title: Revision of Minimally Invasive Sacroiliac Joint Fixation: Technical Considerations and Case Studies Using Decortication and Threaded Implant Fixation.
abstract: BACKGROUND
  Sacroiliac joint (SIJ) disease is increasingly recognized as a common source of low back pain. Arthrodesis of the SIJ has been shown to be clinically effective for this condition. In the last decade, minimally invasive (MI) SIJ fusion procedures have been developed to achieve the clinical effectiveness of open fusion procedures, with lower operative morbidity and faster recovery. However, SIJ fusion patients occasionally present with symptomatic nonunions necessitating revision.
  
  
  METHODS
  Four patients who previously underwent MI SIJ arthrodesis returned with complaints of SIJ related pain confirmed by examination. Radiographic assessment showed lucency after fixation with triangular titanium interference implants. Loose implants were removed, and the patients were revised with a different MI SIJ fusion system that utilizes decortication, placement of autograft and graft extender, and fixation with cannulated threaded implants. The trajectory of the revision implants was in a more ventral-to-dorsal and caudal-to-cranial trajectory to place the implants perpendicularly through the articular portion of the SIJ.
  
  
  RESULTS
  The triangular implants typically exhibited haloing lucency on radiographs and CT scans, and most were easily removed using the manufacturer's instrumentation; only one implant was left in place as it was well-fixed. The removed implants exhibited little or no bony ongrowth. Decortication of the SIJ was performed, followed by placement of local autograft and fixation with 12.5 mm or 14.5mm diameter implants, as required. A more ventral-todorsal and caudal-to-cranial trajectory was established for the revision implants through the center of the articular region of the joint in order to maximize implant purchase in residual bone stock and achieve bony fusion through the articular portion of the SIJ. By six to twelve months post-revision, the presenting symptoms were successfully resolved in all patients.
  
  
  CONCLUSIONS
  Patients demonstrating symptomatic pseudoarthrosis after SIJ fixation surgery can be successfully revised with decortication, grafting and fixation with threaded implants utilizing MI surgical techniques. Implant trajectory is an important consideration for primary or revision MIS SIJ fusion. Studies with longer-term follow-up of both primary and revision procedures are needed to further understand fusion rates for both primary and revision procedures utilizing both triangular and threaded implant systems.
authors.affiliation: Reno Orthopedic Clinic, Reno, NV.
authors.forename: Brett
authors.initials: B
authors.lastname: MenMuir
authors.affiliation: Tahoe Labs, LLC, San Carlos, CA.
authors.forename: Louis C
authors.initials: LC
authors.lastname: Fielding
keywords: implant loosening; minimally invasive; revision; sacroiliac joint fusion