Vertebral Body Fracture after Oblique Lumbar Interbody Fusion in 2 Patients: A Case Report

Patient 1 was a 60-year-old woman (body mass index [BMI] 32, osteopenia T-score −1.1) presenting with back pain, radiating pain from the posterior area of both thighs to the calves, and neurogenic claudication for 6 months. Preoperative radiography, computed tomography (CT), and magnetic resonance imaging (MRI) demonstrated L3–L4, L4–L5 spinal stenosis and L3–L4 spondylolisthesis. The preoperative disc height was 10mm at L3–4 and 9.5mm at L4–5 was. She underwent surgery including OLIF at L3–L4, L4–L5 with decompression and posterior instrumentation at L3–L5. L3–4 used 6 degrees, 14mm height cage and L4–5 used 6 degrees, 12mm height cage. Back pain occurred 1 week postoperatively. Radiologic and CT images showed coronal fracture at L3 and L4 vertebra. The patient had no radiculopathy symptoms, and radiologically, no neuroforaminal stenosis associated with fracture was deemed to have occurred and we decided to treat it conservatively. She was followed up and allowed to walk with wearing orthosis. Bone union was seen without any complication at 6 months postoperatively (Fig. 1).

Fig. 1
(A) Preoperative and (B) immediate postoperative lateral radiographs of a 60-year-old female patient. (C) Computed tomography scans showing a L3-4 vertebral coronal fracture at 1 week postoperatively. The fracture site showed union at 6 months postoperatively. (D) The fracture site showed union at 6 months postoperatively.

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Patient 2 was a 68-year-old man (BMI 24, osteopenia T-score −1.3) presenting with back pain, radiating pain from the right calf to the foot, and claudication for 2 years. He underwent right L4–L5 and left L5–S1 laminotomy in 2007. Preoperative radiography and MRI demonstrated L3–L5, L5–S1 spinal stenosis. The preoperative disc height was 10mm at L3–4, 10.5mm at L4–5 and 8mm at L5–S1. He underwent surgery including three-level OLIF, L3–L5 and L5–S1, without posterior instrumentation. L3–4 used 6 degrees and 12mm height cage, L4–5 used 12 degrees and 14mm height cage and L5–S1 used 12 degrees and 12 mm interbody spacer. The posterior instrument was planned to be performed two weeks later. At 10 days postoperatively, without inciting trauma, he developed acute severe back pain. CT demonstrated coronal plane fracture of the L4 vertebral body. Neuroforaminal space narrowing findings are seen. Thus, he underwent posterior instrumentation and distraction at L3–L5, L5–S1 (Fig. 2). On the follow-up, some neural compression due to cage migration and vertebral fracture are continued, but the symptoms are mildly observed.

Fig. 2
(A) Preoperative and (B) immediate postoperative lateral radiographs of a 68-year-old male patient. (C) At 2 weeks postoperatively, a radiograph showed a L4 vertebral body coronal fracture. (D) Additional posterior instrumentation was performed.

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The two patients were supplemented with Solera (Medtronic, Memphis, TN, USA) posterior instrumentation by using the cortical bone trajectory. Anterior polyether ether ketone cages (Clydesdale, Medtronic) and demineralized bone matrix (Sofamor Danek, Medtronic) was mixed with bone marrow aspirate.

This paper has been reviewed since IRB approval (KYUH 2017-11-011).

Recently, the frequency of OLIF has increased and various groups have provided early evidence supporting OLIF as a viable alternative to existing LIF techniques, by showing radiologic and clinical improvements in patients with degenerative lumbar diseases, including degenerative spondylolisthesis, kyphoscoliosis, and discogenic pain.4)

Author performed a total of 39 cases OLIF procedure. The average operating time of OLIF was 85.1 min, mean blood loss was 185 mL, and average length of postoperative hospital stay was 10.3 days. Indirect spinal canal decompression, independent of posterior laminectomy, after OLIF surgery has been described with a 19.0%–28.5% increase in cross-sectional thecal sac area and a 51.0%–78.3% increase in disc height on MRI. Vertebral body fracture complications occurred in 2 cases (5.13%).

Although OLIF has recently been used with good results, there are few reports on complications related to OLIF. Woods et al.3) reported the complication and fusion rates in a study comprising 137 patients surgically treated with the oblique lateral interbody fusion approach. They observed a complication rate of 11.7%, which included subsidence, postoperative ileus, and vascular injury (2.9%). There were no neurologic, ureteral, or visceral injuries. The fusion rate was 97.9% at 6 months after surgery.

Li et al.4) reported an incidence of intraoperative complications of 1.5% and that of postoperative complications of 9.9%. Major vessel injury was observed in 0.9% of cases and was the most common intraoperative complication; others included peritoneal injury, dural tear, and transient motor electrophysiology deficits.

However, some studies reported higher complications than the above studies. Abe et al.5) reported the development of complications during the perioperative period after oblique lateral interbody fusion surgery in 155 patients. The complication rate was 48.3%. The most common complication was endplate fracture/subsidence (18.7%), and other complications included transient psoas weakness and thigh numbness (13.5%) and segmental artery injury (2.6%). Almost all complications were transient, except for 1.9% that involved neurologic and ureter injuries.

Despite a report showing that most complications were significantly reduced with OLIF compared with previous surgical procedures,6) there are no established results yet.

Karan et al.7) reported vertebral body fracture in patients with osteoporosis undergoing extreme lateral interbody fusion. However, few cases of vertebral fracture caused by the interbody cage after OLIF in patients with relatively low osteoporosis, as in our cases, have been reported. So, we discuss the complications of OLIF and factors that may cause complications.

Some biomechanical scenarios may have resulted in this coronal vertebral fracture pattern. Interbody fusion cages concentrate stress at the interface between the cage and the adjacent end plates. This places a stress riser in an area of stress concentration, possibly resulting in fracture. And, if the OLIF cage subsides into the vertebral end plates, some settling of the instrumented segment and loss of disc height will result. As the disc space loses height, the OLIF screws would tend to cut through the vertebral bodies in the coronal plane, leading to fracture.

Coronal plane vertebral fractures can occur in non-osteoporotic patients treated with OLIF. Factors such as obesity, osteopenia, intraoperative end-plate breach, graft subsidence, destruction by screws, cage rolling because of the cage aspect ratio, overdistraction, oversized graft placement, and inadequate construct stability in the sagittal plane could contribute to the development of vertebral body fractures after OLIF.8)

In the author's case, the two patient may have caused a fracture of the vertebral body using a relatively large cage compared to the disc height. Complications may occur in the OLIF in relation to the cage size. An attempt at inserting an oversized cage may also lead to nerve root injury. It is critical that care be taken to protect the dural sac and exiting nerve root during discectomy, end-plate preparation, and cage insertion. But, failure to achieve adequate distraction of the annulus fibrosus and undersizing the cage can risk pseudarthrosis and cage migration with potential injury to the neural elements.

The second case was caused by segmental instability immediately after surgery without posterior instrument. In the standing position, 80% of spine loads are transmitted through the anterior column.9) The implant or graft must be capable of withstanding these loads to allow fusion to occur. Cage migration rates as high as 8% have been seen after uninstrumented PLIF surgery and often require revision surgery.10) Spinal posterior instrumentation has been shown to increase the fusion rate by limiting the motion across the fusion segments. The vertebral body fracture was caused by laminotomy in past history and uninstrumentation, and the loading of cage in unbonded state.

In both cases, the lateral release was well performed in all cases, but the absence of anterior longitudinal ligament release was considered to be one of the factors causing the coronal fracture of the vertebral body. Our cases serve to caution surgeons that OLIF is not without risks of postoperative clinical complications, even in non-osteoporotic patients, especially in cage-related fractures of the vertebrae.