The use of flat-panel detectors to perform CBCT image acquisition has recently revolutionised the field of minimally invasive radio-diagnostics. It is increasingly being used for fractures of the extremities, allowing for multiplanar reconstruction. Although a recent metanalysis has been performed on the diagnostic accuracy of CBCT for scaphoid fractures, our study is the first to evaluate its use in acute carpal and distal radius fractures. An excellent diagnostic accuracy of CBCT (AUC 0.99) was seen for all reported radiocarpal fractures [10, 15, 17, 18], with 93.5% sensitivity and 99.9% specificity. Moreover, our results support the use of CBCT in the diagnosis of scaphoid fractures with a pooled sensitivity and specificity of 87% and 99%, respectively, and an overall AUC of 0.98.
Clinical examination in the diagnosis of scaphoid fracture has a wide range of sensitivity (15–100%) and specificity (13–98%). This substantial variation in diagnostic accuracy suggests clinical suspicion is a poor diagnostic indicator of scaphoid fracture if used in isolation [27]. Radiographs are the initial imaging modality of choice but display a relatively poor diagnostic accuracy with a sensitivity between 66 and 81% for scaphoid fractures, 39% for carpal fractures overall and 58% for wrist fractures. Carpal bones have a more complex geometry making them are harder to analyse compared to long bones on radiographs [18]. Radiographs also have a 20–54% false negative rate soon after injury and offer limited information even after 2–6 weeks post-injury. Moreover, it provides unreliable information about fracture alignment, with up to 30–50% of displaced scaphoid fractures missed [26, 28,29,30]. Thus, the diagnostic value of radiographs in the assessment of radiocarpal fractures is questionable given the varying sensitivity and specificity and poor inter-rater agreement reported by multiple studies [28].
Despite its novelty, there is a very slight difference in inter-rater agreement with CBCT use [18]. Four of the included studies reported substantial or almost perfect inter-rater agreement, as per Landis and Koch agreement scale [31], with excellent confidence as reported by Neubauer et al. [36]. Our analysis demonstrated an almost perfect agreement in the diagnosis of scaphoid fractures using CBCT, with a pooled kappa value of 0.89, irrespective of the radiologist’s experience. In contrast, inter-observer agreement has been shown to be poor for radiographs [24]. This limitation of radiographic assessment is corroborated in the study by Neubauer et al. [19] demonstrating a reduced confidence in reported findings based on radiographs.
In addition to detecting occult fractures, CBCT can aid surgical planning for scaphoid fractures. Grunz et al. [10] showed a change in the management plan for approximately a third of patients based on CBCT findings. Three undetected scaphoid fractures on radiographs underwent surgery based on CBCT findings, whilst five presumed carpal fractures on radiographs were ruled out by CBCT, which would have had unnecessary immobilisation. Similarly, Neubauer et al.’s [19] study reported CBCT imaging resulting in a 15% change in management, with 7% upgraded and 8% downgraded. These findings are comparable to Brink et al. [32] who investigated patients who underwent a single shot MDCT after radiography. In four studies, MRI was performed when there was ongoing clinical concern about occult carpal fractures, which detected additional scaphoid fractures missed on radiography and CBCT scanning [10, 15, 17, 19]. A potential reason for false negative results may be osteopenia, resulting in reduced trabecular and cortical bone thickness.
For scaphoid fractures, conventional computerized tomography (CT) has a sensitivity and specificity of 82% and 96% respectively. CBCT has a comparable diagnostic accuracy to MDCT but with additional benefits [11, 33]. It produces a more detailed image which allows greater visualisation of the area. Spatial resolution which indicates the scanner ability to depict fine detail is an important measure of image quality with regards to bone imaging [14]. CBCT produces sub-millimetre resolution ranging from 0.4 mm to as low as 0.09 mm, whilst standard CT has a spatial resolution of 1–2 mm [34]. Although, to date, no cost–benefit analysis has been performed radiocarpal fractures, Faccioli et al. [35] demonstrated that the introduction of CBCT compared to MDCT in the management of complex finger fractures reduces the time of diagnostic work-up and number of diagnostic procedures, improves quality of life and reduces costs. When trialled in the emergency radiology department, CBCT offered a feasible alternative to MDCT for detection of extremity fractures also increasing patient turnover and reducing radiation exposure [36].
Relative to the annual background radioactivity exposure of 2.4 mSv, and CT effective dose (ED) of 0.03 mSv, CBCT has a very low ED of 0.007 mSv [37]. Grunz et al. [10] used a lower dose for scanning compared to existing literature, with an ED of 4.3 microSv (3.3–5.3), whilst Gibney et al. [15] reported the use of 0.5–1.4 microSv. In comparison, the combined ED for conventional radiography in the assessment for scaphoid injuries has been shown to be up to 2 microSv [38]. Inferentially, CBCT may be performed with an almost comparable ED to radiographs and has an up to 90% lower radiation compared to conventional CT scans [25]. Additionally, it enables the use of lead shielding which is an easy and effective method for further reducing patient exposure to radiation [39]. Lastly, it can be performed with similar positioning of patients for X-ray and thus can be incorporated into a ‘one-stop-shop’ imaging in acute trauma of the extremities [10].
MRI remains the gold standard for wrist fracture diagnoses with a higher sensitivity than CBCT. Nevertheless, our study supports the implementation of CBCT as a reliable examination for the diagnosis of radiocarpal bone fractures, reducing the MRI burden on radiology departments. Diagnosing fractures earlier potentially reduces unnecessary immobilisation, improving cost-effectiveness and reducing patient morbidity.
One of the limitations of CBCT is image acquisition time. The included studies had an acquisition time range of 15–36 s [10, 15, 17,18,19]. Due to potential positional instability, there is an increased risk of motion artefacts [19]. Whilst Borel et al. [18] suggested stabilisation with straps, Grunz et al. [10] observed no motion artefact in 72.8% of patients with a dedicated extremity machine, and a significantly lower proportion in upper limb extremities compared to lower limb [40]. On the other hand, MRI has a considerably longer acquisition time with image post-processing susceptible to movement artefacts [41].
Additionally, CBCT has been shown to be less effective in diagnosing trabecular bone fractures compared to cortical bone fractures, as it cannot detect soft tissue and bony changes related to such injuries [2]. Nonetheless, trabecular fractures are less common and the clinical implication of this is uncertain as there is no clear consensus on their management [14]. Moreover, CBCT has a limited correlation of bone density with Hounsfield units which may augment image artefacts due to metal implants [12]. Lastly, CBCT has a limited field of vision (FoV) which makes it unsuitable for shoulder and hip fracture assessments, and hence is limited to use in extremities only.
There are several limitations to this meta-analysis. The studies included varying imaging protocols and had a lack of a uniform reference standard. Our studies assumed fractures detected on CBCT to be accurate. Moreover, most studies included patients with ongoing clinical suspicion of scaphoid fractures with negative initial radiography, which may affect the true representativeness of the study population thus limiting the conclusions drawn in this review. Only studies in English were included which may introduce further selection bias. Two of the studies included only occult scaphoid fractures. As occult fractures are more diagnostically challenging, the overall sensitivity and specificity of CBCT might be higher than reported in this study. Given the small number of studies in our review, we were unable to estimate heterogeneity. The use of CBCT for distal upper limb fracture diagnosis is a new initiative and many centres do not have access to CBCT. Further studies with a more robust methodology are required to implement CBCT as a low-dose diagnostic modality for upper limb extremity fractures.
Our study has shown that CBCT is superior to radiographs for radiocarpal cortical fractures. Despite its relatively longer acquisition time, CBCT may be helpful in the diagnostic algorithm as a replacement or supplement (depending on resources available) to radiographs and may improve cost-effectiveness when used in the acute setting. With minimal exposure to radiation, it can obviate the need for unnecessary immobilisation and reduce the burden on the number of follow-up MRI scans required.