Occipitoatlantoaxial malformation with atlantoaxial subluxation in a cat

Occipitoatlantoaxial malformation and atlantoaxial subluxation was diagnosed in a three-year-old castrated male domestic shorthair cat. Clinical signs included ataxia, postural reaction deficits, abnormal spinal reflexes, and behaviour changes. Radiographic examination revealed malformation and hypoplasia of the occipital condyles, hypoplasia of the dens, and atlantoaxial subluxation. Electroencephalographic (EEG) findings included high voltage slow activity and sharp waves with superimposed low voltage fast activity in the occipital leads and sinusoidal beta waves in the frontal leads. Basilar artery compression as a result of atlantoaxial instability is suspected to have caused the behavioural changes and EEG abnormalities in this patient. The cat was treated by stabilisation of the atlantoaxial subluxation by ventral cross pin fixation, odontectomy, and arthrodesis of the atlantoaxial articulation. The patient responded well to treatment and was neurologically normal 18 months after surgery.     

Risk factors affecting the outcome of surgery for atlantoaxial subluxation in dogs: 46 cases (1978-1998)

OBJECTIVE: To identify risk factors for successful surgical management of dogs with atlantoaxial subluxation (AAS). DESIGN: Retrospective study. ANIMALS: 46 dogs managed surgically for AAS. PROCEDURE: Age at onset of clinical abnormalities, duration of clinical abnormalities prior to surgery, radiographic appearance of the dens, type (dorsal or ventral procedure) and number (1 or 2) of surgeries performed, grade of postoperative atlantoaxial joint reduction, and neurologic status prior to surgery (preoperative), when dogs were discharged from the hospital (postoperative), and during a follow-up evaluation (final) were obtained from the dogs' medical records. Risk factors for surgical success and degree of neurologic improvement were identified and analyzed for predictive potential. RESULTS: Age at onset of clinical abnormalities < or = 24 months was significantly associated with greater odds of a successful first surgery and final outcome and a lower postoperative neurologic grade. Duration of clinical abnormalities < or = 10 months was significantly associated with greater odds of a successful final outcome and a lower final neurologic grade. A preoperative neurologic grade of 1 or 2 was significantly associated with a lower final neurologic grade. Potential risk factors that did not affect odds of a successful outcome included type of surgery performed, grade of atlantoaxial joint reduction, radiographic appearance of the dens, or need for a second surgery. CONCLUSIONS AND CLINICAL RELEVANCE: Age at onset of clinical abnormalities, duration of clinical abnormalities prior to surgery, and preoperative neurologic status are risk factors for success of surgical management of AAS in dogs.     

Ventral approach for stabilization of atlantoaxial subluxation secondary to odontoid fracture in a foal

Atlantoaxial subluxation secondary to odontoid fracture in a 30-day-old foal was corrected by alignment of the atlantoaxial joint and stabilization with 2 ventrally placed dynamic compression plates. At 90 days after surgery, healing of the fracture, with adequate alignment of the atlantoaxial joint, was confirmed radiographically. The foal was only slightly tetraparetic at that time. At 1 year after surgery, the gait was normal. It was concluded that the technique has advantages over the use of Steinmann's pins or external coaptation for stabilization. The ventral approach allows decompression, anatomic alignment, and immediate stabilization of the subluxation. Potential complications of the ventral approach include laryngeal paralysis.     

A modified ventral fixation for surgical management of atlantoaxial subluxation in 19 dogs

OBJECTIVE: To describe a modified ventral stabilization technique for surgical management of atlantoaxial subluxation in dogs and to evaluate the outcome. STUDY DESIGN: Retrospective clinical study. SAMPLE POPULATION: Nineteen client-owned dogs. METHODS: Medical records of 19 dogs with a radiographic diagnosis of atlantoaxial subluxation surgically managed by a modified ventral fixation technique (cortical screws, Kirschner wires, polymethylmethacrylate) were reviewed. Data on pre- and post-operative neurologic status, surgical technique, and complications were retrieved. Follow-up evaluation was performed at approximately 1 month. Telephone interview of the owner was used for long-term assessment (median follow-up for 17 surviving dogs was 10.5 months). RESULTS: Adequate reduction and stabilization was achieved in all dogs based on radiographic assessment immediately after surgery. Improved neurologic outcome occurred in 16 dogs at 1 month and in 15 dogs at follow-up; 2 dogs died of post-operative complications within 24 hours of surgery. One dog was euthanatized at the owners' request because of recurrent neck pain associated with implant failure after 1 month. Two dogs required surgery to remove broken and migrated implants, but further stabilization was not necessary. CONCLUSIONS: Adequate stabilization and improved neurologic outcome was achieved in most dogs. However, on account of the small size of the study and the variable neurologic signs of the dogs on admission, the surgical technique described could not be compared to those previously reported. CLINICAL RELEVANCE: The surgical technique described is an effective means of surgical treatment for atlantoaxial subluxation.     

Treatment of a coxofemoral luxation in a pony using a prosthetic capsule technique

Objective: To report open reduction and joint stabilization using a prosthetic capsule technique for treatment of a craniodorsal coxofemoral luxation in a lightweight pony. Study Design: Clinical report. Animals: Pony stallion (8 years old, 113 kg). Methods: A craniodorsal approach to the coxofemoral joint was performed under general anesthesia. After open reduction, a prosthetic capsule technique was used. Four 3.5 mm self‐tapping cortical anchor screws were implanted: 2 screws were inserted above the cranial aspect of the dorsal acetabular rim, and 2 screws were inserted into the femoral neck. Subsequently, a #5 USP ultra‐high molecular weight polyethylene suture was placed through these anchor screws in figure‐8 fashion to serve as a prosthetic capsule. Routine closure and a medial patellar desmotomy completed the surgical procedure. Postoperatively, the pony was cross tied for 4 weeks to prevent it from lying down. Results: Neither short‐term nor long‐term complications occurred and the pony was sound at the follow‐up examination performed 15 months postoperatively. Conclusions: A prosthetic capsule technique can be used successfully to stabilize the coxofemoral joint after open reduction of a craniodorsal luxation in a lightweight pony.     

Extraluminal,C Shaped Polyethylene Prostheses in Two Ponies with Tracheal Collapse

Objective: To describe the surgical technique, complications, and outcome after use of extraluminal prostheses in 2 ponies with severe tracheal collapse. Study Design: Clinical report. Animals: Ponies (n=2) with severe tracheal collapse. Methods: A ventral median approach was used to expose the trachea from the larynx to the manubrium. Extraluminal, high‐density polyethylene, C‐shaped prostheses were sutured to the dorsal tracheal membrane and tracheal rings to provide external tracheal support. Results: The surgical approach provided good tracheal access and placement of the rings was uncomplicated. Initial estimates of the tracheal diameter from preoperative radiographs resulted in prostheses that were too small at surgery requiring a 2nd surgical procedure in 1 pony. Postoperative complications were coughing, right laryngeal hemiplegia, seroma formation, and antimicrobial induced colitis. Both ponies had marked resolution of clinical abnormalities after surgery. Recurrent esophageal obstruction resulted in euthanasia of 1 pony 3.5 years after surgery. The other pony was doing well 1 year after surgery. Conclusions: Extraluminal support of the trachea resulted in rapid resolution of clinical signs in 2 ponies with tracheal collapse. Clinical Relevance: Extraluminal tracheal prostheses can resolve clinical abnormalities in ponies with severe tracheal collapse.     

Stabilisation of atlantoaxial subluxation in the dog through ventral arthrodesis

Ten miniature breed dogs with atlantoaxial subluxation underwent ventral lag screw stabilisation. The procedure did not include bone graft packing into the atlantoaxial articulation. Four dogs showed continuous improvement after surgery. Three dogs developed complications due to external trauma and postoperative implant failure but improved with conservative therapy. Three patients died or were euthanized in early perioperative or postoperative period. The long-term outcome was good or favourable in all surviving patients. Suspected fibrous tissue proliferation and stabilisation without permanent bone fusion was found to be clinically satisfactory when the atlantoaxial joint has been subjected to limited stress during a long-term monitoring period.     

A modified ventral approach to the atlantoaxial junction in the dog

Objective— To describe and evaluate a surgical technique using a modified ventral approach for stabilization of the atlantoaxial (AA) junction in dogs with AA subluxation.
Study Design— Retrospective study.
Animals— Dogs (n=5) with AA subluxation.
Methods— Medical records (2000–2006) of 5 dogs with AA treated by stabilization via a right parasagittal approach were reviewed and outcome assessed by clinical examination and phone interviews with owners.
Results— The AA joint was clearly visualized and fixation devices were placed in all dogs. A right parasagittal approach provided excellent access to the AA junction and avoided dissection around the thyroid gland, trachea, and recurrent laryngeal nerve. Recovery was considered good to excellent by owners, and dogs returned to good function.
Conclusions— A right parasagittal approach to the AA junction provides improved exposure and allows for surgical stabilization with minimal complications.
Clinical Relevance— In dogs that require surgical stabilization of the AA joint, a right parasagittal approach should be considered. This approach offers advantages over the standard ventral median approach by improved surgical exposure, less dissection, and provides protection of vital structures during insertion of fixation devices used for ventral AA stabilization.     

Surgical decompression for traumatic atlantoaxial subluxation in a weanling filly.

A filly with ataxia and splinting and crepitation in the neck was found to have atlantoaxial subluxation. Radiographic diagnosis was based on the same criteria as those used in other species, ie, increased distance between the atlas and spine of the axis and increased distance between the dens and floor of the atlas. Extensive hemilaminectomy was performed to decompress the spinal cord. Stabilization was not attempted. Immediate postoperative response was encouraging, but the untimely death of the filly prevented further evaluation of the procedure.     

Use of the Kishigami Atlantoaxial Tension Band in Eight Toy Breed Dogs with Atlantoaxial Subluxation

Objective— To determine the applicability, complications, and long-term functional outcome of the Kishigami Atlantoaxial Tension Band (Kishigami AATB) for management of congenital and traumatic atlantoaxial (AA) instability in toy breed dogs.
Study Design— Case series.
Animals— Toy breed dogs (n=8) with congenital or traumatic AA instability.
Methods— The AA joint of each dog was surgically stabilized through a dorsal approach using the original or a modified version of the Kishigami AATB. Pre- and postoperative neurologic status, radiographs, and complications were reviewed. Follow-up examination was performed at 1 and 12 months.
Results— Functional improvement occurred in 5 dogs; 1 dog did not improve or worsen and 2 dogs were euthanatized at owner request. Adequate reduction and stabilization was achieved in 7 dogs based on immediate postoperative radiographs; failure of reduction was evident in 1 dog. No relevant complications occurred.
Conclusions— Kishigami AATB may be acceptable as an alternative method for dorsal stabilization of AA subluxation in toy breed dogs in which use of ventral screws or pins is challenging. Experience with this technique in a larger population is necessary to compare our results to those reported by ventral approach.
Clinical Relevance— The surgical technique described is effective, safe, and simple in the surgical treatment of AA subluxation in toy breed dogs.     

Treatment of coxofemoral luxation in a mature Welsh pony by femoral head ostectomy: Long‐term outcome

A 233 kg, 4‐year‐old Welsh pony stallion presented with a unilateral coxofemoral luxation and a history of previous upward fixation of the patella. This condition was surgically managed by femoral head ostectomy using a craniodorsal approach to the luxated coxofemoral joint, without greater trochanteric osteotomy. Immediate improvement in weightbearing was observed after surgery and primary intention healing was recorded. Long‐term outcome, 4 years after surgery, was assessed by radiographic, ultrasonographic and lameness examination. The pony was in good body condition and the initial weight of this patient was restored. Despite fetlock hyperlaxity of the contralateral hindlimb, amyotrophy and mechanical lameness of the affected hindlimb, the pony showed evident comfort without apparent signs of pain and was able to trot and gallop. Bone callus was observed at imaging examination.     

Atlantoaxial subluxation and absence of transverse ligament of the atlas in a dog

Absence of the transverse ligament of the atlas was diagnosed at necropsy in an 8-month-old Shih Tzu with radiographic signs of atlantoaxial subluxation. Symmetric ataxia, tetraparesis, and signs of pain in the vertebral canal suggested a lesion in the cervical portion of the spinal cord. Necropsy revealed absence of the transverse ligament of the atlas and malformation of dens and atlas. In addition, the alar ligaments were distinct and thick, and the atlanto-occipital and atlantoaxial joint capsules were markedly thicker than normal. Histologic examination revealed focal compressive myelopathy of the spinal cord at the level of the atlantoaxial joint.     

Surgical stabilization of an occipitoatlantoaxial malformation in an adult dog

Objective: To report surgical planning, technique, and outcome of stabilization surgery in an adult dog with occipitoatlantoaxial malformation (OAAM). Study Design: Clinical report. Animal: A 19‐month‐old, 25.5 kg, male castrated, Shiba Inu. Methods: Radiographic and magnetic resonance imaging were used to identify and characterize OAAM. Using a ventral approach to the cranial cervical region 2 cortical bone screws were inserted from the axis into the malformed atlas and occiput. Results: Ambulation was conserved postoperatively. Within 4 weeks, neurologic examination was mostly normal except for decreased proprioception in the right pelvic limb. At 9 months, the dog retained an extended neck posture, but had no neurologic abnormalities. Conclusion: OAAM should be considered as a differential diagnosis in an adult dog with cervical myelopathy. Surgical fixation with cortical bone screws using a ventral approach can be successful.     

Laminotomy of the Axis for Surgical Access to the Cervical Spinal Cord A Case Report

A cranially hinged laminotomy of vertebra C2 was used to expose the cervical spinal cord of a dog with a meningioma in the region of the atlantoaxial articulation. By preserving the dorsal atlantoaxial ligament, the technique seemed to result in greater and more physiologic stability between the atlas and axis than dorsal laminectomy and prosthetic replacement of the dorsal atlantoaxial ligament. The procedure allowed a dorsal approach, avoiding injury to the vertebral arteries and limited exposure, which are potential problems with hemilaminectomy of C1-C2. Further investigation is needed to evaluate long-term consequences of this procedure.     

Bone plating to stabilize atlantoaxial subluxation in four dogs

Four dogs with atlantoaxial subluxation were treated surgically via a ventral approach and the application of an ASIF mini H plate and 2·0 mm screws to the vertebral bodies. Three dogs recovered and are well but one dog died of a cardiac arrest postoperatively.     

Surgical Management of Atlantoaxial Subluxation in 23 Dogs

Twenty-eight surgical procedures were performed in 23 dogs with atlantoaxial subluxation. Dorsal stabilization in seven dogs resulted in two recoveries and five failures of fixation. Ventral decompression and stabilization in 18 dogs resulted in eight recoveries and four failures of fixation. Six dogs died or were euthanatized within 7 days of ventral stabilization. Using either technique, four of seven nonambulatory dogs recovered.     

Diagnosis,treatment and outcome of spinal lymphoma in a pony

This report describes the diagnostic approach to, and treatment of, a case of severe pelvic limb ataxia in a Miniature Shetland pony. Diagnosis of an intradural‐extramedullary lesion at the level of T11–12 was made using CT myelography. Dorsolateral hemilaminectomy allowed surgical debulking of an intradural mass, diagnosed histopathologically as T cell rich B cell lymphoma. Post operative treatment with prednisolone, cytarabine and cyclophosphamide was tolerated well and the degree of ataxia reduced markedly, allowing the pony to return to normal management.     

Atlantoaxial Instability: A Ventral Surgical Technique for Decompression, Fixation, and Fusion

Atlantoaxial stability was evaluated in 12 surgically stabilized dogs and 6 control dogs after odontoidectomy and dorsal atlantoaxial ligament separation. The atlantoaxial instabilities were stabilized with transarticular pins from a ventral approach. Cancellous bone grafts harvested from the proximal humerus were used to promote joint fusion. Good joint stability, alignment, and early fusion were documented clinically, radiographically, and histopathologically in stabilized dogs. Because of our consistent results despite variable pin angles, we recommend this technique for use in dogs with atlantoaxial instability requiring surgical stabilization.     

Stabilization of atlantoaxial subluxation secondary to atlantooccipital malformation in a Devon calf

Atlantoaxial subluxation secondary to atlantooccipital malformation in a 14-day-old female Devon calf was corrected by alignment and stabilization of the atlantoaxial joint. Stabilization was achieved by the ventral placement of pins and screws, and the dorsal placement of a figure 8 tension band wire. At 2 and 14 days post operatively, adequate alignment of the atlantoaxial joint was confirmed radiographically. Following surgery the calf improved clinically, but was terminated 14 days following the surgery due to a pneumonia. At necropsy the fixation was stable and spinal cord decompression had been achieved. It was concluded that this technique could be utilized to allow decompression, anatomical alignment, and stabilization of an atlantoaxial subluxation secondary to atlantooccipital malformation in a calf. At necropsy, there was gross and histologic evidence of congenital fusion of the basioccipital bone to the malformed atlas.     

Surgical management of a pony with a traumatic medial luxation of the patella

This report describes a successful surgical repair of medial patellar luxation in a Miniature Shetland pony where manual reduction of the patella was not possible. The surgical procedure involves transection of the medial femoropatellar ligament to facilitate patellar release, the placement of a prosthetic suture to replace the lateral femoropatellar ligament and reinforcement of the lateral retinaculum by the use of a mesh implant. This is a newly described surgical technique for the rare but recognised condition of a medial luxation of the patella.