The Smith-Robinson Approach to the Subaxial Cervical Spine: A Stepwise Microsurgical Technique Using Volumetric Models From Anatomic Dissections

Management Considerations for Cervical Corpectomy: Updated Indications and Future Directions

Together, lower back and neck pain are among the leading causes of acquired disability worldwide and have experienced a marked increase over the past 25 years. Paralleled with the increasing aging population and the rise in chronic disease, this trend is only predicted to contribute to the growing global burden. In the context of cervical neck pain, this symptom is most often a manifestation of cervical degenerative disc disease (DDD). Traditionally, multilevel neck pain related to DDD that is recalcitrant to both physical and medical therapy can be treated with a procedure known as cervical corpectomy. Presently, there are many flavors of cervical corpectomy; however, the overarching goal is the removal of the pain-generating disc via the employment of the modern anterior approach. In this review, we will briefly detail the pathophysiological mechanism behind DDD, overview the development of the anterior approach, and discuss the current state of treatment options for said pathology. Furthermore, this review will also add to the current body of literature surrounding updated indications, surgical techniques, and patient outcomes related to cervical corpectomy. Finally, our discussion ends with highlighting the future direction of cervical corpectomy through the introduction of the "skip corpectomy" and distractable mesh cages.

Surgical management of tumors of the cervical spine and craniovertebral junction involving the vertebral artery: A narrative review

BACKGROUND

The vertebral artery (VA) is in close proximity to bony structures, nerves and nerve sheaths of the cervical spine and craniovertebral junction (CVJ). These structures can be sources of tumors that are responsible for displacement, encasement and sometimes invasion of the VA. Removing these tumors while minimizing the risk of vascular injury requires thorough knowledge of the vascular anatomy, risk factors of vascular injury, the relationships of each tumor type with the VA, and the different surgical approaches and techniques that result in the best outcomes in terms of vascular control, tumoral exposure and resection.

OBJECTIVE

To present an overview of preoperative and anatomical considerations, differential diagnoses and various approaches to consider in cases of tumors in close relationship with the VA.

METHOD

A review of recent literature was conducted to examine the anatomy of the VA, the tumors most frequently affecting it, surgical approaches, and the necessary pre-operative preparations for ensuring safe and maximal tumor resection. This review aims to underscore the principles of treatment.

CONCLUSION

Tumors located at the CVJ and the cervical spine intimately involved with the VA, pose a surgical challenge and increase the risk of incomplete removal of the lesion. Detailed knowledge of the patient-specific anatomy and a targeted pre-operative work-up enable optimal planning of surgical approach and management of the VA, thereby reducing surgical risks and improving extent of resection.

Does Preoperative Radiation Therapy Performed for Metastatic Spine Cancer at the Cervical Spine Increase Perioperative Complications of Anterior Cervical Surgery?

Background

Radiation therapy (RT) performed before anterior cervical spine surgery (ACSS) may cause fascial plane fibrosis, decreased soft-tissue vascularity, and vertebral body weakness, which could increase the risk of esophageal and major vessel injuries, wound complications, and construct subsidence. Therefore, this study aimed to evaluate whether preoperative RT performed for metastatic spine cancer (MSC) at the cervical spine increases perioperative morbidity for ACSS.

Methods

Forty-nine patients who underwent ACSS for treatment of MSC at the cervical spine were retrospectively reviewed. All the patients underwent anterior cervical corpectomy via the anterior approach. Patient demographics, surgical factors, operative factors, and complications were recorded. Results of patients who were initially treated with RT before ACSS (RT group) were compared with those who did not receive RT before ACSS (non-RT group).

Results

Eighteen patients (36.7%) were included in the RT group, while the remaining 31 (63.3%) were included in the non-RT group. Surgery-related factors, including operation time (p = 0.109), estimated blood loss (p = 0.246), amount of postoperative drainage (p = 0.604), number of levels operated (p = 0.207), and number of patients who underwent combined posterior fusion (p = 0.768), did not significantly differ between the 2 groups. Complication rates, including esophageal injury, dural tear, infection, wound dehiscence, and mechanical failure, did not significantly differ between the RT and non-RT groups. Early subsidence was significantly greater in the non-RT group compared to that in the RT group (p = 0.012).

Conclusions

RT performed before surgery for MSC does not increase the risk of wound complication, mechanical failure, or vital structure injury during ACSS. The surgical procedural approach was not complicated by previous RT history. Therefore, surgeons can safely choose the anterior approach when the number of levels or location of MSC favors anterior surgery, and performing a posterior surgery is unnecessary due to a concern that previous RT may increase complication rates of ACSS.

Photogrammetry Applied to Neurosurgery: A Literature Review

Photogrammetry refers to the process of creating 3D models and taking measurements through the use of photographs. Photogrammetry has many applications in neurosurgery, such as creating 3D anatomical models and diagnosing and evaluating head shape and posture deformities. This review aims to summarize the uses of the technique in the neurosurgical practice and showcase the systems and software required for its implementation. A literature review was done in the online database PubMed. Papers were searched using the keywords "photogrammetry", "neurosurgery", "neuroanatomy", "craniosynostosis" and "scoliosis". The identified articles were later put through primary (abstracts and titles) and secondary (full text) screening for eligibility for inclusion. In total, 86 articles were included in the review from 315 papers identified. The review showed that the main uses of photogrammetry in the field of neurosurgery are related to the creation of 3D models of complex neuroanatomical structures and surgical approaches, accompanied by the uses for diagnosis and evaluation of patients with structural deformities of the head and trunk, such as craniosynostosis and scoliosis. Additionally, three instances of photogrammetry applied for more specific aims, namely, cervical spine surgery, skull-base surgery, and radiosurgery, were identified. Information was extracted on the software and systems used to execute the method. With the development of the photogrammetric method, it has become possible to create accurate 3D models of physical objects and analyze images with dedicated software. In the neurosurgical setting, this has translated into the creation of anatomical teaching models and surgical 3D models as well as the evaluation of head and spine deformities. Through those applications, the method has the potential to facilitate the education of residents and medical students and the diagnosis of patient pathologies.

Simplified Easy-Accessible Smartphone-Based Photogrammetry for 3-Dimensional Anatomy Presentation Exemplified With a Photorealistic Cadaver-Based Model of the Intracranial and Extracranial Course of the Facial Nerve

BACKGROUND AND OBJECTIVES

Smartphone-based photogrammetry (SMPhP) was recently presented as a practical and simple algorithm to create photorealistic 3-dimensional (3D) models that benefit from volumetric presentation of real anatomic dissections. Subsequently, there is a need to adapt the techniques for realistic depiction of layered anatomic structures, such as the course of cranial nerves and deep intracranial structures; the feasibility must be tested empirically. This study sought to adapt and test the technique for visualization of the combined intracranial and extracranial course of the facial nerve's complex anatomy and analyze feasibility and limitations.

METHODS

We dissected 1 latex-injected cadaver head to depict the facial nerve from the meatal to the extracranial portion. A smartphone camera alone was used to photograph the specimen, and dynamic lighting was applied to improve presentation of deep anatomic structures. Three-dimensional models were created with a cloud-based photogrammetry application.

RESULTS

Four 3D models were generated. Two models showed the extracranial portions of the facial nerve before and after removal of the parotid gland; 1 model showed the facial nerve in the fallopian canal after mastoidectomy, and 1 model showed the intratemporal segments. Relevant anatomic structures were annotated through a web-viewer platform. The photographic quality of the 3D models provided sufficient resolution for imaging of the extracranial and mastoid portions of the facial nerve, whereas imaging of the meatal segment only lacked sufficient precision and resolution.

CONCLUSION

A simple and accessible SMPhP algorithm allows 3D visualization of complex intracranial and extracranial neuroanatomy with sufficient detail to realistically depict superficial and deeper anatomic structures.

Two-Level Corpectomy and Fusion vs. Three-Level Anterior Cervical Discectomy and Fusion without Plating: Long-Term Clinical and Radiological Outcomes in a Multicentric Retrospective Analysis

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) and anterior cervical corpectomy and fusion (ACCF) represent effective alternatives in the management of multilevel cervical spondylotic myelopathy (CSM). A consensus on which of these techniques should be used is still missing.

METHODS

The databases of three centers were reviewed (January 2011-December 2018) for patients with three-level CSM, who underwent three-level ACDF without plating or two-level ACCF with expandable cage (VBRC) or mesh (VBRM). Demographic data, surgical strategy, complications, and implant failure were analyzed. The Neck Disability Index (NDI), the Visual Analog Scale (VAS), and the cervical lordosis were compared between the two techniques at 3 and 12 months. Logistic regression analyses investigated independent factors influencing clinical and radiological outcomes.

RESULTS

Twenty-one and twenty-two patients were included in the ACDF and ACCF groups, respectively. The median follow-up was 18 months. ACDFs were associated with better clinical outcomes at 12 months (NDI: 8.3% vs. 19.3%, p < 0.001; VAS: 1.3 vs. 2.6, p = 0.004), but with an increased risk of loss of lordosis correction ≥ 1° (OR = 4.5; p = 0.05). A higher complication rate in the ACDF group (33.3% vs. 9.1%; p = 0.05) was recorded, but it negatively influenced only short-term clinical outcomes. ACCFs with VBRC were associated with a higher risk of major complications but ensured better 12-month lordosis correction (p = 0.002). No significant differences in intraoperative blood loss were noted.

CONCLUSIONS

Three-level ACDF without plating was associated with better clinical outcomes than two-level ACCF despite worse losses in lordosis correction, which is ideal for fragile patients without retrovertebral compressions. In multilevel CSM, the relationship between the degree of lordosis correction and clinical outcome advantages still needs to be investigated.

Photorealistic 3-Dimensional Models of the Anatomy and Neurosurgical Approaches to the V2, V3, and V4 Segments of the Vertebral Artery

BACKGROUND

The vertebral artery (VA) has a tortuous course subdivided into 4 segments (V1-V4). For neurosurgeons, a thorough knowledge of the 3-dimensional (3D) anatomy at different segments is a prerequisite for safe surgery. New technologies allowing creation of photorealistic 3D models may enhance the anatomic understanding of this complex region.

OBJECTIVE

To create photorealistic 3D models illustrating the anatomy and surgical steps needed for safe neurosurgical exposure of the VA.

METHODS

We dissected 2 latex injected cadaver heads. Anatomic layered dissections were performed on the first specimen. On the second specimen, the two classical approaches to the VA (far lateral and anterolateral) were realized. Every step of dissection was scanned using photogrammetry technology that allowed processing of 3D data from 2-dimensional photographs by a simplified algorithm mainly based on a dedicated mobile phone application and open-source 3D modeling software. For selected microscopic 3D anatomy, we used an operating microscope to generate 3D models.

RESULTS

Classic anatomic (n=17) and microsurgical (n=12) 3D photorealistic models based on cadaver dissections were created. The models allow observation of the spatial relations of each anatomic structure of interest and have an immersive view of the approaches to the V2-V4 segments of the VA. Once generated, these models may easily be shared on any digital device or web-based platforms for 3D visualization.

CONCLUSIONS

Photorealistic 3D scanning technology is a promising tool to present complex anatomy in a more comprehensive way. These 3D models can be used for education, training, and potentially preoperative planning.

Three-Dimensional Modeling and Extended Reality Simulations of the Cross-Sectional Anatomy of the Cerebrum, Cerebellum, and Brainstem

BACKGROUND

Understanding the anatomy of the human cerebrum, cerebellum, and brainstem and their 3-dimensional (3D) relationships is critical for neurosurgery. Although 3D photogrammetric models of cadaver brains and 2-dimensional images of postmortem brain slices are available, neurosurgeons lack free access to 3D models of cross-sectional anatomy of the cerebrum, cerebellum, and brainstem that can be simulated in both augmented reality (AR) and virtual reality (VR).

OBJECTIVE

To create 3D models and AR/VR simulations from 2-dimensional images of cross-sectionally dissected cadaveric specimens of the cerebrum, cerebellum, and brainstem.

METHODS

The Klingler method was used to prepare 3 cadaveric specimens for dissection in the axial, sagittal, and coronal planes. A series of 3D models and AR/VR simulations were then created using 360° photogrammetry.

RESULTS

High-resolution 3D models of cross-sectional anatomy of the cerebrum, cerebellum, and brainstem were obtained and used in creating AR/VR simulations. Eleven axial, 9 sagittal, and 7 coronal 3D models were created. The sections were planned to show important deep anatomic structures. These models can be freely rotated, projected onto any surface, viewed from all angles, and examined at various magnifications.

CONCLUSION

To our knowledge, this detailed study is the first to combine up-to-date technologies (photogrammetry, AR, and VR) for high-resolution 3D visualization of the cross-sectional anatomy of the entire human cerebrum, cerebellum, and brainstem. The resulting 3D images are freely available for use by medical professionals and students for better comprehension of the 3D relationship of the deep and superficial brain anatomy.

Facet Distraction and Dysphagia: A Prospective Evaluation of This Common Postoperative Issue Following Anterior Cervical Spine Surgery

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

Our primary study was to investigate whether the degree of postoperative facet and disk space distraction following anterior cervical discectomy and fusion (ACDF) affects the rate of postoperative dysphagia.

SUMMARY OF BACKGROUND DATA

Although ACDF is safe and well tolerated, postoperative dysphagia remains a common complication. Intervertebral disk space distraction is necessary in ACDF to visualize the operative field, prepare the endplates for fusion, and facilitate graft insertion. However, the degree of distraction tolerated, before onset of dysphagia, is not well characterized ACDF.

MATERIALS AND METHODS

A prospective cohort study was conducted of 70 patients who underwent ACDF between June 2018 and January 2019. Two independent reviewers measured all preoperative and postoperative radiographs measured for interfacet distraction distance and intervertebral distraction distance, with intrareviewer reproducibility measurements after one month. For multilevel surgery, the level with the greatest distraction was measured. Primary outcomes were numerical dysphagia (0-10), Eating Assessment Tool 10, and Dysphagia Symptom Questionnaire score collected at initial visit and two, six, 12, and 24 weeks postoperatively.

RESULTS

A total of 70 patients were prospectively enrolled, 59 of whom had adequate radiographs. An average of 1.71 (SD: 0.70) levels were included in the ACDF construct. Preoperatively, 13.4% of patients reported symptoms of dysphagia, which subsequently increased in the postoperative period at through 12 weeks postoperatively, before returning to baseline at 24 weeks. Intrareviewer and interreviewer reliability analysis demonstrated strong agreement. There was no relationship between interfacet distraction distance/intervertebral distraction distance and dysphagia prevalence, numerical rating, Eating Assessment Tool 10, or Dysphagia Symptom Questionnaire.

CONCLUSIONS

Patients who had an ACDF have an increased risk of dysphagia in the short term, however, this resolved without intervention by six months. Our data suggests increased facet and intervertebral disk distraction does not influence postoperative dysphagia rates.

LEVEL OF EVIDENCE

3.

The user experience design of a novel microscope within SurgiSim, a virtual reality surgical simulator

PURPOSE

Virtual reality (VR) simulation has the potential to advance surgical education, procedural planning, and intraoperative guidance. "SurgiSim" is a VR platform developed for the rehearsal of complex procedures using patient-specific anatomy, high-fidelity stereoscopic graphics, and haptic feedback. SurgiSim is the first VR simulator to include a virtual operating room microscope. We describe the process of designing and refining the VR microscope user experience (UX) and user interaction (UI) to optimize surgical rehearsal and education.

METHODS

Human-centered VR design principles were applied in the design of the SurgiSim microscope to optimize the user's sense of presence. Throughout the UX's development, the team of developers met regularly with surgeons to gather end-user feedback. Supplemental testing was performed on four participants.

RESULTS

Through observation and participant feedback, we made iterative design upgrades to the SurgiSim platform. We identified the following key characteristics of the VR microscope UI: overall appearance, hand controller interface, and microscope movement.

CONCLUSION

Our design process identified challenges arising from the disparity between VR and physical environments that pertain to microscope education and deployment. These roadblocks were addressed using creative solutions. Future studies will investigate the efficacy of VR surgical microscope training on real-world microscope skills as assessed by validated performance metrics.

Microsurgical anatomy and the importance of the petrosal process of the sphenoid bone in endonasal surgery

OBJECTIVE

The petrosal process of the sphenoid bone (PPsb) is a relevant skull base osseous prominence present bilaterally that can be used as a key surgical landmark, especially for identifying the abducens nerve. The authors investigated the surgical anatomy of the PPsb, its relationship with adjacent neurovascular structures, and its practical application in endoscopic endonasal surgery.

METHODS

Twenty-one dried skulls were used to analyze the osseous anatomy of the PPsb. A total of 16 fixed silicone-injected postmortem heads were used to expose the PPsb through both endonasal and transcranial approaches. Dimensions and distances of the PPsb from the foramen lacerum (inferiorly) and top of the posterior clinoid process (PCP; superiorly) were measured. Moreover, anatomical variations and the relationship of the PPsb with the surrounding crucial structures were recorded. Three representative cases were selected to illustrate the clinical applications of the findings.

RESULTS

The PPsb presented as a triangular bony prominence, with its base medially adjacent to the dorsum sellae and its apex pointing posterolaterally toward the petrous apex. The mean width of the PPsb was 3.5 ± 1 mm, and the mean distances from the PPsb to the foramen lacerum and the PCP were 5 ± 1 and 11 ± 2.5 mm, respectively. The PPsb is anterior to the petroclival venous confluence, superomedial to the inferior petrosal sinus, and inferomedial to the superior petrosal sinus; constitutes the inferomedial limit of the cavernous sinus; and delimits the upper limit of the paraclival internal carotid artery (ICA) before the artery enters the cavernous sinus. The PPsb is anterior and medial to and below the sixth cranial nerve, forming the floor of Dorello's canal. During surgery, gentle mobilization of the paraclival ICA reveals the petrosal process, serving as an accurate landmark for the location of the abducens nerve.

CONCLUSIONS

This investigation revealed details of the microsurgical anatomy of the PPsb, its anatomical relationships, and its application as a surgical landmark for identifying the abducens nerve. This novel landmark may help in minimizing the risk of abducens nerve injury during transclival approaches, which extend laterally toward the petrous apex and cavernous sinus region.

Three-Dimensional Immersive Photorealistic Layered Dissection of Superficial and Deep Back Muscles: Anatomical Study

Introduction

The distinct anatomy of the superficial and deep back muscles is characterized by complex layered courses, fascial planes, specific vascularization, and innervation. Knowledge of these anatomical parameters is important for some surgical approaches, including lumbar disc herniation, cerebrospinal fluid fistula repair, vascularized muscle pedicle flaps, and posterior fossa extra-intracranial bypass. In the present study, we use modern techniques of three-dimensional (3D) surface scanning to help better illustrate the layered anatomy of the back muscles.

Material and methods

We dissected in layers the back muscles of one cadaver. Every step of the dissection was 3D scanned using a technique called photogrammetry, which allows the extraction of 3D data from 2D photographs. The 3D data were processed using Blender software, and the 3D photorealistic models were uploaded to a dedicated website for 3D visualization. This allows users to see the 3D models from every desktop or mobile device, as well as augmented (AR) and virtual reality (VR) formats.

Results

The photorealistic 3D models present the back muscles' anatomy in a volumetric manner, which can be visualized on any computer device. The web 3D features, including AR and VR, allow users to zoom, pan, and rotate the models, which may facilitate learning.

Conclusion

The technology of photorealistic surface scanning, modern 3D visualization possibilities of web-dedicated formats, as well as advances in AR and VR, have the potential to help with a better understanding of complex anatomy. We believe that this opens the field for further research in the field of medical education.