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CLINICAL RESEARCH

What Is the Diagnostic Accuracy of Flat-panel Cone-beam CT Arthrography for Diagnosis of Scapholunate Ligament Tears?

Dornberger, Jenny E. MD; Rademacher, Grit MD; Stengel, Dirk MD, PhD, MSc; Hönning, Alexander MSc; Dipl-Phys, Gabriele Schüler; Eisenschenk, Andreas MD, PhD; Mutze, Sven MD, PhD; Goelz, Leonie MD

Author Information
Clinical Orthopaedics and Related Research: January 2021 - Volume 479 - Issue 1 - p 151-160
doi: 10.1097/CORR.0000000000001425

Abstract

Introduction

Conventional radiography is the primary radiologic method for diagnosing scapholunate ligament (SLL) injuries, but it detects only static forms of these injuries with good accuracy [27]. Early stages of SLL dissociation can be discovered through dynamic approaches using cineradiography, four-dimensional CT, and cine MRI [5, 18, 27]. Multislice CT (MSCT) and static MRI of the carpal joints aim to visualize SLL tears directly. The diagnostic accuracy of both methods can be enhanced profoundly, from 56% to 100%, with direct arthrography [19, 26]. Nevertheless, arthrography and the additional rearrangement of patients to perform another examination are time-consuming and require tight schedules and structured processes. Cone-beam CT (CBCT), or digital volume tomography, is another diagnostic method with growing indications in orthopaedic radiology. Dedicated CBCT scanners have been implemented in odontology because of their compact format and simple handling [1]. Compared with MSCT scans, CBCT has been shown to reduce effective radiation doses [21]. More recently, studies on injuries of the wrist and hand have suggested additional indications for CBCT for detecting ligament and cartilage defects [17, 25]. Furthermore, flat-panel CT and C-arm CBCT use existing angiography devices equipped with flat-panel detectors to acquire CBCT images [24]. However, to our knowledge, the accuracy of these techniques for diagnosing SLL tears has not been reported.

This study aims to answer the following questions: (1) What is the diagnostic accuracy of CBCT and how does it relate to the accuracy of multislice CT arthrography and conventional arthrography in diagnosing scapholunate ligament tears? (2) What is the estimated magnitude of skin radiation doses of each method?

Patients and Methods

Patients

We performed a secondary analysis of the patient cohort as described by the “Accuracy of simple plain radiographic signs and measures to diagnose acute scapholunate ligament injuries of the wrist” (ACCORDS) study (Current Controlled Trials ISRCT N57744239). That study investigated the diagnostic accuracy of common radiological findings on plain radiographs for diagnosing SLL tears. The authors found that an enlarged SL distance on Stecher’s projection was the most accurate index and that plain radiographs are a valuable tool in the diagnostic work-up for suspected SLL tears. Details of the protocol and methods were reported in our previous report [10]. In summary, 72 male and female patients of at least 18 years who were treated for a traumatic wrist injury and suspected SLL tear between March 2008 and April 2011 at a Level I trauma center with a dedicated hand surgery unit were prospectively enrolled. Patients were eligible if they had been scheduled to undergo wrist arthroscopy because of continuing wrist pain for 3 weeks. Patients with chronic wrist pain, rheumatoid arthritis or related diseases; previous injuries, or surgeries of the same hand or wrist; and pregnant or breastfeeding women were excluded from the study. Of 160 eligible patients, 89 were excluded; 28 because their radiographs were taken at an outside institution, 42 refused arthroscopy, 18 refused trial participation, and one patient did not undergo arthrography. This was a secondary analysis of prospectively collected data to compare diagnostic accuracies of conventional, MSCT, and CBCT arthrography. One of 72 patients was excluded from the secondary analysis because of a fracture of the triquetral bone as possible cause for pain on ambulatory radiographs.

Before arthroscopy, the first 36 patients included in the study cohort received MSCT arthrography. The remaining 35 patients were diagnosed with CBCT arthrography, forming two consecutive groups with similar baseline profiles.

Demographics

Seventy-one patients were included in this study. The first 36 patients were diagnosed with conventional arthrography and MSCT arthrography. The remaining 35 patients received a diagnosis after undergoing conventional arthrography and flat-panel CBCT arthrography before surgery. The independent reference test, wrist arthroscopy, was performed in all 71 patients after MSCT and CBCT arthrography. There were no dropouts after acquisition of the designated imaging technique. The mean patient age was 41 years, and most patients in both groups were men. The mean time period between image acquisition and arthroscopy differed between the groups (p < 0.001; Table 1).

Table 1. - Baseline demographics of participants receiving CBCT arthrography and those receiving MSCT arthrography
Variable MSCT arthrography CBCT arthrography Total
Number 36 35 71
Mean ± SD age, years 42 ± 13 41 ± 10 41 ± 12
Sex, % (n)
 Male 58 (21) 66 (23) 62 (44)
Mean ± SD injury time, days 17 ± 15; n = 33b 25 ± 19; n = 35 21 ± 18; n = 68
Injuries of dominant hand 18 25 43
Extraarticular radius fractures 2 2 4
Mean ± SD time to arthroscopy, days 11 ± 8a 5 ± 4.7a 8.5 ± 7.1
ap < 0.05.
bInjury date was not known in three cases.
CBCT = cone-beam CT; MSCT = multislice CT.

The local institutional review board approved the study (Charité University Medical Centre, Berlin, Germany, EA1/210/07), and all patients provided written informed consent.

Arthrography

Arthrography was performed with the patient in the prone position, using sterile precautions in an angiography suite. A two-site protocol was chosen for this study to be able to detect leakage of contrast medium through the SL joint from both directions [22]. A third injection into the distal radioulnar joint was not considered necessary to examine the SL joint [4] because none of the patients presented with ulnar sided wrist pain and suspected injuries of the triangular fibrocartilage complex [23]. During local fluoroscopy-guided anesthesia, a total of approximately 10 mL of xylocaine and Isovist (1:1) (iotrolan; Schering, Berlin, Germany) were injected through a 23-G butterfly needle. The needle was first inserted into the lunate-capitate (midcarpal) joint space, followed by injection of the radioscaphoid joint through a dorsal approach. During the injections, images were acquired using a flat-panel angiography imager (Allura XPER FD 20/20, Philips Medical Systems, Amsterdam, the Netherlands) in standard AP projections and digital subtraction mode (Table 2).

Table 2. - Acquisition parameters and dose-related indices of conventional arthrography
Acquisition parameter Value
Tube voltage, kV 65
Tube current, mAs Variable
Number of projections 1
Magnification Flat-panel detector 15
Image acquisition rate 1 per second
Source image distance, cm 90
Flat detector, cm 15
Filtration 2.5-mm aluminum
Dose area product, cGy x cm2 Variable
Area, cm2 Variable

Flat-panel CBCT Arthrography

Flat-panel CBCT was performed immediately after fluoroscopy without repositioning the patient inside the angiography suite. The same flat-panel angiography imager rotated in 8 seconds for one scan using variable acquisition parameters, which were recorded (Table 3). Postprocessing software (Allura 3D-RA, Philips, Amsterdam, the Netherlands) was used to reconstruct images (Fig. 1A-B).

Table 3. - Acquisition parameters and dose-related indices of flat-panel CBCT arthrography
Acquisition parameter Value
Tube voltage, kV Variable
Milliamperage, mAs Variable
Magnification Flat-panel detector 15
Rotation time, seconds 8
Source image distance, cm 90
Rotation (°) 180
Flat detector, cm 15
Filtration 2.5-mm aluminum
Image reconstruction Sagittal, coronal, axial in 2 mm
Dose area product, cGy x cm2 Variable
CBCT = cone-beam CT.

Fig. 1
Fig. 1:
A-D These images show coronal reconstructions after CBCT arthrography in a patient with (A) a negative reference test and (B) a positive reference test. In comparison, coronal reconstruction after MSCT arthrography in a patient with (C) a negative reference test and (D) a positive reference test.

Multislice CT Arthrography

Patients in the CT arthrography group were transferred to the CT scanner. Images were acquired with the patient in the prone position, using two different 64-row detector scanners (Ingenuity, Philips, Netherlands of Brilliance, Philips, the Netherlands) with two optimized protocols (Table 4). Variable scan parameters (scan length and dose length product) were recorded. Reconstruction was performed with a designated workstation (IntelliSpace Portal Version 5, Philips, Amsterdam, the Netherlands) (Fig. 1C-D).

Table 4. - Acquisition parameters and dose-related indices of MSCT arthrography
Acquisition parameter Value
Tube voltage, kV 61/120a
Tube current, mAs 150/100a
Section thickness, mm 0.625
Collimation 64 mm x 0.625 mm
CT dose index, mGy 2.7/5.9a
Reconstruction matrix Bone kernel
Image reconstruction Sagittal, coronal, axial in 2 mm
Scan length, cm Variable
Dose length product, cGy x cm Variable
aParameters were used for Brilliance 64-row Philips scanner.
MSCT = multislice CT.

Radiographs were stored in a Picture Archiving and Communication System (IntelliSpace, Philips, Amsterdam, the Netherlands) for further processing and evaluation.

Image Interpretation

Images were interpreted before arthroscopies by a board-certified radiologist (SM) with experience in musculoskeletal imaging blinded to the individual patient’s medical history. Conventional angiography was classified as Stadium Types 0 to III depending on the distribution of contrast medium (Stadium Type 0 = no distribution; Stadium Type I = distribution through the SLL only after manipulation after injection; Stadium Type II = distribution through a small defect of the SLL; Stadium Type III = distribution through a large defect of the SLL) and width of the SLL. As suggested by Schimmerl-Metz et al. [30] and Lee et al. [20], the SLL distance in all patients was measured on conventional arthrography images in the middle of the facet of the scaphoid and lunate, and the injury was classified as pathologic when the distance was larger than 3 mm. After MSCT arthrography and flat-panel CBCT arthrography, rupture of the palmar and dorsal portions of the SLL were recorded. A patent SLL was characterized by a slim SL joint with little or no contrast medium inside the joint (Fig. 1A,C) whereas ruptured SLL resulted in enlarged SL joints with contrast medium (Fig. 1B, D). As a result, the SLL was described as intact or injured (Table 5).

Table 5. - Radiologic classification of SLL injuries in MSCT or flat-panel CBCT arthrography
Radiologic stadium type Pathologic findings on CT or CBCT arthrography
0 Smooth, intact
I Elongated, intact
II Thickened or thinned, intact
III Palmar rupture
IV Dorsal rupture
V Complete rupture with residual SLL stumps
VI Complete rupture, wide joint
MSCT = multislice CT; CBCT = cone-beam CT.

Results of the Index Tests (Imaging)

Pathologic widening of the SLL was documented in 29 conventional arthrographies. Spontaneous passage of the contrast agent through the SLL was observed in 34 of 71 (48%) patients.

Palmar ruptures (Stadium Type III) were suspected in four patients who underwent MSCT arthrography. Dorsal ruptures of the SLL (Stadium Type IV) were suspected in four patients who underwent MSCT arthrography and three who underwent CBCT arthrography. Complete ruptures (Stadium Type V) were diagnosed in seven patients who underwent MSCT arthrography and in 11 who underwent CBCT arthrography. Additional widening of the SLL was recorded in two patients who underwent MSCT arthrography and in one who underwent CBCT arthrography. We expected that the SLL would be intact in 23 patients after MSCT arthrography and in 20 after CBCT arthrography (Fig. 2).

Fig. 2
Fig. 2:
This flow diagram shows the patients who were included in and excluded from the study according to the Standards of Reporting Diagnostic Accuracy. Positive index test results were defined as Stadium Types IV to VI with reported sensitivities and specificities. A positive reference test was defined as a Geissler Grade III or IV SLL tear proven by arthroscopy. No relevant SLL tear was categorized as Geissler Grade < III.

Skin Doses

For arthrography and CBCT arthrography, dose area products (DAP), as recorded automatically by angiography consoles, were analyzed together with areas of AP projections. Skin doses were estimated using a backscatter correction factor of 1.4 for a 15-cm flat-panel detector and 2.5-mm aluminum filter in a simplified formula:SD (mSv)=DAPAmean1.410

Estimations of effective doses were based on the tissue weighting factor of the skin of 0.01 [14]. The skin of the hand constitutes only 1% of the body’s surface [9]; therefore, the conversion factor was adapted to 0.0001.

CT dose-index and dose length product were documented by the scanner. The scan length was measured individually. Skin doses were estimated by the software program CT Expo V2.5 (Sascrad, Buchholz, Germany) [33].

Arthroscopy

Wrist arthroscopy was performed by two experienced board-certified hand surgeons. At the time of arthroscopy, surgeons were aware of radiologic assessments. The procedure was performed with the patient under general or regional anesthesia. Traction of 3 kg to 5 kg was applied, and standard 3-4, 4-5, 6R, and midcarpal (midcarpal radial and midcarpal ulnar ) portals were used to insert a 2.4-mm arthroscope with a 30° wide angle lens (Storz, Erlangen, Germany). The SLL was inspected and probed with a hook. Instability was described according to the system of Geissler et al. [11] who classified five severities of SLL tears during arthroscopy. A positive reference test (“relevant SLL tear”) was defined by a Geissler Grade III or IV SLL tear resulting in spontaneous or iatrogenic widening of the SL joint during manipulation.

Results of the Reference Test (Arthroscopy)

The 71 wrist arthroscopies revealed 27 Grade III or IV SLL lesions (38%) according to Geissler’s classification [11]. Thirteen positive reference tests were diagnosed using MSCT arthrography and 14 using CBCT arthrography (Fig. 2). These injuries were treated by open ligament repair and Kirschner wire fixation.

Statistical Analyses

Stadium Types IV to VI SLL tears were defined as a positive test result (that is, relevant or unstable ruptures of the SLL, including the stabilizing dorsal portion) for MSCT arthrography and CBCT arthrography (Table 5). For conventional arthrography, Stadium Types II and III indicated relevant SLL tears. Imaging results were analyzed for diagnostic accuracy compared with the reference test arthroscopy indicating relevant Grade III or IV SLL tears according to Geissler et al.’s classification [11].

Our reporting adhered to the Standards for Reporting of Diagnostic Accuracy statement and recommendations [3]. Descriptive statistics included arithmetic means (mean), median, SDs, minimum and maximum (range), and absolute (n) and relative (%) proportions. Differences between MSCT arthrography and CBCT arthrography groups at baseline in terms of demographics and further parameters that characterized the study population were compared via independent samples t-test for continuous variables. If normal distribution was not expected or in case of ordinal variables the Wilcoxon-Mann-Whitney test was performed.

The outcomes of MSCT arthrography and CBCT arthrography after conventional arthrography compared with that of the reference standard arthroscopy were reported as true positives, false positives, true negatives, and false negatives. The diagnostic accuracy of binary radiologic signs compared with reference test findings were expressed as the sensitivity, specificity, positive predictive value (PPV), and negative predicted value (NPV) with 95% Clopper Pearson [7] confidence intervals. The SPSS software package for Windows, version 25 (IBM, Armonk, NY, USA) was used for all statistical analyses.

For arthrography and CBCT arthrography, the median skin doses are presented. For MSCT arthrography, the median dose length product and scan length were used to calculate two estimated skin doses for both MSCT protocols with a CT dose index of 2.7 mGy and 5.9 mGy.

Results

Diagnostic Accuracies

Diagnostic accuracy was high for all imaging methods with sensitivities ranging between 92% and 100% and specificities ranging between 81% and 96% (Table 6). However, 95% CIs were broad for all three methods, largely due to the small sample sizes. Descriptive comparisons of sensitivity and specificity values might suggest that CBCT arthrography is slightly more accurate and conventional arthrography rather inferior to the other techniques, but overlapping CIs do not allow for the assumption that differences actually exist between the diagnostic groups.

Table 6. - Measures of the diagnostic accuracy of CBCT and MSCT arthrography for diagnosing SLL tears
Index test TP FP TN FN Sensitivity (95% CI) Specificity (95% CI) PPV (95% CI) NPV (95% CI)
CBCT arthrography 14 1 20 0 100% (77 to 100) 95% (76 to 99.9) 93% (68 to 99.8) 100% (83 to 100)
MSCT arthrography 12 1 22 1 92% (64 to 99.8) 96% (78 to 99.9) 92% (64 to 99.8) 96% (78 to 99.9)
Arthrography 26 8 35 1 96% (81 to 99.9) 81% (67 to 92) 77% (59 to 89) 97% (86 to 99.9)
CBCT = cone-beam CT; MSCT = multislice CT; TP = true positive; FP = false positive; TN = true negative; FN = false negative.

Estimated Skin Doses

Estimated median (range) skin doses for CBCT were 3.2 mSv (2.0 to 4.8) and 12.9 mSv for conventional arthrography (4.5 to 24.9). Calculated skin doses of MSCT depended on the CT protocol as described above (Table 4) resulting in skin doses of 0.2 mSv and 12 mSv.

For CBCT, the median (range) tube current was 185 mAs (range 137 mAs to 303 mAs). Median area of exposure was 87.7 cm2 (60.9 to 117.4) and median dose area product was 21.4 cGy x cm2 (12.6 to 33.5 ). For MSCT, the median dose length product was 37.5 mGy*cm (35.9 to 90.1) and the median scan length was 8.3 cm (6 to 13.7). For conventional arthrography, the median tube current was 8 mAs (3 to 18). Mean area of exposure was 84 cm2 with a broad range (37 to 142.5), and dose area products differed accordingly (median 76.8 cGy x cm2, range 31.2 to 177.2).

The effective doses of all diagnostic methods were estimated to be close to 0 mSv (less than 0.0013 mSv).

Discussion

Most imaging techniques for suspected SLL tears are well described in the evidence with information about execution and reliability. CBCT of the wrist has been described to be able to detect SLL injuries [17] but conclusive data about its accuracy is not available. This study aimed to describe the diagnostic accuracy of CBCT and to relate the technique to the accuracy of multislice CT arthrography and conventional arthrography in diagnosing scapholunate ligament tears. For the second part, we estimated radiation skin doses of each method.

Certain limitations of this study must be addressed. First, this study includes data from a single-center study that involved 71 patients without randomization. The first 36 patients to be enrolled were examined using MSCT arthrography and the remaining 35 patients were examined with CBCT arthrography. Since the order of patient enrollment resulted from their consultation of the study site during the study period and thus by chance, selection bias can be ruled out to a great extent. Nevertheless, an analysis of the study population showed the types of SLL injuries differed between the two groups. However, these inhomogeneities were mainly created by random. Furthermore, most baseline characteristics were similar between the groups but the interval between imaging and arthroscopy differed between the groups with shorter intervals observed with CBCT. This difference can be explained by the study team’s increasing comfort with the routine throughout the study, but it must be addressed as a source of confounding with possible effects on diagnostic accuracy of MSCT arthrography.

Second, because of accumulating radiation exposure, an intraindividual comparison of CBCT and MSCT arthrography could not be conducted to ensure perfectly homogenous study groups. Still, prospective enrollment of patients according to well-described criteria is an effective method to minimize inhomogeneities of study groups, reducing the risk of confounding factors. Baseline characteristics of this study revealed that patients in both groups showed comparably distinct wrist injuries; thus, interindividual comparisons should be acceptable after careful cost-benefit analysis.

Third, radiologists were unaware of later surgical findings, and surgeons were aware of images but had to perform arthroscopy in any case. This approach minimized both selection and partial-verification bias. Still, differential classification of the Geissler stage may have occurred during arthroscopy given knowledge of imaging results. However, this conscious decision to risk observer bias presented surgeons with additional information before initiating invasive treatment in cases of instability of the SLL seen during the initial arthroscopy. Moreover, it has to be stressed that the decision to perform arthroscopy was not based on preoperative imaging. Study participation depended on arthroscopy, therefore, all patients who were diagnosed with CBCT or MSCT arthroscopy underwent arthroscopy. This is reflected by a low (38%) overall prevalence of severe SLL injuries in the whole cohort, a percentage which presumably would have been higher if radiological imaging had influenced the decision to perform arthroscopy. Finally, patients were transferred immediately from the angiography suite to the nearby CT scanner. The transfer time from the angiography suite to the CT scanner for MSCT was not assessed by this study. Even though both rooms are usually in proximity in radiology departments, repositioning patients for the MSCT arthrography might have diluted the contrast medium and thus altered the diagnostic performance. For this reason, it must be emphasized that the uncomplicated process of CBCT acquisition just after arthrography in an angiography suit might contribute to its diagnostic performance when compared with MSCT arthrography.

Our study confirms that CBCT arthrography and MSCT arthrography had comparably high sensitivities of 92% to 100% and specificities of 95% to 95.7% (Table 6). The specificity of conventional arthrography alone for diagnosing SLL tears seemed to be slightly lower than for CBCT and MSCT arthrography, while sensitivity was comparably high. Still, broad overlapping CIs did not allow us to draw conclusions about the superiority of one of the tests. Koskinen et al. [17] described an accuracy of 90% to 98% of CBCT arthrography for detecting cartilage abnormalities but a sensitivity of only 58% for detecting SLL tears in a study with MR arthrography as the reference standard. Another in vivo study with six patients reported a sensitivity of 63% and specificity of 87% for diagnosing SLL tears [32]. Just like our presented study, Suojärvi et al. [32] performed reference testing against the current gold standard arthroscopy; however, our reported results reach the high diagnostic accuracy of MSCT arthrography [2, 19, 31] and of CBCT arthrography of cadaveric wrists, with sensitivity and specificity between 82% and 100% [29]. Studies about conventional arthrography reported sensitivities ranging from 20% to 74% [6, 15]. This discrepancy might be attributed to the digital subtraction mode used in the current study, which was not described in previous studies. Although experienced radiologists can detect microlesions of carpal ligaments during conventional arthrography, the clinical relevance of these lesions is not always convincing [16]. Despite the excellent sensitivity of conventional arthrography based on our data, the lower PPV of conventional arthrography favors modern techniques.

The rough estimation of skin dose in this study suggests that implementation of CBCT arthrography immediately after arthrography does not increase effective radiation skin doses compared with MSCT arthrography. Current studies about radiation doses of wrist CBCT described effective radiation doses as low as 3.7 µSv [8, 24, 28, 29, 35], while image quality seems to be high [13, 36]. Other groups acknowledged that MSCT protocols may allow for a reduction in radiation dose [12, 25], which is reflected by the fundamental difference in skin dose estimations in the current study (0.2 mSv versus 12 mSv), depending on the protocol. Further studies including in vivo measurements of effective doses could substantiate these hypotheses. Moreover, because of the high NPV of CBCT and MSCT arthrography, conventional arthrography after fluoroscopy-guided injections of contrast medium could be omitted in future diagnostic pathways, with a further reduction in the total radiation exposure. Nonetheless, the wrist is a radiation-insensitive part of the body, and calculations based on conversion factors that are tailored to radiation-sensitive organs are questionable and highly speculative [14]. Nevertheless, there are recurrent concerns about deterministic cell damage by CT examinations [34]. In young patients, pregnant women, and minors, MR arthrography shows similar accuracy compared with CBCT and MSCT arthrography [21] and should probably be favored as a work-up tool.

Future studies on CBCT arthrography should focus on precise in vivo measurements of effective radiation doses with thermoluminescence dosimeters and investigate whether CBCT imaging in angiography suites is quicker, more precise due to undiluted concentrations of contrast medium in the SL joint, and thus more economical than transferring patients to a CT scanner.

In conclusion, diagnostic performance of flat-panel CBCT arthrography is comparable to MSCT arthrography and conventional arthrography and can be recommended as an accurate technique in diagnosing SLL injuries after wrist trauma. Estimated skin doses are low for CBCT arthrography and adapted MSCT arthrography protocols, but diagnostic processes might be more efficient for CBCT.

Acknowledgments

We thank Jens Birnich MD, and Frank Eichenauer MD, for performing the arthroscopies.

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