Osteoid Osteoma Ablation in the Hand Using CT-guided Radiofrequency: Methodology

Osteoid osteomas (OO) are benign tumors that typically form in the bones of children and young adults. The lesions have a vascular center, the nidus, which creates a bony reaction around it with calcified osteoid tissue seen on plain x-ray. The pain from the benign mass is localized and is usually worse at night. Symptoms are typically relieved temporarily with nonsteroidal anti-inflammatory (NSAID) medication. The lesion is composed of a variably calcified meshwork of bony trabeculae on a background of fibrous, vascular and nerve tissue. Most often, OO are found in long bones such as the femur and tibia and more rarely in the spine or distal extremities such as the feet or hands.1

Diagnosis is typically made by history and plain x-rays and confirmed by computed tomography (CT) scan. Magnetic resonance imaging (MRI) can also be helpful. Once diagnosed, the typical treatment in the hand would normally be open surgical excision of the lesion. The technique of using radiofrequency (RF) is rarely considered since the concern in the hand is the close proximity of the probe to tendons and local neurovascular structures. We present a case and details of the technique used to ablate an OO in the metacarpal head using RF.

TECHNIQUE

The patient is a 31-year-old right-handed man. He works on a fish farm doing heavy manual labor. He consented to this publication. In August 2017, the patient experienced some irritation in his right hand, though he did not seek treatment and the discomfort resolved spontaneously after 2 months. Six months later, the discomfort recurred and gradually became more painful. He was seen by a hand specialist who identified the lesion using plain x-rays and confirmed the diagnosis by CT scan. The patient complained of pain sometimes while at rest and worse at night. He took ibuprofen to help him sleep at night. There was mild pain with heavy use of the hand while working but mostly he complained of locally sensitivity when touched. The patient presented for treatment ~1 year after his symptoms began. Examination was generally unremarkable except for mild local swelling of his right fourth metacarpal head and local tenderness. Range of motion was normal. Preoperative CT images showed the characteristic nidus of the OO (Figs. 1A–C). An MRI was performed to determine the distance from the lesion to the neurovascular bundle. The distance measured 0.40 cm from the external edge of the metacarpal to the bundle (Fig. 2).

F1FIGURE 1:

A–C, Computed tomography (CT) images at level of F4 metacarpal head showing characteristic nidus (A=axial, B=sagittal, C=coronal).

F2FIGURE 2:

Magnetic resonance imaging T2-weighted, fat-suppressed axial image demonstrating bone marrow edema and soft tissue swelling with 0.40 cm distance from the metacarpal to the digital neurovascular bundle.

The patient underwent general anesthesia then was placed in a prone position. General anesthetic is used since once the CT coordinates of the lesion are determined, the patient is not allowed any movement in order to accurately place the probe. His hand was extended overhead and stabilized in the pronated position. The hand was placed on an ice pack to cool the palmar tissues. A metal grid (providing multiple radiopaque markers) was placed over the hand and the CT used to localize the lesion and determine the probe entry point using a dorsal approach. One dose of cefazolin was given before starting the procedure. A 3 mm skin incision was made just ulnar to the extensor tendon and under CT guidance, a 13-G Jamshidi-type hollow biopsy needle was placed in the dorsal metacarpal metaphysis through which the probe was introduced. The dorsal approach left the volar articular cartilage intact. The RF probe used was Covidien 7. A 21-G needle was introduced under CT guidance through a dorsal approach and its tip was placed near the neurovascular bundle (Fig. 3). Three milliliters of 5% dextrose were injected through the needle deep to the metacarpal to further increase the distance between the bone, the neurovascular bundle, and the tendons. The time was set for 6 minutes noncooled. Settings were 500 Ohms, 7 to 13 W and 0.1 to 0.2 amps and maximum probe tip temperature of 90°C. The wound was small enough that Dermabond and not suture was used to close the wound. The patient was monitored 4 hours for both recovery after the general anesthetic and to monitor the hand, then discharged home the same day. He reported pain relief immediately after the procedure. His follow-up was uneventful with return to full function within a week after the procedure. At 13 months from the procedure, he remained asymptomatic and x-rays showed a healed lesion and no evidence of recurrence.

F3FIGURE 3:

Axial computed tomography image showing the probe tip in the lesion while injecting dextrose using a needle placed deep in the tissue and the hand placed on ice. RF indicates radiofrequency.

EXPECTED OUTCOME

The most common techniques for OO treatment include open surgical excision and CT-guided radiofrequency thermal ablation (RTA). The minimally invasive technique of RTA has several advantages. This includes less soft tissue damage to reach the lesion, a smaller entry of the bone with less risk of later pathological fracture, CT-guided ablation for specific and focused destruction of the lesion, and an overall faster recovery.

COMPLICATIONS

RTA is routinely used in our center for OO lesions.2 RTA uses high-frequency radio waves to transfer energy to local tissue which is dissipated as heat. The heat results in thermal necrosis of the affected tissues. The treatment zone is typically twice the length of the bare tip.3 The cool-tip probe was not used in this case. The cool-tip (Valleylab, Boulder, CO) uses a continuous cooling of the tip. The cooling of the probe tip minimizes charring which allows higher temperatures further away from the probe since otherwise, the charred tissue next to the probe would act as an insulator and reduce the probe effectiveness. The cool tip was purposely not chosen in this case to avoid the greater radius of effect in order to keep the energy more localized.

In recent years, there has been an increase in treating OO in long bones and the spine via RTA, however, for niduses in the hand, surgery has been the preferred method. Jafari et al4 report their retrospective series of 25 cases of OO in the hand and wrist treated over a 25-year period. All of these niduses were removed with open surgical excision. They had 5 recurrences (20%) treated with re-excision.

RTA has rarely been described for treatment in the hand. Pinto et al3 shows one illustrative example of RTA used for a lesion in a metacarpal. Vanderschueren et al5 describe 4 cases in the hand, 3 involving the metacarpal.

The main concern for RTA in the hand is the close proximity to the neurovascular bundle. Vanderschueren et al5 note that the temperature at the probe tip can reach 90°C which puts the local structures at risk. However, with proper attention to detail, ablation can be safely performed even when local structures are nearby. There were many such precautions taken with the method described here. This starts with preoperative planning. The preoperative CT along with knowledge of the local anatomy was used to plan the entry point and direction of the probe. At the start of the procedure, precise localization was done before beginning. Additional precautions included the noncool setting, injection of dextrose to increase the distance from the probe to the local structures and cooling of the hand on the side of the lesion. Soft tissue burn of the skin can be avoided by withdrawing the outer cannula above the level of the active part of the tip. The grounding pad was placed on the thigh as recommended by the manufacturer. The temperature and time were carefully monitored. Cooled water, not saline is used to cool the tip since saline would act as a conductor. We believe that the details described in this report can give the surgeon a greater safety of margin to gain the benefits of RF treatment while minimizing the risks.

We present a rare case of RF used to safely treat an OO lesion in a metacarpal head. Complications using RF are primarily related to injury to local structures from the heat produced during ablation. In the hand, this may include injury to nerve, artery, tendon, skin, and cartilage. In addition, recurrence is a potential risk of treatment, whether open or with RF, though not considered a complication. We focus here on techniques to minimize risk of RF ablation when used for lesions in the hand.

We describe the methodology that is both effective and safe.

REFERENCES 1. Cohen MD, Harrington TM, Ginsberg WW. Osteoid Osteoma: 95 cases and a review of the literature. Semin Arthritis Rheum. 1983;12:265–281. 2. Peyser A, Applbaum Y, Simanovsky N, et al. CT-guided radiofrequency ablation of pediatric osteoid osteoma utilizing a water-cooled tip. Ann Surg Oncol. 2009;16:2856–2861. 3. Pinto CH, Taminiau AH, Vanderschueren GM, et al. Technical considerations in CT-guided radiofrequency thermal ablation of osteoid osteoma: tricks of the trade. AJR Am Roentgenol. 2002;179:1633–1642. 4. Jafari D, Shariatzade H, Mazhar FN, et al. Osteoid osteoma of the hand and wrist: a report of 25 cases. Med J Islam Repub Iran. 2013;27:62–66. 5. Vanderschueren GM, Taminiau AH, Obermann WR, et al. Osteoid osteoma: clinical results with thermocoagulation. Radiology. 2002;224:82–86.

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