Flexed radiographic angles for determination of atlantoaxial instability in dogs

Abstract

Objective To determine a flexed position for radiographic diagnosis of atlantoaxial instability (AAI) and to identify radiographic measurement cutoffs to differentiate affected dogs from neurologically healthy toy breeds. Study design Retrospective case series and prospective case controls. Animals Thirty‐nine client‐owned toy breed dogs in which AAI had been diagnosed and 20 neurologically healthy client‐owned toy breed dogs. Methods Medical records from three institutions were retrospectively reviewed to identify dogs affected with AAI. Flexed lateral images were reviewed, and measurements were obtained by using anatomic landmarks. Radiography was performed with control dogs to obtain the same measurements. Results Flexed lateral radiographs of thirty dogs affected with AAI were found to be positioned at a mean of 51° flexion. When flexed lateral radiographs were evaluated with a cutoff value for atlas to axis angle (AAA) >10°, evaluation of all breeds represented revealed a 90% sensitivity and 90% specificity. When this cutoff was evaluated in Yorkshire terriers, Chihuahuas, and mixes of these breeds, the sensitivity was 92%, and the specificity was 92%. When the control sample was positioned at 51° ± 10°, only two of the dogs were within the AAA cutoff value of >10°. There was no difference between the measurements obtained by using the flexed lateral view (mean = 50.9°) and the exaggerated flexed lateral view (mean = 38.9°) in the control sample. Conclusion This study established objective measurements for the positioning and diagnosis of AAI on flexed lateral radiographs in toy breed dogs. Clinical significance Atlantoaxial instability can be objectively diagnosed in sedated or anesthetized toy breed dogs when applying 51° flexion to cervical radiographs.

Influence of the Head Neck Position on Imaging Measurements Used to Assess the Craniovertebral Junction in Small Breed Dogs: A Cadaveric Study

“…8,14 A recent study of White and colleagues also reports that a mild degree of cervical flexion could aid in the diagnosis of AAI. 19 In conclusion, a slight flexion as standardized head neck position should be used both for reasons of safety and standardized evaluation of the CVJ. We propose 50 degrees flexion for the angle of head position to target as described in the publication of Upchurch and colleagues.…”

Determination of cutoff values on computed tomography and magnetic resonance images for the diagnosis of atlantoaxial instability in small‐breed dogs

“…Indeed, the ventral atlantodental interval as well as the VCI were shown to be higher in maximal flexion compared to slight flexion and extension in control dogs (P = .00001). 9 In the same study, White et al also fixed a cutoff value of >10 for the atlas to axis angle (AAA) when the head was placed in slight flexion, 21 corresponding to >190 for the C1-C2 angle in our study. The reported sensitivity and specificity were 90%, and 92% when this cutoff was evaluated in Yorkshire terriers, Chihuahuas or mixes of these breeds only.…”

“…If the diagnosis remains unclear, we recommend repeating the examination in a slightly flexed head position, which is considered to be closer to dogs' physiologic position in an awake state and could lead to dorsal angulation of the axis in cases with dynamic AAI 19,20 . A recent study by White et al reports that a mild degree of cervical flexion could favor the diagnosis of AAI in dogs, which further supports this recommendation 21 . A hyperflexion of the head is, however, contraindicated due to the risk of exacerbating focal pressure of the dens axis on the spinal cord in cases of AAI.…”

“…19,20 A recent study by White et al reports that a mild degree of cervical flexion could favor the diagnosis of AAI in dogs, which further supports this recommendation. 21 A hyperflexion of the head is, however, contraindicated due to the risk of exacerbating focal pressure of the dens axis on the spinal cord in cases of AAI. Indeed, the ventral atlantodental interval as well as the VCI were shown to be higher in maximal flexion compared to slight flexion and extension in control dogs (P = .00001).…”

Novel transforaminal approach allows surgical decompression of an atlantoaxial band in dogs: a cadaveric study and clinical cases

“…Laterolateral radiography of the neck in the neutral and ventroflexed positions was conducted to rule out AAI. 10,24,25 Next, samples were excluded from the study if AA joint instability or rupture of the DAAL were identified. The specimens were randomly classified into the surgery and control groups using a computer program (Excel; Microsoft, Redmond, WA).…”