Cerebrospinal Fluid Homeostasis and Hydrodynamics: A Review of Facts and Theories.

BACKGROUND AND PURPOSE: According to the classical hypothesis, the cerebrospinal fluid (CSF) is actively secreted inside the brain's ventricular system, predominantly by the choroid plexuses, before flowing unidirectionally in a cranio-caudal orientation toward the arachnoid granulations (AGs), where it is reabsorbed into the dural venous sinuses. This concept has been accepted as a doctrine for more than 100 years and was subjected only to minor modifications. Its inability to provide an adequate explanation to questions arising from the everyday clinical practice, in addition to the ever growing pool of experimental data contradicting it, has led to the identification of its limitations. Literature includes an increasing number of studies suggesting a more complex mechanism than that previously described. This review article summarizes the proposed mechanisms of CSF regulation, referring to the key clinical and experimental developments supporting or defying them. METHODS: A non-systematical literature search of the major databases was performed for studies on the mechanisms of CSF homeostasis. Gray literature was additionally assessed employing a hand-search technique. No restrictions were imposed regarding the time, language, or type of publication. CONCLUSION: CSF secretion and absorption are expected to take place throughout the entire brain's capillaries network under the regulation of hydrostatic and osmotic gradients. The unidirectional flow is defied, highlighting the possibility of its complete absence. The importance of AGs is brought into question, potentiating the significance of the lymphatic system as the primary site of reabsorption. However, the definition of hydrocephalus and its treatment strategies remain strongly associated with the classical hypothesis.

Long-term Outcome Following Three-Level Stand-Alone Anterior Cervical Discectomy and Fusion: Is Plating Necessary?

BACKGROUND: Anterior cervical discectomy with fusion (ACDF) is a proven method for the treatment of selected patients. The necessity of use of an anterior plate is controversial. The article aims to assess the fusion rates (FRs) and long-term outcomes following three-level ACDF. MATERIALS AND METHODS: Data were collected from the medical records of patients operated on due to degenerative cervical disease. All patients were treated with three-level ACDF employing polyether ether-ketone cages without anterior plating. Visual analog scale (VAS), neck disability index (NDI), and plain radiographs were used in the clinical and radiological postsurgery assessment. Fusion evaluation was performed according to the <1 mm motion between spinous processes rule. Subsidence was defined as a more than 2 mm decrease in the interbody height. RESULTS: A total of 234 treated levels on 78 patients were assessed. The mean presurgery NDI score was 23.07 ± 4.86, with a mean disability of 46.03% ± 9.64. The mean presurgery VAS score of the neck was 7.58 ± 0.85, while VAS score of the arm was 7.75 ± 1.008. Post surgery, NDI stated no disability, while VAS score of the neck and arm showed no presence of pain. The mean FR was 19.50 ± 21.71 levels per month, with a peak from 3rd to 6th month. Presurgery evaluation showed 12 (15.38%) patients with a high T2 sequence signal. Magnetic resonance imaging screening detected 31 (39.24%) patients with coexisting cervical and lumbar findings. Post surgery, transient dysphagia was reported by 1 patient (1.28%), while subsidence was registered in 15 (6.41%) levels, situated in 12 patients (15.38%), most often at C6-7 (66.6%). Clinical and radiological follow-up extended to 69.47 ± 11.45 months. CONCLUSION: Multilevel stand-alone ACDF is a safe, cost-effective procedure providing favorable clinical and radiological results with minimal complications. The incidence of subsidence is usually clinically insignificant and can be decreased with a careful surgical technique.

Pedicle screw placement accuracy impact and comparison between grading systems.

BACKGROUND: Pedicle screw instrumentation is widely used for spinal stabilization. However, the accuracy for free-hand screw placement ranges from 69% to 94%. This study assesses the value of the existing classification systems, and investigates their impact on the ability to assess the accuracy of free-hand screw placement. METHODS: Data were collected retrospectively from the medical records of 34 patients who received 224 pedicle screws placed utilizing a free-hand technique. Screw placement was evaluated employing the 2-mm increment and Zdichavsky et al. classification systems. Kappa coefficient and Landis and Koch interpretations were employed for statistical analysis. RESULTS: The 2-mm increment classification system resulted in a total of 18 (8.03%) misplaced screws. Lateral screw misplacement was observed in 13 (5.8%) instances, with medial pedicle wall penetration being noted in 5 (2.23%). Of the 18 misplaced screws, 4 (22.22%) were classified as minor (≤2 mm), 12 (66.67%) as moderate (2-4 mm), and 2 (11.11%) as severe (>4 mm) (K = 0.882). The Zdichavsky et al. grading system categorized 208 (92.84%) pedicle screws as Ia, 10 (4.46%) as Ib, 1 (0.45%) as IIa, 2 (0.90%) as IIb, 2 (0.90%) as IIIa, and 1 (0.45%) as IIIb grade; this resulted in a total of 16 (7.14%) misplaced screws (K = 0.980). One patient exhibited a new postoperative radiculopathy attributed to poor screw placement. There were no additional early or late postsurgical complications attributed to screw misplacement. CONCLUSION: The free-hand pedicle screw placement technique is both safe and effective. Postoperative computed tomography studies; however, are useful to confirm the accuracy of screw placement. Although, the available grading systems proved reliable, easy to use, and clearly reflected the individual surgeon's skills, they do not clearly document whether screws are safely placed.