Occipitoatlantoaxial Malformation in a Dog Treated with a Custom-Made Implant

Clare Rusbridge,Carina Rotter,Noel Fitzpatrick

doi:10.1055/s-0040-1721030

Abstract

AbstractBackground Occipitoatlantoaxial malformation (OAAM) is reported rarely in dogs and few treatment options are described. The congenital condition is thought to be associated with a proatlas re-segmentation failure resulting in malformation and malalignment of the craniovertebral junction which can result in C1 to 5 myelopathic signs.Methods Customized three-dimensional printed locking plate with trajectory screw implantation points for the stabilization of the atlantoaxial joint in a dog with OAAM. The dog was evaluated at time points 0, 2, 6 and 9 months to determine clinical outcome, degree of fusion, implant positioning and subsidence.Results New bone formation was noted 9 months after surgery, but complete fusion remained absent, although no implant failure occurred. Clinically, the dog made a good recovery and was able to exercise normally 9 months after surgery. The only residual deficit was a subtle left-sided cervical torticollis.Clinical Significance This report illustrates a management option and outcome of a dog treated with OAAM. Collaboration between clinicians and engineers provides a new dimension of care for patients with vertebral malformations.

Highlights

Combination of radiographs, computed tomography (CT) and MRIs enabled a detailed description of malformations and malarticulation
The aetiology of os odontoideum is undetermined as could be the result of an embryological defect or due to postnatal fracture of the apex of the dens.[15,16]
All detected anomalies could be explained by failure of re-segmentation of the proatlas, responsible for the development of the dens apex, apical, cruciate and alar ligaments, occipital condyles, occipital bone, the superior portion of the posterior arch of C1 and lateral mass of C2, to name a few and the first spinal sclerotome forming the dens, the anterior arch of C1 and the inferior portion of the posterior arch of C1.2,5,6,11–14 Treatment guidelines in human medicine are independent of the underlying aetiology

Summary

Introduction

Occipitoatlantoaxial malformation (OAAM) describes triosseous anomalies of the craniovertebral junction affecting the occipital bones, axis and atlas.[1,2,3,4,5,6,7,8] Case reports of OAAM exist in various species, such as the cat, dog, goat, dromedary camel and wild Japanese serow.[1,3,4,5,6,7,8,9,10,11] The condition is thought to be inherited in Arabian horses and Holstein cattle, whereas in other species postnatal fracture, trauma or inflammation has been reported.[1,5,6,7,8,9] The theory of a developmental anomaly is supported by genetic models where suppression of the Hox-3d gene in mice led to occipitoatlantal assimilation and C2 deformity.[3,12] HOX and PAX genes regulate the development of sclerotomes from the somites and their re-segmentation which establishes the vertebral boundaries.[12,13] Most important in the development of the craniovertebral junction is the proatlas sclerotome (4th occipital sclerotome) and 1st spinal sclerotome. Occipitoatlantoaxial malformation (OAAM) is reported rarely in dogs and few treatment options are described. Methods Customized three-dimensional printed locking plate with trajectory screw implantation points for the stabilization of the atlantoaxial joint in a dog with OAAM. The dog was evaluated at time points 0, 2, 6 and 9 months to determine clinical outcome, degree of fusion, implant positioning and subsidence

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Results

Conclusion