Usefulness of dynamic stabilisation with mobile percutaneous pedicle screw for thoracic vertebral fractures in diffuse idiopathic skeletal hyperostosis

Abstract

We report a case of vertebral fracture with diffuse idiopathic skeletal hyperostosis (DISH) who underwent posterior dynamic stabilisation using mobile percutaneous pedicle screws (PPS) with 1 above-1 below and obtained good bone fusion. A 76-year-old man experienced severe low back pain after he fell backward 1 m off a stepladder during work. A 12th thoracic vertebral fracture with DISH was observed. As the fractured part was unstable due to a three-column injury, and the conservative treatment of resting was not successful, posterior dynamic stabilisation with a mobile PPS between T11–L1 was performed the 38th day after injury. Immediately after surgery, a fracture gap was observed, but 5 months later, vertebral body height was shortened by about 4 mm, and good bone fusion was observed without loosening of the screw. The mobile PPS flexibly adapts to spinal plasticity and may be useful for bone union in vertebral fractures associated with DISH.

Background

Vertebral fractures with diffuse idiopathic skeletal hyperostosis (DISH) have increased due to societal ageing. DISH is characterised by fusion of the vertebral bodies caused by bone proliferation that results in osteophytes and bone bridges anteriorly and posteriorly on the vertebral bodies. The vertebral bodies become shaped like a long bone. DISH-related fractures are prone to three-column injuries, and there is a high risk of spinal cord injury due to instability of the fractured part, so early fusion surgery is recommended.^{1 2} However, as most cases are in elderly people, patients often have osteoporosis and problems with the fixation of the pedicle screws are likely to occur. In addition, many patients are kyphotic. The prone position during surgery causes a gap in the vertebral fracture, which is disadvantageous for bone union, creating a high risk of postoperative correction loss and screw loosening. Since loosening and back out of screws are likely to occur in the fixed range of 2 above-2 below, more reports are recommending posterior fixation with pedicle screws 3 above-3 below.^{3 4}

The Segmental Spinal Correction System (SSCS) is an implant developed by von Strempel^{5 6} in Germany and being used since 1988. The rod is solid, but the screw head of the pedicle screw is mobile and laterally bent. Rotational and translational movements are completely dampened, but some movement is allowed in the anteroposterior (sagittal plane) direction.

CosmicMIA (Ulrich Medical, Ulm, Germany), which is a load-sharing system, has been developed in recent years as a percutaneous SSCS.⁷ Eguchi et al⁸ previously reported that the mobile percutaneous pedicle screws (PPS) using cosmicMIA in combination with oblique lateral interbody fusion (OLIF) promotes bone healing without the loosening of screws and can be a better vertebral fusion technique.

We report a case of vertebral fracture with DISH who underwent posterior dynamic stabilisation using mobile PPS with 1 above-1 below and obtained good bone fusion.

Case presentation

A 76-year-old man without relevant medical history experienced severe low back pain after he fell backward 1 m off a stepladder at work. The first day after the injury, he consulted a physician who diagnosed a compression fracture of the 12th thoracic vertebra (T12). On the second day after the injury, he was admitted to our hospital due to difficulty in moving.

At the first visit to our hospital, his neurological function was assessed using the manual muscle test and was as follows (right side/left side): iliotibialis 5/5, quadriceps 5/5, tibialis anterior 5/5, extensor hallucis longus 5/5, flexor hallucis longus 5/5 and gastrocnemius 5/5. A neurological examination detected no reduction in muscle strength, loss of sensation, or bladder and rectal disorders. The Japanese Orthopaedic Association (JOA) score was 10/29 points (normal score, 29 points); the visual analogue scale (VAS; from 100 (extreme amount of pain) to 0 (no pain)) score for low back pain was 70/100. CT at the time of injury revealed a three-column injury that passed from the centre of the T12 vertebral body to the posterior pedicle and spinous process of T12. Continuous ossification was observed anterior to the vertebral body from T12 to T1 on the cranial side, and DISH was diagnosed (figure 1A–C). MRI T2-weighted images in the sagittal plane exhibited low intensity of the T12 vertebral body, but no spinal canal stenosis at that level. MRI short tau inversion recovery images in the same plane indicated high signal intensity in the T12 vertebral body, T11–12 and T12–L1 intervertebral discs, and the spinous processes of T11 and T12 showed a three-column injury (figure 1D, E).

Figure 1.

Preoperative CT of the lumbar spine (A, B) and cervicothoracic spine (C), and MRI (D, E) findings. Sagittal plane CT of the lumbar spine (A), cervicothoracic spine (C) and a frontal plane view of the lumbar spine (B) revealed a T12 vertebral body fracture with a three-column injury that passed from the centre of T12 to the posterior pedicle and spinous process of T12 (red arrow). Continuous ossification was observed anterior to the vertebral body from T12 to T1 on the cranial side (arrowheads). Diffuse idiopathic skeletal hyperostosis was diagnosed. A sagittal plane MRI T2-weighted image (D) showed low intensity in the T12 vertebral body, but no spinal canal stenosis at the same level. Sagittal plane MRI short tau inversion recovery images (E) exhibited a high signal intensity in the T12 vertebral body, the intervertebral discs at T11–12 and T12–L1, and the spinous processes of T11 and T12, indicating a three-column injury.

Treatment

Initially, the patient was treated conservatively and rest was recommended because an orthopaedic surgeon at our hospital diagnosed a simple vertebral compression fracture. However, the patient had persistent severe low back pain and difficulty moving, so he was re-examined by a spine surgeon (YE) and was found to have a vertebral fracture with DISH.

On the 38th day after the injury, posterior dynamic stabilisation was performed surgically by inserting mobile PPS at T11 and L1. The dynamised pedicle screw is available elsewhere in the cosmicMIA system (figure 2). The operation took 48 min and there was 23 mL of blood loss.

Figure 2.

CosmicMIA. The cosmicMIA is a load-sharing system that controls rotation and translation but allows flexion and extension. Frontal view (A) and lateral view (B). The hinged screw allows 20° of mobility in both the cranial and caudal directions.

Outcome and follow-up

Clinical symptoms

Immediately after the operation, the patient wore a hard corset and began to stand and walk. Five months after surgery, the low back pain VAS improved to 10/100, the JOA score improved to 24/29 points, and it became possible for him to stand and walk with minimal pain. The hard corset was worn for 6 months after surgery, and a soft corset was worn until 9 months after surgery.

Image evaluation

Immediately after surgery, CT showed that the T12 anterior vertebral body height was 21 mm, posterior vertebral body height was 23 mm, and a fracture gap was observed. Five months after surgery, the anterior vertebral body height was 17 mm and the posterior vertebral body height was 19 mm; there was a reduction in vertebral body height of 4 mm, but bone fusion was observed lateral and anterior to the vertebral body (figure 3). Complete bone fusion was observed 9 months after surgery (figure 4). The mobile pedicle screws at T11 and L1 were parallel immediately after surgery (figure 5A), but the screw direction was closer to the fracture side due to bone fusion of the T12 vertebral fracture and shortening of vertebral body height. No screw loosening was observed 5 months after the surgery (figure 5B). On a standing X-ray, the sagittal vertical axis (SVA) changed minimally from 65 mm before surgery to 67 mm 5 months after surgery, and there was no change in the spinal sagittal alignment (figure 5C, D).

Figure 3.

CT immediately after surgery (A, C) and 5 months after surgery (B, D). Frontal (A, B) and sagittal (C, D) CT. Immediately after surgery (A, C), the height of the anterior T12 vertebral body was 21 mm, the height of the posterior T12 vertebral body was 23 mm, and a fracture gap was observed (red arrow). Five months after surgery (B, D), the anterior vertebral body height was 17 mm and the posterior vertebral body height was 19 mm, but bone fusion was observed laterally and anteriorly to the vertebral body (arrowhead).

Figure 4.

CT findings 9 months after surgery. Frontal (A) and sagittal (B) CT demonstrated complete bone fusion (arrowhead) without loosening of the pedicle.

Figure 5.

3D-CT and standing whole spine X-rays preoperatively and postoperatively. Based on 3D-CT images (A, B), the mobile pedicle screws at T11 and L1 were parallel (A) immediately after surgery due to bone fusion of the T12 vertebral body fracture and shortening of vertebral body height. Five months (B) after surgery, the screw direction was closer to the fracture side, but no loosening of the screw was observed. On a standing lateral plain X-ray, the sagittal vertical axis (SVA) changed from 65 mm before surgery (C) to 67 mm 5 months after surgery (D), showing no significant change in spinal sagittal alignment. The SVA was measured as the distance from the C7 plumb line to a perpendicular line drawn from the superior posterior end plate of the S1 vertebral body on standing lateral radiographs.

Discussion

Forestier disease or DISH, a systemic non-inflammatory disease of unknown aetiology, is characterised by continuous ossification of ligaments and entheses.⁹ Forestier first described this entity in 1950 as a case of senile ankylosing hyperostosis of the spine, and it was renamed DISH by Resnick and Niwayama in 1975.¹⁰ Radiological diagnostic criteria include (1) flowing bridging ossification of at least four contiguous vertebrae without disc degeneration, which is estimated from preservation of the intervertebral disc space and (2) absence of degeneration or fusion of the sacroiliac and apophyseal joints.

A spinal fracture associated with DISH has a long lever arm due to extensive ossification of the spine, and stress is concentrated on the injured part, resulting in a pathological condition similar to a transverse fracture in long bones. As the three-column fracture is extremely unstable, it is easy to dislocate the fractured part and cause delayed spinal cord injury.¹¹ In addition, bone fusion is likely to be prolonged and non-union is likely to occur due to kyphotic deformation and instability of the fractured part.¹² For these reasons, for spinal fractures with DISH, instrumented spinal fusion is recommended at an early stage.^{1 2}

However, in the elderly, the pedicle screws often cannot be sufficiently fixed due to the marked decrease in bone mineral density (BMD) in the vertebral body. Reinhold et al¹³ reported that in the spine of elderly patients with DISH, bone bridge formation external to the vertebral body and loss of BMD inside the vertebral body progress simultaneously. Westerveld et al¹⁴ reported similar findings, suggesting that the osteophytes and bone bridging cause stress shielding that results in the lower trabecular BMD.

Caron et al³ reported that in 112 consecutive patients with ankylosing spinal disorders (ASD), 19% of patients had delayed diagnosis of their spine fracture, 81% of whom had resulting neurological compromise. Schiefer et al¹⁵ identified the following causes of delayed diagnosis: (1) doctors do not suspect serious trauma if the injury is caused by minor trauma; (2) DISH and ankylosing spondylitis cannot be diagnosed; (3) simple plain radiography of the spine may fail to reveal the fracture with ASD. In this case as well, the patient was initially diagnosed with a vertebral compression fracture and was treated conservatively.

Instrumentation for vertebral fractures with DISH is generally performed using a posterior approach via the pedicle rather than an anterior approach due to problems with bone quality and the lever arm of the vertebral body. Compared with the anterior approach, the advantages of the posterior approach are that various instrumented fixation methods can be selected, and that decompression also is possible.²

Pedicle screws can loosen and back out in the fixed range of 2 above-2 below. Many recent reports recommend posterior fixation with 3 above-3 below, or more pedicle screws.^{3 4}

Several studies have reported the efficacy of a transdiscal screw technique with its strong fixation force for some lumbar degenerative diseases.^{16 17} Hishiya et al reported the efficacy of posterior spinal fixation with penetrating endplate screws for DISH-related thoracolumbar fractures providing more rigid and less invasive fixation than conventional pedicle screws.¹⁸

The spine with DISH often exhibits kyphosis. During surgery, the kyphosis should be maintained to prevent the fracture gap from separating due to the prone position of the patient. Several studies reported that insertion of PPS with the patient in a lateral position may be useful for DISH-related fractures, providing sufficient lumbar flexion and fracture reduction.¹⁸

The SSCS is a pedicle screw-based system with a rigid rod, but the unique structure of having a hinge in the screw head allows for micromotion.¹⁹ The screw moves 20° in the sagittal plane, but is rigid in the coronal plane and for rotation. The SSCS does not allow for lateral bending, rotation or translation except for sagittal plane motion. With the SSCS, the rod and the screw head are tightened in a neutral position. Therefore, facet joint sliding is controlled while still allowing 2°–3° micromotion of the disc because of the hinge between the screw head and the screw thread. It is thought that the micromotion works as a shock absorber, like a car suspension, and prevents adjacent segment disorder.²⁰ Eguchi et al previously reported that the mobile PPS, in combination with OLIF, promoted bone healing, contributed to fewer implant fractures and reduced screw loosening.⁸ The cosmicMIA mobile PPS is not suitable for multilevel fixation because the rotational and translational motion of the screw head is completely damped and the rod connection is difficult like the monoaxial screw. The flexibility of the PPS provided by the hinge mechanism relieves the stiffness and provides greater flexibility for the spine, but can result in screw loosening or instrument breakage. However, a short segment dynamic stabilisation may prevent these negative consequences.

In this study, the posterior dynamic stabilisation system with 1 above-1 below using the mobile PPS was performed for a thoracic vertebral fracture with DISH, and good bone fusion was obtained without loosening of the PPS. Although a fracture gap was observed immediately after surgery due to the intraoperative prone position, vertebral body height was shortened by about 4 mm and bone union was observed without loosening of the pedicle screws 5 months after surgery. A short segment dynamic stabilisation of 1 above-1 below (T11–L1) at the bottom of the T1–T12 long lever arm may disperse stress and reduce adjacent segment disease and instrument breakage. The mobile PPS is minimally invasive, flexibly adapts to spinal plasticity and is thought to be useful for bone fusion in vertebral fractures with DISH. This study is the first to perform posterior dynamic stabilisation with the mobile PPS for thoracic spine fractures with DISH.

Patient’s perspective.

During work, I fell from a height of 1 m and hit my back. I was hospitalised because I had a severe low back pain and could not stand up. At first, I wore a corset and was at rest, but my low back pain did not improve and I chose fusion surgery. I was able to walk immediately after the surgery. Even when I took off the corset 9 months after the surgery, I was able to lead a daily life without low back pain. I am very happy with the fusion surgery.

Learning points.

• We experienced a case of thoracic vertebral fracture with diffuse idiopathic skeletal hyperostosis (DISH) who underwent the posterior dynamic stabilisation system using mobile percutaneous pedicle screws (PPS) with 1 above-1 below.

• Although the fracture gap was observed immediately after surgery, the vertebral body height was shortened by about 4 mm and good bone union was observed without loosening of the pedicle screws 5 months after surgery.

• Mobile PPS flexibly adapts to spinal plasticity and may be useful for bone fusion in vertebral fractures with DISH.