A needlestick injury, percutaneous injury, or percutaneous exposure incident is the penetration of skin by a needle or other sharp object, which was in contact with blood, tissue, or other body fluid before the exposure. Occupational needlestick injuries primarily affect healthcare workers, who make up 80% of needlestick injuries in the United States. Various other occupations are also at increased risk of needlestick injury, including law enforcement, laborers, tattoo artists, food preparers, and agricultural workers. Though the acute physiological effects of a needlestick injury are generally negligible, these devices can transmit blood-borne diseases, placing those exposed at increased risk of contracting infectious diseases, such as hepatitis B (HBV), hepatitis C (HCV), and the human immunodeficiency virus (HIV). Among healthcare workers and laboratory personnel worldwide, more than 25 blood-borne viruses have been reported to be caused by needlestick injuries.

It is estimated that half of all occupational needlestick injuries are not reported. Additionally, an unknown number of occupational needlestick injuries are reported by the affected employee, yet due to organizational failure, institutional record of the injury does not exist. Increasing recognition of the unique occupational hazard posed by needlestick injuries, as well as the development of efficacious interventions to minimize the largely preventable occupational risk, encouraged legislative regulation in the US, causing a decline in needlestick injuries among healthcare workers.

An occupational injury is bodily damage resulting from working. The most common organs involved are the spine, hands, the head, lungs, eyes, skeleton, and skin. Occupational injuries can result from exposure to occupational hazards (physical, chemical, biological, or psychosocial), such as temperature, noise, insect or animal bites, blood-borne pathogens, aerosols, hazardous chemicals, radiation, and occupational burnout.

While many prevention methods are set in place, injuries may still occur due to poor ergonomics, manual handling of heavy loads, misuse or failure of equipment, exposure to general hazards, and inadequate safety training.

Needlestick injuries are a common event in the healthcare environment. When drawing blood, administering an intramuscular or intravenous drug, or performing any procedure involving sharps, accidents can occur and facilitate the transmission of blood-borne diseases. Injuries also commonly occur during needle recapping or via improper disposal of devices into an overfilled or poorly located sharps container. Lack of access to appropriate personal protective equipment, or alternatively, employee failure to use provided equipment, increases the risk of occupational needlestick injuries. Needlestick injuries may also occur when needles are exchanged between personnel, loaded into a needle driver, or when sutures are tied off while still connected to the needle. Needlestick injuries are more common during night shifts and for less experienced people; fatigue, high workload, shift work, high pressure, or high perception of risk can all increase the chances of a needlestick injury. During surgery, a surgical needle or other sharp instrument may inadvertently penetrate the glove and skin of operating room personnel; scalpel injuries tend to be larger than a needlestick. Generally, needlestick injuries cause only minor visible trauma or bleeding; however, even in the absence of bleeding the risk of viral infection remains.

The World Health Organization (WHO) developed the International Classification of External Causes of Injury (ICECI). Under this system, injuries are classified by

- mechanism of injury;

- objects/substances producing injury;

- place of occurrence;

- activity when injured;

- the role of human intent;

and additional modules. These codes allow the identification of distributions of injuries in specific populations and case identification for more detailed research on causes and preventive efforts.

The United States Bureau of Labor Statistics developed the Occupational Injury and Illness Classification System (OIICS). Under this system injuries are classified by

- nature,

- part of body affected,

- source and secondary source, and

- event or exposure.

The OIICS was first published in 1992 and has been updated several times since.

The Orchard Sports Injury Classification System (OSICS) is used to classify injuries to enable research into specific sports injuries.

Injury is damage to the body caused by external force. This may be caused by accidents, falls, hits, weapons, and other causes. Major trauma is injury that has the potential to cause prolonged disability or death.

In 2013, 4.8 million people died from injuries, up from 4.3 million in 1990. More than 30% of these deaths were transport-related injuries. In 2013, 367,000 children under the age of five died from injuries, down from 766,000 in 1990. Injuries are the cause of 9% of all deaths, and are the sixth-leading cause of death in the world.

Severe head injuries can lead to permanent vegetative states or death, therefore being able to recognize symptoms and get medical attention is very important. Symptoms of a severe closed-head injury include:

- coma

- seizures

- loss of consciousness

Because the brain swelling that produces these symptoms is often a slow process, these symptoms may not surface for days to weeks after the injury.

Common symptoms of a closed-head injury include:

- headache

- dizziness

- nausea

- slurred speech

- vomiting

Headache is the most common mTBI symptom. Others include dizziness, vomiting, nausea, lack of motor coordination, difficulty balancing, or other problems with movement or sensation. Visual symptoms include light sensitivity, seeing bright lights, blurred vision, and double vision. Tinnitus, or a ringing in the ears, is also commonly reported. In one in about seventy concussions, concussive convulsions occur, but seizures that take place during or immediately after concussion are not "post-traumatic seizures", and, unlike post-traumatic seizures, are not predictive of post-traumatic epilepsy, which requires some form of structural brain damage, not just a momentary disruption in normal brain functioning. Concussive convulsions are thought to result from temporary loss or inhibition of motor function, and are not associated either with epilepsy or with more serious structural damage. They are not associated with any particular sequelae, and have the same high rate of favorable outcomes as concussions without convulsions.

Symptoms reported by sufferers include: pain and aching to the neck and back, referred pain to the shoulders, sensory disturbance (such as pins and needles) to the arms and legs, and headaches. Symptoms can appear directly after the injury, but often are not felt until days afterwards. Whiplash is usually confined to the spine. The most common areas of the spine affected by whiplash are the neck and middle of the spine. "Neck" pain is very common between the shoulder and the neck. The "missing link" of whiplash may be towards or inside the shoulder and this would explain why neck therapy alone frequently does not give lasting relief.

Cognitive symptoms following whiplash trauma, such as being easily distracted or irritated, seems to be common and possibly linked to a poorer prognosis.

Cognitive symptoms include confusion, disorientation, and difficulty focusing attention. Loss of consciousness may occur, but is not necessarily correlated with the severity of the concussion if it is brief. Post-traumatic amnesia, in which events following the injury cannot be recalled, is a hallmark of concussion. Confusion, another concussion hallmark, may be present immediately or may develop over several minutes. A person may repeat the same questions, be slow to respond to questions or directions, have a vacant stare, or have slurred or incoherent speech. Other MTBI symptoms include changes in sleeping patterns and difficulty with reasoning, concentrating, and performing everyday activities.

Concussion can result in changes in mood including crankiness, loss of interest in favorite activities or items, tearfulness, and displays of emotion that are inappropriate to the situation. Common symptoms in concussed children include restlessness, lethargy, and irritability.

Symptoms are dependent on the type of TBI (diffuse or focal) and the part of the brain that is affected. Unconsciousness tends to last longer for people with injuries on the left side of the brain than for those with injuries on the right. Symptoms are also dependent on the injury's severity. With mild TBI, the patient may remain conscious or may lose consciousness for a few seconds or minutes. Other symptoms of mild TBI include headache, vomiting, nausea, lack of motor coordination, dizziness, difficulty balancing, lightheadedness, blurred vision or tired eyes, ringing in the ears, bad taste in the mouth, fatigue or lethargy, and changes in sleep patterns. Cognitive and emotional symptoms include behavioral or mood changes, confusion, and trouble with memory, concentration, attention, or thinking. Mild TBI symptoms may also be present in moderate and severe injuries.

A person with a moderate or severe TBI may have a headache that does not go away, repeated vomiting or nausea, convulsions, an inability to awaken, dilation of one or both pupils, slurred speech, aphasia (word-finding difficulties), dysarthria (muscle weakness that causes disordered speech), weakness or numbness in the limbs, loss of coordination, confusion, restlessness, or agitation. Common long-term symptoms of moderate to severe TBI are changes in appropriate social behavior, deficits in social judgment, and cognitive changes, especially problems with sustained attention, processing speed, and executive functioning. Alexithymia, a deficiency in identifying, understanding, processing, and describing emotions occurs in 60.9% of individuals with TBI. Cognitive and social deficits have long-term consequences for the daily lives of people with moderate to severe TBI, but can be improved with appropriate rehabilitation.

When the pressure within the skull (intracranial pressure, abbreviated ICP) rises too high, it can be deadly. Signs of increased ICP include decreasing level of consciousness, paralysis or weakness on one side of the body, and a blown pupil, one that fails to constrict in response to light or is slow to do so. Cushing's triad, a slow heart rate with high blood pressure and respiratory depression is a classic manifestation of significantly raised ICP. Anisocoria, unequal pupil size, is another sign of serious TBI. Abnormal posturing, a characteristic positioning of the limbs caused by severe diffuse injury or high ICP, is an ominous sign.

Small children with moderate to severe TBI may have some of these symptoms but have difficulty communicating them. Other signs seen in young children include persistent crying, inability to be consoled, listlessness, refusal to nurse or eat, and irritability.

Presentation varies according to the injury. Some patients with head trauma stabilize and other patients deteriorate. A patient may present with or without neurological deficit. Patients with concussion may have a history of seconds to minutes unconsciousness, then normal arousal. Disturbance of vision and equilibrium may also occur. Common symptoms of head injury include coma, confusion, drowsiness, personality change, seizures, nausea and vomiting, headache and a lucid interval, during which a patient appears conscious only to deteriorate later.

Symptoms of skull fracture can include:

- leaking cerebrospinal fluid (a clear fluid drainage from nose, mouth or ear) may be and is strongly indicative of basilar skull fracture and the tearing of sheaths surrounding the brain, which can lead to secondary brain infection.

- visible deformity or depression in the head or face; for example a sunken eye can indicate a maxillar fracture

- an eye that cannot move or is deviated to one side can indicate that a broken facial bone is pinching a nerve that innervates eye muscles

- wounds or bruises on the scalp or face.

- Basilar skull fractures, those that occur at the base of the skull, are associated with Battle's sign, a subcutaneous bleed over the mastoid, hemotympanum, and cerebrospinal fluid rhinorrhea and otorrhea.

Because brain injuries can be life-threatening, even people with apparently slight injuries, with no noticeable signs or complaints, require close observation; They have a chance for severe symptoms later on. The caretakers of those patients with mild trauma who are released from the hospital are frequently advised to rouse the patient several times during the next 12 to 24 hours to assess for worsening symptoms.

The Glasgow Coma Scale (GCS) is a tool for measuring degree of unconsciousness and is thus a useful tool for determining severity of injury. The Pediatric Glasgow Coma Scale is used in young children. The widely used PECARN Pediatric Head Injury/Trauma Algorithm helps physicians weigh risk-benefit of imaging in a clinical setting given multiple factors about the patient—including mechanism/location of injury, age of patient, and GCS score.

Diffuse axonal injury, or DAI, usually occurs as the result of an acceleration or deceleration motion, not necessarily an impact. Axons are stretched and damaged when parts of the brain of differing density slide over one another. Prognoses vary widely depending on the extent of damage.

In medicine, a stinger, also called a "burner" or "nerve pinch injury", is a neurological injury suffered by athletes, mostly in high-contact sports such as ice hockey, rugby, American football, and wrestling. The spine injury is characterized by a shooting or stinging pain that travels down one arm, followed by numbness and weakness. Many athletes in contact sports have suffered stingers, but they are often unreported to medical professionals.

Anyone who experiences significant trauma to his or her head or neck needs immediate medical evaluation for the possibility of a spinal injury. In fact, it's safest to assume that trauma victims have a spinal injury until proven otherwise because:

- The time between injury and treatment can be critical in determining the extent of complications and the amount of recovery

- A serious spinal injury is not always immediately obvious. If it is not recognized, more severe injury may occur

- Numbness or paralysis may develop immediately or come on gradually as bleeding or swelling occurs in or around the spinal cord

Systems also exist to classify TBI by its pathological features. Lesions can be extra-axial, (occurring within the skull but outside of the brain) or intra-axial (occurring within the brain tissue). Damage from TBI can be focal or diffuse, confined to specific areas or distributed in a more general manner, respectively. However, it is common for both types of injury to exist in a given case.

Diffuse injury manifests with little apparent damage in neuroimaging studies, but lesions can be seen with microscopy techniques post-mortem, and in the early 2000s, researchers discovered that diffusion tensor imaging (DTI), a way of processing MRI images that shows white matter tracts, was an effective tool for displaying the extent of diffuse axonal injury. Types of injuries considered diffuse include edema (swelling) and diffuse axonal injury, which is widespread damage to axons including white matter tracts and projections to the cortex. Types of injuries considered diffuse include concussion and diffuse axonal injury, widespread damage to axons in areas including white matter and the cerebral hemispheres.

Focal injuries often produce symptoms related to the functions of the damaged area. Research shows that the most common areas to have focal lesions in non-penetrating traumatic brain injury are the orbitofrontal cortex (the lower surface of the frontal lobes) and the anterior temporal lobes, areas that are involved in social behavior, emotion regulation, olfaction, and decision-making, hence the common social/emotional and judgment deficits following moderate-severe TBI. Symptoms such as hemiparesis or aphasia can also occur when less commonly affected areas such as motor or language areas are, respectively, damaged.

One type of focal injury, cerebral laceration, occurs when the tissue is cut or torn. Such tearing is common in orbitofrontal cortex in particular, because of bony protrusions on the interior skull ridge above the eyes. In a similar injury, cerebral contusion (bruising of brain tissue), blood is mixed among tissue. In contrast, intracranial hemorrhage involves bleeding that is not mixed with tissue.

Hematomas, also focal lesions, are collections of blood in or around the brain that can result from hemorrhage. Intracerebral hemorrhage, with bleeding in the brain tissue itself, is an intra-axial lesion. Extra-axial lesions include epidural hematoma, subdural hematoma, subarachnoid hemorrhage, and intraventricular hemorrhage. Epidural hematoma involves bleeding into the area between the skull and the dura mater, the outermost of the three membranes surrounding the brain. In subdural hematoma, bleeding occurs between the dura and the arachnoid mater. Subarachnoid hemorrhage involves bleeding into the space between the arachnoid membrane and the pia mater. Intraventricular hemorrhage occurs when there is bleeding in the ventricles.

The "Québec Task Force" ("QTF") has divided whiplash-associated disorders into five grades.

- Grade 0: no neck pain, stiffness, or any physical signs are noticed

- Grade 1: neck complaints of pain, stiffness or tenderness only but no physical signs are noted by the examining physician.

- Grade 2: neck complaints and the examining physician finds decreased range of motion and point tenderness in the neck.

- Grade 3: neck complaints plus neurological signs such as decreased deep tendon reflexes, weakness and sensory deficits.

- Grade 4: neck complaints and fracture or dislocation, or injury to the spinal cord.

Penile fractures are the result of rupture of the tunica albuginea. They are fairly rare and can co-occur with partial or complete urethral rupture, though this is rare. Urethral damage occurs in 10–38% of cases. Fractures are treated with emergency surgery, and can be diagnosed with ultrasound, especially in pediatric cases. Penile fractures are caused by trauma to the erect penis, typically by suddenly bending it laterally during penetrative intercourse with the receptive partner on top of the penetrating partner, or during masturbation. They can be diagnosed by the "eggplant sign" and are characterized by a loud popping sound at the time of the injury, the result of the tunica albuginea rupturing. Other symptoms include severe pain, loss of erection, and swelling. Symptoms of urethral injury include hematuria, blood at the meatus, and dysuria. If left untreated, complications result in 28–53% of cases; these include permanent curvature of the penis, fistula, urethral diverticulum, priapism, and erectile dysfunction.

Degloving and avulsion injuries involve the removal of the penis skin, which is a serious medical emergency. Treatment of these injuries involves either closure of the torn skin, or a skin graft to replace the skin lost in the injury. Skin grafts are constructed to attempt to preserve erectile function and sensation.

A common condition associated with PCS is headache. While most people have headaches of the same type they experienced before the injury, people diagnosed with PCS often report more frequent or longer-lasting headaches. Between 30% and 90% of people treated for PCS report having more frequent headaches and between 8% and 32% still report them a year after the injury.

Dizziness is another common symptom reported in about half of people diagnosed with PCS and is still present in up to a quarter of them a year after the injury. Older people are at especially high risk for dizziness, which can contribute to subsequent injuries and higher rates of mortality due to falls.

About 10% of people with PCS develop sensitivity to light or noise, about 5% experience a decreased sense of taste or smell, and about 14% report blurred vision. People may also have double vision or ringing in the ears, also called tinnitus. PCS may cause insomnia, fatigue, or other problems with sleep.

A stinger is an injury that is caused by restriction of the nerve supply to the upper extremity via the brachial plexus. The brachial plexus is formed by the anterior rami of the nerves at the 5th cervical level of the spinal cord all the way to the nerves at the 1st thoracic level of the spinal cord. The brachial plexus innervates the upper extremity as well as some muscles in the neck and shoulder. Damage to the brachial plexus can occur when the nerves are stretched too far from the head and neck; specifically the upper trunk of the plexus –nerve roots at the 5th and 6th cervical level –are primarily affected. The upper trunk provides part of the nerve to supply to the upper extremity via the Musculocutaneous, Axillary, Radial and Median nerves. It is for this reason that stingers do not affect both arms simultaneously, however it is possible for both arms to accrue injuries. Repeated nerve trauma can cause recurring stingers, chronic pain, and muscle weakness, while recovery can take weeks to months in severe cases.

The primary symptom, hemorrhage, presents differently depending on the degree of injury, with the symptoms of major hemorrhage, shock, abdominal pain, and distention being clinically obvious. Minor hemorrhage often presents as upper left quadrant pain. Patients with unexplained left upper quadrant pain, particularly if there is evidence of hypovolemia or shock, are generally inquired regarding any recent trauma.

In the past, the term PCS was also used to refer to immediate physical symptoms or post-concussive symptoms following a minor TBI or concussion. The severity of these symptoms typically decreases rapidly. In addition, the nature of the symptoms may change over time: acute symptoms are most commonly of a physical nature, while persisting symptoms tend to be predominantly psychological. Symptoms such as noise sensitivity, problems with concentration and memory, irritability, depression, and anxiety may be called 'late symptoms' because they generally do not occur immediately after the injury, but rather in the days or weeks after the injury. Nausea and drowsiness commonly occur acutely following concussion. Headache and dizziness occur immediately after the injury, but also can be long lasting.

Virtually all organ systems experience a progressive decline in function as a result of the aging process. One example is a decline in circulatory system function caused in part by thickening of the cardiac muscle. This can lead to congestive heart failure or pulmonary edema.

Atrophy of the brain begins to accelerate at around seventy years of age, which leads to a significant reduction in brain mass. Since the skull does not decrease in size with the brain, there is significant space between the two when this occurs which puts the elderly at a higher risk of a subdural hematoma after sustaining a closed head injury. The reduction of brain size can lead to issues with eyesight, cognition and hearing.

The primary concern in any splenic trauma is internal hemorrhage, though the exact amount of hemorrhage may be small or large, depending on the nature and degree of injury. Small or minor injuries often heal spontaneously, especially in children. Larger injuries hemorrhage extensively, often causing hemorrhagic shock. A splenic hematoma sometimes ruptures, usually in the first few days, although rupture can occur from hours to even months after injury.

A progressive decline in central nervous system function leads to a loss of proprioception, balance and overall motor coordination, as well as a reduction in eye–hand coordination, reaction time and an unsteady gait. These degenerative changes are often accompanied by osteoarthritis (degenerative joint disease), which leads to a reduction in the range of motion of the head, neck and extremities. Furthermore, elderly people frequently take multiple medications for control of various diseases and conditions. The side effects of some of these medications may either predispose to injury, or may cause a minor trauma to result in a much more severe condition. For example, a person taking warfarin (Coumadin) and/or clopidogrel (Plavix) may experience a life-threatening intracranial hemorrhage after sustaining a relatively minor closed head injury, as a result of the defect in the hemostatic mechanism caused by such medications. The combined effects of these changes greatly predisposes elderly people to traumatic injury. Both the incidence of falls and the severity of associated complications increase with advancing age.