What is the benefit of using an oblique angle of 5-10 degrees when placing an epidural steroid injection at L5/S1?

Benefits of 5-10 Degree Oblique Angle for L5/S1 Epidural Steroid Injections

Using a 5-10 degree oblique angle for L5/S1 epidural steroid injections improves needle passage time and visualization of the S1 foramen, resulting in more accurate placement and potentially reduced procedure time compared to traditional anteroposterior approaches. 1

Anatomical and Technical Advantages

Improved Visualization of the Foramen

• The oblique "Scotty dog" approach provides better visualization of the S1 foramen by rotating the C-arm to an ipsilateral oblique angle of 5-10 degrees
• This technique creates a recognizable anatomic landmark (the "S1 Scotty dog") that facilitates more predictable visualization of the foramen 2
• The oblique view allows for more medial needle placement with better epidural flow of contrast material

Procedural Efficiency

• Research demonstrates significantly shorter needle passage time into the S1 foramen with the oblique approach (24.4 ± 24.0 seconds) compared to the anteroposterior approach (47.8 ± 53.2 seconds) 1
• Total procedure time is also reduced with the oblique approach (93.3 ± 35.0 seconds vs 160.0 ± 98.7 seconds) 1
• When performing simultaneous L5 and S1 transforaminal ESIs, a single oblique view can be used to guide both needles, potentially reducing radiation exposure 2

Clinical Implications

Safety Considerations

• Accurate needle placement is critical for epidural steroid injections to minimize risks of complications
• Fluoroscopic guidance is essential for correct placement of epidural injections, as demonstrated by studies showing incorrect placement in up to 38.3-47.7% of non-fluoroscopically directed injections 3
• The oblique approach may help reduce the risk of intravascular injection, though this has not been statistically confirmed (11.4% with oblique vs 22.8% with AP approach, p=0.205) 1

Precision and Accuracy

• The oblique approach allows for more precise needle placement into the epidural space
• Studies using robotic systems have shown that improved angular orientation leads to better procedural accuracy in transforaminal epidural injections 4
• For cervical epidural injections, specific contralateral oblique angles (50-60 degrees) have been shown to optimize needle tip visualization depending on placement 5

Practical Application

Technique Recommendations

• For S1 transforaminal epidural injections, use an ipsilateral oblique fluoroscopic view of 5-10 degrees to visualize the S1 "Scotty dog"
• This approach is particularly beneficial when performing simultaneous L5 and S1 injections
• The procedure may be more challenging in patients with higher BMI, as body mass index has been identified as a risk factor for longer procedure times 1

Patient Selection Considerations

• The oblique approach is suitable for patients with L5 and S1 foraminal and paracentral disk herniation with concurrent L5-S1 radicular pain 2
• Patients should have failed at least 4 weeks of conservative treatment before considering epidural injections 6
• Imaging findings should correlate with clinical symptoms to ensure appropriate patient selection 6

Potential Limitations

• The benefits of the oblique approach may be less pronounced in obese patients 1
• As with all epidural procedures, proper training and experience are necessary to maximize the benefits of this technique
• While the oblique approach improves visualization and procedure time, it does not eliminate all risks associated with epidural injections

The oblique "Scotty dog" approach represents a technical refinement that can improve the efficiency and potentially the safety of L5/S1 epidural steroid injections through better visualization of anatomical landmarks and more precise needle placement.