Femorotibial synostosis in the management of periprosthetic infection: analysis of the factors associated with adverse outcome

Introduction Femorotibial synostosis (FTS) is a primary salvage surgical procedure for failed total knee arthroplasty complicated by periprosthetic joint infection (PJI). Despite its widespread use, clinical outcomes with FTS are highly variable, indicating the significant role of a combination of patient-related, infectious, and surgical factors in shaping treatment outcomes. Analysis of the factors that lead to failed synostosis outcomes is of practical interest for optimizing surgical treatment techniques and predicting outcomes.

The purpose of the study was to evaluate factors associated with an FTS adverse course and outcomes as an option for restoring limb weight-bearing ability in patients with PJI.

Materials and methods A retrospective study included 46 patients who underwent FTS for PJI. The influence of patient-related (gender, age, body mass index, comorbidities), infectious (PJI type according to D.T. Tsukayama, microbiological profile), and surgical factors (number of previous debridement surgeries, anatomical and functional features of bone defects according to AORI, fixation method) associated with poor outcomes was analyzed. Univariate binary logistic regression analysis was used with calculation of odds ratio (OR) and 95 % confidence interval (95 % CI). The prognostic significance of the model was assessed using discriminant analysis.

Results Adverse FTS outcomes were statistically significantly associated with rheumatoid arthritis (OR = 6.89; 95 % CI 3.78–12.35; p = 0.002), immunodeficiency states (OR = 2.7; 95 % CI 0.44–8.24; p = 0.02) and the predominance of gram-negative microflora (OR = 7.1; 95 % CI 1.23–35.77; p = 0.028). Large bone defects (AORI type III) and five or more debridement surgeries had a significant impact on functional results and residual limb shortening. The use of an intramedullary nail for fixation correlated with an increased risk of systemic complications (OR = 6.69; 95 % CI 1.33–9.9; p = 0.035) and severe functional limitations (OR = 10.67; 95 % CI 1.201–15.72; p = 0.034). A direct relationship was established between the number of risk factors and the probability of adverse outcome (p < 0.001). The constructed prognostic model had sensitivity (77.8 %) and specificity (85.7 %).

Discussion The findings obtained indicate the heterogeneous nature of adverse FTS outcomes. The cumulative effect of individual factors, rather than their isolated presence, is important. This nature of the relationships explains the high variability of clinical outcomes, creating the need for an integrated risk assessment and the development of a surgical treatment algorithm for patients.

Conclusion Adverse FTS outcomes in PJI results from the combined impact of patient-related, infectious, and surgical factors. The most significant factors are the patient's comorbidity, the microbiological profile of the infection, the complexity of the anatomical and functional changes in the limb due to bone defects, and the chosen fixation method. A comprehensive assessment of risk factors allows for more accurate prediction of treatment outcomes.

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