Potential significance of facet joint fusion or posteromedial fusion observed on CT imaging following attempted posterolateral or posterior interbody fusion

BACKGROUND CONTEXTRadiologic evidence of successful lumbar fusion has traditionally been based on bridging bone spanning the intertransverse processes (posterolateral fusion or PLF) or disc space (interbody fusion, or IBF). Often, postoperative computed tomography (CT) of unsuccessful PLF and IBF demonstrates bridging bone across the facet joints or connecting the medial transverse process to the ipsilateral superior articular facet of the caudal vertebra. The significance of this finding in terms of implant stability and clinical outcomes has not previously been reported.PURPOSETo determine rates of facet joint fusion (FJF)/posteromedial fusion (PMF) following single-level PLF surgery, with or without interbody. A secondary goal was to determine comparative outcomes associated with isolated FJF/PMF versus PLF and IBF.STUDY DESIGNRetrospective CT-based review.PATIENT SAMPLETwo hundred-three patients underwent single-level PLF surgery with local autograft bone or PLF+IBF with local autograft bone.OUTCOME MEASURESFusion was assessed at 6-months and 12-months postoperatively using strict CT criteria. Patient reported outcome measures included visual analogue scale (VAS) scores for back pain and leg pain, Oswestry Disability Index (ODI), and SF-36.METHODSThin-cut CTs were examined to determine whether successful fusion had occurred in seven different anatomic locations. One-way analysis of variance was used to determine significant differences in mean outcome scores and other continuous measures between groups at baseline and follow-up. Chi-square test of independence or Fisher's exact test was used to compare proportions between groups on categorical measures.RESULTSTwo hundred-three patients and 157 patients completed 6- and 12 month follow-up, respectively. At 12 months, 35.1% of PLF patients demonstrated successful unilateral/bilateral PLF. Including unilateral or bilateral FJF/PMF, the fusion rate was 73.4%. Among PLF+IBF patients, 38.1% demonstrated successful IBF/PLF. Including unilateral or bilateral FJF/PMF, the fusion rate was 55.6%. All fusion groups demonstrated significant improvement in back pain and leg pain scores as well as ODI and SF-36 PF at 6- and 12 months compared with pre-op. No significant difference in any outcome measure, rates of implant loosening or reoperation was observed between successful PLF/IBF and FJF/PMF groups.CONCLUSIONSFJF/PMF is often observed on postoperative CT evaluation following surgery originally performed to achieve PLF or IBF. Short-term follow-up suggests no significant difference in implant loosening rates or patient reported outcomes when FJF/PMF is observed versus PLF or IBF in such patients. Long-term clinical outcomes of FJF/PMF versus PLF or IBF remain unknown. These findings apply solely to single-level instrumented spinal fusion surgery utilizing pedicle screws with or without IBF.