Annals of Surgical Oncology Cite Track
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10.1245/s10434-006-9293-4
Annals of Surgical Oncology 14:591-596 (2007)
© 2007 Society of Surgical Oncology
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Original Article

Osteoid Osteoma: CT-Guided Radiofrequency Ablation Using a Water-Cooled Probe

A. Peyser, MD1, Y. Applbaum, MD2, A. Khoury, MD1, M. Liebergall, MD1 and K. Atesok, MD1

1 Department of Orthopaedic Surgery, The Hadassah-Hebrew University Medical Center, P.O. Box 12000, Jerusalem 91120, Israel
2 Department of Radiology, The Hadassah-Hebrew University Medical Center, Jerusalem, Israel

Correspondence: Address correspondence and reprint requests to: A. Peyser, MD; E-mail: peysera{at}hadassah.org.il


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: The purpose of this study was to assess the safety and efficacy of computed tomography (CT) guided percutaneous radiofrequency (RF) ablation of osteoid osteoma by using the water-cooled probe.

Methods: During the period from July 2002 to February 2006, fifty-one patients with osteoid osteomas localized in femur (29), tibia (10), calcaneus (2), talus (2), metatarsus (2), humerus (1), sacrum (1), scapula (1), olecranon (1), patella (1) and thoracic vertebra (1) were treated with CT-guided RF ablation using the CooltipTM Tyco Healthcare probe. Mean age was 20 (range, 3.5–57 years) and male to female ratio was 36/15. Mean follow-up period was reported 2 years (range, 9–51 months). The procedures were carried out under general anesthesia and the patients were discharged from the hospital within 24 h.

Results: Technical failure was reported in only one procedure. Pain disappeared postoperatively in all the patients within 2–3 days and no patients needed analgesic treatment after a week. All patients were allowed fully weight bear and function without limitation after the procedure. Recurrence of the pain was observed in one patient who was treated successfully with a second ablation. Our primary and secondary clinical success rates were 98 and 100% respectively. In one case, wound infection was observed after the procedure as the only postoperative complication in our series.

Conclusion: CT-guided percutaneous RF ablation of osteoid osteomas using the water-cooled probe is a safe, effective and minimally invasive procedure with high success rate and lack of relapses.

Key Words: Osteoid osteoma • CT • Radiofrequency ablation • Water-cooled probe


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Osteoid osteoma is a small, benign osteogenic tumor with little or no growth potential. It accounts for 10–12% of all benign bone tumors and occurs mainly in children and young adults.22 The tumor is seen predominantly in males (male/female ratio >2:1). At least half of the lesions arise in the femur or tibia. Osteoid osteoma consists of a central nidus, composed of variably calcified bony trabeculae on a background of fibrous, vascular and nerve tissue.15 Clinically, the most common presenting symptom is local pain, typically more severe at night that often promptly responds to aspirin and other non-steroidal anti-inflammatory drugs. Other possible signs and symptoms include growth disturbances, leg length discrepancy, bony deformity, painful scoliosis, and depending on the proximity to a joint: swelling, synovitis, limited movements, and contractures.12

According to Schulman and Dorfman, the cause of pain is the stimulation of the unmyelinated nerve endings in the nidus by the marked vascularity of the lesions.19 Makley and Dunn showed a remarkable increase in prostaglandin synthesis in osteoid osteoma which supported the pathophysiological explanation of the pain by vasodilation in the nidus.13

Spontaneous resolution of pain and healing of the lesions within an average time of 5 years were reported by some authors.11,14 However, long-term conservative medical therapy may be unacceptable because of the complications of chronic anti-inflammatory agent use and refractory pain. Successful treatment is achieved with total removal or destruction of the nidus. Since intraoperative localization of these small lesions can be very difficult, open surgical removal of the tumor often necessitates significant bone resection, and, consequently, internal fixation and/or bone grafting may be required.14

Minimally invasive therapies that have been developed for osteoid osteoma aim to achieve removal or destruction of the nidus with minimal tissue invasion. These include percutaneous excision with relatively large-caliber hollow needles and drills, magnetic resonance imaging-guided cryotherapy, arthroscopic removal, computed tomography (CT)-guided drill resection of the nidus with or without the subsequent injection of ethanol, thermal destruction by means of laser photocoagulation or percutaneous radiofrequency (RF) thermocoagulation.9

Since the first report in the literature by Rosenthal et al.16 in 1992, CT-guided radiofrequency thermal ablation has been proven to be an accepted, safe, minimally invasive, and cost-effective treatment for osteoid osteoma.

The purpose of our study is to evaluate CT-guided radiofrequency ablation of osteoid osteoma using the Cool-tipTM Tyco probe. In this technique the active tip of the probe is cooled by saline pumped through it. It is primarily used in RF ablation of tumors in the liver and other organs due to the greater diameter of tissue ablated compared to non-cooled tips.20 We postulated that this radiofrequency technique would be at least as successful as the reported success rate with non-cooled RF devices.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
This retrospective study was performed with the approval of our institutional review board.

Patients
Between July 2002 and January 2006, percutaneous CT-guided radiofrequency thermal ablation was performed in a series of 51 consecutive patients with osteoid osteoma at the Hebrew University Hadassah Medical Center. The files of all the patients and radiographs were available for investigation.

Of the 51 patients, 36 were male and 15 were female with a mean age of 20 years (range, 3.5–57 years). Twenty-nine lesions were located in the femur, ten in the tibia, two in the calcaneus, two in the talus, two in metatarsi and one in each of the following sites; humerus, sacrum, scapula, olecranon, patella and vertebra (Fig. 1Go). The osteoid osteomas were intraarticular in seven patients and the locations of these lesions were: femoral head (2), neck of talus (2), calcaneus (1), olecranon (1) and patella (1) (Fig. 1Go). In six patients the nidus was located in the femoral neck.


Figure 1
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  		FIG. 1. A 22-year-old male patient with osteoid osteoma of the patella. a Intraarticular lesion located in lateral patello-femoral facet (arrow). b RF ablation of the lesion.

 
A patient was chosen as a candidate for the procedure after a diagnostic consensus was reached by two authors, a senior orthopaedic surgeon fellowship trained in tumor surgery (author A.P.) and a senior radiologist fellowship trained in musculoskeletal imaging (author Y.A.). The diagnosis was made on the basis of a clinical picture characteristic of osteoid osteoma (pain predominantly at night that disappears or improves after administration of salicylates or non steroidal anti-inflammatory drugs) and of typical radiological findings of the lesion. All patients had X-rays, computed tomography with a visible nidus and positive bone scintigraphy. All of the patients decided to proceed with radiofrequency ablation for improved pain relief after a variable period of conservative treatment with medication.

Principles
Radiofrequency thermal ablation is a form of electrosurgery in which an alternating current of high-frequency radio waves passes from an electrode tip into the body tissue and dissipates its energy as heat. A radiofrequency generator forms an electric current that flows from the generator, through the electrode into the patient, and out through a grounding electrode or pad to the generator. The primary source of heat is the interaction between the current and the biologic ions of local tissue around the electrode tip.15

Procedures
Patients were referred for RF ablation by the same author (A.P.) after the procedure and alternative treatment options were explained. Informed consent was obtained in all cases. All procedures were performed in the CT suite by two authors (A.P. and Y.A.) under general anesthesia for a pain-free intervention and absolute patient immobilization. After the patients were properly positioned and immobilized, the nidus was visualized by a CT scan. During the CT scan intravenous contrast media was injected according to the proximity of the nidus to the vital structures. In general, the patients were positioned accordingly for an easy and safe entrance of the probe vertically and through the shortest distance into the nidus. To avoid tissue burns during the procedure, adhesive-gel grounding pads were placed overlying muscle close to the lesion site and connected to the RF unit.

A skin incision of 0.5 cm was made and the nidus was entered with the use of an 8 or 11-gauge Jamshidi type hollow biopsy needle under CT image guidance. At this step, biopsy samples and cultures were taken. Through the hollow cannula of the Jamshidi needle the RF needle was introduced into the nidus. The track and final position of the probe in the nidus was verified by additional CT scans. RF ablation was performed with a 1 or 2-cm exposed water cooled-tip electrode according to the size and shape of the nidus (Fig. 2Go). The electrode was connected to the radio-frequency generator (Radionics® Cool-tip® RF System, Burlington, Massachusetts, USA) and the temperature at the tip was monitored throughout the procedure. RF thermal ablation was performed in two consecutive cycles for each lesion. First, automatically with impedance-controlled energy delivery and saline cooling by peristaltic perfusion pump for 7 min to heat the lesion up to a target temperature of 60°C and afterwards manually for 5 min up to 90°C without water cooling.


Figure 2
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  		FIG. 2. Spindle-shaped osteoid osteoma with 2.3 cm long axis located longitudinally in tibia. Thermal ablation of this large lesion was successfully performed using the 2 cm cool-tip probe.

 
At the end of the procedure, the incision was approximated by sterile strips. The patients were discharged from the hospital within 24 h and given prophylactic antibiotic treatment (500 mg cefazolin), 1 dose intraoperatively IV and two more doses orally after the surgery. They were allowed to resume normal activity and bear full weight immediately after the procedure.

Definitions and Follow-up
The interventions were accepted as technically successful if the probe tip could be placed within the center of the nidus and the lesion could be heated up to the desired temperature.

Clinical success was defined as immediate and permanent relief of pain without any additional treatment.

Follow-up visits were scheduled routinely to the same senior orthopaedic surgeon (A. P.) at 2 weeks, 3 months, 6 months and every year after the procedure. Mean follow-up period was 2 years (range, 9–51 months).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The mean duration of pain before treatment was 11 months (range, 2 months–8 years) and all of the patients received daily anti-inflammatory medication preoperatively. All the patients were examined in routine pre- and postoperative outpatient visits by the same author (A. P.). In 28% (4/14) of the patients from the pediatric age group (<14 years), the involved extremity was longer in 1 cm in physical examination. Quadriceps muscle atrophy (~1–2 cm) of the involved extremity was observed in 27% (14/51) of the patients. Mild limping was reported in 13% (6/46) of the patients with a tumor located in the lower extremities.

Duration of hospital stay did not exceed 24 h postoperatively in any of the patients. All the patients underwent RF thermal ablation as the primary operative intervention. In 5 procedures we used 2 cm-long exposed tip water cooled probe and rest of the thermal ablations (46) were performed using a 1 cm-long probe tip.

Technical and Clinical Success
We experienced technical problems in only one procedure due to damage to the cable connecting the probe to the RF generator. During this procedure, conversion to CT-guided excision was required in order to complete the intervention. 76% (39/51) of the patients described disappearance of the characteristic pain even the first night after the procedure and no analgesic treatment was needed in any of the patients after 1 week. Only in one patient with a lesion located in the posterior calcaneal facet, recurrence of characteristic osteoid osteoma pain was observed within 3 months after the procedure. This particular patient was treated successfully with a second ablation. Our primary and secondary success rates were 98 and 100%, respectively.

Biopsy
Although attempted in all the procedures, specimens for biopsy could be obtained in 32 patients in-traoperatively before beginning the ablation. In 15 cases biopsy confirmed the diagnosis of osteoid osteoma. The rest of the biopsy specimens were either not diagnostic or inadequate.

Complications
Surgical wound infection was reported in one patient in whom the nidus was located in the superficial anterior aspect of the tibial shin. In this procedure we used an anterior approach to place the RF probe into the nidus. This was the only procedure related complication in our series and was successfully treated with limited surgical debridement and antibiotic therapy.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
RF thermal ablation using non-cooled tip (5 mm) probes has been proven to be an effective treatment for osteoid osteoma, yet has a considerable rate of treatment failure and late recurrences may occur.18,22 In their study, Vanderschueren et al.21 reported that the reason for the initial failures was the inadequate bone volume they could destroy and that several passes would be required for the procedure to be successful. The size of the electrode is the most essential factor that determines the amount of tissue that could be ablated. Pinto et al.2 showed that the long and transverse axis of the treatment zone using the RF thermal ablation is directly proportional to the length of bare tip.

In RF ablation with water-cooled probe, the length of the exposed tip may be 1 or 2-cm depending on the size and shape of the nidus. This, in comparison to non-cooled electrodes with shorter active tips (5-mm-long), can be considered as a remarkable advantage because of the larger amount of tissue that can be successfully ablated. Another big advantage of this technique is the cooled probe that prevents heated tissue from sticking to the needle. This feature is an important factor that allows us to perform thermal ablation in a constant targeted temperature which also eliminates the need for probe replacement during the procedure. Cant-well et al.4 in their MRI study, reported larger diameter of thermal ablation zone with cooled than regular probes.

To our knowledge, this study represents the largest series reporting the results of treatment of osteoid osteoma with RF ablation using the cool-tip electrodes. Our results with 98% primary and 100% secondary success rates could be related to the type of electrode we used and correlate well with the previous studies.5,6,14

In contrary to Vanderschueren et al.21 we do advocate the use of water-cooled electrode with longer exposed tip on the basis of our minimal complication rates and excellent clinical outcomes. We did not observe any negative effect that can be attributed to the use of this type of probe such as burns, vaporization within the tissue or unintended injury to vital structures near the lesion. We successfully treated two spinal lesions with RF thermal ablation using the 1 cm-long exposed tip water-cooled probe in our series. The first case was a patient with an osteoid osteoma of the sacrum and the nidus was at least 2 cm away from any dural and/or neural structure (Fig. 3Go). The second patient had an osteoid osteoma of the transverse process of T11. However, open surgery should be considered for spinal lesions where thermal ablation can not be safely carried out without the risk of damage to neural structures due to close proximity of the nidus.


Figure 3
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  		FIG. 3. a Osteoid osteoma of body of sacrum (arrow). b Distance (d) of the probe tip (pt) to sacral foraminas (F) is more than 2 cm (sc: sacral canal).

 
Fourteen percent (7/51) of the patients in our study had intraarticular lesions. In spite of this, no joint pain or arthritis was observed as a result of the procedure. The only complication in our series was a surgical site infection after ablation of a tibial mid-shaft nidus through an antero-medial approach. This patient was our first of three cases with a nidus in the midshaft of the tibia. In our opinion, introducing the probe antero-medially through the tibial shin where soft tissue coverage is minimal was the main cause of this limited infection. For the other two patients with similar nidus localization, lateral passage through thicker soft tissue was preferred to introduce the electrode into the nidus.

Immediate weight bearing and return to normal function is one of the major advantages of this technique.2,10,23 Our series included 46 lower extremity lesions: 6 in the femoral neck, 16 in tibia or femur diaphysis and the remainder (24) were in other sites. However, none of the patients were restricted in weight bearing and returned to normal function after the procedure.

To perform this pin-point treatment technique most efficiently and safely, intraoperative positioning of the patient may be a critical issue due to the proximity of vascular or neural structures to the tract of the probe. For example, in one patient with a dorsal proximal femoral lesion, to obtain the safest and most convenient entrance to the lesion, we transposed the sciatic nerve by a simple method of displacing the soft tissue mass that was pulled laterally by a large plaster tape applied to the skin with traction and attached to CT table (Fig. 4Go).


Figure 4
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  		FIG. 4. A 20-year-old patient with osteoid osteoma of midshaft femur posterior aspect. a Arrow head shows the nidus and the passage way of the probe. Before plaster strapping sciatic nerve (S) lies on the passage tract of the probe (BF: biceps femoris). b The soft tissue bulk of the thigh was moved laterally by plaster traction. The tract for the RF probe entrance is already clear of the sciatic nerve for a safe thermal ablation.

 
Lack of histological verification is a concern in most of the percutaneous techniques due to the difficulty in obtaining sufficient amounts of tissue for pathological examination. In our series, biopsy specimens could be taken successfully in 63% (32/51) of the cases and 47% (15/32) of the specimens confirmed the diagnosis of osteoid osteoma. These results correlated with the results from previous studies in which the rate of positive histological confirmation was less than 50%.1,10,12 Although the histological confirmation was not sufficient, excellent clinical outcomes showed that this disadvantage should not be seen as a major insufficiency of RF ablation. Moreover, it is well accepted that osteoid osteoma can be reliably diagnosed by means of clinical and imaging features alone.3,8

Beyond histological verification, the present study had other limitations that need to be taken into consideration. We performed the study retrospectively without using any validated pain status assessment scores. We believe, however, that the clinical outcomes of osteoid osteoma treatment with this technique can only be judged by disappearance of the pain characteristic to this lesion. The current study did not compare the effectiveness and disadvantages of different probe types used in RF thermal ablation. On the other hand, our results showed higher clinical success rates and lower recurrences compared to studies used regular RF probes.7,17,18,23 Future prospective comparative clinical studies are indicated to further evaluate the effects of different RF probe type on clinical outcomes.

In conclusion, percuteneous CT-guided RF thermal ablation using a water-cooled probe is a simple, highly effective, minimally invasive and safe technique for treatment of osteoid osteoma.

Received for publication October 17, 2006. Accepted for publication November 9, 2006.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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