PEEK Satellite nucleus replacement sphere.

INTRODUCTION

Building on the early work of Dr. Paul Harmon, Dr. Ulf Fernström and Dr. Alvin McKenzie, a revised procedure has been developed from a posterior approach, using minimally invasive techniques, that inserts an appropriately sized implant into the nuclear recess of the lumbar intervertebral disc to help stabilize the motion segment with effective surgical and clinical outcomes. The concept is to assist the natural history of the degenerative spine cascade process by stabilizing, not replacing, the intervertebral disc space. The technique and implant are an effective alternative to the discectomy procedure, which has a documented history of disc height loss, reherniations and adjacent level breakdowns.
Primary indications include symptomatic Degenerative Disc Disease with or without disc herniations, midline disc herniations, recurrent disc herniations and mild translational deformities with instability. The spherical implant also can be inserted through a variety of approaches including posterior, posterior lateral, direct lateral or anterior using standard or minimally-invasive procedures.

Implant Features

• Inserted via a minimally-invasive posterior approach
• Radiolucent PEEK material with radiographic markers
• Potential for less patient morbidity; faster recovery
• Broad size range to match varying anatomy (11mm to 16mm diameter available)
• Sphere restores disc space height and sagittal balance
• Fits within the natural concavity of the vertebral bodies
• May lessen adjacent-level degeneration
• Rests in the anatomic center of rotation
• Retains or restores motion
• Restores load transmission through vertebral body endplates

Clinical history on similar devices

Dr. Ulf Fernström of Uddevalla, Sweden, was the first to publish the results of replacing a disc with a mechanical prosthesis. Now known as the Fernström Ball, the prosthesis consisted of a solid stainless steel sphere, implanted through a posterior approach following a lumbar discectomy.
Between 1962 and 1964, Dr. Fernström replaced 191 lumbar discs in 125 cases. In 1966, he published the two year results from 105 of the lumbar cases. In his report, Dr. Fernström compared the results of disc replacement with his steel ball to a control group of 100 discectomies, both of which he followed for five to eight
years.1 He divided the cases into two groups: Group I consisted of patients with a herniated disc, and Group II consisted of patients with disc degeneration (i.e., positive discography and no root compression).
At two-year follow-up, 12% of the patients who underwent disc replacement and 60% of those who underwent discectomy in Group I reported back pain. In Group II , 40% of the disc replacement patients and 88% of the discectomy patients reported back pain. In Group I, 14% of the disc replacement patients and 50% of the discectomy patients reported sciatica. In Group II , 47% of the disc replacement patients and 80% of the discectomy patients reported sciatica.
Dr. Fernström also reported total disc collapse occurred in 0% of the disc replacement patients and in 48% of the discectomy patients.
Dr. Fernström concluded that the results obtained as a result of disc replacement were better than those achieved as a result of discectomy, and that the results were similar to the results of discectomy combined with fusion.

Preoperative planning and patient positioning

The patient is placed on the operating table in the prone position, making sure to allow enough room for lateral fluoroscopy (Figure 1). A midline incision provides the approach and unilateral exposure of the interlaminar space and facet joints at the affected level. A hemi-laminectomy is performed to expose both the dura and annulus lateral to the dura (Figure 2). If needed, the spinous process can be undercut to gain access (Figure 3).
Care should be taken to identify the lateral dura and traversing nerve root at the affected level. The epidural veins are coagulated over the annulus, and any other tethering of the traversing root is dissected to allow for sufficient retraction of the dura and root.

Figure-1	Figure-2	Figure-3

Distraction and disc removal

Distraction can be achieved with a lamina or interspinous spreader. Using the table frame to place the patient in a kyphotic position may provide an adequate opening of the disc space (Figure 4).
While protecting the dura and nerve root, perform a discectomy by incising the annulus lateral to the dura. Use the Pituitary Rongeur to remove the excised annulus and nuclear material. Remove any extruded fragments to decompress the neural elements and provide entry to the disc space for distraction with minimal or no nerve
root retraction.

TRAILS

Trials are used to confirm the appropriate final sphere diameter. The Trials are tapered on the leading and trailing edge for easier insertion and removal from the disc space. Align the flat ends of the Trial parallel to the endplates. Lightly tap the trial into the disc space and turn the handle 90° to assess the fit. The trial should fully engage the endplates and restore the disc space to its normal height (Figure 6). Lateral fluoroscopic imaging is helpful to assess the fit of the Trial.
To remove the Trial, turn the handle 90°, attach the Slap Hammer to the Extension Handle and gently tap it to remove the Trial from the disc space. Continue to use sequentially larger Trials until the final sphere diameter is determined.

FINAL PREPARATION

The Sphere curettes can be used to remove any excess nucleus material. Using a curette equal to the final Trial diameter, insert the curette into the disc space with the smooth side oriented toward the surrounding neural structures. Care should be taken to preserve the endplates where possible. Position the curette at the desired location of the implant. Generally, this is in the center of the disc space and slightly posterior to midline (Figure 5a). Turn the Curette 360° to remove excess nucleus (Figure 5b). Remove the instrument by orienting the smooth side of the Curette toward the neural structures and gently removing it from the disc space (Figure 5c).

Figure-5a	Figure-5b	Figure-5c

Implantation

Thread the appropriately sized sphere onto the Inserter (Figure 6). Slide the Inserter’s outer sleeve forward so the pin engages the small anti-rotation dimple on the sphere and tighten the wingnut to lock into place. Gently impact the sphere into the disc space by orienting the sphere toward midline of the disc space (Figure 6). Once the sphere is fully seated, turn the Inserter’s handle counter-clockwise to disengage the implant. The Angled graft impacter can be used to achieve the desired position of the implant. In the event that the implant needs to be removed, thread the inserter into the implant and remove.

Indications

The SATELLITE System PEEK Nucleus Replacement is indicated for use in skeletally mature patients (at least 17 years old) undergoing surgery of the lumbar spine for symptomatic degenerative disc disease.

Contraindications

The SATELLITE System PEEK Nucleus Replacement should not be implanted in patients who have an active infection, or who are pregnant. Nor should the device be used in patients who do not meet the criteria listed above.

Postoperative course

Gradually increase your activity. May be required to wear a back brace after surgery and to avoid repetitive bending, lifting, twisting, and athletic activities while recovering. Cautioned to avoid vibrations, like experience when driving a car, for a period of time after surgery.
Contact your doctor immediately if:
• There is a fever
• The incision starts leaking fluids
• There is trouble swallowing or breathing
• There is trouble urinating
• New or increased back or leg pain or numbness

Postoperative Complications

Potential risks to any surgical procedure include unforeseeable complications caused by anesthesia, blood clots, undiagnosed medical problems, such as silent heart disease, and rare allergic reactions. Some risks of spinal surgery include incomplete pain relief, damage to the nerve roots, infection, and complications with the device. Most of these complications can be treated once they are detected, but sometimes they require a longer period of hospitalization or recovery, additional medications, and sometimes even additional surgery.
In general, these complications happen very infrequently, but it is important to remember that surgery is a human endeavor, and, therefore, mistakes and unforeseeable complications do occur.