Obturator Muscles: Testing, Function, and Clinical Assessment

How Do You Test an Obturator?

Testing the obturator muscles (Obturator Internus and Externus) involves a comprehensive assessment of hip strength, range of motion, and specific orthopedic maneuvers, primarily focusing on resisted external rotation and adduction, alongside careful palpation and functional observation.

Understanding the Obturator Muscles

The obturator muscles are part of the deep external rotators of the hip, crucial for hip stability and movement.

• Obturator Internus: Originates from the inner surface of the obturator membrane and surrounding bone, exiting the pelvis through the lesser sciatic foramen. It inserts onto the medial surface of the greater trochanter of the femur. Its primary action is hip external rotation, and it assists in abduction when the hip is flexed.
• Obturator Externus: Originates from the outer surface of the obturator membrane and surrounding bone. It wraps posteriorly around the femoral neck to insert into the trochanteric fossa of the femur. Its primary action is powerful hip external rotation and it assists in hip adduction.

Both muscles play vital roles in maintaining hip joint integrity, contributing to dynamic stability during walking, running, and single-leg stance. Dysfunction can manifest as deep gluteal pain, hip stiffness, or altered gait mechanics.

General Principles of Muscle Testing

When assessing any muscle, a systematic approach is essential. This includes:

• Subjective History: Gathering information about pain, onset, duration, aggravating activities, and previous injuries.
• Observation: Looking for postural asymmetries, muscle atrophy, or swelling.
• Palpation: Feeling the muscle for tenderness, tone, or trigger points.
• Range of Motion (ROM): Assessing both active and passive movements to identify limitations or pain patterns.
• Resisted Movements (Manual Muscle Testing - MMT): Applying resistance against the muscle's primary action to assess strength and provoke pain.
• Special Tests: Performing specific orthopedic tests to rule in or rule out particular conditions.

Due to their deep location, isolating the obturator muscles from other hip rotators (e.g., piriformis, gemelli, quadratus femoris) can be challenging, necessitating a nuanced approach.

Clinical Assessment of Obturator Muscle Function

A thorough assessment begins with a broader look at the hip and pelvis:

• Subjective History: Inquire about deep buttock or groin pain, clicking, catching, or symptoms radiating down the leg (which might suggest sciatic nerve involvement, as the nerve passes close to the obturator internus).
• Observation: Note any pelvic tilt, hip rotation biases, or asymmetry in gluteal muscle bulk.
• Palpation:
  • Obturator Internus: Can be challenging due to its deep location. Palpation is typically performed in the deep gluteal region, medial to the greater trochanter and superior to the ischial tuberosity, with the hip in slight flexion and internal rotation to bring it closer to the surface. Tenderness here might indicate a strain or trigger point.
  • Obturator Externus: Even deeper and generally not directly palpable. Its function is primarily assessed through resisted movements.

Specific Tests for Obturator Muscle Strength and Integrity

Testing the obturator muscles involves assessing their primary actions and using orthopedic tests that stress the deep hip rotators.

• Manual Muscle Testing (MMT) for Hip External Rotation:

  • Positioning: The patient can be supine or prone. For supine, the hip is typically flexed to 90 degrees, and the knee is flexed to 90 degrees (foot flat on the table). For prone, the knee is flexed to 90 degrees.
  • Execution: The examiner stabilizes the thigh and applies resistance to the ankle or distal lower leg in the direction of internal rotation, while the patient attempts to externally rotate their hip.
  • Focus: While this tests all hip external rotators, a weakness or pain specifically felt deep within the hip, especially when attempting to isolate the deep rotators (e.g., by minimizing gluteus maximus contribution), can point towards obturator involvement.
  • Grading: Muscle strength is graded on a scale (e.g., 0-5), noting any pain or compensatory movements.

• Manual Muscle Testing (MMT) for Hip Adduction (for Obturator Externus):

  • Positioning: Patient supine, hips and knees extended.
  • Execution: The examiner supports the leg and applies resistance against the medial aspect of the distal thigh/knee in the direction of abduction, while the patient attempts to adduct their leg.
  • Focus: The obturator externus is a significant adductor. Pain or weakness during resisted adduction, particularly if felt deep in the groin/anterior hip, can suggest obturator externus dysfunction.

• Range of Motion (ROM) Assessment:

  • Passive External Rotation: With the patient supine, the examiner passively moves the hip into external rotation. Limited ROM or pain may indicate tightness or pathology of the external rotators or hip capsule.
  • Passive Internal Rotation: Assessing internal rotation can also be informative. Excessively increased internal rotation might suggest laxity or lengthening of the external rotators, while limited internal rotation might indicate tightness of the external rotators or bony impingement.

• Orthopedic Special Tests (Indirect Assessment):

  • FABER Test (Flexion, Abduction, External Rotation):
    • Positioning: Patient supine. The examiner places the patient's ankle on the opposite knee, creating a "figure-4" position.
    • Execution: The examiner gently applies overpressure to the medial knee, pushing it towards the examination table.
    • Interpretation: While primarily a test for hip joint pathology (e.g., labral tears, FAI) or SI joint dysfunction, pain deep in the posterior hip or groin during this maneuver can also indicate stress on the deep external rotators, including the obturators.
  • FAIR Test (Flexion, Adduction, Internal Rotation):
    • Positioning: Patient supine. The examiner flexes the hip to 90 degrees, adducts, and internally rotates the hip.
    • Interpretation: Primarily used to assess piriformis syndrome (due to sciatic nerve compression), this test also stresses the deep external rotators. Pain in the deep gluteal region with this maneuver could implicate the obturator muscles or other deep rotators.

Interpreting Test Findings

• Weakness: Indicates muscle inhibition, injury, or neurological compromise.
• Pain: Localized pain during resisted movements or palpation points to muscular strain, tendinopathy, or trigger points.
• Limited ROM: Suggests muscle tightness, capsular restriction, or bony impingement.
• Asymmetry: Significant differences between sides warrant further investigation.

It's crucial to differentiate obturator issues from other common hip pathologies, such as piriformis syndrome, gluteal tendinopathy, hamstring strains, sacroiliac joint dysfunction, femoroacetabular impingement (FAI), or labral tears. A comprehensive assessment, often involving imaging (e.g., MRI) and consultation with a physician or physical therapist, is frequently necessary for an accurate diagnosis.

Considerations and Best Practices

• Holistic Assessment: Always integrate findings from the history, observation, palpation, ROM, MMT, and special tests. No single test is definitive.
• Functional Movement: Observe the patient during functional movements like squatting, lunging, or single-leg stance to see how the obturator muscles contribute to dynamic stability and identify any compensation patterns.
• Referral: If significant pain, weakness, neurological symptoms, or suspected structural damage is present, refer to a qualified healthcare professional (e.g., orthopedic surgeon, sports medicine physician, physical therapist) for a definitive diagnosis and treatment plan.
• Rehabilitation: Once diagnosed, targeted exercises focusing on strengthening, stretching, and motor control are essential for recovery and prevention.