![]() The C1 anterior arch-os complex moved forwards, 4.5 mm or more, relative to anterior margin of the attached part of odontoid process–body of axis. In all patients, during neck flexion, a C1-2 anterolisthesis was evident. These images were supplemented with multiplanar computed tomographic (CT) and/ or magnetic resonance (MR) images. The patients were diagnosed with lateral plain radiographs of cervical spine in neutral, flexed and extended neck positions. 2, 4, 5 None of the patients had a syndromic AAD (Down’s syndrome, Morquio’s syndrome or metatropic dysplasia). Diagnosis of OO was based upon the presence of a prominent C1 anterior arch associated with a rounded, uniformly symmetrical and well-corticated ossicle constituting OO situated well above the remnant odontoid with the presence of smooth bony intervening margins between them. We attempt to study the biomechanical issues, radiological features and management of OO with free-floating atlantal arch and review pertinent literature.įourteen patients (male-female ratio, 10:4 mean age, 17±5.6 years) having reducible AAD with OO were included in this study. Whenever OO and C1-2 anterolisthesis and retrolisthesis are present, their specific and unique management issues require adequate and timely intervention. 6 Free-floating atlantal arch may be missed due to lack of awareness or because investigations directed at diagnosing it are often not carried out. 1, 6, 8, 9 Excessive mobility at the C1-2 joints has the potential to cause cervicomedullary injury both from the anterior and posterior aspects, both in flexion and extension movements of the neck. 3 – 5 The presence of OO commonly leads to reducible atlantoaxial dislocation (AAD) 3, 5 – 7 its association, however, with “free-floating” atlantal arch that causes anterior and posterior dislocation is a rare phenomenon. 1 – 3 An “orthotopic” OO is closely approximated to C1 anterior arch and moves in unison with it, and a “dystopic” one is intimately related to the clivus. ![]() Os odontoideum (OO) is a rounded, corticated and smooth-marginated ossicle clearly separated from base of the odontoid process.
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