Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Even though many studies about complications following transpedicular instrumentation have been reported [2, 11, 17, 20], the possibility of adjacent superior facet joint violation that may lead to instability, which can bring about adjacent segmental degeneration, has not been studied in detail.
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