Because of the complex anatomy of the ankle joint and foot, the wide array of possible bone and soft-tissue injuries, and the uncommon occurrence of tumors at these sites, osteoid osteomas (OOs) are often not included in the differential diagnosis of foot and ankle pain.1,2 Patients with OO usually complain of severe pain that is worse at night and is relieved with use of nonsteroidal anti-inflammatory drugs (NSAIDs).1-4 This classic clinical presentation, combined with the characteristic imaging features, facilitates making an accurate diagnosis.
OOs were first described in 1935 by Jaffe,5 who characterized them as benign, solitary, osteoblastic tumors consisting of atypical bone and osteoid. On radiographs and thin-slice computed tomography (CT), these tumors are small osteolytic lesions surrounded by a larger region of cortical thickening, medullary sclerosis, and benign periosteal new bone formation.4,6,7 They often contain a central focus of calcification—the nidus. OOs typically occur in children and young adults; the majority of patients are younger than 25 years. OOs show a predilection for the appendicular skeleton, with the majority of the lesions in the femur and tibia.4,6,7 OOs infrequently occur in the bones of the hands and feet.8-12 Previous studies of foot and ankle OOs have been predominantly limited to case reports; the largest study, conducted almost 20 years ago, included only 10 patients.1
We conducted a study to evaluate the epidemiology and radiographic features of foot and ankle OOs, to evaluate surgical treatment options and outcomes in patients with foot and ankle OOs, and to evaluate the disease course of patients with foot and ankle OOs treated surgically or with radiofrequency ablation (RFA).
Materials and Methods
After obtaining approval from our institutional review board, we retrospectively reviewed all cases of patients who underwent a surgical or an interventional radiologic procedure and had a preoperative diagnosis of a lower extremity OO between 1990 and 2010. Only patients with a histologically confirmed diagnosis of OO were included in the review of foot and ankle cases.
The medical records of patients with a diagnosis of foot or ankle OO were reviewed for patient sex, age, OO site, clinical presentation, radiographic studies, pain characteristics, treatment modality, histologic diagnosis, and clinical outcome of the surgical or RFA procedure. Preoperative and postoperative clinical outcome scores were calculated using American Orthopedic Foot and Ankle Society (AOFAS) scores.
Whether to perform surgical excision or RFA was discussed between the treating surgeon and the radiologist before treatment. The goal was to treat each lesion while minimizing damage to normal, surrounding structures. If there was any question whether a lesion could be something other than OO based on radiographic features, the lesion was treated with surgical excision. Surgical excision consisted of curettage and bone grafting or en bloc removal. Surgical hardware was placed only when an osteotomy was needed to access the lesion. RFA was performed by consultant musculoskeletal radiologists. Before ablation, a CT-guided needle biopsy of the lesion was performed to obtain tissue for pathologic diagnosis. Recurrence was defined as return of preoperative symptoms after treatment, along with radiographic features of recurrence.
Statistical analysis was done with SPSS software (IBM, New York, New York) using unpaired Student t tests and Fisher exact tests. Statistical significance was set at P < .05.
Of the 117 patients with a lower extremity OO, 13 (11%) had it in the bones of the foot or ankle (Table). Mean age at presentation was 20.1 years (range, 9-38 years). There was no statistically significant difference in age between patients with foot or ankle OO and patients with OO of the long bones of the lower extremity (P = .27). Of the 13 patients, 12 were male and 1 was female (Table). The foot and ankle OO sites were the talus (n = 5), the distal tibia/plafond (n = 3), the calcaneus (n = 2), the tarsal bones (n = 2), and the phalanx (n = 1). All 13 foot and ankle lesions were histologically confirmed as OO.
The 13 patients’ primary complaint was foot or ankle pain. Ten of the 13 were referred to our institution for clinical workup and management of foot or ankle pain and for assessment of radiographic features of OO (Figure 1). For all patients in the study, preoperative plain film radiographs of the affected extremity were obtained. Nine patients (69%) had a CT scan (Figure 2), 6 (46%) had a magnetic resonance imaging (MRI) scan, and 2 (15%) had a bone scan. Despite undergoing advanced imaging (1 CT, 1 MRI), 2 patients (15%) did not get a differential diagnosis of OO before being treated. The same 2 patients did not have radiographic images available for review to determine why a differential diagnosis of OO was not included based on imaging features prior to surgery. For the patients who did not have a diagnosis of OO before being evaluated at our institution, preliminary diagnoses included osteomyelitis and painful osteophytes. Twelve of the 13 patients complained of pain that was worse at night and was not relieved with use of NSAIDs. Mean time from symptom onset to presentation at our institution was 14.4 months (range, 3-42 months). All patients reported pain relief after the procedure. There was a significant (P = .0001) increase in AOFAS scores after surgery. Mean AOFAS score was 65.42 (range, 54-80) before surgery and 97.91 (range, 90-100) after surgery.