Total knee arthroplasty using a hybrid navigation technique
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The use of computer navigation is becoming a well-recognized technical alternative to conventional total knee arthroplasty (TKA). However, computer navigation has a substantial learning curve and the use of commercially available navigation systems increases surgical time. In addition, the potential risks associated with the navigation TKA, such as, registration errors, notching of the anterior femoral cortex, oversizing of the femoral component, and overresection must be taken into consideration. On the other hand, conventional techniques are familiar and intuitive to most practicing surgeons, and thus, are easier to perform and are less prone to anterior notching and femoral component oversizing. However, conventional techniques have greater risks of inaccurate and inconsistent component alignment than computer navigation. This paper describes a novel technique that combines computer navigation and conventional TKA.
KeywordsTotal Knee Arthroplasty Femoral Component Computer Navigation Component Alignment Conventional Total Knee Arthroplasty
The use of computer navigation for primary total knee arthroplasty (TKA) provides the benefits of accurate bone resection, low outlier frequencies, and the restoration of overall mechanical alignment. However, its use also involves the disadvantage of change in technique and workflow that have been associated with steep learning curve and increased surgical time. Furthermore, several investigators have described the potential risks associated with the use of navigation, which include registration errors, notching of the anterior femoral cortex, oversizing of the femoral component, and overresection [1, 2, 3, 4]. These risks mean that surgical plans provided by navigation software might require modification intra-operatively, based on the surgeon's experience and knowledge. On the other hand, conventional TKA has the advantages of familiarity and simplicity. Furthermore, decisions regarding bony resection level are based on measurements taken using a traditional jig and rod, and thus, anterior notching and femoral component oversizing can be avoided. Unfortunately, the conventional technique is more inaccurate and inconsistent in terms of its component alignment ability than computer navigation [5, 6]. In this paper, we describe a hybrid technique that combines the benefits of computer navigation and conventional TKA. This hybrid navigation technique was developed to allow TKA to be performed in-line with accepted conventional TKA practice, but with the accuracy of computer navigation.
Indications & Contraindications
The devised hybrid navigation technique was indicated for all 3500 knees that underwent TKA at our institute between Jan 2007 and April 2010. In no case was the hybrid navigation technique deemed to be contraindicated, and the procedure was not aborted intraoperatively in any case. With regard to contraindication, in theory, hardware in the distal femoral metaphysis and diaphysis that might interfere with intramedullary rod placement would pose the only potential contraindication to the use of the technique.
No special preoperative planning was performed before hybrid navigation. In our practice, we routinely obtain standing anteroposterior (AP), posteroanterior (PA) and lateral radiographs for all patients scheduled for TKA. These images provide an overall picture of deformities present and of the corrections necessary. In addition, they provide information on the presence of hardware, extra-articular deformity, and bone loss. The goal of surgery is to achieve a final mechanical axis of 0 degrees, but we accept up to 3 degrees of overall varus or valgus malalignment.
More than 3500 knees underwent primary total knee replacement from Jan 2007 to April 2010. The first 50 knees treated (mean age 65.2 years) and the last 50 knees treated (mean age 64.3 years) were compared with respect to surgical time and component alignment to assess the effects of the learning process. Coronal and sagittal alignments of femoral components for the first 50 knees were mean valgus 0.5°and mean flexion 3.5° and these values were similar for the last 50 knees (mean valgus 0.2° and mean flexion 3.6°). For tibial components of the first 50 knees, mean coronal and sagittal alignments were valgus 0. 3° and flexion 2.5°, and these were also similar for the last 50 knees (mean valgus 0.3° and mean flexion 2.7°). Overall mechanical alignments for the first and last knee groups were mean varus 1.5° and 1°, respectively, and mean operation times (skin incision to skin closure) were 61 and 50 minutes, respectively. There were three cases of tibial fracture attributed to a tracker pin, but these fractures were considered to be related to general concerns of navigation TKR, and not to a system-specific problem. Ten cases developed a superficial infection at a tracker pin site, but no case of fat embolism occurred.
Computer navigation is becoming a well-recognized technical alternative to conventional total knee replacement, but its merits and demerits continue to be widely debated [7, 8, 9, 10, 11]. Computer navigation has the disadvantages of a protracted learning curve and increased surgical time  In addition, several investigators have suggested that navigation might increase the risks of notching of the anterior femoral cortex and oversizing of the femoral component. In particular, Minoda et al.  found that 40-85% male cases and 65-100% of elderly female cases treated with navigation showed anterior notching. Matsumoto et al.  suggested that surgeons should be aware of the potential for oversizing when determining the size of the femoral component, particularly when the femoral bone is anteriorly bowed. Kim et al.  also reported a higher incidence of anterior femoral notching in navigation treated knees than in conventionally treated knees. However, these problems might be due to discrepancies between the anterior bow of the femur and its straight mechanical. More specifically, computer navigation calculates the sagittal axis of the femur by drawing a straight line between the center of the femoral head and the center of the knee, and thus, femoral bow is not taken into consideration, and therefore, cannot be determined from anatomic registration points. Furthermore, decision making regarding resection level using navigation might be difficult, especially in knees with a deformed articular surface, such as, severe varus or valgus knees, as compared with decision making using the conventional technique. Kim et al.  reported overresection of proximal tibial bone as a complication of navigation, and thus, the surgical planning provided by the navigation software might require modification based on surgeon's experience and knowledge of the surgical procedures. The hybrid navigation system described here was devised to combine the ease of use of classic conventional resection instruments and the accuracy of the navigation technique. Furthermore, the use of an intramedullary rod in conjunction with navigation allows femoral bow to be taken into consideration. In theory and practice, the rod is deflected by femoral bow, which allows flexion of the femoral component to accommodate femoral bow, which facilitates appropriate flexion of the femoral component and prevents inadvertent notching of the anterior femoral cortex. This use of an intramedullary rod in conjunction with navigation represents an advantage of the hybrid technique over the pure navigation technique wherein femoral bow is not taken in account when determining femoral component position.
Although it has been reported that the use of a femoral intramedullary IM rod might increase the possibility of a fat embolism [12, 13], it appears that the use of a smaller diameter, shorter IM rod may reduce this risk. On the other hand, Kim et al.  found that the use of an IM rod did not increase the risk of fat embolism or increase perioperative blood loss.
The present study shows that the hybrid navigation technique increases the accuracy of component alignment versus the conventional technique and requires less time than navigation technique. Furthermore, our findings indicate that hybrid technique does not require a protracted learning process. In addition, no case of fat embolism was encountered. Accordingly, we believe that the described hybrid navigation technique enables TKA to be conducted safely and precisely without femoral notching or femoral component oversizing.
Considering several manufactures' navigation systems with their own successful benefits, We do not present the devised hybrid navigation technique as a definitive method for navigation TKR. Nevertheless, we believe that this technique should be considered as an alternative means of conducting navigation TKR.
All authors certify that the human research protocol used during this investigation was approved by our institution and that all investigations conducted during this study conformed with ethical research principles.
- 3.Minoda Y, Kobayashi A, Iwaki H, Mitsuhiko I, Kadoya Y, Ohashi H, Takaoka K, Nakamura H: The risk of notching the anterior femoral cortex with the use of navigation systems in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2010, 18 (6): 718-722. 10.1007/s00167-009-0927-5.CrossRefPubMedGoogle Scholar
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