February 27, 2017- Hideki Ueyama, MD ; Yoshio Matsui, MD , PhD; Yukihide Minoda, MD , PhD; Masanori Matsuu ra, MD ;
Hiroaki Nakamura, MD , PhD
Total knee arthroplasty (TKA) is one of the most successful surgeries for patients with degenerative joint disease, and many studies have shown good results from TKA.1-3 Implant alignment is an important factor for good clinical outcomes and survivorship.2 Bone resection in TKA has conventionally been performed with intra- and extra-medullary guides. However, severe femoral bowing can increase bone cut errors in TKA performed with conventional techniques.3 The anatomical features of the lower limb in Asian individuals have been investigated in previous reports.3-6 These studies suggest that Asian individuals, including Japanese individuals, have shorter and stronger femoral bowing than do other races.7
Computer-assisted navigation surgery (CAS) can help ensure more precise TKA implant alignment than the conventional method can.8-10 Even in cases of severe femoral deformities, navigation systems contribute to accurate bone resection.11 However, most CAS requires numerous large devices and is associated with high capital cost, increased operative time, and complex procedures.12 Portable navigation may be a solution for these problems due to its small size and easy handling (Figure 1).13 However, there have been no reports on the utility of this device for Asian patients with strong femoral bowing. The aim of the current study was to evaluate the accuracy of this new device for bone resection compared with that of the conventional method in Asian patients with strong femoral bowing.
Materials and Methods
This retrospective, comparative study included 142 knees from 102 Japanese patients who underwent TKA at the authors’ hospital between July 2013 and April 2015. Informed consent was obtained from all patients. The authors began performing TKA with a portable navigation system, including an accelerometer (KneeAlign2 system; OrthAlign Inc, Aliso Viejo, California), in September 2014. Between September 2014 and April 2015, sixty-seven patients (8 men, 59 women) underwent TKA using the KneeAlign2 device (navigation group). Between July 2013 and August 2014, seventy-five patients (14 men, 61 women) underwent TKA using the conventional method (conventional group) (Table 1). All surgeries were performed by 2 senior surgeons (Y.M., M.M.). An air tourniquet was inflated to 250 mm Hg during surgery. The medial parapatellar approach was used for all surgeries. The Vanguard posterior stabilized implant (Biomet Inc, Warsaw, Indiana) was used for all cases. Postoperative therapy was the same for all patients.
In the navigation group, the surgeon inserted a narrow screw into the center of the exposed distal femoral end on Whiteside’s line and attached the femoral jig with the screw.14 The reference sensor and cutting block were then attached to the jig. The KneeAlign2 system included an accelerometer as a reference sensor (Figure 1A). This small navigation device did not require drilling, as is required with the conventional method. The center of the hip was registered by maneuvering the knee with navigation, and the mechanical axis was detected (Figure 1B). After successful registration, the KneeAlign2 device was able to adjust the resection angle digitally in the coronal (varus/valgus) and sagittal (flexion/extension) planes (Figure 1C). The authors adjusted the cutting angle vertical to the mechanical axis as closely as possible to the ideal cutting angle.
The KneeAlign2 registered the tibial mechanical axis based on the insertion of the anterior cruciate ligament, anterior cortex of the distal tibia, and the lateral and medial malleoli. Once registration was successful, the surgeon adjusted the cutting angle for the tibia. The perpendicular cutting angle was adjusted to the mechanical axis on the coronal plane (varus/valgus), and a 3° posterior slope on the sagittal plane was set as the ideal resection angle.15,16
In the conventional group, the surgeon planned the angle for distal femur and proximal tibia resection using plain radiography, with the ideal resection angle of the femur and tibia perpendicular to the mechanical axis. The surgeon drilled a hole at the center of the distal femur to insert an intramedullary rod during the operation. Then, a distal femur cutting guide was set depending on the preoperative planning of the coronal plane (varus/valgus). The sagittal plane resection angle (flexion/extension) was estimated to be perpendicular to the anatomical femoral axis. An extramedullary cutting guide was used for the proximal tibia. The tibia was cut perpendicular to the tibial mechanical axis in the coronal plane (varus/valgus) and with a 3° posterior slope in the sagittal plane (flexion/extension). The rotational axis of the tibial component was determined to be a line connecting the medial one-third of the tibial tuberosity and the center of the posterior cruciate ligament insertion.17
Clinical information, including laboratory data, was obtained from institutional patient records. Age, sex, diagnosis, and body mass index (BMI) were obtained. Intraoperative blood loss was minimal because of tourniquet use; therefore, the authors calculated blood loss during the perioperative period based on the patient’s hematocrit levels and estimated blood volume using the Gross formula.18 Blood loss was defined as estimated blood loss. The angle of knee flexion and the Knee Society knee and functional scores were estimated as functional outcomes.19 These data were measured preoperatively at the outpatient clinic. In addition, postoperative functional outcomes were also measured at the final outpatient visit.
Radiographic evaluation was performed as follows. Standing lower-extremity radiographs were taken using long films preoperatively and at 2 weeks after TKA. The femoral mechanical axis was defined by a line drawn from the center of the femoral head to the most distal point of the intercondylar notch of the femur, and the tibial mechanical axis was defined by a line drawn from the center of the tibial plateau to the center of the tibial plafond. The angle between the femoral and tibial mechanical axes was measured as the mechanical axis (MA) pre- and postoperatively (Figure 2A).20,21 In addition, the authors estimated femoral and tibial bowing on coronal plain radiographs using Yau’s method.3 Bowing of greater than 3° was defined as marked femoral or tibial bowing (Figure 2B).3 The positioning of each component was confirmed with postoperative frontal and lateral radiographs.12,22 The authors measured the angle between the mechanical axis and the tangent of the component on the long radiographs to use as the coronal femoral and tibial component alignment (Figures 3A-B).5,23 On lateral radiographs, the authors measured the angle between the femoral anatomical axis and the femoral distal cut surface as the sagittal femoral component alignment, and they measured the angle between the tibial shaft axis and the tibial proximal cut surface as the sagittal tibial component alignment (Figure 3C). Ideal bone resection was defined as 90º from the mechanical axis. However, for the tibia, a 3° posterior slope in the sagittal plane was defined as ideal. The acceptable position of each component was within 3° of the ideal position, as in previous reports.15,24,25 Outliers were defined as angles of less than 87° (varus) or greater than 93° (valgus) in the femoral and tibial coronal planes, less than -3° (extension) or greater than 3° (flexion) in the femoral sagittal plane, and less than 84° (backward tilt) or greater than 90° (forward tilt) in the tibial sagittal plane.
Continuous variables were analyzed with the Student’s t test, and discrete variables were analyzed with Fisher’s exact test. To determine an adequate sample size, a power analysis using the hypothesis test with a power of 80% and a significance of .05 was performed. It showed that 36 knees were required per group to detect a difference of 1 point and 1.5 standard deviations. These analyses were performed with R software (Vienna, Austria).
A total of 142 patients were included in the current study; 67 underwent TKA with the KneeAlign2 (navigation group) and 75 underwent TKA with the conventional method (conventional group). Patients’ mean±SD age at operation was 77.5±5.5 years (range, 53-88 years), with a mean BMI of 25.1±4.7 kg/m2 (range, 16.4-35.5 kg/m2). The mean±SD follow-up periods for the navigation and conventional groups were 10.8±1.8 months (range, 6.1-16.9 months) and 21.1±4.8 months (range, 5.9-30.5 months), respectively (P<.01). The follow-up periods were significantly different because the authors started using portable navigation only in September 2014. The preoperative mean±SD angle for knee flexion and the Knee Society knee and functional scores were 115.6°±14° (range, 80°-135°), 43.3±9.6 (range, 16-72), and 43.8±8.9 (range, 30-65), respectively. Preoperative MAs were 169.1°±4.5° (range, 157°-179°). The only significant between-groups difference was the length of the follow-up period (Table 1).
The mean±SD operation time overall was 114±12 minutes (range, 85-180 minutes). Estimated blood loss after TKA was calculated to be 622±268 mL (range, 224-1670 mL). Postoperative Knee Society knee and functional scores were 75.7±8.3 (range, 57-95) and 74.7±6.0 (range, 60-85), respectively. There were no significant differences between the navigation and conventional groups in clinical outcomes (Table 2).
Regarding radiographic outcomes, the postoperative mean±SD MA was 178.9°±1.3° (range, 176°-182°). Regarding the coronal positioning of components, the mean±SD femoral coronal angle was 89.4°±1.6° (range, 84°-94°) and the mean±SD tibial coronal angle was 89.9°±1.4° (range, 87°-94°). Regarding the sagittal positioning of components, the mean±SD femoral sagittal angle was 0.42°±2.6° (range, -6° to +7°) and the mean±SD tibial sagittal angle was 87.1°±2.0° (range, 81°-92°). The rate of outliers for the femoral coronal component was 1.5% (1 knee) in the navigation group, significantly lower than that of 13.3% (10 knees) in the conventional group (P=.01). Other outliers were not significantly different between the 2 groups (Table 2).
Results were then analyzed by subgroups based on the presence or absence of femoral bowing. The femoral coronal angle and the outlier of femoral coronal component were significantly different between the navigation and conventional groups in the marked femoral bowing subgroup (P<.05). The femoral coronal alignments of the prosthesis were not deviated in the portable navigation groups (Figure 4).
There was no significant difference in the subgroup without marked femoral bowing (Table 3).
The current study showed more accurate implant alignment for TKA using an accelerometer-based portable navigation system than for TKA using the conventional method in Asian individuals with marked femoral bowing. This new device has been verified as useful for accurate prosthesis alignment in TKA.13,26,27 However, there has been no evaluation of its utility in cases of anatomical variations, such as marked femoral bowing. This is the first report to show the utility of a portable navigation in Asian patients with marked femoral bowing.
Total knee arthroplasty is one of the most successful procedures for treating degenerative knee joint disease, and many reports have already indicated its good long-term results.2,28 However, malpositioning of the prosthesis is one of the most serious complications, and it necessitates revision. Ritter et al28 reported that obtaining neutrality on the mechanical axis in TKA is important for component survival. Some have reported that setting the component within ±3° from the mechanical axis predicts good results, including function and quality of life.2,15 Femoral bowing influences the accuracy of bone resection using an intramedullary nail.6 One anatomical feature that is stronger in Asian individuals than in Caucasian individuals is a strong femoral bow.3,4,7 Therefore, it is important to present the results of TKA for Asian patients using the portable navigation system.
Computer-assisted navigation surgery helps in the planning of accurate bone resection for ideal prosthesis setting.29 Some randomized controlled trials showed that TKA with CAS led to more accurate postoperative component placement than did conventional methods.29,30 It had been reported that CAS is useful for avoiding outliers in TKA for patients with strongly deformed legs.31 However, it was unclear whether a portable navigation system with an accelerometer was beneficial as well.
In the current study, the rate of outliers for the femoral coronal component in navigation group was 1.5%. This is similar to results of TKA with the same portable navigation system.13,26,27 It is impossible to compare the results with previous reports in patients with marked femoral bowing directly, but the results of this study showed a 0% rate of outliers for this group. Therefore, the results suggest that portable navigation systems are effective even in marked femoral deformity.
The TKA with CAS showed accurate prosthesis settings in previous studies. The rates of outliers for the femoral coronal component were 3.1%32 to 0.83%.33 The previous reports showed good postoperative alignment after TKA using CAS for patients with severe bowing femur.31 Another report showed that there was no outlier of femoral coronal component alignment even in the severe femoral bowed cases.5 These results suggest that the common CAS and portable navigation should help surgeons to perform TKA precisely in cases with strong curved limbs as well.
Previous reports presented outliers associated with prosthesis alignments in conventional TKA. Sparman et al33 reported that the rate of outliers for the femoral coronal component was 28.3% and that of the tibial coronal component was 10%. Importantly, many reports indicate that the outlier of implant alignment of navigated TKA is significantly less than non-navigated TKA in severe deformity cases.11,20 In marked femoral bowing cases, the risk of malalignment increases.24 In previous reports, approximately 30% of outliers were for the femoral component in bowed femurs that underwent the conventional bone resection technique.3 Even without marked femoral bowing, the rate of outliers for conventional TKA was 12.4% from the mechanical axis in a meta-analysis.34 The utilities of CAS and an accelerometer based portable navigation system were certain.
Computer-assisted navigation surgery has some disadvantages, including the additional time needed to set up the devices, which prolongs the operation time.12,13 Portable navigation may be the solution for these problems due to its small size and easy handling. This device includes an accelerometer, and it does not require the use of other devices, such as a large monitor. The portable navigation system certainly is more convenient and easier to use than are most standard CASs.26 The current authors found that the total operation time was not significantly different between the 2 groups. In addition, there are no reports of pin tract fracture related to accelerometer-based portable navigation systems, as with the current study. Some previous reports have reported CAS pin tract fracture: 1.64% in the femur35 and 1.36% in the tibia.36
Total perioperative estimated blood loss associated with intramedullary rod use has been discussed in previous reports.37 In general, the amount of postoperative blood loss is larger with conventional TKA than with CAS TKA.37,38 Postoperative hemorrhage was larger for conventional TKA than for CAS,37 but the postoperative decrease in hemoglobin was smaller.38 However, this study did not show significant differences between the navigation group and the conventional group. The authors always injected 1 g of tranexamic acid into the joint intraoperatively to reduce blood loss; therefore, drilling for the intramedullary guide did not cause significant blood loss perioperatively.39
The limitation of the current study is that TKA was performed only by expert surgeons. The rates of outliers of tibial components in conventional TKA were lower than those in previous reports,32,33 which may have been a result of the surgeons’ experience.40 Therefore, the actual differences between accelerometer-based portable navigation systems and conventional methods may be larger.
This study showed that accelerometer-based portable navigations improved femoral coronal alignment, even for Asian patients, and did not increase the operation time and blood loss. Surgeons should consider using accelerometer-based portable navigation system, especially for patients with a marked femoral bow.
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- Attar FG, Khaw FM, Kirk LM, Gregg PJ. Survivorship analysis at 15 years of cemented press-fit condylar total knee arthroplasty. J Arthroplasty. 2008; 23(3):344-349.
- Yau WP, Chiu KY, Tang WM, Ng TP. 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(1):32-36.
- Maratt J, Schilling PL, Holcombe S, et al. Variation in the femoral bow: a novel high-throughput analysis of 3922 femurs on cross-sectional imaging. J Orthop Trauma. 2014; 28(1):6-9.
- Lasam MP, Lee KJ, Chang CB, Kang YG, Kim TK. Femoral lateral bowing and varus condylar orientation are prevalent and affect axial alignment of TKA in Koreans. Clin Orthop Relat Res. 2013; 471(5):1472-1483.
- Kim JM, Hong SH, Kim JM, et al. Femoral shaft bowing in the coronal plane has more significant effect on the coronal alignment of TKA than proximal or distal variations of femoral shape. Knee Surg Sports Traumatol Arthrosc. 2015; 23(7):1936-1942.
- Nagamine R, Miura H, Bravo CV, et al. Anatomic variations should be considered in total knee arthroplasty. J Orthop Sci. 2000; 5(3):232-237.
- Decking R, Markmann Y, Fuchs J, Puhl W, Scharf HP. Leg axis after computer-navigated total knee arthroplasty: a prospective randomized trial comparing computer-navigated and manual implantation. J Arthroplasty. 2005; 20(3):282-288.
- Weng YJ, Hsu RW, Hsu WH. Comparison of computer-assisted navigation and conventional instrumentation for bilateral total knee arthroplasty. J Arthroplasty. 2009; 24(5):668-673.
- Zhang GQ, Chen JY, Chai W, Liu M, Wang Y. Comparison between computer-assisted-navigation and conventional total knee arthroplasties in patients undergoing simultaneous bilateral procedures: a randomized clinical trial. J Bone Joint Surg Am. 2011; 93(13):1190-1196.
- 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; 9:122.
- William M. Arthroplasty of the knee. In: Canale ST, Beaty JH, eds. Campbell’s Operative Orthopaedics. 11th ed. Philadelphia, PA: Mosby; 2008:376-444.
- Nam D, Weeks KD, Reinhardt KR, Nawabi DH, Cross MB, Mayman DJ. Accelerometer-based, portable navigation vs imageless, large-console computer-assisted navigation in total knee arthroplasty: a comparison of radiographic results. J Arthroplasty. 2013; 28(2):255-261.
- Whiteside LA, Arima J. The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty. Clin Orthop Relat Res. 1995; (321):168-172.
- Ensini A, Catani F, Leardini A, Romagnoli M, Giannini S. Alignments and clinical results in conventional and navigated total knee arthroplasty. Clin Orthop Relat Res. 2007; (457):156-162.
- Gromov K, Korchi M, Thomsen MG, Husted H, Troelsen A. What is the optimal alignment of the tibial and femoral components in knee arthroplasty? Acta Orthop. 2014; 85(5):480-487.
- Akagi M, Oh M, Nonaka T, Tsujimoto H, Asano T, Hamanishi C. An anteroposterior axis of the tibia for total knee arthroplasty. Clin Orthop Relat Res. 2004; (420):213-219.
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- Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res. 1989; (248):13-14.
- Huang TW, Hsu WH, Peng KT, Hsu RW, Weng YJ, Shen WJ. Total knee arthroplasty with use of computer-assisted navigation compared with conventional guiding systems in the same patient: radiographic results in Asian patients. J Bone Joint Surg Am. 2011; 93(13):1197-1202.
- Tipton SC, Sutherland J, Schwarzkopf R. Using the anatomical axis as an alternative to the mechanical axis to assess knee alignment. Orthopedics. 2015; 38(12):e1115-e1120.
- Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res. 1989; (248):9-12.
- Park A, Stambough JB, Nunley RM, Barrack RL, Nam D. The inadequacy of short knee radiographs in evaluating coronal alignment after total knee arthroplasty. J Arthroplasty. 2016; 31(4):878-882.
- Mullaji AB, Shetty GM, Lingaraju AP, Bhayde S. Which factors increase risk of malalignment of the hip-knee-ankle axis in TKA? Clin Orthop Relat Res. 2013; 471(1):134-141.
- Choong PF, Dowsey MM, Stoney JD. Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty. 2009; 24(4):560-569.
- Nam D, Jerabek SA, Haughom B, Cross MB, Reinhardt KR, Mayman DJ. Radiographic analysis of a hand-held surgical navigation system for tibial resection in total knee arthroplasty. J Arthroplasty. 2011; 26(8):1527-1533.
- Nam D, Nawabi DH, Cross MB, Heyse TJ, Mayman DJ. Accelerometer-based computer navigation for performing the distal femoral resection in total knee arthroplasty. J Arthroplasty. 2012; 27(9):1717-1722.
- Ritter MA, Davis KE, Meding JB, Pierson JL, Berend ME, Malinzak RA. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am. 2011; 93(17):1588-1596.
- Cheng T, Zhao S, Peng X, Zhang X. Does computer-assisted surgery improve postoperative leg alignment and implant positioning following total knee arthroplasty? A meta-analysis of randomized controlled trials? Knee Surg Sports Traumatol Arthrosc. 2012; 20(7):1307-1322.
- Hetaimish BM, Khan MM, Simunovic N, Al-Harbi HH, Bhandari M, Zalzal PK. Meta-analysis of navigation vs conventional total knee arthroplasty. J Arthroplasty. 2012; 27(6):1177-1182.
- Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty. 2009; 24(8):1164-1169.
- Brin YS, Nikolaou VS, Joseph L, Zukor DJ, Antoniou J. Imageless computer assisted versus conventional total knee replacement: a Bayesian meta-analysis of 23 comparative studies. Int Orthop. 2011; 35(3):331-339.
- Sparmann M, Wolke B, Czupalla H, Banzer D, Zink A. Positioning of total knee arthroplasty with and without navigation support: a prospective, randomised study. J Bone Joint Surg Br. 2003; 85(6):830-835.
- Hetaimish BM, Khan MM, Simunovic N, Al-Harbi HH, Bhandari M, Zalzal PK. Meta-analysis of navigation vs conventional total knee arthroplasty. J Arthroplasty. 2012; 27(6):1177-1182.
- Sikorski JM, Blythe MC. Learning the vagaries of computer-assisted total knee replacement. J Bone Joint Surg Br. 2005; 87(7):903-910.
- Hoke D, Jafari SM, Orozco F, Ong A. Tibial shaft stress fractures resulting from placement of navigation tracker pins. J Arthroplasty. 2011; 26(3):504.
- Hinarejos P, Corrales M, Matamalas A, Bisbe E, Cáceres E. Computer-assisted surgery can reduce blood loss after total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2009; 17(4):356-360.
- Dutton AQ, Yeo SJ, Yang KY, Lo NN, Chia KU, Chong HC. Computer-assisted minimally invasive total knee arthroplasty compared with standard total knee arthroplasty: a prospective, randomized study. J Bone Joint Surg Am. 2008; 90(1):2-9.
- Yang ZG, Chen WP, Wu LD. Effectiveness and safety of tranexamic acid in reducing blood loss in total knee arthroplasty: a meta-analysis. J Bone Joint Surg Am. 2012; 94(13):1153-1159.
- Mahaluxmivala J, Bankes MJ, Nicolai P, Aldam CH, Allen PW. The effect of surgeon experience on component positioning in 673 Press Fit Condylar posterior cruciate-sacrificing total knee arthroplasties. J Arthroplasty. 2001; 16(5):635-640.
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