Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-012-2088-1
KNEE
Computer-assisted navigation for the intraoperative assessment of lower limb alignment in high tibial osteotomy can avoid outliers compared with the conventional technique Kilian Reising • Peter C. Strohm • Oliver Hauschild Hagen Schmal • Mohmed Khattab • Norbert P. Su¨dkamp • Philipp Niemeyer
•
Received: 31 October 2011 / Accepted: 1 June 2012 Ó Springer-Verlag 2012
Abstract Purpose Longterm outcomes after valgization high tibial osteotomy (HTO) to treat varus osteoarthritis seem to depend mainly on correction precision. Intraoperative assessment of leg alignment based on radiological visualization of the mechanical axis is difficult and its precision is limited. A promising approach to improving precision is to make use of navigation systems. The case–control study reported here involved the evaluation of patients whose varus osteoarthritis had been treated by open-wedge high tibial ostoetomy, and an analysis of the effect of computerguided navigation on postoperative leg alignment. Methods Forty patients with medial varus osteoarthritis managed by open-wedge high tibial osteotomy using a surgical navigation system were included in the present study (Group 1). They were compared with a retrospective control group (Group 2) of 40 patients with respect to postoperative leg alignment, correlation of planned and definitive correction, and postoperative deviation from the Fujisawa point. Results The mean values for planned and definitive correction showed no significant differences for identical demographic data. As a percentage of the width of the tibial plateau the postoperative weight-bearing radiographs showed a mechanical line that intersected with the knee
K. Reising (&) P. C. Strohm O. Hauschild H. Schmal N. P. Su¨dkamp P. Niemeyer Department of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098 Freiburg, Germany e-mail:
[email protected] M. Khattab Orthopaedic Department, Faculty of Medicine, Ain Shams University, Cairo, Egypt
base line at the desired value of 62 % (Fujisawa point) in 58.8 % (SD ± 6.1) in Group 1 and in 58.6 % (SD ± 8.1) in Group 2. Despite similar mean values a significantly higher number of corrections were outside the reference area (n = 7) in the non-navigated group, whereby all corrections were within the desired range in the navigated group. There were no significant differences in operation time. Conclusions This study showed that the use of a navigation system can not increase the precision of the openwedge HTO procedure in patients with varus osteoarthritis but it can eliminate the outliers of a well defined range. Level of evidence Case-control study, Retrospective comparative study, Level III. Keywords High tibial osteotomy Kinematic navigation system Computer aided orthopedic surgery
Introduction Valgization high tibial osteotomy (HTO) is a widely accepted procedure for the treatment of varus gonarthritis [29, 38, 39]. The efficacy of this procedure has been proven in various studies [2, 15]. The reduction of complication rates through the introduction of fixed-angle implants and the advancement of surgical techniques [28, 29] has been proven and since this procedure allows sliding adjustment of the correction so that the desired position can be precisely achieved [14, 17] it is currently enjoying a renaissance. Optimal correction seems of high clinical relevance in particular, a procedure that avoids the lateral approach with the need for fibula osteotomy and the risk of peroneal nerve lesion offers clear advantages and a lower complication rate [33, 38, 39].
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In the meantime, several studies have been published that substantiate the short and midterm effects of the procedure, whereby the longterm outcomes appear to depend mainly on correction precision [4, 11, 20, 39]. However, optimal correction cannot always be achieved by precise planning alone, but rather there is a need for reliable intraoperative assessment of correction in the operating room. Various techniques are available intraoperatively to facilitate visualization of the mechanical axis of the leg. Conventional methods such as the cable method, grid lines, or reference to the joint surfaces can be helpful but their precision is limited and there is a high risk of technical error [16, 42]. One promising approach is to improve precision by application of navigation system [8, 18, 40]. The benefit of this specialized equipment has already been demonstrated in experimental and initial clinical studies with a small number of patients [16]. Various navigation procedures have been described. Other passive navigation systems such as CT and C-arm navigation have the particular disadvantage of radiation exposure. The focus of the present study was the evaluation of the effect of a kinematic navigation system on the precision of the definitive axial correction. To this end correction precision in 40 patients being treated for distinctly medial varus osteoarthritis after the introduction of a navigation system was compared with precision in a retrospective control group in this matched-pair study. The hypothesis of the present study was that use of navigation in high tibial osteotomy improves the accuracy of correction and helps to reduces the number of outliers.
Materials and methods All patients osteoarthritis degeneration open-wedge
diagnosed with unicompartmental varus or varus deformity with isolated cartilage in the medial compartment who underwent high tibial osteotomy (TomoFix implant,
Fig. 1 Intraoperative radiological assessment of the leg axis
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Solothurn, Synthes) with the assistance of a surgical navigation system in the period 2005–2009 at our hospital were included in the present study. These patients were assigned to Group 1 (navigated). Exclusion criteria for the retrospective radiological study were preoperative weightbearing radiographs from another hospital since standardization of radiographic technique could not be assumed, and atypical types of varus deformity not being caused by a tibial varus malalignment which consecutively needed correction of malalignment at different anatomical sites. After consideration of the exclusion criteria 40 patients were recruited to Group 1 of the present study. In accordance with matched-pair design a control group was formed from a historic patient sample of cases treated in the period 2005–2009 without intraoperative navigation and the same exclusion criteria were applied (85 patients). Matching the subjects of the two groups was based on ‘‘sex’’, ‘‘age’’, and ‘‘preoperative deformity’’. The patients identified in this way formed Group 2. In compliance with study design the groups were homogeneous with regard to sex and age distribution and likewise in terms of preoperative deformity based on the anatomical axis and intersection of the mechanical axis at the tibial plateau. Detailed characteristics of the study population are given in Fig. 1. All operations were performed under general anaesthesia. Intravenous antibiotic (single shot, cefuroxim 1.5 mg i.v.) and standard thromboembolic prophylaxis were administered. Arthroscopy was performed prior to correction osteotomy to verify the presence of an intact lateral compartment and to treat concomitant intraarticular lesions. In most cases prior cell harvesting ensured that autologous chondrocyte transplantation (ACT) could be done at the same surgery and followed by a second arthroscopy. Regardless of the surgical technique applied, all osteotomies were intentionally aimed at slight overcorrection of varus malalignment as described by Fujisawa [13] and
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others [1]. In line with these findings, the mechanical axis was shifted to cross the lateral aspect of the tibial plateau at a point located at approximately 62 % on the cross sectional diameter. The osteotomy was stabilized with the Synthes TomoFixTM instrument and implant system (TomoFix TM, Synthes, Solothurn, Switzerland) in all patients. ‘‘Overcorrection’’ was defined as a lateralization of the mechanical axis to a point located at more than 70 % on the cross sectional diameter of the tibial plateau, while ‘‘undercorrection’’ was identified as a shift of the mechanical axis to less than 50 % of the cross sectional diameter. These definitions are in accordance with earlier studies [38]. Computer-assisted intraoperative visualization of limb alignment was performed for all patients in Group 1 (OrthopilotTM; Aesculap Co. Tuttlingen, Germany; Software: Orthopilot-software for HTO V 1.5). At the start of surgery, the navigation pins (rigid bodies) were anchored in the region of the distal femur or proximal tibia using 4.5 mm screws. The pins were positioned at an angle of 90° to the diaphyseal axis and 30°–45° from the medial side to the vertical axis so that the transmitter when attached would be constantly visible to the camera regardless of limb position. After entering patient and operation data the center of the knee joint was recorded by means of a straight pointer. Acquisition of the hip, knee and ankle centers followed. At the same time, the Orthopilot software scanned and recorded data for the medial and lateral epicondyles, medial and lateral malleolus, anterior ankle joint and the medial tibial plateau. In addition, preoperative mechanical axis and ligament stability were recorded and stored. Intraoperative evaluation of the leg axis in Group 2 was based on image intensifier images (Ziehm Vision, Ziehm Imaging GmbH, Nu¨rnberg, Germany). A metal rod was placed across the leg so that it intersected with the hip and upper ankle joints. The point of intersection at the knee was identified and documented (Fig. 1). The position of the leg was accepted as correct when the patella had been centered and alignment confirmed radiologically [25]. Anteroposterior long-leg weight-bearing radiographs were obtained for all patients to determine the degree of varus malalignment before and after surgery. Limb alignment of the affected leg was assessed using the technique of Pauwels and respecting the recommendations given by Hsu and Moreland [19, 35]. According to this technique the limb alignment was taken as connecting line through the centre of the hip, knee and ankle [7]. Weight-bearing radiographs were obtained with the tabletop of the X-ray unit in the upright position (OmniDiagnost Philips, Hamburg, Germany) at a plate distance of 3 m. After position the roentgenopaque raster, X-ray filming commenced with the camera centred on the femoral head. Filming was
conducted at a frequency of 3 s-1 with the table moving at a constant speed of 7.5 cm/s. The radiographs obtained in this manner were combined to form the long leg radiograph (Easyvision, Philips, Hamburg, Germany). The indication for treatment was based on the preoperative diagnosis; radiological evaluation of limb alignment was conducted postoperatively once the patient could achieve full extension and painless distribution of 50 % bodyweight to the affected extremity. This resulted in an interval of 2 to 45 days between surgery and postoperative weight-bearing radiograph. Data relevant to the study was recorded for all participating patients (age, sex, diagnosis, etc.) and numeric parameters relevant to the exclusion of significant differences between groups were identified by analysis of normal distribution using the student’s t test and compared across groups. P values \0.05 were considered statistically significant. Analysis of radiographs was performed with the Impax viewer (ImpaxEE version 3.3.20, Agfa, Mortsel, Belgium). Analysis of all data was done by two independent investigators, who were both specialists in orthopaedics and traumatology. The following parameters were recorded: pre- and postoperative anatomical axis of the leg, pre- and postoperative intersection of the Mikulicz line with the tibial plateau, planned axial correction with reference to the
Table 1 Patient demographics
Subjects (n)
Navigated group
Non-navigated group
P value
40
40
NS
Age (years)
43.6 ± 11.4
43.6 ± 11.5
NS
Sex (male/ female)
32/8
32/8
NS
Fig. 2 Comparison of preoperative limb alignment in relation to the evaluation method: intersection of the Mikulicz line with the tibial plateau
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Knee Surg Sports Traumatol Arthrosc Table 2 Measurements Navigated group
Nonnavigated group
P value
Planned correction
8.3 ± 3.1
8.9 ± 3.3
NS
Definitive correction
9.8 ± 2.9
10.1 ± 3.3
NS
Intersection of Mikulicz line/ tibial plateau preop (%)
21.4 ± 12.7
18.9 ± 11.8
NS
Intersection of Mikulicz line/ tibial plateau postop (%)
58.8 ± 6.1
58.6 ± 8.1
NS
Fig. 4 Result of the correction, demonstration of the single values Table 3 Statistical results Navigated group
Non-navigated group
P value
Subjects (n)
40
40
NS
Value within target range
40
31
\0.05
Fig. 3 Comparison of postoperative limb alignment in relation to the evaluation method: intersection of the Mikulicz line with the tibial plateau
Value outside target range
0
9
\0.05
Fujisawa scale and definitive correction. The mean values from the investigators were entered into the statistical analysis. The incidence of relevant malalignments was analyzed by application of the v2 test. Statistical significance was set at P \ 0.05. Results were analyzed using SPSS (version 17; SPSS Inc., Chicago, IL, USA). This study was evaluated and approved by the Ethics Commission of the University of Freiburg.
values of 9.8° and 10.1° for Groups 1 and 2 respectively. The postoperative anatomical axis in both groups was also similar with values of 8.9° and 9.1° valgus. The average point of intersection of the mechanical axis with the tibial plateau was also similar in both groups. The target criterion for the intersection of the Mikulicz line with the tibial plateau was set at 50–70 %. This objective was achieved in all patients in Group 1 and in 31 of 40 patients in Group 2 (see Figs. 3, 4). This difference is significant (see Table 3). Operation time (MV) for both groups was 141 min (range group 1 90–223 min; range group 2 82–246 min), i.e. there was no significant difference.
Results Groups 1 and 2 were comprised of the same number of male and female patients with an average age of 43.6 years (see Table 1). The preoperative deformities were similar in both Groups 1 and 2 with an average varus deviation of the femoro-tibial axis of 0.9°. The intersection of the Mikulicz line with the tibial plateau was at 21.4 % in the navigated and 18.9 % in the non-navigated group (see Fig. 2). The quantified corrections were consequently within a similar range in both groups (see Table 2). The correction planned preoperatively was in a similar range in both groups, namely, 8.3° and 8.9° in Groups 1 and 2 respectively. When compared to the definitive correction, slight overcorrection was identified and yielded
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Discussion Although valgization high tibial osteotomy (HTO) for medial compartment gonarthritis in patients with varus deformity can be regarded as standard procedure in younger and active patients there are some important prognostic factors associated with good clinical outcomes or failure. These include factors specific to the individual such as congenital varus in the region of the proximal tibial metaphysis [39]. Other important factors are age, sex, BMI, ligament stability and previous surgeries [20, 37].
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The most important finding of the present study was that there is no significant difference of the accuracy between the navigated and non-navigated group but a significant amount of outliers in the non-navigated group. An essential and extremely important parameter for the success of clinical management is correction precision [3, 10–12], especially undercorrection is associated with inferior clinical outcome [12]. This requires good and exact planning as well as a precisely defined target alignment whereby standardized definitions of over- and undercorrection are absent from current scientific literature. Based on the assumption that good correction is characterized by a postoperative weight-bearing axis that intersects the knee base line at 50–70 % of the cross sectional tibial diameter [12, 38, 39], it can be stated that neither over- nor undercorrection occurred in the navigated group. The majority of authors define the correction target as an intersection of the mechanical axis with the tibial plateau at 62 % in accordance with the work of Fujisawa et al. [13]. However, the information given on acceptable reference values differs. The range in our study was defined as 50–70 % as has been described in earlier studies [38, 39]. An ideal range of 60–70 % was supposed by Miniaci et al. [34], but only achieved this goal in 50 % of cases in their own study. Dugdale et al. [11] give the lower value as 50 % and found 75 % to be a tolerable upper limit. Other authors confirmed these findings in clinical studies and tend to favor slight overcorrection [12]. A survival and failure analysis was conducted by Sprenger et al. [44] over a period of 22 years. They reported an ideal range of correction of the weight-bearing axis as 8°–16° valgus. Other authors recommend a slightly narrower average range of 8°–12° valgus [9, 21, 45]. Mu¨ller et al. [36] propose a modified procedure depending on the extent of cartilage lesion. However, even if the target correction is selected in relation to the individual pathologies, ultimately, as in the present study, correction must be performed with the Fujisawa point as its goal. In previous studies undercorrection in particular, but also distinct overcorrection were correlated with a reduced osteotomy survival time [11, 39, 44]. Important differences in survival rate at long-term follow-up were showed by Sprenger et al. [44] showed for a group with valgus angles of 8°–16° and a group with varus angles of \8° and [16°. In this study there is a significant difference between groups, e.g. 22.5 % suboptimal corrections in the nonnavigated group. There were four cases of slight overcorrection. As already discussed, slight overcorrection is much less disadvantageous in terms of outcome than undercorrection [11, 44]. The undercorrections were mostly in the range of 42–49 %. One patient required revision surgery; in the other cases the outcome was discussed with the patient and no further action was taken.
The incidence of 22.5 % unsatisfactory corrections may seem high at first but is comparable to the early results reported by Billing et al. [5] who identified malalignments in 17.5 % of cases. It is more difficult to make comparisons with the numerous more recent studies since the mean value of the postoperative alignments is often discussed without allusion to the reference values or the number of values outside the stipulated range [3]. Bae et al. [4] in their comparative study recorded good outcomes for navigated closed-wedge osteotomies and their non-navigated control group actually yielded a mean value of 47.3 % for correct mechanical axis. After analysis of postoperative femorotibial limb alignment we found a mean value of 8.9° (SD 1.5°) in Group 1 and 9.1° (SD 2.5°) in Group 2 whereby this difference was non significant. Hereby, it should be noted that the mean values of all corrections whether navigated or not were within the target range. The clinical outcomes of the current study with regard to the incidence of outliers after correction osteotomy confirm the findings of existing experimental studies. A significantly higher average correction precision found Hankemeier et al. [16] in their cadaver study, but did not give reference values or discuss the number of outliers, if any. Lu¨tzner et al. [30] were able to achieve very high precision with navigation with intra- and interobserver reliability at a maximum deviation of around 1°. This was verified for all investigators regardless of their professional standing. In another investigation (cadaver study) the same group recorded a highly significant difference compared with HTO in conventional technique [31]. Surgical technique and the ability to visualize the weight-bearing patterns during surgery are key factors in achieving the desired correction. Standard technique requires intraoperative quantification of limb alignment. This is achieved by positioning a roetgenopaque rod such that it passes through the center of the femoral head and the center of the ankle joint. Alternatively, visualization by means of diathermy cable or grid lines has been described [16, 27, 42]. Despite modern techniques this approach to intraoperative assessment of limb alignment is still standard procedure and was used in the current study. The main limitation of these methods is however their dependence on correct positioning. In their experimental study Brouwer et al. [6] were able to demonstrate the effects of joint flexion and rotation on apparent axial alignment. Radtke et al. [41] also found significant effects, especially rotational, on the mechanical axis. Schmitt et al. [43] found the same effects on limb alignment. This group also present an alternative means of calculating the axis based on digital photographs and were able to show a significant correlation with the radiological weight-bearing radiographs.
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Computer-assisted evaluation of limb alignment essentially offers the opportunity to monitor the entire operation live in order to increase the precision of the osteotomy [23]. Experimental studies have already confirmed the important benefit derived from avoiding outliers in the sense of obvious malalignments [16]. There are already several studies that have addressed the use of navigation systems in clinical practice as the main purpose of the investigation. The majority of these reports focus on operation time, radiation exposure and other parameters, whereas correction accuracy is often only compared in the form of mean values for the treatment and control groups. However, it is better to demonstrate the accuracy and reliablity of a monitoring method such as surgical navigation in the operating room by critical inspection of the scatter of the individual values [25]. ‘‘Cable technique’’, which used to be very popular, [26, 27] is quite susceptible to error, especially if the cable bends or is incorrectly positioned. Efforts to eliminate cable instability as a source of error led to the use of a system of rods. In one current study, Liodakis et al. [26] showed that good outcomes were achieved with an ‘‘axis board’’ with an average deviation of only 1° away from the axis identified intraoperatively. However, this study not only evaluated HTO but also fractures of the femur and tibia. The so-called ‘‘axis board’’ can no doubt solve the problem of slack cable but does not eliminate errors arising from malrotation. There was no difference in operation time between the two groups. However, it is not really possible to obtain reliable data because of the number of different interventions taking place at the same surgery such as operations on the menisci or procedures for cartilage regeneration. This also explains the relatively long mean operation time of 141 min. The initially longer phase required to mount the pins and read the data into the navigation device is however partially equivalent to the less complex adjustment of the image intensifier. Apart from correction precision, continuous visualization and additional imaging of the sagittal plane can be regarded as particular advantages. The importance of taking this plane into account has already been confirmed by earlier studies [10, 32]. The sagittal plane was not specifically evaluated in the present study. The main problem of analysis is the difficulty of obtaining adequate postoperative lateral images. An additional advantage of direct visualization is that it facilitates assessment of stability and this in turn permits a better assessment of the postoperative weight-bearing axis [16]. This aspect examined Kendoff et al. [24] in a cadaver study and found a tendency towards axial deviation under load after osteotomy. They found that the incidence of axial deviation was related to the correction angle and to the necessity of partial release of the
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MCL (medial collateral ligament). The precision of the method and the correlation of navigated data with the postoperative weight-bearing radiographs was also confirmed by Iorio et al. [22] but for a smaller patient sample. Analysis of the findings from this study must include remarks about the limitations of the study. After the navigation system had been introduced, it was in continuous use so patients were not randomized. Surgical technique was the same in the two treatment groups and all osteotomies were stabilized with identical implants. Despite the retrospective nature of the investigation, the matched-pair study design permitted homogeneous distribution of essential patient characteristics and thus facilitated isolated observation of the effect of the surgical navigation system to the greatest extent possible. Further limitations of the current study are those that apply to the ‘‘gold standard’’ imaging technique for evaluation of limb alignment. However, knowledge of these weaknesses does not alter the fact that no better method is available at this time for intraoperative visualization of limb alignment and, therefore, it appeared logical and feasible in terms of clinical considerations to compare navigation precision with radiographic axial assessment in our control group.
Conclusion In conclusion, the use of a navigation device did not lead to any improvement in the overall good outcomes generally achieved without navigation, but it was found that over- and undercorrection could be reliably prevented, thus eliminating outliers outside the target range. Since the latter have been associated with inferior outcomes in previous studies, it appears that computer-assisted intraoperative assessment of lower limb alignment is an important and promising approach to achieving further improvements in clinical outcomes after HTO. This might be the focus of future clinical studies that take into account treatment outcomes after HTO with and without navigational assistance. Conflict of interest No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
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