The Journal of Arthroplasty 30 (2015) 1531–1536
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
The Influence of Alignment on Midterm Outcome after Total Knee Arthroplasty in Patients With Marked Coronal Femoral Bowing Tsan-Wen Huang, MD a,b, Ching-Yu Lee, MD a, Shih-Jie Lin, MD a, Mel S. Lee, MD, PhD a,b, Robert Wen-Wei Hsu, MD a,b, Wun-Jer Shen, MD c a b c
Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chiayi, Taiwan Chang Gung University, Taoyuan, Taiwan Po-Cheng Orthopaedic Institute, Kaohsiung, Taiwan
a r t i c l e
i n f o
Article history: Received 20 December 2014 Accepted 18 March 2015 Keywords: total knee arthroplasty bowing of the femur mechanical axis polyethylene wear implant longevity
a b s t r a c t Whether the mechanical axis should be restored to neutral remains controversial when the patient has marked coronal femoral bowing. Eighty-four total knee arthroplasties were retrospectively reviewed. In the neutralaligned group A the immediate postoperative mechanical axis of 179 ± 1° held stable (P = 0.841). The postoperative mechanical axis decreased from 176 ± 1° to 173 ± 1° (P = 0.024) in the outlier group. Progressive varus in the outlier group at follow-up was probably due implant instability and ligament imbalance as well as excessive polyethylene wear. At a mean follow-up of 75.8 months, no statistically significant difference was detected between the two groups. Long-term follow up will be needed to determine if the maintenance in radiographic results translates to better clinical outcomes. © 2015 Elsevier Inc. All rights reserved.
Femoral bowing deformity in the coronal plane is not unusual in the Asian population, with a rather high prevalence reported in China, India, Japan, Korea and Taiwan [1–8]. The bowing deformity alters the relationship between the mechanical axis (MA) and anatomical axis (AA) of the femur, thereby affecting the placement of the femoral component and the postoperative MA [4–7]. Recently, there has been greater awareness of this deformity and its relationship to implant performance [4–8]. Finite element modeling and long-term survivorship studies suggest that malaligned TKAs compromise function and place the implants at a higher risk for failure [9–14]. Since the success of total knee arthroplasty (TKA) depends on the achievement of proper limb and prosthetic alignment and wellbalanced gaps [15], many surgical techniques and alternatives have been proposed to overcome these bowing related difficulties and achieve a neutral mechanical axis [4,5,8,16–22]. The concept of constitutional varus, as described in the award winning paper by Bellemans et al. [23], asserts that for patients with coronal femoral bowing, some degree of varus alignment is not only tolerable, but may actually be normal. Several authors have questioned whether it is necessary to
Source of Funding: There was no external funding for this study. 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.2015.03.027. Reprint requests: Robert Wen-Wei Hsu, MD or Mel S. Lee, MD, PhD, Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chiayi, No. 6, West Section, Chia-Pu Road, Pu-Tz City, Chia-Yi Hsien 613, Taiwan, ROC. http://dx.doi.org/10.1016/j.arth.2015.03.027 0883-5403/© 2015 Elsevier Inc. All rights reserved.
completely correct the MA and have challenged the importance of restoration of neutral limb alignment [10,23,24]. The purpose of this study was to investigate the effect of immediate postoperative alignment on eventual MA and survivorship by comparing neutral-aligned and outlier TKAs at midterm follow-up. We also sought to determine if postoperative non-neutral alignment of MA leads to suboptimal functional results in this group of patients when modern cemented prostheses are used.
Materials and Methods Since January 2002, all TKAs performed at our institution were done using the same treatment protocol. Demographic data, radiographic data and preoperative functional scores (including International Knee Society score and patellar score) of the patients were preoperatively collected and entered into a joint registry. Patients with osteoarthritis of the knee joint who underwent primary TKA by a single experienced orthopedic surgeon using the P.F.C. Sigma Knee System (DePuy Orthopaedics, Warsaw, Indiana, USA) were identified by computer database search. Patients with marked coronal femoral bowing (measured by Mullaji’s method [3] and according to Mullaji’s criteria [8], a coronal femoral bowing magnitude of N 5° was defined as marked coronal femoral bowing deformity) were flagged and reviewed. The study protocol was approved by the institutional review board, and all patients provided signed informed consent. The inclusion criteria required all patients to have marked coronal femoral bowing. Patients meeting the following criteria were excluded from analysis: (a) minimum follow-up of less than 60 months.
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T.-W. Huang et al. / The Journal of Arthroplasty 30 (2015) 1531–1536 Table 1 The Demographic Data and Radiographic Data in the Patient of the Neutral-Alignment Group and the Outlier Group.
Parameters Demographic Data Age at time of operation (years) Gender Male Female Body Height (cm) Body Weight (Kg) Body Mass Index (kg/m2) Follow up period (months) Radiographic data of Leg Axis Valgus correction angle of the distal femur (°) Coronal femoral bowing angle(°) Preoperative coronal MA (°) Postoperative coronal MA (°)
Group A Group B N = 38 N = 46 p-value 71 ± 4
70 ± 4
3 35 150 ± 6 68 ± 8 30.3 ± 3.7 74 ± 8
3 43 150 ± 6 69 ± 8 30.2 ± 3.9 77 ± 7
9±1 10 ± 3 166 ± 4 179 ± 1
10 ± 1 10 ± 2 167 ± 4 176 ± 1
0.463 0.567
0.841 0.936 0.931 0.119 0.815 0.971 0.812 b0.001a
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° MA = mechanical axis Values are shown as mean ± SD P values for between-group comparison were determined by Mann-Whitney U test a Statistically significant (p value b0.05).
Fig. 1. The femoral alignment angle (α) is defined as the medial angle formed by a line drawn between the distal ends of the femoral condyles and the femoral mechanical axis line. The tibial alignment angle (β) is defined as the medial angle formed by a line drawn along the base of the tibial component and the tibial mechanical axis line.
(b) extra-articular deformity of the femur or tibia related to previous trauma or surgery, and (c) incomplete medical records, radiographic analyses, and clinical functional assessments. The knees were divided into 2 groups. Those with a postoperative MA ≦ 3° of neutral were assigned to the neutral-alignment group (Group A). Those with a postoperative MA deviation of N3° from neutral were assigned to the outlier group (Group B). Clinical data and radiographic parameters were compared. To determine adequate sample size, an a priori power analysis using the two-sided hypothesis test with a power of 80% and a significance of 0.05 was done. It was calculated that 33 knees were required to detect a difference of 5 points in the Knee Society score (estimated SD of N 8). The cutoff value was selected because a difference of 5 points has been suggested as the minimal clinically important difference for the Knee Society score [25]. All patients had preoperative and postoperative anteroposterior (AP) and lateral radiographs of the knees, along with full-length
standing scanograms of the lower extremity, taken as described in detail in a previous publication by the senior author [26]. This radiograph was used to measure the valgus correction angle, the coronal femoral bowing angle, and the preoperative MA. Films were taken at 3 months after surgery and at each follow-up, and the postoperative MA, femoral and tibial alignments were measured. The magnitude of coronal femoral bowing angle was measured using the method of Mullaji et al. [3]. The femoral alignment angle is defined as the medial angle formed by a line drawn between the distal ends of the femoral condyles and the femoral mechanical axis line. The tibial alignment angle is defined as the medial angle formed by a line drawn along the base of the tibial component and the tibial mechanical axis line (Fig. 1) [27]. Four component alignment angles (the femoral valgus angle, tibial valgus angle, femoral flexion angle, and tibial flexion angle) were assessed [28]. A postoperative MA of N 3° was considered outlier. All measurements were made by two investigators using digital radiographs on a computer. The intraobserver and interobserver reliability of assessments of all radiographic measurements were evaluated using intraclass correlation coefficients and found to be greater than 0.84 (range, 0.84–0.92) and considered to be reliable. Demographic data and clinical information was retrieved from records by an independent investigator. Preoperative clinical status and postoperative outcomes were evaluated using knee range of motion (ROM), patellar score [29], and International Knee Society (IKS) scores [30]. Active maximum ROM of the knee was measured using a goniometer. All data were entered in an Excel spreadsheet (Microsoft, Redmond, Washington), rechecked for missing and illogical data and subsequently copied into SPSS version 13.0 (SPSS, Chicago, Illinois). Statistical analysis was performed by an independent statistician. The Mann-Whitney U test, Fisher’s exact test, pair-t test, and Student’s t test were used to determine statistically significant differences between the two groups. Significance was set at p b 0.05. Results Between January 2003 and July 2009, there were 124 patients (139 knees) with marked femoral bowing and underwent TKA. Among them, 9 patients died of causes unrelated to TKA surgery, 8 patients had minimum follow-up of less than 60 months, 24 patients had extraarticular deformity of the femur or tibia related to previous trauma, 11 patients had incomplete medical records, radiographic analyses, and clinical functional assessments. Therefore, a total of 72 patients
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Table 2 The Comparisons of Limb Alignment Between the Neutral-Alignment Group and the Outlier Group at Post-Operation and at Last Follow-up. Coronal MA
Group A Group B
Coronal Femoral Bowing Angle
Postoperation
Last Follow-Up
Postoperation
179 ± 1 176 ± 1
178 ± 1 173 ± 1a
10 ± 3 10 ± 2
Femoral Alignment
Last Follow-Up 10 ± 3 10 ± 3
Tibial Alignment
Postoperation
Last Follow-Up
Postoperation
90 ± 2 88 ± 3
89 ± 3 86 ± 4a
90 ± 2 89 ± 3
Last Follow-Up 90 ± 2 89 ± 3
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° Values are shown as mean ± standard deviation MA = mechanical axis p-values were determined by a pair-t test a Statistically significant (p value b0.05).
(84 knees) were studied. There were 38 knees in group A, 46 knees in group B. The mean follow-up time was 75.8 months (range, 60 to 126 months). Demographically, there were no statistical differences in age at time of operation, body height, body weight, body mass index, and length of follow-up period (Table 1). Comparing the alignment data between group A and B, it is noted that the valgus correction angle, magnitude of coronal femoral bowing deformity, and the preoperative MA are very similar (Table 1). In group A, the immediate postoperative MA of 179 ± 1° held stable, changing only to 178 ± 1° (P = 0.841). In Group B, the postoperative MA decreased from 176 ± 1° to 173 ± 1° (P = 0.024). There was no difference noted between 3 months after surgery and at the last follow-up for tibial alignment (p = 0.936 and p = 0.900, respectively) and coronal femoral bowing angle (p = 0.578 and p = 0.525, respectively). The femoral alignment was also not significantly different in group A between 3 months after surgery and at the last follow-up (p = 0.717), however, there was significant differences in the femoral alignment in group B (p = 0.036) (Table 2). The chief difference in the coronal plane lies with the femoral alignment, which results in the postoperative MA becoming significantly different between 3 months after surgery and at the last follow-up. Radiographic analysis of component alignment angles in the coronal and sagittal planes showed no difference between 3 months after surgery and at the last follow-up for femoral valgus angle (p = 0.538 and p = 0.534, respectively), tibial valgus angle (p = 0.987 and p = 0.794, respectively), femoral flexion angle (p = 0.286 and p = 0.073, respectively), and tibial flexion angle (p = 0.554 and p = 0.548, respectively) (Table 3). The mean preoperative patellar scores and IKS scores in both groups were similar. The patellar score in both groups were significantly improved at final follow-up compared with preoperative scores, but there was no difference between groups A and B (P = 0.876). Using the IKS rating system, there was marked improvement of the pain score, the clinical knee score, and the functional knee score after surgery compared with preoperative, but between the two groups, the difference did not achieve statistical significance in any of the subscores (Table 4). In this study, two (4.3%) patients in group B had polyethylene wear with instability of knee joint and received revision surgery (Fig. 2). One knee in each group sustained a periprosthetic femoral fracture. The patient in group A underwent open reduction and internal fixation with dynamic condylar screws (Synthes, Basel, Switzerland). The patient in group B was managed with open reduction and internal
fixation using Less Invasive Surgical Stabilization locking plates (Synthes, West Chester, Pennsylvania). Both healed uneventfully. Pulmonary emboli, deep vein thrombosis, and postoperative wound infection were not encountered in this series. Discussion The most important finding in this investigation was that initial neutral alignment appears predictive of future radiographic results. Those who were not neutrally aligned immediately postoperative gradually developed more varus over the next 5 years. However, we also found that there was no statistically significant difference in clinical function between the two groups, confirming the adage that radiological difference is not the same as clinical difference. This study is a retrospective practice audit. At the time of surgery, the surgeon was aiming for a neutral MA in all patients. Appropriate preoperative planning to adjust the cuts to accommodate the deformity was done. The angle of the cutting block was adjusted according to the valgus correction angle of the distal femur, which was measured using a full-length standing scanograms of the lower extremity. Incomplete insertion of intramedullary rods may contribute to subsequent erroneous distal femur resection and result in an undesired postoperative MA [6]. In this series of patients with marked coronal femoral bowing, the goal of neutral alignment proved elusive, with only 38 of 84 knees corrected to within 3° of neutral. Population surveys have shown that the prevalence of marked coronal femoral bowing deformity is higher in ethnic Asians [1–8], making TKA malalignment more likely. Finite element model studies suggest that eccentric loading and malalignment are detrimental to long term survival of the TKA [13,14]. There is little data available regarding the mid-term to long-term impact of marked coronal femoral bowing deformity. A school of thought views this condition mainly as a technical challenge. Several surgical techniques (such as staged or simultaneous femoral osteotomy combined with total knee arthroplasty [16]) and alternatives (including computer-assisted navigation [4,5,8,20–22] and patient-specific instruments [19]) have been developed to facilitate achievement of a neutral MA, and satisfactory results were reported after short-term to midterm follow-up. The intra-articular bone resection technique described by Wang et al. [17,18], using the intramedullary (IM) guidance system, modification of the starting hole in the lateral femoral condyle provided satisfactory results. In
Table 3 The Comparisons of Component Alignment Between the Neutral-Alignment Group and the Outlier Group at Post-Operation and at Last Follow-up. Femoral Valgus Angle Postoperation Group A Group B
99 ± 1 96 ± 1
Last Follow-Up
Tibial Valgus Angle Postoperation
99 ± 2 96 ± 2
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° Values are shown as mean ± standard deviation p-values were determined by a pair-t test *Statistically significant (p value b0.05)
90 ± 1 90 ± 1
Last Follow-Up 90 ± 1 89 ± 1
Femoral Flexion Angle Postoperation 3±2 4±3
Last Follow-Up 4±2 6±3
Tibial Flexion Angle Postoperation 88 ± 3 88 ± 4
Last Follow-Up 88 ± 3 87 ± 3
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Table 4 Comparison of Preoperative and Postoperative Knee Scores in both Groups. Group A Group B N = 38 N = 46 p-value
Parameters Preoperative knee scores Patellar score International Knee Society pain score International Knee Society knee score International Knee Society function score Preoperative range of motion (°) Final postoperative knee scores Patellar score International Knee Society pain score International Knee Society knee score International Knee Society function score Postoperative range of motion (°)
17.3 21.4 60.4 40.9 103
± ± ± ± ±
2.2 10.1 14.6 12.6 14
16.4 22.2 58.3 38.1 101
± ± ± ± ±
2.1 7.1 7.8 8.5 13
0.868 0.732 0.462 0.288 0.472
26.2 47.0 93.4 92.7 121
± ± ± ± ±
1.7 2.5 2.9 6.0 10
25.7 45.4 91.4 90.4 120
± ± ± ± ±
2.1 2.5 3.2 5.3 10
0.876 0.655 0.894 0.342 0.850
Group A: Patient with a postoperative mechanical axis of ≦3°. Group B: Patient with a postoperative mechanical axis of N3°. MA = mechanical axis. Values are shown as mean ± SD. P values for between-group comparison were determined by Mann-Whitney U test. *Statistically significant (p value b0.05).
addition, an intra-operative radiograph can be taken with the IM rod or trial components in place and adjustments subsequently made. There is debate on whether it is necessary to correct the MA to neutral. The concept of an alignment safe zone has been proposed [10,23,24]. Ritter et al. [9,11] retrospectively reviewed 6070 knees in 3992 patients
and found that outliers in overall alignment have a higher rate of revision than well-aligned knees. Attaining neutrality in of tibiofemoral alignment, femoral and tibial component alignment is important in maximizing total knee implant survival. Conversely, Bellemans et al. analyzed 250 asymptomatic adults between 20 and 27 years of age [23]. 32% of adult men and 17% of adult women had constitutional varus knees with a natural MA N 3° varus. They concluded that restoration of MA to neutral in these cases may not be desirable and in fact may be unnatural for said persons. Limited release of soft tissue may result in a less painful and more stable TKA compared with scenarios in which extensive ligament releases are done in an attempt to obtain a completely aligned TKA [31]. Several recently published studies demonstrated no difference in survivorship and clinical performance for malaligned TKAs [10,24]. Parratte et al. [10] reported a fifteen-year survival study and demonstrated that a MA goal of 0° ± 3° is of little practical value in predicting the durability of modern, cemented total knee prostheses. Matziolis et al. [24] compared clinical outcomes between the outlier and well-aligned TKAs at a minimum follow-up of 5 years and concluded that significant varus malalignment did not contribute to inferior outcomes in terms of the WOMAC and the SF36 scores. In this study, the radiographic assessment showed that the MA becomes more varus from post-operation to final follow-up in the outlier group. Conversely, the postoperative MA held stable in the aligned group (Fig. 3). There were no significant differences in tibial alignment angle, coronal femoral bowing angle, and in the four component angles between 3 months after surgery and at the last follow-up.
Fig. 2. A through E. Radiographs of knee joint before and after surgery. A. A full-length standing scanogram of the lower extremity showing significant femoral bowing in the coronal plane. The post-operative mechanical axis is 175° after surgery. B. Weight-bearing radiographs of the left knee showed symmetric joint space (0°). C. The postoperative mechanical axis worsened from 175 to 167° at 5 years after primary TKA. D. Asymmetric joint space (1.5°) was observed on weight-bearing radiograph. E. After revision total knee arthroplasty, standing scanograms show residual 5° varus deformity.
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Fig. 3. A through E. Radiographs of knee joint before and after surgery. A. A full-length standing scanogram of the lower extremity showing full restoration of limb alignment after undergoing TKA. B. The postoperative mechanical axis is neutral at 6 years after primary TKA. C. Ten years later, the limb remains in excellent alignment.
However, asymmetric joint space was noted on weight-bearing radiographs of the knee joint (Fig. 2B and Fig. 2D). The most possible reasons of this circumstance were implant instability and ligament imbalance as well as excessive polyethylene wear. The asymmetric joint space contributes to varus change of femoral alignment, which results in the postoperative MA becoming significantly different between 3 months after surgery and at the last follow-up. With regard to functional outcomes, however, the patellar score was 26.2 ± 1.7 points in group A and 25.7 ± 2.1 points in group B (p = 0.876). Likewise in the IKS scores, neither in the sum nor in the individual scores was a
significant difference found between groups A and B. Our results were consistent with Matziolis et al. [24]. The proper reconstructed MA does not translate into significantly superior clinical outcomes at midterm follow-up. Several limitations in this study must be acknowledged. First, this is a retrospective investigation with all the inherent limitations of this type of study. That being said, all patients underwent TKA by a single experienced surgeon, the same prosthesis was used, and the same protocol, so there may be fewer biases. Second, plain radiographic evaluation is recognized as less sensitive and inferior to computed
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tomographic assessment for determining alignment [27]. Third, the number of patients studied was small. Although we calculated that 33 knees per group should be adequate, a larger number of patients in a prospective study is always better. In conclusion, patients with marked coronal femoral bowing deformity with neutral-aligned TKA immediate postoperative maintained better radiographic limb alignment at a mean follow-up of 75.8 months. Progressive varus of MA in group B at follow-up was probably due to implant instability and ligament imbalance as well as excessive polyethylene wear. Clinically, however, there was no statistically significant difference in function. Our current TKA protocol still seeks to achieve a neutral mechanical axis. A prospective randomized study comparing two groups of patients with neutral and slight constitutional varus alignment respectively and with a minimum follow up of ten years should be of greater value. References 1. Nagamine R, Miura H, Bravo CV, et al. Anatomic variations should be considered in total knee arthroplasty. J Orthop Sci 2000;5:232. 2. Yau WP, Chiu KY, Tang WM, et al. Coronal bowing of the femur and tibia in Chinese: its incidence and effects on total knee arthroplasty planning. J Orthop Surg (Hong Kong) 2007;15:32. 3. Mullaji AB, Marawar SV, Mittal V. A comparison of coronal plane axial femoral relationships in Asian patients with varus osteoarthritic knees and healthy knees. J Arthroplasty 2009;24:861. 4. Huang TW, Hsu WH, Peng KT, et al. Total knee replacement in patients with significant femoral bowing in the coronal plane: a comparison of conventional and computerassisted surgery in an Asian population. J Bone Joint Surg (Br) 2011;93:345. 5. Lee CY, Huang TW, Peng KT, Lee MS, Shen RW, Hsu WJ, et al. Variability of Distal Femoral Valgus Resection Angle in Patients with End-stage Osteoarthritis and Genu Varum Deformity: Radiographic Study in an Ethnic Asian Population. Biomed J 2015. http://dx.doi.org/10.4103/2319-4170.151030. 6. Mullaji AB, Shetty GM, Lingaraju AP, et al. Which factors increase risk of malalignment of the hip-knee-ankle axis in TKA? Clin Orthop Relat Res 2013;471:134. 7. Lasam MP, Lee KJ, Chang CB, et al. Femoral lateral bowing and varus condylar orientation are prevalent and affect axial alignment of TKA in Koreans. Clin Orthop Relat Res 2013;471:1472. 8. Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty 2009;24:1164.e1. 9. Fang DM, Ritter MA, Davis KE. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty 2009;24(6 Suppl.):39. 10. Parratte S, Pagnano MW, Trousdale RT, et al. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am 2010;92:2143. 11. Ritter MA, Davis KE, Meding JB, et al. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am 2011;93:1588.
12. Vessely MB, Whaley AL, Harmsen WS, et al. Long-term survivorship and failure modes of 1000 cemented condylar total knee arthroplasties. Clin Orthop 2006;452:28. 13. Perillo-Marcone A, Barrett DS, Taylor M. The importance of tibial alignment: finite element analysis of tibial malalignment. J Arthroplasty 2000;15:1020. 14. Taylor M, Barrett DS. Explicit finite element simulation of eccentric loading in total knee replacement. Clin Orthop Relat Res 2003;414:162. 15. Lombardi Jr AV, Nett MP, Scott WN, et al. Primary total knee arthroplasty. J Bone Joint Surg Am 2009;91(Suppl. 5):52. 16. Lonner JH, Siliski JM, Lotke PA. Simultaneous femoral osteotomy and total knee arthroplasty for treatment of osteoarthritis associated with severe extra-articular deformity. J Bone Joint Surg Am 2000;82:342. 17. Wang JW, Wang CJ. Total knee arthroplasty for arthritis of the knee with extraarticular deformity. J Bone Joint Surg Am 2002;84:1769. 18. Wang JW, Chen WS, Lin PC, et al. Total knee replacement with intra-articular resection of bone after malunion of a femoral fracture: can sagittal angulation be corrected? J Bone Joint Surg (Br) 2010;92:1392. 19. Thienpont E, Paternostre F, Pietsch M, et al. Total knee arthroplasty with patientspecific instruments improves function and restores limb alignment in patients with extra-articular deformity. Knee 2013;20:407. 20. Huang TW, Hsu WH, Peng KT, et al. Total knee arthroplasty with use of computerassisted navigation compared with conventional guiding systems in the same patient: radiographic results in Asian patients. J Bone Joint Surg Am 2011;93:1197. 21. Huang TW, Peng KT, Huang KC, et al. Differences in component and limb alignment between computer-assisted and conventional surgery total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:2954. 22. Lee CY, Lin SJ, Kuo LT, et al. The benefits of computer-assisted total knee arthroplasty on coronal alignment with marked femoral bowing in Asian patients. J Orthop Surg Res 2014;9(1):122. 23. Bellemans J, Colyn W, Vandenneucker H, et al. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 2012;470:45. 24. Matziolis G, Adam J, Perka C. Varus malalignment has no influence on clinical outcome in midterm follow-up after total knee replacement. Arch Orthop Trauma Surg 2010;130:1487. 25. Lizaur-Utrilla A, Sanz-Reig J, Trigueros-Rentero MA. Greater Satisfaction in Older Patients With a Mobile-Bearing Compared With Fixed-Bearing Total Knee Arthroplasty. J Arthroplasty 2012;27:207. 26. Hsu RWW, Himeno S, Coventry MB, et al. Normal axial alignment of the lower extremity and load-bearing distribution at the knee. Clin Orthop Relat Res 1990;255:215. 27. Kim YH, Kim JS, Yoon SH. Alignment and orientation of the components in total knee replacement with and without navigation support: a prospective, randomised study. J Bone Joint Surg (Br) 2007;89:471. 28. Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989;248:9. 29. Feller JA, Bartlett RJ, Lang DM. Patellar resurfacing versus retention in total knee arthroplasty. J Bone Joint Surg (Br) 1996;78:226. 30. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989;248:13. 31. Howell SM, Howell SJ, Kuznik KT, et al. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res 2013;471(3):1000.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
The Influence of Alignment on Midterm Outcome after Total Knee Arthroplasty in Patients With Marked Coronal Femoral Bowing Tsan-Wen Huang, MD a,b, Ching-Yu Lee, MD a, Shih-Jie Lin, MD a, Mel S. Lee, MD, PhD a,b, Robert Wen-Wei Hsu, MD a,b, Wun-Jer Shen, MD c a b c
Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chiayi, Taiwan Chang Gung University, Taoyuan, Taiwan Po-Cheng Orthopaedic Institute, Kaohsiung, Taiwan
a r t i c l e
i n f o
Article history: Received 20 December 2014 Accepted 18 March 2015 Keywords: total knee arthroplasty bowing of the femur mechanical axis polyethylene wear implant longevity
a b s t r a c t Whether the mechanical axis should be restored to neutral remains controversial when the patient has marked coronal femoral bowing. Eighty-four total knee arthroplasties were retrospectively reviewed. In the neutralaligned group A the immediate postoperative mechanical axis of 179 ± 1° held stable (P = 0.841). The postoperative mechanical axis decreased from 176 ± 1° to 173 ± 1° (P = 0.024) in the outlier group. Progressive varus in the outlier group at follow-up was probably due implant instability and ligament imbalance as well as excessive polyethylene wear. At a mean follow-up of 75.8 months, no statistically significant difference was detected between the two groups. Long-term follow up will be needed to determine if the maintenance in radiographic results translates to better clinical outcomes. © 2015 Elsevier Inc. All rights reserved.
Femoral bowing deformity in the coronal plane is not unusual in the Asian population, with a rather high prevalence reported in China, India, Japan, Korea and Taiwan [1–8]. The bowing deformity alters the relationship between the mechanical axis (MA) and anatomical axis (AA) of the femur, thereby affecting the placement of the femoral component and the postoperative MA [4–7]. Recently, there has been greater awareness of this deformity and its relationship to implant performance [4–8]. Finite element modeling and long-term survivorship studies suggest that malaligned TKAs compromise function and place the implants at a higher risk for failure [9–14]. Since the success of total knee arthroplasty (TKA) depends on the achievement of proper limb and prosthetic alignment and wellbalanced gaps [15], many surgical techniques and alternatives have been proposed to overcome these bowing related difficulties and achieve a neutral mechanical axis [4,5,8,16–22]. The concept of constitutional varus, as described in the award winning paper by Bellemans et al. [23], asserts that for patients with coronal femoral bowing, some degree of varus alignment is not only tolerable, but may actually be normal. Several authors have questioned whether it is necessary to
Source of Funding: There was no external funding for this study. 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.2015.03.027. Reprint requests: Robert Wen-Wei Hsu, MD or Mel S. Lee, MD, PhD, Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chiayi, No. 6, West Section, Chia-Pu Road, Pu-Tz City, Chia-Yi Hsien 613, Taiwan, ROC. http://dx.doi.org/10.1016/j.arth.2015.03.027 0883-5403/© 2015 Elsevier Inc. All rights reserved.
completely correct the MA and have challenged the importance of restoration of neutral limb alignment [10,23,24]. The purpose of this study was to investigate the effect of immediate postoperative alignment on eventual MA and survivorship by comparing neutral-aligned and outlier TKAs at midterm follow-up. We also sought to determine if postoperative non-neutral alignment of MA leads to suboptimal functional results in this group of patients when modern cemented prostheses are used.
Materials and Methods Since January 2002, all TKAs performed at our institution were done using the same treatment protocol. Demographic data, radiographic data and preoperative functional scores (including International Knee Society score and patellar score) of the patients were preoperatively collected and entered into a joint registry. Patients with osteoarthritis of the knee joint who underwent primary TKA by a single experienced orthopedic surgeon using the P.F.C. Sigma Knee System (DePuy Orthopaedics, Warsaw, Indiana, USA) were identified by computer database search. Patients with marked coronal femoral bowing (measured by Mullaji’s method [3] and according to Mullaji’s criteria [8], a coronal femoral bowing magnitude of N 5° was defined as marked coronal femoral bowing deformity) were flagged and reviewed. The study protocol was approved by the institutional review board, and all patients provided signed informed consent. The inclusion criteria required all patients to have marked coronal femoral bowing. Patients meeting the following criteria were excluded from analysis: (a) minimum follow-up of less than 60 months.
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T.-W. Huang et al. / The Journal of Arthroplasty 30 (2015) 1531–1536 Table 1 The Demographic Data and Radiographic Data in the Patient of the Neutral-Alignment Group and the Outlier Group.
Parameters Demographic Data Age at time of operation (years) Gender Male Female Body Height (cm) Body Weight (Kg) Body Mass Index (kg/m2) Follow up period (months) Radiographic data of Leg Axis Valgus correction angle of the distal femur (°) Coronal femoral bowing angle(°) Preoperative coronal MA (°) Postoperative coronal MA (°)
Group A Group B N = 38 N = 46 p-value 71 ± 4
70 ± 4
3 35 150 ± 6 68 ± 8 30.3 ± 3.7 74 ± 8
3 43 150 ± 6 69 ± 8 30.2 ± 3.9 77 ± 7
9±1 10 ± 3 166 ± 4 179 ± 1
10 ± 1 10 ± 2 167 ± 4 176 ± 1
0.463 0.567
0.841 0.936 0.931 0.119 0.815 0.971 0.812 b0.001a
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° MA = mechanical axis Values are shown as mean ± SD P values for between-group comparison were determined by Mann-Whitney U test a Statistically significant (p value b0.05).
Fig. 1. The femoral alignment angle (α) is defined as the medial angle formed by a line drawn between the distal ends of the femoral condyles and the femoral mechanical axis line. The tibial alignment angle (β) is defined as the medial angle formed by a line drawn along the base of the tibial component and the tibial mechanical axis line.
(b) extra-articular deformity of the femur or tibia related to previous trauma or surgery, and (c) incomplete medical records, radiographic analyses, and clinical functional assessments. The knees were divided into 2 groups. Those with a postoperative MA ≦ 3° of neutral were assigned to the neutral-alignment group (Group A). Those with a postoperative MA deviation of N3° from neutral were assigned to the outlier group (Group B). Clinical data and radiographic parameters were compared. To determine adequate sample size, an a priori power analysis using the two-sided hypothesis test with a power of 80% and a significance of 0.05 was done. It was calculated that 33 knees were required to detect a difference of 5 points in the Knee Society score (estimated SD of N 8). The cutoff value was selected because a difference of 5 points has been suggested as the minimal clinically important difference for the Knee Society score [25]. All patients had preoperative and postoperative anteroposterior (AP) and lateral radiographs of the knees, along with full-length
standing scanograms of the lower extremity, taken as described in detail in a previous publication by the senior author [26]. This radiograph was used to measure the valgus correction angle, the coronal femoral bowing angle, and the preoperative MA. Films were taken at 3 months after surgery and at each follow-up, and the postoperative MA, femoral and tibial alignments were measured. The magnitude of coronal femoral bowing angle was measured using the method of Mullaji et al. [3]. The femoral alignment angle is defined as the medial angle formed by a line drawn between the distal ends of the femoral condyles and the femoral mechanical axis line. The tibial alignment angle is defined as the medial angle formed by a line drawn along the base of the tibial component and the tibial mechanical axis line (Fig. 1) [27]. Four component alignment angles (the femoral valgus angle, tibial valgus angle, femoral flexion angle, and tibial flexion angle) were assessed [28]. A postoperative MA of N 3° was considered outlier. All measurements were made by two investigators using digital radiographs on a computer. The intraobserver and interobserver reliability of assessments of all radiographic measurements were evaluated using intraclass correlation coefficients and found to be greater than 0.84 (range, 0.84–0.92) and considered to be reliable. Demographic data and clinical information was retrieved from records by an independent investigator. Preoperative clinical status and postoperative outcomes were evaluated using knee range of motion (ROM), patellar score [29], and International Knee Society (IKS) scores [30]. Active maximum ROM of the knee was measured using a goniometer. All data were entered in an Excel spreadsheet (Microsoft, Redmond, Washington), rechecked for missing and illogical data and subsequently copied into SPSS version 13.0 (SPSS, Chicago, Illinois). Statistical analysis was performed by an independent statistician. The Mann-Whitney U test, Fisher’s exact test, pair-t test, and Student’s t test were used to determine statistically significant differences between the two groups. Significance was set at p b 0.05. Results Between January 2003 and July 2009, there were 124 patients (139 knees) with marked femoral bowing and underwent TKA. Among them, 9 patients died of causes unrelated to TKA surgery, 8 patients had minimum follow-up of less than 60 months, 24 patients had extraarticular deformity of the femur or tibia related to previous trauma, 11 patients had incomplete medical records, radiographic analyses, and clinical functional assessments. Therefore, a total of 72 patients
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Table 2 The Comparisons of Limb Alignment Between the Neutral-Alignment Group and the Outlier Group at Post-Operation and at Last Follow-up. Coronal MA
Group A Group B
Coronal Femoral Bowing Angle
Postoperation
Last Follow-Up
Postoperation
179 ± 1 176 ± 1
178 ± 1 173 ± 1a
10 ± 3 10 ± 2
Femoral Alignment
Last Follow-Up 10 ± 3 10 ± 3
Tibial Alignment
Postoperation
Last Follow-Up
Postoperation
90 ± 2 88 ± 3
89 ± 3 86 ± 4a
90 ± 2 89 ± 3
Last Follow-Up 90 ± 2 89 ± 3
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° Values are shown as mean ± standard deviation MA = mechanical axis p-values were determined by a pair-t test a Statistically significant (p value b0.05).
(84 knees) were studied. There were 38 knees in group A, 46 knees in group B. The mean follow-up time was 75.8 months (range, 60 to 126 months). Demographically, there were no statistical differences in age at time of operation, body height, body weight, body mass index, and length of follow-up period (Table 1). Comparing the alignment data between group A and B, it is noted that the valgus correction angle, magnitude of coronal femoral bowing deformity, and the preoperative MA are very similar (Table 1). In group A, the immediate postoperative MA of 179 ± 1° held stable, changing only to 178 ± 1° (P = 0.841). In Group B, the postoperative MA decreased from 176 ± 1° to 173 ± 1° (P = 0.024). There was no difference noted between 3 months after surgery and at the last follow-up for tibial alignment (p = 0.936 and p = 0.900, respectively) and coronal femoral bowing angle (p = 0.578 and p = 0.525, respectively). The femoral alignment was also not significantly different in group A between 3 months after surgery and at the last follow-up (p = 0.717), however, there was significant differences in the femoral alignment in group B (p = 0.036) (Table 2). The chief difference in the coronal plane lies with the femoral alignment, which results in the postoperative MA becoming significantly different between 3 months after surgery and at the last follow-up. Radiographic analysis of component alignment angles in the coronal and sagittal planes showed no difference between 3 months after surgery and at the last follow-up for femoral valgus angle (p = 0.538 and p = 0.534, respectively), tibial valgus angle (p = 0.987 and p = 0.794, respectively), femoral flexion angle (p = 0.286 and p = 0.073, respectively), and tibial flexion angle (p = 0.554 and p = 0.548, respectively) (Table 3). The mean preoperative patellar scores and IKS scores in both groups were similar. The patellar score in both groups were significantly improved at final follow-up compared with preoperative scores, but there was no difference between groups A and B (P = 0.876). Using the IKS rating system, there was marked improvement of the pain score, the clinical knee score, and the functional knee score after surgery compared with preoperative, but between the two groups, the difference did not achieve statistical significance in any of the subscores (Table 4). In this study, two (4.3%) patients in group B had polyethylene wear with instability of knee joint and received revision surgery (Fig. 2). One knee in each group sustained a periprosthetic femoral fracture. The patient in group A underwent open reduction and internal fixation with dynamic condylar screws (Synthes, Basel, Switzerland). The patient in group B was managed with open reduction and internal
fixation using Less Invasive Surgical Stabilization locking plates (Synthes, West Chester, Pennsylvania). Both healed uneventfully. Pulmonary emboli, deep vein thrombosis, and postoperative wound infection were not encountered in this series. Discussion The most important finding in this investigation was that initial neutral alignment appears predictive of future radiographic results. Those who were not neutrally aligned immediately postoperative gradually developed more varus over the next 5 years. However, we also found that there was no statistically significant difference in clinical function between the two groups, confirming the adage that radiological difference is not the same as clinical difference. This study is a retrospective practice audit. At the time of surgery, the surgeon was aiming for a neutral MA in all patients. Appropriate preoperative planning to adjust the cuts to accommodate the deformity was done. The angle of the cutting block was adjusted according to the valgus correction angle of the distal femur, which was measured using a full-length standing scanograms of the lower extremity. Incomplete insertion of intramedullary rods may contribute to subsequent erroneous distal femur resection and result in an undesired postoperative MA [6]. In this series of patients with marked coronal femoral bowing, the goal of neutral alignment proved elusive, with only 38 of 84 knees corrected to within 3° of neutral. Population surveys have shown that the prevalence of marked coronal femoral bowing deformity is higher in ethnic Asians [1–8], making TKA malalignment more likely. Finite element model studies suggest that eccentric loading and malalignment are detrimental to long term survival of the TKA [13,14]. There is little data available regarding the mid-term to long-term impact of marked coronal femoral bowing deformity. A school of thought views this condition mainly as a technical challenge. Several surgical techniques (such as staged or simultaneous femoral osteotomy combined with total knee arthroplasty [16]) and alternatives (including computer-assisted navigation [4,5,8,20–22] and patient-specific instruments [19]) have been developed to facilitate achievement of a neutral MA, and satisfactory results were reported after short-term to midterm follow-up. The intra-articular bone resection technique described by Wang et al. [17,18], using the intramedullary (IM) guidance system, modification of the starting hole in the lateral femoral condyle provided satisfactory results. In
Table 3 The Comparisons of Component Alignment Between the Neutral-Alignment Group and the Outlier Group at Post-Operation and at Last Follow-up. Femoral Valgus Angle Postoperation Group A Group B
99 ± 1 96 ± 1
Last Follow-Up
Tibial Valgus Angle Postoperation
99 ± 2 96 ± 2
Group A: Patient with a postoperative mechanical axis of≦3° Group B: Patient with a postoperative mechanical axis of N3° Values are shown as mean ± standard deviation p-values were determined by a pair-t test *Statistically significant (p value b0.05)
90 ± 1 90 ± 1
Last Follow-Up 90 ± 1 89 ± 1
Femoral Flexion Angle Postoperation 3±2 4±3
Last Follow-Up 4±2 6±3
Tibial Flexion Angle Postoperation 88 ± 3 88 ± 4
Last Follow-Up 88 ± 3 87 ± 3
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Table 4 Comparison of Preoperative and Postoperative Knee Scores in both Groups. Group A Group B N = 38 N = 46 p-value
Parameters Preoperative knee scores Patellar score International Knee Society pain score International Knee Society knee score International Knee Society function score Preoperative range of motion (°) Final postoperative knee scores Patellar score International Knee Society pain score International Knee Society knee score International Knee Society function score Postoperative range of motion (°)
17.3 21.4 60.4 40.9 103
± ± ± ± ±
2.2 10.1 14.6 12.6 14
16.4 22.2 58.3 38.1 101
± ± ± ± ±
2.1 7.1 7.8 8.5 13
0.868 0.732 0.462 0.288 0.472
26.2 47.0 93.4 92.7 121
± ± ± ± ±
1.7 2.5 2.9 6.0 10
25.7 45.4 91.4 90.4 120
± ± ± ± ±
2.1 2.5 3.2 5.3 10
0.876 0.655 0.894 0.342 0.850
Group A: Patient with a postoperative mechanical axis of ≦3°. Group B: Patient with a postoperative mechanical axis of N3°. MA = mechanical axis. Values are shown as mean ± SD. P values for between-group comparison were determined by Mann-Whitney U test. *Statistically significant (p value b0.05).
addition, an intra-operative radiograph can be taken with the IM rod or trial components in place and adjustments subsequently made. There is debate on whether it is necessary to correct the MA to neutral. The concept of an alignment safe zone has been proposed [10,23,24]. Ritter et al. [9,11] retrospectively reviewed 6070 knees in 3992 patients
and found that outliers in overall alignment have a higher rate of revision than well-aligned knees. Attaining neutrality in of tibiofemoral alignment, femoral and tibial component alignment is important in maximizing total knee implant survival. Conversely, Bellemans et al. analyzed 250 asymptomatic adults between 20 and 27 years of age [23]. 32% of adult men and 17% of adult women had constitutional varus knees with a natural MA N 3° varus. They concluded that restoration of MA to neutral in these cases may not be desirable and in fact may be unnatural for said persons. Limited release of soft tissue may result in a less painful and more stable TKA compared with scenarios in which extensive ligament releases are done in an attempt to obtain a completely aligned TKA [31]. Several recently published studies demonstrated no difference in survivorship and clinical performance for malaligned TKAs [10,24]. Parratte et al. [10] reported a fifteen-year survival study and demonstrated that a MA goal of 0° ± 3° is of little practical value in predicting the durability of modern, cemented total knee prostheses. Matziolis et al. [24] compared clinical outcomes between the outlier and well-aligned TKAs at a minimum follow-up of 5 years and concluded that significant varus malalignment did not contribute to inferior outcomes in terms of the WOMAC and the SF36 scores. In this study, the radiographic assessment showed that the MA becomes more varus from post-operation to final follow-up in the outlier group. Conversely, the postoperative MA held stable in the aligned group (Fig. 3). There were no significant differences in tibial alignment angle, coronal femoral bowing angle, and in the four component angles between 3 months after surgery and at the last follow-up.
Fig. 2. A through E. Radiographs of knee joint before and after surgery. A. A full-length standing scanogram of the lower extremity showing significant femoral bowing in the coronal plane. The post-operative mechanical axis is 175° after surgery. B. Weight-bearing radiographs of the left knee showed symmetric joint space (0°). C. The postoperative mechanical axis worsened from 175 to 167° at 5 years after primary TKA. D. Asymmetric joint space (1.5°) was observed on weight-bearing radiograph. E. After revision total knee arthroplasty, standing scanograms show residual 5° varus deformity.
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Fig. 3. A through E. Radiographs of knee joint before and after surgery. A. A full-length standing scanogram of the lower extremity showing full restoration of limb alignment after undergoing TKA. B. The postoperative mechanical axis is neutral at 6 years after primary TKA. C. Ten years later, the limb remains in excellent alignment.
However, asymmetric joint space was noted on weight-bearing radiographs of the knee joint (Fig. 2B and Fig. 2D). The most possible reasons of this circumstance were implant instability and ligament imbalance as well as excessive polyethylene wear. The asymmetric joint space contributes to varus change of femoral alignment, which results in the postoperative MA becoming significantly different between 3 months after surgery and at the last follow-up. With regard to functional outcomes, however, the patellar score was 26.2 ± 1.7 points in group A and 25.7 ± 2.1 points in group B (p = 0.876). Likewise in the IKS scores, neither in the sum nor in the individual scores was a
significant difference found between groups A and B. Our results were consistent with Matziolis et al. [24]. The proper reconstructed MA does not translate into significantly superior clinical outcomes at midterm follow-up. Several limitations in this study must be acknowledged. First, this is a retrospective investigation with all the inherent limitations of this type of study. That being said, all patients underwent TKA by a single experienced surgeon, the same prosthesis was used, and the same protocol, so there may be fewer biases. Second, plain radiographic evaluation is recognized as less sensitive and inferior to computed
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tomographic assessment for determining alignment [27]. Third, the number of patients studied was small. Although we calculated that 33 knees per group should be adequate, a larger number of patients in a prospective study is always better. In conclusion, patients with marked coronal femoral bowing deformity with neutral-aligned TKA immediate postoperative maintained better radiographic limb alignment at a mean follow-up of 75.8 months. Progressive varus of MA in group B at follow-up was probably due to implant instability and ligament imbalance as well as excessive polyethylene wear. Clinically, however, there was no statistically significant difference in function. Our current TKA protocol still seeks to achieve a neutral mechanical axis. A prospective randomized study comparing two groups of patients with neutral and slight constitutional varus alignment respectively and with a minimum follow up of ten years should be of greater value. References 1. Nagamine R, Miura H, Bravo CV, et al. Anatomic variations should be considered in total knee arthroplasty. J Orthop Sci 2000;5:232. 2. Yau WP, Chiu KY, Tang WM, et al. Coronal bowing of the femur and tibia in Chinese: its incidence and effects on total knee arthroplasty planning. J Orthop Surg (Hong Kong) 2007;15:32. 3. Mullaji AB, Marawar SV, Mittal V. A comparison of coronal plane axial femoral relationships in Asian patients with varus osteoarthritic knees and healthy knees. J Arthroplasty 2009;24:861. 4. Huang TW, Hsu WH, Peng KT, et al. Total knee replacement in patients with significant femoral bowing in the coronal plane: a comparison of conventional and computerassisted surgery in an Asian population. J Bone Joint Surg (Br) 2011;93:345. 5. Lee CY, Huang TW, Peng KT, Lee MS, Shen RW, Hsu WJ, et al. Variability of Distal Femoral Valgus Resection Angle in Patients with End-stage Osteoarthritis and Genu Varum Deformity: Radiographic Study in an Ethnic Asian Population. Biomed J 2015. http://dx.doi.org/10.4103/2319-4170.151030. 6. Mullaji AB, Shetty GM, Lingaraju AP, et al. Which factors increase risk of malalignment of the hip-knee-ankle axis in TKA? Clin Orthop Relat Res 2013;471:134. 7. Lasam MP, Lee KJ, Chang CB, et al. Femoral lateral bowing and varus condylar orientation are prevalent and affect axial alignment of TKA in Koreans. Clin Orthop Relat Res 2013;471:1472. 8. Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty 2009;24:1164.e1. 9. Fang DM, Ritter MA, Davis KE. Coronal alignment in total knee arthroplasty: just how important is it? J Arthroplasty 2009;24(6 Suppl.):39. 10. Parratte S, Pagnano MW, Trousdale RT, et al. Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am 2010;92:2143. 11. Ritter MA, Davis KE, Meding JB, et al. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am 2011;93:1588.
12. Vessely MB, Whaley AL, Harmsen WS, et al. Long-term survivorship and failure modes of 1000 cemented condylar total knee arthroplasties. Clin Orthop 2006;452:28. 13. Perillo-Marcone A, Barrett DS, Taylor M. The importance of tibial alignment: finite element analysis of tibial malalignment. J Arthroplasty 2000;15:1020. 14. Taylor M, Barrett DS. Explicit finite element simulation of eccentric loading in total knee replacement. Clin Orthop Relat Res 2003;414:162. 15. Lombardi Jr AV, Nett MP, Scott WN, et al. Primary total knee arthroplasty. J Bone Joint Surg Am 2009;91(Suppl. 5):52. 16. Lonner JH, Siliski JM, Lotke PA. Simultaneous femoral osteotomy and total knee arthroplasty for treatment of osteoarthritis associated with severe extra-articular deformity. J Bone Joint Surg Am 2000;82:342. 17. Wang JW, Wang CJ. Total knee arthroplasty for arthritis of the knee with extraarticular deformity. J Bone Joint Surg Am 2002;84:1769. 18. Wang JW, Chen WS, Lin PC, et al. Total knee replacement with intra-articular resection of bone after malunion of a femoral fracture: can sagittal angulation be corrected? J Bone Joint Surg (Br) 2010;92:1392. 19. Thienpont E, Paternostre F, Pietsch M, et al. Total knee arthroplasty with patientspecific instruments improves function and restores limb alignment in patients with extra-articular deformity. Knee 2013;20:407. 20. Huang TW, Hsu WH, Peng KT, et al. Total knee arthroplasty with use of computerassisted navigation compared with conventional guiding systems in the same patient: radiographic results in Asian patients. J Bone Joint Surg Am 2011;93:1197. 21. Huang TW, Peng KT, Huang KC, et al. Differences in component and limb alignment between computer-assisted and conventional surgery total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:2954. 22. Lee CY, Lin SJ, Kuo LT, et al. The benefits of computer-assisted total knee arthroplasty on coronal alignment with marked femoral bowing in Asian patients. J Orthop Surg Res 2014;9(1):122. 23. Bellemans J, Colyn W, Vandenneucker H, et al. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 2012;470:45. 24. Matziolis G, Adam J, Perka C. Varus malalignment has no influence on clinical outcome in midterm follow-up after total knee replacement. Arch Orthop Trauma Surg 2010;130:1487. 25. Lizaur-Utrilla A, Sanz-Reig J, Trigueros-Rentero MA. Greater Satisfaction in Older Patients With a Mobile-Bearing Compared With Fixed-Bearing Total Knee Arthroplasty. J Arthroplasty 2012;27:207. 26. Hsu RWW, Himeno S, Coventry MB, et al. Normal axial alignment of the lower extremity and load-bearing distribution at the knee. Clin Orthop Relat Res 1990;255:215. 27. Kim YH, Kim JS, Yoon SH. Alignment and orientation of the components in total knee replacement with and without navigation support: a prospective, randomised study. J Bone Joint Surg (Br) 2007;89:471. 28. Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989;248:9. 29. Feller JA, Bartlett RJ, Lang DM. Patellar resurfacing versus retention in total knee arthroplasty. J Bone Joint Surg (Br) 1996;78:226. 30. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989;248:13. 31. Howell SM, Howell SJ, Kuznik KT, et al. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res 2013;471(3):1000.
