Fate of the facet joints after instrumented intertransverse process fusion

A success or failure of an intertransverse process fusion has been determined by the fusion status of the intertransverse fusion mass alone, and little consideration has been given to the fusion status of the facet joint. The purpose of this study was to assess the fusion status of the facet joints at the fusion level and its impact on the overall fusion outcome. Sixteen patients (19 levels) treated with decompression and intertransverse process fusion using pedicle screw fixation without facet arthrodesis were entered into a cross sectional study in which the fusion status of the intertransverse fusion masses and facet joints at each fusion level were evaluated and combined at an average duration of followup of 35 months (range, 22-61 months). Union rate of the intertransverse process fusion (58%, 22 of 38) was lower than the spontaneous fusion rate of the facet joint (68%, 26 of 38). However, the combination of the two fusion statuses at each fusion level generated 89% of the overall fusion rate (17 of 19 levels). With surgery, all patients had a good or excellent clinical outcome, but the outcome had no relation to the overall fusion status. The results suggest that the fusion status of the facet joint should be considered in determining overall fusion status after combined decompression with instrumented intertransverse process fusion.