Probability analysis of peri-implant infection following external transpedicular spine fixation
Authors:   Institute of Immunology and Physiology of the Ural Branch of the Russian Academy of Sciences, Ekaterinburg, Russian Federation, Berdiugina O.V. 
Published: January 2022

The main purpose of spinal fixation is to provide conditions for vertebral fusion at the level of injury. Bone fusion is associated with many factors including stability of injured segment, restoration of the anterior support column, condition of the bone tissue and other aspects. The timing of bone formation can be affected by soft tissue inflammation at the site of the rods of the external fixation system. Peri-implant infection is reported to occur in 0.7-20 % of cases with external transpedicular fixation. The timing of the complication and the dependence of the frequency of the occurrence on the patient's treatment strategy are debatable. Another topical issue is the study of the consequences of peri-implant infection with the need to establish the validity of the assumption about the effect of peri-implant infection on the rate of bone formation using a clinical model. This would allow the findings to be used for new methods of treatment considering the risk of possible complications, giving preference to low-traumatic semi-closed methods of spine fixation. Nevertheless, external transpedicular fixation is practical for open spinal injury or significant vertebral displacement with the need of significant reduction efforts to be applied. The purpose was to explore the effect of soft tissue inflammation on the timing of bone formation with spinal fusion surgery using different surgical methods of treatment of uncomplicated spinal fractures. Material and methods The review included 111 patients with uncomplicated fractures of the lower thoracic and lumbar spine. Based on a retrospective analysis the participants were assigned to three groups depending on the presence/absence of peri-implant infection and the timing of the occurrence: 81 patients experienced no complications, 16 had serous-purulent inflammation of soft tissues at the site of the rods of the external fixation device that developed on average after 20 days with 14 patients seen with pin tract infection after 2 months of anterior fusion surgery and failed bone formation. Results Peri-implant infection rate was found to be higher with external fixation (14.4 %) than that with anterior fusion surgery (12.6 %). The complication rate was 1.85 times less with one-stage surgical treatment as compared to two-stage treatment. Peri-implant infection developed later (after 21‑63 days) with one-stage treatment as compared with two-stage procedure (after 12-24 days). Infection associated with the external fixation led to increase in timing of bone formation by 6-7 %, by 2-4 weeks on average. Bone formation failed in 35 % of cases (p < 0.0002) due to peri-implant inflammation caused by Staphylococcus aureus, as the common pathogen and the bacteria detected resulted in ineffective antibacterial therapy. Immunological parameters (IgM and haptoglobin) were quantified to assess the risk of peri-implant infection. Discussion Peri-implant infection rate associated with external transpedicular fixation was shown to be comparable with the previously obtained data. Sharply defined notions were reported earlier to differentiate between infectious peri-implant osteolysis and mechanical loosening. We compared the data on the duration of bone formation and the timing of peri-implant infection and developed a model that with high sensitivity (73 %) and specificity (100 %) allowed description of cases with impaired osteogenesis. Changes in some immunological parameters (immunoglobulins, acute-phase proteins) were shown to affect both bone formation and stability of bone fixation.