Mitral Valve Regurgitation in Klippel-Feil Syndrome With Related Thoracic Deformity.

Klippel-Feil syndrome, characterized by congenital fusion of any 2 or more cervical vertebrae, is a rare disorder in which skeletal and other organ system-related abnormalities have been reported. This article reports a case of mitral valve regurgitation in a patient with Klippel-Feil syndrome and related thoracic deformity who underwent mitral valvuloplasty. Postoperatively, the mitral valve regurgitation disappeared, and there has been no recurrence for 3 years. This case highlights mitral valvuloplasty via median sternotomy as an excellent treatment for mitral valve regurgitation in a patient with thoracic deformity related to Klippel-Feil syndrome.

Genetic insights into the 'sandwich fusion' subtype of Klippel-Feil syndrome: novel FGFR2 mutations identified by 21 cases of whole-exome sequencing.

BACKGROUND: Klippel-Feil syndrome (KFS) is a rare congenital disorder characterized by the fusion of two or more cervical vertebrae during early prenatal development. This fusion results from a failure of segmentation during the first trimester. Although six genes have previously been associated with KFS, they account for only a small proportion of cases. Among the distinct subtypes of KFS, "sandwich fusion" involving concurrent fusion of C0-1 and C2-3 vertebrae is particularly noteworthy due to its heightened risk for atlantoaxial dislocation. In this study, we aimed to investigate novel candidate mutations in patients with "sandwich fusion." METHODS: We collected and analyzed clinical data from 21 patients diagnosed with "sandwich fusion." Whole-exome sequencing (WES) was performed, followed by rigorous bioinformatics analyses. Our focus was on the six known KFS-related genes (GDF3, GDF6, MEOX1, PAX1, RIPPLY2, and MYO18). Suspicious mutations were subsequently validated through in vitro experiments. RESULTS: Our investigation revealed two novel exonic mutations in the FGFR2 gene, which had not previously been associated with KFS. Notably, the c.1750A > G variant in Exon 13 of FGFR2 was situated within the tyrosine kinase domain of the protein, in close proximity to several established post-translational modification sites. In vitro experiments demonstrated that this certain mutation significantly impacted the function of FGFR2. Furthermore, we identified four heterozygous candidate variants in two genes (PAX1 and MYO18B) in two patients, with three of these variants predicted to have potential clinical significance directly linked to KFS. CONCLUSIONS: This study encompassed the largest cohort of patients with the unique "sandwich fusion" subtype of KFS and employed WES to explore candidate mutations associated with this condition. Our findings unveiled novel variants in PAX1, MYO18B, and FGFR2 as potential risk mutations specific to this subtype of KFS.

Transient binocular vision loss and pain insensitivity in Klippel-Feil syndrome: a case report.

BACKGROUND: Klippel-Feil syndrome is a rare congenital bone disorder characterized by an abnormal fusion of two or more cervical spine vertebrae. Individuals with Klippel-Feil syndrome exhibit diverse clinical manifestations, including skeletal irregularities, visual and hearing impairments, orofacial anomalies, and anomalies in various internal organs, such as the heart, kidneys, genitourinary system, and nervous system. CASE PRESENTATION: This case report describes a 12-year-old Pashtun female patient who presented with acute bilateral visual loss. The patient had Klippel-Feil syndrome, with the typical clinical triad symptoms of Klippel-Feil syndrome, along with Sprengel's deformity. She also exhibited generalized hypoalgesia, which had previously resulted in widespread burn-related injuries. Upon examination, bilateral optic disc swelling was observed, but intracranial pressure was found to be normal. Extensive investigations yielded normal results, except for hypocalcemia and low vitamin D levels, while parathyroid function remained within the normal range. Visual acuity improved following 2 months of calcium and vitamin D supplementation, suggesting that the visual loss and optic nerve swelling were attributed to hypocalcemia. Given the normal parathyroid function, it is possible that hypocalcemia resulted from low vitamin D levels, which can occur after severe burn scarring. Furthermore, the patient received a provisional diagnosis of congenital insensitivity to pain on the basis of the detailed medical history and the findings of severe and widespread loss of the ability to perceive painful stimuli, as well as impaired temperature sensation. However, due to limitations in genetic testing, confirmation of the congenital insensitivity to pain diagnosis could not be obtained. CONCLUSION: This case highlights a rare presentation of transient binocular vision loss and pain insensitivity in a patient with Klippel-Feil syndrome, emphasizing the importance of considering unusual associations in symptom interpretation.

Molecular landscape of congenital vertebral malformations: recent discoveries and future directions.

Vertebral malformations (VMs) pose a significant global health problem, causing chronic pain and disability. Vertebral defects occur as isolated conditions or within the spectrum of various congenital disorders, such as Klippel-Feil syndrome, congenital scoliosis, spondylocostal dysostosis, sacral agenesis, and neural tube defects. Although both genetic abnormalities and environmental factors can contribute to abnormal vertebral development, our knowledge on molecular mechanisms of numerous VMs is still limited. Furthermore, there is a lack of resource that consolidates the current knowledge in this field. In this pioneering review, we provide a comprehensive analysis of the latest research on the molecular basis of VMs and the association of the VMs-related causative genes with bone developmental signaling pathways. Our study identifies 118 genes linked to VMs, with 98 genes involved in biological pathways crucial for the formation of the vertebral column. Overall, the review summarizes the current knowledge on VM genetics, and provides new insights into potential involvement of biological pathways in VM pathogenesis. We also present an overview of available data regarding the role of epigenetic and environmental factors in VMs. We identify areas where knowledge is lacking, such as precise molecular mechanisms in which specific genes contribute to the development of VMs. Finally, we propose future research avenues that could address knowledge gaps.

[The multisystem deformities features of Klippel-Feil syndrome patients combined with congenital scoliosis].

Objective: To summarize the characteristics of multisystem deformities in patients with Klippel-Feil syndrome (KFS) combined with congenital scoliosis (CS). Methods: Within the framework of the "Deciphering Disorders Involving Scoliosis and Comorbidities (DISCO)" research collaboration, a retrospective analysis was conducted on patients diagnosed with KFS and CS at Peking Union Medical College Hospital between April 2005 and August 2022. Patient data, including imaging examinations and medical records, were collected to summarize the spinal and associated deformities. Results: A total of 82 KFS patients with concurrent CS were included, comprising 42 males and 40 females. The average age was (12.8±8.9) years. Among the KFS patients, there were 31 cases of Type Ⅰ, 12 cases of Type Ⅱ, and 39 cases of Type Ⅲ. The most common location for the major curve of scoliosis was the mid-thoracic segment (42 cases, 51.2%). Hemivertebrae deformities were most frequently observed in the upper thoracic segment (31 cases, 60.8%). There were no statistically significant differences in age, gender, major curve Cobb angle, or region of hemivertebrae occurrence among the different types of KFS (all P>0.05). Apart from spinal vertebral deformities, intraspinal deformities had the highest comorbidity rate (33 cases, 40.2%). The subjects were divided into two groups based on the presence or absence of intraspinal deformity (absence as group G0, presence as group G1), there was a statistically significant difference in the main Cobb angle [M(Q1, Q3)] between the two groups, which was 45.0° (27.5°, 62.0°) and 60.0° (37.5°, 83.5°), respectively (P=0.044). Additionally, a portion of the patients had concurrent cardiovascular system abnormalities (13 cases, 15.9%), craniofacial-ocular-auricular abnormalities (8 cases, 9.8%), genitourinary system abnormalities (7 cases, 8.5%), and gastrointestinal abnormalities (2 cases, 2.4%). Conclusions: Patients with KFS combined with CS commonly present with a major curve of spinal deformity in the mid-thoracic segment and often have comorbidities involving multiple systems. When combined with intraspinal anomalies, the major curve exhibits a greater degree of curvature.

Chiari type III malformation associated with Klippel-Feil syndrome, a case report with a narrative review of the literature.

BACKGROUND: Chiari malformation type III (CM III), a rare hindbrain anomaly, often presents with various concurrent anomalies. This paper reports a unique case of CM III associated with Klippel-Feil syndrome (KFS), a condition previously unreported in Saudi Arabia and documented in only one other case globally in Turkey. This study aims to share insights into the unusual association between CM III and KFS, considering their close embryological development and involvement in the craniocervical junction. METHODOLOGY: The study presents a case of a 2.5-year-old female diagnosed with CM III and KFS. Diagnostic tools such as ultrasound, CT scans, MRI, and physical examinations were used to confirm the patient's condition. Surgical interventions, including decompression and encephalocele repair, were performed. RESULTS: Successful surgical interventions, including encephalocele repair and duraplasty, were carried out. Follow-up visits indicated a stable condition, marked improvement in lower limb strength, and the patient's ability to walk with assistance. CT follow-up affirmed a satisfactory surgical outcome. CONCLUSION: This case study illustrates the potential for an optimistic prognosis in CM III, even when accompanied by complex conditions such as KFS, through early diagnosis and intervention. It underscores the significance of antenatal screening for effective care planning and calls for further research and publications due to the rarity of this association. These findings contribute to our understanding of CM III and its related conditions, emphasizing the need for open-minded consideration of potential embryological associations.

Klippel-Fiel syndrome with rare presentation of bilateral temporomandibular joint osteoarthritis - A case report.

BACKGROUND: Klippel-Fiel syndrome (KFS) is a rare congenital skeletal disorder characterized clinically by presence of a triad of short neck, limited neck mobility (due to fused cervical vertebrae) and low posterior hair line. It was first described by Maurice Klippel and Andre Feil in 1912. Various skeletal and non-skeletal anomalies may be seen in association with KFS. CASE PRESENTATION: This report aims to highlight orofacial manifestations of a 16-year-old male patient with KFS along with a rare presentation of bilateral osteoarthritic changes in the temporomandibular joint. The treatment planning and execution for such a case has also been described. CONCLUSION: Bilateral osteoarthritic changes of temporomandibular joint have been rarely reported in KFS. This report emphasizes that early diagnosis of various associated anomalies and timely intervention through an interdisciplinary approach is very essential in the management of patients with KFS.

Tetraparesis following thoracic spine surgery in a patient with Klippel-Feil syndrome and ABCB4 mutation: a case report.

BACKGROUND: Klippel-Feil syndrome is a rare condition described in 1912 by Maurice Klippel and André Feil. It is defined as a congenital cervical fusion of at least two vertebrae, associated with a classical triad of clinical signs: short neck, low posterior hairline, and limited range of movement. However, Klippel-Feil syndrome manifests with a vast spectrum of phenotypes, ranging from no symptoms to complete triad, with or without other associated malformations. Most commonly, CCF results from sporadic mutations, even though autosomal recessive, autosomal dominant, or even X-linked inheritance can be detected. The ATP-binding cassette subfamily B member 4 is only expressed in the liver and is involved in biliary phospholipid secretion. The clinical spectrum includes various hepatobiliary pathologies, including low phospholipid-associated cholelithiasis, and has never been associated with musculoskeletal anomalies. CASE PRESENTATION: A 55-year-old male Caucasian patient presenting with low phospholipid-associated cholelithiasis syndrome with ATP-binding cassette subfamily B member 4 mutation and liver cirrhosis was referred to our clinic for a liver transplant. A period of 6 months before, the patient underwent a T7-T9 posterior fixation for a T8 osteoporotic fracture. Postoperatively, he was tetraparetic, whereas he was neurologically intact before the operation. At admission to our hospital, he was still tetraparetic and presented with clinical signs of cervical myelopathy. Moreover, he suffered a limitation of cervical range of motion in all directions, short neck, and low posterior hairline. Imaging showed multiple cervical and thoracic vertebral bodies fusion, as well as cervical spine stenosis. Based on the available data, we diagnosed a type 3 Klippel-Feil syndrome according to Samartzis' classification. CONCLUSIONS: The heterogeneity of KFS and the various potential hereditary links that are known indicate that it is important to highlight all potential cases related to known genetic defects. At present, no association between ATP-binding cassette subfamily B member 4 mutation and congenital cervical fusions has been reported. The other important clinical focus of this case is the appearance of spontaneous tetraparesis after thoracic spine surgery. This mechanism remains unclear, but considering different spinal anatomy it might have been due to difficult intubation and patient's positioning during his previous operation.

Brown Sequard syndrome in a patient with Klippel-Feil syndrome following minor trauma: a case report and literature review.

BACKGROUND: There are some cases of Klippel-Feil syndrome with spinal cord injury in clinical work. However, there is no literature report on Brown-Sequard syndrome after trauma. We report a case of Brown-Sequard syndrome following minor trauma in a patient with KFS type III. Her Brown-Sequard syndrome is caused by Klippel-Feil syndrome. CASE PRESENTATION: We found a 38-year-old female patient with KFS in our clinical work. She was unconscious on the spot following a minor traumatic episode. After treatment, her whole body was numb and limb activity was limited. Half an hour later, she felt numb and weak in the right limb and weak in the left limb. She had no previous hypertension, diabetes, or coronary heart disease. After one-month treatment of medication, hyperbaric oxygen, rehabilitation, and acupuncture in our hospital, her muscle strength partially recovered, but the treatment effect was still not satisfactory. Then, she underwent surgical treatment and postoperative comprehensive treatment, and rehabilitation training. She was able to take care of herself with assistance, and her condition improved from grade B to grade D according to the ASIA (ASIA Impairment Scale) classification. CONCLUSION: KFS, also known as short neck deformity, is a kind of congenital deformity characterized by impaired formation and faulty segmentation of the cervical spine, often associated with abnormalities of other organs. The cervical deformity in patients with KFS can alter the overall mechanical activity of the spine, as well as the compensatory properties of the spine for decelerating and rotatory forces, thus increasing the chance of spinal cord injury (SCI) following trauma. Many mechanisms can make patients more susceptible to injury. Increased range of motion of the segment adjacent to the fused vertebral body may lead to slippage of the adjacent vertebral body and altered disc stress, as well as cervical instability. SCI can result in complete or incomplete impairment of motor, sensory and autonomic nervous functions below the level of lesion. This woman presented with symptoms of BSS, a rare neurological disorder with incomplete SCI. Judging from the woman's symptoms, we concluded that previously she had KFS, which resulted in SCI without fracture and dislocation following minor trauma, with partial BSS. After the comprehensive treatment of surgery, hyperbaric oxygen, rehabilitation therapy, and neurotrophic drugs, two years later, we found her symptoms significantly improved, with ASIA Impairment Scale from grade B to grade D, and her ability to perform activities of daily living with aids.

Evolving Concepts of Craniovertebral and Spinal Instability.

Weakness of the muscles of the nape of the neck and back of the spine and its related instability is the nodal point of pathogenesis of a number of clinical and pathological events at the craniovertebral junction and the spine. Whilst acute instability results in sudden and relatively severe symptoms, chronic or long-standing instability is associated with a range of musculoskeletal and structural spinal alterations. Telescoping of the spinal segments results in "vertical" spinal instability in the subaxial spine and central or axial atlantoaxial instability (CAAD) at the craniovertebral junction. Instability in such cases might not be observed on dynamic radiological imaging. Chiari formation, basilar invagination, syringomyelia, and Klippel-Feil alteration are some of the secondary alterations as a result of chronic atlantoaxial instability. Radiculopathy/myelopathy related to spinal degeneration or ossification of posterior longitudinal ligament appears to have their origin from vertical spinal instability. All the secondary alterations in the craniovertebral junction and subaxial spine that are traditionally considered pathological and to have compressive and deforming role are essentially protective in nature, are indicative of instability, and are potentially reversible following atlantoaxial stabilization. Stabilization of unstable spinal segments is the basis of surgical treatment.

Síndrome de Wildervanck: reporte de un caso clínico / Wildervanck syndrome: clinical case report

El síndrome de Wildervanck (cérvico-óculo-acústico) es una patología muy rara, caracterizada por la tríada clásica de fusión de vértebras cervicales o anomalía de Klippel-Feil, síndrome de Duane (paresia del VI par craneal) e hipoacusia. Se han descrito, además, otras afecciones a nivel vascular, cardíaco y musculoesquelético. En este caso clínico, describimos a una paciente que cumple la tríada cardinal, además de presentar datos clínicos adicionales que no han sido reportados con anterioridad, lo cual contribuye a la ampliación del fenotipo de la enfermedad. Asimismo, realizamos una revisión de la literatura respecto a este síndrome

Wildervanck syndrome (also known as cervico-oculo-acoustic dysplasia) is a very rare disease, characterized by the typical triad of cervical vertebral fusion or Klippel-Feil anomaly, Duane syndrome (paresis of the sixth cranial nerve), and hearing loss. Other vascular, cardiac, and musculoskeletal conditions have also been described. In this case report, we describe a patient who met the cardinal triad and also presented additional clinical data that have not been previously reported, which contribute to broadening the disease phenotype. We have also reviewed the bibliography related to this syndrome.

Transmandibular Cervical Corpectomy for Persistent Spinal Cord Compression in a Patient With Klippel-Feil Syndrome: A Technical Note and Systematic Review.

BACKGROUND: Few studies have described a transmandibular approach for decompression in a patient with Klippel-Feil syndrome (KFS) for cervical myelopathy. OBJECTIVE: To describe the transmandibular approach in a KFS patient with cervical myelopathy and to perform a systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. METHODS: A systematic review was performed using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Embase and PubMed databases were searched from January 2002 to November 2022 for articles examining patients with KFS undergoing cervical decompression and/or fusion for cervical myelopathy and/or radiculopathy were included. Articles describing compression due to nonbony causes, lumbar/sacral surgery, nonhuman studies, or symptoms only from basilar invagination/impression were excluded. Data collected were sex, median age, Samartzis type, surgical approach, and postoperative complications. RESULTS: A total of 27 studies were included, with 80 total patients. Thirty-three patients were female, and the median age ranged from 9 to 75 years. Forty-nine patients, 16 patients, and 13 patients were classified as Samartzis Types I, II, and III, respectively. Forty-five patients, 21 patients, and 6 patients underwent an anterior, posterior, and combined approach, respectively. Five postoperative complications were reported. One article reported a transmandibular approach for access to the cervical spine. CONCLUSION: Patients with KFS are at risk of developing cervical myelopathy. Although KFS manifests heterogeneously and may be treated through a variety of approaches, some manifestations of KFS may preclude traditional approaches for decompression. Surgical exposure through the anterior mandible may prove an option for cervical decompression in patients with KFS.

Cervicothoracic dislocation due to congenital and bone-dysplasia-related vertebral malformations.

PURPOSE: To evaluate the approaches to treatment of congenital and bone-dysplasia-related pediatric cervicothoracic dislocations and define the optimal treatment method. METHODS: The publications available in PubMed and Google Scholar data bases were selected following such criteria as the disease in question, pediatric age, the treatment description, and follow-up results. The paper also includes the descriptions of our own six cases of the cervicothoracic dislocations detected in children with different vertebral malformations. RESULTS: Only eight patients meeting the abovementioned selection criteria were found in the publications: three of them had the Klippel-Feil syndrome (KFS), two had one-level vertebral anomaly, one had neurofibromatosis (NF type 1), one had the Larsen syndrome, and one had a variation of VACTERL association. Their treatment was long term, multi stage, and complicated. Among six our own cases, four patients also had KFS, one had a variation of VACTERL association, and one had NF type 1. All the patients suffered from preoperative neurological disorders. Posterior instrumental fixation with posterior vertebral body resection was performed in four cases and one patient underwent a combined surgery. The parents of one of the patients refused the operation, so he was observed while receiving bracing treatment. Since the treatment was long term and complicated by reoperations, the average follow-up period comprised 5 years. CONCLUSION: Congenital cervicothoracic dislocations are an extremely rare pathology that manifests itself in early age and requires an early surgical treatment. Failure to provide the treatment leads to the patient's disability. The surgical tactics for such patients is determined individually, but the published data and our own experience demonstrate that early multi-stage combined treatment has been the best option available so far. The cervicothoracic dislocations due to NF 1 manifest later and have a more favorable forecast.

Wildervanck syndrome: clinical case report. / Síndrome de Wildervanck: reporte de un caso clínico.

Wildervanck syndrome (also known as cervico-oculo-acoustic dysplasia) is a very rare disease, characterized by the typical triad of cervical vertebral fusion or Klippel-Feil anomaly, Duane syndrome (paresis of the sixth cranial nerve), and hearing loss. Other vascular, cardiac, and musculoskeletal conditions have also been described. In this case report, we describe a patient who met the cardinal triad and also presented additional clinical data that have not been previously reported, which contribute to broadening the disease phenotype. We have also reviewed the bibliography related to this syndrome.

El síndrome de Wildervanck (cérvico-óculo-acústico) es una patología muy rara, caracterizada por la tríada clásica de fusión de vértebras cervicales o anomalía de Klippel-Feil, síndrome de Duane (paresia del VI par craneal) e hipoacusia. Se han descrito, además, otras afecciones a nivel vascular, cardíaco y musculoesquelético. En este caso clínico, describimos a una paciente que cumple la tríada cardinal, además de presentar datos clínicos adicionales que no han sido reportados con anterioridad, lo cual contribuye a la ampliación del fenotipo de la enfermedad. Asimismo, realizamos una revisión de la literatura respecto a este síndrome.

Congenital Cervical Spinal Deformities.

Malformations of the cervical spine are a challenge in pediatric orthopedic surgery since the treatment options are limited. These congenital anomalies are often syndrome-related and have multiple repercussions on the function and statics of the cervical spine in all three planes. They are related to developmental abnormalities during the somite segmentation that occurs during the third week of embryonic development. Successful somitogenesis requires proper functioning of a clock regulated by complex signaling pathways that guide the steps needed to form the future spine. There is no specific classification for vertebral malformations at the cervical level. To characterize the progressive nature of a malformation, one must use general classifications. In the specific case of Klippel-Feil syndrome, these malformations can affect several vertebral levels in a continuous or discontinuous manner, but also the vertebral body and vertebral arch in a variable way. Thus, establishing a reliable prognosis in the coronal and sagittal planes is a complex undertaking. While technical mastery of certain osteotomy procedures has led to advances in the surgical treatment of rigid deformities of the cervical spine, the indications are still very rare. Nevertheless, the procedure has become safer and more accurate because of technical aids such as surgical navigation, robotics and 3D printed models or patient-specific guides. Occipitocervical transitional anomalies have embryological specificities that can explain the bony malformations seen at this level. However, most are rare, and the main concern is identifying any instability that justifies surgical stabilization. The presence of a cervical spine anomaly should trigger the search for occipitocervical instability and vice-versa.

Klippel-Feil Syndrome Associated with Renal and Cardiac Anomalies in an Infant: A Case Report.

Klippel-Feil syndrome is a rare congenital bone disorder characterised by a triad of short neck, low posterior hairline and limited lateral bending of the neck with an annual incidence of 1 in 40,000 live births. It has remained an obscure term in the medical literature because of its variability in presentation and wide spectrum of anomalies involving multiple organ systems. It is unusual to find a case that has all three classical triad features. Here, we present a case of a 9-month-old infant who manifests not only all three classical triad features associated with Klippel-Feil syndrome but also demonstrates the presence of congenital heart disease, scoliosis, and renal ectopia. An early comprehensive evaluation of a suspected case is essential for diagnosis and counselling which impacts its prognosis, helps minimize social stigma and affords parents the opportunity to consider cosmetic surgery as an option, should they choose to pursue it. Keywords: case reports; congenital; heart diseases; Klippel-Feil syndrome; scoliosis.

Application of C2 subfacetal screws for the management of atlantoaxial dislocation in patients with Klippel-Feil syndrome characterized by a narrow C2 pedicle and high-riding vertebral artery.

OBJECTIVE: This study aims to investigate the clinical application and feasibility of C2 subfacetal screws in patients with Klippel-Feil syndrome (KFS), narrow C2 pedicles, and high-riding vertebral arteries (HRVAs). METHODS: The clinical data of seven patients with KFS, atlantoaxial dislocation, narrow C2 pedicles, and HRVAs treated with C2 subfacetal screws were analyzed in this retrospective study. The internal height, isthmus height, and pedicle width of C2 vertebra were measured using preoperative computed tomography (CT). Subfacetal screws were inserted for 7 patients (12 sides). The position and length of the screws were observed using postoperative CT. Intraoperative dura mater and vertebral artery (VA) injuries were recorded. Bone fusion was observed using follow-up CT. RESULTS: The internal height was 10.5 ± 3.2 mm, the isthmus height was 3.7 ± 1.8 mm, the pedicle width was 3.0 ± 1.4 mm, and the screw length was 19.7 ± 1.5 mm. All patients had HRVAs and narrow pedicles. No injury to the dura mater and vertebral artery (VA) occurred in this group of patients. Bone fusion was achieved in all patients during follow-up. CONCLUSIONS: In patients with KFS, HRVA, and a narrow C2 pedicle, there is sufficient space below the C2 articular surface for screw insertion. When the pedicle is narrow and the C2 pedicle screw is not suitable for placement due to possible injury to the VA, subfacetal screws are a feasible alternative.