In patients with metastatic cancer, survival and local tumor control are largely determined by the response to systemic therapy and local radiation therapy. Spinal surgery plays a largely palliative role, preserving or restoring neurologic function and spinal stability as well as permitting safe high-dose radiation without risking spinal cord toxicity.
Because tumors weaken the osseous structure of the spine, the associated mechanical instability may result in significant pain and loss of function. These developments may prevent patients from undergoing radiation or systemic therapy, because the mechanical pain inhibits them from lying down on the radiation treatment couch. Or the tumors may significantly decrease Karnofsky Performance Scale (KPS) scores and disqualify the patients from systemic treatment.
For these reasons, restoration of spinal stability in patients with symptomatic spinal fractures represents an important intervention indication. The Spinal Instability Neoplastic Score (SINS) was developed by the Spine Oncology Study Group to facilitate recognition of spinal instability by all healthcare professionals.(2)
Unfortunately, open spinal surgery may raise concerns regarding wound healing, causing a delay (potentially several weeks) in initiating systemic therapy and conventionally fractionated radiation therapy.
With the advent of modern minimally invasive techniques, however, we now have favorable alternatives that allow for restoration of spinal stability without interrupting or delaying systemic and radiation therapy.
Kyphoplasty and Vertebroplasty
Kyphoplasty and vertebroplasty have long been employed in patients with osteoporotic and tumor-related fractures. But the use of kyphoplasty as a salvage technique in those with spinal instrumentation-associated fractures and the use of percutaneously placed instrumentation in combination with kyphoplasty represent novel minimally invasive techniques for restoring spinal stability in patients with spinal tumors.
Initially developed to treat tumor-related pain, these techniques play a prominent role in patients with cancer—despite questions recently posed regarding their utility for those with osteoporotic fracture.
Findings from the Cancer Patient Fracture Evaluation (CAFE) group, which carried out a prospective randomized trial involving 22 medical centers in Europe, the United States, Canada, and Australia(1), reinforce the efficacy of kyphoplasty in the treatment of painful tumor-related vertebral body fractures.
Results also confirmed that the procedure provides quick pain relief and improves the quality of life and functional status of patients with cancer. In the study, participants with painful vertebral compression fractures were randomized to undergo kyphoplasty or nonsurgical management.
At one- and six-month follow-up, those who underwent kyphoplasty experienced a significant improvement in their Roland-Morris disability scores, compared to the patients assigned to the non-surgical treatment.
Clearly, patient selection plays a key role in successful treatment of tumor-related vertebral body fractures, and certain fracture characteristics decrease the likelihood of successful pain relief.
In our experience, planum fractures and fractures with extension into the pedicles or joints do not reliably respond to kyphoplasty.
The complete loss of height of the vertebral body in planum fractures usually eliminates the option of receiving effective cement injection. Nor can cement be injected into the pedicle or the facet in order to restore stability of the posterior elements.
In many cases, patients with epidural extension of the tumor cannot safely undergo kyphoplasty due to the risk that additional tumor tissue may be pushed into the epidural space and result in symptomatic cord compression.
Minimally Invasive Instrumentation
At Memorial Sloan Kettering, we use percutaneously placed spinal instrumentation in patients with mechanical back pain who are not kyphoplasty candidates for the above-mentioned reasons.
Minimally invasive spinal instrumentation allows for placement of pedicle screws above and below the fracture using very short incisions, eliminating the need for muscle dissection. The instrumentation provides an internal brace around the fracture, reducing the mechanical forces on the fractured level and thereby eliminating movement-related pain.
We use cement in order to fortify the screw purchase and to provide additional support in the fractured vertebral body (when technically feasible). Unlike the case in open surgery, the small incisions heal readily and therefore do not require interruption of systemic or radiation therapy (Figure 1).
We analyzed the outcomes of this technique in 17 patients, with median follow-up of eight months (range: three to 27 months). Patients experienced a significant decrease in their VAS scores after surgery, from an average of 8.3 to 1.7 (p<0.001).
Nine patients underwent surgery within four weeks of radiation therapy, and five of these underwent conventional external beam radiation therapy (cEBRT). This time period is generally thought to place patients at high risk of wound complications after open surgery. However, none of the patients in this series experienced any wound complications or any other surgery-related morbidity.
Treatment of Instrumentation-Associated Fractures
Vertebroplasty and kyphoplasty have also proved to be effective in the treatment of vertebral fractures within or adjacent to spinal instrumentation.
Open surgery for revision of hardware or stabilization of fractures adjacent to spinal hardware often requires large incisions with extension of existing constructs. Such surgery would require interruption of systemic or radiation therapy for several weeks.
Cement augmentation has proved to be an effective alternative to open surgery, obviating the need for interruption of therapy in patients with symptomatic fractures (Figure 2).
Analysis of 11 patients who underwent this salvage intervention with median follow-up of 24 months revealed that all experienced a significant decrease in their pain, with a mean reduction of 6 VAS points (p<0.003). The procedures were carried out in the thoracolumbar spine with no complications.
Effective Alternatives to Open Surgery
Minimally invasive techniques such as vertebroplasty, kyphoplasty, and percutaneous spinal instrumentation have proved to be effective alternatives to open surgery in patients requiring stabilization for cancer-associated spinal instability.
These techniques consistently reduce or resolve pain with minimal morbidity risk and do not require interruption of systemic or radiation therapy.
SINS criteria should facilitate diagnosis of spinal instability for physicians involved in the care of oncologic patients.
We expect that minimally invasive techniques will continue to gain prominence in the care of cancer patients.