Lumbar Disc Replacement
THE GENERAL PROCEDURE:
1. Surgical approach
A three-inch to five-inch incision is made on the left side of the abdomen or alternatively in the midline. The abdominal muscles are retracted to the side.
Since the anterior abdominal muscle in the midline (rectus abdominis) runs vertically, it does not need to be cut and easily retracts to the side. The abdominal contents lay inside a large sack (peritoneum) that can also be retracted, thus allowing the surgeon access to the front of the spine.
Alternatively, the peritoneum can be cut and the abdominal contents retracted to approach the spine. This is performed most commonly at L5-S1.
The large blood vessels that continue to the legs (aorta and vena cava) are gently retracted off of the anterior spine. This part of the procedure is often performed by a general or vascular surgeon.
2. Disc removal
A needle is then inserted into the disc space and an x-ray is done to confirm that the surgeon is at the correct level of the spine.
After the correct disc space has been identified on x-ray, the disc is then removed by first cutting the outer annulus fibrosis (fibrous ring around the disc) and removing the nucleus pulposus (the soft inner core of the disc)
Dissection is carried out from the front to back of the disc.
3. Preparation of the disc space
After the disc is removed, a space remains between the vertebral bodies.
Disc space shavers and spacers may be used to template the height, width, and depth of implant that is needed.
The surfaces of the vertebral bodies are meticulously prepared by burring any irregularities. This allows surface area for the contact of the implant, and maintenance of structural integrity of the bone to support the implant.
The appropriate sized spacer is placed, making sure to place it in the midline of the disc, with good fill of the disc space from anterior to posterior and from side to side.
The risks of this procedure are the same as with anterior lumbar discectomy and fusion. The difference is that this device is not a fusion. With motion, the device can migrate or wear down. These possibilities are being studied. This device is not released for general use, only as an investigational FDA device.
The procedure is performed in close proximity to the large blood vessels that go to the legs. Damage to these large blood vessels may result in excessive blood loss. Quoted rates in the medical literature put this risk at 1% to 15%. There is also a small risk of injury to the bowel or ureter, since they are in the proximity of the lower lumbar discs.
For males, another risk unique to this approach is that approaching the L5-S1 (lumbar segment 5 and sacral segment 1) disc space from the front has a risk of creating a condition known as retrograde ejaculation.
In males, there is a small risk of retrograde ejaculation with anterior approaches at L5-S1. The nerves that control ejaculation lay over the front of the L5-S1 disc. They are very sensitive, and therefore even with retraction the normal coordination of ejaculation can be disrupted resulting in the ejaculation occurring backward into the bladder. It should be noted that erection and sex drive are not affected. Fortunately, retrograde ejaculation happens in less than 1% of cases (but in some studies is higher) and tends to resolve over time (a few months to a year).
In skilled hands, this is a very safe procedure. Possible reported risks and complications may include, but are not limited to:
- Retrograde ejaculation (in men)
- Injury to the ureter
- Injury to the bowel
- Incisional hernia
- Damage to nerve roots
- Continued pain
- Adjacent disc disease kidney
- Implant extrusion
Patients are allowed gradually increased activity after the operation. Bracing may be used for one week for comfort, but motion is encouraged. The outcome of this procedure is pending FDA investigational study.