A Clinical Comparison in Cervical Epidural Pressure Changes Between Midline and Paramedian Approaches

• precipitous decrease [ Time Frame: It will be measured at the moment of puncture of ligamentum flavum during interventional procedure, then participants will be followed for the duration of hospital stay, an expected average of 1 hour. ] [ Designated as safety issue: No ]
  Existence of the precipitous decrease in pressure at the moment of entering the cervical epidural space (exist or not)
  
  

• popping sensation [ Time Frame: It will be measured at the moment of puncture of ligamentum flavum during interventional procedure, then participants will be followed for the duration of hospital stay, an expected average of 1 hour. ] [ Designated as safety issue: No ]
  Existence of the tactile sensation of give by pain experts (exist or not)
  
  
• spreading levels of dye according to dye volume [ Time Frame: It will be measured during interventional procedure, then participants will be followed for the duration of hospital stay, an expected average of 1 hour. ] [ Designated as safety issue: No ]
  Dye Volume / Dye Spreading Level after injection of 0.5 cc contrast dye, then check the spreading level such as the number of vertebral body and unilateral or bilateral spreading
  
  
• cervical epidural pressure [ Time Frame: It will be measured during interventional procedure, then participants will be followed for the duration of hospital stay, an expected average of 1 hour. ] [ Designated as safety issue: No ]
  The bevel of the needle is considered to have entered the epidural space when a typical waveform is observed, which consists of small cardiac oscillations superimposed on greater respiratory oscillations. The needle is then held immobile in the epidural space for 120 s to allow the epidural pressure to stabilize, and CEP is measured.
  
  

Ligamentum flavum in the cervical region is thin or not fused at the midline. The distinct elastic resistance offered by the ligamentum flavum before entering the epidural space when using the loss of resistance (LOR) technique may be blunted or even absent. The investigators inferred that the size and elasticity of the ligamentum flavum, in combination with mildline appraoch, the gaps could be responsible for a failure to recognize a LOR in some patients. If so, the investigators hypothesized that the paramedian approach would be advantageous for finding cervical epidural space more easily during cervical epidural steroid injections (CESIs). Therefore, the investigators randomly divide our patients into 2 groups; the midline approach group and the paramedian group. Then, the investigators examine the patterns of the pressure changes at the moment of a puncture of the ligamentum flavum during CESIs.