Inaccurate implant positioning often causes complications in TDR surgery

Surgeon offers surgical considerations for primary and revision total disc replacement procedures.

Issue: February 2007

At first glance, complications after total disc replacement may appear related to a faulty implant, but in most cases, poor positioning of the implant actually causes the complications, according to Hallett H. Mathews, MD, of Richmond, Va.

Other causes of complication: poor patient selection and failure to locate the cause of pain.

"We're no different than a pain physician who is seeing a patient with pain pathology. ... In reality, we select a lot of bad patients, which creates bad outcomes," Mathews said at the North American Spine Society 21st Annual Meeting.

He offered key considerations for avoiding and treating complications after total disc replacement (TDR).

Inaccurate implant positioning

Common complications after TDR include disassembly of multiple-piece prostheses, subsidence, dislodgement, dislocation, unanticipated fusion and wear debris, Mathews said. Surgeons also see late complications, such as polyethylene or metal-on-metal wear. These complications are often related to inaccurate implant positioning, sizing and indications.

Hallet H. Matthews, MD [photo]
Hallet H. Matthews

"If you overdistract the segment to place the largest disc possible, you'll have problems. If you create a fracture of that segment, you'll have problems. If you place too small of a device because you're being conservative, you'll have problems because of subsidence," Mathews said.

Neurologic events also occur, such as a misplaced prosthesis in the foramen that causes nerve compression, stenosis after artificial disc placement, and bone and disc fragments that enter the spinal canal after inadequate cleanout and mobilization of the disc space, Mathews said.

Wound complications are also typically related to the surgical approach.

Avoiding complications

Literature reports further reveal venous and arterial complications in disc replacement patients, as well as injuries to bowels, lymphatics and other structures around the dissection, Mathews said.

For these reasons, access during surgery is key, especially with venous tissues around the bifurcation and the dissection of the large anterior vessels of the lumbar spine, he added.

Surgeons should understand the patient's anatomy and respect it at the risk of causing catastrophic complications, Mathews said. "Respecting tissue tolerances are important, because the way you retract one large vessel is not necessarily the way you would retract another large vessel," he said.

Before discectomy and segment mobilization, surgeons must also appropriately place the retractors to maintain and stabilize the anatomy in a safe position.

Another crucial point: identifying the midline. "One of the biggest complications of total disc replacement is making false assumptions to where the midline is located," Mathews said. "If that's not identified and documented from the beginning, the whole surgery is skewed."

Even with ideal surgical technique, however, complications can occur if surgeons do not acknowledge the potential for catastrophic bone failure in their osteoporotic patients, Mathews said. Osteoporosis is a main cause of failure in TDR.

"We [need to ask] the hard questions about bone density and ... nutrition," Mathews said.

Revising after complications

When revising TDRs, Mathews said, surgeons should consider their own surgical capabilities, the patient's pathology and the location of the pathology. They should also create a rationale for, and design of, the procedure.

"Each surgical failure represents a unique circumstance that requires an analysis of why there was an adverse outcome. Inclusion criteria and surgical technique require critical analysis in a revision consideration," he said.

"Arthroplasty procedures are not like standard fusion stabilization. You can't just do a fusion operation [quickly] and get away with it," Mathews said. "These devices have to be put in precisely and with good calculation in tissue balancing. You can't assume that a specific prosthesis or design will always cure back pain. It may not. Specific attention to an accurate diagnosis, an exceptional surgical technique and planning will go a long way toward achieving a successful outcome."

He also advised surgeons to know the indications for removing a disc replacement. "If the disc replacement is in a good position and there's continued pain, you have to prove [the disc replacement] is the source of the pain," Mathews said. "It may not be, so you have to find the pain generator and obtain an exact diagnosis. There may be other causes of pain that were there prior to the index surgery or have developed since surgery was performed."

Overall, Mathews stressed that surgeons should consider all aspects of avoiding a complication, asking questions such as, "How long will the patient live? What are the patient's expectations and goals of the procedure and are they realistic? What are the anticipated activity levels of the patient? What are the material characteristics of the prosthesis? Will that prosthesis perform safely for the lifetime of the patient? When could one anticipate a revision procedure, even under optimal situations?"

For more information:
Mathews HH. Symposium: Complications in spine care management. Presented at the North American Spine Society 21st Annual Meeting. Sept. 26-30, 2006. Seattle.
Hallett H. Mathews, MD, Midatlantic Spine Specialists, 7650 Parham Road, Suite 301, Richmond, VA 23294; 804 270-5163; masshhmathews@aol.com. He is a research consultant for Medtronic Spine and Biologics, serves on the boards of the North American Spine Society and Spine Arthroplasty Society, and is the current president of the International Society for Minimal Intervention in Spine Surgery.