obtain accurate and more physiologically-relevant soft tissue balancing. (Matsumoto et al., 2007, 2006a; Muratsu et al., 2003) We further described that when performing intra-operative measurements with this tensor and the navigation system, reducing the PF joint after femoral trial placement significantly affects the soft tissue balance in a PS TKA. (Matsumoto et al., 2009b) In addition, we reported that joint gap and varus/valgus balance in CR TKA were different from that in PS TKA and influenced by the condition of the PF joint as well. (Matsumoto et al., 2009a, In press) In the present study, we compared the soft tissue balance with conventional osteotomy gap measurement and under more physiologically-relevant joint condition with reduced PF joint orientation after femoral trial component placement. At first in this comparison, we showed significant differences in joint gap at extension. Significant decrease in joint gap was observed at extension after femoral trial placement. We hypothesize the mechanism for explaining this joint gap decrease with physiological joint condition as follows; the joint gap is significantly reduced at full extension due to the tension of the supporting posterior structures including joint capsule and tendons stretched by the posterior condyles of the femoral trial, which might play an important role on the prevention of knee hyperextension. As a result, a remarkable reduction of the joint gap could be seen after femoral component placement. We measured the “joint component gap”, which is remarkably different from a more conventional gap measurement. The joint component gap is measured with the femoral component in place, whereas the conventional gap measurement is made between the cutting surfaces of the femur and tibia. By keeping the femoral component in place, the knee is afforded a greater degree of extension because of its curving arc. In this arrangement, the posterior condyles of the component tighten the posterior capsule, resulting in a smaller joint gap at full extension (Fig. 4). In addition, due to 7° of posterior slope of tibia and a slight femoral anterior bowing, we can consider the “conventional extension gap” to be at about 10° of knee flexion angle. Mihalko et al. stated that the release of more posterior
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structures had a greater effect on the extension gap than on the flexion gap in explaining the importance of the relationship between posterior structures and the extension gap in a cadaver study. (Mihalko et al., 2003) Sugama et al. reported in their operative study that bone cut from the posterior femoral condyles could change the tension of the posterior soft tissue structures and so alter the width and shape of the extension gap. (Sugama et al., 2005) These previous reports support our hypothetical mechanism. At second in our comparison, varus ligament imbalance was shown to be significantly decreased at extension and increased at flexion after femoral component placement with PF joint repaired. Regarding rotational alignment of the femoral component, we performed TKAs using measured resection technique with 3° of external rotation osteotomy for the femoral osteotomies. We hypothesize the mechanism for explaining these varus ligament imbalance changes with physiological joint condition as follows; the tension at the posterior structures is increased at full extension as described above, and the tension in the posterior structures at the lateral side would be higher than that at the medial, because the less soft tissue release was performed at the lateral side comparing to the medial side in our varus osteoarthritic patients. These differences could explain the joint narrowing at the lateral side with the existence of the posterior condyle of the femoral trial component, and reduced varus imbalance at extension after femoral component placement. Furthermore, lateral femoral posterior condyle pushed posterior structures at knee extension more than the medial because of 3° of femoral external rotational alignment. At knee flexion, PF joint repair with femoral component might be physiological and increased the anterior soft tissue tension. Especially, repaired medial side was tensed more than the lateral side with 3° of external rotation of femoral component, and increased varus ligament imbalance. Tokuhara et al. reported that the tibiofemoral flexion gap at 90° of flexion in the normal knee was not rectangular and lateral joint laxity was significantly more than medial in their in vivo study using MRI estimated by the application of varus-valgus stress (Tokuhara et al., 2004). We reported the ligament balance in the intact knee underwent CR TKA shows varus ligament imbalance throughout range of motion (Tanaka et al., 2007). The magnitude of varus imbalance was higher at knee flexion. Therefore, for the soft tissue balancing procedures, we paid attentions not to loosen too much medial structures at both extension and flexion, and accepted slight varus imbalance during soft tissue release. Our new findings in this study support our principles in the soft tissue balancing procedures to acquiring proper post-operative stability. There are some limitations in this study. The TKA procedures with the new tensor in our present study were performed following the independent cut manner, in which soft tissue balance was assessed after the bone cuts. However the best method of obtaining rotational alignment of the femoral component in flexion remains controversial, with some surgeons advocating the measured resection technique, and others, the tensioned gap technique. (Dennis, 2008; Fehring, 2000; Freeman et al., 1971; Hanada et al., 2007; Whiteside et al., 1987; Windsor et al., 1989) Our tensor can also be used in TKA with the tensioned gap technique. (Tanaka et al., 2007) When we select tibia cut first, we can determine the rotational alignment of the femoral component in flexion using the tensor. After that, depending on the balance, we are able to perform a posterior cut of the femur. Accordingly, in the near future, we should compare these techniques to acquire true post-operative data of aligned soft tissue balance. 5. Conclusions
Fig. 4. Illustration of the relationship between the conventional extension gap and component extension gap (modified using illustration of J Bone Joint Surg Br 2009; 91 (4): 475–80 [27]).
In the present study, we elucidate the intra-operative soft tissue balance before and after femoral trial component placement had significant differences. Surgeons might better not to intensively release medial soft tissue depending on the conventional gap
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measurement without femoral component and PF joint everted or shifted, which may result in the medial looseness at extension after TKA. Although varus ligament imbalance at knee flexion is expected to increase after femoral trial placement and PF joint repair, this is relatively small change and acceptable comparing to the physiological knee condition. We believe that the surgeon will be able to adjust the soft tissue balance more accurately by maintaining a reduced patella with femoral trial component in place for each intra-operative measurement, and thereby expect a better post-operative outcome. Acknowledgment The authors would like to thank Mrs. Janina Tubby for her assistance in preparation of this manuscript. References Attfield, S.F., Warren-Forward, M., Wilton, T., Sambatakakis, A., 1994. Measurement of soft tissue imbalance in total knee arthroplasty using electronic instrumentation. Med. Eng. Phys. 16, 501–505. Bathis, H., Perlick, L., Tingart, M., Luring, C., Perlick, C., Grifka, J., 2004. Radiological results of image-based and non-image-based computer-assisted total knee arthroplasty. Int. Orthop. 28, 87–90. Dennis, D.A., 2008. Measured resection: an outdated technique in total knee arthroplasty. Orthopedics 31 (940), 943–944. Dorr, L.D., Boiardo, R.A., 1986. Technical considerations in total knee arthroplasty. Clin. Orthop. Relat. Res. 5–11. Fehring, T.K., 2000. Rotational malalignment of the femoral component in total knee arthroplasty. Clin. Orthop. Relat. Res. 72–79. Freeman, M.A., Day, W.H., Swanson, S.A., 1971. Fatigue fracture in the subchondral bone of the human cadaver femoral head. Med. Biol. Eng. 9, 619–629. Gejo, R., Morita, Y., Matsushita, I., Sugimori, K., Kimura, T., 2008. Joint gap changes with patellar tendon strain and patellar position during TKA. Clin. Orthop. Relat. Res. 466, 946–951. Griffin, F.M., Insall, J.N., Scuderi, G.R., 2000. Accuracy of soft tissue balancing in total knee arthroplasty. J. Arthroplasty 15, 970–973. Hanada, H., Whiteside, L.A., Steiger, J., Dyer, P., Naito, M., 2007. Bone landmarks are more reliable than tensioned gaps in TKA component alignment. Clin. Orthop. Relat. Res. 462, 137–142. Incavo, S.J., Coughlin, K.M., Beynnon, B.D., 2004. Femoral component sizing in total knee arthroplasty: size matched resection versus flexion space balancing. J. Arthroplasty 19, 493–497. Insall, J.N., Easley, M.E., 2001. Surgical techniques and instrumentation in total knee arthroplasty. In: Insall, J.N., Scott, W.N. (Eds.), Surgery of the knee. Churchill Livingstone, New York, p. 1553. Insall, J., Tria, A.J., Scott, W.N., 1979. The total condylar knee prosthesis: the first 5 years. Clin. Orthop. Relat. Res. 68–77. Insall, J.N., Binazzi, R., Soudry, M., Mestriner, L.A., 1985. Total knee arthroplasty. Clin. Orthop. Relat. Res. 13–22. Jenny, J.Y., Boeri, C., 2001. Computer-assisted implantation of a total knee arthroplasty: a case-controlled study in comparison with classical instrumentation. Rev. Chir. Orthop. Reparatrice Appar. Mot. 87, 645–652. Kaufman, K.R., Kovacevic, N., Irby, S.E., Colwell, C.W., 1996. Instrumented implant for measuring tibiofemoral forces. J. Biomech. 29, 667–671. Laskin, R.S., Rieger, M.A., 1989. The surgical technique for performing a total knee replacement arthroplasty. Orthop. Clin. North. Am. 20, 31–48. Lutzner, J., Krummenauer, F., Wolf, C., Gunther, K.P., Kirschner, S., 2008. Computerassisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation. J. Bone Joint Surg. Br. 90, 1039–1044. Matsumoto, T., Tsumura, N., Kurosaka, M., Muratsu, H., Kuroda, R., Ishimoto, K., Tsujimoto, K., Shiba, R., Yoshiya, S., 2004. Prosthetic alignment and sizing in computer-assisted total knee arthroplasty. Int. Orthop. 28, 282–285.
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Clinical Biomechanics j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l i n b i o m e c h
Femoral component placement changes soft tissue balance in posterior-stabilized total knee arthroplasty Hirotsugu Muratsu a,⁎, Tomoyuki Matsumoto b, Seiji Kubo b, Akihiro Maruo a, Hidetoshi Miya a, Masahiro Kurosaka b, Ryosuke Kuroda b a b
Department of Orthopaedic Surgery, Nippon Steel Hirohata Hospital, Japan Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Japan
a r t i c l e
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Article history: Received 11 March 2010 Accepted 29 June 2010 Keywords: Soft tissue balance Total knee arthroplasty Femoral component Joint gap Ligament balance
a b s t r a c t Background: We developed a new tensor for total knee arthroplasty enabling the soft tissue balance measurement after femoral trial placement with the patello-femoral joint reduced. The purpose of the present study is to compare the measurements of joint gap and ligament balance between osteotomized femoral and tibial surfaces in posterior-stabilized total knee arthroplasty with that between surfaces of femoral trial component and tibial osteotomy. Methods: Using this tensor, the effect of femoral trial placement on the soft tissue balance was analyzed in 80 posterior-stabilized total knee arthroplasties for varus osteoarthritic knees. Both joint gap and varus ligament imbalance were measured with 40 lb of joint distraction force at extension and flexion, and compared between before and after femoral trial placement. Findings: In assessing the joint gap, there was significant decrease as much as 5.3 mm at extension, not flexion, after femoral trial prosthesis placement. Varus ligament imbalances were significantly reduced with 3.1° at extension and increased with 1.2° in average at flexion after femoral trial placement. Interpretation: These changes at extension were caused by tensed posterior structures of the knee with the posterior condyle of the externally rotated aligned femoral trial. At the knee flexion, medial tension in the extensor mechanisms might be increased after femoral trial placement with patello-femoral joint repaired, and increased varus imbalance. Accordingly, we conclude that intensive medial release before femoral component placement to obtain rectangular joint gap depending on the conventional osteotomy gap measurement has a possible risk of medial looseness after total knee arthroplasty. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction Acquisition of successful long-term outcomes in total knee arthroplasties (TKAs), to achieve stable tibiofemoral and patellofemoral (PF) joints, relies on accurately aligning these joint components and balancing the soft tissues. In order to achieve these criteria, it is important to utilize the appropriate surgical techniques and welldesigned implants.(Dorr and Boiardo, 1986; Insall et al., 1979, 1985) To this end successfully, accurate femoral and tibial osteotomies and implantations in TKA have recently become relatively easily, because of the improvement of surgical instruments such as computerassisted navigation system.(Bathis et al., 2004; Jenny and Boeri, 2001; Lutzner et al., 2008; Mizu-uchi et al., 2008; Saragaglia et al., 2001; Sparmann et al., 2003; Stulberg et al., 2002) We have similarly reported the accuracy of osteotomies and implantation using CT-free
⁎ Corresponding author. Department of Orthopaedic Surgery, Nippon Steel Hirohata Hospital, 3-1 Yumesaki-cho, Hirohata-ku, Himeji city, Hyogo, Japan 671-1122. E-mail address: [email protected] (H. Muratsu). 0268-0033/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2010.06.020
navigation system and its early clinical outcome. (Matsumoto et al., 2004, 2006b) On the other hand, evaluation of soft tissue balance during TKAs remains difficult, and management is left much to the surgeon's subjective feel and experience. Although several methods and devices for assessing soft tissue balance such as manual distraction, (Griffin et al., 2000) tensors/balancer, (Insall and Easley, 2001; Laskin and Rieger, 1989; Sambatakakis et al., 1993; Unitt et al., 2008; Winemaker, 2002) and electric instruments (Attfield et al., 1994; Kaufman et al., 1996; Morris et al., 2001; Wallace et al., 1998) have been previously described, they can only be used for measurement between osteotomized bone surfaces without components with an everted or shifted patellar orientation. These joint conditions for assessing soft tissue balance were unphysiological and have poor relevancy with post-operative joint condition. In order to permit soft tissue balancing under more physiological conditions, we developed a new tensor to obtain soft tissue balancing throughout the range of motion with reduced PF and aligned tibiofemoral joints, as previously described. (Muratsu et al., 2003) We have reported our experience using this device for intra-operative measurement with the posterior-stabilized
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(PS) TKA and further discussed the clinical relevance of this tensor. (Matsumoto et al., 2007, 2006a, 2009b) At first, we reported that the joint gap increased with knee flexion to mid-range but decreased to deep flexion when acquired physiological and reproducible conditions with reduced PF joint.(Matsumoto et al., 2006a) Second, we reported that the intra-operative joint gap kinematic assessment with reduced PF joint has the possibility to predict the post-operative flexion angle and thus allows evaluation of surgical technique throughout the range of knee motion.(Matsumoto et al., 2007) Third, we demonstrated that the correlations between the soft tissue balance assessed by the tensor and the navigation system were higher with reduced PF joint than everted PF joint, suggesting that surgeons had better assess soft tissue balance during PS TKA with the PF joint reduced condition when using a navigation system. (Matsumoto et al., 2009b) Furthermore, we reported that joint gap and ligament balance in cruciate-retaining (CR) TKA demonstrated relative constant kinematic pattern compared with PS TKA (Matsumoto et al., 2009a, in press). In addition to our reports, some studies are emphasizing the importance of physiological post-operative knee condition in assessing soft tissue balance; PF joint reduction and femoral trial replacement in place (Gejo et al., 2008; Yoshino et al., 2009). The previous series of our studies were mainly focused on the effect and importance of reduced PF joint during TKA procedures. The main concepts of measurement using the new tensor are, different from the conventional tensioning devise, with femoral trial component in place as well as reduced PF joint. In the present study, accordingly, we focused on the difference in soft tissue balancing between with femoral trial component in place and with conventional osteotomized condition. The purpose of the present study is to compare the measurements of joint gap and ligament balance between osteotomized femoral and tibial surfaces in PS TKA with that between surfaces of femoral trial component and tibial osteotomy. 2. Methods Eighty consecutive osteoarthritic knees implanted with the PS TKA (NexGen LPS Flex, Zimmer, Inc,. Warsaw, IN) were subjected to the intra-operative soft tissue balance evaluation. Sixty-three females and 17 males were involved and the age at surgery was 74.5 ± 6.2 (mean ± standard deviation) years. Preoperative range of motion averaged −11.2 ± 8.4° for extension and 112.4 ± 16.1° for flexion. After excluding patients with valgus deformity and severe bony de-
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fects, remaining patient had a varus deformity with an average preoperative coronal plane alignment of 9.7 ± 4.8° in varus. Each surgery was performed by the first author (H.M) with a standardized surgical technique. 2.1. TKA tensor As previously described, our TKA tensor consists of three parts: an upper seesaw plate, a lower platform plate with a spike and an extraarticular main body. (Matsumoto et al., 2009a, 2007, 2006a, 2009b, in press); Muratsu et al., 2003) The offset connection arms from the main body connecting two independent plates at the anteromedial corner of the tibia are passed through the medial parapatellar arthrotomy. The seesaw plate is attached to the offset connection arm of the main body via a single shaft providing a central pivot in the coronal plane. In addition, the seesaw plate can move in a proximal– distal direction by means of a rack and pinion mechanism within the main body. Following both tibial and femoral osteotomies, two flat plates are placed at the center of the knee, and the tensor can be firmly fixed to the osteotomized tibia by spikes and additional pins on the platform plate. The seesaw plate has a post at the center proximally to fit the inter-condylar space and the cam of the femoral trial prosthesis of PS TKA. This post and cam mechanism controls the tibiofemoral position in both the coronal and sagittal planes, reproducing the joint constraint and alignment after the prostheses are implanted (Fig. 1). This device is ultimately designed to permit surgeons to measure the ligament balance and center joint gap both before and after femoral trial prosthesis placement, while applying a constant joint distraction force. Joint distraction forces ranging from 30 lb (13.6 kg) to 80 lb (36.3 kg) can be exerted between the seesaw and platform plates using a specially made torque driver which can change maximum torque value. After sterilization, this torque driver is placed on a rack that contains a pinion mechanism along the extra-articular main body, and the appropriate torque is applied to generate the designated distraction force; in preliminary in-vitro experiments, we obtained an error for joint distraction within ±3%. Once appropriately distracted, attention is focused on two scales that correspond to the tensor: the angle (°, positive value in varus imbalance) between the seesaw and platform plates, and the distance (mm) between the center midpoints of upper surface of the seesaw plate and the proximal tibial cut. By measuring these angular deviations and
Fig. 1. New PS TKA tensor. The new tensor consists of three parts: upper seesaw plate (a); lower platform plate (b) and extra-articular main body (c). Two plates are connected to the extra-articular main body by the offset connection arm (d) through a medial parapatellar arthrotomy, which permits reduction of the PF joint while performing measurements. The seesaw plate has a post (e) at the center proximally to fit the inter-condylar space and the cam of the femoral trial prosthesis of PS TKA. With reduced PF joint, soft tissue balance including center joint gap and ligament balance are measured with joint distraction forces using torque driver (f).
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distances under a constant joint distraction force, we are able to measure the ligament balance and center joint gaps respectively. 2.2. Intra-operative measurement We performed all TKAs using measured resection technique with a conventional resection block. After inflating the air tourniquet with 280 mm Hg at the outset of each procedure, we performed a medial parapatellar arthrotomy. The ACL and PCL were both resected. We performed distal femoral osteotomy perpendicular to the mechanical axis of the femur according to the long standing X-ray film. Femoral external rotation was preset at 3° relative to the posterior condylar axis in all patients. After this, we performed a proximal tibial osteotomy, ensuring that each cut was made perpendicular to the mechanical axis in the coronal plane and with 7° of posterior inclination along the sagittal plane; there were no bony defects noted along the eroded medial tibial plateau in any of these cases. Following each osteotomy, we removed osteophytes, released the posterior capsule along the femur, and corrected any ligament imbalances that occurred in the coronal plane by appropriately releasing soft tissues along the medial structures of the knee. We performed soft tissue release depending on the soft tissue balance with a spacer block. Following each bony resection and soft tissue release, we fixed the tensor to the proximal tibia, fitted the flat upper plate to the femoral osteotomized surface, and applied a joint distraction force of 40 lb between osteotomized surfaces in all patients. The measurements were performed at extension and flexion of the knee with opposite bone surfaces in parallel orientation as usually done with conventional gap measurement. All measurements were done in the condition with the PF joint reduced. After soft tissue balance evaluation between osteotomy surfaces, the femoral trial component was placed with tensor on the tibial bone cut, and PF joint was temporally reduced by applying stitches both proximally and distally to the connection arm of the tensor. We also loaded 40 lb of distraction force in all patients with knee at 0°and 90° of flexion. The joint distraction force was also set at 40 lb, because it re-created a joint gap at full extension with femoral trial in place which corresponded to the insert thickness of our preliminary clinical studies. We loaded this joint distraction force several times until the joint component gap remained constant; this was done to reduce the error which can result from creep elongation of the surrounding soft tissues. During each measurement, the thigh was held and knee was aligned in the sagittal plane so as to eliminate the external load on the knee at 90° of knee flexion. 2.3. Data analysis
Fig. 2. Joint gap before and after femoral component placement. With femoral trial in place with a reduced patella, the average joint gap value at extension is significantly decreased and shows significant difference between that at flexion. (*: P b 0.01 vs. before femoral trial placement, †: P b 0.01 vs. at extension).
extension and flexion each respectively. The mean varus ligament imbalances were 5.4 (SE 0.4), 3.4 (SE 0.5) and 2.3 (SE 0.3), 4.6 (SE 0.5)° before and after femoral trial placement at extension and flexion each respectively. In assessing the joint gap, there was significant decrease as much as 5.3 mm at extension after femoral trial prosthesis placement. On the other hand, joint gap at flexion showed no significant changes after femoral trial placement (Fig. 2). Varus ligament imbalances were significantly reduced with 3.1° at extension and increased with 1.2° in average at flexion after femoral trial placement (Fig. 3). 4. Discussion Conventionally, after osteotomy, an identical extension and flexion gap with no inclination between the medial and the lateral gap has been generally advocated as the most appropriate for soft tissue balance in the TKA procedure. (Insall and Easley, 2001) However, some experienced surgeons have noted difficulties in matching these balances and have begun to suggest that the flexion gap may not be rectangular as previously thought. (Griffin et al., 2000; Incavo et al., 2004) Furthermore, our original questions were whether soft tissue balance measured by conventional method between osteotomized surfaces without femoral component with everted PF joint alignment was relevancy to that after TKA procedures.
At this point, we measured the joint gap (mm) and varus ligament imbalance (°) with the knee at extension and flexion either before or after femoral trial prosthesis in place. Joint gap value before femoral trial placement was subtracted from conventional osteotomy gap by the thickness of femoral component at extension (9 mm) and flexion (11 mm), and compared with those after femoral trial placement. After expressing each measurement as a mean ± standard error of the mean (SE), we utilized a statistical software package (Statview 5.0, Abacus Concepts Inc, Berkeley, CA) to analyze the data. We performed the paired Student's t-test to compare the joint gap and varus ligament imbalance before and after femoral trial prosthesis placement and to compare those between extension and flexion. P b 0.05 was considered statistically significant. 3. Results The mean conventional osteotomy gaps were 24.8 (SE 0.4) and 27.9 (SE 0.4) mm at extension and flexion respectively. The mean joint gaps were 15.8 (SE 0.4), 16.9 (SE 0.4) and 10.5 (SE 0.2), 17.1 (SE 0.4) mm before and after femoral trial prosthesis placement at
Fig. 3. Varus ligament imbalance before and after femoral component placement. With femoral trial in place with a reduced patella, the average varus ligament imbalance at extension is significantly decreased and increased at flexion. (*: P b 0.01 vs. before femoral trial placement,).
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We have previously reported studies using this new TKA tensor, in which we discuss the importance of maintaining a reduced and anatomically oriented PF joint with femoral trial component in place, in order to obtain accurate and more physiologically-relevant soft tissue balancing. (Matsumoto et al., 2007, 2006a; Muratsu et al., 2003) We further described that when performing intra-operative measurements with this tensor and the navigation system, reducing the PF joint after femoral trial placement significantly affects the soft tissue balance in a PS TKA. (Matsumoto et al., 2009b) In addition, we reported that joint gap and varus/valgus balance in CR TKA were different from that in PS TKA and influenced by the condition of the PF joint as well. (Matsumoto et al., 2009a, In press) In the present study, we compared the soft tissue balance with conventional osteotomy gap measurement and under more physiologically-relevant joint condition with reduced PF joint orientation after femoral trial component placement. At first in this comparison, we showed significant differences in joint gap at extension. Significant decrease in joint gap was observed at extension after femoral trial placement. We hypothesize the mechanism for explaining this joint gap decrease with physiological joint condition as follows; the joint gap is significantly reduced at full extension due to the tension of the supporting posterior structures including joint capsule and tendons stretched by the posterior condyles of the femoral trial, which might play an important role on the prevention of knee hyperextension. As a result, a remarkable reduction of the joint gap could be seen after femoral component placement. We measured the “joint component gap”, which is remarkably different from a more conventional gap measurement. The joint component gap is measured with the femoral component in place, whereas the conventional gap measurement is made between the cutting surfaces of the femur and tibia. By keeping the femoral component in place, the knee is afforded a greater degree of extension because of its curving arc. In this arrangement, the posterior condyles of the component tighten the posterior capsule, resulting in a smaller joint gap at full extension (Fig. 4). In addition, due to 7° of posterior slope of tibia and a slight femoral anterior bowing, we can consider the “conventional extension gap” to be at about 10° of knee flexion angle. Mihalko et al. stated that the release of more posterior
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structures had a greater effect on the extension gap than on the flexion gap in explaining the importance of the relationship between posterior structures and the extension gap in a cadaver study. (Mihalko et al., 2003) Sugama et al. reported in their operative study that bone cut from the posterior femoral condyles could change the tension of the posterior soft tissue structures and so alter the width and shape of the extension gap. (Sugama et al., 2005) These previous reports support our hypothetical mechanism. At second in our comparison, varus ligament imbalance was shown to be significantly decreased at extension and increased at flexion after femoral component placement with PF joint repaired. Regarding rotational alignment of the femoral component, we performed TKAs using measured resection technique with 3° of external rotation osteotomy for the femoral osteotomies. We hypothesize the mechanism for explaining these varus ligament imbalance changes with physiological joint condition as follows; the tension at the posterior structures is increased at full extension as described above, and the tension in the posterior structures at the lateral side would be higher than that at the medial, because the less soft tissue release was performed at the lateral side comparing to the medial side in our varus osteoarthritic patients. These differences could explain the joint narrowing at the lateral side with the existence of the posterior condyle of the femoral trial component, and reduced varus imbalance at extension after femoral component placement. Furthermore, lateral femoral posterior condyle pushed posterior structures at knee extension more than the medial because of 3° of femoral external rotational alignment. At knee flexion, PF joint repair with femoral component might be physiological and increased the anterior soft tissue tension. Especially, repaired medial side was tensed more than the lateral side with 3° of external rotation of femoral component, and increased varus ligament imbalance. Tokuhara et al. reported that the tibiofemoral flexion gap at 90° of flexion in the normal knee was not rectangular and lateral joint laxity was significantly more than medial in their in vivo study using MRI estimated by the application of varus-valgus stress (Tokuhara et al., 2004). We reported the ligament balance in the intact knee underwent CR TKA shows varus ligament imbalance throughout range of motion (Tanaka et al., 2007). The magnitude of varus imbalance was higher at knee flexion. Therefore, for the soft tissue balancing procedures, we paid attentions not to loosen too much medial structures at both extension and flexion, and accepted slight varus imbalance during soft tissue release. Our new findings in this study support our principles in the soft tissue balancing procedures to acquiring proper post-operative stability. There are some limitations in this study. The TKA procedures with the new tensor in our present study were performed following the independent cut manner, in which soft tissue balance was assessed after the bone cuts. However the best method of obtaining rotational alignment of the femoral component in flexion remains controversial, with some surgeons advocating the measured resection technique, and others, the tensioned gap technique. (Dennis, 2008; Fehring, 2000; Freeman et al., 1971; Hanada et al., 2007; Whiteside et al., 1987; Windsor et al., 1989) Our tensor can also be used in TKA with the tensioned gap technique. (Tanaka et al., 2007) When we select tibia cut first, we can determine the rotational alignment of the femoral component in flexion using the tensor. After that, depending on the balance, we are able to perform a posterior cut of the femur. Accordingly, in the near future, we should compare these techniques to acquire true post-operative data of aligned soft tissue balance. 5. Conclusions
Fig. 4. Illustration of the relationship between the conventional extension gap and component extension gap (modified using illustration of J Bone Joint Surg Br 2009; 91 (4): 475–80 [27]).
In the present study, we elucidate the intra-operative soft tissue balance before and after femoral trial component placement had significant differences. Surgeons might better not to intensively release medial soft tissue depending on the conventional gap
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measurement without femoral component and PF joint everted or shifted, which may result in the medial looseness at extension after TKA. Although varus ligament imbalance at knee flexion is expected to increase after femoral trial placement and PF joint repair, this is relatively small change and acceptable comparing to the physiological knee condition. We believe that the surgeon will be able to adjust the soft tissue balance more accurately by maintaining a reduced patella with femoral trial component in place for each intra-operative measurement, and thereby expect a better post-operative outcome. Acknowledgment The authors would like to thank Mrs. Janina Tubby for her assistance in preparation of this manuscript. References Attfield, S.F., Warren-Forward, M., Wilton, T., Sambatakakis, A., 1994. Measurement of soft tissue imbalance in total knee arthroplasty using electronic instrumentation. Med. Eng. Phys. 16, 501–505. Bathis, H., Perlick, L., Tingart, M., Luring, C., Perlick, C., Grifka, J., 2004. Radiological results of image-based and non-image-based computer-assisted total knee arthroplasty. Int. Orthop. 28, 87–90. Dennis, D.A., 2008. Measured resection: an outdated technique in total knee arthroplasty. Orthopedics 31 (940), 943–944. Dorr, L.D., Boiardo, R.A., 1986. Technical considerations in total knee arthroplasty. Clin. Orthop. Relat. Res. 5–11. Fehring, T.K., 2000. Rotational malalignment of the femoral component in total knee arthroplasty. Clin. Orthop. Relat. Res. 72–79. Freeman, M.A., Day, W.H., Swanson, S.A., 1971. Fatigue fracture in the subchondral bone of the human cadaver femoral head. Med. Biol. Eng. 9, 619–629. Gejo, R., Morita, Y., Matsushita, I., Sugimori, K., Kimura, T., 2008. Joint gap changes with patellar tendon strain and patellar position during TKA. Clin. Orthop. Relat. Res. 466, 946–951. Griffin, F.M., Insall, J.N., Scuderi, G.R., 2000. Accuracy of soft tissue balancing in total knee arthroplasty. J. Arthroplasty 15, 970–973. Hanada, H., Whiteside, L.A., Steiger, J., Dyer, P., Naito, M., 2007. Bone landmarks are more reliable than tensioned gaps in TKA component alignment. Clin. Orthop. Relat. Res. 462, 137–142. Incavo, S.J., Coughlin, K.M., Beynnon, B.D., 2004. Femoral component sizing in total knee arthroplasty: size matched resection versus flexion space balancing. J. Arthroplasty 19, 493–497. Insall, J.N., Easley, M.E., 2001. Surgical techniques and instrumentation in total knee arthroplasty. In: Insall, J.N., Scott, W.N. (Eds.), Surgery of the knee. Churchill Livingstone, New York, p. 1553. Insall, J., Tria, A.J., Scott, W.N., 1979. The total condylar knee prosthesis: the first 5 years. Clin. Orthop. Relat. Res. 68–77. Insall, J.N., Binazzi, R., Soudry, M., Mestriner, L.A., 1985. Total knee arthroplasty. Clin. Orthop. Relat. Res. 13–22. Jenny, J.Y., Boeri, C., 2001. Computer-assisted implantation of a total knee arthroplasty: a case-controlled study in comparison with classical instrumentation. Rev. Chir. Orthop. Reparatrice Appar. Mot. 87, 645–652. Kaufman, K.R., Kovacevic, N., Irby, S.E., Colwell, C.W., 1996. Instrumented implant for measuring tibiofemoral forces. J. Biomech. 29, 667–671. Laskin, R.S., Rieger, M.A., 1989. The surgical technique for performing a total knee replacement arthroplasty. Orthop. Clin. North. Am. 20, 31–48. Lutzner, J., Krummenauer, F., Wolf, C., Gunther, K.P., Kirschner, S., 2008. Computerassisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation. J. Bone Joint Surg. Br. 90, 1039–1044. Matsumoto, T., Tsumura, N., Kurosaka, M., Muratsu, H., Kuroda, R., Ishimoto, K., Tsujimoto, K., Shiba, R., Yoshiya, S., 2004. Prosthetic alignment and sizing in computer-assisted total knee arthroplasty. Int. Orthop. 28, 282–285.
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