Minimally invasive augmented reality–guided lumbopelvic fixation for a large sacral plasmacytoma: illustrative case

Abstract

BACKGROUND

Plasma cell neoplasms can present as solitary plasmacytomas or multiple myeloma. Osseous solitary plasmacytomas commonly affect the axial skeleton and are treated with radiation therapy; surgery is needed as an adjunct to address instability or progressive neurological symptoms. Traditional open spinal fixation poses risks of increased infection and wound dehiscence. Minimally invasive surgery may minimize these challenges and limit delays in definitive radiation therapy.

OBSERVATIONS

A 61-year-old male presented with chronic low back pain with intermittent shooting pain along the S1 distribution to the bilateral lower extremities. MRI revealed a large, expansile sacral mass causing severe spinal canal stenosis, and CT demonstrated marked bony destruction. Biopsy confirmed plasma cell neoplasm. Because of his progressive instability, the patient underwent minimally invasive spinopelvic fixation using augmented reality (AR) guidance, with dual S2-alar-iliac screws for stabilization. Postoperatively, he received intensity-modulated radiation therapy, 4500 cGy, 180 cGy per fraction in 25 fractions per day for a month. Imaging at 5 months demonstrated unchanged bony erosion, stable instrumentation, and symptom improvement.

LESSONS

Progressive pain due to instability in patients with osseous solitary plasmacytoma may necessitate surgical stabilization. Minimally invasive AR-guided lumbopelvic fixation offers an effective stabilization strategy, minimizing postoperative recovery and time to definitive therapy.

https://thejns.org/doi/10.3171/CASE25634

Plasma cell neoplasms are malignancies that arise from abnormal plasma cell proliferation and are typically classified as solitary plasmacytomas if a single lesion is present or as multiple myeloma if two or more lesions are present.¹ Solitary plasmacytomas can develop within the bone or soft tissue and carry a significant risk of progressing to multiple myeloma if left untreated.² Osseous solitary plasmacytomas most often occur within the axial skeleton, particularly within the vertebra.^3,4 The mainstay of treatment for these lesions is radiotherapy, but surgery may be required as an additional intervention in cases with instability or compromise of neural elements.⁵ In cases of sacral plasmacytoma, spinopelvic fixation is commonly performed to provide stability prior to starting definitive radiation therapy due the increased risk of fracture and instability after radiation treatment. Historically, the surgical incisions required for exposure to perform open spinopelvic fixation are associated with a heightened risk of wound complications and infection in the setting of radiation therapy.^6–8 This poses a challenge to treatment, as delaying radiation therapy to allow the surgical wound to heal results in delay of care. Here we present a case of a patient with a large sacral plasmacytoma who underwent preradiation spinopelvic fixation through a minimally invasive augmented reality (AR)–guided approach to provide biomechanical stability while minimizing risk of wound-related complications.

Illustrative Case

History of Presenting Illness and Physical Examination

A 61-year-old male presented with progressive low back pain, initially attributed to a motor vehicle accident 6 years prior. His pain was localized to the low back and buttocks and was mechanical. The patient also reported intermittent shooting pain following the S1 distribution in the bilateral lower extremities. He denied any bladder or bowel incontinence or ambulatory dysfunction and continued to work until his presentation. Physical examination was unremarkable, without any motor or sensory deficits.

Imaging Studies

The patient initially underwent lumbar spine radiographic imaging that revealed only degenerative changes. Because of his progressive symptoms, MRI of the lumbar spine was obtained, revealing a large, expansile mass, consistent with plasma cell neoplasm, involving the S1 vertebral body with extension into the S2 posterior elements, resulting in severe spinal canal and S1–2 foraminal stenosis, along with extensive bony destruction involving the majority of the sacrum (Fig. 1). He then underwent CT-guided biopsy, which confirmed the diagnosis of plasmacytoma.

FIG. 1.

Preoperative sagittal (A) and axial (B) MR images showing a large expansile mass involving the S1 vertebral body and extending into the S2 posterior elements. Preoperative sagittal (C) and axial (D) CT scans showing extensive bony destruction involving most of the sacrum. Preoperative PET scans (E and F) showing an FDG-avid plasmacytoma.

Operative Intervention

Given progressive mechanical pain attributable to the destructive sacral lesion, preradiation spinopelvic fixation was recommended. The plan was to utilize a minimally invasive approach to promote wound healing and limit any delay to radiation therapy.

The patient was positioned prone and intraoperative monitoring was utilized. A stab incision was made over the right posterior superior iliac spine (PSIS), and a percutaneous PSIS pin was placed. A patient registration marker was attached, and intraoperative CT imaging was performed for registration. The acquired data were then sent to the Augmedics xvision headsets for intraoperative navigation. Pedicle screw trajectories for L4 and L5 were planned bilaterally using AR guidance. Small incisions were made at the L4 and L5 pedicle screw entry points and pedicle screws were placed using AR navigation (Fig. 2). Next, dual S2-alar-iliac (S2AI) screw trajectories were planned, and a midline incision was made over the sacrum. Through this single incision, bilateral dual S2AI screws were placed. The S2AI screws were all 9 mm in diameter and either 90 or 100 mm in length. Using the same incisions, we decorticated the L4−5 and L5–S1 facet joints for arthrodesis.

FIG. 2.

A: Postoperative photograph demonstrating the three skin incisions used for minimally invasive spinopelvic fixation. B: Intraoperative photograph of the user interface for AR-guided screw insertion.

Rods were then passed using the minimally invasive towers from L4 to the dual S2AI screws, ensuring proper alignment. Final intraoperative fluoroscopic imaging, including anteroposterior and lateral views, confirmed optimal alignment and positioning of the instrumentation. The patient was ambulating on postoperative day (POD) 1 and discharged on POD 6, largely due to coordination of oncological care.

Follow-Up

After discharge, the patient received intensity-modulated radiation therapy (IMRT), 4500 cGy, 180 cGy per fraction in 25 fractions per day for a month. Radiation therapy began on POD 23. At initial neurosurgical follow-up, he reported a dull tingling sensation at the surgical site but noted overall improvement in his condition. At the 5-month follow-up, his radicular symptoms had resolved. He had mild low back pain with ambulation but was doing well enough to return to work the following week. At this time, he was fully weight-bearing and ambulatory without assistance, able to carry out his activities of daily living independently and participate fully at work. During this follow-up period, he was monitored for disease progression, with MRI demonstrating treatment-related changes, CT revealing unchanged bony erosion of the sacrum, and radiographic imaging redemonstrating stable positioning of instrumentation (Fig. 3). At the 10-month follow-up, he continued to do well from a surgical perspective but had ongoing pain related to the tumor. New standing radiographic imaging demonstrated stable construct and spinal alignment (Fig. 3). However, the size of the mass had not significantly changed, so repeat interventional radiology biopsy was obtained per the oncology team that was consistent with radio-refractory plasmacytoma. Chemotherapy daratumumab plus lenalidomide/bortezomib/dexamethasone is now planned for him.

FIG. 3.

Postoperative sagittal (A) and axial (B) MR images showing a decrease in the size of the lesion in the sacrum. Postoperative coronal (C) and axial (D) CT scans, lateral (E) and anteroposterior (F) 5-month radiographs, and lateral (G) and anteroposterior (H) 10-month radiographs showing proper alignment and placement of hardware.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

The primary treatment for solitary plasmacytoma in the spine is radiotherapy; however, this treatment strategy fails to address the structural instability that occurs in the diseased segment, which can lead to catastrophic morbidity. There is a paucity of studies and no specific evidence addressing pelvic fixation for the treatment of sacral plasmacytoma particularly in cases in which there is significant bony destruction and resultant instability. In this case, our patient presented with a large, expansile mass comprising most of the sacrum with severe destructive changes leading to instability symptoms requiring early surgical intervention.

Sacral neoplasms present a significant challenge to spinal biomechanics, particularly when involving critical load-bearing structures.^9,10 The differential diagnosis of large, osseous, sacral neoplasms includes chordoma, chondrosarcoma, giant cell tumors, osteosarcoma, nerve sheath tumor, plasma cell neoplasms (as in this case), and metastasis. MRI and CT are useful diagnostic tools, but ultimately tissue diagnosis is necessary to determine the pathology and final treatment plan.¹⁰ The sacrum in particular is biomechanically critical for spinopelvic stability and serves as the keystone for load transfer between the spine and the pelvis; thus, osteolysis is this region can have profound clinical implications.^5,11–14 In this case, the patient presented with progressive, mechanical low back pain and bilateral S1 radiculopathy, consistent with biomechanical instability resulting from bony destruction. Although radiotherapy remains the standard of care for solitary plasmacytoma, it does not address the underlying mechanical compromise.^1,15,16 Left untreated, the instability may progress to pathological fracture, spinal deformity, and severe mechanical instability.¹² Surgical intervention was therefore necessary to restore structural stability and prevent further neurological and mechanical complications.

The choice of surgical technique depends on the degree of instability and extent of bony destruction, and, as in this case, gross instability and bony destruction were amenable to percutaneous screw fixation. While most published data are derived from patients with metastatic or myelomatous lesions, these principles can be extrapolated to the management of sacral plasmacytoma due to similar patterns of bone destruction and instability.^11,17,18

Minimally invasive spinal fusion techniques have demonstrated favorable outcomes due to reduced blood loss, shorter hospital length of stay, lower rates of medical and surgical complications, and comparable patient satisfaction rates to traditional approaches.^19–24 However, recent studies have highlighted an evolving complication profile associated with these modern techniques,^25–28 including screw malpositioning and loosening.²⁹

Spine surgery continues to benefit from advances in image-guided technologies, including the recent introduction of AR. While data specific to AR remain limited, prior studies have shown that image-guided techniques can improve pedicle screw accuracy and clinical outcomes.^30–35 Intraoperative navigation is important for achieving optimal screw placement in compromised bone and for facilitating complex constructs when the sacrum is extensively destroyed. In this case, the navigational techniques used enabled precise screw placement, minimizing the risk of malpositioning and loosening. AR guidance provided real-time, 3D visualization of the spinal anatomy, which allowed for enhanced accuracy in pedicle and iliac screw trajectories. Additionally, this patient has experienced no immediate or delayed postoperative complications to date.

Additionally, a key aspect of this case was the use of dual S2AI screws, which played a critical role in ensuring a strong distal construct. S2AI screws provide strong anchorage, minimizing the risk of screw loosening—a major concern in lumbopelvic fusion. Authors have found that due to the lower profile of these screws, there tends to be less irritation to the surrounding soft tissue as well as fewer wound complications requiring revision surgery.^36–39 A meta-analysis that was conducted by De la Garza Ramos et al. found that S2AI screws outperformed iliac screw fixation while displaying significantly lower rates of mechanical failure and complications.⁴⁰ In this case, the patient did not experience any postoperative complications, and imaging revealed proper alignment and excellent instrumentation positioning without the need for consideration of further surgical structural support at this time.

The progression of plasmacytoma to multiple myeloma is a feared outcome of the disease. In a study conducted by Bataille and Sany, it was reported that 53% of patients with plasmacytoma eventually progressed to multiple myeloma, with other studies reporting as many as 78% of patients presenting with recurrence.^41,42 Because of this, it was imperative that our patient receive IMRT, 4500 cGy, 180 cGy per fraction in 25 fractions per day for a month, to eradicate the disease. Ensuring structural stability with preradiation spinopelvic fixation in a manner that did not delay definitive treatment was crucial to ensure the best outcome.

Lessons

Minimally invasive AR-guided spinopelvic fixation provides a viable and effective approach for stabilization surgery in patients with sacral plasmacytoma or potentially other causes of lumbopelvic instability, reducing surgical morbidity while ensuring accurate instrumentation placement. The use of dual S2AI screws enhances biomechanical stability, addressing the structural challenge posed by destructive sacral lesions. Our case highlights the importance of early spinal stabilization and reducing a delay in definitive treatment.

Disclosures

Dr. Witham reported personal fees from Augmedics (surgical advisory board member) and Kuros Biosciences and Cerapedics (advisory board consultant) and being an investor in Augmedics, outside the submitted work.

Author Contributions

Conception and design: Witham, Hughes, Azad. Acquisition of data: Witham, Shafi, Hughes. Analysis and interpretation of data: all authors. Drafting the article: Shafi, Hughes, Azad. Critically revising the article: Witham, Hughes, Azad. Reviewed submitted version of manuscript: Witham, Shafi, Hughes. Approved the final version of the manuscript on behalf of all authors: Witham. Study supervision: Witham.

Correspondence

Timothy F. Witham: Johns Hopkins University School of Medicine, Baltimore, MD. twitham2@jhmi.edu.