Bearing CT Allows for More Accurate Bone Position (Angle) Measurement than Radiographs or CT

, Francois Lintz², Cesar de Cesar Netto³, Alexej Barg⁴, Arne Burssens⁵ and Scott Ellis⁶

(1)

Department for Foot and Ankle Surgery, Hospital Rummelsberg, Schwarzenbruck, Germany

(2)

Foot and Ankle Surgery Centre, Clinique de l’Union, Toulouse, France

(3)

Department of Orthopedics and Rehab, University of Iowa, Iowa City, IA, USA

(4)

University Orthopedic Center, University of Utah, Salt Lake City, UT, USA

(5)

Department of Orthopedics and Trauma, University Hospital of Ghent, Ghent, OVL, Belgium

(6)

Department of Orthopedic Surgery, Hospital for Special Surgery, New York, NY, USA

Keywords

RadiographComputer tomography (CT)Weight bearingWeight bearing CT

Introduction

The standard for diagnostic radiographic imaging in foot and ankle surgery is radiographs with full weight bearing [1, 2]. The three-dimensional relationships of the bones in the foot are difficult to assess with standard radiographs due to superimposition of the different bones [1, 3]. Angle measurements with standard radiographs could be inaccurate due to inaccuracies of the projection (orientation of (central) beam) and/or foot orientation [1, 4–6]. 3D imaging with conventional computed tomography (CT) allows for exact analysis within the 3D data that is not influenced by projection and/or foot orientation but lacks weight bearing [1, 3, 7]. WBCT (PedCAT, CurveBeam, Warrington, USA) is a new technology that allows 3D imaging with full weight bearing which should be not influenced by projection and/or foot orientation (Figs. 3.1 and 3.2) [1].

../images/484112_1_En_3_Chapter/484112_1_En_3_Fig1_HTML.png — Fig. 3.1

WBCT scan and software screen. An X-ray emitter and a flat panel sensor on the opposite side are rotating horizontally around the feet. Resolution and contrast which are the principal parameters for image quality are comparable with modern conventional CT. Left, patient positioned in WBCT during scan. Sitting position is also possible for patients that are not allowed or able to stand. The gray part is a sliding door that is opened before and after the scan. The patient can walk into the device of the door is open. Right, software screen view with 3D reformation (top left), axial reformation (top right, red frame), parasagittal reformation (bottom left, green frame), and coronal reformation (bottom right, blue frame). The standard view is with 1 mm slice thickness, shown by the red, green, and blue lines. The red lines are corresponding to the axial reformation in the red frame, the green lines are corresponding to the parasagittal reformation in the green frame, and the blue lines are corresponding to the coronal reformation in the blue frame

../images/484112_1_En_3_Chapter/484112_1_En_3_Fig2_HTML.png — Fig. 3.2

WBCT software screen view with increased slice thickness to create virtual radiographs. Top right, in red frame, virtual dorsoplantar radiograph created by increased slice thickness that contains entire foot (red arrow). Bottom left, in green frame, virtual lateral radiograph created by increased slice thickness that contains entire foot (green arrow). Bottom right, in blue frame, virtual metatarsal head skyline view radiograph created by increased slice thickness that contains the metatarsal heads (blue arrow)

The aim of this study was to compare time spent on the image acquisition, and comparison of specific angle measurements between the three methods (radiographs, CT, WBCT), and to analyze and compare inter- and intraobserver reliability.

Methods

In a prospective consecutive study, 30 patients in which standard digital radiographs with full weight bearing in standing position, CT without weight bearing in supine position, and WBCT with full weight bearing in standing position were included, starting July 1, 2013 [1]. The potential pathologies of the feet were registered but not further analyzed.

Inclusion and Exclusion Criteria: Ethics

The inclusion criteria were age ≥18 years, presentation at the local foot and ankle outpatient clinic, and indication for radiographs and 3D imaging (CT, WBCT). The indication for radiograph and 3D imaging (CT, WBCT) was defined following the local standard. For example, no indication for 3D imaging (CT, WBCT) was given for isolated forefoot deformities, whereas indication for 3D imaging (CT, WBCT) was given for deformities in the midfoot and/or hindfoot region.

The exclusion criteria were age <18 years, no indication for radiograph and/or 3D imaging (CT, WBCT) and participation in other studies.

All three methods (radiographs, CT, WBCT) were approved by the relevant authority for diagnostic use at the local institution. Approval from the local ethical committee was granted for simultaneous use of all three methods (radiograph, CT, WBCT) based on the indications as described above. Informed consent was obtained from all subjects.

Image Acquisition

The radiographic image acquisition followed a standardized protocol with a fully digital device (Model Buck Diagnost, Philips, Hamburg, Germany) [2, 8]. The patient was positioned on a special step with a holding apparatus for the digital film, the X-ray emitter was adjusted, and the images were taken (feet bilateral dorsoplantar and lateral views and Saltzman hindfoot view) [8]. The radiation exposure time was approximately 1/10th of a second for each image. For CT (Model Optima 520, General Electric Healthcare, Solingen, Germany; helical technique, 20 lines), the patient was positioned in supine position, and the feet were placed in a special holding device to ensure neutral foot and ankle position [9]. Both feet and ankles were scanned from 10 cm proximal to the ankle level. The slice thickness was adjusted to 1 mm, and the pure scanning time was 60 seconds. For WBCT (PedCAT, CurveBeam, Warrington, USA), the patient walked into the device and was positioned in bipedal standing position as shown in Fig. 3.1. Technically, an X-ray emitter and a flat panel sensor on the opposite side are rotating horizontally around the feet. Resolution and contrast which are the principal parameters for image quality are comparable with modern conventional CT. The scanning time was 68 seconds.

Time Spent

The time spent on the image acquisition was registered. Time spent was defined as the sum of the time needed for positioning the patient for the imaging and the time needed for the imaging as such as described above. The time for epidemiological data entry was not included. For the radiograph group, the times for all four images (feet bilateral dorsoplantar, right foot lateral, left foot lateral, Saltzman hindfoot view bilateral) were added up to a total time.

Angle Measurements

The angles were digitally measured with specific software (Radiographs, JiveX, VISUS, Bochum, Germany; CT, Syngo XS version VE31GSL19P21VC10ASL129P167SP1, Siemens, Erlangen, Germany; PedCAT, CubeVue, version 2.4.0.5, CurveBeam, Warrington, USA).

The following angles were measured for the right foot by three different investigators three times: 1st–2nd intermetatarsal angle, talo-1st metatarsal (TMT) angle dorsoplantar and lateral projection, hindfoot angle, and calcaneal pitch angle [8, 10].

The 1st–2nd intermetatarsal angle was defined as the angle created between the axis of the 1st and the 2nd metatarsal in the dorsoplantar view (radiograph) or axial/horizontal reformation (CT, WBCT). For CT and WBCT, the plane for the measurement was virtually rotated within the 3D dataset to achieve an exact congruency to the bone axes of first and second metatarsals.

The TMT angle was defined as the angle created between the axis of the 1st metatarsal and the talus [10] (Fig. 3.3, image top right and bottom left). The dorsoplantar TMT angle was measured in the dorsoplantar view (radiograph) or axial/horizontal reformation (CT, WBCT) (Fig. 3.3, image top right). The lateral TMT angle was measured in the lateral view (radiograph) or parasagittal reformation (CT, WBCT) (Fig. 3.3, image bottom left). For CT and WBCT, the plane for the measurement was virtually rotated within the 3D dataset to achieve an exact congruency to the bone axis of talus and 1st metatarsal.

../images/484112_1_En_3_Chapter/484112_1_En_3_Fig3_HTML.png — Fig. 3.3

WBCT software screen showing an example of some angle measurements. The 3D reformation (top left) shows how the 3D dataset was virtually rotated to allow for exact congruency of the plane of the reformations with the bone axes as described in the methods section. Top right, measurement of the dorsoplantar TMT angle; bottom left, measurement of the dorsoplantar TMT angle; bottom right, measurement of the hindfoot angle also as described in the methods section. The hindfoot angle measurement was typically performed in another plane which cannot be displayed simultaneously with planes for the dorsoplantar and lateral TMT angles. This modified presentation was chosen for this figure for to allow simultaneous presentation of three angles within one figure. The lines that define the centers of the bones proximally or distally are exactly 50% of the measured entire bone thickness

The hindfoot angle was defined as the angle created between the axis of the distal tibia and the line between the center of the talar dome and the posterior calcaneal process (Fig. 3.3, image bottom right). This angle is defined to be positive for hindfoot valgus and negative for hindfoot varus. It is measured Saltzman view (radiograph) or coronal reformation (CT, WBCT). For CT and WBCT the plane for the measurement was virtually rotated within the 3D dataset to achieve an exact congruency to the bone axis of the tibia and the axis of the hindfoot. This was typically the case when this plane was congruent with the axis of the ankle, i.e. a line between medial and lateral malleolus comparable to a mortise orientation but within a 3D pace. Figure 3.3 (image bottom right) shows the orientation within the 3D dataset as described above with the adjusted rotation with the fibula and tibia aligned in the same virtual plane comparable to a mortise view.

The calcaneal pitch angle was defined as the angle created between a horizontal line, between the lowest part of the posterior calcaneal process and the lowest part of the anterior calcaneal process. The calcaneal pitch was measured in the lateral view (radiograph) or parasagittal reformation (CT, WBCT). For CT and WBCT the plane for the measurement was virtually rotated within the 3D dataset to achieve an exact congruency to an exactly parasagittal plane.

All bone axes (tibia, talus, metatarsals) were defined as the straight line between the centers of the bones proximally and distally. These bone centers were defined by linear measurements (Fig. 3.3). The TMT angles were defined to be negative for abduction in the dorsoplantar radiograph and for dorsiflexion in the lateral radiographs [10].

Statistics

The parameters were compared to intra- and interobserver and between the different methods (radiograph, CT, WBCT) (ANOVA with post hoc Scheffe test). The null hypothesis at a significant level of 0.05 was formulated that the different angles did not differ between the three methods. For nonsignificant findings, a power analysis was indicated. Sufficient power was defined as ≥0.8.

Results

Time Spent

The time spent for the image acquisition was 902 ± 70 seconds for radiographs, 415 ± 46 seconds for CT and 270 ± 44 seconds for WBCT on average (ANOVA, p < 0.001).

Angle Measurement: Differences Between Methods

The angles differed between radiographs, CT, and WBCT (ANOVA, all p ≤ 0.01) (Table 3.1). The angles differed between WBCT and both radiographs and CT (post hoc Scheffe test, each p ≤ 0.05) except for TMT dorsoplantar and calcaneal pitch angles for WBCT versus radiographs. The null hypothesis was rejected for all angles except for TMT dorsoplantar and calcaneal pitch angles between WBCT and radiograph.

Table 3.1

One-way ANOVA radiographs versus CT versus WBCT and post hoc test WBCT versus radiographs and CT

One-way ANOVA
Parameter	Radiographs		CT		WBCT		p
	Mean	STD	Mean	STD	Mean	STD
IM-angle	7.7	3.3	7.8	3.9	9.3	3.5	<0.001
TMT dorsoplantar	−6.2	12.4	4.3	10.0	−5.0	12.0	<0.001
TMT lateral	−5.2	8.2	0.5	8.4	−7.6	8.2	<0.001
Hindfoot angle	2.4	6.9	5.4	5.6	10.1	7.1	<0.001
Calcaneal pitch angle	17.5	6.3	16.5	5.0	17.8	5.4	0.01
Post hoc Scheffe test
Parameter	WBCT vs.	p
IM-angle	Radiographs	<0.001
IM-angle	CT	<0.001
TMT dorsoplantar	Radiographs	0.561
TMT dorsoplantar	CT	<0.001
TMT lateral	Radiographs	0.003
TMT lateral	CT	<0.001
Hindfoot angle	Radiographs	<0.001
Hindfoot angle	CT	<0.001
Calcaneal pitch angle	Radiographs	0.701
Calcaneal pitch angle	CT	0.013

IM 1st–2nd intermetatarsal angle, TMT talo-1st metatarsal angle, STD standard deviation

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Tags: Weight Bearing Cone Beam Computed Tomography (WBCT) in the Foot and Ankle

Apr 25, 2020 | Posted by admin in MUSCULOSKELETAL MEDICINE | Comments Off

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