Is atlantoaxial instability the cause of type 3 Klippel-Feil anomaly? Outcome analysis of 99 patients treated by atlantoaxial fixation: A case series.

Aim: The authors analyze their experience with 99 patients having Type 3 Klippel-Feil anomaly (KFA), signifying fusion of cervical vertebrae at and below the level of C3 vertebra. Materials and Methods: During the period January 2004-November 2024, 99 patients presented with clinical symptoms and radiological characteristics that indicated the presence of Type 3 KFA and associated musculoskeletal and neural alterations. There were 57 males and 42 females, and their ages ranged from 4 to 54 years (average 26 years). Apart from symptoms that included longstanding pain in the nape of the neck, spasm of neck muscles, and restricted neck movement, all patients had a range of spastic quadriparesis and sensory dysfunction. Associated entities included Chiari formation (30 cases), syringomyelia (17 cases), Group A (58 cases) and Group B basilar invagination (12 cases), bifid arch of atlas (17 cases), assimilation of atlas (49 cases), C2-3 fusion (44 cases), os-odontoideum (3 cases), torticollis (29 cases), and dorsal kyphoscoliosis (3 cases). Results: All patients were treated by atlantoaxial fixation. No bone decompression was done at any spinal level. The follow-up ranged from 3 to 189 months. Clinical improvement was observed in all patients. Conclusions: Vertebral fusion/s in KFA and other associated or related clinically obvious musculoskeletal and radiologically obvious neural compressive, neural deforming, or neural altering and otherwise considered "pathological" entities are secondary to chronic atlantoaxial instability, are naturally protective or adaptive, and are potentially or manifestly reversible following atlantoaxial stabilization. Successful atlantoaxial fixation can lead to a gratifying "life-changing" clinical outcome.