M43.21 Fusion of spine, occipito-atlanto-axial region

Billable ICD-10-CM code, FY2026.

Applies from M43 Other deforming dorsopathies

Excludes1 (never code together)

• congenital spondylolysis and spondylolisthesis (Q76.2)
• hemivertebra (Q76.3-Q76.4)
• Klippel-Feil syndrome (Q76.1)
• lumbarization and sacralization (Q76.4)
• platyspondylisis (Q76.4)
• spina bifida occulta (Q76.0)
• spinal curvature in osteoporosis (M80.-)
• spinal curvature in Paget's disease of bone [osteitis deformans] (M88.-)

Applies from M43.2 Fusion of spine

Applicable to

• Ankylosis of spinal joint

Excludes1 (never code together)

• ankylosing spondylitis (M45.0-)
• congenital fusion of spine (Q76.4)

Excludes2 (not included here)

• arthrodesis status (Z98.1)
• pseudoarthrosis after fusion or arthrodesis (M96.0)

MS-DRG index

Defines the logic of DRG(s) 551-552 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 724.9 Other unspecified back disorders (approximate)

Code annotations containing back-references to M43.21

Back-references to M43.2

• Type 2 Excludes: M24.6 Ankylosis of joint ("spine (M43.2-)")

Back-references to M43

• Type 2 Excludes: M95 Other acquired deformities of musculoskeletal system and connective tissue ("deforming dorsopathies (M40-M43)")

Diagnosis Index entries for M43.21

• Fusion, fused (congenital) › spine (acquired) NEC › occipito-atlanto-axial region

Nearby codes

• M43.17 Spondylolisthesis, lumbosacral region
• M43.18 Spondylolisthesis, sacral and sacrococcygeal region
• M43.19 Spondylolisthesis, multiple sites in spine
• M43.2 Fusion of spine
• M43.20 Fusion of spine, site unspecified
• M43.21 Fusion of spine, occipito-atlanto-axial region (this code)
• M43.22 Fusion of spine, cervical region
• M43.23 Fusion of spine, cervicothoracic region
• M43.24 Fusion of spine, thoracic region
• M43.25 Fusion of spine, thoracolumbar region
• M43.26 Fusion of spine, lumbar region