Can the human intervertebral disc be compared to a diarthrodial joint?

Area of Science:

• Spine Anatomy and Biomechanics
• Cartilaginous Joint Classification
• Vertebral Joint Histology

Background:

• The intervertebral disc (IVD) is traditionally classified as a symphysis, a type of cartilaginous joint.
• Some researchers have proposed comparing the IVD to a diarthrodial (synovial) joint, citing historical descriptions and cellular/imaging findings.

Purpose of the Study:

• To review and discuss the evidence supporting and refuting the analogy between the intervertebral disc (IVD) and a synovial joint.
• To determine if the IVD can be accurately classified as a diarthrodial joint based on comprehensive scientific data.

Main Methods:

• Literature review encompassing historical descriptions, histological and ultrastructural studies of the nucleus pulposus (NP) and annulus fibrosus.
• Analysis of magnetic resonance imaging (MRI) and discography findings in relation to IVD pathology.
• Consideration of embryological, biochemical, radiological, and clinical data pertaining to IVD structure and function.

Main Results:

• Historical viewpoints and some cellular/imaging interpretations suggested similarities to synovial joints.
• However, significant objections based on general morphology, embryology, biochemistry, histology, radiology, and clinical presentation were identified.
• Key differences in structural, mechanical, and developmental principles distinguish the IVD from synovial joints.

Conclusions:

• The hypothesis comparing the intervertebral disc (IVD) to a synovial joint is refuted by extensive scientific evidence.
• The IVD's unique characteristics mean its pathological features differ significantly from those of appendicular skeleton synovial joints.
• Accurate classification of the IVD as a symphysis remains appropriate, guiding a better understanding of spinal pathology.