Question

Although he was 18 months old, the youngster was not walking properly and waddled when he tried. Apart from his reluctance to walk, he was developing normally. When Mum managed to get him to demonstrate his walking to the orthopedic surgeon, the boy clearly limped and had a rolling gait. As his left leg swung forward when he walked, he leaned his torso over to the right and swung the leg outwards as well, as if it was too long. Examination confirmed shortening of the right leg with some external rotation of the right foot. The skin creases at the top of the thigh were asymmetrical and his Trendelenburg sign was positive. • How would you perform the Trendelenburg test?

• Why would damage to the superior gluteal nerve cause a positive Trendelenberg sign? • Why would damage to the inferior gluteal nerve not cause a positive Trendelenberg sign?
• Where do the gluteal nerves originate from?
• What course do the gluteal nerves follow to reach the muscles they innervate?
• Between which bony points would you measure to confirm his right lower limb was shorter than the left? Distinguish between apparent and true limb shortening.
• What would you measure to show the shortening was in the hip?

Answer 1

To perform the Trendelenburg test, the patient is asked to stand on one leg while the examiner observes the position of the pelvis. A positive Trendelenburg sign is observed when the pelvis on the unsupported side drops down instead of staying level.

Damage to the superior gluteal nerve can cause a positive Trendelenberg sign because this nerve innervates the gluteus medius muscle, which is responsible for stabilizing the pelvis during walking. If the nerve is damaged, the gluteus medius muscle cannot function properly, leading to a drop in the pelvis on the unsupported side.

Damage to the inferior gluteal nerve would not cause a positive Trendelenberg sign because this nerve innervates the gluteus maximus muscle, which is not involved in pelvis stabilization during walking.

The gluteal nerves originate from the sacral plexus.

The gluteal nerves follow a course through the pelvis and exit through the greater sciatic foramen to reach the muscles they innervate.

To confirm the right lower limb is shorter than the left, the distance between the anterior superior iliac spine (ASIS) and the medial malleolus of both legs is measured. Apparent limb shortening can be caused by factors such as scoliosis or pelvic tilt, while true limb shortening is caused by a structural difference in the length of the bones.

To show the shortening is in the hip, the distance between the ASIS and the lateral malleolus of both legs is measured. This measurement confirms the presence of hip dysplasia or dislocation.