PANCE Review for Physician Assistant Certification Exam Prep + CME

The sciatic nerve lies immediately posteriorly to the acetabulum and is the most commonly injured nerve in acetabular fractures. The femoral nerve lies immediately anteriorly to the acetabulum, but is separated from the bony structures of the pelvis by large muscles. In comparison to the sciatic nerve, the femoral nerve is therefore relatively protected during an acetabular fracture. Follow this link for an example of an acetabular fracture.

Reference:
Marx: Rosen’s Emergency Medicine, Concepts and Clinical Practice, 7th ed., 2009

Central cord syndrome is manifested by decreased strength and, to a lesser extent, decreased pain and temperature sensation in the upper--rather than lower--extremities. It is not associated with compromise of the muscles of respiratory function.

Myasthenia gravis is an autoimmune disorder of the neuromuscular junction, which can be complicated by myasthenic crisis and respiratory failure. Indeed, respiratory failure is the most significant complication of myasthenia gravis seen in the emergency department.

Botulism produces a symmetric-descending flaccid paralysis and Guillain-Barre syndrome creates a symmetric-ascending flaccid paralysis. Both may potentially compromise respiratory function and require mechanical ventilation.

Tick paralysis is an acute ascending flaccid paralysis that, without treatment (ie, tick removal), may progress to involve bulbar and diaphragmatic muscles leading to respiratory failure.

References:

Andrus P, Jagoda A. Acute peripheral neurologic lesions. In: Tintinalli JE, et al.Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed., 2011:1159-1166.

Baron BJ, et al. Spine and spinal cord trauma. In: Tintinalli JE, et al Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed., 2011: 1709-1730.

Sloan EP, et al. Chronic neurologic disorders. In: Tintinalli JE, et al Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 7th ed., 2011: 1166-1172.

Findings on foot radiographs for a Lisfranc injury can range from obvious fracture dislocations to virtually normal-appearing x-rays. In order to reliably detect all degrees of a Lisfranc injury, radiographs need to be methodically examined, with an assessment of bones, alignments, and soft tissues. The first 4 metatarsals should each line up with their respective tarsal articulation along their medial edge on anteroposterior and oblique radiographic views. The most consistent relationship is the alignment of the medial edge of the base of the second metatarsal with the medial edge of the middle cuneiform. Disruption of this alignment is diagnostic for Lisfranc injury (see radiographs below). Metatarsal fractures per se are not indicative of a Lisfranc injury, even though fractures can be a component of this type of injury.

Lisfranc fracture, anteroposterior view. Note the lateral dislocation of the second through fifth metatarsals and increased space between the first and second metatarsal, best seen on the anteroposterior view.

Lisfranc fracture, oblique view (same patient as previous image). Note the lateral dislocation of the second through fifth metatarsals and increased space between the first and second metatarsal, best seen on the anteroposterior view.

Review: The foot can be divided into 3 anatomic/functional regions: the hindfoot (calcaneus and talus), midfoot (navicular, cuboid, cuneiforms), and forefoot (metatarsals, phalanges, sesamoids). The hindfoot and midfoot are joined together by the midtarsal joints, which are collectively referred to as Chopart’s joint. The midfoot and forefoot are joined together by the tarsometatarsal joints, which are collectively referred to as Lisfranc’s joint. Any injury (dislocation or fracture-dislocation) to any of the tarsometatarsal joints is called a Lisfranc injury. Since Lisfranc’s joint really refers to 5 joints (the cuneiforms to metatarsals 1 through 3 and the cuboid bone to the fourth and fifth metatarsals), it becomes obvious that “Lisfranc injury” can present in many ways.

Lisfranc injuries are rare because tremendous energy is required to disrupt the joint. Most are incurred in motor vehicle crashes or sports in which the foot remains fixed (equestrian sports, wind surfing). About one third of Lisfranc injuries arise from trivial mechanisms such as stumbles or falls. Usually, Lisfranc injuries are closed.

Reference:
Riyad B. Abu-Laban and Kendall Ho. Marx: Rosen's Emergency Medicine, 7th ed.: Mosby; 2009. CHAPTER 55 - Ankle and Foot

Multiple exogenous and endogenous substances collectively referred to as pyrogens produce fever. The exogenous pyrogens are produced by bacteria, viruses, and their related toxins.

These exogenous pyrogens stimulate cells of the immune system to produce endogenous pyrogens, including cytokines (interleukins, tumor necrosis factor, and interferon), which, in turn, induce the production of prostaglandin E2 in the hypothalamus. The increased level of endogenous prostaglandin E2 raises the set point of the temperature.

The hypothalamus does not release cyclooxygenase inhibitors; rather, external agents, such as aspirin, are cyclooxygenase inhibitors; they LOWER rather than raise temperature. Leukocytes do not release prostaglandin E2 (it is produced by the hypothalamus). Bacteria do not produce or release interleukins, but instead, these are released as endogenous pyrogens by the human immune system in response to bacterial and viral exogenous pyrogens. Thyroxin B2 does not exist.

Reference:

Blum FC, Biros MH. Fever in the adult patient. In: Marx JA, et al, eds. Rosen's Emergency Medicine. 8th ed., 2014:119-123.

Pain from pulmonary embolism is more often lateral pleuritic and abrupt in onset. Dyspnea is often present and at times may be the prominent symptom. Pregnancy or recent pregnancy is a recognized risk factor.

Reference:

Brown J. Chest pain. In: Marx JA, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed., 2014:221.