Total Disc Replacement - ProDisc

Total Disc Replacement - ProDisc

PRODisc
Fig. 6: Three components of the ProDisc (larger view)

Prodisc
Fig. 7: Assembled ProDisc
(larger view)

prodisc
Fig. 8: Insertion of the ProDisc metal endplate
(larger view)

disc inserted and complete
Fig. 9: Disc inserted and complete (with polyethylene core in place)
(larger view)

implanted prodisc
Fig. 10: Implanted ProDisc artificial disc (larger view)

prodisc patient bending backwards
Fig. 11: ProDisc artificial disc (patient bending backwards)
(larger view)

implanted prodisc
Fig. 12: Implanted ProDisc artificial disc view from the front
(larger view)

side view of prodisc
Fig. 13: Side view of ProDisc artificial disc at L4-L5 and L5 -S1
(larger view)

Several manufacturers are currently researching, developing and testing total disc replacement in the US. The Charite has been approved by the FDA for the surgical treatment of single-level disease at the L4-5 or L5-S1 levels. Four other lumbar devices currently in clinical trials in the US are:

  • ProDisc (Spine Solutions/Synthes)
  • Maverick (Medtronic Sofamor Danek)
  • Flexicore (SpineCore)
  • Kineflex (SpinalMotion). Investigational centers are currently recruiting patients.

ProDisc

The ProDisc was designed in the late 1980's by Thierry Marnay, a French Orthopaedic Spine Surgeon. From 3/90 to 2/93, Marnay implanted this artificial disc into 64 patients. In 1999, these patients were studied to determine the long-term results of implantation. Three of these patients had died from unrelated causes, but 58 of the surviving 61 patients (95%) were found and studied extensively at 7-11 year follow-ups. All implants were intact and functioning. There had been no implant removals, revisions, or failures.

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There was no evidence of subsidence (sinking or settling in bone) on follow-up radiographs compared to the peri-operative films, as reported by the operating surgeon as well as by an independent US Orthopaedic spine surgeon.

A significant (p <0.001) reduction in patient-reported back pain and leg pain was identified. 92.7% of these patients were "satisfied" or "extremely satisfied" with the procedure.

Two-thirds of these patients had single level implants while one-third had two level ProDiscs. There was no outcome difference between the 1 and 2 level ProDisc implantations.

Most importantly, at this long-term follow-up, there were no device-related safety issues, no untoward effects, no complications, and no adverse events.

The ProDisc is based on spherical articulations. It has metal endplates made of a cobalt chromium molybdenum alloy (CoCrMo).

Figure 6: Three components of the ProDisc

Figure 7: Assembled ProDisc

The convex bearing surface, snap-fit into the inferior end plate, is made of ultra-high molecular weight polyethylene (UHMWPE). The artificial disc is attached through a large central keel and two spikes on each endplate. Physiologically, the ProDisc matches the range of motion in flexion, extension, axial rotation, and lateral bending as a normal spine.

The device is modular, so the surgeon can customize the device to each patient's unique anatomic and physiologic requirements. There are two endplate sizes (medium and large), three heights of the polyethylene component (10, 12, and 14 mm), and two lordosis angles (6 and 11 degrees).

The implantation instrumentation is straightforward and user-friendly. Minimal access approaches to the lumbar spine, (typically through a mini-retroperitoneal approach) are possible given the streamlined design of the instrumentation.

The endplates are inserted in a collapsed form, so that over-distraction (jacking open) of the disc space is not required. Only after the metal endplates are seated in the vertebral bodies is the disc space distracted. The surgeon can appreciate the soft tissue tension, and insert an appropriately-sized UHMWPE implant within the disc space, snap-fitting it into the lower metal endplate to complete the assembly process within the body.

Figure 8: Insertion of the ProDisc metal endplate

Figure 9: Disc inserted and complete (with polyethylene core in place)

The ProDisc has been implanted in over 8000 patients in Europe since December 1999. A multicenter FDA study was started in the United States in October 2001. The first ProDisc in the United States was implanted at the Texas Back Institute on October 3, 2001. Nineteen study centers participated in the prospective randomized study, comparing the ProDisc to the current standard treatment of a 360° (front and back) fusion using allograft in the intervertebral space and pedicle screws with autograft posteriorly.

The randomization protocol was 2:1, with 2 out of every three Study participants getting a ProDisc and 1 in three receiving the fusion. ProDisc could be implanted at L3-L4, L4-L5, or at L5-S1. There was also a concurrently running two-level PRODISC disc replacement study. In the two-level study, patients could be randomized into a 2:1 format if they have two adjacent levels of symptomatic disc disease between L3 and S1.

After surgery, patients are to be followed for 24 months and then annually until the last patient in the study is 24 months postoperatively.

The single level study arm completed enrollment in April 2003. Since May 2003, ProDisc study centers have been allowed to implant a small number of nonrandomized patients with single-level ProDiscs as part of an FDA-allowed Continued Access trial. Patients must meet the same inclusion criteria as in the randomized study. Safety data is collected on these patients in the same way it was collected on the randomized patients, but they are assured a ProDisc.

The two level study arm completed enrollment in November 2003. Continued Access in this arm began in January 2004, where a limited number of patients may be treated at study sites with two-level ProDisc surgery as long as they meet the original study criteria, and continue follow-up for collection of safety data.

ProDisc is the only one of the artificial discs undergoing FDA trials that is being investigated for multiple level lumbar disc disease.

Figure 10: Implanted ProDisc artificial disc

Figure 11: ProDisc artificial disc (patient bending backwards)

Inclusion criteria are degenerative disc disease in 1 or 2 adjacent L3-S1 segments causing back and /or leg pain with radiographic corroboration. Patients must be 18-60 years old, have failed at least 6 months of conservative (nonsurgical) therapy, have an Oswestry Score >20/50, and able to comply with the protocol and follow-up.

Exclusion criteria include more than two symptomatic diseased levels, known allergy to the implant components, prior lumbar fusion surgery, clinically compromised vertebral bodies from trauma, clinically significant degenerative facet disease, lytic spondylolisthesis or spinal stenosis, degenerative spondylolisthesis >Grade I, pain that defies diagnosis, osteoporosis, metabolic bone disease (including Paget's, osteomalacia), or small vertebral bodies.

Figure 12: Implanted ProDisc artificial disc view from the front

Figure 13: Side view of ProDisc artificial disc at L4-L5 and L5-S1

Additional exclusion criteria are morbid obesity, pregnancy (or interest in becoming pregnant within the next 3 years), active infection, medication that interferes with healing (for example, steroids), Rheumatoid Arthritis or other autoimmune disease, systemic disease such as AIDS, HIV, or active hepatitis, and active malignancy (clinical signs within the past 5 years).

Patients are followed up at standard intervals. At each follow up visit, patients complete short forms, are examined, and have X-rays taken. The post op follow up intervals are at 2 weeks, 6 weeks, 3 months, 6 months, 12 months, and 2 years. Annual visits are required until the study closes.

Interim data analyses from Texas Back Institute has demonstrated that ProDisc patients have lower blood loss, shorter operative times, and average one day less hospital stay than the randomized fusion controls. Return to work data suggests that disc replacement patients can return to work earlier, both for light duty as well as unrestricted work activity, than the fusion patients. Both arthroplasty and fusion groups show a statistically significant reduction in their Visual Analog Scores and functional Oswestry scores compared to their preoperative levels. Combined data from the two largest contributing ProDisc centers have demonstrated less pain, improved function, and better patient satisfaction compared to fusion. Additionally, more patients would consider doing the ProDisc procedure again as opposed to a repeat fusion.

The ProDisc-L was approved by the U.S. FDA on August 14, 2006 for use at a single vertebral level.

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Dr. Jack Zigler, Orthopedic Surgeon, Plano, TX, 75093
Article written by: Jack Zigler, MD