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Issue: February 2008
February 01, 2008
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‘Shockingly low’ fusion rate for patients with early implant-associated infections

Investigation finds external beam radiation is a risk factor for delayed union, not smoking or diabetes.

Issue: February 2008

A new study indicates that early-onset spinal implant-associated infections are linked to high morbidity, and that a regimen of debridement, implant retention and antibiotics may be effective for most of these patients.

In a retrospective review of more than 3,600 spinal fusions (2,800 instrumented), investigators found 29 cases of early-onset implant-associated infections. A treatment course made up of surgical debridement, up to 6 weeks of intravenous antibiotics, implant retention and oral antibiotic suppression succeeded in treating the infection for 72% of these cases.

“That was well below what we would expect in an elective surgical population,” Paul M. Huddleston, MD, said during his presentation at the 17th Annual Open Scientific Meeting of the Musculoskeletal Infection Society.

The research also revealed a 35% fusion rate at 1 year in patients with early-onset implant-associated infections and a 2-year fusion rate in 80% range. It identified external beam radiation as a risk factor for delayed fusion in these patients (P=.02).

Treatment algorithm

Huddleston and his colleagues reviewed the cases of patients who underwent spinal fusion between 1994 and 2002 and identified the 29 patients with infections. Patients in the study group were about 60 years old and had a body mass index of 30. Nearly half of the group were smokers (48%) or had previous spinal surgery (48%) and 31% underwent radiation treatment for cancer.

Using the treatment protocol, the patients had an average of 2.2±1.3 surgical debridements, 41±12 days of IV antibiotics, 303±29 days of oral suppression and nearly a month-long hospital stay. They were cured in an average of 7.3±3 months. Investigators deemed patients cured if they had normal lab results, healed wounds and no systemic signs of infection. While the protocol was successful in more than 70% of the patients, nearly 30% required additional surgery, Huddleston said. The study revealed various infections including 22 cases of Staphylococcus species, 11 cases of Staphylococcus alone and five instances of methicillin-resistant Staphylococcus aureus (MRSA).

Fusion rates

“The spinal fusion rate, the thrust of our paper, was very low — shockingly low,” Huddleston said. The investigators discovered a 35% fusion rate at 1 year and an initial rate of 96% at 2 years. However, two recent additional surgeries lowered the 2-year fusion rate. Of the patients who fused at 2 years, 44% had significantly disabling pain and 41% used opiates for pain.

The investigators also found that nine of the 29 patients had loose implants requiring removal. Five patients had nonunion. “Three of the five patients who developed true, visualized, verified nonunion were patients who had an external beam radiation treatment for cancer and three of 29 had to have revision of their instrumentation,” Huddleston said.

Regarding risk factors, Huddleston said oncologic radiation therapy was most detrimental for these patients. While 41% of patients without X-ray treatment fused at 1 year, only 17% of those who underwent X-ray treatment fused. “Shockingly though, we didn’t see that smoking, diabetes and some of the other usual suspects had any effect on their fusion rate,” Huddleston said.

An intraoperative image of a solid fusion
An intraoperative image of a solid fusion seen at the time of spinal implant removal following infection. The patient was initially treated for infection postoperatively then suppressed with antibiotics for 1 year. He had symptomatic loose implants and had them removed. At the time of surgery his fusion was seen to be healed.

A patient that had a postoperative implant
A patient that had a postoperative implant associated infection following posterior spinal fusion. This patient had been managed nonoperatively with oral antibiotics and at 2 years postoperatively was still symptomatic. He had exploration of his wound, cultures taken and the loose implants removed. He had a large psuedoarthrosis (as demonstrated by the black line) through the middle of his fusion mass. He underwent revision fusion and instrumentation.

Images: Huddleston PM
For more information:
  • Paul M. Huddleston, MD, is a consultant in the Department of Orthopedic Surgery at Mayo Clinic, 200 First St. SW, Mayo 14th Floor, Rochester, MN 55905; 507-284-2511; e-mail: huddleston.paul@mayo.edu. He has no direct financial interest in any products or companies mentioned in this article.

Reference:

  • Ali MH, Kowalski T, Berbari, et al. Spinal fusion rate in patients with early-onset spine implant associated infections. Presented at the 17th Annual Open Scientific Meeting of the Musculoskeletal Infection Society. Aug. 10-11. San Diego.