Bone Abstracts

Juvenile idiopathic arthritis (JIA) is associated with low bone mass, poor bone strength, and an increased fracture risk. Children with JIA enter adulthood with suboptimal bone mass. In children with JIA, fracturing of the 2nd metatarsal is common due to poor bone strength. Currently no gold standard measure exists for bone quality in the foot. A reproducible protocol is required to assess key bone outcomes at the 2nd metatarsal using pQCT.

Objective: To develop a pQCT scan protocol for the measurement of 2nd metatarsal bone outcomes.

Methods: A custom-made foot plate standardised the optimal scanning position. Eleven embalmed cadaveric lower leg specimens were scanned six times; three times with, and three times without repositioning. 66 scans were obtained at 15% (distal end) and 50% (mid shaft) of the 2nd metatarsal. Voxel size and scan speed were reduced to 0.40 mm and 25 mm/s, respectively. The reference line was positioned at the most distal portion of the 2nd metatarsal. To maximise trabecular bone analysis at the 15% distal end, we selected a zero contour threshold, 650 mg/cm² inner threshold, peel mode four, and 1% concentric peel. At 50% mid shaft, a 600 mg/cm² threshold and separation mode two were used.

Results: Reliability of scans without repositioning: trabecular area (intraclass correlation coefficient (ICC) 0.86, 95% CI 0.63–0.96), trabecular density (ICC 0.96, 95% CI 0.90–0.99), strength strain index (SSI) (ICC 0.99, 95% CI 0.99–1.0), cortical area (ICC 0.99, 95% CI 0.98–1.0). Reliability for scans after repositioning: trabecular area (ICC 0.96, 95% CI 0.90–0.98), trabecular density (ICC 0.98, 95% CI 0.95–0.99), SSI (ICC 0.99, 95% CI 0.98–1.0), cortical area (ICC 0.99, 95% CI 0.98–1.0).

Conclusion: The scanning protocol generated excellent reliability for key bone outcomes measured at the distal and mid-shaft regions of the 2nd metatarsal. The pQCT protocol will now be applied to children with JIA for identifying insufficiency fractures.