Fluoroscopy Orthopedic Assessment, Protocols, and Interpretation

Indications

Indications of Fluoroscopy in Orthopedics

Ionizing radiation is routinely used in diagnosis, during daycare procedures, and in trauma and cold orthopedic surgery to facilitate preoperative planning and intra-operative evaluation. The following are examples of uses of fluoroscopy in regular orthopedic practice:

Diagnostic Fluoroscopy

• Joint assessment: To see for joint degeneration and deformity
• Arthrography: Joint is assessed after injection of radio-opaque contrast to assess for stability, impingement, and congruent reduction in pediatric hips[3]
• Spinal stability assessment in cervical spine injuries
• Guidance for percutaneous biopsy of the diseased vertebra

Daycare Procedures

• Guidance for diagnostic and therapeutic injections into various joints for patients with adhesive capsulitis, synovitis, and osteoarthritis
• Guidance for accurate placement of intra-articular contrast for computed tomography (CT) or magnetic resonance (MR) arthrograms
• Facet joint injections
• Spinal nerve root blocks and medial branch blocks
• Assessment of the accuracy of closed reduction of joints and fractured bones

Preoperative Assessment and Per-operative Assessment

• Assessment of pre-operative deformity under anesthesia in deformity correction procedures

Trauma Surgery

• Improves the accuracy of osteosynthesis in iliosacral joint and pelvic/acetabular fractures, intramedullary nailing, extra- and intracapsular femoral neck fracture fixation, and physeal injuries[4][5][6]
• Guidance of pedicle screw placement in spinal surgery
• Percutaneous vertebroplasty

Equipment

Knowledge of the equipment used in fluoroscopy is mandatory to understand the manipulation of X-rays for safe and sharp imaging that can be used for diagnostic and therapeutic purposes. The basic equipment necessary to generate X-rays include:[7]

• X-ray generator and X-ray tube: A high voltage generator and X-ray tube are used to generate X-radiation. Electrons are emitted by heating from the negatively charged cathode, and they are accelerated towards the positively charged tungsten anode by the electric field between the cathode and anode. The spectrum of X-ray photons (bremsstrahlung) is generated when these high-energy electrons are slowed down in the anode. The radiation output can be pulsed or continuous waves as necessary.

• Beam filters: Aluminum or copper filters are used to filter the low-energy X-ray photons from the beam. These low-energy X-ray photons are absorbed in shallow depths and hence do not contribute to the image quality. If they are not filtered, they contribute to the Entrance Surface Dosage and increase the effective radiation dosage given to patients. The selection of an appropriate filter is a balance between the quality of the image and the absorbed dose of the patient. As the photons pass through filters, the average photon energies are higher than the unfiltered spectra. The radiation penetrates easily, reducing the average dose needed to achieve a good image, but the image contrast may be reduced, so a compromise is to be reached.

• Collimator: X-rays are emitted in all directions from the X-ray tube. Collimators are used to limit the X-ray field to a particular area and minimize spillover radiation out of the field of view. Unnecessarily large X-ray fields have two major disadvantages: 1) increased patient dose and 2) reduced image quality. Therefore, two sets of separately adjustable shutters are attached to the X-ray tube to limit the field. To help alignment, a light is used to form a field projecting an image of the X-ray field on the patient. 

• Patient table: The table must be strong enough to support the patient but absorb less radiation to minimize over-exposure to obtain an adequate image.

• Grid plate: Anti scatter grids are common components of fluoroscopy and are used in procedures with high scatter. They consist of absorbing lead strips separated by transparent materials like paper. They minimize scatter of radiation and can be detached based on the requirement of the procedure.

• Image intensifier: The image intensifier is an important component that converts the intensity of the remnant ray beam into an image suitable for video capture or display on the monitor. Image intensifiers electronically amplify electron optics to obtain a higher quality image at modest dose radiation. In recent years, the image intensifier with video capture has been replaced by flat-panel receptors. These are physically compact, flexible, without image distortion, and the entrance dose is proportional to the field of view.

• Television and recording system: High-quality displays are required for the investigator to appreciate fine details and subtle contrast differences. Usually, flat-panel LCDs with high contrast ratios are calibrated to achieve the widest range of grey levels possible.

Preparation

Fluoroscopy is associated with harmful radiation exposure and hence, requires the patient and staff to be well informed of the impending risks associated with it. In addition, the surgeon should be aware of the basic physics for effective minimization of the radiation dose.

Pre-procedural Care

Informed consent must be obtained regarding the radiation exposure.[8] The physician must be well-informed of the patient's allergic history. Renal profiling is required if using contrast enhancement. Pregnancy must be ruled out in females of reproductive age. The sterility of C-arm surfaces must be ensured if there is an intraoperative use.

Technique or Treatment

Obtaining optimum diagnostic quality image is critical while decreasing patient and surgeon dosage during the procedure. We outline some techniques to limit the radiation exposure and scatter, and at the same time, obtain a good image.

The primary beam is the main source of radiation to the patient, whereas the scatter is the source of exposure to the surgeon and operator. Fluoroscopy systems contain variables that regulate the amount of radiation and adjust image quality. For example, the tube voltage is adjusted in kilovolts (kV), the tube current in milliampere, and the pulse duration in milliseconds. A higher kilovolt setting will allow lower current (milliampere) delivery and hence lower radiation exposure. Hence, the equipment includes a variety of options for specific procedures.

The intensifier must be as close to the patient as feasible. This prevents the beam from dispersing and reduces the radiation required for a sharp image. Removal of the anti-scatter grid decreases the total radiation dose but with a slight increase in the amount of radiation scatter. A balance must be attained between the total dosage and the amount of scatter. Pulsed fluoroscopy reduces fluoroscopy time by 76% and radiation dose by 64% compared with continuous fluoroscopy. Decreasing the frame rate further decreases the effective radiation. Collimation must be used whenever feasible.[9] A reduced field of view (FOV) decreases scatter and decreases the exposure of the patient to unwanted parts.

Magnification increases the radiation dose as well as the scatter. The need for magnification is limited by digital zooming and the use of large displays. An increase of scattered radiation is seen when the gantry position is more than 30 degrees in left or right anterior oblique angulations or 15 degrees in cranial angulation. Additional exposure can be due to incorrect coordination between radiographers and surgeons due to non-standard means of communication. Effective methods of communication with accurate terminology must be developed between the surgical team and C-arm technicians.[10]

Joint Injections Under Fluoroscopic Guidance

All joint injections are carried out under strict aseptic precautions and require appropriate draping and preparation. Proper patient positioning before the procedure ensures safe and efficient access to the joint as well as patient comfort. A radio-opaque object is placed on the skin over the target joint to mark the skin entry. Sterile preparation is performed. Local anesthetic is injected into the overlying skin and tract (e.g., 2% lidocaine). The appropriate length and gauge needle is chosen and is advanced into the joint with intermittent fluoroscopic guidance.[11] 

Imaging provides a visual reference, but it is necessary to develop a tactile sense of the needle encountering different tissues. The intra-articular position of the needle is confirmed either by air arthrogram, which shows an intra-articular air ring, or by saline distension of the joint. Needle placement is further confirmed when the contrast medium can be injected with little resistance. It flows into the joint recesses rather than clustering around the needle tip if the needle is intra-articular. For diagnostic injections, an iodinated contrast medium is used. Therapeutic injections include steroids such as triamcinolone, hyaluronic acid, platelet-rich plasma, etc.

A summary of commonly used approaches to joint injections is given below:

Considerations in Individual Joints

Shoulder

The shoulder joint can be approached anteriorly or posteriorly. Anterior approaches are the most commonly used shoulder approaches.[12] Anteriorly the Schneider approach and rotator interval approach can be used. The patient is supine, and the shoulder is positioned in an anteroposterior view. The arm is held in external rotation with a weight in hand. 

In the rotator interval approach, the target is the upper medial quadrant of the humeral head. The coracoid process is avoided in this position. The needle enters the space between the supraspinatus and subscapularis muscles. The external rotation draws the biceps tendon out of the needle path. It is a shorter distance from the skin and avoids damage to other structures. An unintentional bursal injection is a common problem with this method.[13]

In the Schneider approach, the needle enters the junction of the middle and inferior thirds of the medial humeral head. This may be painful as the needle enters through the subscapularis muscle and risks damaging the labrum. A 22-gauge needle is inserted until it contacts the bone and is slightly withdrawn. The flow of contrast medium and opacification of the joint space and the subcoracoid recess confirm intra-articular positioning. For the posterior approach, the patient can be placed either in a prone position with the arm in a neutral position or a sitting position. In the prone position, the shoulder is elevated with a triangular foam pad placed under the torso. The needle is advanced into the glenohumeral joint through the infraspinatus between the free edge of the posterior labrum and the hypoechoic articular cartilage of the posterior humeral head. With this technique, injury to neurovascular bundles, the suprascapular nerve, and the circumflex scapular vessels may occur if the needle is placed too medially.[14]

Elbow

The patient is either prone with arms hanging or seated with the arm in 90-90 over a radiolucent table.[15] The hand is supinated with the thumb up to open the joint. The radiocapitellar joint is positioned parallel to the beam. For the trans-triceps approach, the elbow is flexed, and a point is marked immediately above and lateral to the olecranon. The needle is advanced until it comes into contact with the olecranon fossa of the humerus. The advantage of this approach is that it decreases the likelihood of contrast leakage in the lateral aspect of the joint, thus avoiding a diagnostic dilemma with subsequent CT or MRI, especially when injury to the lateral elbow soft tissue is suspected.

Wrist 

Injection into the radiocarpal joint is performed to evaluate the triangular fibrocartilage complex and intrinsic ligaments for complete tears. The patient lies prone on the table or sits on a stool with the palm facing down on the table. A dorsal approach is used for all wrist compartments. To improve the profile, a soft towel is placed beneath the wrist to maintain passive wrist flexion.[16] Osseous overlap can be corrected by a slight craniocaudal tilt of the fluoroscope. Ulnar deviation opens the joint on the radial side, the more common site of injection. For radial-side injection, the needle is advanced to the proximal cortex of the scaphoid, ulnar to the tubercle. An ulnar-side injection of the radiocarpal joint is performed by directing the needle to the proximal edge of the triquetrum, adjacent to the pisiform. For injection into the distal radioulnar joint, the radial margin of the distal ulna is targeted just proximal to the physeal scar.

The mid-carpal compartment injection is done at the confluence of the triquetrum, lunate, capitate, and hamate. This space may communicate with the common carpometacarpal joint but not with the radio-carpal joint.

Hip

The hip capsule must be pierced on the anterolateral surface of the femoral head or neck between the acetabular rim and the intertrochanteric line. The patient is supine, and the lower extremity is internally rotated 10 to 15 degrees.[17] To avoid the neurovascular bundle and iliopsoas tendon, the lateral aspect of the femoral head-neck junction is targeted. The tip of the greater trochanter and the anterior superior iliac spine (ASIS) is marked, and a line is drawn between them. At the junction between the upper third and lower two-thirds at the anterior border of the gluteus medius is the needle entry point with a posterior tilt of 30 degrees. The needle is inserted till it touches the bone; if it does not touch the bone, the needle is reinserted with a lesser angle. The needle placement is confirmed by air arthrogram or saline injection.

Fluoroscopic Arthrography in DDH

Hip arthrography is a dynamic study of the hip joint. It is performed by injecting a radiopaque dye into the hip joint and carrying out a fluoroscopic examination with the patient under anesthesia and is usually performed in conjunction with a closed reduction. Arthrography helps in determining the underlying cartilaginous profile and also the dynamic stability of the hip. Arthrography performed in combination with a closed reduction can assess the adequacy of the reduction. An increased medial joint space, demonstrated by medial pooling of the dye and a rounded or interposing limbus, is indicative of poor results.[18]

Fluoroscopy in Trauma

The anatomical reconstruction of joint surfaces, limb alignment, and rotation orientation are crucial in fracture fixation to achieve optimum function and range of motion. With continuing advancements in implants and surgical techniques, high-resolution intra-operative imaging has become imperative in trauma surgery. Without the real-time visualization of the anatomy and the position of implants in relation to the bone and evaluation of the reconstruction of joint surfaces and bony alignment, the rapid evolution of minimally invasive surgery would not have been possible. Intra-operative fluoroscopy aids in continuously controlling these parameters while doing fracture fixation.[19] For example, the percutaneous placement of pedicle screws in spine surgery, tunneling of implants in the tibial or femoral metaphyseal fractures with specially designed plates, calcaneus osteosyntheses with slit-in plates, and closed reduction and intramedullary nailing of femur/tibia shaft fractures, require intra-operative fluoroscopy guidance.[20]

Even with complete access to the surgical view in conventional total hip arthroplasty, intra-operative images are performed to confirm the acetabular cup's alignment and orientation and rule out fractures of the acetabulum or the femoral shaft. Standards for axis alignments and patient positioning exist in radiology departments, but the intra-operative settings vary due to the positioning requirement of the surgical procedure as well as patient-related factors such as obesity or limitations in joint movement.[21][22] The surgeon must ensure the correct position of the operational field and acquire the standard views of the region with the C-arm.[23][24] Knowledge of standard position on the operating table ensures decreased exposure and precise imaging.

The Distal Radius

The joint surface is tilted volar by 5 to 10 degrees in the AP view.[24] When controlling the volar plate position and reduction, the elbow has to be elevated to the extent of 5 degrees to 10 degrees to balance out this anatomical tilt. It is possible to accurately assess reduction, implant positioning, and screw placement in this position. In the lateral view, where the joint line is tilted 23 to 30 degrees, the hand is similarly elevated to this level for proper joint visualization.

The Proximal Humerus

The patient is positioned in the beach-chair position in osteosynthesis of the proximal humerus. Hence, the upper arm is already tilted towards the floor. This is evened out by tilting the C-arm so that the beam is perpendicular to the humeral shaft axis. The standard views are defined as an AP view with a maximum extension of the greater tubercle and a lateral view with 90 degrees external rotation of the humerus. The spherical shape of the humeral head must be considered when assessing screw length. Dynamic fluoroscopy while rotating the arm might be helpful to assess the screw length.

The Proximal Femur

A traction table is usually used for fracture reduction, and the contralateral leg is elevated in a leg holder.[21] The C-arm is placed perpendicular to the floor for an ap view and obliquely between the legs for an axial view. When adjusting the axial view, the anteversion of the femoral neck of 10 to 15 degrees is compensated by tilting the C-arm.

The Ankle Joint

While positioning the C-arm for osteosynthesis of the ankle joint, the hazard of collision of the device with the patient is less. The lower leg is internally rotated by 15 to 20 degrees to obtain the Mortise view. In this view, the medial and lateral joint space should be equal, and no double contour of the margins of the talus should be seen. For the lateral view, the condyles of the talus must be exactly above each other, and the tibiotalar joint space must be completely visible.[25]

Spinal Fluoroscopy- Facet Joint Injections

Facet joints are one of the most common causes of low back pain (LBP). Hence, facet joint interventions like intraarticular steroid injections and medial branch blocks are commonly performed.

Anatomical Considerations

Synovial facet joints are simple in the cervical and thoracic regions but very complex in the lumbar region. Engel and Bogduk described three types of lumbar intracapsular structures. The first structure includes adipose tissue pads covered by the synovial membrane. The second is fibro-adipose meniscoid tissue which is also covered by the synovial membrane and projects out from the joint capsule at the superior and inferior poles. The third is the connective tissue rims located along the anterior and posterior margins and are folds of the fibrous layer of the joint capsule. Each lumbar facet joint has space that can accommodate 1 to 1.5 ml of fluid.[26]

Indications For Facet Joint Injections

1. Average pain levels >5 on a scale of 0 to 10
2. Intermittent or continuous LBP causing functional disability
3. Somatic or non-radicular LBP and lower extremity pain lasting at least three months
4. Failed conservative treatment
5. Lack of evidence of either discogenic or sacroiliac joint pain or radiculitis
6. Contraindications or inability to undergo physical therapy or inability to tolerate oral medications. 

The Technique of Localization of Facet Joint Under the Fluoroscope

The fluoroscopic-guided technique of lumbar facet injection is considered the most reliable. The patient is placed prone on the procedure table with the fluoroscope over the target level. A pillow is placed under the abdomen to reduce lumbar curvature, allowing easier entry into the joint. It also allows for the patient's head and face to be supported comfortably. A baseline anteroposterior (AP) fluoroscopic view of the lumbar spine should be obtained, and the C-arm is oriented. The patient is turned slowly so that the side to be injected is off the table till the facet joint is seen in profile and the position is secured. Alternatively, the tube may be tilted. The posterior aspect of the facet joint is further from the midline than the anterior.[27]

During posteroanterior(PA) fluoroscopy, first, the posterior portion of the joint is seen. Over-rotation has to be avoided as it brings the anterior portion of the joint into the profile. This makes needle placement into the joint impossible. The upper lumbar spine requires an obliquity of 30 degrees, while the lower lumbar spine requires up to 60 degrees obliquity. Once localized, the needle is directed vertically into the center of the joint space. Alternatively, the inferior recess is targeted since it lies posteriorly, has no direct neural relations, and is relatively capacious, hence easy to enter.

Clinical Significance

Fluoroscopy in Pregnancy

Trauma affects up to 8% of pregnancies; the cause varies from motor vehicle accidents to self-fall and is one of the leading causes of maternal morbidity and mortality. The National Council on Radiation Protection and Measurements and the International Commission on Radiological Protection have set a recommended maximum exposure of a fetus to radiation at 5 cGy. At this level of exposure, the assumed risk to the developing embryo is less than the spontaneous risks present during the development of any human fetus. It is observed that exposure of the maternal thyroid gland to diagnostic radiation was associated with a slight decrease in birth weight.[28]

Guidelines for imaging in pregnancy:

1. Women must be counseled that X-ray exposure from a single diagnostic procedure does not result in harmful fetal effects.
2. Specifically, exposure to less than 5 rad is not associated with increased fetal anomalies or pregnancy loss.
3. Concern about high-dose ionizing radiation exposure should not prevent medically indicated diagnostic procedures from being performed in pregnancy.
4. Imaging procedures not associated with ionizing radiation should be considered instead of X-rays when appropriate.
5. The use of radioactive isotopes of iodine is contraindicated during pregnancy.
6. Radiopaque and paramagnetic contrast agents are unlikely to cause harm and may be of diagnostic benefit.

Recent Advances

The continuing advances in imaging have resulted in a variety of components like image intensifiers which automatically adjust the sharpness and contrast of an image irrespective of the exposure, view of the latest image to provide a continuum in pulsed fluoroscopy, and real-time radiation dose display to keep the surgeon aware of the exposure.[29]

Flat-panel detectors are a revolution in medical imaging as they provide high image quality and dose reduction compared with a standard C-arm. Mobile flat-panel C-arms reduce intra-operative radiation dose, have an increased field of view of images due to a larger detector diameter, and give better soft-tissue resolution. Compared with standard C-arms, the source to image distance increases, and the surgeon has a larger workspace with decreased scatter.

Intra-operative three-dimensional (3D) imaging can ensure adequate fracture reduction in situations where the joint surface is not completely visible in 2D imaging, especially in joints having a concave configuration, such as the acetabulum or in joints irregularly shaped bones like the calcaneus. Cone-beam CT is a 3D data set that can be used with a flat-panel detector. It acquires a large number of images that are converted to 3D images by computational methods.[30] Intra-operative 3D imaging with mobile C-arms is an important adjunct in the reconstruction of complex joint fractures. Control of fracture reduction and implant positioning with high image quality reduces the need for secondary revisions in trauma surgeries.[31] O-arm, the intraoperative navigation system significantly reduces the malposition rate of the pedicle screws and improves ilio-sacral screw placement.

Enhancing Healthcare Team Outcomes

A diagnostic or therapeutic intervention involving fluoroscopy involves a team of professionals ranging from the surgeon to the anesthetist, the radiographer, and the theatre staff. Interprofessional communication is essential to improve the efficient use of fluoroscopy with decreased exposure to all team members. Proper coordination with physicians, nurses, and X-ray technicians will lead to less radiation and shorter surgeries. Evidence shows a common language between surgeon and operator, and knowledge of terms during C-arm usage can go a long way in decreasing radiation exposure and surgery time. 

Diagnostic and intraoperative fluoroscopy in special situations such as in pregnancy and young children should utilize an interdisciplinary team to ensure safety from ionizing radiation to the mother and the fetus. Fluoroscopy in acute polytrauma patients can be challenging as it is difficult to maintain adequate positioning. Pre-planning with the intensivists and the radiology team helps better interpret images, decreases surgical time, and minimizes radiation exposure.

Nursing, Allied Health, and Interprofessional Team Interventions

Team Safety Protocol

Natural radiation exposure up to a dose of 2 to 200 mSv per year is presently based on the geographical area.[32] The average dose due to radiation exposure from medical devices is about 2 mSv. The maximum permissible dose (MPD) is the upper limit of the radiation dose that one can receive without the risk of significant side effects. The annual whole-body dose limit for physicians is 50 mSv. C-arms pose a potential threat to the patient as well as to the staff in the operating room. As low as reasonably achievable (ALARA) suggests that even a small dose of diagnostic radiation must be avoided if it has no direct benefit in the procedure.[33] This is achieved by using three basic protective measures in radiation safety: time, distance, and shielding.

The surgeons have to weigh the hazard to benefit ratio due to the radiation and monitor the individual dose.[34] The use of a personal dosimeter within the radiation control zone of 4 meters is compulsory in many countries. Lead gowns with thyroid protection must be worn by all staff in the operating room. The lead gowns with thyroid protection need to be checked regularly to ensure intact material. The patient must be protected with lead mats as long as they do not hinder the surgical field. The surgeon's knowledge of the settings of the device and its application decreases the dosage of exposed radiation. Pulsed fluoroscopy and single images are commonly used instead of continuous fluoroscopy as it decreases the radiation. Dynamic fluoroscopy should be used only if necessary and for a very short duration.[34]

The surgeon needs to keep his hands out of the beam effectively. By making the field of view smaller and using a split diaphragm, scattered radiation can be reduced, thereby decreasing the exposure to the surgeon's hand. Distance is the most effective method to reduce exposure as exposure is decreased exponentially with distance. For all personnel with the risk of regular exposure to ionizing radiation, the use of dosimeters must be made mandatory. Real-time dosimeters allow for direct visualization of the radiation dose, which will help increase awareness regarding radiation hazards in personnel.