The Journal of Arthroplasty 30 (2015) 1155–1159
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Influence of Intraoperative Soft Tissue Balance on Postoperative Active Knee Extension in Posterior-Stabilized Total Knee Arthroplasty Kanto Nagai, MD a,b, Hirotsugu Muratsu, MD, PhD a, Tomoyuki Matsumoto, MD, PhD b, Shunsuke Takahara, MD a, Ryosuke Kuroda, MD, PhD b, Masahiro Kurosaka, MD, PhD b a b
Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital, Himeji, Japan Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
a r t i c l e
i n f o
Article history: Received 16 October 2014 Accepted 31 January 2015 Keywords: soft tissue balance active knee extension offset type tensor posterior-stabilized total knee arthroplasty flexion contracture
a b s t r a c t We evaluated the influence of intraoperative soft tissue balance on postoperative active knee extension using Offset Repo-Tensor® among 73 varus osteoarthritic knees underwent primary posterior-stabilized total knee arthroplasty. The joint center gap between osteotomized surfaces and the component gap after femoral trial component placement were measured using a joint distraction force of 40 lb. The active knee extension angle was measured 4 weeks after surgery. The postoperative extension angle was not correlated with the joint center gap at 0°, but positively correlated with the component gap at 0°, and the joint looseness at 0° which was calculated by subtracting insert thickness from the component gap. Thus, intraoperative soft tissue measurement with femoral trial component placement would be useful to predict the postoperative knee extension angle. © 2015 Elsevier Inc. All rights reserved.
Although both accurate component placement and adequate soft tissue balance are recognized as essential surgical principles in total knee arthroplasty (TKA) [1–3], the influence of intraoperative soft tissue balance on the postoperative clinical results has not been fully investigated. The prevention of flexion contracture after TKA is one of the most important outcomes for TKA. If flexion contracture occurs postoperatively, the quadriceps muscle would need to generate an increased force to stabilize the flexed knee during weight-bearing actions. This force would be distributed between the posterior half of the tibial plateau and the patellofemoral (PF) joint [4,5]. Therefore, patients with persistent flexion contracture would experience anterior knee pain and altered gait mechanics, and thus would be unsatisfied with their TKAs [6–8]. The risk factors for postoperative flexion contracture include preoperative flexion contracture, male gender, and/or advanced age [7,9]. In addition, several reports have indicated that the likelihood of postoperative flexion contracture was greater when intraoperative soft tissue tension was higher during extension at the time of surgery [10–12]. On the other hand, looseness of soft tissue balance may cause extension instability, which is related to the patients' symptoms and implant survival [13,14]. Therefore, appropriate intraoperative soft tissue balance would be crucial for postoperative knee extension, and the One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.01.053. Reprint requests: Hirotsugu Muratsu, MD, PhD, Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital, 3–1, Yumesaki-cho, Hirohata-ku, Himeji, 671–1122, Japan. http://dx.doi.org/10.1016/j.arth.2015.01.053 0883-5403/© 2015 Elsevier Inc. All rights reserved.
relationship between intraoperative soft tissue balance and postoperative active knee extension angle needs to be investigated. In previous studies using an offset-type tensor, we discussed the importance of maintaining a reduced and anatomically oriented PF joint, with the femoral trial component in place, in order to obtain accurate and more physiologically relevant soft tissue balance [15,16]. Furthermore, the relationship between intraoperative soft tissue balance and the postoperative active/passive flexion angle was demonstrated using an offset-type tensor in posterior-stabilized (PS) and cruciateretaining TKA [17–19]. However, only a few reports have described the relationship between intraoperative soft tissue balance and the postoperative active extension angle. In the present study, we aimed to investigate the influence of the intraoperative soft tissue balance on postoperative active knee extension. We hypothesized that intraoperative soft tissue balance affected the postoperative active knee extension angle in cases undergoing PS TKA. Materials and Methods The hospital ethics committee approved the study protocol, and the patients provided informed consent for participation in the study. The inclusion criteria were the presence of substantial pain and loss of function due to osteoarthritis of the knee. The exclusion criteria were the presence of knees with valgus deformity, severe bony defects that require bone graft or augmentation, and/or active knee joint infection; patients undergoing revision TKA were also excluded. In total, 73 knees that met the above criteria and underwent primary PS TKA between January 2008 and November 2011 were enrolled. The patient population comprised 64 females and 9 males, with a mean age of 73.8 ±
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5.8 years. The average preoperative coronal plane alignment was 11.5 ± 5.6° in varus, and the average preoperative active knee flexion angles was 111.9 ± 13.1°. Each surgery was performed by the same surgeon—the senior author (H.M.)—using PS TKA (NexGen LPS Flex, Zimmer, Inc, Warsaw, IN), with a standardized surgical technique.
the center midpoints of the upper surface of the seesaw plate and the proximal tibial cut. By measuring these angular deviations and distances under a constant joint distraction force, we were able to measure the ligament balance and joint center gap, respectively. Intraoperative Measurement
Surgical Procedure TKAs were performed using the measured resection technique with a conventional resection block. After inflating the air tourniquet with 280 mmHg at the start of the procedure, a medial parapatellar arthrotomy was performed. Both the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were resected. A distal femoral osteotomy was performed perpendicular to the mechanical axis of the femur using an intramedullary resection guide, according to preoperative long-leg radiographs. Thereafter, a proximal tibial osteotomy was performed perpendicular to the mechanical axis in the coronal plane and with 7° of posterior inclination along the sagittal plane using an extramedullary resection guide. No bony defects were observed along the eroded medial tibial plateau. After neutral alignment was confirmed with each cut of the distal femur and proximal tibia, a posterior femoral cut was made using the anterior referencing technique. Femoral external rotation was set at 3° or 5° relative to the posterior condylar axis, while referring to Whiteside's line and the transepicondylar axis, measured using preoperative computed tomography images. After each osteotomy, we removed the osteophytes, released the posterior capsule along the femur, and corrected any ligament imbalances in the coronal plane by appropriately releasing the medial soft tissues. The osteotomy and soft tissue release were performed by using a spacer block. Intraoperative Measurement With the Offset Repo-Tensor® (OFR tensor; Zimmer, Warsaw, IN) The OFR tensor consists of 3 parts: an upper seesaw plate, a lower platform plate with a spike, and an extra-articular main body, as previously described [20]. This device is designed to facilitate the measurement of ligament balance and joint center gap, both before and after femoral trial prosthesis placement, while applying a constant joint distraction force. Joint distraction forces ranging from 20 lb (9.1 kg) to 60 lb (27.2 kg) can be exerted between the seesaw and platform plates, using a specially made torque driver that can change the maximum torque value. We evaluated 2 scales that corresponded to the tensor: the angle (°, positive value in varus balance) between the seesaw and the platform plates and the distance (mm, joint center gap) between
A conventional gap measurement was performed between the osteotomized surfaces, in joint center and neutral rotational orientation, at extension and flexion of the knee (Fig. 1A). A distraction force of 40 lb. was loaded and the joint center gap and varus ligament balance were measured at extension and flexion. All measurements were obtained with reduction of the PF joint. In our preliminary studies, we measured and compared the joint component gap after femoral trial placement with a distraction force of 20, 40 and 60 lb, and these results showed the joint component gap at 0° with a joint distraction force of 40 lb was most similar to the selected insert thickness. Accordingly, we used a joint distraction force of 40 lb in this study. We loaded this distraction force several times until the joint component gap remained constant. This was performed to reduce the error that can result from creep elongation of the surrounding soft tissues. After evaluating the soft tissue balance between the osteotomized surfaces, the femoral trial component was placed with the OFR tensor on the surface of the tibial bone cut and established anterior–posterior and medial–lateral alignment with post-cam mechanism of the tensor and femoral trial component (Fig. 1B). The PF joint was temporarily reduced by applying sutures proximally and distally to the connecting arm of the OFR tensor (Fig. 1C). Joint component gap assessments were performed at 8 knee flexion angles of 0°, 10°, 30°, 45°, 60°, 90°, 120°, and 135°, with a joint distraction force of 40 lb exerted at each angle. The knee flexion angle was measured using a goniometer. During each measurement, the thigh was held and the knee was aligned in the sagittal plane, to eliminate the external load on the knee at each angle of knee flexion. After measurements were obtained, a NexGen prosthesis was implanted using cement, and a polyethylene insert was also implanted. Examined Parameters The joint center gap (mm) and varus ligament balance (°) between the osteotomized surfaces of the knee were measured at extension and flexion. After the femoral trial component was placed, the joint component gap (mm) and varus angle (°) between the component surfaces were also measured at each flexion angle. Moreover, the medial
Fig. 1. Intraoperative measurement of soft tissue balance using an Offset Repo-Tensor. (A) Measurement between osteotomized surfaces at flexion. The patella was laterally sifted to show the tensor. (B) The picture just after the placement of the femoral trial and the tensor. (C) Measurement with the femoral trial placement. The patellofemoral joint was temporarily reduced. All images were right knees. The joint space was distracted using torque driver, and the attention was focused on two scales that correspond to the tensor: the angle (right scale) between the seesaw and platform plates, and the distance (left scale) between the center midpoints of the upper surface of the seesaw plate and the proximal tibial surface.
K. Nagai et al. / The Journal of Arthroplasty 30 (2015) 1155–1159
and lateral compartment gaps (mm) were calculated at each flexion angle using the joint component gap, varus angle, and the width between the medial and lateral apexes of the femoral component; these apexes represent the contact points of the polyethylene insert where the width varies depending on the implant size. The lateral compartment gap = [component gap] + 0.5 × [width between the medial and lateral apexes of the femoral component that represent the contact points of the polyethylene insert] × sin (varus angle). The medial compartment gap = [component gap] − 0.5 × [width between the medial and lateral apexes of the femoral component that represent the contact points of the polyethylene insert] × sin (varus angle), as we previously reported [20]. In addition, joint looseness (mm) was calculated by subtracting the insert thickness from the joint component gap at each flexion angle. Furthermore, medial and lateral compartment looseness (mm) were also calculated by subtracting the insert thickness from the medial and lateral compartment gap, respectively. The active knee extension angle (°) was measured for each patient using the lateral radiograph of the knee, under maximum active extension in the supine position, before and 4 weeks after surgery. The angle of the postoperative posterior slope of tibia (°) was also measured for each patient using the lateral radiograph of the knee 4 weeks after surgery.
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Table 1 Correlations Between the Intraoperative Soft Tissue Balance Parameters and Postoperative Knee Extension Angle (Values Were Presented as Mean ± S.D.). Factor Joint center gap (at extension) (mm) Varus ligament balance (at extension) (°) Joint component gap (at 0°) (mm) Varus angle (at 0°) (°) Medial compartment gap (at 0°) (mm) Lateral compartment gap (at 0°) (mm) Joint looseness (at 0°) (mm) Medial compartment looseness (at 0°) (mm) Lateral compartment looseness (at 0°) (mm)
Value 26.0 5.9 11.8 2.8 10.7 12.8 0.2 −0.9 1.2
± ± ± ± ± ± ± ± ±
2.3 3.0 1.8 2.3 1.7 2.3 1.3 1.4 1.7
R-Value
P-Value
0.17 0.15 0.43 0.01 0.47 0.34 0.48 0.45 0.36
0.15 0.21 0.0002 0.95 b 0.0001 0.004 b 0.0001 b 0.0001 0.002
⁎ Statistically significant difference.
Correlations Between Postoperative Active Knee Extension and Soft Tissue Parameters Between Osteotomized Surfaces The postoperative active knee extension angle was not correlated with the joint center gap and varus ligament balance between osteotomized surfaces during both knee flexion and extension. Correlations Between Postoperative Active Knee Extension and Soft Tissue Parameters After Femoral Trial Prosthesis Placement
Statistical Analysis All values were expressed as a mean ± standard deviation (SD). The results were analyzed statistically using a statistical software package (StatView 5.0, Abacus Concepts Inc, Berkeley, CA, USA). We performed linear regression analysis to assess the correlations between each factor and the postoperative active knee extension angle. A P value of b0.05 was considered statistically significant.
Results The average pre-operative and post-operative active knee extension angles were −6.2 ± 8.1° and −3.4 ± 5.2°, respectively. The postoperative active knee extension angle was positively correlated with the preoperative active extension angle (R = 0.49, P b 0.0001, Fig. 2). There was no correlation between the postoperative extension angle and the postoperative posterior slope of tibia (R = 0.013, P = 0.91). There was moderate correlation of the joint component gap at 0° with joint center gap at extension (R = 0.46, P b 0.0001). The correlations between the postoperative extension angle and the intraoperative soft tissue balance parameters are shown in Table 1.
Fig. 2. Correlations between postoperative knee extension angle and preoperative knee extension angle. The postoperative knee extension angle was positively correlated with the preoperative extension angle (R = 0.49, P b 0.0001).
The postoperative active knee extension angle was not correlated with the joint component gap and varus angle at flexion, or with the varus angle at extension. However, the postoperative active knee extension angle was positively correlated with the joint component gap at 0° (R = 0.43, P = 0.0002, Fig. 3) and at 10° (R = 0.32, P = 0.006). Furthermore, the postoperative active knee extension angle was more positively correlated with the medial compartment gap at 0° than with the lateral compartment gap at 0° (medial: R = 0.47, P b 0.0001, lateral: R = 0.34, P = 0.004, Fig. 4). Moreover, the postoperative active knee extension angle was positively correlated with joint looseness at 0° (R = 0.48, P b 0.0001, Fig. 5A). In particular, the postoperative active knee extension angle was more positively correlated with medial compartment looseness at 0° (R = 0.45, P b 0.0001, Fig. 5B) than with lateral compartment looseness at 0° (R = 0.36, P = 0.002). Discussion The main findings of the present study were that a postoperative active knee extension angle was positively correlated with the component gap at 0° (R = 0.43, P = 0.002), although the postoperative active knee extension angle was not correlated with the joint center gap at extension between osteotomized surfaces (R = 0.17, P = 0.15). Furthermore, the postoperative active knee extension angle was positively correlated
Fig. 3. Correlations between postoperative knee extension angle and component gap at 0°. The postoperative knee extension angle was positively correlated with the component gap at 0° (R = 0.43, P = 0.0002).
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Fig. 4. Correlations between postoperative knee extension angle and compartment gap at 0°. (A) The postoperative knee extension angle was positively correlated with the medial compartment gap at 0° (R = 0.47, P b 0.0001). (B) The postoperative knee extension angle was positively correlated with the lateral compartment gap at 0° (R = 0.34, P = 0.004).
with joint looseness at 0° (R = 0.48, P b 0.0001). These results indicate that the component gap is more representative of the physiological state and relevant to the condition after implantation than the joint center gap between the osteotomized surfaces. Furthermore, joint looseness at 0° could be useful as a predictor of the postoperative active knee extension angle. As previously reported [21,22], the extension gap was affected by the femoral posterior condyle, and the osteotomized gap at extension was different from the postoperative condition. Muratsu et al [21] showed that the femoral component placement changed the soft tissue balance in PS TKA and that the joint gap and varus ligament imbalance were significantly decreased as much as 5.3 mm and 3.1° respectively, at extension after femoral trial prosthesis placement. These changes at extension might be caused by tensed posterior structures of the knee, in relation with the posterior condyle. Mitsuyasu et al [22] also reported that an enlarged postoperative posterior condyle tightened the extension gap in PS TKA. These reports indicated the importance of soft tissue balance measurement with trial component placement. Interestingly, the postoperative active knee extension angle was more positively correlated with the medial compartment gap at 0° than with the lateral compartment gap at 0° (medial: R = 0.47, P b 0.0001, lateral: R = 0.34, P = 0.004), and was also correlated with medial compartment looseness at 0° (R = 0.45, P b 0.001) in the present study. These results indicate that the patients who had a smaller medial compartment looseness at 0° tended to have postoperative flexion contracture. This result might be related to the difference between medial and lateral compartment stiffness, which may be a result of several underlying mechanisms. First, preoperative osteoarthritic varus knee
joints exhibit contracture of the medial compartment and looseness of the lateral compartment. Moreover, we previously reported that lateral compartment stiffness was significantly lower than medial compartment stiffness throughout the range of motion [20]. Second, there is a physiological laxity in the lateral compartment of the normal knee, as demonstrated by Tokuhara et al [23]. They used an open MRI system to assess the varus and valgus joint laxity of normal functioning knees during flexion, and found that the lateral flexion gap was significantly larger (by 4.6 mm) than the medial flexion gap. These discrepancies indicated that the tibiofemoral flexion gap in normal knees is not rectangular and that the lateral joint gap has significantly more laxity. Third, we ensured slight lateral laxity in the coronal plane in PS TKA for varus osteoarthritic knee patients, in order to avoid the development of medial compartment instability caused by excessive medial release. Theoretically, the medial compartment tended to be stiffer than the lateral compartment, and the medial compartment gap at 0° affected the postoperative active knee extension angle to a greater extent as compared to the lateral compartment gap at 0°. Several previous studies have investigated the relationship between intraoperative soft tissue balance and postoperative knee extension. Asano et al [24] demonstrated that soft tissue tension during an operation affected the postoperative knee extension and stability. Soft tissue tension at extension was measured during the operation by using a balancer/tensor device. The knee extension angle was then measured using a goniometer, with the patient lying in a supine position, 1 year after the operation. They showed that the postoperative knee extension deficit became significantly larger with an increase in the intraoperative soft tissue tension at extension. Okamoto et al [25] reported that the
Fig. 5. Correlations between postoperative knee extension angle and joint looseness at 0°. (A) The postoperative knee extension angle was positively correlated with joint looseness at 0°(R = 0.48, P b 0.0001). (B) The postoperative knee extension angle was positively correlated with medial compartment looseness at 0° (R = 0.45, P b 0.0001).
K. Nagai et al. / The Journal of Arthroplasty 30 (2015) 1155–1159
intraoperative extension gap was related to the postoperative extension angle and medial component gap; this was calculated by subtracting the selected thickness of the tibial component, including the polyethylene liner, from the extension gap at the medial side. They divided the patients into three groups according to the medial component gap: group 1, the medial component gap was more than 1 mm; group 2, the medial component gap was between 0 and 1 mm; and group 3, the medial component gap was less than 0 mm. The results showed a flexion contracture of more than 5°, 1 year after the operation, in 0/34 patients in group 1, 2/26 (8%) patients in group 2, and 3/15 (20%) patients in group 3. Thus, they concluded that a laxity of more than 1 mm in the medial compartment after implantation was needed to avoid postoperative flexion contracture in PS TKA, thus supporting our present findings. Despite the important findings in this study, there are several limitations. First, the postoperative knee extension angle can be affected by various factors. The posterior condylar offset, tibial posterior slope, cementing technique, the thickness of femoral component and different prosthetic designs may yield varying values for the postoperative knee extension angle. However, the postoperative posterior slope angle of tibia was not correlated with the postoperative active knee extension angle. In addition, the thickness of femoral component used in this study was same regardless of the implant size (9 mm at extension and 12 mm at flexion), and this factor also would not affect the postoperative extension angle. Second, the knee extension angle was measured by active motion in a supine position. These results would vary with passive knee extension or any other alternative method of evaluation, and hence, further investigation is needed. Third, the postoperative active knee extension angle was evaluated 4 weeks after surgery, and therefore, the long-term results might be different from the present results. Fourth, we could not determine the appropriate soft tissue balance at extension in PS TKA, even though the present results suggest that the intraoperative component gap measurement is important for postoperative knee function and that some intraoperative factors are correlated with the postoperative knee extension angle. In conclusion, intraoperative soft tissue measurement significantly affected the postoperative active knee extension over the short term after PS TKA in patients with osteoarthritic varus knees, as we hypothesized. Thus, the proposed component gap evaluation in intraoperative soft tissue balance measurement is more physiologically relevant to the joint condition after TKA, and might be useful for predicting the short-term postoperative clinical results.
Acknowledgment The authors thank Drs. Hidetoshi Miya and Akihiro Maruo from the Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital for collecting data.
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References 1. Dorr LD, Boiardo RA. Technical considerations in total knee arthroplasty. Clin Orthop Relat Res 1986:5. 2. Insall J, Tria AJ, Scott WN. The total condylar knee prosthesis: the first 5 years. Clin Orthop Relat Res 1979:68. 3. Insall JN, Binazzi R, Soudry M, et al. Total knee arthroplasty. Clin Orthop Relat Res 1985:13. 4. Anania A, Abdel MP, Lee YY, et al. The natural history of a newly developed flexion contracture following primary total knee arthroplasty. Int Orthop 2013;37:1917. 5. McPherson EJ, Cushner FD, Schiff CF, et al. Natural history of uncorrected flexion contractures following total knee arthroplasty. J Arthroplasty 1994;9:499. 6. Magit D, Wolff A, Sutton K, et al. Arthrofibrosis of the knee. J Am Acad Orthop Surg 2007;15:682. 7. Ritter MA, Lutgring JD, Davis KE, et al. The role of flexion contracture on outcomes in primary total knee arthroplasty. J Arthroplasty 2007;22:1092. 8. Tew M, Forster IW. Effect of knee replacement on flexion deformity. J Bone Joint Surg (Br) 1987;69:395. 9. Lam LO, Swift S, Shakespeare D. Fixed flexion deformity and flexion after knee arthroplasty. What happens in the first 12 months after surgery and can a poor outcome be predicted? Knee 2003;10:181. 10. Asano H, Muneta T, Hoshino A. Stiffness of soft tissue complex in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2008;16:51. 11. Bengs BC, Scott RD. The effect of distal femoral resection on passive knee extension in posterior cruciate ligament-retaining total knee arthroplasty. J Arthroplasty 2006;21: 161. 12. Smith CK, Chen JA, Howell SM, et al. An in vivo study of the effect of distal femoral resection on passive knee extension. J Arthroplasty 2010;25:1137. 13. Song SJ, Detch RC, Maloney WJ, et al. Causes of instability after total knee arthroplasty. J Arthroplasty 2014;29:360. 14. Schroer WC, Berend KR, Lombardi AV, et al. Why are total knees failing today? Etiology of total knee revision in 2010 and 2011. J Arthroplasty 2013;28:116. 15. Muratsu H, Tsumura N, Yamaguchi M, et al. Patellar eversion affects soft tissue balance in total knee arthroplasty. Trans Orthop Res 2003;28:242. 16. Matsumoto T, Muratsu H, Tsumura N, et al. Joint gap kinematics in posteriorstabilized total knee arthroplasty measured by a new tensor with the navigation system. J Biomech Eng 2006;128:867. 17. Matsumoto T, Mizuno K, Muratsu H, et al. Influence of intra-operative joint gap on post-operative flexion angle in osteoarthritis patients undergoing posteriorstabilized total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2007;15: 1013. 18. Takayama K, Matsumoto T, Kubo S, et al. Influence of intra-operative joint gaps on post-operative flexion angle in posterior cruciate-retaining total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2012;20:532. 19. Nagai K, Muratsu H, Matsumoto T, et al. Influence of intra-operative parameters on postoperative early recovery of active knee flexion in posterior-stabilized total knee arthroplasty. Int Orthop 2013;37:2153. 20. Nagai K, Muratsu H, Matsumoto T, et al. Soft tissue balance changes depending on joint distraction force in total knee arthroplasty. J Arthroplasty 2014;29:520. 21. Muratsu H, Matsumoto T, Kubo S, et al. Femoral component placement changes soft tissue balance in posterior-stabilized total knee arthroplasty. Clin Biomech (Bristol, Avon) 2010;25:926. 22. Mitsuyasu H, Matsuda S, Fukagawa S, et al. Enlarged post-operative posterior condyle tightens extension gap in total knee arthroplasty. J Bone Joint Surg (Br) 2011;93: 1210. 23. Tokuhara Y, Kadoya Y, Nakagawa S, et al. The flexion gap in normal knees. An MRI study. J Bone Joint Surg (Br) 2004;86:1133. 24. Asano H, Muneta T, Sekiya I. Soft tissue tension in extension in total knee arthroplasty affects postoperative knee extension and stability. Knee Surg Sports Traumatol Arthrosc 2008;16:999. 25. Okamoto S, Okazaki K, Mitsuyasu H, et al. Extension gap needs more than 1-mm laxity after implantation to avoid post-operative flexion contracture in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:3174.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Influence of Intraoperative Soft Tissue Balance on Postoperative Active Knee Extension in Posterior-Stabilized Total Knee Arthroplasty Kanto Nagai, MD a,b, Hirotsugu Muratsu, MD, PhD a, Tomoyuki Matsumoto, MD, PhD b, Shunsuke Takahara, MD a, Ryosuke Kuroda, MD, PhD b, Masahiro Kurosaka, MD, PhD b a b
Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital, Himeji, Japan Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
a r t i c l e
i n f o
Article history: Received 16 October 2014 Accepted 31 January 2015 Keywords: soft tissue balance active knee extension offset type tensor posterior-stabilized total knee arthroplasty flexion contracture
a b s t r a c t We evaluated the influence of intraoperative soft tissue balance on postoperative active knee extension using Offset Repo-Tensor® among 73 varus osteoarthritic knees underwent primary posterior-stabilized total knee arthroplasty. The joint center gap between osteotomized surfaces and the component gap after femoral trial component placement were measured using a joint distraction force of 40 lb. The active knee extension angle was measured 4 weeks after surgery. The postoperative extension angle was not correlated with the joint center gap at 0°, but positively correlated with the component gap at 0°, and the joint looseness at 0° which was calculated by subtracting insert thickness from the component gap. Thus, intraoperative soft tissue measurement with femoral trial component placement would be useful to predict the postoperative knee extension angle. © 2015 Elsevier Inc. All rights reserved.
Although both accurate component placement and adequate soft tissue balance are recognized as essential surgical principles in total knee arthroplasty (TKA) [1–3], the influence of intraoperative soft tissue balance on the postoperative clinical results has not been fully investigated. The prevention of flexion contracture after TKA is one of the most important outcomes for TKA. If flexion contracture occurs postoperatively, the quadriceps muscle would need to generate an increased force to stabilize the flexed knee during weight-bearing actions. This force would be distributed between the posterior half of the tibial plateau and the patellofemoral (PF) joint [4,5]. Therefore, patients with persistent flexion contracture would experience anterior knee pain and altered gait mechanics, and thus would be unsatisfied with their TKAs [6–8]. The risk factors for postoperative flexion contracture include preoperative flexion contracture, male gender, and/or advanced age [7,9]. In addition, several reports have indicated that the likelihood of postoperative flexion contracture was greater when intraoperative soft tissue tension was higher during extension at the time of surgery [10–12]. On the other hand, looseness of soft tissue balance may cause extension instability, which is related to the patients' symptoms and implant survival [13,14]. Therefore, appropriate intraoperative soft tissue balance would be crucial for postoperative knee extension, and the One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.01.053. Reprint requests: Hirotsugu Muratsu, MD, PhD, Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital, 3–1, Yumesaki-cho, Hirohata-ku, Himeji, 671–1122, Japan. http://dx.doi.org/10.1016/j.arth.2015.01.053 0883-5403/© 2015 Elsevier Inc. All rights reserved.
relationship between intraoperative soft tissue balance and postoperative active knee extension angle needs to be investigated. In previous studies using an offset-type tensor, we discussed the importance of maintaining a reduced and anatomically oriented PF joint, with the femoral trial component in place, in order to obtain accurate and more physiologically relevant soft tissue balance [15,16]. Furthermore, the relationship between intraoperative soft tissue balance and the postoperative active/passive flexion angle was demonstrated using an offset-type tensor in posterior-stabilized (PS) and cruciateretaining TKA [17–19]. However, only a few reports have described the relationship between intraoperative soft tissue balance and the postoperative active extension angle. In the present study, we aimed to investigate the influence of the intraoperative soft tissue balance on postoperative active knee extension. We hypothesized that intraoperative soft tissue balance affected the postoperative active knee extension angle in cases undergoing PS TKA. Materials and Methods The hospital ethics committee approved the study protocol, and the patients provided informed consent for participation in the study. The inclusion criteria were the presence of substantial pain and loss of function due to osteoarthritis of the knee. The exclusion criteria were the presence of knees with valgus deformity, severe bony defects that require bone graft or augmentation, and/or active knee joint infection; patients undergoing revision TKA were also excluded. In total, 73 knees that met the above criteria and underwent primary PS TKA between January 2008 and November 2011 were enrolled. The patient population comprised 64 females and 9 males, with a mean age of 73.8 ±
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5.8 years. The average preoperative coronal plane alignment was 11.5 ± 5.6° in varus, and the average preoperative active knee flexion angles was 111.9 ± 13.1°. Each surgery was performed by the same surgeon—the senior author (H.M.)—using PS TKA (NexGen LPS Flex, Zimmer, Inc, Warsaw, IN), with a standardized surgical technique.
the center midpoints of the upper surface of the seesaw plate and the proximal tibial cut. By measuring these angular deviations and distances under a constant joint distraction force, we were able to measure the ligament balance and joint center gap, respectively. Intraoperative Measurement
Surgical Procedure TKAs were performed using the measured resection technique with a conventional resection block. After inflating the air tourniquet with 280 mmHg at the start of the procedure, a medial parapatellar arthrotomy was performed. Both the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were resected. A distal femoral osteotomy was performed perpendicular to the mechanical axis of the femur using an intramedullary resection guide, according to preoperative long-leg radiographs. Thereafter, a proximal tibial osteotomy was performed perpendicular to the mechanical axis in the coronal plane and with 7° of posterior inclination along the sagittal plane using an extramedullary resection guide. No bony defects were observed along the eroded medial tibial plateau. After neutral alignment was confirmed with each cut of the distal femur and proximal tibia, a posterior femoral cut was made using the anterior referencing technique. Femoral external rotation was set at 3° or 5° relative to the posterior condylar axis, while referring to Whiteside's line and the transepicondylar axis, measured using preoperative computed tomography images. After each osteotomy, we removed the osteophytes, released the posterior capsule along the femur, and corrected any ligament imbalances in the coronal plane by appropriately releasing the medial soft tissues. The osteotomy and soft tissue release were performed by using a spacer block. Intraoperative Measurement With the Offset Repo-Tensor® (OFR tensor; Zimmer, Warsaw, IN) The OFR tensor consists of 3 parts: an upper seesaw plate, a lower platform plate with a spike, and an extra-articular main body, as previously described [20]. This device is designed to facilitate the measurement of ligament balance and joint center gap, both before and after femoral trial prosthesis placement, while applying a constant joint distraction force. Joint distraction forces ranging from 20 lb (9.1 kg) to 60 lb (27.2 kg) can be exerted between the seesaw and platform plates, using a specially made torque driver that can change the maximum torque value. We evaluated 2 scales that corresponded to the tensor: the angle (°, positive value in varus balance) between the seesaw and the platform plates and the distance (mm, joint center gap) between
A conventional gap measurement was performed between the osteotomized surfaces, in joint center and neutral rotational orientation, at extension and flexion of the knee (Fig. 1A). A distraction force of 40 lb. was loaded and the joint center gap and varus ligament balance were measured at extension and flexion. All measurements were obtained with reduction of the PF joint. In our preliminary studies, we measured and compared the joint component gap after femoral trial placement with a distraction force of 20, 40 and 60 lb, and these results showed the joint component gap at 0° with a joint distraction force of 40 lb was most similar to the selected insert thickness. Accordingly, we used a joint distraction force of 40 lb in this study. We loaded this distraction force several times until the joint component gap remained constant. This was performed to reduce the error that can result from creep elongation of the surrounding soft tissues. After evaluating the soft tissue balance between the osteotomized surfaces, the femoral trial component was placed with the OFR tensor on the surface of the tibial bone cut and established anterior–posterior and medial–lateral alignment with post-cam mechanism of the tensor and femoral trial component (Fig. 1B). The PF joint was temporarily reduced by applying sutures proximally and distally to the connecting arm of the OFR tensor (Fig. 1C). Joint component gap assessments were performed at 8 knee flexion angles of 0°, 10°, 30°, 45°, 60°, 90°, 120°, and 135°, with a joint distraction force of 40 lb exerted at each angle. The knee flexion angle was measured using a goniometer. During each measurement, the thigh was held and the knee was aligned in the sagittal plane, to eliminate the external load on the knee at each angle of knee flexion. After measurements were obtained, a NexGen prosthesis was implanted using cement, and a polyethylene insert was also implanted. Examined Parameters The joint center gap (mm) and varus ligament balance (°) between the osteotomized surfaces of the knee were measured at extension and flexion. After the femoral trial component was placed, the joint component gap (mm) and varus angle (°) between the component surfaces were also measured at each flexion angle. Moreover, the medial
Fig. 1. Intraoperative measurement of soft tissue balance using an Offset Repo-Tensor. (A) Measurement between osteotomized surfaces at flexion. The patella was laterally sifted to show the tensor. (B) The picture just after the placement of the femoral trial and the tensor. (C) Measurement with the femoral trial placement. The patellofemoral joint was temporarily reduced. All images were right knees. The joint space was distracted using torque driver, and the attention was focused on two scales that correspond to the tensor: the angle (right scale) between the seesaw and platform plates, and the distance (left scale) between the center midpoints of the upper surface of the seesaw plate and the proximal tibial surface.
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and lateral compartment gaps (mm) were calculated at each flexion angle using the joint component gap, varus angle, and the width between the medial and lateral apexes of the femoral component; these apexes represent the contact points of the polyethylene insert where the width varies depending on the implant size. The lateral compartment gap = [component gap] + 0.5 × [width between the medial and lateral apexes of the femoral component that represent the contact points of the polyethylene insert] × sin (varus angle). The medial compartment gap = [component gap] − 0.5 × [width between the medial and lateral apexes of the femoral component that represent the contact points of the polyethylene insert] × sin (varus angle), as we previously reported [20]. In addition, joint looseness (mm) was calculated by subtracting the insert thickness from the joint component gap at each flexion angle. Furthermore, medial and lateral compartment looseness (mm) were also calculated by subtracting the insert thickness from the medial and lateral compartment gap, respectively. The active knee extension angle (°) was measured for each patient using the lateral radiograph of the knee, under maximum active extension in the supine position, before and 4 weeks after surgery. The angle of the postoperative posterior slope of tibia (°) was also measured for each patient using the lateral radiograph of the knee 4 weeks after surgery.
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Table 1 Correlations Between the Intraoperative Soft Tissue Balance Parameters and Postoperative Knee Extension Angle (Values Were Presented as Mean ± S.D.). Factor Joint center gap (at extension) (mm) Varus ligament balance (at extension) (°) Joint component gap (at 0°) (mm) Varus angle (at 0°) (°) Medial compartment gap (at 0°) (mm) Lateral compartment gap (at 0°) (mm) Joint looseness (at 0°) (mm) Medial compartment looseness (at 0°) (mm) Lateral compartment looseness (at 0°) (mm)
Value 26.0 5.9 11.8 2.8 10.7 12.8 0.2 −0.9 1.2
± ± ± ± ± ± ± ± ±
2.3 3.0 1.8 2.3 1.7 2.3 1.3 1.4 1.7
R-Value
P-Value
0.17 0.15 0.43 0.01 0.47 0.34 0.48 0.45 0.36
0.15 0.21 0.0002 0.95 b 0.0001 0.004 b 0.0001 b 0.0001 0.002
⁎ Statistically significant difference.
Correlations Between Postoperative Active Knee Extension and Soft Tissue Parameters Between Osteotomized Surfaces The postoperative active knee extension angle was not correlated with the joint center gap and varus ligament balance between osteotomized surfaces during both knee flexion and extension. Correlations Between Postoperative Active Knee Extension and Soft Tissue Parameters After Femoral Trial Prosthesis Placement
Statistical Analysis All values were expressed as a mean ± standard deviation (SD). The results were analyzed statistically using a statistical software package (StatView 5.0, Abacus Concepts Inc, Berkeley, CA, USA). We performed linear regression analysis to assess the correlations between each factor and the postoperative active knee extension angle. A P value of b0.05 was considered statistically significant.
Results The average pre-operative and post-operative active knee extension angles were −6.2 ± 8.1° and −3.4 ± 5.2°, respectively. The postoperative active knee extension angle was positively correlated with the preoperative active extension angle (R = 0.49, P b 0.0001, Fig. 2). There was no correlation between the postoperative extension angle and the postoperative posterior slope of tibia (R = 0.013, P = 0.91). There was moderate correlation of the joint component gap at 0° with joint center gap at extension (R = 0.46, P b 0.0001). The correlations between the postoperative extension angle and the intraoperative soft tissue balance parameters are shown in Table 1.
Fig. 2. Correlations between postoperative knee extension angle and preoperative knee extension angle. The postoperative knee extension angle was positively correlated with the preoperative extension angle (R = 0.49, P b 0.0001).
The postoperative active knee extension angle was not correlated with the joint component gap and varus angle at flexion, or with the varus angle at extension. However, the postoperative active knee extension angle was positively correlated with the joint component gap at 0° (R = 0.43, P = 0.0002, Fig. 3) and at 10° (R = 0.32, P = 0.006). Furthermore, the postoperative active knee extension angle was more positively correlated with the medial compartment gap at 0° than with the lateral compartment gap at 0° (medial: R = 0.47, P b 0.0001, lateral: R = 0.34, P = 0.004, Fig. 4). Moreover, the postoperative active knee extension angle was positively correlated with joint looseness at 0° (R = 0.48, P b 0.0001, Fig. 5A). In particular, the postoperative active knee extension angle was more positively correlated with medial compartment looseness at 0° (R = 0.45, P b 0.0001, Fig. 5B) than with lateral compartment looseness at 0° (R = 0.36, P = 0.002). Discussion The main findings of the present study were that a postoperative active knee extension angle was positively correlated with the component gap at 0° (R = 0.43, P = 0.002), although the postoperative active knee extension angle was not correlated with the joint center gap at extension between osteotomized surfaces (R = 0.17, P = 0.15). Furthermore, the postoperative active knee extension angle was positively correlated
Fig. 3. Correlations between postoperative knee extension angle and component gap at 0°. The postoperative knee extension angle was positively correlated with the component gap at 0° (R = 0.43, P = 0.0002).
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Fig. 4. Correlations between postoperative knee extension angle and compartment gap at 0°. (A) The postoperative knee extension angle was positively correlated with the medial compartment gap at 0° (R = 0.47, P b 0.0001). (B) The postoperative knee extension angle was positively correlated with the lateral compartment gap at 0° (R = 0.34, P = 0.004).
with joint looseness at 0° (R = 0.48, P b 0.0001). These results indicate that the component gap is more representative of the physiological state and relevant to the condition after implantation than the joint center gap between the osteotomized surfaces. Furthermore, joint looseness at 0° could be useful as a predictor of the postoperative active knee extension angle. As previously reported [21,22], the extension gap was affected by the femoral posterior condyle, and the osteotomized gap at extension was different from the postoperative condition. Muratsu et al [21] showed that the femoral component placement changed the soft tissue balance in PS TKA and that the joint gap and varus ligament imbalance were significantly decreased as much as 5.3 mm and 3.1° respectively, at extension after femoral trial prosthesis placement. These changes at extension might be caused by tensed posterior structures of the knee, in relation with the posterior condyle. Mitsuyasu et al [22] also reported that an enlarged postoperative posterior condyle tightened the extension gap in PS TKA. These reports indicated the importance of soft tissue balance measurement with trial component placement. Interestingly, the postoperative active knee extension angle was more positively correlated with the medial compartment gap at 0° than with the lateral compartment gap at 0° (medial: R = 0.47, P b 0.0001, lateral: R = 0.34, P = 0.004), and was also correlated with medial compartment looseness at 0° (R = 0.45, P b 0.001) in the present study. These results indicate that the patients who had a smaller medial compartment looseness at 0° tended to have postoperative flexion contracture. This result might be related to the difference between medial and lateral compartment stiffness, which may be a result of several underlying mechanisms. First, preoperative osteoarthritic varus knee
joints exhibit contracture of the medial compartment and looseness of the lateral compartment. Moreover, we previously reported that lateral compartment stiffness was significantly lower than medial compartment stiffness throughout the range of motion [20]. Second, there is a physiological laxity in the lateral compartment of the normal knee, as demonstrated by Tokuhara et al [23]. They used an open MRI system to assess the varus and valgus joint laxity of normal functioning knees during flexion, and found that the lateral flexion gap was significantly larger (by 4.6 mm) than the medial flexion gap. These discrepancies indicated that the tibiofemoral flexion gap in normal knees is not rectangular and that the lateral joint gap has significantly more laxity. Third, we ensured slight lateral laxity in the coronal plane in PS TKA for varus osteoarthritic knee patients, in order to avoid the development of medial compartment instability caused by excessive medial release. Theoretically, the medial compartment tended to be stiffer than the lateral compartment, and the medial compartment gap at 0° affected the postoperative active knee extension angle to a greater extent as compared to the lateral compartment gap at 0°. Several previous studies have investigated the relationship between intraoperative soft tissue balance and postoperative knee extension. Asano et al [24] demonstrated that soft tissue tension during an operation affected the postoperative knee extension and stability. Soft tissue tension at extension was measured during the operation by using a balancer/tensor device. The knee extension angle was then measured using a goniometer, with the patient lying in a supine position, 1 year after the operation. They showed that the postoperative knee extension deficit became significantly larger with an increase in the intraoperative soft tissue tension at extension. Okamoto et al [25] reported that the
Fig. 5. Correlations between postoperative knee extension angle and joint looseness at 0°. (A) The postoperative knee extension angle was positively correlated with joint looseness at 0°(R = 0.48, P b 0.0001). (B) The postoperative knee extension angle was positively correlated with medial compartment looseness at 0° (R = 0.45, P b 0.0001).
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intraoperative extension gap was related to the postoperative extension angle and medial component gap; this was calculated by subtracting the selected thickness of the tibial component, including the polyethylene liner, from the extension gap at the medial side. They divided the patients into three groups according to the medial component gap: group 1, the medial component gap was more than 1 mm; group 2, the medial component gap was between 0 and 1 mm; and group 3, the medial component gap was less than 0 mm. The results showed a flexion contracture of more than 5°, 1 year after the operation, in 0/34 patients in group 1, 2/26 (8%) patients in group 2, and 3/15 (20%) patients in group 3. Thus, they concluded that a laxity of more than 1 mm in the medial compartment after implantation was needed to avoid postoperative flexion contracture in PS TKA, thus supporting our present findings. Despite the important findings in this study, there are several limitations. First, the postoperative knee extension angle can be affected by various factors. The posterior condylar offset, tibial posterior slope, cementing technique, the thickness of femoral component and different prosthetic designs may yield varying values for the postoperative knee extension angle. However, the postoperative posterior slope angle of tibia was not correlated with the postoperative active knee extension angle. In addition, the thickness of femoral component used in this study was same regardless of the implant size (9 mm at extension and 12 mm at flexion), and this factor also would not affect the postoperative extension angle. Second, the knee extension angle was measured by active motion in a supine position. These results would vary with passive knee extension or any other alternative method of evaluation, and hence, further investigation is needed. Third, the postoperative active knee extension angle was evaluated 4 weeks after surgery, and therefore, the long-term results might be different from the present results. Fourth, we could not determine the appropriate soft tissue balance at extension in PS TKA, even though the present results suggest that the intraoperative component gap measurement is important for postoperative knee function and that some intraoperative factors are correlated with the postoperative knee extension angle. In conclusion, intraoperative soft tissue measurement significantly affected the postoperative active knee extension over the short term after PS TKA in patients with osteoarthritic varus knees, as we hypothesized. Thus, the proposed component gap evaluation in intraoperative soft tissue balance measurement is more physiologically relevant to the joint condition after TKA, and might be useful for predicting the short-term postoperative clinical results.
Acknowledgment The authors thank Drs. Hidetoshi Miya and Akihiro Maruo from the Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital for collecting data.
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