High-Pressure Injection Injuries

In 1937, Rees published a case of a high-pressure injection (HPI) injury to the finger. This injury involved diesel fuel.[1] Before Rees’s report, Hesse had described a similar injury in 1925.[2]

HPI injuries involving grease and paint are considered surgical emergencies, whereas HPI injuries with other substances require careful clinical evaluation, surgical intervention, or both.[3] Clean water and air injuries may result in good functional outcomes with simple monitoring and conservative management (see Treatment). Generally, surgeons should have a low threshold for surgical management of HPI injuries.[4]

For patient education materials, see the Hand, Wrist, Elbow, and Shoulder Center, as well as Finger Injuries, Hand Injuries, and Puncture Wound.

High-pressure guns emit jet streams at pressures of thousands of pounds per square inch (psi). At these extreme pressures, material is forced through the skin, where diffusion can occur along fascial planes, tendon sheaths, and neurovascular bundles.[5]

Various mechanisms can be adduced to explain the clinical picture of HPI injuries. Ischemia, necrosis from high-velocity mechanical impact, the direct toxic effect of the involved chemical, and infection play major roles in these types of injuries.[6, 7, 8, 9] Factors contributing to digital ischemia include massive vessel thrombosis from volatilization of the injected material, temporary vascular spasm as a response to trauma, venous outflow obstruction from tissue distention, and digital artery compression.[10] The volume of material injected into a closed space and the resultant edema can exacerbate ischemia.[11]

The chemical properties of the injected material have a considerable effect on clinical injury. With viscous substances, such as grease and oil-based compounds, dispersion is less marked than it is with more fluid materials. These substances tend not to penetrate the flexor sheath, resulting in infiltration of the surrounding neurovascular bundles. Low-viscosity solvents, such as paint thinners, may disperse more readily into the soft tissues. Injection pressure is also reported to be a factor in the extent of injury.[12]

It has been suggested that the predominant mechanism of tissue damage is chemical irritation and that this is more important than ischemia. Ramos et al concluded that an injection of isotonic sodium chloride solution under high pressure into tissue does not produce a significant inflammatory reaction.[9, 13] Clinically, Pai et al noted that injected water did not induce extensive soft-tissue destruction, even when the injury was treated conservatively.[14]

Paint thinners lead to more extensive damage and may cause lipid dissolution and destruction of tissues, even when not injected under high pressure.[7, 15] Also, paints and paint thinners produce the most severe inflammatory responses, leading to high amputation rates.[5, 16] Grease has been shown to be associated with oleogranulomata formation (a reaction to foreign bodies), fistula formation, fibrosis, and poor functional outcomes.[8, 15, 17] Joint contractures and ankylosis are also seen.[18]

Common substances involved in HPI injuries include the following[18, 19, 20] :

• Grease (accounting for 57% of injuries, at pressures of up to 5000-10,000 psi)
• Paint (up to 5000 psi; see the images below)
• Diesel fuel (accounting for 14% of injuries, with pressures of up to 2000-6000 psi)

In a 1970 report, Kaufman compared the kinetic energy from a grease gun to a 1000-kg weight falling from a height of 25 cm.[6] Injuries with compressed air (at pressures of up to 50-300 psi) and high-pressure water injection (up to 6000-8000 psi) are also seen.[21, 22, 12, 23, 24, 25, 26] HPI injuries continue to be caused by an increasing number of substances, including paint, wax, molten metal, air, water, paint thinner, and other solvents.[27, 28]

Although more than 100 case reports of HPI injuries of the hand can be found in the literature, the incidence is difficult to assess. Nonetheless, a group from the University of Colorado described an estimated incidence of 1 in 600 hand injuries seen in their emergency department.[18] These numbers suggest that HPI injuries to the hand are relatively common, given the widespread use of pressure machinery.

HPI injuries often manifest as innocuous lesions on the fingertip of a patient's nondominant hand. Depending on the substance involved, these injuries may follow a benign clinical course (for air and clean water) or may be deceptively destructive and lead to soft-tissue necrosis and amputation (for grease and paint).

Proper triage and management of HPI injuries of the hand is imperative; the attending physician should recognize grease and paint injuries as surgical emergencies. A delay in treatment may result in inferior functional outcomes.[7, 29] In the digits, amputation rates are as high as 48%.[18, 7, 13]

Overall, HPI injuries result in significant impairment of function and reintegration into the work force, as well as aesthetic deformity. The most common long-term impairments include cold intolerance and hypersensitivity; however, grip strength, pinch, range of motion, and two-point discrimination are also affected.[30, 31, 32]

In cases of high-pressure injection (HPI) injury, a complete history should be obtained that includes the mechanism of injury, the nature of the materials injected, the timeline, and, if possible, the pressure of the machine at the time of injury.[33] Following a physical examination of the involved upper extremity that notes circulation in the digit and evaluates for compartment syndrome, further investigations, such as radiographs, may be helpful (see Workup).

Most frequently, the site of injury is a small puncture wound on the terminal segment of the index finger of the nondominant hand. The average patient is in their second decade of life.[13] The left hand is twice as likely to be damaged as the right hand.[18, 7, 34] A common explanation for this pattern is that inexperienced workers sometimes clean the end of a pressure gun with the tip of a finger. The injection can be painless, and the individual may continue to work[5, 33] ; however, these substances may be absorbed systemically and, within hours of injury, may result in fever, leukocytosis, and lymphadenitis.[16, 35]

The entrance site of an HPI injury is often deceptively small. The injected material acts as a projectile. The physician must look for possible exit sites as well.[12] This seemingly benign appearance may lead some clinicians to send the patient home with analgesia and reassurance.[36] Invariably, the patient returns to the hospital experiencing excruciating pain and unable to move the involved finger or hand.[37]

Depending on the volume and materials injected, the finger may be distended, swollen, and tender on palpation. If vessels in the involved digit have been thrombosed or compressed, the digit may be pale, anesthetic, or even ischemic.[13] In the case of an air-injection injury, associated crepitus and subcutaneous emphysema are possible.[11] Interestingly, Temple et al reported a case of pneumomediastinum after an injection injury to the hand.[38]

The severity of the injury is dependent on many factors, including the following[7, 39] :

• Type, toxicity, temperature, amount, and viscosity of the material injected
• Pressure of injection
• Involvement of synovial sheaths
• Anatomy and distensibility of the injection site
• Secondary infection
• Time interval between injury and surgery

With paint and other solvents, factors affecting dispersion of the material include the pressure of injection, the elasticity of tissue, and the viscosity of the substance itself.[35, 40] In addition, the site of penetration can influence the extent of injury.[39]

Kaufman performed experiments on cadaver hands in which he injected wax at 750 psi.[41] By varying the site of injection, he discovered that injection over the fibrous tendon sheath resulted in the injected materials collecting in the tissues around the sheath, rather than within the sheath itself. When the membranous portion of the sheath was involved, the result was filling of the sheath with the injected material.

The former situation resulted in extensive neurovascular damage, with spread of the substance through loose subcutaneous tissues and into fascial planes; the latter situation caused the injected material to travel long distances.[41] In some cases, the proximal elbow may be reached along the flexor tendon sheath. Injected material may also travel into the deep spaces of the hand.[17]

Infection following HPI injuries is seen more commonly in digits that have not been treated. Ischemia and necrotic tissue are a haven for the proliferation of microbes. Coincidentally, many materials injected have antimicrobial properties.[18, 11] Amputation rates for HPI injuries range from 16% to 55%.[18, 7, 13, 39, 42]

Complications associated with HPI injuries include the following:

• Infection
• Tenodesis
• Contracture
• Amputation
• Chronic pain
• Poor wound healing
• Abnormal scarring
• Limb dysfunction

A complete blood count (CBC) may show leukocytosis. Paint and paint solvents can cause an acute chemical reaction associated with fever.[5, 15]

Electrolyte abnormalities may occur with systemic absorption of some substances.[35]

Cultures of the wound may be collected when appropriate; these can help direct future management.[27]

Preoperative radiography can help delineate the extent of the tissue involved and facilitate the planning of incisions and debridement. On radiography, marked soft-tissue swelling is visible in the involved hand.

With radiopaque paint (especially lead-based paints) and grease (many commercial forms of grease have a lead component to prevent dissolution of lubrication), a random array of substances dispersed throughout the neurovascular bundles, synovial tendon sheaths, and lumbrical and interosseous muscles may be seen. Injected water may result in air densities on radiography. Some substances may be radiolucent.[5, 7, 14, 15]

Magnetic resonance imaging (MRI) can also show dispersion of injected materials in most circumstances; however, MRI is rarely required for assessing high-pressure injection (HPI) injuries.

Ultrasonography (US) has also been described as a potentially useful diagnostic tool for HPI injury to the hand.[43]

Following a thorough history, physical examination, and additional workup, tetanus prophylaxis, analgesia, and intravenous (IV) broad-spectrum antibiotic therapy should be administered.[27, 44]

In cases involving clean water and air injuries, good functional outcomes may be achieved with simple monitoring and conservative management. Such injuries should not be regarded as trivial, however.[45, 46]

High-pressure injection (HPI) injuries are considered surgical emergencies. Surgical consultation should be obtained quickly. Pai et al suggested that the time interval from injury to treatment is a determinant of the eventual result.[14]

As with other hand injuries, the extremity should be elevated and splinted. With HPI injuries, ice should not be used as a treatment, because it promotes vasoconstriction and further exacerbates poor circulation.[27]

Grease, paint, and other chemical injuries

After the procedures mentioned above, wide surgical decompression with timely debridement of necrotic tissue and foreign material is essential. The patient should be under general anesthesia. Affected digits should be opened by using a Brunner incision or midlateral incision through their entire length.[5, 16] If material is adherent to the neurovascular bundles and cannot be removed, it should be left in place.[33]  (See the images below.)

Intraoperatively, an Esmarch bandage should be avoided for hemostasis because the increased pressure spreads injected materials deeper into the subcutaneous tissues. The use of solvents other than isotonic sodium chloride solution for irrigation of a wound is not recommended.[41, 47] Furthermore, digital or local nerve blocks are contraindicated because they increase compartment pressures and are associated with poorer outcomes.[48]

Returning to the operating room for further irrigation and debridement is recommended, and the wound should be left open.[27]  The use of negative-pressure wound therapy (NPWT) for these injuries has been described.[49, 50, 51]

Amputation rates range from 16% to 55% for HPI injuries.[18, 7, 13] Some physicians advocate amputation if the damage is severe and paint was injected into a digit. If a digit is initially cool or poorly perfused, consider early amputation.[7, 17, 52]

Because inflammation plays a key role in the extent of damage following HPI injuries, adjunctive use of steroids has been suggested for severe cases. Bottoms described using dexamethasone as an adjunct.[53] Since then, others have concurred with the use of high-dose systemic corticosteroids for HPI injuries, despite the theoretically increased risk of sepsis resulting from immunosuppression.

Lewis et al recommended that "steroids should be used with antibiotic coverage in all cases, with the exception of grease gun injuries with minimal tissue extension." They argued that the organic chemicals usually injected generally do not support bacterial growth.[7]

Clean water and air injuries

In contrast to HPI injuries with materials such as paint, grease, and other solvents, clean water and air injuries may result in good functional outcomes with simple monitoring and conservative management.

In a 1991 report, Peters suggested that, because of the clean and relatively nonirritating nature of the water supply in the city where the injuries were reported, aggressive surgical debridement was not warranted[19] ; however, if water from a polluted source is involved, immediate surgical exploration is warranted. HPI injuries with air have also been described as having a benign course.[21]

With all HPI injuries, physiotherapy in the early postinjury period is imperative for a good functional outcome. (See the image below.) Along with this treatment, swelling has been found to respond well to the application of custom-made intermittent-pressure garments.[36]

A retrospective study of HPI injury to the hand by Chaput et al suggested that performing a systematic "second look" 48-72 hours after initial debridement surgery may be useful in that it permits additional washing or debridement and gives the surgeon the option of performing a more conservative initial procedure.[54]

Follow-up care should revolve around physical and occupational therapy, social work, and the psychosocial services team, in addition to close follow-up by the hand surgeon. Once maximum physical and occupational therapy and optimal splinting have been achieved by the patient, secondary surgical procedures should be considered. Capsulotomy, neurolysis, tenolysis, and soft-tissue reconstruction are all procedures that can be considered for restoring maximal function.[7]