Posterior Anatomy Research Articles

Treatment of failed cervical total disc replacements in a series of 53 cases and description of a management strategy.

To describe modes of failure of cervical TDR, their related treatment strategies, and to describe a management strategy for the treatment of failed cervical TDR. This retrospective study was based on a consecutive series of 53 cervical TDR patients who underwent removal or revision surgery. Chart review was conducted to collect general descriptive data, reasons for TDR removal/revision, duration from index implantation to re-operation, and the subsequent procedure performed. Among 53 patients, 36 underwent TDR removal and fusion, 16 underwent TDR removal and replacement with another TDR, and one patient's TDR was revised by repositioning. The mean duration from index surgery to removal/revision was 40.1months (range: 3days-222months). In all cases, removal/revision surgery was completed without complication. The most common reason for removal was severe osteolysis, often involving C. acnes infection, and was primarily associated with one implant type. TDR removal and fusion were performed for subsidence, device migration, treatment of symptoms arising from posterior anatomy (facet joints, etc.), approach-related complications and pain. TDR replacement was feasible for hypermobility, metal allergy, implant locked in kyphosis, and oversized implant use. In one case of TDR malpositioning, the device was successfully revised into appropriate position. After cervical TDR failure, replacing a TDR with another implant can be feasible. Reasons for revision or removal after cervical TDR surgery include biomechanical failure, implant migration, surgeon or technical error, or biological reasons. The type of failure can help the surgeon create a strategy to address these complications.

Video-Assisted Thoracoscopic Lateral Interbody Fusion for Symptomatic Pseudarthrosis in Neurofibromatosis 1-Associated Spinal Deformity

The treatment of symptomatic pseudarthrosis via posterior-only approaches in the setting of neurofibromatosis 1 (NF1) is challenging due to dural ectasias, resulting in erosion of the posterior elements. The purpose of this report is to illustrate a minimally invasive method for performing anterior thoracic fusion for pseudarthrosis in a patient with NF1-associated scoliosis and dysplastic posterior elements. To the best of our knowledge, this is the first documented case of using video-assisted thoracoscopic lateral interbody fusion to treat pseudarthrosis for NF1-associated spinal deformity. The patient underwent video-assisted thoracoscopic anterior spinal fusion via a direct lateral interbody approach with interbody cage placement at T10-T11 and T11-T12, followed by revision of his posterior spinal fusion and instrumentation. The patient had an uneventful postoperative course. At 6 months of follow-up, the patient had complete resolution of his preoperative symptoms and had returned to full-time work with no complaints. At 3 years postoperatively, the patient reported being satisfied with the operation and had continued to work full-time without restrictions. To the best of our knowledge, this is the first report of pseudarthrosis in the setting of NF1-associated scoliosis treated via minimally invasive anterior thoracic fusion facilitated by video-assisted thoracoscopic surgery. This is a powerful technique that allows for safe access for anterior thoracic fusion in the setting of dysplastic posterior anatomy and poor posterior bone stock.

Poster 237: Menisco-Tibial Ligament Complex Anatomy and Biomechanics – Implications for Meniscus Repairs, Ramp Lesions and Transplants

Poster 237: Menisco-Tibial Ligament Complex Anatomy and Biomechanics – Implications for Meniscus Repairs, Ramp Lesions and Transplants

Cerebrovascular Variants and the Role of the Selfish Brain in Young-Onset Hypertension.

Background:Variants in the posterior anatomy of the cerebral circulation are associated with hypertension and lower cerebral blood flow in midlife (age ≈55 years); however, whether these variants are a result of aging or long-term exposure to high blood pressure is unclear. Additionally, the role these variants play in early onset of hypertension (<40 years) and poor cerebral perfusion in this population is unknown.Methods:We retrospectively examined whether specific cerebrovascular variants (vertebral artery hypoplasia and absent/hypoplastic posterior communicating arteries (an incomplete posterior circle of Willis) measured via magnetic resonance angiography) were associated with a diagnosis of hypertension in 220 young adults (<40 years; n=164 primary hypertensive [mean age±SD, 32±6 years] and n=56 [30±6 years] normotensive adults). Whether cerebrovascular variants were associated with lower cerebral blood flow (phase-contrast angiography) was measured in the hypertensive group only (n=146).Results:Binary logistic regression (adjusted for age, sex, and body mass index) showed that vertebral artery hypoplasia with an incomplete posterior circle of Willis was associated with hypertension diagnosis (P<0.001, odds ratio; 11.79 [95% CI, 3.34–41.58]). Vertebral artery hypoplasia plus an incomplete circle of Willis was associated with lower cerebral blood flow in young adults with hypertension (P=0.0172).Conclusions:Vertebral artery hypoplasia plus an incomplete posterior circle of Willis independently predicts hypertension in young adults suggesting that this variant is not acquired with aging into midlife. Importantly this variant combination was associated with lower cerebral perfusion, which may have long-term consequences on cerebrovascular health in young adults with hypertension.

The Convergent procedure for AF: A surgeon's perspective.

The Converge IDE Trial demonstrated improved patient outcomes in a challenging persistent and long-standing persistent atrial fibrillation population using a heart team hybrid approach with epicardial and endocardial staged ablations. Surgeons encounter unique circumstances with the surgical epicardial stage of the Convergent procedure which includes unfamiliarity with left atrial posterior anatomy, endoscopic/thoracoscopic visualization, minimally invasive left atrial appendage management, and expanded indications for the procedure. Overcoming these unique challenges is key to the adoption of the Convergent procedure as a critical off-pump approach that should be part of the surgical armamentarium in the treatment of atrial fibrillation.

Freehand screw insertion technique without image guidance for the cortical bone trajectory screw in posterior lumbar interbody fusion: what affects screw misplacement?

Cortical bone trajectory (CBT) screw insertion using a freehand technique is considered less feasible than guided techniques, due to the lack of readily identifiable visual landmarks. However, in posterior lumbar interbody fusion (PLIF), after resection of the posterior anatomy, the pedicles themselves, into which implantation is performed, are palpable from the spinal canal and neural foramen. With the help of pedicle wall probing, the authors have placed CBT screws using a freehand technique without image guidance in PLIF. This technique has advantages of no radiation exposure and no requirement for expensive devices, but the disadvantage of reduced accuracy in screw placement. To address the problem of symptomatic breaches with this freehand technique, variables related to unacceptable screw positioning and need for revisions were investigated. From 2014 to 2020, 182 of 426 patients with single-level PLIF were enrolled according to the combined criteria of L4-5 level, excluding cases of revision and isthmic spondylolisthesis; using screws 5.5 mm in diameter; and operated by right-handed surgeons. We studied the number of misplaced screws found and replaced during initial surgeries. Using multiplanar reconstruction CT postoperatively, 692 screw positions on images were classified using previously reported grading criteria. Details of pedicle breaches requiring revisions were studied. We conducted a statistical analysis of the relationship between unacceptable (perforations > 2 mm) misplacements and four variables: level, laterality, spinal deformity, and experiences of surgeons. Three screws in L4 and another in L5 were revised during initial surgeries. The total rate of unacceptable screws on CT examinations was 3.3%. Three screws in L4 and another in L5 breached inferomedial pedicle walls in grade 3 and required revisions. The revision rate was 2.2%. The percentage of unacceptable screws was 5.2% in L4 and 1.7% in L5 (p < 0.05), whereas other variables showed no significant differences. A freehand technique can be feasible for CBT screw insertion in PLIF, balancing the risks of 3.3% unacceptable misplacements and 2.2% revisions with the benefits of no radiation exposure and no need for expensive devices. Pedicle palpation in L4 is the key to safety, even though it requires deeper and more difficult probing. In the initial surgeries and revisions, 75% of revised screws were observed in L4, and unacceptable screw positions were more likely to be found in L4 than in L5.

Arthroscopic Synovectomy for Tenosynovial Giant Cell Tumor/Pigmented Villonodular Synovitis in the Posterior Knee Using the Posterior Trans-Septal Portal Technique.

The patient is positioned such that the contralateral leg will not obstruct the ability to work in the posteromedial portal. Diagnostic arthroscopy is performed through standard anteromedial and anterolateral portals. Next, with visualization from the anterolateral portal and the knee in 90° of flexion, the posteromedial portal is created with use of a transilluminated spinal needle. The posterolateral portal is made in the same fashion as the posteromedial portal, with use of a trans-notch view from the anteromedial portal. With the arthroscope in the posteromedial portal, a blunt instrument or motorized shaver can be placed through the posterolateral portal to perforate the posterior septum and create the TSP. The mass can then be identified, biopsied, and removed with use of a motorized shaver or tissue grasper. Arthroscopic exploration through the TSP can then be done to confirm adequate excision. Alternatives include synovectomy either by arthrotomy, arthroscopy via a posteromedial or posterolateral portal with trans-notch views, or a combination of both. To limit the risk of recurrent diffuse PVNS, radiosynovectomy with yttrium-90 or phosphorus-32, either combined with surgery or alone, has been described2,17. External beam radiation has also been utilized, but radiation toxicity is seen as a major limitation17. Macrophage-colony stimulating factor (M-CSF) or CSF-1 inhibitors have recently been developed. In 2019, the FDA approved the use of CSF-1 inhibitors, and they are considered an acceptable treatment for patients who are not candidates for surgical resection17. Advantages involve increased posterior anatomy visualization to ensure adequate synovectomy, more working capacity for instruments, and decreased disruption of anatomical planes and scar tissue formation around neurovascular structures compared with open dissection10-16. Excellent clinical results (defined by return to full knee function) have been reported for the TSP technique for PVNS synovectomy. In a study of 10 cases of posterior-knee PVNS masses removed via arthroscopic synovectomy with use of a TSP, Shekhar et al. reported good functional outcomes and no operative complications2. Keyhani et al. reported a series of 21 patients who underwent the same procedure for diffuse PVNS with similar findings9. Patients can expect to retain close to full knee function following this procedure2,9. Baseline magnetic resonance imaging is recommended for all patients at 3 to 6 months after excision, as asymptomatic recurrence can occur, and patients should be followed for a minimum of 2 years post-excision2,3,7,9,18. Keeping the knee in 90° of flexion provides the furthest distance from the saphenous vein on the medial side, the peroneal nerve on the lateral side, and the popliteal artery near the posterior septum when making the posterior portals10-16.Transillumination of the posterior portals is recommended10-16.Perforation of the septum should be in the posterolateral to posteromedial direction, allowing surgeons to have a wider "safe zone" to decrease the chance of vascular injury to the popliteal artery14. CSF = colony-stimulating factorMCL = medial collateral ligamentMRI = magnetic resonance imagingPL = posterolateralPM = posteromedialPA = popliteal arteryROM = range of motionTS = trans-septalIKDC = International Knee Documentation Committee.

Nuclear receptor NR4A is required for patterning at the ends of the planarian anterior-posterior axis.

Positional information is fundamental to animal regeneration and tissue turnover. In planarians, muscle cells express signaling molecules to promote positional identity. At the ends of the anterior-posterior (AP) axis, positional identity is determined by anterior and posterior poles, which are putative organizers. We identified a gene, nr4A, that is required for anterior- and posterior-pole localization to axis extremes. nr4A encodes a nuclear receptor expressed predominantly in planarian muscle, including strongly at AP-axis ends and the poles. nr4A RNAi causes patterning gene expression domains to retract from head and tail tips, and ectopic anterior and posterior anatomy (e.g., eyes) to iteratively appear more internally. Our study reveals a novel patterning phenotype, in which pattern-organizing cells (poles) shift from their normal locations (axis extremes), triggering abnormal tissue pattern that fails to reach equilibrium. We propose that nr4A promotes pattern at planarian AP axis ends through restriction of patterning gene expression domains.

Surgical and Practical Posterior Anatomy to Endometriosis: Tips and Tricks

Objective: Describe and demonstrate some important and practical anatomical features to deal with endometriosis from a laparoscopic perspective.

How to Get to the Distal Posterior Tibial Malleolus? A Cadaveric Anatomic Study Defining the Access Corridors Through 3 Different Approaches

Our objective is to review the anatomy and exposure of the posterior column and posterior tibial malleolus (the posterior tibial plafond) by defining the access corridors through 3 different approaches-posteromedial, posterolateral, and modified posteromedial. Cadaveric dissection with percentage of posterior tibial malleolus exposed, and strain gauge measurements to evaluate traction on the neurovascular bundle. The 3 different approaches are applicable for exposure of different portions of the distal posterior tibial malleolus. Strain gauge measurements reveal the least traction on the flap containing the neurovascular bundle with the modified posteromedial approach (7.0 N) compared with the posteromedial (21.5 N) and posterolateral (16.8 N) approaches. Exposure of the posterior tibial malleolus was greater with the modified posteromedial approach (91%) compared with the other 2 approaches (posteromedial = 64%, posterolateral = 40%). Depending on the location of the principal fracture fragments, particularly in high energy ankle and pilon fractures, each of the posterior approaches has its indication, with the modified posteromedial approach revealing more of the posterior anatomy than the other 2 approaches. The latter approach places the least traction on the flap containing the neurovascular bundle.

Ophthalmologic wax models as an educational tool for 18th-century vision scientists.

The Medical Faculties of the University of Padua (Italy) and the University of Vienna (Austria) preserved two series of wax models, made by the Austrian Johann Nepomuk Hoffmayr at the beginning of the 19th century. These models were created in a period of evolution of both medical specialties and organ pathology, which brought morbid organs at the centre of medical investigation. Ceroplastic was considered a useful tool for didactic and research, as it provided a three-dimensional realistically coloured reproduction of organic lesions. The models represent the typical eye diseases of the period, in particular those affecting external parts, which could be investigated without the need for specific instruments devised for the observation of the inner and posterior anatomy of the eye, at that time not yet available. Even if the nosological categories then employed by Hoffmayr were different from those currently used, it has been possible to find a correspondence thanks to the ophthalmological literature of his period. Ceroplastic started to decline at the end of 19th century, substituted by the much less expensive method of preservation of morbid organs in formalin and by new techniques of investigation of the inner body, such as X-ray.

Posterior anatomy considerations

Posterior anatomy considerations

A direct morphometric comparison of five labeling protocols for multi-atlas driven automatic segmentation of the hippocampus in Alzheimer's disease

Hippocampal volumetry derived from structural MRI is increasingly used to delineate regions of interest for functional measurements, assess efficacy in therapeutic trials of Alzheimer's disease (AD) and has been endorsed by the new AD diagnostic guidelines as a radiological marker of disease progression. Unfortunately, morphological heterogeneity in AD can prevent accurate demarcation of the hippocampus. Recent developments in automated volumetry commonly use multi-template fusion driven by expert manual labels, enabling highly accurate and reproducible segmentation in disease and healthy subjects. However, there are several protocols to define the hippocampus anatomically in vivo, and the method used to generate atlases may impact automatic accuracy and sensitivity - particularly in pathologically heterogeneous samples. Here we report a fully automated segmentation technique that provides a robust platform to directly evaluate both technical and biomarker performance in AD among anatomically unique labeling protocols. For the first time we test head-to-head the performance of five common hippocampal labeling protocols for multi-atlas based segmentation, using both the Sunnybrook Longitudinal Dementia Study and the entire Alzheimer's Disease Neuroimaging Initiative 1 (ADNI-1) baseline and 24-month dataset. We based these atlas libraries on the protocols of (Haller et al., 1997; Killiany et al., 1993; Malykhin et al., 2007; Pantel et al., 2000; Pruessner et al., 2000), and a single operator performed all manual tracings to generate de facto "ground truth" labels. All methods distinguished between normal elders, mild cognitive impairment (MCI), and AD in the expected directions, and showed comparable correlations with measures of episodic memory performance. Only more inclusive protocols distinguished between stable MCI and MCI-to-AD converters, and had slightly better associations with episodic memory. Moreover, we demonstrate that protocols including more posterior anatomy and dorsal white matter compartments furnish the best voxel-overlap accuracies (Dice Similarity Coefficient=0.87-0.89), compared to expert manual tracings, and achieve the smallest sample sizes required to power clinical trials in MCI and AD. The greatest distribution of errors was localized to the caudal hippocampus and the alveus-fimbria compartment when these regions were excluded. The definition of the medial body did not significantly alter accuracy among more comprehensive protocols. Voxel-overlap accuracies between automatic and manual labels were lower for the more pathologically heterogeneous Sunnybrook study in comparison to the ADNI-1 sample. Finally, accuracy among protocols appears to significantly differ the most in AD subjects compared to MCI and normal elders. Together, these results suggest that selection of a candidate protocol for fully automatic multi-template based segmentation in AD can influence both segmentation accuracy when compared to expert manual labels and performance as a biomarker in MCI and AD.

Laminar screw fixation of the axis

Laminar fixation of the axis with crossing bilateral screws has been shown to provide rigid fixation with a theoretically decreased risk of vertebral artery damage compared with C1-2 transarticular screw fixation and C-2 pedicle screw fixation. Some studies, however, have shown restricted rigidity of such screws compared with C-2 pedicle screws, and others note that anatomical variability exists within the posterior elements of the axis that may have an impact on successful placement. To elucidate the clinical impact of such screws, the authors report their experience in placing C-2 laminar screws in adult patients over a 2-year period, with emphasis on clinical outcome and technical placement. Sixteen adult patients with cervical instability underwent posterior cervical and cervicothoracic fusion procedures at our institution with constructs involving C-2 laminar screws. Eleven patients were men and 5 were women, and they ranged in age from 28 to 84 years (mean 57 years). The reasons for fusion were degenerative disease (9 patients) and treatment of trauma (7 patients). In 14 patients (87.5%) standard translaminar screws were placed, and in 2 (12.5%) an ipsilateral trajectory was used. All patients underwent preoperative radiological evaluation of the cervical spine, including computed tomography scanning with multiplanar reconstruction to assess the posterior anatomy of C-2. Anatomical restrictions for placement of standard translaminar screws included a deeply furrowed spinous process and/or an underdeveloped midline posterior ring of the axis. In these cases, screws were placed into the corresponding lamina from the ipsilateral side, allowing bilateral screws to be oriented in a more parallel, as opposed to perpendicular, plane. All patients were followed for >2 years to record rates of fusion, instrumentation failure, and other complications. Thirty-two screws were placed without neurological or vascular complications. The mean follow-up duration was 27.3 months. Complications included 2 revisions, one for pseudarthrosis and the other for screw pullout, and 3 postoperative infections. Placement of laminar screws into the axis from the standard crossing approach or via an ipsilateral trajectory may allow a safe, effective, and durable means of including the axis in posterior cervical and cervicothoracic fusion procedures.

Synchrotron X-ray tomographic microscopy of fossil embryos

Fossilized embryos from the late Neoproterozoic and earliest Phanerozoic have caused much excitement because they preserve the earliest stages of embryology of animals that represent the initial diversification of metazoans. However, the potential of this material has not been fully realized because of reliance on traditional, non-destructive methods that allow analysis of exposed surfaces only, and destructive methods that preserve only a single two-dimensional view of the interior of the specimen. Here, we have applied synchrotron-radiation X-ray tomographic microscopy (SRXTM), obtaining complete three-dimensional recordings at submicrometre resolution. The embryos are preserved by early diagenetic impregnation and encrustation with calcium phosphate, and differences in X-ray attenuation provide information about the distribution of these two diagenetic phases. Three-dimensional visualization of blastomere arrangement and diagenetic cement in cleavage embryos resolves outstanding questions about their nature, including the identity of the columnar blastomeres. The anterior and posterior anatomy of embryos of the bilaterian worm-like Markuelia confirms its position as a scalidophoran, providing new insights into body-plan assembly among constituent phyla. The structure of the developing germ band in another bilaterian, Pseudooides, indicates a unique mode of germ-band development. SRXTM provides a method of non-invasive analysis that rivals the resolution achieved even by destructive methods, probing the very limits of fossilization and providing insight into embryology during the emergence of metazoan phyla.

The urosome of the Pan- and Peracarida

We have examined the caudal regions of diverse peracarid and pancarid malacostracans using light and scanning electronic microscopy. The traditional view of malacostracan posterior anatomy is not sustainable, viz., that the free telson, when present, bears the anus near the base. The anus either can occupy a terminal, sub-terminal, or mid-ventral position on the telson; or can be located on the sixth pleomere – even when a free telson is present. Furthermore, there is information that might be interpreted to suggest that in some cases a telson can be absent. Embryologic data indicates that the condition of the body terminus in amphipods cannot be easily characterized, though there does appear to be at least a transient seventh segment that seems to fuse with the sixth segment. Our understanding of the genesis of the so-called telson of amphipods could be subject to alternative interpretations than those traditionally put forth.

CO 2-Enhanced CT Imaging for the Detection of Pulmonary Emboli : Feasibility Study in a Porcine Model

Rationale and Objectives The authors investigated the feasibility of using computed tomography (CT) with CO 2 gas as a negative contrast agent for detecting pulmonary emboli in a porcine model. Materials and Methods Seven pigs with or without pulmonary emboli underwent thoracic imaging with multi–detector row spiral CT. To identify optimal injection and scanning protocols, the first four pigs were scanned repeatedly in the supine and prone positions with different scan delays (10, 15, and 20 seconds) and different volumes of CO 2 (60, 120, 180, and 240 mL), which were hand infused (each infusion took 10–15 seconds). The last five pigs with emboli were scanned with iodinated contrast medium and then rescanned with 120 or 180 mL of CO 2. The CO 2 volumes and scan delays were qualitatively assessed. The supine and prone CT scans and the number and location of thrombi depicted in the CO 2- and contrast material–enhanced CT scans were compared. Results Because the pulmonary artery in pigs is in the posterior anatomy, the prone position was more effective than the supine position with CO 2 enhancement. An infusion of 120 mL of CO 2 was sufficient to enhance the entire pulmonary artery, and scanning timed to coincide with the completion of infusion was the most effective. Both the CO 2- and con-trast-enhanced CT scans demonstrated all thrombi. Thrombi were more apparent on the CO 2-enhanced CT scans than on the contrast-enhanced scans because of the high contrast interface between soft tissue and gas. However, two of the seven pigs with thrombi experienced abrupt cardiac arrest after CO 2-enhanced scanning and could not be resuscitated. The cause of these events was not determined in the current study. Conclusion The CT depiction of pulmonary emboli is feasible with CO 2 gas as a negative contrast agent and may even be superior to that with iodinated contrast media. Further studies are required to evaluate the safety of this method and to develop an improved delivery of CO 2 gas for this application.

THE INGUINOFEMORAL AREA FROM A LAPAROSCOPIC STANDPOINT: History, Anatomy, and Surgical Applications

No significant difference has been found between early and new diagrams of the posterior anatomy of the inguinofemoral area from a laparoscopic standpoint because anatomy is unique to each individual. But new dangers can arise from new approaches, even if the anatomic structures are well known, so anatomic research is still useful. It provides, relative to new surgical techniques, new vision of structures known for centuries.

ANAL PORES IN LEPTOSYNAPTA CLARKI (APODA)

Anal pores were observed in living specimens of Leptosynapta clarki. Subsequent histological preparations substantiated these observations. The posterior anatomy of the animal and the possible functions of the anal pores is discussed.