Intrathecal drug delivery is an effective and safe option for the treatment of chronic pathology refractory to conventional pain therapies. Typical intrathecal administered drugs are opioids, baclofen, local anesthetics and adjuvant medications. Although knowledge about mechanisms of action of intrathecal drugs are every day more clear many doubt remain respect the correct location of intrathecal catheter in order to achieve the best therapeutic result. We analyze the factors that can affect drug distribution within the cerebrospinal fluid. Three categories of variables were identified: drug features, cerebrospinal fluid (CSF) dynamics and patients features. First category includes physicochemical properties and pharmacological features of intrathecal administered drugs with special attention to drug lipophilicity. In the second category, the variables in CSF flow, are considered that can modify the drug distribution within the CSF with special attention to the new theories of liquoral circulation. Last category try to explain inter-individual difference in baclofen response with difference that are specific for each patients such as the anatomical area to treat, patient posture or reaction to inflammatory stimulus. We conclude that a comprehensive evaluation of the patients, including imaging techniques to study the anatomy and physiology of intrathecal environment and CSF dynamics, could become essential in the future to the purpose of optimize the clinical outcome of intrathecal therapy.
Analgesics, Opioid ; Anesthetics, Local ; Baclofen ; Catheters ; Chronic Pain ; Humans ; Posture

Bones are the third most common location for solid tumor metastasis affecting up to 10% of patients with solid tumors. When the spine is involved, thoracic and lumbar vertebrae are frequently affected. Access to spinal lesions can be through minimally invasive surgery (MIS) or traditional open surgery (OS). This study aims to determine which method provides an advantage. Following the PRISMA (Preferred Inventory for Systematic Reviews and Meta-Analysis) guidelines, a systematic review was conducted to identify studies that compare MIS with OS in patients with spinal metastatic disease. Data were analyzed using Review Manager ver. 5.3 (RevMan; Cochrane, London, UK). Ten studies were included. Operative time was similar among groups at -35.23 minutes (95% confidence interval [CI], -73.36 to 2.91 minutes; p=0.07). Intraoperative bleeding was lower in MIS at -562.59 mL (95% CI, -776.97 to -348.20 mL; p<0.00001). OS procedures had higher odds of requiring blood transfusions at 0.26 (95% CI, 0.15 to 0.45; p<0.00001). Both approaches instrumented similar numbers of levels at -0.05 levels (95% CI, -0.75 to 0.66 levels; p=0.89). We observed a decreased need for postoperative bed rest at -1.60 days (95% CI, -2.46 to -0.74 days; p=0.0003), a shorter length of stay at -3.08 days (95% CI, -4.50 to -1.66 days; p=0.001), and decreased odds of complications at 0.60 (95% CI, 0.37 to 0.96; p=0.03) in the MIS group. Both approaches revealed similar reintervention rates at 0.65 (95% CI, 0.15 to 2.84; p=0.57), effective rates of reducing metastasis-related pain at -0.74 (95% CI, -2.41 to 0.94; p=0.39), and comparable scores of the Tokuhashi scale at -0.52 (95% CI, -2.08 to 1.05; p=0.41), Frankel scale at 1.00 (95% CI, 0.60 to 1.68; p=1.0), and American Spinal Injury Association Scale at 0.53 (95% CI, 0.21 to 1.37; p=0.19). MIS appears to provide advantages over OS. Larger and prospective studies should fully detail the role of MIS as a treatment for spine metastasis.