Diagnosis and treatment of a chronic atlanto-occipital subluxation in a dog

C1 Facetectomy and Ventral Fixation of Occipitoatlantoaxial Complex for Concurrent Congenital Atlanto-Occipital Dislocation and Atlantoaxial Instability in a Toy Poodle

An 8-month-old, 3.4 kg, castrated male Toy Poodle was referred for progressive tetraparesis and respiratory disorder without a history of trauma. Repeated computed tomography (CT) and magnetic resonance imaging (MRI) with different positions of the neck revealed concurrent atlanto-occipital dislocation (AOD) and atlantoaxial instability (AAI) with spinal cord compression. This case was unique due to its congenital nature and the absence of trauma. The surgical treatment involved precise removal of the C1 vertebra's ventral articular facet, which was compressing on the spinal cord, attributed to its fixed and malaligned position within the atlantooccipital joint. Following facetectomy, the stabilization of the occipital bone to the C2 vertebra was achieved by screws, wire, and polymethyl methacrylate. Two days after surgery, the dog recovered ambulation and showed gradual improvement in gait, despite mild residual ataxia. Postoperative CT and radiographs showed successful decompression of the spinal cord. The screw loosening was confirmed at 114 days, which was managed successfully by extracting the affected screws. Through the 21-month monitoring period, the dog showed a normal gait with a wide-based stance of the pelvic limbs when standing and experienced no pain. This case represents the first report of concurrent congenital AOD and AAI treated with a ventral surgical approach, contributing new insights to the understanding and management of such complex cranio-cervical junction disorders in veterinary neurosurgery.

Evaluation of a Novel Dorsal-Cemented Technique for Atlantoaxial Stabilisation in 12 Dogs

Dorsal atlantoaxial stabilisation (DAAS) has mostly been described to treat atlantoaxial instability using low stiffness constructs in dogs. The aim of this study was to assess the feasibility and surgical outcome of a rigid cemented DAAS technique using bone corridors that have not previously been reported. The medical records of 12 consecutive dogs treated with DAAS were retrospectively reviewed. The method involved bi-cortical screws placed in at least four of eight available bone corridors, embedded in polymethylmethacrylate. Screw placement was graded according to their position and the degree of the breach from the intended bone corridor. All DAAS procedures were completed successfully. A total of 72 atlantoaxial screws were placed: of those, 51 (70.8%) were optimal, 17 (23.6%) were suboptimal, and 4 (5.6%) were graded as hazardous (including 2 minor breaches of the vertebral canal). Surgical outcome was assessed via a review of client questionnaires, neurological examination, and postoperative CT images. The clinical outcome was considered good to excellent in all but one case that displayed episodic discomfort despite the appropriate atlantoaxial reduction. A single construct failure was identified despite a positive clinical outcome. This study suggests the proposed DAAS is a viable alternative to ventral techniques. Prospective studies are required to accurately compare the complication and success rate of both approaches.

Evaluation of atlantooccipital overlapping and cerebral ventricle size in dogs with atlantoaxial instability

This study investigated cerebral ventricle size and concurrent craniocervical junction abnormality in relation to atlantooccipital overlapping (AOO) in dogs with atlantoaxial instability (AAI). A total of 61 dogs were treated with atlantoaxial ventral fixation. Medical records of each dog, including magnetic resonance (MR) and computed tomography (CT) images, were retrospectively reviewed. CT images were assessed for the presence of AOO and the dogs were then assigned to either an AOO group or a non-AOO group accordingly. CT images were also evaluated to determine the foramen magnum (FM) index. Syringomyelia, cerebellar compression, dorsal compression, and the degree of enlargement of each cerebral ventricle were evaluated using MR images. Of the 61 dogs, 23 had AOO and 38 did not. Furthermore, the ventricle/brain height ratio, the fourth ventricle height/cerebellum length ratio, and the fourth ventricle width/cerebellum length ratio were significantly higher in the AOO group than in the non-AOO group. However, the FM index, third ventricle/brain height ratio, and incidence of syringomyelia did not differ significantly between the two groups. Dogs with concurrent AOO exhibited significantly more dilatation of the lateral and fourth ventricles.

Dorsal surgical stabilisation using tension bands for treatment of traumatic atlanto-occipital instability in a cat

CASE REPORT

An atlanto-occipital instability secondary to a dog bite was diagnosed in a 4-year-old Persian cat. Dorsal stabilisation of the instability was made with two OrthoFiber prostheses (Securos), which were used as tension bands between the nuchal crests of the occipital bone and the spinous process of the axis. Total recovery was achieved 4 days after surgery. Normal alignment of the atlanto-occipital joint was observed on survey radiographs taken 6 weeks post-surgery. Although the right loop had failed, the alignment was still normal and no neurological after-effects could be identified.

CONCLUSION

Dorsal divergent tension bands between the nuchal crests of the occipital bone and the spinous process of the axis can be used to stabilise traumatic atlanto-occipital instability.

Zygomatic arch-atlas wing stabilization in 5 dogs with atlanto-occipital dislocation

The aim of this work was to present a novel minimally invasive surgical stabilization technique for canine atlanto-occipital dislocation and to report the associated magnetic resonance imaging (MRI) findings. All 5 dogs in this case series underwent 1.5 T MRI of the head and neck and 3 underwent both MRI and computed tomography (CT). Atlanto-occipital dislocations were diagnosed based on the increased joint space between the occipital condyles and the atlas on MRI. Surgery was performed immediately with a never previously described fixation technique based on an external ligature. The stabilization was performed via 4 holes drilled in the zygomatic processes and in the atlas wings on each side. A nylon monofilament of 1 mm diameter was inserted in the 4 holes, and an O-shaped ligature was carried out externally to the skin through the ipsilateral zygomatic arch. Ligatures were removed within 2 months. At the postsurgical follow-up examination, 14 days after surgery, all dogs were found to be ambulatory. Atlanto-occipital stability was assessed by clinical examination with an average of 24 months of follow-up. The positive outcomes in this case series suggest that atlanto-occipital dislocation may be surgically treated with this novel technique, irrespective of the severity of the clinical presentation and associated lesions observed on MRI.

Diagnóstico clínico e radiográfico de luxação traumática da articulação atlanto-occipital em dois cães

A luxação da articulação atlanto-occipital é considerada uma afecção incomum no homem e nos animais. Radiografias laterais são recomendadas para o diagnóstico. No entanto, estão sujeitas a erros relacionados ao ângulo de radiação, ao alvo da imagem, à distância e à sobreposição óssea. Objetivou-se neste relato descrever os achados clínicos e radiográficos de dois cães com luxação traumática da articulação atlanto-occipital que apresentavam tetraparesia, dor cervical cranial, incapacidade de elevar a cabeça e déficits de nervos cranianos. No primeiro animal, observaram-se deslocamento craniodorsal do processo articular do atlas em relação a um dos côndilos do occipital, ausência de sobreposição dos forames vertebrais laterais e sobreposição do côndilo do occipital ao processo articular do atlas, no lado direito, caracterizando uma luxação unilateral. No segundo animal, observou-se deslocamento craniodorsal dos processos articulares do atlas em relação aos côndilos do occipital, com sobreposição dos forames vertebrais laterais e ausência de visibilização dos côndilos do occipital em virtude da projeção cranial dos processos articulares do atlas em direção ao crânio, caracterizando luxação bilateral. Conclui-se que o exame radiográfico simples, nas projeções laterolateral e ventrodorsal, apesar da dificuldade de ser interpretado, é eficiente para confirmar o diagnóstico da luxação atlanto-occipital traumática, tanto a simétrica quanto a assimétrica.

Ventral fixation of chronic atlanto-occipital luxation in a dog

A 4·5-year-old male Australian Kelpie was presented for evaluation of ambulatory tetraparesis and neck pain of five weeks duration. Atlanto-occipital luxation was diagnosed by computed tomography. The joint was unstable following closed reduction, and a ventral surgical approach to the cranial cervical spine and occiput permitted manual reduction and stabilisation of the atlanto-occipital joint. The thickened joint capsule and articular cartilage were removed to promote AO arthrodesis. Eight cortical screws, inserted into the occipital condyles and C1, were embedded in polymethylmethacrylate to stabilise the atlanto-occipital articulation. The dog recovered uneventfully after it was placed in a neck brace and rested for six weeks. Neurologic examination at six weeks was normal and the dog returned to normal farm work 12 weeks after surgery.