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:But, pedicle screw fixation has its own risks, so that spinal fixation using pedicle screws is technically demanding [2, 5, 7, 10, 12, 13] and many reports have been published about complications following transpedicular instrumentation [2, 4, 6, 17, 20].
Category: