Giant cell tumor (GCT) is one of the commonest benign bone tumors encountered by an orthopedic surgeon. It commonly affects females, and the peak incidence is seen in the third decade of life ^[1]. The tumor is commonly seen around the knee, with the ephiphysio-metaphyseal region of the distal femur being the most common site, followed by the proximal tibia. Distal radius is the 3^rd most common site of occurrence ^[2]. These patients most commonly present with pain of variable severity that may be associated with a mass present from a few weeks to several months. There may be an antecedent history of trauma. Lateral ankle sprain is another clinical entity commonly encountered in the outpatient department (OPD) by orthopedicians. These patients present with pain and swelling in the lateral aspect of foot and ankle after an episode of twisting injury to the ankle. These symptoms may last from a few weeks to months. We present to you a rare case of calcaneal GCT masquerading as lateral ankle sprain in a 27-year-old female.

A 27-year-old female presented to OPD with complaints of swelling and tenderness in the lateral aspect of the left ankle and foot for 3 months. There is a history of twisting injury to the left ankle while riding a bicycle 3 months back, after which the patient noticed the swelling. The patient has received conservative management for lateral ankle sprain but, however, no radiographs were taken during such consultations. On clinical examination, there was a diffuse swelling involving the lateral aspect of the left ankle (Fig. 1) which was tender on palpation without any local rise of temperature. There is no history of any constitutional symptoms. Ankle and foot examination are within normal limits. On roentgenography (Fig. 2), we found an expansile, lytic lesion in the proximal aspect of the body of the left calcaneus. The lesion has a narrow zone of transition. There was no periosteal reaction, no matrix, no soft-tissue component. There was no sclerotic margin. Multiple septae appear to be traversing the length of the lesion, producing a trabeculated appearance. Radiologic evaluation of other body parts ruled out multicentric lesions.

On the Non contrast CT scan (Fig. 3), we observed that there was thinning, but no breach in continuity, of the native bone cortices. The trabeculations observed on X-ray were not visualized in computed tomography (CT) cross sections. The articular surfaces did not appear to be involved.

On magnetic resonance imaging (MRI) (Fig. 4), areas of low-signal intensity were observed on both T1- and T2-weighted images just below the region of the posterior facet which corresponded to the solid tumor component as was subsequently confirmed during surgery. There was a high-signal intensity region in the posterior aspect of the lesion, which was due to intratumoral hemorrhage. No marrow edema was observed. No fluid-fluid levels, classical of aneurysmal bone cysts, were observed. There was no extraosseous component or joint involvement. The lesion was visualized on short tau inversion recovery sequence and hence an intraosseous lipoma was ruled out.

A core needle biopsy with a Jamshidi needle was performed under local anesthesia from the lateral aspect of the ankle by the primary surgeon. The histopathological examination showed the presence of mononuclear stromal cells and osteoclast-like multinucleated giant cells, conclusive with our diagnosis of GCT of the calcaneus.

The patient was planned for extended curettage through an extended lateral approach, and the cavity filled with autologous cancellous bone graft and bone cement by the Sandwich technique (Fig. 5). The immediate post-operative X-ray image is shown in Fig. 6.

Postoperatively, the patient was kept non-weight bearing for 6 weeks, followed by partial weight bearing up to 3 months, and allowed full weight bearing then onward. The patient was followed up at 3 months (Fig. 7), 6 months (Fig. 8), and 1 year (Fig. 9) for any evidence of recurrence or articular collapse.

Primary bone tumors of the foot are a rare occurrence ^[3]. In a study by Yan et al., ^[4] primary calcaneus tumors accounted for 35% of osseous foot tumors, and GCT of calcaneum consisted of <1% ^[5,6] of all calcaneal tumors. The usual age of occurrence in primary GCT of long bones is the 3^rd decade of life, and is more common in females, which is similar to that observed for calcaneal GCT ^[1]. This rare site of occurrence poses unique diagnostic and prognostic challenges. In this case, a temporal delay in diagnosis occurred due to aligning of the patient’s chief complaints with a diagnosis of lateral ankle sprain, which is a commonly encountered condition. Calcaneal GCT has previously been reported as mimicking other common ankle pathologies such as heel pain ^[7]. A delay in diagnosis can result in worsening of prognosis for the patient, even leading to amputation of the foot ^[1], as GCT of foot bones is generally more aggressive as compared to that in long bones ^[8]. We also performed a skeletal survey to rule out any synchronous lesions as there are previous reported cases of multicentricity [9-11]. Roentgenographic evaluation in this case revealed findings classically attributed to GCT ^[12]. The computed tomography  and MRI findings were also characteristic of GCT and were similar to those described in previous literature [2, 12-14]. As is universally acknowledged protocol, core needle biopsy was performed after all non-invasive diagnostic modalities and histopathological findings were characteristic of GCT ^[2]. A decision regarding extended curettage was taken after careful evaluation of the tumor dimensions and assessment of the host bone stock. Sandwich technique of bone grafting and bone cement application was performed in a conventional manner, as is the practice in most Campanacci grade 2 and grade 3 GCTs for adjacent joint preservation ^[15] (Table 1).

As seen in the literature, most patients presented with localized pain and swelling, with imaging revealing characteristic lytic lesions. Treatment across these cases has typically involved intralesional curettage, often augmented with bone grafts or cementation. The outcomes were generally favorable, with low recurrence reported during follow-up.

This case report highlights the unpredictable nature of primary bone tumors in terms of their location and presenting features. Orthopedicians must be vigilant of these rare presentations and must be thorough in evaluation to diagnose these conditions early. The value of radiological investigation in these scenarios cannot be overemphasized. An algorithmic approach to diagnosis can help in detection of these rare conditions. Treatment modalities must be considered on a case to case basis and must aim at preserving maximum functionality.

Thorough clinical and radiological investigation holds the key to accurate clinical diagnosis. Even the simplest of clinical conditions must be thoroughly evaluated. Protocols must be adhered to for commonly encountered symptom complexes and must be adhered to during routine practice. In case of bone tumors, the clinical presentations may not always be classical and in the cases, meticulous radiological and histopathological investigations are of paramount importance. Cases with anomalous presentations may be best referred to a surgeon with experience of managing such orthopedic oncology cases.