Abdominal and pelvic conditions
Abdominal and pelvic disease processes such as infection, hematoma and trauma may result in femoral neuropathy if the elements of the lumbar plexus (L2–L4) are directly affected. For example, contained rupture of an abdominal aortic aneurysm occasionally presents with pain in the distribution of the femoral nerve in the thigh. Another example of a pelvic condition causing leg pain is obturator hernia which occurs when a defect in the internal obturator fascia becomes sufficiently large to allow herniation of abdominal or pelvic contents into the obturator foramen. Incarceration or strangulation may result, with signs of inflammation or bowel obstruction. The diagnosis is often delayed because of the rarity of the condition.
A mass may be evident in the medial thigh with the hip externally rotated and a pelvic mass may be apparent on rectal or vaginal examination. The Howship–Romberg sign may be elicited by external rotation of the hip causing pain radiating down the medial thigh in the distribution of the obturator nerve. Though somewhat controversial, the piriformis syndrome consists of sciatic neuropathy produced by impingement upon the sciatic nerve by the piriform muscle as both structures exit the greater sciatic foramen in the pelvis.
Soft tissue infection
Carbuncle, furuncle and cellulitis result from breakdown of the skin barrier. Diabetics are particularly susceptible, as are people with other conditions which affect the integrity of the skin. Chronic venous and arterial insufficiency are therefore often complicated by soft tissue infection. Seemingly trivial injury, insect bites or more substantial trauma all offer a portal for infection.
When contained to the skin and subcutaneous tissue, a carbuncle or furuncle is produced, most frequently by skin organisms such as Staphylococcus aureus. Localized swelling, redness and pain are typical, often maturing (‘pointing’) with spontaneous drainage. Lymphangitis may occur, classically with β-hemolytic streptococcus, even with a trivial initiating focus of infection. A linear red streak is present from the portal of entry following the course of the lymphatics up the leg. Tender, swollen lymph nodes are evident in the groin or popliteal space and a high fever with systemic malaise are often present due to bacteremia. Cellulitis affects the subcutaneous tissues to a variable extent with induration, redness, swelling, and tenderness. A variety of organisms may be involved. Subfascial infection is very unusual without significant trauma or recent surgery, except in the foot. Classically in diabetics, a relatively innocuous appearing local portal of entry such as a plantar ulcer or paronychia gives rise to deep penetrating infection which ascends via the tendon sheaths into the joint spaces and deep structures of the foot and even into the ankle and calf. Necrosis of skin and deep tissue is common. Multiple organisms, including anaerobes such as Bacteroides fragilis, are often present working in synergy. Surgical drainage is usually an important adjunct to antibiotics in order to gain control of these infections.
On less frequent occasions, soft tissue infection results in necrotizing fasciitis or myonecrosis. These infections result in marked systemic response with fever and hemodynamic manifestations and local findings of progressive ecchymosis, bullae, dermal gangrene, edema and crepitus due to gas formation in the tissues. Although Gram-positive Clostridia species can produce gas gangrene, Gram-negative organisms such as Escherichia coli also produce gas in the tissues. These infections typically respond poorly to antibiotics alone and require urgent surgical debridement for control.
Differential diagnosis of soft tissue infection is mainly with superficial thrombophlebitis and other local inflammatory conditions such as gout and joint sepsis.
Forceful extension of the ankle may produce acute calf pain on the basis of musculotendinous strain or tear. Patients with plantaris muscle rupture usu-ally have a suggestive history such as sudden onset of calf pain after stepping off a curb. Examination demonstrates tenderness in the calf exacerbated by ankle extension but with voluntary flexion intact, as opposed to complete Achilles tendon rupture in which flexion is lost. A similar traumatic history is consistent with painful tearing of muscles in the thigh. Hematoma results in an inflammatory reaction which adds to the pain syndrome. If encountered days after the injury, patients with rupture of thigh or calf muscles typically have ecchymosis at the ankle behind the medial malleolus from hematoma dissecting down the leg. Early ice, analgesics and rest are the cornerstones of management. Though the history is nearly pathognomonic for such injuries, either primary or secondary deep vein thrombosis and ruptured Baker’s cyst must be kept in mind.
Chronic compartment syndrome
Chronic overuse or overconditioning of the legs, such as occurs with long distance running or other types of vigorous athletics, may result in recurring abnormally high fascial compartment pressure after onset of exercise. Pain occurs in the involved compartment at variable times after beginning repetitive muscle contraction with enough severity to compel cessation of exercise. Compartment pressure recedes with rest and the pain subsides. Evidence supporting the diagnosis may be obtained by correlating intracompartment pressure changes with symptoms during exercise on a treadmill. Therapy may require surgical fasciotomy if exercise moderation is not successful. Diagnosis involves exclusion of other entities, most importantly vascular disease causing arterial or venous claudication, and popliteal artery entrapment syndrome.
Causalgia, otherwise known as reflex sympathetic dystrophy and complex regional pain syndrome, is a disabling pain syndrome which occurs after trauma to the limb. The injury may be relatively slight, but more typically involves significant fracture or soft tissue damage involving surgery and immobilization. Though post-traumatic neuralgia, neuroma and neuropathy occur as a direct result of injury to the nerves themselves, causalgia is distinguished by the absence of motor or sensory deficits in the symptomatic portion of the extremity. Pain does not follow a clear anatomic dermatome and is generally constant with episodic exacerbation for no apparent reason. There are frequently accompanying vasomotor findings such as coolness and pallor. Sweating may occur as another manifestation of increased efferent sympathetic nerve activity. With chronicity, the muscles of the limb atrophy from disuse and the joints become stiff and even frozen. These late consequences may be sufficiently severe to become irreversible. Early diagnosis is critical to management, and relies on clinical presentation and trial temporary sympathetic blockade for confirmation.
Phantom pain is a subjective complaint which occurs in mild form in a majority of patients early after major limb amputation. It persists at a significantly disabling level in no more than 10% of such patients. Patients report sensations which give the impression that the amputated limb is still present. The sensations are unpleasant and disquieting and may be interpreted as pain, particularly if the limb had been chronically painful prior to amputation. Symptoms tend to subside with time, and neurotropic medications may be helpful. Differential includes neuroma at the amputation site, usually evident on tapping the surgical stump for a Tinel’s sign on physical examination.
Spontaneous muscular cramps occur in many people, and are frequently encountered in relatively elderly and less active individuals who present with multiple other causes of lower limb pain. Such cramps are common at night, interrupting sleep, and most often involve the muscles of the calves and feet. Patients on diuretics are more commonly afflicted. The cramps may be sporadic and unpredictable or chronically recurrent every night. They can be very painful, recede within a few minutes but frequently promptly recur. With familiarity, patients can feel a cramp coming on and may be able to ablate it by standing or massaging to stretch or relax the muscle. Prophylactic stretching of the ankles before bed can help reduce the incidence of cramps. Alternatively, quinine sulfate at bedtime is generally effective in preventing cramp attacks.
A related complaint has been called the restless leg syndrome. This benign condition involves an inability to find a comfortable and relaxed position for the limbs at night while trying to fall asleep. Patients describe dull aching, burning, drawing or numbness sensations, often bilateral, relieved by moving the legs. The condition can be sufficiently distracting to cause disabling insomnia, both in the patient and his bedmate. The cause is unknown, though there is an association with tension, stress and depression. Mild analgesics or tranquilizers at bedtime are typically effective in ablating the syndrome.
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