Whiplash
Whiplash
Definition
Whiplash is an injury resulting from a sudden extension or flexion of the neck. Whiplash can also be termed neck sprain or neck strain or, more technically, cervical acceleration/deceleration trauma. It is most often associated with being struck from behind in a car, although it also occurs during contact sports, falls, or other physical activities. Whiplash may also cause damage to vertebrae, ligaments, cervical muscles, or nerve roots.
Description
Whiplash occurs when the body is struck, usually from behind, and the head travels backwards to catch up with the body. The neck will flex until either the facet joints in the back of the vertebrae or the anterior longitudinal ligament in the front of the vertebrae stop the motion.
The muscles that are most often injured during an impact that causes whiplash are the sternocleidomastoids and the longus colli. The sternocleidomastoids are the large straplike muscles running down the front of the neck that pop out when the jaw is flexed. They are used to turn and support the head. The longus colli is a muscle that runs directly in front of the spine is used to turn the head from side to side and to bend the neck forward. The longus colli muscle aids the sternocleidomastoids in holding up the head and moving the neck. Often, the lognus colli muscle is weakened during whiplash and the sternocleidomastoid muscles become overworked as they compensate.
The facet joints in the anterior of the neck may also be damaged during a whiplash injury. There are two facet joints on the back of each vertebra. They are about a centimeter in size and guide the movement of the spine. When the neck bends backward during a whiplash impact, the joints can be compressed and then swell in response. This can cause pain , both in the neck and can also refer pain to other parts of the body. For example, if the facet joints between the second and third cervical vertebrae are compressed, pain may be felt in the back of the head.
A whiplash impact can also damage the anterior longitudinal ligament, which is a tough band of tissue that runs down the front of the vertebral column and holds the vertebral bones together. In automobile accidents, this ligament is often overstretched or torn. If it is torn, it can lead to vertebral disc herniation or to excessive movement of the spinal column. Such movement can result in pain spasms in the neck, cracking and grinding in the neck, or even numbness in the hands and feet.
Whiplash can also result in a herniated vertebral disc. The vertebral bones are cushioned between vertebral discs that are made up of an interior gel-like substance surrounded by a tougher outer layer. If this outer layer becomes damaged, the disc may rupture and the gel-like interior will be compressed out. The ruptured disc can put pressure on adjacent nerve roots and cause tingling, numbness or burning.
Damage to the central nervous system or the peripheral nervous system may occur during a whiplash injury. Most of the damage to the nervous systems involves compression injuries during which pressure is applied to nervous tissues, although damage can also be caused by stretching or torquing (twisting) of nervous tissues. In severe cases, compression injuries can affect the brain resulting in subdural or extradural hematomas (pooling of blood between the brain and the skull). Symptoms of this complication include anosmia (loss of smell), double vision, brief loss of consciousness, confusion and loss of motor skills.
Compression, stretching, and torque injuries to the spinal cord may also occur during trauma associated with whiplash. The most frequently occurring is root syndrome. Nerve roots exit the spinal cord on both sides of the body between vertebrae. When the spaces between vertebrae, also called foramen, become compressed, the nerve roots can be compressed or damaged. This can result in slight numbness, burning or tingling in any of the parts of the body that the nerve enervates. In more severe car accidents, whiplash can cause more critical damage to the spinal cord resulting in major neurological dysfunction or paralysis below the location of the injury. The important variables controlling the severity of the symptoms appear to be the force and the direction of the impact on the spine. As the area impacted by the trauma increases due to increased force, a greater portion of the cord is involved resulting in greater neurological dysfunction.
The peripheral nervous system can also suffer damage in a whiplash injury. These nerves can be compressed in the vertebral foramen and can also be stretched or compressed by other anatomical structures along their path. Only a very small compression or stretching is required to interrupt blood flow to a nerve cell. For example, blood flow to a nerve cell can be completely stopped if the nerve cell is stretched to 15% more than its original length. Such trauma to a nerve cell can result in numbness or tingling in the region affected by the nerve, but usually not pain. It is the irritation of the nerve following the trauma that causes pain in the peripheral nervous system.
Demographics
Anyone can suffer from whiplash, in particular people who drive in automobiles. Whiplash has been documented in people who are driving as slowly as five miles per hour. About 20% of people who are involved in rearend accidents in cars suffer symptoms of whiplash. In the United States, it is estimated that about 1.8 million people are subject to chronic pain and disability after an automobile accident, the majority of whom suffer from neck pain.
Causes and symptoms
Symptoms of whiplash include neck pain and stiffness, shoulder pain and stiffness, lower back pain , headaches in the back of the head, pain, and/or tingling in the hand or arm, dizziness , ringing in the ears and blurred vision. Often the pain associated with whiplash worsens several days following the injury. Some people suffer cognitive or psychological symptoms including difficulty concentrating, difficulty sleeping, memory loss, depression and irritability.
Symptoms of whiplash appear to follow one of two courses. In most people, symptoms will slowly abate within approximately three months. In a smaller proportion of people who experience whiplash, the symptoms become chronic and disability may result.
Diagnosis
Orthopedists (physicians specializing in the bones and joints) use a variety of diagnostic tools to evaluate the extent of injury following whiplash. This usually begins with a history of the accident and the symptoms experienced. A physical examination allows the physician to evaluate the range of motion in the neck, locations of pain in the neck, arms and legs, and function of nerves. An xray is almost always used to determine if any vertebrae have been damaged in the accident. However, because many of the injuries are to soft tissues, they are not well visualized using a standard x ray. The orthopedist may then recommend other diagnostic procedures that visualize these tissues more effectively. Magnetic resonance imaging (MRI) allows for visualization of the spinal cord and nerve roots that emerge between the vertebrae. A computed tomography study (CT ) gives precise information about the bone and spinal canal using specialized xray technology. Another technology called a myelogram combines x rays with an injection of dye into the spinal canal and allows for detailed visualization of the spinal canal and nerve roots. An electromyogram (EMG) may also be used to determine the health of nerves and muscles using electrical impulses.
Treatment
Treatment for whiplash includes a variety of techniques and medications including exercises, pain-relieving medications, traction, massage, heat and ice, and ultrasound, depending on the symptoms. Although a physician should evaluate people who suffer whiplash, most of the time whiplash can be treated using home treatments and extensive medical care is not prescribed.
Both heat and cold are useful for treatment of symptoms of whiplash. Initial treatment for whiplash usually includes cold packs of ice applied to the neck for the first 24 hours. Heat may then be used to relieve pain throughout the neck and shoulders either using heating pads or hot showers. Physical therapists can apply deep heat treatments using ultrasound equipment.
Medications are useful for relieving acute pain associated with whiplash. Non-steroidal anti-inflammatory medications can be very helpful in relieving pain. Antidepressants may be prescribed because they inhibit the transfer of nervous signals along pain pathways.
A soft cervical collar may provide some relief for symptoms of whiplash; however, most physicians recommend that the use of the collar be limited to two to three weeks. Using the cervical collar for long periods may cause muscle strength to decrease and inhibit muscle flexibility.
Physicians have found that movement is important in preventing chronic symptoms of whiplash. Many doctors assert that simple exercises such as walking, muscle strengthening, and range of motion exercises help improve symptoms more quickly than remaining sedentary. In 2000, a study reported in the journal Spine demonstrated that patients who frequently performed a set of exercises immediately following an injury that caused whiplash recovered faster than patients who exercised less. The more active group performed a set of repetitive motion exercises 10 times an hour beginning within 96 hours of injury, while the less active group performed exercises a few times a day beginning two weeks after the injury. Of the more active group, nearly 40% reported that they had no symptoms of whiplash six months following the accident, compared with only 5% of the less active group.
Traction, under the supervision of an orthopedic professional, removes the pressure from the neck, and some people report relief from pain for several hours to several days following treatments. Physical therapy and/chiropractic adjustments are often prescribed to treat symptoms of whiplash. In rare cases, surgery is required to correct whiplash injuries.
Clinical trials
The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) conducting a study in 2004 focused on preventing acute pain, such as that associated with whiplash, from becoming chronic pain. Research suggests that the emotional response to an injury to the neck, particularly fear of reinjury, contributes significantly to the development of chronic pain from whiplash. The study focused on two anxiety-reducing treatments as a way to prevent such chronic pain from developing. The principal investigator on the two-year study is Dennis C. Turk, Ph.D. (telephone number: 206-543-3387, or email: [email protected]). Information is available on the institute's website at <http://www.depts.washington.edu/wads>.
Resources
BOOKS
Foreman, Stephen M. and Arthur C. Croft. Whiplash Injuries: The Cervical Acceleration/Deceleration Syndrome. Second Edition. Philadelphia: Lippincott, Williams & Wilkins, 1995.
PERIODICALS
Cote, P., J. D. Cassidy, L. Carroll, et al. "A systematic review of the prognosis of acute whiplash and a new conceptual framework to synthesize the literature." Spine 26, no. 19 (2001): e445–e458.
Rosenfeld, M., R. Gunnarsson, and P. Borenstein. "Early Intervention in whiplash-associated disorders: A comparison of two treatment protocols." Spine 25, no. 14 (2000): 1882–1787.
OTHER
Centeno, Christopher J. "What is Whiplash?" Whiplash 101. (January 19, 2004). <http://www.whiplash101.com/default1.htm>.
Mayo Clinic Staff. "Neck Pain: Sometimes Serious." The Mayo Clinic. (February 07, 2002). <http://www.mayoclinic.com/invoke.cfm?id=HQ01111>.
"Neck Pain." American Academy of Orthopaedic Surgeons. 2000. (January 23, 2004). http://orthoinfo.aaos.org/brochure/thr_report.cfm?thread_id=11&topcategory=neck.
"Neck Sprain." The America Academy of Orthopaedic Surgeons. May 2000 (January 23, 2004). http://orthoinfo.aaos.org/fact/thr_report.cfm?thread_id=141&topcategory=neck.
"Whiplash." The America Academy of Orthopaedic Surgeons. October 2000 (January 23, 2004). http://orthoinfo.aaos.org/fact/thr_report.cfm?Thread_ID=232&topcategory=Neck.
"NINDS Whiplash Information Page." National Institute of Neurological Disorders and Stroke. July 1, 2001 (January 23, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/whiplash.htm?format=printable>.
ORGANIZATIONS
American Chronic Pain Association (ACPA). P.O. Box 850, Rocklin, CA 95677. (916) 632-0922 or (800) 533-3231; Fax: (916) 632-3208. [email protected].
National Chronic Pain Outreach Association (NCPOA). P.O. Box 274, Millboro, VA 24460. (540) 862-9437; Fax: (540) 862-9485. [email protected].
National Headache Foundation. 820 N. Orleans, Suite 217, Chicago, IL 60610. (773) 388-6399 or (888) NHF-5552; Fax: (773) 525-7357. [email protected]. <http://www.headaches.org>.
Juli M. Berwald, Ph.D.
Whiplash
Whiplash
Definition
Whiplash is the mechanism that causes the neck injury often suffered in a rear-end automobile collision. People also use the same term, whiplash, to mean the resultant neck injury itself. Whiplash produces a wide range of symptoms, but almost all victims experience pain. About 1,000,000 whiplash injuries occur in the United States every year.
Description
An occupant of a car struck suddenly from the rear undergoes rapid acceleration and deceleration. The head and neck swing freely while the body remains supported by the seat and seatbelts. The rapid movement of the head causes variable amounts of hyperextension, hyperflexion, stretching, and twisting of neck structures, in a fashion similar to the snapping of a whip.
The structures often affected include muscles, ligaments, nerves, intervertebral disks, and spinal joints. Specific damage may range from minimal strains to complicated tears, hemorrhage, and joint injury, as shown by animal studies and autopsies of accident victims.
Causes and symptoms
Besides motor vehicle accidents, causes of whiplash include sports and other recreational activities, falls, and fights. Women tend to have more persistent symptoms than men do, perhaps because women's smaller neck muscles are more vulnerable.
Symptoms following a whiplash injury may begin immediately or any time up to a few days later. Symptoms include variable combinations of:
- pain or stiffness in the neck, jaw, shoulders, arms, or back
- dizziness
- headache
- loss of feeling in the upper extremities
- problems with vision or hearing
- problems with concentration
- depression, anxiety, or other changes in mood
Symptoms may last for no more than a day or two, or may persist for months or years.
Diagnosis
Many patients with whiplash receive evaluation by emergency medical technicians (EMTs) at the scene of an accident, always starting with the ABCs of resuscitation: airway, breathing, and circulation. At the same time, in head or neck trauma, initial care providers always worry about the possibility of dangerous injury to the spine bones or spinal cord. Often, the EMTs will immobilize the neck in a stiff brace and strap the patient flat on a board, until a physician determines that it is safe for the neck to move. This minimizes the risk that any serious injury could progress and cause irreversible nerve damage. Unfortunately, this immobilization is usually very uncomfortable for the patient.
When such a patient arrives at the emergency department (ED), the nurse will further assess the patient for stable vital signs, proper alertness, and good ability to move and feel the extremities. A patient strapped to a spine immobilization board often demands to remove the neck brace and get up, but the nurse must ensure that the patient remains still until cleared by the physician. The nurse quickly asks the doctor to examine the patient.
Another danger is that a patient may vomit while immobilized. This presents a risk for aspiration of stomach contents, which can threaten breathing. The nurse must be alert to quickly turn the patient on the side, while still immobilized and with the neck brace still in place, to prevent this complication.
The physician obtains the patient's description of the event, then looks for injury to other organs, especially in the head, chest, abdomen, and back. The doctor will check for bony tenderness or limitation of movement, and examine the functions of deep tendon reflexes plus motor and sensory nerves. When the physician is confident that no injury threatens the spinal cord the patient is "cleared." The physician will remove the brace and free the patient from the rigid board.
The physician may order x-ray studies to exclude fracture or displacement of bone, but in typical whiplash these tests rarely show any abnormality. When there is severe or persistent pain or numbness, magnetic resonance imaging (MRI) may detect more subtle damage.
Treatment
Patients should apply ice in the first 24-48 hours. Physicians prescribe medicines such as ibuprofen (Motrin, Advil) or aspirin, acetaminophen, muscle relaxants, or narcotics (codeine, hydrocodone, Vicodin).
Use of soft cervical collars is controversial. Many doctors prescribe them, but some studies have shown that these devices prolong the return to normal activities. Physical therapy or exercises may reduce pain or limitation of movement.
Many patients use balms or salves, and seek alternative treatments such as chiropractic manipulation, biofeedback, acupuncture, or acupressure. In cases of protracted symptoms, patients may benefit from traction, ultrasound treatments, local injections of cortisone, or use of a nerve stimulator.
Prognosis
The course of an individual whiplash injury is unpredictable. Most people improve within a month, but 20% or more have symptoms that last longer than a year. The risk of greater symptoms increases for an unrestrained victim of a rear-end collision, or for one whose head is turned or tilted at the time of injury.
Controversy surrounds the role that accident-related litigation plays in delaying recovery from whiplash. An April 2000, article in The New England Journal of Medicine examined this issue. The authors showed a decreased incidence and improved prognosis of whiplash injury when the province of Saskatchewan changed to a new insurance claim system that eliminated payments for pain and suffering. However, other authors downplay the effect of psychosocial factors on recovery from whiplash.
Health care team roles
The EMT performs rescue, assessment, and initial treatment at the scene of an accident. A nurse in the ED or medical office also assesses the patient with whiplash. The nurse carries out physician orders for medication and treatments, monitors the patient throughout the stay, and instructs the patient and caregivers before discharge. The aide assists the nurse.
A radiology technician performs the x-ray or MRI studies. A physical therapist helps with exercise, massage, ultrasound, and other treatments. A social worker may coordinate later care.
Prevention
Proper adjustment of the automobile headrest is important to reduce the severity of a whiplash injury, because a headrest that does not come up behind the head offers no protection. Driving habits that reduce the frequency of abrupt stops make it less likely that a driver will suffer a rear-end collision.
KEY TERMS
Aspiration— The inhaling of stomach contents or other unwanted material, potentially leading to a form of pneumonia.
Hyperextension— Overstretching toward the back.
Hyperflexion— Overstretching toward the front.
Intervertebral disk— A cushioning structure between two adjacent spine bones.
Resources
BOOKS
Clark, Charles R., et al, ed. The Cervical Spine. Philadelphia: Lippincott-Raven, 1998.
Goetz, Christopher G., and Eric J. Pappert. Textbook of Clinical Neurology. Philadelphia: W. B. Saunders, 1999.
PERIODICALS
Cassidy, J. David, et al. "Effect of Eliminating Compensation for Pain and Suffering on the Outcome of Insurance Claims for Whiplash Injury." New England Journal of Medicine 342, no. 16 (April 20, 2000): 1179-86.
ORGANIZATIONS
American Academy of Orthopaedic Surgeons. 6300 North River Road, Rosemont, IL 60018-4262. (800) 346-AAOS. 〈http://www.aaos.org〉.
Whiplash
WHIPLASH
DEFINITION
Whiplash is an injury that occurs when the neck and head experience a sudden, sharp motion. The injury often affects the bones, muscles, nerves, and tendons of the neck.
DESCRIPTION
About one million whiplash injuries occur in the United States every year. Most occur during car accidents or sporting events. In such cases, an unexpected force jerks the head backward and then, almost immediately, forward causing the bones of the neck to snap out of position. Nerves in the neck may be pinched, resulting in damage to or destruction of certain body parts.
Poor driving habits can increase the risk of whiplash injury. A person who is tired, tense, or under the influence of alcohol may drive carelessly. Bad weather conditions can also increase the chance of an accident. Finally, the medical condition known as osteoarthritis (pronounced AHS-tee-oh-arr-THRY-tiss), which weakens the joint cartilage, increases the risk of whiplash injury (see arthritis entry).
CAUSES
Whiplash is likely to occur when a person's muscles are either too tight or too lose. In such cases, the chance of damage to the neck is especially high.
SYMPTOMS
The symptoms of whiplash may occur immediately after an accident. Or they may not develop for hours, days, or weeks after an injury. Some symptoms of whiplash are the following:
- Pain or stiffness in the neck, jaw, shoulders, or arms
- Dizziness
- Headache
- Loss of feeling in an arm or hand
- Nausea and vomiting
Less common symptoms include vision problems and feelings of depression.
DIAGNOSIS
Whiplash injuries are often difficult to diagnose. X rays and other imaging techniques may not reveal any damage to bones or muscles. Diagnosis is usually based, instead, on other techniques, such as observation of a patient's symptoms and a physical examination. Sometimes, further examination of the patient's nervous system may also be necessary.
TREATMENT
Whiplash is usually treated by one or more of three methods: medication, physical therapy, and supportive devices. Medication helps relieve pain and reduce inflammation. Physical therapy is used to realign the spine to relax pinched nerves and improve blood flow. Padded collars and other supportive devices hold the head and neck in position while they heal. In severe cases, cervical traction, may be used. Cervical traction involves a steady pull on the neck to keep it in the correct position as it heals.
Self-care
Some simple methods of self-care can often be used with whiplash injuries. For example, the injured area can be wrapped with ice for ten to twenty minutes every hour for the first day. After twenty-four hours, cold packs can be alternated with heat treatments. Letting a warm shower run on the neck and shoulders for ten to twenty minutes twice a day is recommended. Between showers, warm towels or a heat lamp can be used to warm and soothe the neck for ten to fifteen minutes several times a day.
Gentle massage and attention to one's posture can also be helpful. Sleeping without a pillow can promote healing. The use of a cervical collar, a device that holds the neck in place, or a small rolled towel under the chin can also provide support and prevent muscle fatigue.
Self-care, however, is seldom sufficient for the treatment of whiplash injury. The patient should consult a family doctor, an orthopedic specialist, or a chiropractor after such an injury. Professional care is especially important if the injury results in pain, weakness, or numbness in the face or arms following an injury.
Whiplash: Words to Know
- Cervical traction:
- The process of using a mechanism to create a steady pull on the neck in order to keep it in the correct position while it heals.
- Osteoarthritis:
- A type of arthritis that weakens the joint cartilage. It is most common among the elderly.
PROGNOSIS
With proper treatment, whiplash injuries can usually be cured in a week to a few months after injury occurs. In severe cases, numbness and weakness may last until recovery is complete.
PREVENTION
Whiplash injuries are less likely to occur when one is in good physical health. A proper diet and program of exercise help reduce stress and tension. The use of seatbelts is an important factor in preventing whiplash injuries. Careful, defensive driving techniques also can greatly reduce the risk of injury.
FOR MORE INFORMATION
Books
Ferrari, Robert. The Whiplash Encyclopedia: The Facts and Myths of Whiplash. Gaithersburg, MD: Aspen Publishers, Inc., 1999.
Melton, Michael R. The Complete Guide to Whiplash. Body Mind Publications, 1998.
Whiplash
Whiplash
Definition
Whiplash is a sudden, moderate-to-severe strain affecting the bones, discs, muscles, nerves, or tendons of the neck.
Description
The neck is composed of seven small bones. Known as the cervical spine, these bones:
- support the head
- help maintain an unobstructed enclosure for the spinal cord
- influence the shape and structure of the spine
- affect posture and balance
About 1,000,000 whiplash injuries occur in the United States every year. Most are the result of motor vehicle accidents or collisions involving contact sports. When unexpected force jerks the head back, then forward the bones of the neck snap out of position and irritated nerves can interfere with flow of blood and transmission of nerve impulses. Pinched nerves can damage or destroy the function of body parts whose actions they govern.
Risk factors
Osteoarthritis of the spine increases the risk of whiplash injury. So do poor driving habits, driving in bad weather, or driving when tired, tense, or under the influence of alcohol or other drugs.
Causes and symptoms
Tension shortens and tightens muscles. Fatigue relaxes them. Either condition increases the likelihood that whiplash will occur and the probability that the injury will be severe.
Sometimes symptoms of whiplash appear right away. Sometimes they do not develop until hours, days, or weeks after the injury occurs. Symptoms of whiplash include:
- pain or stiffness in the neck, jaw, shoulders, or arms
- dizziness
- headache
- loss of feeling in an arm or hand
- nausea and vomiting
Depression and vision problems are rare symptoms of this condition.
Diagnosis
Whiplash is difficult to diagnose because x rays and other imaging studies do not always reveal changes in bone structure. Organs affected by nerve damage or reduced blood supply may generate symptoms not clearly related to whiplash.
Diagnosis is based on observation of the patient's symptoms, medical history, physical examination, and neurological studies to determine whether the spine has been injured.
Treatment
Medication, physical therapy, and supportive measures are used to treat whiplash. Chiropractors gently realign the spine to relax pinched nerves or improve blood flow. A patient whose symptoms are severe may wear a soft, padded collar (Thomas collar or cervical collar) until the pain diminishes.
When pressure on the root of the nerve causes loss of strength or sensation in a hand or arm, a cervical traction apparatus may be recommended.
Self-care
Inflammation and cramping can be alleviated by wrapping ice or an ice pack in a thin towel and applying it to the injured area for 10-20 minutes every hour. After the first 24 hours, painful muscle spasms can be prevented by alternating cold packs with heat treatments. Letting a warm shower run on the neck and shoulders for 10-20 minutes twice a day is recommended. Between showers, warm towels or a heat lamp should be used to warm and soothe the neck for 10-15 minutes several times a day.
Improving posture is important, and gentle massage can be beneficial. Sleeping without a pillow promotes healing, and a cervical collar or small rolled towel pinned under the chin can provide support and prevent muscle fatigue.
Alcohol should be avoided. A chiropractor, primary care physician, or orthopedic specialist should be notified whenever a painful neck injury occurs. Another situation requiring attention is if the face or arm weaken or become painful or numb following a neck injury.
Prognosis
With treatment, whiplash can usually be cured in one week to three months after injury occurs. If nerve roots are damaged, numbness and weakness may last until recovery is complete.
Prevention
Chiropractors can recommend diet and exercise techniques to reduce stress and tension. Careful, defensive driving, wearing seatbelts, and using padded automobile headrests can lessen the likelihood of whiplash.
Resources
OTHER
Haggerty, Maureen. "Whiplash." A Healthy MePage. June 7, 1998. 〈http://www.ahealthyme.com/topic/topic100587681〉.
whiplash
whip·lash / ˈ(h)wipˌlash/ • n. 1. [usu. in sing.] the lashing action of a whip: fig. he cringed before the icy whiplash of Curtis's tongue. ∎ the flexible part of a whip or something resembling it.2. injury caused by a severe jerk to the head, typically in a motor-vehicle accident.• v. [tr.] jerk or jolt (someone or something) suddenly, typically so as to cause injury: the force of impact had whiplashed the man's head. ∎ [intr.] move suddenly and forcefully, like a whip being cracked: he rammed the yacht, sending its necklace of lights whiplashing from the bridge.
whiplash
Bibliography
Greenhalgh (ed.) (2000);
Lewis & Darley (1986);
Tschudi-Madsen (1967)