21 consecutive PVDO patients treated with TIDF with AIBG at a single institution between March 2014 and January 2017 with minimum of 2 years follow-up were retrospectively enrolled. Clinical and radiographic data were collected for all patients with thoracic or lumbar spine infections and who presented with neurologic deficit, spine instability, or intractable pain, and whose pathogens had not been identified or whose response to antibiotics had failed. Patients with tuberculosis bacilli infection and post-spinal operation infections were excluded. The study was approved by the institutional review board (CRMH IRB No. 201801075B0).
From the medical record, demographic data, diagnosis, affected levels, placement of screws, imaging results, laboratory data, duration of antibiotic treatment, neurologic status, and functional outcomes were collected. All patients wore Taylor braces for at least 3 months after surgery. Patients were followed-up at two weeks, and then one, three, and six months, then annually until at least 2 years.
Choice of parenteral antibiotics was based opinion of an infectious disease specialist and culture results. Because some patients initially receiving conservative treatment, antibiotic treatment of some patients began prior to their operations. Serial C-reactive protein (CRP) levels were collected. The normal range of CRP is below 5.0 mg/L. The duration of treatment using parenteral antibiotics was determined based on clinical symptoms and lab parameters. If the patient’s CRP declined to below 25 mg/L and they were afebrile without any signs of infection, we discharged the patient on oral antibiotics. All patients were prescribed oral antibiotics for 2 ~ 3 months after discharge.
The clinical outcomes assessed were VAS for back pain and the American Spinal Injury Association (ASIA) impairment scale for neurological status. In addition, local kyphotic angles of the superior and inferior endplates of the affected levels were measured on standing XR before and after surgery and at final follow-up. Fusion was assessed by two of our authors who didn’t participate in the surgery on the final follow up x-ray and defined as continuous trabeculae bridging across the interface of the treated segments, whereas the presence of any radiolucent interruption at the treated segments was defined as pseudarthrosis. Functional outcomes were evaluated using the Kirkaldy-Willis classification [23]. Finally, CRP levels and duration of antibiotic administration in the AIBG patients was compared to a control group[5, 11] from a cohort of 28 patients receiving an identical TIDF procedure with the same indications but without AIBG.
Statistical analysis
Differences between the “non-antibiotic-impregnated control group” and the “antibiotic-impregnated group” were compared using the Mann-Whitney U test. All statistical operations were performed using SPSS version 22.0 (IBM, Armonk, NY, USA). A p-value < 0.05 was considered significant.
Operative procedures technique note
A modified transforaminal lumbar interbody fusion (TLIF) surgical approach was performed. This single posterior approach included debridement, fusion, and pedicle screw instrumentation. A midline open approach was used keeping the posterior elements of the spine as intact as possible. The paraspinal muscles were detached subperiosteally. Unilateral facetectomy and limited laminotomy were performed (Fig. 1A), followed by radical debridement to remove abscess, infected disc material, endplates, and sequestrum from the intervertebral space by curved curettes and disc roungeurs. (Fig. 1B). The site of entry was determined based on the expected extend of debridement necessary based on symptom severity, radiographs, CT, and MRI. Posterior stability was maintained by preserving the spinous processes, supraspinous ligaments, and the contralateral facet joint if possible.
Tissue samples were analyzed for aerobic, anaerobic, tuberculous bacilli, and fungi. Residual tissue was sent for histopathologic examination. If iliac autograft was not sufficient to fill the residual bone defect after debridement, allograft was added to the autograft (Fig. 3D).
Graft was mixed with antibiotics based on the results of pre-operative cultures if available. If no culture result was available, vancomycin 2 g plus gentamicin 80 mg was added to ensure both gram-positive and gram-negative coverage. After radical debridement, the resulting void was packed with AIBG as solidly as possible (Fig. 1C). Sites of fixation were based on bone quality and clinical condition. Pedicle screws were inserted into segments with sufficient bone mass to secure the screw and far enough away from the destroyed areas of bone to avoid recurrence of infection.