Pain in the leg, like pain in the arm, has many causes. Common causes are degenerative and traumatic joint and soft tissue processes, lumbar disk herniation, and pathology in the lumbar spinal canal. Others include polyneuropathies, entrapment neuropathies, and restless legs syndrome. Vascular diseases, too, play an important role, particularly arterial occlusive disease.
Pain in the hip is usually due to diseases of the hip joint, most often degenerative arthritis (coxarthrosis). A diagnosis that is often missed is periarthropathy of the hip: in this condition, the joint itself is not diseased, but the soft tissues around it give rise to intractable pain, which frequently lasts for months. In algodystrophy of the hip, local pain is followed, some time afterward, by the development of osteopenia of the femoral head. Both the pain and the osteopenia usually resolve spontaneously.
Thigh pain may be due to a local process such as a sarcoma. An upper lumbar disk herniation or other lesion causing nerve root irritation can produce referred pain in the thigh. Meralgia paresthetica, a type of entrapment neuropathy causing pain in the thigh, is described on p. 234. Acute thigh pain and femoral nerve palsy can be caused either by diabetic neuropathy or by a hematoma in the psoas sheath.
Knee pain is usually of orthopedic, rheumatological, or traumatic origin. A proximal lesion of the obturator n. produces referred pain in the popliteal fossa in How-ship-Romberg syndrome (p. 236). Spontaneous or mechanically induced lesions of the infrapatellar branch of the saphenous n. are a further cause of pain in the knee.
Pain in the lower leg that is present only when the patient walks is typical of vasogenic intermittent claudication, a syndrome whose cause usually lies in the arteries, less commonly in the veins. Neurogenic intermit tent claudication is caused by compression of the cauda equina in lumbar spinal stenosis (p. 213). Vasogenic intermittent claudication is worse when the patient walks uphill, while the neurogenic type is worse when the patient walks downhill. In the anterior tibial artery syndrome, pain develops acutely on the anterior aspect of the lower leg, particularly with exercise (p. 239). The saphenous n. can be caught in a fascial gap on the medial side of the lower leg, or, alternatively, in Hunter's canal in the thigh; pain ensues in the cutaneous zone innervated by this nerve (entrapment neuropathy).
Pain in the foot is a common complaint. It is usually unilateral and caused by an orthopedic condition, or by trauma. Tarsal tunnel syndrome, which typically arises after an ankle sprain, causes pain in the sole of the foot when the patient walks; it is described on p. 241. Morton's metatarsalgia is described in the same section. Bilateral, burning pain in the feet characterizes ery-thromelalgia of vasomotor origin, otherwise known as burning feet syndrome. Similar symptoms may arise in polyneuropathy, but are then usually accompanied by objective neurological findings (loss of Achilles reflexes, distal sensory deficit). In "restless legs syndrome," the restlessness, which is perceived as painful, forces the sufferer to stand up, walk around, and move the legs time and again, particularly at night or after prolonged sitting in a soft chair. This syndrome usually responds to small doses of L-DOPA, as well as to dopamine agonists.
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