Eur J Orthop Surg Traumatol DOI 10.1007/s00590-016-1796-5
ORIGINAL ARTICLE • HIP - ARTHROPLASTY
The correlation between clinical radiological outcome and contact state of implant and femur using three-dimensional templating software in cementless total hip arthroplasty Daisuke Inoue1 • Tamon Kabata1 • Toru Maeda1 • Yoshitomo Kajino1 • Takashi Yamamoto1 • Tomoharu Takagi1 • Takaaki Ohmori1 • Hiroyuki Tsuchiya1
Received: 12 February 2016 / Accepted: 6 May 2016 Springer-Verlag France 2016
Abstract Background Initial fixation is a key factor in the success of cementless THA using a tapered wedge stem. The purpose of this study was to use three-dimensional templating software to examine the correlation between quantitative contact state and important clinical radiological outcomes, specifically stem subsidence, stress shielding, and cortical hypertrophy. Methods We conducted a retrospective consecutive review of 75 hips in 70 patients over a minimum 3-year follow-up period. X-rays and CT scans were investigated to assess preoperative planning, quantify the contact state of implant and femur, and assess stem alignment, stem subsidence, stress shielding, and cortical hypertrophy. We evaluated the correlation between radiological outcomes and threedimensional quantitative contact state according to Gruen Zone in each Dorr classification. Results Density mapping indicated that stem subsidence increased postoperatively if the stem had less cortical contact in the middle to distal portion of the implant in terms of initial fixation. Cases having too much cortical contact in the distal portion of the implant tended to have increased stress shielding. We found no correlation between cortical hypertrophy and the contact state of implant and femur. Conclusions Density mapping with three-dimensional templating software can be useful in predicting stem subsidence and stress shielding following cementless THA
& Tamon Kabata
[email protected] 1
Department of Orthopaedic Surgery, Graduate School of Medical Science, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8641, Japan
with a tapered wedge stem. Further analysis is required to accurately depict the correlation between cortical hypertrophy and the contact state. Keywords Density mapping Radiological outcome Three-dimensional templating software Total hip arthroplasty
Introduction Primary total hip arthroplasty (THA) is an extremely successful orthopedic procedure for reducing pain and restoring joint function [1]. Several studies have reported good mid- and long-term results for cementless THA using a tapered wedge stem [2–4]. But if ideal initial fixation of the femoral component is not achieved with the tapered wedge stem, stem subsidence in the early postoperative period, severe stress shielding, and aseptic loosening may result, thereby requiring revision THA [5]. A past report showed that the ideal fixation of a tapered wedge stem is a proximal metaphyseal fit to engage the metaphyseal cortical bone in the medial to lateral plane [6]. The initial fit and fill state between implant and femur has commonly been analyzed using plain radiography. Clearly, the fit and fill parameter cannot always be predicted because the cortico-cancellous interfaces can be difficult to standardize using plain radiography, and determining their contact state requires a subjective decision by the examiner [7, 8]. In our previous report, we investigated the usefulness of three-dimensional templating software to quantify the contact state [9]. We think that using such software can serve a useful clinical purpose if it shows correlations between the contact state and clinically important radiological outcomes such as stem subsidence, stress shielding,
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and cortical hypertrophy. However, no previous studies have reported using three-dimensional templating software to detail the correlation between those radiological outcomes and the quantitative contact state. The purpose of this study, then, was to examine the correlation between clinical radiological outcomes and quantitative contact state using three-dimensional templating software.
Materials and methods This investigative protocol was conducted with the approval of our institutional ethical committee. In accordance with the requirements of this review, all patients provided informed consent. We conducted a retrospective consecutive review of 75 hips in 70 patients (16 men and 54 women) who underwent cementless primary THA between February 2009 and September 2012 using Accolade TMZF (Stryker, Mahwah, NJ, USA), a tapered wedge stem. The cases in this study had a minimum follow-up period of 3 years. Patient demographics are given in Table 1. The mean age of the patients was 64.4 ± 8.9 years (39–85 years). The mean follow-up period was 4.3 years (3–6.4 years). There were 43 left hips and 32 right hips. Primary osteoarthritis (OA) was diagnosed in 22 hips, and secondary OA was diagnosed in 32 hips, of which 23 were Crowe group 1, 3 were Crowe group 2, and 6 were Crowe group 3 [10]. Osteonecrosis of the femoral head was diagnosed in 15 hips, rheumatoid arthritis in 3 hips, and rapidly destructive coxoarthropathy in 3 hips. Preoperatively, all patients were given an anteroposterior or mediolateral hip X-ray and CT scan. A hip X-ray was taken immediately after the operation and postoperatively at 2 weeks, 3 months, 6 months, and 1 year to investigate radiological outcomes: stem alignment, stem subsidence, stress shielding, and cortical hypertrophy. Thereafter, X-rays were taken at one-year intervals. A CT scan was taken Table 1 Patient demographic data Patient characteristics (n = 75) Age
64.4 ± 8.9 (39–85)a
Sex (female/male)
51/2
Side (left/right)
43/32
Diagnosis
a
Secondary osteoarthritis
32 hips
Primary osteoarthritis
22 hips
Osteonecrosis of the femoral head
15 hips
Rheumatoid arthritis
3 hips
Rapidly destructive coxoarthropathy
3 hips
Mean ± standard deviation (range)
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2 weeks after the operation for postoperative assessment of the preoperative planning and to quantify the contact state of implant and femur. Preoperative and postoperative CT scans from the iliac wing to the femoral condyle were performed using a helical CT scanner (LightSpeed VCT; GE Medical Systems, Milwaukee, WI, USA). Slice thickness was 1 mm, and pitch was 2.5 mm (160–250 slices depending on body size). All preoperative planning and postoperative evaluations were completed on the CT-based templating software ZedHip (Lexi Co., Tokyo, Japan). All preoperative planning and postoperative evaluations were performed by the author (DI), and all operations were performed by the senior surgeon (TK). The approaches used were 64 posterolateral and 11 anterolateral. Clinical outcomes using plain radiography The Dorr classification system was used to evaluate preoperative bone quality based on the cortical thickness and proximal taper visualized in preoperative hip X-rays [11]. The stem insertion angle was defined as the angle between proximal femoral axis and stem axis in coronal or sagittal planes, and we measured the stem insertion angle in coronal or sagittal planes using the postoperative hip X-ray. We defined malalignment cases as those with 3 degrees error compared with the neutral position in the coronal and sagittal planes. Postoperative and final X-rays were compared in order to evaluate the following clinical radiological outcomes: more than 3 mm stem subsidence, more than 2 degrees stress shielding following the procedures reported by Engh et al, and cortical hypertrophy which was defined as fusiform enlargements of the cortical bone in the bone-implant region [12, 13]. The bone ingrowth of the implant was investigated by using the Engh et al. [12] evaluation method on mediolateral hip X-rays. Description of ZedHip density mapping ZedHip is software which enables the surgeon to position the prosthetic components properly in the three-dimensional space of the CT data. Eight reference points (femoral head, piriformis fossa, the most posterior point of the proximal femur, bilateral posterior condyles, bilateral femoral condyles, and knee center) were taken on the femoral side, as described in our previous study [14]. ZedHip has the capability to perform density mapping which can visualize and digitize the contact state of implant and femur. Density mapping is a function which delineates the contact state by color, based on the Hounsfield (HU) value taken from the CT data (see Fig. 1). On the HU scale, the X-ray absorption of distilled water at STP is defined as 0, and that of air is defined as -1000 [15]. The contact region is shown in three colors: yellow shows the
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quantitative contact state according to Gruen Zone in each Dorr classification. Statistical analysis Statistical analysis was performed using SPSS software (PASW Statistics Base version 19; SPSS, Chicago, Illinois). The value of the contact state of implant and femur was expressed as mean ± standard deviation. An unpaired T test was used in this evaluation. A p-value \ 0.05 was considered statistically significant.
Results Clinical outcomes using plain radiography Fig. 1 ZedHip density mapping. The contact region is shown in three colors: yellow delineates the contact with cortical bone, red shows the contact with dense cancellous bone, and green is sparse cancellous bone. The density mapping returns the results both in values and percentages with respect to the total stem area and Gruen Zone (color figure online)
contact with cortical bone, red shows the contact with dense cancellous bone, and green shows the contact with sparse cancellous bone. Finally, the density mapping function returns the results in both values and percentages with respect to the total stem area and Gruen Zone. In this examination, we defined the effective contact region as the area where an implant is in contact with cortical bone (namely, the yellow part). The density thresholding of the cortico-cancellous interface was established at 543 HU, as described in our previous report [9]. Analyzing the contact state of implant and femur Using postoperative CT data, we measured the stem insertion angle (stem anteversion, stem insertion depth, stem coronal alignment, and stem sagittal alignment) by using ZedHip to manually superimpose computer-aided design (CAD) models of the Accolade TMZF on the postoperative multiplanar reconstruction CT images. Next, the postoperative CT image including the stem insertion angle data was matched to the preoperative CT image. Image matching was performed for the portion in which metal halation had not been created by the implant insertion. Finally, we reproduced the postoperative state by making the preoperative CT data reflect the insertion angle of the postoperative implant and then measuring the contact state of implant and femur according to Gruen Zones by using density mapping, as noted in our previous report [9, 16] (see Fig. 2). In our examination, we evaluated the correlation between radiological outcomes and three-dimensional
In the evaluation of preoperative bone quality, 22 hips were Dorr type A, 50 hips were type B, and 3 hips were type C. The stem insertion alignment evaluation revealed no cases with malalignment in the coronal and sagittal planes. Furthermore, all hips achieved stable bone ingrowth according to the evaluation criteria of Engh et al. The clinical outcomes using plain radiography are given in Table 2. Only 2 cases had more than 3 mm stem subsidence; both hips were Dorr type A. Twenty hips had more than 2 degrees stress shielding: 19 hips had 2 degrees and 1 hip had 3 degrees; no hips had 4 degrees. Also, 6 hips exhibited cortical hypertrophy. The correlation between radiological outcomes and quantitative contact state To establish the correlation between stem subsidence and the three-dimensional contact state of stem and femur, we evaluated the relationships by comparing the no stem subsidence group (cases with no more than 2 mm stem subsidence) with the stem subsidence group (cases with more than 2 mm stem subsidence). In Dorr type A hips, there was a tendency to achieve low cortical contact in Gruen Zones 3, 5, 6, and 7 in the subsidence group compared with the no subsidence group (see Fig. 3). Next, to correlate stress shielding with the contact state of implant and femur, we evaluated the relationship by comparing the no stress shielding and stress shielding groups, as in the evaluation of the stem subsidence. There was a tendency to achieve high cortical contact in Gruen Zone 3 in the stress shielding group compared with the no stress shielding group in Dorr type A and B hips. In Dorr type A, there was a tendency to achieve increased cortical contact in Gruen Zone 5 although there was no statistical difference between the two groups (see Fig. 4).
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Eur J Orthop Surg Traumatol Fig. 2 a Measuring the stem insertion angle by manually superimposing CAD models on the postoperative CT images with ZedHip. b Reproducing the postoperative state by making preoperative CT data reflect the postoperative implant insertion angle. c Using density mapping to measuring the contact state of implant and femur according to Gruen Zone
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Eur J Orthop Surg Traumatol Table 2 Clinical outcome by using plain radiography Dorr type A (n = 22) Stem subsidence
Dorr type B (n = 50)
Dorr type C (n = 3)
2
0
0
Second degree
4
13
2
Third degree
0
0
1
Fourth degree
0
0
0
0
4
2
Stress shielding
Cortical hypertrophy
Fig. 3 Mean contact state in non-stem subsidence and stem subsidence groups. There were statistically significant differences in Gruen Zones 3, 5, 6, and 7
However, we could find no clear relationship between cortical hypertrophy and the contact state of stem and femur. For cortical hypertrophy, we give a case presentation (see Fig. 5). The patient is a 61-year-old male. Bone classification of this case is Dorr type C. The patient suffered from osteonecrosis of the left femoral head. The implant was an Accolade stem; The density mapping system shows that initial fixation was achieved in Gruen Zones 2, 3, and 5 (namely distal fixation) (Fig. 5a), but cortical hypertrophy emerged in Gruen 5 of the Accolade stem (Fig. 5b). The initial fixation points do not correspond with the emergence of cortical hypertrophy.
Discussion Favorable initial fixation of implant and femur is considered to influence bone-remodeling processes at the proximal femur [17]. Furthermore, preoperative bone geometry and the medullary canal affect load transfer into the femoral bone and impact its bone-remodeling processes and thus may be likely to affect the clinical outcome. Several reports showed the correlation between clinical
Fig. 4 Mean contact state in non-stress shielding and stress shielding groups. There was a statistically significant difference in Gruen Zone 3. a Dorr type A. b Dorr type B
radiological outcome and contact state of implant and femur by using plain radiograph in detail. Issa et al. [18] investigated the effect of preoperative bone type on clinical outcomes and postoperative remodeling after THA for 345 cases in which a tapered wedge stem was used. This report concluded that a preoperative evaluation of bone type may be useful to predict the magnitude and extent of periprosthetic remodeling after THA. However, Van der Wal et al. [19] reported that their radiological analysis of bone remodeling in 64 THAs found no correlation between the contact state of implant and femur and the radiological outcomes. Considering with this report, a subjective decision of fit and fill parameters by using plain radiograph may be likely to influence the correlation between femoral fit and radiological outcomes. Recent studies have expanded the use of CT-based three-dimensional templating to establish the contact state of implant and femur, to achieve more precise preoperative planning and to evaluate the implant insertion state [20–22]. In an earlier report, we established the usefulness of CTbased three-dimensional templating software for
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Fig. 5 Case presentation of a 61-year-old male patient. a The density mapping system indicates that initial fixation was achieved in Gruen Zones 2 and 3. b Cortical hypertrophy emerged in Gruen 5. The initial fixation point does not correspond with the emergence of cortical hypertrophy
quantifying the contact state between implant and femur, and outlined the advantages of this density mapping technique [9]. In particular, density mapping makes it possible to digitally quantify the contact state in every Gruen Zone. It is important to investigate the relationship between the three-dimensional contact state of implant and femur and the clinical radiological outcome and apply these data to future preoperative planning. Several studies have reported good mid- and long-term results for cementless THA using a tapered wedge stem [2–4]. However, some reports reported that tapered proximally porous wedge stem raised failure of osteointegration and the progressive stem subsidence due to distal fixation of tapered wedge stem and the mismatch between implant and femur [5, 23, 24]. Therefore, these reports indicated that achieving the good adaptability of contact state between implant and femur is very important factor in using tapered wedge stem. In this study, we saw a tendency to achieve low cortical contact in Gruen Zones 3, 5, 6, and 7 in the subsidence group compared with the no subsidence group in Dorr type A hips. Density mapping indicated that stem subsidence tended to increase postoperatively if the Accolade stem had less cortical contact in the middle to distal portion of the implant in terms of initial fixation. Khanuja et al. [6] have reported that the initial fixation pattern of a tapered wedge stem is a proximal metaphyseal fit that engages the metaphyseal cortical bone in the medial to lateral plan, and thus, the Accolade stem must have cortical contact in the middle to distal portion of the implant in order to retain good alignment and achieve good initial fixation. Our results are compatible with this previous report. They show that with more than 2 degrees stress shielding there was a tendency to achieve high cortical contact in Gruen 3 in the stress shielding group compared
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with the no stress shielding group in Dorr A and B hips. Furthermore, in Dorr type A, there was a tendency to achieve high cortical contact in Gruen Zone 5, with no statistical difference between the two groups. Density mapping indicated that the cases having too much cortical contact in the distal portion of the implant tended to have increased stress shielding in the follow-up period. White et al reported that the distal fixation of the implant may lead to more than 2 degrees stress shielding, and thus, the data in our study are also considered acceptable regarding stem subsidence [5]. We therefore believe that three-dimensional contact state evaluation using density mapping may help predict stem subsidence or more than 2 degrees stress shielding after surgery. However, we found no correlation between cortical hypertrophy and the contact state of implant and femur. The reason is as follows: Postoperatively the implant was forced to sustain a vertical load. Because it was not necessary to correlate initial fixation with stress concentration in continuous load application, the results do not show a correspondence with cortical hypertrophy. In order to accurately depict the correlation between cortical hypertrophy and the contact state of implant and femur, it would be necessary to perform finite element analysis (FEM) to reflect the actual loading condition. It must be noted that there are several disadvantages to the use of three-dimensional templating software. One is that it can increase planning time by 10–15 min. Another is that using three-dimensional templating software results in higher radiation exposure for the patient compared to conventional radiography, and a third concern is that it may increase preoperative planning costs. This third concern may not be of major importance in the Japanese insurance system, but it could be a stronger consideration elsewhere.
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Huppertz et al. [25] have reported that preoperative CT for THA is associated with a slight but justifiable increase in per-patient costs. There were some limitations to this study. First, technical errors may have been introduced when the postoperative CT data were matched to the preoperative CT data in analyzing the contact state of implant and femur. However, we do not think that matching system error was very large because the reference points were not influenced by the postoperative metal halation. Second, the ideal fixation pattern is thought to vary according to the stem design. Therefore, it will be necessary to investigate the correlation between radiological outcomes and quantitative contact state using this CT-based three-dimensional templating software for each of the different stem designs. Despite these limitations, however, we believe our results show that the use of density mapping to quantify this contact state can be clinically helpful in the prediction of stem subsidence and stress shielding, which are clinically important radiological outcomes.
Conclusion We used three-dimensional templating software to investigate the correlation between radiological outcomes and quantitative contact state. Our results indicated that this technique can be clinically helpful in predicting stem subsidence and stress shielding, which are important radiological outcomes following cementless THA with tapered wedge stems. Compliance with ethical standards Conflict of interest The authors did not receive any benefits or findings from any commercial party related directly or indirectly to the subjects of this article. Ethical approval All procedures performed in studies were in accordance with the ethical standards of our institutional ethical committee. In accordance with the requirements of this study, all patients provided informed consent.
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