title: Cadaveric study of sacroiliac joint innervation: implications for diagnostic blocks and radiofrequency ablation.
abstract: OBJECTIVE
  Optimization of clinical outcomes of lateral branch radiofrequency ablation or blocks for sacroiliac joint (SIJ) pain requires precise nerve localization; however, there is a lack of comprehensive morphological studies. The objectives of this cadaveric study were to document SIJ innervation relative to bony landmarks in 3 dimensions and to identify reference points visible under ultrasound and fluoroscopy for optimal needle placement.
  
  
  METHODS
  In 25 cadaveric hemipelves, L5-S4 lateral branches were exposed, digitized, and modeled in 3 dimensions. The models were used to compare innervation patterns between specimens and to quantify the distances of the nerves innervating the SIJ relative to the transverse sacral tubercles (TSTs) and posterior sacral foramina. Quadrants of origin of the nerves were recorded.
  
  
  RESULTS
  The SIJ was innervated by the posterior sacral network: S1-S2 contributed in all specimens, S3 in 88%, L5 in 8%, and S4 in 4%. Most frequently, the lateral branch(es) emerged from the inferolateral S1, superolateral and inferolateral S2, and superolateral S3 quadrants. All TSTs were easily identifiable elevations that were used to landmark the nerves innervating the SIJ. The majority of branches of the posterior sacral network crossed the lateral sacral crest between TST1-3, with the greatest concentration between TST2-3. Only 3 specimens had a branch superior or inferior to these landmarks.
  
  
  CONCLUSIONS
  Based on the innervation pattern and using bony landmarks identifiable under ultrasound and fluoroscopy, 2 radiofrequency ablation techniques were proposed. Further research is required to determine the accuracy and reliability of needle placement and to evaluate clinical outcomes.
authors.affiliation: From the *Division of Anatomy, Department of Surgery, University of Toronto, Toronto, Ontario; †Division of Physical Medicine and Rehabilitation, University of Alberta, Edmonton, Alberta; and ‡Department of Physical Medicine and Rehabilitation, University of Western Ontario, London, Ontario, Canada.
authors.forename: Shannon L
authors.initials: SL
authors.lastname: Roberts
authors.forename: Robert S
authors.initials: RS
authors.lastname: Burnham
authors.forename: Kajeandra
authors.initials: K
authors.lastname: Ravichandiran
authors.forename: Anne M
authors.initials: AM
authors.lastname: Agur
authors.forename: Eldon Y
authors.initials: EY
authors.lastname: Loh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks; D002102:Cadaver; D017115:Catheter Ablation / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D006801:Humans; D008875:Middle Aged; D009339:Needles; D009407:Nerve Block / Q000295:instrumentation / Q000379:methods; D011237:Predictive Value of Tests; D015641:Radiography, Interventional; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging / Q000294:innervation* / Q000601:surgery*; D013127:Spinal Nerves / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000601:surgery*; D018084:Ultrasonography, Interventional