What are the sciatic notches?

Sciatic Notches: Anatomical Features and Clinical Significance

The sciatic notches are important anatomical landmarks of the hip bone (os coxae) that consist of the greater and lesser sciatic notches, with the greater sciatic notch serving as a passage for the sciatic nerve and various neurovascular structures between the pelvis and gluteal region.

Anatomical Description

Greater Sciatic Notch

• Located on the posterior border of the hip bone between the posterior inferior iliac spine and the ischial spine
• Width averages approximately 63.09 ± 13.59 mm 1
• Forms a significant indentation in the posterior hip bone
• Serves as a major passageway for:
  • Sciatic nerve (the largest nerve in the body)
  • Piriformis muscle
  • Superior and inferior gluteal vessels and nerves
  • Internal pudendal vessels and pudendal nerve
  • Nerves to obturator internus and quadratus femoris

Lesser Sciatic Notch

• Located below the ischial spine
• Smaller than the greater sciatic notch
• Serves as a passageway for:
  • Tendon of the obturator internus muscle
  • Internal pudendal vessels and pudendal nerve

Clinical Significance

Sexual Dimorphism

• The greater sciatic notch demonstrates significant sexual dimorphism, making it valuable for forensic identification 2, 3
• Female characteristics:
  • Wider notch
  • Larger total angle and posterior segment angle
  • Greater posterior segment width
  • Higher index II values
• Male characteristics:
  • Narrower notch
  • Smaller total angle and posterior segment angle
  • Shorter posterior segment width
  • Lower index II values

Pathological Considerations

1. Piriformis Syndrome

   • The sciatic nerve passes through the greater sciatic notch, typically below the piriformis muscle
   • In piriformis syndrome, the sciatic nerve becomes compressed as it passes through the greater sciatic notch 1
   • During the piriformis stretch test (hip flexion, adduction, and internal rotation), the infrapiriforme foramen becomes narrower, potentially compressing the sciatic nerve 1

2. Tumors

   • Sciatic notch tumors are rare but can have various etiologies 4
   • Tumors may present as "dumbbell-shaped" with intra- and extra-pelvic components 5
   • Surgical approaches for tumor resection depend on the anatomical location and extent of the tumor 4, 5

3. Local Recurrence of Rectal Cancer

   • The Leeds classification for locally recurrent rectal cancer includes the lateral wall type, which involves structures of the pelvic sidewall including the sciatic foramina 6
   • Tumors can extend through this area to affect the sciatic nerve, piriformis muscle, and gluteal region 6

Imaging Considerations

• MRI is the mainstay of plexus imaging, providing superior definition of intraneural anatomy 6
• CT with IV contrast can be useful for detecting and characterizing soft tissue lesions that may involve the plexus 6
• For suspected sciatic nerve involvement, MRI lumbosacral plexus is usually appropriate (rating 7-8/9) 6
• FDG-PET/CT can be complementary to MRI lumbosacral plexus or used if the patient cannot have MRI 6

Common Pitfalls and Caveats

• Anatomical variations exist in the relationship between the sciatic nerve and piriformis muscle, which can predispose to piriformis syndrome 1
• The sciatic nerve typically intersects the piriformis muscle in its medial second quarter 1
• When evaluating sciatic nerve symptoms, consider both spinal causes (radiculopathy) and plexus/peripheral nerve causes (plexopathy), as clinical presentations may overlap 6
• For suspected sciatic nerve compression at the notch, dynamic MRI and MR neurography may be necessary for accurate diagnosis 1