Comprehensive anatomic and clinical analyses of 39 patients with injuries involving the transverse atlantal ligament or its osseous insertions were performed to assess the morphology of the injured ligaments and the patients' capacity to heal. Injuries of the upper cervical spine were screened with plain radiographs, thin-section computed tomography, and magnetic resonance imaging studies. The injuries were classified as disruptions of the substance of the ligament (Type I injuries, n = 16) or as fractures and avulsions involving the tubercle for insertion of the transverse ligament on the C1 lateral mass (Type II injuries, n = 23). These two types of injuries had distinctly different clinical characteristics that were useful for determining treatment. Type I injuries were incapable of healing satisfactorily without internal fixation; they should be treated with early surgery. Type II injuries, which rendered the transverse ligament physiologically incompetent even though the ligament substance was not torn, should be treated initially with a rigid cervical orthosis, because they had a 74% success rate nonoperatively. Surgery should be reserved for patients with Type II injuries that have nonunion with persistent instability after 3 to 4 months of immobilization. Type II injuries had a 26% rate of failure of immobilization; therefore, close monitoring is needed to detect patients who will require delayed operative intervention.

Type II odontoid fractures have the highest nonunion rate and were associated with dens displacement of 6 mm or greater. Early surgical fusion is recommended for acute fracture instability despite external immobilization, transverse ligament disruption, Type II odontoid fractures with dens displacement of at least 6 mm on admission, or severe Francis grade or Effendi-type hangman's fractures. Otherwise, nonoperative management is sufficient.