Atlantoaxial dislocation with vertebral artery anomaly: A case report

Abstract

BACKGROUND

Surgical intervention is a critical treatment approach for symptomatic atlantoaxial dislocation. However, vertebral artery injury remains a significant challenge during such procedures. We present a case of successful treatment of atlantoaxial dislocation with concurrent vertebral artery injury using interlaminar screw technology, and review the relevant literature.

CASE SUMMARY

A 69-year-old female patient, with no history of trauma, was diagnosed with atlantoaxial dislocation based on X-ray, computed tomography (CT), and magnetic resonance imaging. Preoperative CT angiography (CTA) revealed vertebral artery developmental anomalies, and she underwent posterior cervical surgery. Postoperative follow-up showed improvement in the patient’s clinical symptoms such as unstable walking and dizziness, as well as functional scores compared to pre-surgery. Intraoperative vertebral artery injury was successfully managed, and postoperative CTA review revealed no complications related to vascular damage.

CONCLUSION

Thorough preoperative evaluation, such as CTA imaging, and the surgeon’s expertise in various spinal screw placement techniques are crucial for improving the success rate of atlantoaxial dislocation surgeries.

Key Words: Atlantoaxial dislocation; Vertebral artery injury; Vertebral artery congenital; Screw techniques; Computed tomography angiography; Case report

Core Tip: Symptomatic atlantoaxial dislocation can cause persistent spinal cord compression if not treated promptly, potentially leading to paralysis or death. Surgical intervention is currently recommended. Iatrogenic vertebral artery injury (IVAI) is a severe complication of cervical spine surgery, including atlantoaxial dislocation treatment. Vertebral artery anomalies increase the risk of IVAI during the procedure. We treated a patient with atlantoaxial dislocation complicated by vertebral artery anomalies, and the case is reported subsequently

INTRODUCTION

Symptomatic atlantoaxial dislocation can cause persistent spinal cord compression if not treated promptly, potentially leading to paralysis or death. Surgical intervention is currently recommended[1]. Iatrogenic vertebral artery injury (IVAI) is a severe complication of cervical spine surgery, including atlantoaxial dislocation treatment. Vertebral artery anomalies increase the risk of IVAI during the procedure. We treated a patient with atlantoaxial dislocation complicated by vertebral artery anomalies, and the case is reported subsequently.

CASE PRESENTATION

Chief complaints

A 69-year-old women presented with headaches and upper limb numbness lasting > 2 months. She reported that the headaches began without any obvious triggers and were accompanied by shoulder and neck pain. A few days later, she developed numbness in both upper limbs but had no bowel or bladder dysfunction.

History of past illness

Past medical history includes renal cysts and chronic bronchitis.

Personal and family history

Denies any significant genetic disorders or family history of diseases.

Physical examination

Physical examination revealed normal vital signs and a visual analogue scale (VAS) score of 4. She exhibited tenderness in the posterior neck and bilateral scapular regions, numbness in both upper arms and hands, and diminished superficial sensation. Neck movement was restricted, and limb muscle strength was rated as IV-V. Both the Eaten and Spurling tests were negative, as were the Tinel’s signs at the elbows and wrists, Hoffmann’s sign, and tendon reflexes.

Laboratory examinations

Serological tests revealed a normal blood count, liver function, kidney function, and rheumatic and immunological markers. Markers of infection, including C-reactive protein, erythrocyte sedimentation rate, and interleukin-6, were within normal limits.

Imaging examinations

Magnetic resonance imaging (MRI) and computed tomography angiography (CTA) revealed a tortuous right vertebral artery, left vertebral artery dominance, C3/4 and C4/5 disc herniations, synovitis, anterior joint space effusion in the atlantoaxial joint, partial dislocation of the atlantoaxial joint, and posterior displacement of the odontoid process compressing the spinal cord (Figure 1). Dynamic cervical spine radiography revealed instability at C1/2 (Figure 2).

Figure 1 The computed tomography and magnetic resonance imaging images of the patient. A: There are degenerative changes in the cervical spine, with a herniated disc at C3/4; B and C: The cervical spine computed tomography scans show that the odontoid is located 7.32 mm above the chamberlain line, suggesting basilar invagination and compression of the cervical spinal cord.

Figure 2 Cervical dynamic X-ray examination suggests instability at C1/2. A: The active dose indicator (ADI) measures 9.49 mm in extension; B: The ADI measures 5.36 mm in the neutral position, 9.49 mm in extension; C: The ADI measures 10.75 mm in flexion, diagnosing atlantoaxial dislocation.

FINAL DIAGNOSIS

The primary diagnosis was basilar invagination with atlantoaxial dislocation (Goel A).

TREATMENT

After induction of anesthesia, the patient underwent posterior occipitocervical fusion. Preoperative CTA suggested abnormal development of the vertebral artery, with the left vertebral artery at V3 segment invading the lateral mass of C2, and the left vertebral artery at V4 segment adjacent to the posterior arch of C1 (Figure 3). Active bleeding was observed during the exposure of the left C2 screw placement site, suggesting possible vertebral artery injury. Gelatin sponges and brain cotton pads were used for hemostasis, which partially reduced the bleeding. Continued local pressure with a mixture of bone wax and gelatin sponge controlled the bleeding after approximately 40 minutes of persistent pressure by an assistant. To prevent bilateral vertebral artery injury that could lead to compromised cranial blood supply, we refrained from attempting lateral mass or pedicle screw placement on the right side of C1 and C2. C2 Lamina screws were then placed, followed by the insertion of screws into the occipital bone plate, installation of pre-bent connecting rods, and traction and extension of the cervical spine with locking of the rod tail cap. We choose to perform bone grafting with autogenous iliac bone grafts between the laminae to increase stability. Postoperatively, the patient wore a cervical collar for stabilization, with close monitoring of vital signs, drainage volume and characteristics, and neurological status, including eye-opening, speech, and upper limb sensory and motor function.

Figure 3 Preoperative computed tomography reconstruction and magnetic resonance tomography images of the patient. A: Computed tomography (CT) reconstruction scans demonstrated spontaneous atlanto-occipital fusion; B-D: CT cross-sectional images indicate a high-riding vertebral artery anomaly and restricted placement of screws on the left side of the C2 vertebra. Vascular MRI imaging indicates invasion of the left vertebral artery into the lateral mass of C2 and the left posterior arch of C1.

OUTCOME AND FOLLOW-UP

The drain was removed on postoperative day 3, following which cervical spine radiography and CT scans were obtained (Figure 4). The patient was discharged on postoperative day 7 with no unsteadiness, dizziness, or discomfort. Headaches significantly improved compared to those at admission, with a VAS score of two, and upper limb numbness also showed improvement. At the postoperative follow-up, the patient recovered well, with the Japanese Orthopaedic Association increasing from 12 preoperatively to 15 postoperatively, indicating a 60% improvement, and no clinical signs of posterior circulation ischemia, such as dizziness, nausea, or vomiting. In the follow-up one year after the surgery, the patient reported no numbness, weakness, or decline in mobility in the limbs. Additionally, there were no reports of dizziness, headaches, gait instability, or increased fall risk, nor any disturbances in bowel or bladder function.

Figure 4 Images of the patient after surgery and during follow-up. A: Postoperative cervical computed tomography (CT) scans demonstrated screws in situ within the C2 Lamina; B and C: Postoperative CT angiography showed a patent left vertebral artery without post-traumatic stenosis; D: Postoperative radiographs revealed the internal fixation to be well-positioned.

DISCUSSION

Classic posterior atlantoaxial fixation techniques include wire binding, transarticular screw fixation, pedicle screw/Laminar screw/rod plate systems, and occipitocervical fusion. Anterior approaches include transoral repositioning plate fixation and anterior cervical transarticular screw techniques. Common posterior cervical screw techniques include lateral mass and pedicle screws[2]. Miyakoshi et al[3] introduced the C2 Laminar screw technique, which is an effective alternative to reduce the risk of intraoperative vertebral artery injury in hospitals lacking surgical microscopes and other advanced instruments[2]. However, there is a risk of spinal cord injury from screw insertion into the spinal canal. Researchers have also proposed techniques, such as spinous process double-cortex screws and facet screws (Magerl screws). Magerl screws provide good resistance to flexion, extension, and rotation. However, biomechanically, C1/2 pedicle screws provide the best mechanical strength. Because of the greater amount of cancellous bone in the spinous process and lamina, laminar screws have weaker resistance to lateral bending and anchoring than that of pedicle screws[1]. If a single technique cannot achieve bilateral fixation, a combination of two or more internal fixation techniques is often used. Additionally, transoral or posterior lateral mass joint release may reduce fixation stress[3].

Clinically, the vertebral artery is divided into four segments, with variations commonly occurring in the V2 and V3 segments. The V3 segment is particularly relevant for upper cervical spine surgeries[4]. Vertebral artery development at the craniocervical junction often exhibits variations due to abnormal bone structure development. Researchers have classified developmental anomalies into four types. Types I and III have a low angle of the vertebral artery groove, which facilitates pedicle screw placement, whereas Types II and IV have grooves closer to the inner wall of the pedicle, posing a high risk of screw insertion[5]. Vertebral artery developmental anomalies, such as high-riding vertebral arteries or small pedicles with transverse foramen fusion, pose significant technical challenges for the implantation of C1 Lateral mass screws and C2 pedicle screws, and for surgical procedures in these areas[6]. Detailed preoperative preparation is crucial for surgical safety. Common assessment methods include CTA of the head and neck, vertebral artery angiography, and MRA of the head and neck. Some studies have proposed screw placement assessment methods based on thin-slice CT tomography. For instance, if more than four continuous images of the atlas show a pedicle thickness greater than 4 mm, pedicle screws can be used. If fewer than two layers are visible, lateral mass screws are recommended. The use of 3D-printed guides allows for a clearer assessment of vertebral artery anatomy and variations, improves screw placement accuracy and reduces the risk of intraoperative IVAI[7]. In cases with a dominant-side vertebral artery supply, after a thorough preoperative evaluation, it is preferable to use pedicle screws on the non-dominant side to achieve optimal mechanical strength. Alternative techniques, such as laminar screws or vertebral body screws are recommended to minimize the risk of vertebral artery injury.

The complications of cervical spine surgery include IVAI, venous plexus injury, cerebrospinal fluid leakage, and surgical site infections. Research indicates that the incidence of vertebral artery injury during cervical spine surgery is approximately 8.2%[8]. This can lead to severe complications, such as pseudoaneurysm of the vertebral artery, delayed hemorrhage, cerebral ischemic infarction, or even death. The causes of such injuries include the use of high-speed drills, inadequate exposure of the surgical area, and screw placement in the upper cervical vertebrae. For bleeding in the venous plexus, electrocautery should be avoided during hemostasis. Instead, methods, such as applying gelatin sponges and brain cotton pledgets under pressure, should be used. Once IVAI occurs, treatment goals are to control local bleeding, prevent ischemia and embolism, and minimize the risk of postoperative embolic complications. The primary method is direct packing for hemostasis using materials, such as gelatin sponges, brain cotton, bone wax, and hemostatic gauze. However, packing carries a high risk of delayed bleeding and pseudoaneurysm formation[7]. If the packing fails, life-saving options include surgical ligation, endovascular embolization of the affected vertebral artery, or stent placement. However, ligation and occlusion of the vertebral artery are significantly associated with posterior cerebral circulation ischemia and cerebral infarction. Therefore, when damage occurs to the dominant side of the artery, vascular repair techniques, such as vessel suturing or bypass should be actively considered. However, these methods are technically difficult[9,10].

CONCLUSION

After the occurrence of IVAI, postoperative vertebral artery CTA or related vascular examinations should be performed to assess the effectiveness of hemostasis, vessel patency, and the presence of pseudoaneurysms. Following a thorough assessment of rebleeding risk, anticoagulant and antiplatelet medications should be used to reduce the impact of local thrombosis on the cerebral blood supply and minimize the occurrence of cerebral infarction and other sequelae. Therefore, a thorough preoperative evaluation and planning are crucial for preventing IVAI.