Odontoid fractures account for 9% to 15% of adult cervical spine fractures with the majority being type II fractures according to the Anderson and D’Alonzo classification [4].

In the elderly population, these fractures are the most common upper cervical spine fracture and, in the population, older than 80 years, the most common spine fracture of all.

These injuries usually result from hyperflexion or hyperextension of the cervical spine during low-energy impacts in the elderly or high-energy impacts in the young and middle aged. Neurologic injury associated with these fractures is rare [5-7].

The management of odontoid fractures is challenging, particular in the elderly. The objective is a rapid restoration of autonomy while limiting morbidity and mortality due to prolonged immobilisation [8].

Multiple factors determine the management of odontoid fracture, including fracture type, presence of associated fracture of the posterior elements, patient age and comorbidities. Generally, type I and type III injuries require non-operative treatment [9]. Type II often require surgical treatment, however there is no clearly consensus concerning the technique to use [10].

To overcome this pitfall, Roy-Camille proposed a classification based on the evaluation of the risk of displacement [11]: Type II with backward sloping or horizontal fractures can be managed by anterior screw fixation of the odontoid. The association with forward sloping fracture is an indication for posterior fusion [12].

Several techniques can be used for cervical posterior fusion, in the last decade, techniques based on instrumentation of lateral masses of C1/pedicles of C2 (Harms or Goel technique), and C1/C2 joints (Magerl’s technique) became popular [13,14], However they are technically more demanding and have the added risk of serious complications; Vertebral artery injury is the most common complication [15].

In contrast to Harms and Magerl’s techniques, posterior fixation with modern laminar claw hook–rod instrumentation is a safe and effective technique with comparable results in terms of fusion and neurological improvement. Also, it is technically less demanding with a lower morbidity [16], but it requires intact posterior elements.

Regardless of specific methods and instruments, a variety of complications have been reported following posterior spine fusion. In a reports published by Lall et al. [17], the most commonly encountered perioperative complications were related to instrumentation failure after non-union. Other commonly encountered complications included injury to the vertebral artery, dural tears, and wound infection. But, the screw fracture after trans-pedicle screws and screw-rod constructs is very rare with no relevant article in the literature review [18].

A quite rare complication of rod migration into the posterior cranial fossa as shown in the present case, was reported by Chun et al. [19]. A similar case was also reported by Plant et Ruff [20]. The authors of both cases have no culprit that the migration of the rod was attributed to any operative technical errors.

In the current case, we conclude that the rod was not well locked, then eroded the occipital bone, and finally migrated into the posterior fossa.