The advantages of TDR over fusion, say proponents, are faster recovery time, less postoperative pain and the retention of full motion.
This artificial disc will do for spine surgery what the artificial joint.
The goal of the disc prosthesis is to relieve pain caused by problems and pinched nerves in the lower spine. The diseased disc is replaced by special metal and polyethylene implants.
The Spine Institute at Saint John's Health Center offers total disc replacement with the ProDisc® implant. The aim of total disc replacement is to recreate normal dynamic function. It can be considered for patients with low back pain as an alternative to spinal fusion.
The ProDisc was designed in the late 1980 by Thierry Marnay, a French Orthopedic Spine Surgeon. The ProDisc is based on spherical articulations. It has metal endplates made of a cobalt chromium molybdenum alloy (CoCrMo).
Figure 7: Three components of the ProDisc
Figure 8: 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 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 9: Insertion of the ProDisc metal endplate
Figure 10: Disc inserted and complete (with polyethylene core in place)
The ProDisc has been implanted in 500 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. Up to fifteen study centers will ultimately be participating 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 is 2:1, with 2 out of every three Study participants getting a ProDisc and 1 in three receiving the fusion. ProDisc can be implanted at L3-L4, L4-L5, or at L5-S1. There is also a concurrently running two-level PRODISC disc replacement study. In the two-level study, patients can 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 followed for 24 months and then annually until the last patient in the study is 24 months postoperatively.
Figure 11: Implanted ProDisc artificial disc
Figure 12: 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 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, osteomalacia), or small vertebral bodies.
Figure 13: Implanted ProDisc artificial disc view from the front
Figure 14: 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, a patient's 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.