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Hip and knee pain are common complaints, especially among athletes and the obese due to increased forces on their joints. Knee pain is usually due to local pathology, whereas hip pathology commonly causes referred pain in the buttocks and lower extremity and may be due to extraarticular pathology. Each pain has a broad differential diagnosis, but a focused history and physical examination will often lead to the diagnosis (Table 179-1).

Table 179-1

Suggested Clues for the Differential Diagnosis of Hip and Knee Pain


Abscess of the psoas muscle usually occurs through hematogenous spread and may present with abdominal pain radiating to the hip or flank, fever, and limp, or other constitutional symptoms. Eighty percent of the time, it is caused by Staphylococcus aureus. The diagnosis is made by CT. Treatment includes organism-specific antibiotics and surgical drainage.


Meralgia paresthetica, a compressive inflammation of the lateral femoral cutaneous nerve, causes pain in the hip, thigh, or groin, along with burning or tingling paresthesias, and hypersensitivity to light touch. Address the source of nerve irritation (e.g., obesity, pregnancy, tight pants, belt) and provide nonsteroidal anti-inflammatory drugs (NSAIDs) to treat in the ED. Obturator nerve entrapment usually occurs after pelvic fractures, with masses, or in athletes with a fascial band at the distal obturator canal, which causes pain in the groin and down the inner thigh. Surgery may be needed for pain relief. Ilioinguinal nerve entrapment is associated with pregnancy or hypertrophy of the abdominal wall musculature and causes groin pain. Piriformis syndrome, irritation of the sciatic nerve from the piriformis muscle, manifests as pain in the buttocks and hamstring muscles that worsens with sitting, climbing stairs, or squatting. ED treatment is conservative for all of these nerve entrapment syndromes (Table 179-2).

Table 179-2

Selected Syndromes by Location

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