Chapter 179. Hip and Knee Pain

Hip and knee pain are common among all people. Athletes are at increased risk due to excess forces on their joints. Knee pain is usually due to local pathology and is not commonly referred to other sites. Hip pathology commonly causes referred pain in the buttocks and lower extremity, and pain felt in the hip may be due to extraarticular pathology. The differential diagnosis for hip or knee pain is broad but a focused history and physical examination will often lead to the diagnosis (Table 179-1).

Meralgia paresthetica is a compressive inflammation of the lateral femoral cutaneous nerve causing pain in the hip, thigh, or groin, burning or tingling paresthesias, and hypersensitivity to light touch. ED treatment includes addressing the source of nerve irritation (eg, obesity, pregnancy, tight pants belt) and provision of NSAIDs. Obturator nerve entrapment usually occurs after pelvic fractures 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. Piriformis syndrome, irritation of the sciatic nerve from the piriformis muscle, manifests as pain in the buttocks and hamstring muscles that is worsened by sitting, climbing stairs, or squatting. ED treatment is conservative for all of these nerve entrapment syndromes.

Abscess of the psoas muscle may present with abdominal pain radiating to the hip or flank, fever, and limp. The diagnosis is made by CT. Treatment includes antibiotics and surgical drainage.

Hip and knee bursae may cause localized pain due to inflammation, infection, rheumatologic disorders (psoriatic arthritis, rheumatoid arthritis, ankylosing spondylitis) or crystalline disease (gout, pseudogout). Infection may be difficult to distinguish clinically from more benign disorders. (Table 179-2) Treatment is directed at the underlying cause. NSAIDs, rest, heat, and time are the basis of treatment for inflammatory conditions. Steroid injections into readily accessible bursa may be useful if infection has been excluded. Care should be taken to avoid injecting steroids into tendons. For infections, treat with antibiotics (see Chapter 180 “Disorders of the Joints and Bursa,” for specific recommendations). Immunocompromised patients with suspected infections should be admitted for IV antibiotics and orthopedic surgery consultation.

Repetitive microtrauma that outpaces the body's ability to heal results in overuse syndromes (Table 179-3). Treatment generally consists of NSAIDs, heat, and rest, followed by gradual resumption of activities, physical therapy, and strengthening where appropriate.

Osteonecrosis (also known as aseptic necrosis, ischemic necrosis, avascular necrosis) is bone infarction caused by a lack of blood supply. It may be an idiopathic or primary disorder, secondary to a systemic condition, or following trauma. Conditions associated with avascular necrosis of the femoral head include: femoral neck fracture, hip dislocation, occult or minor trauma, sickle cell disease, collagen vascular diseases, alcohol abuse, renal transplant, systemic lupus erythematosus, dysbarism, chronic pancreatitis, exogenous steroid administration, Cushing disease, caisson disease, Gaucher disease, and renal osteodystrophy. Osteonecrosis of the hip may cause pain anywhere from the buttock to the knee. Osteomyelitis is an infection of the bone, resulting in bony destruction. Patients have local pain and may have associated warmth, swelling, and erythema. Acutely ill patients should receive high-dose, broad spectrum, parenteral antibiotics based on the patient's risk factors and most likely organisms. (Table 179-4) Osteitis pubis occurs following pregnancy, in athletes due to overuse of the adductors and gracilis muscles, and after bladder and prostate surgery. It causes pain in the region of the pubis and generally resolves over a period of months with rest and NSAIDs. Myositis ossificans (also known as heterotopic calcification) is the deposition of bone in abnormal sites after direct trauma. Pain and a palpable mass will be present. Pain or physical obstruction may limit motion in the affected muscle or joint. Surgery may be required.