Contralateral screw loosening of through-and-through fixation following unilateral sacroiliac joint fusion: illustrative case.

Abstract

Background: Sacroiliac (SI) joint dysfunction is a frequently underrecognized source of low back pain, implicated in 15%-30% of cases across select populations. Unilateral SI joint fusion remains the most commonly performed technique, utilizing either iliosacral screws or, more recently, through-and-through (TNT) screws.

Observations: A 65-year-old woman with a history of failed right-sided SI joint fusion underwent revision surgery with bilateral TNT screw fixation due to worsening symptoms. Follow-up imaging confirmed solid right-sided arthrodesis. However, progressive haloing and sclerosis were observed around the left iliac portion of the cephalad screw.

Lessons: This case represents the first reported instance of persistent motion and screw haloing using TNT screw fixation when using two spanning screws. These findings highlight a potential limitation of TNT constructs due to load transfer, stress shielding, and asymmetric osseous integration, particularly in patients with a history of prior unilateral SI joint fusion. https://thejns.org/doi/10.3171/CASE25668.