The Canine Sacroiliac Joint: 2. Common Surface Variants

Area of Science:

• Veterinary Anatomy
• Comparative Morphology
• Biomechanics

Background:

• The canine sacroiliac joint (CSIJ) is vital for axial skeleton and pelvic limb load transfer.
• Detailed morphology beyond the primary articulation of the CSIJ is not well-characterized.
• Understanding CSIJ variations is essential for accurate anatomical and clinical interpretations.

Purpose of the Study:

• To systematically describe common morphological variants of the canine sacroiliac joint (CSIJ).
• To assess synovial surface area (SSA) shape types, non-fused ossification centers (NFOC), and accessory sacroiliac joints (ASIJ).
• To evaluate the morphometric characteristics and potential biomechanical relevance of these CSIJ variants.

Main Methods:

• Examination of 29 canine pelves (58 CSIJ).
• Categorization of SSA morphology and identification of NFOC based on articular surface features.
• Documentation of ASIJ frequency, localization, and size, noting their diarthrodial nature and hyaline cartilage lining.

Main Results:

• Seven distinct SSA shape types were identified, with auricular, bifoliate, and phrygian cap-like configurations being most prevalent; only one-third showed the typical auricular/crescent shape.
• NFOC were present in 27.60% of CSIJ, predominantly in larger dogs (CRL > 740 mm).
• Accessory articulations (ASIJ) were found in 74.10% of CSIJ, often bilateral and sometimes multiple, with additional articular surface areas correlating with body size.

Conclusions:

• Canine sacroiliac joints exhibit considerable anatomical variability beyond primary articulations.
• Variations in SSA morphology, NFOC, and ASIJ are frequent physiological variants, not rare anomalies.
• Recognizing these CSIJ features is crucial for accurate anatomical characterization, imaging interpretation, and future biomechanical/clinical research.