Case report

A woman with a history of breast cancer presented with right ankle pain and was referred to the neurointerventional team for consideration of percutaneous calcaneal fracture augmentation.

In the setting 4of known bony metastases, the patient began experiencing increasing right ankle pain. MRI demonstrated abnormality in her right calcaneus bone. A biopsy was performed which did not show any malignancy. As her pain worsened, she had a subsequent bone scan which showed increased uptake in the right ankle, left tibia and pubic ramus. The patient underwent a second biopsy that revealed carcinoma consistent with breast cancer metastasis. She then received a course of palliative radiation therapy to the right ankle. The pain improved somewhat although the patient remained unable to bear her full weight on that side. Three weeks later, she noted a mild swelling of her right foot associated with recurrent severe pain in her foot. CT scan showed a lytic lesion in the anterior calcaneus resulting in cortical destruction of the anterior process of the calcaneus extending to the cuboid facet (figure 1). Given the limitations of conventional medical therapy, neurointerventional radiology consultation was requested based on our experience with percutaneous augmentation of the vertebral column. During her initial clinic visit in our office, she rated her pain on a Visual Analog Scale as 6 of 10 at rest and 10 of 10 with ambulation. She was also utilizing a single prong cane for support. The patient subsequently underwent CT guided PMMA injection into the calcaneus. She was seen in our clinic approximately 3 weeks post-procedure and rated her pain on a Visual Analog Scale as 0 of 10 at rest and as 2 of 10 with ambulation. She no longer required use of the cane or other assistive devices. At the last visit, 5 months post-procedure, she reported complete pain resolution and normal ability to bear weight.

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Figure 1

(A, B) Sagittal and axial CT images demonstrating a lytic lesion in the anterior calcaneus, resulting in cortical destruction of the anterior process of the calcaneus extending to the cuboid facet.

Procedure technique

After obtaining informed consent, the patient underwent CT guided calcaneoplasty. Scout CT imaging was performed, needle trajectory planned and the entry site marked along the lateral margin of the anterior calcaneal lytic lesion. Under conscious sedation, via a single lateral approach, a 10 gauge needle (Medtronic Spine, Memphis, Tennessee, USA) was drilled into the calcaneus. Following each advancement of the needle in small increments, CT images were obtained to assess needle position. Using directional bone filler devices (Medtronic Spine), PMMA was safely placed into the lytic lesion using intermittent CT guidance and monitoring (figure 2). The fracture that extended into the articular surface was used as an endpoint for PMMA deposition because we did not wish PMMA to enter the joint. Once cement instillation was complete, the needle was removed. Approximately 80% of the lytic lesion was filled with the PMMA, which remained entirely intra-osseous, as demonstrated on multiplanar post-procedure CT (figure 3). Of note, the procedure was performed under conscious sedation. As we injected PMMA, the patient reported painful pressure locally at the site. However, this pain quickly resolved between injections.

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Figure 2

(A, B) Demonstration of various time points during deposition of polymethyl methacrylate.

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Figure 3

(A, B) Lateral and calcaneal views of post-procedure volume rendered images demonstrating the extent of polymethyl methacrylate deposition through the lesion without any leakage. Note the preservation of the cuboid joint without cement.

Discussion

Metastatic disease of the skeleton occurs in at least 20–30% of patients with malignancy.1 7 The bones most frequently involved with metastases are the pelvis, vertebrae, ribs, sternum and skull.7 Metastatic disease distal to the knee is unusual, and metastases to the feet are extremely rare.1 7 Diagnosis may be difficult and with the initial presentation of painful, swollen feet these lesions are often mistaken for more common entities such as soft tissue inflammation, trauma, arthritis and osteomyelitis.1 Failure to recognize these lesions has led to delayed diagnosis and/or inappropriate treatment.1

The most common primary tumor metastases to the bones of the feet are colon, kidney, lung, tumors of unknown origin and breast.7 Intra-articular calcaneal fractures are complex injuries with a challenging treatment, ranging from open reduction and internal fixation, calcium phosphate bone augmentation to non-operative management.8 9 10 11 Calcaneal augmentation theoretically allows for earlier weight bearing without loss of reduction and hence a decreased period of disability.11

Surgical intervention demands an incision through tenuous, radiated lateral heel skin and dissection directly down to the lateral border of the calcaneus. Direct exposure of the fracture site provides the surgeon with access into the tumor where PMMA could be placed in an effort to reinforce the weight bearing capability of the calcaneus. Generally, wound healing complications significantly limit open surgery cases of calcaneal pathology in native feet, add to this external beam radiation and the theoretic wound healing trouble intensifies.

Percutaneous augmentation is a minimally invasive procedure that has been increasingly used in the setting of metastatic bone disease.12 In addition, newer data suggest that percutaneous augmentation can be used successfully outside of the vertebral column.13 We are not aware, however, of any study or case report describing the percutaneous placement of PMMA for calcaneal augmentation. Results of prospective studies show that the type of cement used in kyphoplasty (PMMA or calcium phosphate) has no significant influence on pain reduction.14

There are a number of proposed explanations as to the cause of pain reduction.15 The first is that when PMMA cement is used, the heat generated by its exothermic polymerization is sufficient to cause thermal necrosis of the neighboring neural tissue. However, results from ex vivo biomechanical studies on vertebroplasty are contradictory with respect to the degree of temperature elevation.16 17 The second explanation attributes pain relief to the cytotoxicity of the PMMA cement.18 However, some doubt has been raised because the cytotoxic concentration of PMMA is 10–100 times higher than those used in total hip and knee joint replacements.15 The last explanation suggests that pain relief is a direct consequence of the stabilization provided by the procedure.15 16

The management of metastatic bone disease has become a multidisciplinary process. Combining percutaneous augmentation with external beam radiation therapy or internal/radioisotope radiation are promising approaches.19 As cancer survivorship continues to increase, even in patients with metastatic disease,20 it is imperative that we continue to keep palliation a top priority in the management of symptomatic metastases.

In conclusion, this case demonstrates that PMMA augmentation is a potentially effective component in the overall management of pathologic fractures of the calcaneus.