Study Design: Retrospective review.
Objective: The aim of this study is to assess the radiographic characteristics of patients with a retroodontoid pseudotumor and to evaluate the efficacy of posterior fusion.
Summary of Background Data: Retroodontoid pseudotumors are usually caused by chronic atlantoaxial instability in patients with rheumatoid arthritis (RA). However, the pathomechanism and optimum treatment are unknown.
Methods: We reviewed the charts and radiographs of 11 patients (5 RA and 6 non-RA) with a retroodontoid pseudotumor who underwent posterior fusion. Preoperative radiographs were evaluated for atlantodental interval; Redlund-Johnell criterion; O–C1, C1–2, C2–3, and C2–7 angles. The Japanese Orthopaedic Association (JOA) score was used to evaluate clinical outcomes.
Results: All RA patients and 1 non-RA patient displayed atlantoaxial subluxation. Three patients underwent occipitocervical fusion and 8 patients atlantoaxial fusion. The JOA score improved significantly from 10.0 to 12.8 at follow-up (P<0.01). The retroodontoid pseudotumor regressed in 10 patients. Maximal thickness of the pseudotumor decreased from 8.9 mm preoperatively to 5.3 mm (P<0.01) at follow-up. In non-RA patients, the mean differences (Δ) between flexion and extension were 7.8, 13.4, 3.5, and 18.5 degrees for ΔO–C1, ΔC1–2, ΔC2–3, and ΔC2–7, respectively.
Conclusions: In RA patients, a retroodontoid pseudotumor may develop because of atlantoaxial subluxation. In non-RA patients, excessive atlantoaxial angular motion because of the limited range of motion of O–C1 and/or subaxial vertebra may cause a pseudotumor. Atlantoaxial fusion to suppress atlantoaxial instability is one of the optimum treatments.