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Chapter Summary
• Context: Rheumatologic diseases alter spinal anatomy, bone mineral quality, and biomechanics, creating surgical challenges distinct from those encountered in routine degenerative conditions. In rheumatoid arthritis (RA), synovial inflammation, aggressive pannus formation, and ligamentous destruction predominantly affect the cervical spine, leading to atlantoaxial instability, vertical migration (cranial settling), and subaxial subluxation with an insidious risk of compressive myelopathy. In ankylosing spondylitis (AS), progressive ossification and ankylosis convert the spine into a rigid, brittle long bone vulnerable to highly unstable shear fractures following trivial trauma, and susceptible to severe, disabling fixed kyphotic deformities. Advances in instrumentation, navigation, and neuromonitoring have enhanced surgical safety, but these patients remain vulnerable to surgical site infection, hardware failure, pseudarthrosis, and neurological deterioration. This chapter structures management according to anatomical disease patterns, deformity flexibility, neurological risk, and systemic comorbidities, underscoring the necessity of multidisciplinary perioperative planning.
• Chapter Objective: Understand the distinct mechanisms of spinal instability and deformity produced by rheumatoid arthritis and ankylosing spondylitis; recognize clinical and imaging red flags associated with imminent neurological compromise; select optimal stabilization and realignment osteotomy strategies; and anticipate complications related to severe osteopenia, immunosuppression, mechanical leverage, and reconstructive magnitude.
• Two mechanisms, two surgical paradigmsIn rheumatoid arthritis (RA), inflammatory synovitis destroys joint capsules, facet cartilage, and supporting ligaments. The cervical region is especially susceptible, presenting with atlantoaxial subluxation, basilar invagination, and step-ladder subaxial subluxation. In ankylosing spondylitis (AS), the opposite biomechanical problem occurs: progressive syndesmophytic fusion transforms multiple segments into a continuous, rigid lever arm. This severe rigidity generates global kyphosis and drastically increases susceptibility to unstable, three-column fractures.
• Evaluation of the rheumatoid cervical spinePlain flexion-extension radiographs, CT, and MRI play complementary roles. Radiographic parameters of the C1-C2 relationship (anterior atlantodental interval, posterior atlantodental interval), odontoid vertical migration indices (Ranawat, Redlund-Johnell), and space available for the cord dictate severity and neurological risk (Figure 61.1). Preoperative planning must incorporate difficult airway management, systemic bone mineral density, nutritional status, and perioperative management of biologic and conventional DMARDs.
• Atlantoaxial and craniocervical instabilityC1-C2 fixation has evolved from posterior wiring techniques to modern screw-rod constructs. Figure 61.2 demonstrates the C1 lateral mass–C2 pedicle screw fixation (Goel-Harms technique) widely used today, while Figure 61.3 illustrates C2 translaminar screws as a rescue alternative in high-riding vertebral artery anatomy. Cranial settling or basilar invagination with ventral brainstem compression may require traction reduction, decompression, and occipitocervical fusion. Head alignment in the neutral sagittal plane is critical for functional horizontal gaze.
• Subaxial instabilityAdjacent subaxial segments can deteriorate progressively after upper cervical fusion. Instrumented arthrodesis should include only truly unstable levels, balancing the risk of a short construct against the biomechanical morbidity of excessively long fusion.
• Fractures in ankylosing spondylitisThe ankylosed spine behaves biomechanically as a long bone. Fractures (often through ankylosed disc spaces or vertebral bodies) are inherently unstable, easily overlooked on plain radiographs, and carry a high risk of secondary displacement and acute spinal cord injury. Temporary immobilization must respect the patient's pre-injury fixed sagittal deformity until definitive rigid stabilization is achieved.
• Deformity correctionSurgical planning must identify the primary apex of deformity and assess changes between standing, sitting, and supine positions. Lumbar, cervicothoracic, or cervical osteotomies are selected according to the deformity pattern. Table 61.1 classifies cervical osteotomy grades, and Figure 61.6 presents an algorithmic workflow based on flexibility and ankylosis patterns. Figures 61.4 and 61.5 illustrate a cervicothoracic osteotomy and its profound impact on global sagittal alignment and horizontal gaze.
• Clinical Application: In rheumatoid arthritis, the surgeon must actively detect cervical instability before advanced myelopathy becomes irreversible. Mild neck pain may conceal severe radiographic cord compression; dynamic flexion-extension views, high-resolution CT, and MRI must be correlated with careful neurological testing. Once surgery is indicated, implant selection depends on bone purchase and vertebral artery course. Computer-assisted navigation provides essential safety in distorted craniocervical anatomy. In ankylosing spondylitis, every reported trauma must be treated as an unstable fracture until proven otherwise by thin-slice CT. Forcing the neck into anatomical neutral on a flat spine board can displace a fracture and cause quadriplegia; head blocks matching the patient's fixed kyphosis are mandatory. In elective deformity correction, one must evaluate the whole spine, pelvis, hips, and chin-brow vertical angle (CBVA) to determine where osteotomy yields optimal functional horizontal gaze without overcorrection. In both diseases, optimizing immunosuppressive regimens, nutrition, and bone health minimizes infection and pseudarthrosis.
