Musculoskeletal · IR Playbook

CT-Guided Radiofrequency Ablation of Osteoid Osteoma (CT-RFA)

CT-guided radiofrequency ablation places an electrode centrally within the osteoid osteoma nidus and produces focal coagulative necrosis while preserving surrounding bone. It is the established minimally invasive treatment for a symptomatic lesion when prompt definitive therapy is preferred, medical therapy is ineffective or intolerable, or symptoms recur after previous treatment. A 2020 systematic review reported 8.3% primary treatment failure, falling to 3.1% after repeat RFA, with an overall complication rate of 3%.

Learning objectives

• Select patients whose clinical presentation and CT appearance support a diagnosis of symptomatic osteoid osteoma
• Plan a stable osseous trajectory that centers the electrode within the nidus
• Apply the validated RF temperature-time protocol while preventing heat conduction along the access cannula
• Protect neural structures, articular cartilage and skin with displacement, cooling and thermometry when required
• Recognize treatment failure and distinguish it from expected early post-ablation pain

Indications

• Symptomatic osteoid osteoma with concordant clinical and CT findings when prompt definitive pain relief is desired
• Persistent pain or functional limitation despite NSAID therapy
• NSAID intolerance, contraindication or unwillingness to continue prolonged medical therapy
• Recurrent or residual symptomatic osteoid osteoma after previous RFA or surgery
• Accessible lesion for which the entire nidus can be covered while adjacent critical structures can be protected

Absolute contraindications

• Uncorrectable coagulopathy
• Active systemic or access-site infection
• No safe access route and inability to protect an adjacent critical structure
• Lack of informed consent

Relative contraindications

• Diagnostic uncertainty, atypical imaging or concern for infection or malignancy without planned tissue sampling
• Nidus immediately adjacent to a major nerve, spinal cord, articular cartilage or skin without adequate thermal monitoring and protection
• Cardiac implantable electronic device when monopolar RFA is planned
• Pregnancy when CT radiation cannot be justified or adequately minimized
• Anesthesia risk that outweighs the expected benefit

Equipment

• CT scanner with low-dose planning capability; cone-beam CT or navigation may be used when available
• Radiopaque skin grid, sterile preparation set, drapes and local anesthetic such as 1% lidocaine
• 11–14 G insulated bone access cannula or coaxial drill system with compatible stylet, K-wire, drill bit or mallet
• Coaxial bone biopsy trephine or core device when tissue sampling is indicated
• 15–17 G monopolar or bipolar RF electrode with approximately 5–10 mm active tip matched to nidus size
• Compatible RF generator, cables and dispersive grounding pads for monopolar systems
• 20–22 G needles for hydrodissection, joint cooling or thermocouple placement
• Sterile 5% dextrose solution, saline for joint cooling, or carbon dioxide for selected protective dissection according to location
• Temperature probes or thermocouples for vulnerable neural, cutaneous or peri-articular structures
• Ice packs, chilled sterile gauze or external skin cooling for superficial targets
• Standard anesthesia, resuscitation and neurovascular monitoring equipment

Procedure steps

1. Review clinical-imaging concordance and identify the nidus on thin-section CT. Reconsider the diagnosis or obtain tissue if the lesion is atypical, exceeds the expected size, or could represent infection or another tumor.Pearl: The nidus is the ablation target; surrounding sclerosis and MRI edema are reactive findings.
2. Position the patient so the trajectory is short, stable and clear of critical structures. Induce the planned anesthesia, infiltrate the skin and periosteum with local anesthetic, and place dispersive pads away from scars and metal for monopolar RFA.
3. Acquire a limited low-dose CT through the lesion, mark the entry site and confirm the trajectory in multiplanar reconstructions. Measure the distance from the intended active tip to skin, cartilage, nerves, vessels and viscera.Pearl: Use the lowest CT dose that still permits confident nidus and instrument visualization, especially in children.
4. Advance the bone access cannula to the cortex under intermittent CT guidance. Cross dense cortex with a coaxial drill, K-wire system or controlled mallet technique, then advance into the nidus.Pearl: A near-perpendicular cortical entry reduces skiving; make small controlled corrections rather than redirecting forcefully in soft tissue.
5. Before ablation, obtain a coaxial core from the nidus when imaging or clinical features are atypical or when institutional practice requires histology. Preserve the established access for electrode placement.Pearl: A nondiagnostic specimen does not exclude osteoid osteoma when the clinical and CT appearances are classic.
6. If a critical structure is within approximately 10 mm of the predicted ablation zone, use hydrodissection, gas dissection, joint cooling, external skin cooling and temperature monitoring as appropriate. Confirm that the protective separation persists immediately before energy delivery.
7. Advance the RF electrode coaxially so its active tip lies centrally within and is fully surrounded by the nidus. Retract the metallic access cannula sufficiently to expose the active tip and prevent conductive heating along the cannula, then confirm the final position by CT.Pearl: Eccentric active-tip placement is a preventable cause of residual viable nidus and recurrence.
8. Connect the electrode to the compatible generator and perform the validated device-specific cycle. For a conventional temperature-controlled system, the commonly cited protocol is 90 °C for 6 minutes; monitor temperature, impedance, patient physiology and protective thermocouples throughout.Pearl: Temperature and duration are system dependent; do not transfer settings between electrode-generator platforms without validation.
9. Allow the electrode to cool, withdraw it into the insulated cannula and remove the system under controlled conditions. Apply local compression and inspect the skin and puncture tract for bleeding or thermal injury.
10. Obtain limited CT imaging when needed to document instrument removal and exclude hemorrhage, fracture, joint violation or other immediate complication. Perform and document a site-specific neurovascular examination before discharge.Pearl: Clinical pain relief, not disappearance of the nidus on immediate CT, defines clinical success.

Complications

• Expected transient post-ablation pain and local edema
• Skin or soft-tissue thermal injury; skin burns approximately 0.7%
• Infection approximately 0.5%
• Neural injury approximately 0.2%
• Articular cartilage or growth-plate thermal injury
• Hematoma or bleeding less than 0.1%
• Pathologic fracture approximately 0.1%
• Persistent or recurrent osteoid osteoma pain; primary treatment failure approximately 8.3%

Exam pearls

• Target the nidus, not the reactive sclerosis or MRI edema.
• The standard viva answer is 90 °C for 6 minutes, qualified by the device-specific validated protocol.
• Central electrode placement is critical; eccentric placement is a preventable cause of recurrence.
• Retract the metallic introducer from the active tip to prevent conductive tract and skin heating.
• Treat a critical structure within approximately 10 mm as requiring active protection and thermal monitoring.
• Routine antibiotics are not recommended for uncomplicated osteoid osteoma RFA.
• Pain relief defines clinical success; routine follow-up CT is unnecessary in an asymptomatic patient.
• Repeat RFA is effective for confirmed residual or recurrent nidus.

Viva questions

Why is CT preferred for RFA of osteoid osteoma?

CT best depicts the small nidus, central mineralization and surrounding cortical sclerosis and permits precise coaxial targeting. MRI is valuable for edema, cartilage and neurovascular relationships but can obscure the nidus within extensive reactive change.

What is the classic RFA protocol for osteoid osteoma?

The commonly cited temperature-controlled protocol is **90 °C for 6 minutes** with the active tip centered in the nidus. The actual cycle must match the validated electrode-generator system because impedance-controlled and other platforms differ.

Why must the introducer cannula be retracted before ablation?

The metallic cannula can conduct heat toward the skin and soft tissues and can electrically interact with the active electrode. Retracting it exposes the active tip within the nidus and reduces tract and skin burns.

Is biopsy mandatory before RFA?

Tissue sampling is strongly indicated when the clinical or imaging features are atypical or an alternative diagnosis is possible. In a classic lesion, practice varies, and a nondiagnostic specimen does not invalidate a concordant clinical and CT diagnosis.

How do you protect a nerve close to the nidus?

Create separation with hydrodissection or carbon dioxide, use thermal monitoring and consider neurophysiologic monitoring. If a safe buffer and temperature cannot be maintained, stop and choose another modality or surgery.

Are prophylactic antibiotics routinely required?

No. SIR classifies osteoid osteoma ablation as a clean procedure with low infection risk and does not routinely recommend prophylaxis; antibiotics are reserved for specific patient or institutional indications.

What is the difference between technical and clinical success?

Technical success is correct intranidal electrode placement and completion of the planned ablation cycle. Clinical success is durable resolution or major reduction of the characteristic pain without continued analgesic requirement.

How do you manage recurrent pain after RFA?

Exclude infection, fracture, neural injury and another pain source, then obtain symptom-directed MRI and thin-section CT if residual nidus is suspected. Repeat RFA is usually effective when a residual or recurrent target is demonstrated.

References