Defining hyoplasia of the atlas: a cadaveric study

A new etiology of nontraumatic C0-C1-C2-Complex instability - abnormality of musculus rectus capitis posterior minor: a case report

PURPOSE

This study presents an abnormality of the musculus rectus capitis posterior minor (RCPmi) as a new etiological factor for nontraumatic sagittal plane instability in the C0-C1-C2-complex, with a focus on identifying the absence or atrophy of RCPmi on both sides.

METHODS

A 36-year-old male patient presented with recurring neck pain (VAS 8/10) and tingling paresthesia in the entire left hand over a six-month period, without significant neurological deficits. Radiated arm pain was not reported. Imaging examinations revealed sagittal plane instability in the C0-C1-C2-complex, spinal canal stenosis (SCS), and myelopathy at the C1 level. Subsequently, a dorsal C0-1 reposition and fusion with laminectomy were performed.

RESULTS

The congenital absence or atrophy of RCPmi, leading to the lack of cephalad-rearward traction on the C1-tuberculum-posterius, induced a developmental failure of the C1 posterior arch. Consequently, the oblate-shaped C1 posterior arch lost support from the underlying C2 posterior arch and the necessary cephalad-rearward traction throughout the patient's 36-year life. This gradual loss of support and traction caused the C1 posterior arch to shift gradually to the anterior side of the C2 posterior arch, resulting in a rotational subluxation centered on the C0/1 joints in the sagittal plane. Ultimately, this led to SCS and myelopathy. Traumatic factors were ruled out from birth to the present, and typical degenerative changes were not found in the upper cervical spine, neck muscles, and ligaments.

CONCLUSION

In this case, we not only report the atrophy or absence of RCPmi as a new etiological factor for nontraumatic sagittal plane instability in the C0-C1-C2-complex but also discovered a new function of RCPmi. The cephalad-rearward traction exerted by RCPmi on the C1 posterior arch is essential for the development of a normal C1 anterior-posterior diameter.

Anatomical Basis and Clinical Significance of Atlas Stenosis: a Systematic Review

Aim: In this intriguing review, the authors dive into the complex world of atlas stenosis and its clinical impact on cervical myelopathy. The authors shed light on the origins of atlas stenosis, highlighting how congenital abnormalities of the atlas are a result of failures in embryological development. Furthermore, diagnosis and treatment methods are described. Materials and methods:Utilizing a detailed search of the literature in the PubMed database, the authors have compiled a comprehensive analysis of the anatomical and biological basis of this condition. After applying the exclusion criteria, 25 papers were deemed appropriate for the present review. Results:With the help of computed tomography (CT) and magnetic resonance imaging (MRI) scans, diagnosis becomes possible, but the authors emphasize the importance of using special tests for a more accurate assessment. When it comes to treatment, surgical decompression with laminectomy or laminoplasty is the suggested approach. This highlights the severity of atlas stenosis and the need for intervention to alleviate the symptoms and prevent further neurological damage. What sets this review apart is its focus on the clinical profile of atlas stenosis. The authors discuss how the obstruction of cerebrospinal fluid flow can lead to neurological disorders and headaches. This sheds light on the broader impact this condition can have on patients' lives beyond simply the anatomical implications. Conclusion:In the conclusion, the authors emphasize the susceptibility of the spinal cord to injuries even with mild mechanical pressure or instability due to aging in patients with atlas stenosis. Additionally, the instabilities caused by anatomical abnormalities of the atlas further highlight the importance of considering atlas stenosis in cases of cervical trauma. Overall, this review provides a fascinating insight into the connection between atlas stenosis and cervical myelopathy. By exploring the anatomical, biological, diagnostic, and treatment aspects of this condition, the authors have contributed to the understanding of this complex and often overlooked topic.

Cervical Myelopathy Caused by Non-Rheumatic Retro-Odontoid Pseudotumor: An Investigation of Underlying Mechanisms and Optimal Surgical Strategy

STUDY DESIGN

Retrospective case-control study.

OBJECTIVE

This study aimed to identify the underlying pathologies of non-rheumatic retro-odontoid pseudotumors (NRPs), which would help establish an appropriate surgical strategy for myelopathy caused by NRP.

METHODS

We identified 35 patients with myelopathy caused by NRP who underwent surgery between 2006 and 2017. An age- and sex-matched control group of 70 subjects was selected from patients with degenerative cervical myelopathy. Radiographic risk factors for NRP were compared between cases and controls. We also assessed surgical outcomes following occipital-cervical (O-C) fusion, atlantoaxial (C1-2) fusion, or C1 laminectomy.

RESULTS

Patients with NRP had significantly lower C1 sagittal inner diameter, C2-7 range of motion (ROM), C2-7 Cobb angle, and C7 tilt, as well as significantly higher C1-2 ROM, atlantodental interval (ADI), and C1-2 to O-C7 ROM ratio. Multivariate regression analysis revealed that ADI, C2-7 ROM, and C7 tilt were independent risk factors for NRP. Neurological recovery and pseudotumor size reduction were comparable among surgical procedures, whereas post-operative cervical spine function was significantly lower in the O-C fusion group than in the other groups.

CONCLUSION

Non-rheumatic retro-odontoid pseudotumor was associated with an increase in ADI, suggesting that spinal arthrodesis surgery is a reasonable strategy for NRP. C1-2 fusion is preferable over O-C fusion because of the high prevalence of ankylosis in the subaxial cervical spine. Given that 29% of patients with NRP have C1 hypoplasia, such cases can be treated by posterior decompression alone. Our study highlights the need to select appropriate surgical procedures based on the underlying pathology in each case.

Floating Laminoplasty for the Treatment of Compressive Myelopathy Accompanied by C1 Posterior Ring Hypoplasia: A Technical Note and Case Series

Posterior ring hypoplasia of the atlas (C1) is not common and in most cases is found by chance without symptoms. This disorder is sometimes accompanied by a mild C1-C2 instability or the presence of a space-occupying lesion such as ossification of posterior longitudinal ligament, pannus, or retro-odontoid pseudo-tumor, which are indications for surgery if symptomatic cord compression is present. A C1 posterior arch resection has been the procedure of choice but is associated with several fatal complications. We here present a novel posterior arch decompression technique that is relatively safer and easier and that involves mobilization and posterior translation of the posterior arch as a whole, similar to a vertebral body sliding osteotomy.

Clinical and Radiographic Features of the Atlantoaxial Dislocation Associated With Kashin-Beck Disease

OBJECTIVES

Keshin-Beck disease (KBD) is a particular type of osteoarthritis that affects many joints. However, the deformity of atlantoaxial joint has been rarely reported in KBD, and therefore its clinical and radiograph features have not been identified.

METHODS

We reviewed data in 14 patients who were diagnosed with atlantoaxial dislocation (AAD) in KBD at our institution. The demographic data, clinical history, imaging data, operative data, and Japanese Orthopaedic Association score were collected for evaluation.

RESULTS

The mean age at presentation was 50 ± 1.7 years old. The most common features of AAD in KBD were the osteoarthritis, characterized by hypertrophic dens and anterior arch of the atlas. The average inner anteroposterior diameter (IAPD) of C1 was 28 ± 3.5 mm and the average spinal canal diameter was 14 ± 3.3 mm, which were respectively lower than the control level. Five patients had severe C1 stenosis (IAPD < 26mm). Separated odontoid process, like os odontoideum, was seen 9 patients. The tip of dens fused to C1 was observed in 4 patients; 12 patients had high-riding vertebral artery; and 5 patients had severe C1 stenosis, and they underwent C1 laminectomy with C1-C2 interarticular fusion or occipital-cervical fusion. All the patients displayed neurologic improvement after surgery.

CONCLUSIONS

The atlantoaxial level could be affected by KBD, which may lead to typical abnormalities and cause AAD. A C1 laminectomy with an C1-C2 interarticular fusion or occipital-cervical fusion is recommended for the patient with severe stenosis.

Effect of C1 Single-door Laminoplasty on Symptomatic Atlas Canal Stenosis

OBJECTIVE

To verify the effect of single-door laminoplasty combined with atlantoaxial fusion in the treatment of symptomatic atlas canal stenosis.

METHODS

This is a single-center retrospective analysis. From February 2014 to January 2019, 16 patients (five were females) with an average age of 63.4 years (56-71 years) were enrolled in this study. Patients with compressive cervical myelopathy with CT scan showed an inner sagittal diameter (ISD) of C₁ less than 29 mm or C1 canal space available for cord (SAC) of <12 mm were included, while isolated C1 stenosis without myelopathy or isolated C1 stenosis without atlantoaxial subluxation were excluded in this study. All patients underwent continuous heavy-weight skull traction, atlas single-door laminoplasty and atlantoaxial fusion. The differences in the pre- and post-operative inner sagittal diameter, space available for cord, atlas-dens interval (ADI) and compression of the spinal cord were analyzed by using CT and MRI. Functional evaluation was performed by using the Japanese Orthopaedic Association scoring system and the Neck Disability Index scoring system.

RESULTS

Single-door laminoplasty provided a full decompression for the spinal cord while retaining the whole posterior arch. No complications were encountered except a superficial wound infection in one patient. At final follow-up, The ADI was significantly reduced from 5.2 ± 1.8 mm to 1.7 ± 0.6 mm after surgery on average (P < 0.05). Average inner sagittal diameter of C1 was increased from 26.3 ± 2.6 mm to 34.9 ± 2.9 mm and the space available for cord was increased from 6 ± 1.7 mm to 17.8 ± 3.6 mm (P < 0.05). Meanwhile, the Japanese Orthopaedic Association (JOA) score of the 16 cases was improved from 11.4 ± 1.8 to 14.1 ± 1.4 on average (P < 0.05). The postoperative neck pain VAS score decreased significantly, from 2.6 ± 1.0 preoperatively to 1.3 ± 0.9 postoperatively (P < 0.05). The influence of neck pain on patient's life was improved from 17.8 ± 3.9 to 13.9 ± 3.3 after surgery (P < 0.05). At the last follow-up, the healing of the hinge fracture and the fusion between atlas and axis were observed in all patients.

CONCLUSIONS

Single-door laminoplasty combined with atlantoaxial fusion not only provides enough space for decompression but also offers intact arch for bone grafting, suggesting that it might provide a more feasible method for the correction of symptomatic atlas canal stenosis.

Percutaneous full endoscopic C1 laminectomy for developmental atlantal stenosis with myelopathy: a case report of three cases and review of the literature

Background

Developmental atlantal stenosis with myelopathy (DASM) in adults is a rare disease that only sporadic cases have been reported over the years. C1 laminectomy (C1L) is one of the most common operations for its treatment. However, as an open surgery, it has shortcomings such as large trauma and slow postoperative rehabilitation, and minimally invasive spine surgery (MISS) offers alternative treatment options with advantages. MISS instruments expand the technical capabilities of surgeons, which allows safer and more effective therapeutics for difficult and complicated diseases. This case report presents a new minimally invasive approach; percutaneous full endoscopic C1 laminectomy (PFEC1L), for the treatment of DASM, and to consolidate the current literature on the condition to summarize its etiologies, clinical manifestations, diagnostic criteria, surgical management, and prognoses.

Case Description

The patient in Case 1 presented with neck pain and numbness and weakness in the limbs. The patient in Case 2 presented with numbness in the extremities and the patient in Case 3 presented with bilateral hand numbness and left lower limb weakness. They were all diagnosed with DASM and underwent PFEC1L treatment to maintain the enlargement and decompression of the atlantal canal, which achieved favorable outcomes without complications during the postoperative follow-up visit.

Conclusions

DASM is rare but potentially dangerous. Its diagnosis is made based on clinical manifestations combined with radiological imaging examinations, especially computed tomography (CT) scan and magnetic resonance imaging (MRI). While C1L is the most common surgical method, PFEC1L is a new feasible and safe therapeutic option with comparable good outcomes and the advantage of being minimally-invasive. To our knowledge this is the first report that PFEC1L was applied for DASM treatment.

Atlantoaxial stenosis after muscle-preserving selective laminectomy

There are few reports of degenerative atlantoaxial stenosis and new stenosis after cervical decompression. We experienced four cases of atlantoaxial stenosis after muscle-preserving selective laminectomy. We compared these four cases with no stenosis cases after long-term follow-up of selective laminectomy, as well as healthy subjects. A total of 1205 patients who underwent muscle-preserving selective laminectomy due to cervical disorders were included in this study. Postoperative atlantoaxial stenosis, which needed decompression, appeared in 4 cases, and 30 patients did not have radiological stenosis for more than 10 years after surgery. Twenty healthy volunteers were also used as controls. The radiographic parameters measured were C2-C7 angle, C2-C7 sagittal vertical axis (SVA), C2 slope, C7 slope, C2-C5 angle, C5-C7 angle, C1-C2 angle, and atlantodental interval (ADI). We measured the anterior-posterior (AP) diameters of the spinal cord (SC) and dural tube (Dura) at C1/C2 with sagittal MRI. In the cases of atlantoaxial stenosis, the AP of SC and Dura at C1/C2 were smaller preoperatively, and the residual space for SC (SAC) was also smaller. The preoperative ADI was significantly higher in patients with atlantoaxial stenosis, suggesting preoperative instability at C1/C2. Analysis of the ROC curve showed that patients with a preoperative SAC of less than 3.6 mm and an ADI of more than 1.35 mm were more likely to develop postoperative atlantoaxial stenosis. When we perform a muscle-preserving selective laminectomy, decompression of C1/C2 is suggested when the SAC at C1/C2 is less than 3.6 mm and the ADI is more than 1.35 mm.

Classification and Surgical Treatment of Developmental Spinal Canal Stenosis at Atlas Level: A 15-Case Study

STUDY DESIGN

A retrospective study.

OBJECTIVE

Investigate the diagnosis and surgery strategy for treatment of development spinal canal stenosis (DSSA) at atlas plane based on computerized tography (CT) image characters.

SUMMARY OF BACKGROUND DATA

The occurrence of spinal canal stenosis in the atlas plane is relatively rare compared with lower cervical.

METHODS

Fifteen patients diagnosed with DSSA were included from 2014 to 2018. They are divided into four subgroups based on the character of CT images: group I (small size atlas), group II (hypertrophy of posterior arch of the atlas [PAA]), group III (incurved of PAA), and group IV (hypertrophy odontoid).

RESULTS

There are type I 7, type II 3, type III 2, and group IV 3 in the 15 cases. All the patients received different surgery procedures respectively: (1) posterior arch osteotomy were performed for group I/III//IV without atlantoaxial dislocation, (2) posterior arch resect and replantation were performed for group II, (3) occipital cervical fixation and fusion were added to the patients with associated atlantoaxial dislocation (AAD), (4) a new method of odontoid reduce and atlantoaxial fixation by transoral approach were performed for group IV with associated AAD. All cases underwent surgery successfully which included posterior occipitocervical fixation (OCF) + posterior arch resection (PAR) eight cases, PAR four cases, posterior arch remodeling and re-implantation (PARR) two cases, and Dens remodeling + trans-oral anterior reduction and plate fixation (DR+TARP) one case without severe complications. All patients show different improvement in the symptoms. Japanese orthopaedic association score improved from 9.2 to 14.7 in 1 year follow-up.

CONCLUSION

DSSA could be easily diagnosed and divided into four subgroups according to the character of CT image, corresponding surgery strategy could receive a fine clinical result.Level of Evidence: 4.

Symptomatic Atlas Hypoplasia in a Latin-American Patient: Case Report and Literature Review

Background:

Atlas hypoplasia is an infrequent cause of upper cervical stenosis. Only 24 cases in nonsyndromic adult population have been published. We are not aware of previous reports describing isolated fully formed atlas hypoplasia in a Latin-American patient. The purpose of this work was to report a case of an 80-year-old Argentinian woman with cervical myelopathy because of atlas hypoplasia and a literature review about this subject.

Methods:

A clinical case and an extended review of the literature are presented. We assessed from each case: age, sex, posterior atlanto-dens interval, surgical treatment, outcomes, and follow-up period.

Results:

Neurologic symptoms markedly improved after posterior decompression from severe to moderate in the Japanese Orthopaedic Association Scoring System and from four to three on the Nurick scale. Twenty-five patients were analyzed (mean 58.4 years, 32% female). The mean posterior atlanto-dens interval was 8.8 mm. Twenty-three patients underwent decompression alone, and two needed posterior fusion. All patients reported clinical improvement at an average follow-up of 13 months.

Conclusion:

Cervical myelopathy caused by fully formed atlas hypoplasia is not an exclusive pathology of far east population, and it may present in nonsyndromic patients. Surgical treatment by C1 laminectomy improved neurologic impairment.

Study Design:

Case report and literature review.

CT morphometric analysis of the cervical spinal canal with special reference to the correlation with the vertebral level

BACKGROUND

Narrowness of the spinal canal is associated with the development of cervical myelopathy. While studies have addressed the sagittal diameter of the cervical spinal canal, few evaluated the correlation between the size of the spinal canal and the vertebral level. We addressed this issue.

METHODS

Our retrospective study included 102 patients with cranial or spinal disorders. We examined the correlation between the cervical spinal canal diameter (SCD) at C1 to C7 and the inner anteroposterior diameter (IAPD) of the atlas on CT images.

RESULTS

At C1, the SCD was largest, at C4 it was smallest. While there was a strong correlation between the IAPD and the SCD at C1 (r = 0.8), the correlation between the size of the atlas and the SCD at C4 to C7 was weak (r = 0.2-0.3). We divided our patients into a normal group (n = 34, SCD ≥ 12 mm at any levels) and a stenosis group (n = 68, SCD < 12 mm at all levels). The mean SCD at C2 to C7 was significantly larger in the normal group. There was no significant difference between the two groups with respect to the IAPD and the SCD at C1.

CONCLUSIONS

The size of the subaxial spine does not necessarily affect the size of the atlas. The pathophysiology of spinal canal stenosis should be considered separately at the C1- and the subaxial level.

Single door laminoplasty plus posterior fusion for posterior atlantoaxial dislocation with congenital malformation: A case report and review of literature

BACKGROUND

Posterior atlantoaxial dislocation (PAD) is a rare type of upper cervical spine disease. We sought to describe a unreported case of old PAD with os odontoideum (OO) and atlas hypoplasia (AH) and our unique treatment approach consisting of C1 single door laminoplasty with C1-3 posterior fixation and fusion.

CASE SUMMARY

A 70-year-old male patient who suffered from progressive aggravating numbness and limb weakness for 4 years without trauma, was diagnosed with old PAD with OO and AH. The patient underwent closed reduction and C1 single door laminoplasty with C1-3 posterior fixation and fusion instead of C1 laminectomy with occipitocervical fusion. During the 3-year follow-up, he was able to walk by himself instead of using a wheelchair and with a ± 25° range of head rotation as well as a ± 10° range of flexion-extension. Three-year follow-up images showed satisfactory reduction and fusion.

CONCLUSION

C1 single door laminoplasty with cervical fusion in PAD combined with spinal cord compression could be a suitable and effective surgical option. Compared with laminectomy and occipitocervical fusion, it retains more cervical range of motion, has a smaller incision and provides an adequate bone grafting space for atlantoaxial fusion.

Concurrent Ossification of the Posterior Atlantoaxial Interlaminar Membrane and Atlas Hypoplasia: A Case Report

An onset of cervical myelopathy due to ossification of the posterior atlantoaxial membrane (PAAM) is extremely rare in older patients, and its clinical characteristics are still unclear. We report an onset of ossification of PAAM with congenital atlas hypoplasia in an 81-year-old man who presented with a 2-year history of progressive cervical myelopathy. Cervical computed tomography (CT) revealed canal stenosis secondary to a hypoplastic posterior arch of the atlas with a diameter of 20.3 mm between the anterior and posterior process. Magnetic resonance imaging showed marked spinal cord compression at the level of C1-2 secondary to atlas hypoplasia as well as ossification of PAAM. The patient underwent laminectomy of C1 and partial C2, as well as removal of the ossification, without atlantoaxial fusion. His neurological status improved 1 year postoperatively. In older patients, cervical myelopathy secondary to PAAM ossification, in the absence of trauma and atlantoaxial instability, may be induced by age-related pathophysiology associated with congenital atlas hypoplasia.

Ossification of the Transverse Ligament of the Atlas on CT: Frequency and Associated Findings

목적

경추 전산화단층촬영(cervical spine CT; 이하 C-spine CT)과 일반촬영을 이용하여 환추횡인대골화증(ossification of the transverse ligament of the atlas; 이하 OTLA)과 연관된 영상 소견에 대하여 알아보았다.

대상과 방법

11년간 3975명의 환자에게서 촬영한 5201개의 C-spine CT를 분석하여 OTLA의 유무를 확인하였고, 이를 대조군과 비교하여 그 빈도와 연관된 영상 소견의 통계학적 유의성을 확인하였다.

결과

3975명 중 45명에서 OTLA가 확인되었다(1.1%). 그 빈도는 나이에 따라 증가하는 소견을 보였으며(p < 0.005), 80세 이상인 환자의 12%에서 관찰되었다. 척수 공간(space available for spinal cord; 이하 SAC)은 OTLA 환자군에서 유의하게 작은 것으로 확인되었으며(p < 0.005), 전방환추후두막(anterior atlantooccipital membrane)-Barkow 인대 복합체의 광물질침착(mineralization), 황색인대골화증(ossification of ligamentum flavum), 경추후만증 또한 유의미한 양의 상관관계를 보였다(p < 0.005).

결론

OTLA는 환자의 나이, SAC 협소, 경추후만증, 다른 경추인대의 골화증과 연관되어 퇴행성 척추병증, 전신적인 골 과잉 상태, 혹은 기계적 스트레스나 불안정성에 관련이 있을 것으로 생각된다.

C1 Stenosis - An Easily Missed Cause for Cervical Myelopathy

C1 stenosis is often an easily missed cause for cervical myelopathy. The vast majority of cervical myelopathy occurs in the subaxial cervical spine. The cervical canal is generally largest at C1/2, explaining the relatively rare incidence of neurological deficits in patients with odontoid fractures. However, some subjects have anatomical anomalies of the atlas, which may cause stenosis and result in clinical symptoms similar to subaxial cord compression. Isolated pure atlas hypoplasia leading to stenosis is quite rare and may be associated with other anomalies, such as atlas clefts or transverse ligament calcification. It may also be more commonly associated with syndromic conditions such as Down or Turner syndrome. Although the diagnosis can be easily made with a cervical magnetic resonance imaging, the C3/2 spinolaminar test using a lateral cervical plain radiograph is a useful and sensitive tool for screening. Surgical treatment with a C1 laminectomy is generally necessary and any atlantoaxial or occipito-atlanto instability must be treated with spinal stabilization and fusion.

Congenital malformed posterior arch of atlas with fusion defect: a case of developmental canal stenosis causing cervical myelopathy

Congenital anomalies of the posterior arch of the atlas (PAA) are usually asymptomatic and diagnosed incidentally. Very rarely, they present with cervical myelopathy, usually being associated with partial aplasia or agenesis of PAA. We describe a 44-year-old lady with cervical myelopathy secondary to a malformed PAA with developmental atlas-level spinal stenosis and a congenital posterior fusion defect with persistent midline cleft showing significant non-osseous fibro-cartilaginous hypertrophy, causing critical cord compression. Spinal decompression by en-bloc wide excision of anomalous arch with occipito-cervical fusion was performed. Post-operatively, the patient's neurology improved gradually over 12 months, with radicular symptoms being the earliest and gait disturbance being the last symptom to resolve. At 24 months, she was asymptomatic with imaging showing good spinal cord decompression at the level of atlas. Developmental atlas stenosis with hypertrophic posterior arch fusion defect is an unusual cause of cervical myelopathy, which can be effectively treated with decompression with/without stabilization. Being aware of such an entity can avoid diagnostic dilemma and facilitate prognostication of outcomes, accurate surgical planning in the stenotic segment thereby ensuring effective management of these patients.

What Is the Most Representative Parameter for Describing the Size of the Atlas? CT Morphometric Analysis of the Atlas with Special Reference to Atlas Hypoplasia

The spinal canal diameter (SCD) is one of the most studied factors for the assessment of cervical spinal canal stenosis. The inner anteroposterior diameter (IAP), the SCD, and the cross-sectional area (CSA) of the atlas have been used for the evaluation of the size of the atlas in patients with atlas hypoplasia, a rare form of developmental spinal canal stenosis, however, there is little information on their relationship. The aim of this study was to identify the most useful parameter for depicting the size of the atlas. The CSA, the IAP, and the SCD were measured on computed tomography (CT) images at the C1 level of 213 patients and compared in this retrospective study. These three parameters increased with increasing patient height and weight. There was a strong correlation between IAP and SCD (r = 0.853) or CSA (r = 0.822), while correlation between SCD and CSA (r = 0.695) was weaker than between IAP and CSA. Partial correlation analysis showed that IAP was positively correlated with SCD (r = 0.687) and CSA (r = 0.612) when CSA or SCD were controlled. SCD was negatively correlated with CSA when IAP was controlled (r = −0.21). The IAP can serve as the CSA for the evaluation of the size of the atlas ring, while the SCD does not correlate with the CSA. As the patient height and weight affect the size of the atlas, analysis of the spinal canal at the C1 level should take into account physiologic patient data.

Ossification of the posterior atlantoaxial membrane associated with atlas hypoplasia: A case report

RATIONALE

Hypoplasia with an intact posterior arch of the atlas and ossification of the posterior atlantoaxial membrane (PAAM) are individually rare.

PATIENT CONCERNS

The patient presented with a 6-month history of progressive weakness and paresthesia of his lower extremities.

DIAGNOSES

Cervical myelopathy resulting from atlas hypoplasia and ossification of the posterior atlantoaxial membrane.

INTERVENTIONS

Laminectomy of the atlas with duroplasty.

OUTCOMES

Preoperative symptoms were alleviated.

LESSONS

In most reported cases, either atlas hypoplasia or ossification of the PAAM is responsible for patients' myelopathy. The case illustrated here, to the best of our knowledge, is the first one with coexistent atlas hypoplasia and ossification of the PAAM. And laminectomy of the atlas with duroplasty provided satisfied outcome.