Degenerative Zygapophyseal Joint Subluxation of the Lumbar Spine: A Modified Classification and Clinical Considerations

Degenerative lumbar zygapophyseal (facet) joint subluxation without prior trauma, fracture, spondylolysis, or spondylolisthesis is extremely uncommon and represents a distinct clinical entity. This study aims to present rare cases of advanced degenerative facet joint changes combined with unilateral or bilateral facet joint subluxation in the absence of trauma. All patients experienced chronic symptoms unresponsive to conservative treatment. MRI findings demonstrated Grade 4 degeneration per Grogan's classification, along with distinct subluxation patterns not captured by existing grading systems. Surgical treatment, including decompression with or without instrumented fusion, was tailored to the presence of radiological or intraoperative instability. These findings emphasize the clinical relevance of facet joint subluxation as a distinct degenerative entity, suggesting the need for a revised MRI-based grading system that includes subluxation as a separate criterion. This revised classification system, incorporating degenerative causes, could enhance diagnostic precision and therapeutic strategies in these types of injuries.