Overview
This lecture explains the physiology and biomechanics of the Trendelenberg Sign, highlighting the role of hip abductor muscles and their clinical assessment.
Hip Abductors and Innervation
- The main hip abductors are gluteus medius and gluteus minimus.
- Both muscles are innervated by the superior gluteal nerve.
- Damage can occur via hip dislocation, surgery, nerve injury, muscle damage, or motor neuron diseases like poliomyelitis.
Trendelenberg Sign Mechanics
- The Trendelenberg Sign appears when hip abductors on one side are weak or nonfunctional.
- During gait, when standing on the lesioned side, the pelvis dips toward the opposite (contralateral) side.
- Patients lean their torso toward the lesioned (supporting) side to maintain balance.
Joint Movement Principles
- Joint movement depends on which bone is fixed; e.g., dumbbell curl (forearm moves) vs. pull-up (humerus moves).
- Hip abduction usually means moving the femur laterally away from the body (“abduction of the femur at the hip joint”).
- Abduction can also occur by tilting the pelvis laterally (“abduction of the pelvis at the hip joint”).
Hip Abduction During Gait
- Raising a leg laterally while standing involves simultaneous abductor action on both sides.
- The supporting leg’s abductors stabilize the pelvis in a level plane during walking.
- If the supporting leg's abductors are weak, the pelvis tilts downward on the opposite side during single-leg stance.
Clinical Assessment of Trendelenberg Sign
- Ask the patient to stand on one leg for assessment.
- If supporting side abductors are intact, the pelvis stays level.
- With abductor weakness, pelvis tilts away from the supported side and the patient may lean or lose balance.
Key Terms & Definitions
- Trendelenberg Sign — pelvic dip toward the unsupported side due to weak hip abductors during single-leg stance.
- Hip Abductors — gluteus medius and minimus, muscles that move the thigh away from the midline.
- Superior Gluteal Nerve — nerve that supplies the gluteus medius and minimus.
- Abduction — movement away from the midline of the body.
Action Items / Next Steps
- Practice identifying Trendelenberg Sign during patient gait assessment.
- Review anatomy and innervation of the gluteal muscles.