[Atlanto-axial rotation and distance in small children. A postmortem study]

Area of Science:

• Orthopedics
• Anatomy
• Pediatric Spine Research

Background:

• The etiology of atlanto-axial rotatory subluxation (AARS) is not fully understood.
• Evaluating the biomechanics of the atlanto-axial (C1-C2) joints is crucial for understanding AARS.

Purpose of the Study:

• To investigate C1-C2 rotation and translation mobility in pediatric specimens.
• To differentiate between normal joint mobility and instability in the context of AARS.
• To clarify the role of atlanto-axial joints in the development of AARS.

Main Methods:

• Post-mortem investigation of pediatric C1-C2 spinal specimens (ages 2 months, 9 months, 53 months).
• Sequential dissection of atlanto-axial joint capsule, membrane, transverse ligament, and alar ligaments.
• Radiographic recording of atlas rotation and anterior translation over the axis after each dissection step.

Main Results:

• Dissection progressively increased C1-C2 rotation up to 25 degrees.
• Atlanto-axial joint capsules were found to be lax, permitting near-complete subluxation within normal motion.
• Facet interlocking was not observed.
• The atlanto-dental interval asymmetry in AARS is variable and not a reliable radiographic parameter.

Conclusions:

• Atlanto-axial joint laxity, within normal ranges, allows significant rotation and may not be the primary cause of AARS.
• Instability of the atlanto-axial joints is likely not the sole factor in AARS.
• Radiographic assessment of the atlanto-dental interval is variable and unreliable for diagnosing AARS.