Iliopsoas Tendon Stretch During Lithotomy Position

Anatomical Mechanism of Injury

The lithotomy position creates excessive hip flexion beyond 90 degrees combined with external rotation and abduction, which places significant tension on the iliopsoas tendon as it courses over the anterior hip capsule and acetabular rim, according to the American Society of Anesthesiologists 2, 3.
Hip flexion beyond 90 degrees specifically increases tension on the iliopsoas tendon and can lead to compression symptoms, particularly when maintained for prolonged surgical procedures, as noted by the American College of Surgeons 1, 4.

The American Society of Anesthesiologists notes that stretching the hamstring muscle group beyond comfortable range may increase sciatic neuropathy risk, though this typically presents with pain radiating below the knee rather than laterally to the hip 2, 3, 1.
Femoral nerve compression should be considered if there is associated weakness in knee extension, though this is less likely to produce the sensation of dislocation described, according to the American Academy of Orthopaedic Surgeons 1.

Procedures requiring prolonged lithotomy positioning (>2 hours) increase risk through sustained tendon stretch, as reported by the American Society of Anesthesiologists 2, 3.
The American Society of Anesthesiologists notes that flexibility of the hamstring muscle group is important to assess preoperatively when placing patients in lithotomy position, though no consensus exists on specific degree recommendations for hip flexion to reduce femoral or iliopsoas injury risk 2, 3.

Maintaining hip flexion within comfortable limits during lithotomy positioning, generally not exceeding 90 degrees, may reduce risk, though the American Society of Anesthesiologists acknowledges no majority consensus was reached on specific degree recommendations 2, 3, 4, 1.
Periodic assessment of hip position during prolonged procedures is recommended, as suggested by the American College of Surgeons 1.