What does a positive obturator sign indicate and what is the recommended diagnostic and therapeutic approach?

Obturator Sign: Clinical Significance and Management

What the Obturator Sign Indicates

A positive obturator sign indicates irritation of the obturator internus muscle or adjacent pelvic structures, most commonly from appendicitis (particularly with a pelvic or retrocecal appendix), pelvic inflammatory disease, tubo-ovarian abscess, or less commonly from primary obturator muscle pathology. 1

The test is performed by passive internal rotation of the flexed hip, which stretches the obturator internus muscle. Pain with this maneuver suggests inflammation of structures adjacent to or within the obturator fossa.

Primary Differential Diagnoses

In Acute Pelvic Pain (Reproductive Age)

• Appendicitis with pelvic location: The obturator sign is classically associated with appendicitis when the inflamed appendix lies in the pelvis near the obturator internus muscle 1
• Pelvic inflammatory disease (PID): Inflammation can irritate the obturator muscle, producing a positive sign 2
• Tubo-ovarian abscess (TOA): Characterized by ill-defined adnexal mass with thick walls and variable signal intensity 2
• Ovarian torsion: May present with hip pain and positive obturator sign due to adjacent inflammation 2

In Musculoskeletal Presentations

• Obturator internus muscle abscess: Presents with hip/thigh pain, fever, limp, and hip held in flexion, abduction, and external rotation 3
• Obturator muscle tears: Uncommon injuries seen in high-level athletes, particularly soccer players, causing anterior hip pain with internal or external rotation of the flexed hip 4

Recommended Diagnostic Approach

Initial Clinical Assessment

Document the specific location and character of pain, associated symptoms (fever, nausea, vomiting, vaginal discharge), and perform a systematic physical examination including:

• Abdominal examination: Assess for localized versus diffuse tenderness, guarding, rebound, and peritoneal signs 1
• Pelvic examination: Essential in reproductive-age females to assess for cervical motion tenderness, adnexal masses, or discharge 2
• Hip examination: Passive internal rotation of the flexed hip (obturator sign), passive hip flexion with knee extension (psoas sign), and assessment of hip range of motion 3, 4
• Rectal examination: May reveal tenderness or mass in pelvic appendicitis 1

Laboratory Evaluation

• Complete blood count: Assess for leukocytosis and neutrophilia suggesting infection or inflammation 1
• Urinalysis: Rule out urinary tract infection and hematuria 2
• β-hCG: Mandatory in all reproductive-age females to exclude pregnancy-related complications 2
• Lactate and metabolic panel: If concerned for bowel ischemia or severe sepsis 1

Imaging Strategy

The imaging approach depends on the clinical presentation and hemodynamic stability:

For Suspected Gynecological Etiology (Stable Patient)

• Transvaginal ultrasound (TVUS) with transabdominal ultrasound (TAUS): First-line imaging with sensitivity of 83.3% for ovarian torsion, 58.3% for TOA 2
• Power Doppler TVUS: 100% sensitive and 80% specific for PID diagnosis, can identify hyperemia and abnormal flow patterns 2
• MRI pelvis: If ultrasound is non-diagnostic or for better characterization of complex masses 2

For Suspected Appendicitis or Abscess

• CT abdomen/pelvis with IV contrast: Diagnostic standard with >90% accuracy for identifying appendicitis, abscess, or bowel pathology 1
• MRI or CT: Essential for diagnosing obturator internus muscle abscess, showing characteristic findings in all 14 patients in one series 3

For Suspected Musculoskeletal Injury

• MRI: Procedure of choice for imaging obturator muscle lesions, essential for location, classification, and evaluation of injury size 5, 4

Therapeutic Approach

For Infectious/Inflammatory Causes

Appendicitis

• Immediate surgical consultation if peritoneal signs, hemodynamic instability, or CT evidence of perforation 1
• Broad-spectrum IV antibiotics covering enteric organisms 1

Pelvic Inflammatory Disease

• Empiric antibiotic therapy based on CDC guidelines (typically ceftriaxone plus doxycycline with or without metronidazole) 2
• Hospital admission if TOA present, pregnancy, severe illness, or failed outpatient therapy 2

Obturator Internus Muscle Abscess

• CT-guided percutaneous drainage or surgical drainage depending on abscess characteristics 3
• IV antibiotics for median 28 days: Most commonly Staphylococcus aureus, requiring prolonged therapy 3
• Evaluate for associated osteomyelitis (present in 3 of 11 patients in one series) 3

For Ovarian Pathology

Ovarian Torsion

• Emergent surgical detorsion (laparoscopic preferred): Mortality and infertility risk increase with delayed treatment 2
• Surgery indicated even with absent arterial flow, as salvage may still be possible 2

For Musculoskeletal Injuries

Obturator Muscle Tears (Athletes)

• Conservative management: Physical therapy, analgesic medications, symptoms-based rehabilitation protocol 4
• Mean return to play: 11.5 ± 8.8 days with conservative treatment 4
• Functional treatment with orthopedic aids to correct possible deformities and allow short recovery time 5

Critical Pitfalls to Avoid

• Do not dismiss a positive obturator sign in elderly patients: Pain may be less prominent, leading to delayed diagnosis of serious pathology 1
• Do not rely on physical examination alone to exclude surgical emergencies: Physical exam and laboratory tests are neither sufficiently sensitive nor specific to detect complications like strangulation or perforation 1
• Do not delay imaging in favor of observation: CT with IV contrast should be obtained promptly in unstable patients or those with peritoneal signs 1
• Do not confuse obturator internus muscle abscess with septic arthritis of the hip: The hip is typically held in flexion, abduction, and external rotation with OIM abscess, and MRI/CT are diagnostic 3
• In athletes with hip pain and positive obturator sign, consider MRI: Obturator muscle tears are uncommon but have a benign prognosis with conservative treatment 4