Understanding the Facet Joint Fusion Process: A Narrative Review for Clinicians and Surgeons Addressing the Who, Why, What, When, Where, Which, and How

Lumbar facet joint fusion has established itself as an important aspect of the surgical management of degenerative spondylolisthesis (DS) and related pathological conditions of the spine. Understanding the fusion process and its clinical implications is essential for optimizing patient outcomes, particularly in the context of advancing surgical techniques and imaging modalities. This narrative review aims to assess the existing evidence regarding facet joint fusion in the lumbar spine through the structured framework of WHO, WHY, WHAT, WHEN, WHERE, WHICH, and HOW. A structured search of PubMed/MEDLINE-a freely and globally accessible database, selected so that the search can be reproduced by any reader without licensed or subscription-based access-was conducted from inception to the date of the search (15 June 2026), combining the MeSH terms "Spinal Fusion", "Spondylolisthesis", "Lumbar Vertebrae", and "Zygapophyseal Joint" with free-text variants of facet joint fusion and the principal interbody techniques. Peer-reviewed studies, consensus guidelines, and clinical trials addressing facet joint fusion, fusion rates, and postoperative outcomes were included. Facet joint fusion contributes significantly to spinal stability and favorable long-term results in DS. Patient selection (WHO), pathophysiological understanding (WHY), and surgical techniques (WHAT) - anterior lumbar interbody fusion (ALIF), oblique lateral interbody fusion (OLIF), extreme lateral interbody fusion (XLIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF) - are pivotal. Timing (WHEN), anatomical considerations (WHERE), and choice of operative and imaging methods (WHICH) influence success rates. Optimal postoperative care (HOW) is associated with reduced reoperation rates and improved quality of life. Lumbar spinal DS surgery with facet joint fusion is a complex, multifactorial process requiring careful planning, execution, and management in the dynamic process of perioperative care. This review provides a modern perspective for clinicians in the evidence-based care of this patient population.