Uncovering Synergistic Predictors of Complications in Microvascular Breast Reconstruction: A Retrospective Cohort Study

Purpose: Microvascular breast reconstruction is a complex procedure that can be associated with high complication rates. While a number of individual predictors of post-operative complications have been identified, few studies have explored interaction between risk factors.^1,2 Understanding the synergistic effects of multiple risk factors is crucial to accurate and personalised pre-operative risk prediction.³

Methods: We conducted a retrospective cohort study of patients who underwent microvascular breast reconstruction at our institution between 2009 and 2017. All intra- or post-operative complications were recorded. An exploratory multivariable logistic regression model identified independent predictors of complications. Interactions between individual variables were then assessed using the Relative Excess Risk Index (RERI) and Synergy Index (SI). 

Results: Nine hundred and twelve patients were included in the study and 26.1% experienced at least one intra- or post-operative complication. Obesity (OR1.54, p=0.01), immediate reconstruction (OR1.49, p=0.03), and comorbidities (OR1.43, p=0.03) were identified as independent predictors of complications. Obesity and comorbidities had significant synergistic interactions with immediate reconstruction (RERI 0.86, SI 2.35, p=0.0002; RERI 0.54, SI 1.78, p=0.001), bilateral reconstruction (RERI 0.12, SI 1.15, p=0.002; RERI 0.59, SI 3.16, p=0.01) and previous radiotherapy (RERI 0.62, SI 4.43, p=0.01; RERI 0.11, SI 1.23, p=0.04). Smoking had a synergistic interaction with immediate breast reconstruction (RERI 1.99, SI 4.36, p=0.03).

Conclusions: Patient and treatment related variables interact in a synergistic manner to increase the risk of complications for microvascular breast reconstruction. In light of the known multifaceted repercussions of complications, individualized comprehensive risk assessment should guide surgical decision making and patient counselling.

References:

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2. Las DE, de Jong T, Zuidam JM, Verweij NM, Hovius SE, Mureau MA. Identification of independent risk factors for flap failure: A retrospective analysis of 1530 free flaps for breast, head and neck and extremity reconstruction. J Plast Reconstr Aesthet Surg. 2016;69:894–906.
3. Andersson T, Alfredsson L, Källberg H, Zdravkovic S, Ahlbom A. Calculating measures of biological interaction. Eur J Epidemiol. 2005;20:575–579.