Clinical Cases - Hip & Posterior Thigh

Following a major operation, a patient was placed on a course of antibiotics which were to be delivered via intramuscular injection to the buttocks. After one of these injections, the patient complained of more pain than usual in the region of the injection. Later, as the patient was taking his afternoon walk in the hall, the nurse noticed that he was walking with a limp that had not been present before--his left hip dropped every time he lifted his left foot off the floor, but on the right side, his pelvis remained level when he lifted up his right foot. The doctor was called, and after a brief examination, she concluded that the injection had damaged a nerve that resulted in muscle weakness, which caused the patient's unusual limp.

Questions to consider:

1. Based on the vignette above, which muscles are affected? On which side?

   The muscles affected are the gluteus medius, gluteus minimus, and tensor fasciae latae. These muscle are important for stabilizing the pelvis when we walk, preventing our hips from dropping as we lift a foot off the ground to propel it forward. The lesion is on the right side in this case because in this sort of injury the uninjured hip is the one which tends to drop. In other words, the right gluteus medius and gluteus minimus support the pelvis in such a way that when the left foot is lifted off the ground, the left pelvis remains level with the right pelvis, but when the right gluteal muscles are injured, the left side of the pelvis will drop when the left foot is lifted off the ground.

2. If these muscles are affected, which nerve must be damaged? Where is this nerve located in the buttock and where does it originate?

   The injured nerve is the superior gluteal nerve. This nerve originates from the ventral rami of L4, L5, and S1 in the sacral plexus, leaves the pelvis through the upper part of the greater sciatic foramen above the piriformis muscle, and then runs forward between the gluteus medius and minimus in the superomedial quadrant of the buttock.

3. What other structures in the posterior hip/buttocks region might be damaged by an inappropriately administered intramuscular injection or other penetrating injury?

   The inferior gluteal nerve, the sciatic nerve, the posterior femoral cutaneous nerve, and the superior and inferior gluteal arteries and veins may all be damaged by careless intramuscular drug administration or other penetrating injuries.

4. Based on your knowledge of the anatomy of this region, where is the best location for administering intramuscular injections to avoid damaging any important structures?

   The best location for administering intramuscular injections is the superolateral quadrant of the buttock, just inferior and posterior to the anterior superior iliac spine.

5. Why might an intramuscular injection be used instead of a subcutaneous or intravenous injection?

   Intramuscular injections are given when prolonged drug action is preferred (due to relatively slow intramuscular absorption rates), when the solution is oily and cannot be injected directly into the blood stream, or when the substance to be administered is a subcutaneous irritant.

6. What is the clinical name given to the symptoms the patient displayed following the injury and what other conditions might cause it?

   The dropping of the uninjured hip when the same-sided foot is lifted off the ground is called Trendelenburg's sign. It occurs when the nerve supply to the abductors of the thigh (gluteus medius, gluteus minimus, and tensor fasciae latae) is disrupted due to injury or disease (i.e. poliomyelitis), or when conditions such as an unreduced or congenital dislocation of the hip joint exist.