As foot OOs often occur near the joint (7 intra-articular lesions in our study), they often lack the exuberant periosteal reaction, cortical thickening, and reactive medullary sclerosis that characterize these lesions in the appendicular skeleton.17 In addition, the anatomical complexity of the small bones of the foot and ankle, particularly the hindfoot, where the bones are flat and irregular, makes identifying the lesions difficult.17 Conventional radiographs are the initial imaging modality of choice for evaluating patients with a clinical suspicion of OO, and they may identify the tumor. However, if radiographs are nondiagnostic, and the diagnosis of OO is suspected, high-resolution CT should be performed.
MRI is commonly used to assess for ligamentous, tendinous, and articular cartilage injuries in patients with ankle and hindfoot pain. However, as already discussed, and as reported in previous studies,17 accurate diagnosis of OO can be challenging with MRI (Figure 5A), and often the patients who had MRI scans then underwent CT (Table) for the definitive diagnosis (Figure 5B). In only 1 patient in our study was MRI used to make the preoperative diagnosis of OO (Table). In 2 patients (15%), even advanced imaging did not result in OO being included in the differential diagnosis. This is consistent with other reports, which found that a diagnosis was not made in 11% of patients.16 Although almost a quarter of patients did not have radiographic features diagnostic of OO, CT is the modality of choice for all patients who have clinical features suggestive of a diagnosis of OO.
Surgical treatment of OO is effective when the entire nidus is removed, with excision providing rapid pain relief.4,6,7,11,12 Historically, the tumor was often treated with wide, en bloc resection, but this is a large operation involving removal of a substantial amount of surrounding normal bone, as the lesion is often difficult to identify intraoperatively without preoperative localization.4,6,13 Curettage was performed on the lesion to reduce the amount of bone removed.4 Both techniques are reportedly very successful in treating OOs, with recurrence rates ranging from 0% to 15%.18,19 In our study, none of the surgically treated lesions recurred, and their AOFAS score improved from 67.11 (range, 54-80) before surgery to 98.33 (range, 93-100) after surgery. However, all surgically treated patients required a mean of 3 weeks (0-2.5 months) of either partial weight-bearing or non-weight-bearing of the affected extremity. A variety of treatment techniques have been used as alternatives to surgical resection in an attempt to treat OOs effectively and minimize damage to the surrounding normal bone.4,6,13 These techniques have included percutaneous CT-guided tumor excision with a trephine; percutaneous or surgical ablation using laser, cryotherapy, or ethanol; CT-guided localization followed by operative excision; and CT-guided percutaneous RFA.4,6,13,20 Over the past 2 decades, CT-guided percutaneous RFA has evolved to become the treatment of choice for painful OOs of the appendicular skeleton.15,21,22 The success of this procedure depends on accurate preprocedure diagnosis and precise anatomical localization with CT. Our results correlate with those in series reported in the literature, showing no significant difference in tumor recurrence rates between this technique and surgical excision.22
In our study, 3 patients were treated with CT-guided RFA. Because of recurrent pain, 1 of these patients had a repeat RFA 4 months after the initial procedure. After the second procedure, the patient was asymptomatic. Pain recurrence rates have ranged from 2% to 11% in large series of treated nonspinal OOs.21-23 Our RFA patients’ mean AOFAS score notably improved from 60.33 (range, 60-61) before surgery to 96.66 (range, 90-100) after surgery.
One of the distinct advantages of CT-guided RFA of OO is that it provides a minimally invasive technique for curative treatment with minimal damage to the adjacent normal bone by providing selective and controlled ablation of the tumor nidus.15 Additional advantages are that it can be performed as an outpatient procedure, and patients convalesce quickly with unrestricted weight-bearing and immediate return to activities of daily living.21-23 In addition, when RFA and surgical excision were compared on their average costs of hospitalization and treatment for OO, RFA was found to be less expensive.24
There were no RFA-related complications in our study population, but complications have been reported (albeit rarely) in other large studies of using RFA throughout the appendicular skeleton.21,25 Reported complications include skin burns, nerve damage, reflex sympathetic dystrophy, cellulitis, and thrombophlebitis.21,25 To reduce the risk for these complications, the investigators emphasized the importance of avoiding use of RFA for lesions near a neurovascular bundle (<1.5 cm away) or in a superficial location near the surface of the skin (<1.0 cm away).21,25