Delayed Unilateral Facet Interlocking After a Stable Superior Articular Process Fracture of the Cervical Spine: A Case Report.

A 42-year-old man presented with neck pain after a fall from a tree. Spine computed tomography (CT) illustrated the right C5 superior articular process fracture without displacement. Magnetic resonance imaging (MRI) confirmed the fracture and injury of the posterior ligament complex. Initially he was managed conservatively with a neck brace as there were no signs of instability or vertebral body misalignment. However, three days after discharge, right shoulder weakness and numbness of the right upper arm became prominent. X-rays and CT showed anterior slippage of the C4 vertebral body and locked C4/5 facet ??a fractured bony fragment of the C5 superior articular process was pushed forward by the locked inferior articular process of C4 and invaded the neural foramen. Anterior cervical discectomy and fusion (ACDF) was performed using allograft and plate/screws fixation. Although initial imaging showed no evidence of subluxation, surgeons should be aware of occult instability and the possibility of delayed dislocation associated with the unilateral cervical facet fracture.