C-arms are mobile, C-shaped X-ray units that allow dynamic imaging for a wide range of procedures in outpatient clinics, procedure suites, operating rooms, and even emergency departments. Their uses include: fracture reduction and fixation, hardware placement, joint injections, and other image-guided interventional procedures. They are available in a variety of sizes including a mini C-arm that is specifically designed for imaging smaller body parts such as the hands and wrists.

Mini C-arms in emergency departments (ED) are not commonplace but when available they are often in trauma centers and most commonly utilized by orthopedic surgeons. Literature on the use of mini C-arms in the ED has mostly been for distal forearm fractures, where they have been shown to facilitate safe and effective fracture reductions and reduce the need for repeat formal radiographs during reductions [1-4]. Although mini C-arms are not typically used by emergency medicine (EM) physicians, familiarity with this imaging modality may be a valuable skill, especially for trainees rotating on the orthopedics service.

This article reviews mini C-arm anatomy, fluoroscopic principles, radiation safety and equipment, and illustrates its application in a case of a distal radius fracture.

Mini C-arm structure

The C-arm’s name comes from the C-shape that connects the X-ray source on one side to the image detector on the other, allowing rotation around the patient (Figure 1).

Figure 1. Anatomy of a mini c-arm machine

How it works

1. The operator controls acquisition of images through a foot pedal (allowing single images or live imaging).
2. X-rays are generated through a tube which diverge out in a cone-like projection and pass through structures such as bone, which absorb X-rays differently based on characteristics like density and tissue thickness.
3. After passing through structures, X-rays are absorbed on the opposite side by an image detector.
4. The image detector converts this radiation to light, which is then processed by a computer to create a digital image visible on the monitor.

The C-arm has a rotation mechanism and an adjustable arm with various joints that allow movements in multiple planes. It allows orbital rotation, vertical and lateral movements, tilt, or swivel (Figure 2).

Figure 2: Maneuverability of a mini c-arm

How to set up a mini C-arm

1. Plug in the device to a power source
2. Turn on the switch to power on the device
3. Use the monitor and/or keyboard to set up a study (some monitors are touch screen)
4. Enter patient information
   • Find and select the option to begin study
   • Adjust the C-arm to the desired position
5. Position the body part of interest flat and center on the detector
6. Place the foot pedal in an easy to reach position
7. Ensure that everyone in the room has radioprotective equipment (see radiation safety and equipment below)
8. Step on the foot pedal to obtain an image or activate live imaging (review individual devices manuals to determine function of pedals)
9. Save desired images

How to interpret images on a mini C-arm

Interpreting an image with a mini C-arm requires familiarity with fundamental radiographic principles related to image projection.

Laterality:

Unlike formal radiographs which include left or right markers, orientation of fluoroscopic images on a mini C-arm will be displayed based on the orientation of the image detector.

To illustrate this, in Figure 3, the right hand is rested with the palm resting directly on the image detector. On the monitor, the image appears as if the operator were directly looking at the hand, with the thumb on the left-most side. Most C-arms allow inversion of images on the monitor if another orientation is preferred.

Note: The X-ray beam travels from dorsal (posterior) to palmar (anterior), corresponding to a posteroanterior (PA) view.

Figure 3: Illustrated mini C-arm image of hand in posteroanterior view

Magnification and depth

The relative distance between the X-ray source, the object, and the image detector affects image magnification and apparent depth of structures. To put it simply: the closer an object is to an X-ray source, the more magnified it appears; the closer an object is to the image detector, the less magnified it appears. This is analogous to the size of a shadow formed when a finger is moved closer to a light source. This principle affects image interpretation and highlights the importance of standardized positioning when obtaining images [5].

To illustrate this effect, we can consider the lateral view of the hand. Starting from the position in Figure 3, the hand can be supinated so that the ulnar aspect rests on the detector producing a lateral view (Figure 4). In this orientation, the thumb and second metacarpal may appear slightly magnified because they are now closer to the X-ray source. This also applies to the relative appearance of the radius and ulna.

Figure 4: Illustrated mini C-arm image of hand in lateral view

As an analogy, imagine using a mini C-arm to image a rubber duck. If the duck is placed flat on the detector, the part closest to the X-ray source—the head—will appear slightly magnified. If the duck has an abnormally long neck that brings the head closer to the X-ray source, this magnification increases further (Figure 5). This same concept explains the apparent difference in heart size between posteroanterior (PA) and anteroposterior (AP) chest radiographs.

Figure 5: Illustrated mini C-arm image of rubber duck

This concept is important when using the mini C-arm for fracture reduction. You often want to capture as much of the entire body part as possible in the X-ray image while decreasing magnification, which means you will position the extremity directly against the image detector as far away as possible from the X-ray source while performing a reduction.

Radiation safety and protection

C-arms, like standard X-rays, emit ionizing radiation. Although most of the radiation is directed at patients, interactions between X-rays and surrounding matter produce scatter radiation, which is the primary source of radiation exposure to personnel. Repeated exposure is associated with increased lifetime risk of cancer, cataracts, thyroid issues including cancer, and fertility issues [6].

Radiation dose is measured in various units, including millirem (mrem) [5]. For context:

• Average background radiation exposure (due to cosmic rays, radioactive elements in earth’s crust, etc) to U.S. residents is on average 310 mrem/year or <1 mrem/day
• A cross country flight from NY to LA is ~5 mrem
• A chest x-ray is ~10 mrem
• A CT abdomen/pelvis is ~1,000 mrem

A benefit of the mini C-arm is that it emits less radiation than a standard-sized C-arm [8, 9]. In pediatric studies of distal forearm reductions performed with mini C-arm fluoroscopy, the estimated radiation exposure per case ranged from approximately 30 to 80 mrem, with lower exposures observed when trainees had completed radiation safety training, likely reflecting behavioral changes including fewer image acquisitions and shorter fluoroscopy activation [10]. Thus image acquisition should be intentional to reduce unnecessary radiation to both patients and personnel.

Radiation exposure follows the inverse square law, where if you double your distance from the X-ray source, you reduce exposure by one-fourth the original intensity. When possible, standing further away (at least 1 meter) from the X-ray source is recommended to reduce exposure (Figure 6) [5].

Additionally, use of radiation protective equipment such as lead aprons, thyroid shields, and leaded glasses, can significantly attenuate scatter radiation [8]. See Figure 7.

Figure 6: Inverse square law of radiation

Figure 7: Radiation protective equipment

Bottom line:

• Image only when necessary
• Stand at least 1 meter away from the X-ray source when feasible
• Utilize appropriate radiation protective equipment
• By adhering to these principles, radiation exposure can be minimized when using a mini C-arm

Case: Distal radius fracture reduction with mini C-arm fluoroscopy

You are rotating through orthopedics and holding the consult pager. A 30-year-old patient presents to the ED after falling on their right outstretched hand, resulting in a deformity to the right distal forearm.

On examination, the skin appears intact and distal neurovascular exam is normal. Formal three-view wrist radiographs show an impacted, dorsally angulated transverse distal radius fracture without intra-articular extension.

Your senior recommends a reduction under fluoroscopy with your assistance. You perform a hematoma block, apply finger traps, and suspend the extremity vertically under ~10 lbs of traction. While the arm remains in traction, you bring the mini C-arm into the room and apply lead shields.

Obtaining images:

1. Position the C-arm so that the image detector is near the affected arm. For a reduction, you should obtain PA and lateral views (oblique views are excluded in this example for simplicity).
2. To obtain a PA view, ensure the palmar side of the distal forearm is against the detector (Figure 8).
3. To obtain a lateral view, place the ulnar aspect of the distal forearm against the detector (Figure 9).

Note: Since the forearm is suspended in traction, sometimes you will need to rotate the mini C-arm around the extremity to obtain the correct alignment, instead of manipulating the arm.

Figure 8: Illustrated mini C-arm image of a distal radius fracture in posteroanterior view

Figure 9: Illustrated mini C-arm image of a distal radius fracture in lateral view

Important radiographic measurements:

In these views, assess radiographic parameters such as radial height, radial inclination, ulnar variance, and volar versus dorsal angulation angles (Supplemental Figures 1 and 2).

Post-reduction imaging:

Once the fracture appears appropriately reduced, obtain repeat C-arm images prior to applying a splint (Figure 10). After splint placement, obtain another set of images to confirm the reduction was maintained. Finally, order a formal post-reduction three-view wrist radiograph.

Figure 10: Illustrated mini C-arm images of a post-reduction distal radius fracture

Restrictions on the use of fluoroscopy

Before using a mini C-arm, clinicians should confirm that they are appropriately credentialed and permitted to operate the device under local or state regulations, as fluoroscopy use laws differ across states and countries. Alternatively, a fluoroscopy credentialed radiation technologist can operate the device while the clinician performs the reduction.

Conclusions

Mini C-arms are a useful imaging modality available in select emergency departments. With an understanding of proper device operation and radiographic concepts such as image projection and radiation safety, the mini C-arm can be an effective tool to facilitate procedures such as distal radius fracture reduction. Although ultrasound remains the primary imaging modality for many procedures in the emergency department, the mini C-arm may potentially be a useful adjunct in other ED procedures such as joint aspirations and could warrant future exploration.

References

1. Lee SM, Orlinsky M, Chan LS. Safety and effectiveness of portable fluoroscopy in the emergency department for the management of distal extremity fractures. Ann Emerg Med. 1994;24(4):725-730. doi:10.1016/S0196-0644(94)70284-5. PMID: 7998561
2. Lee MC, Stone NE 3rd, Ritting AW, et al. Mini-C-arm fluoroscopy for emergency-department reduction of pediatric forearm fractures. J Bone Joint Surg Am. 2011;93(15):1442-1447. doi:10.2106/JBJS.J.01052. PMID 21915550 
3. Dailey SK, Miller AR, Kakazu R, Wyrick JD, Stern PJ. The effectiveness of mini-C-arm fluoroscopy for the closed reduction of distal radius fractures in adults: a randomized controlled trial. J Hand Surg Am. 2018;43(10):927-931. doi:10.1016/j.jhsa.2018.02.015. PMID: 29573894
4. Sumko MJ, Hennrikus WL, Slough J, King S. Measurement of radiation exposure when using the mini C-arm in pediatric orthopaedics. J Pediatr Orthop. 2016;36(2):122-125. doi:10.1097/BPO.0000000000000418. PMID: 25730377
5. Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM. The essential physics of medical imaging. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
6. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Ionizing Radiation. Atlanta, GA: US Department of Health and Human Services; 1999. Available from: https://www.ncbi.nlm.nih.gov/books/NBK597577/
7. Centers for Disease Control and Prevention. Radiation Thermometer. Updated January 2, 2024. Accessed December 26, 2025. https://www.cdc.gov/radiation-emergencies/causes/radiation-thermometer.html
8. Giordano BD, Ryder S, Baumhauer JF, DiGiovanni BF. Exposure to direct and scatter radiation with use of mini-C-arm fluoroscopy. J Bone Joint Surg Am. 2007;89(5):948-952. doi:10.2106/JBJS.F.00733. PMID: 17473130
9. Giordano BD, Baumhauer JF, Morgan TL, Rechtine GR. Patient and surgeon radiation exposure: comparison of standard and mini-C-arm fluoroscopy. J Bone Joint Surg Am. 2009;91(2):297-304. doi:10.2106/JBJS.H.00407. PMID: 19181973
10. Gendelberg D, Hennrikus W, Slough J, King S. A radiation safety training program results in reduced radiation exposure for orthopedic residents using the mini C-arm. J Pediatr Orthop. 2015;35(8):e123-e129. doi:10.1097/BPO.0000000000000345. PMID: 26566977