High-pressure injection injuries were described as early as 1937 in the English-language literature by Rees,1 who reported a mechanic who sustained a 4,000-lb injection injury of fuel oil while testing the jet of a diesel engine. Despite a benign initial appearance of the involved digit with minimal bleeding at the distal tip, tissue necrosis led to amputation of the finger.
High-pressure injection injuries appear as innocuous punctate wounds, often in laborers using tools, who present with minimal pain resulting in misinterpretation of the severity of the injury (Figure 1, A). Emergent care is rendered but is often insufficient if it does not appreciate the hidden soft-tissue injury from the dissection of the foreign substance.
High-pressure guns are used to inject paint, grease, concrete, plastic, and fuel. Injection injuries are thankfully relatively rare. On average, 1 of 600 hand traumas are high-pressure injection injuries, and an average of 1 to 4 patients present to large surgical hand centers annually.2,3 Most commonly, the patient is a young male laborer involved in industrial cleaning, painting, lubricating, or fueling, and injuries are often sustained when the operator attempts to clean the nozzle with a finger or a cloth. The injury may occur anywhere along the upper extremity, but the nondominant hand is more commonly injured, with >50% of these injuries sustained in the index finger.4,5 The thumb is the second most commonly injured digit, followed by the palm or other regions of the hand.6
Damage to tissue from high-pressure injection is multifactorial, and the injury process may be divided into four primary components: (1) initial injury, (2) chemical irritation, (3) inflammation, and (4) secondary infection.
The force delivered through injection pressure is the precipitant cause of injury and can range from 3,000 to 10,000 psi, with velocities up to 400 mph; pressures can be even higher in the event of nozzle malfunction or blockage.6–8 The kinetic injury of a grease gun injury to the finger is calculated to be equivalent to that of a 1,000-kg (2,205-1b) weight falling from a height of 25 cm (9.8 in).9 Pressure of 100 psi (7 bar) is sufficient to cause skin penetration. Injuries are less severe when a small distance separates the injection source from the skin. Nevertheless, high-pressure jets can penetrate and infiltrate the subcutaneous tissues even without direct bodily contact.10,11
The force of the injection leads to tissue dissection along planes of least resistance, which tend to follow neurovascular bundles. If a fibrous tendon sheath is encountered, such as the stouter annular pulleys, the injected substance usually deflects and passes around the tendon sheath and underlying bone.12 However, if the tendon sheath is penetrated over the thinner, membranous cruciate pulleys that overlay the joints of the hand, the injected material may distend and destroy the tendon sheath itself. Injections into the mid palm usually result in limited material superficial to the palmar aponeurosis and more deposition in the deep palmar space, injuring bones, muscles, and vessels, with occasional throughand-through penetration into the dorsum of the hand.8
Vascular injury via compression, decreased perfusion pressure, venous hypertension, and capillary leaking initiates a cycle of swelling, edema, and further compression, much like a typical compartment syndrome. Caustic chemical reaction secondary to the injected material initiates a second hit with a violent inflammatory response magnifying the injury. This then cycles back as increased tissue pressures further compromise blood flow, triggering vasospasm, thrombosis, and ultimately ischemia.
Local Chemical Irritation
The most common fluids injected are paint, grease, hydraulic fluid, diesel fuel fluid, paint thinner, mud, toluene, molding plastic, paraffin, and cement. Many of these fluids are intrinsically cytotoxic, causing necrosis and inciting inflammatory responses. Paint and turpentine have been shown to be particularly injurious agents. The severe toxicity of paint has led some authors to recommend primary amputation as the initial treatment.13 In contrast, grease is less inflammatory than both paint and paint solvents. Grease contains 88% mineral oil, along with graphite and detergent, and it has a tendency to produce chronic granulomas rather than direct chemical irritation.14
The constituents of paint can be divided into three main categories: a solvent that evaporates shortly after it is applied, a pigment that provides color, and a transport vehicle or binder that acts as an adherent. Each of these constituents can damage tissue directly. The vehicle or binder may be an unsaturated or drying oil, or it may be a synthetic polymer such as an alkyd resin.
Water-based latex paints were introduced in the late 1940s, and they differ in solvent and vehicle compared with oil-based paints, with substantially lower rates of amputation following latex paint injection than following oil paint injection (6% and 58%, respectively).15 This difference is thought to be due to the reduced inflammatory potential of acrylic latex vehicles compared with the alkyd resins of oil-based paints.15 Turpentine and other paint thinners are a mixture of alkylated aromatic hydrocarbons designed to dissolve fats, and they cause lipid dissolution without a high-pressure etilogy.16,17
Water, air, and small quantities of veterinary vaccine have been reported to produce minimal damage and good outcomes even with nonsurgical management, which further highlights the impact of direct chemical irritation on treatment and outcomes.6,18–20
Systemic Inflammatory Response
Granulomatous changes have been observed following injection of oils, waxes, diesel oil, and turpentine into human and animal tissues.11,21 Postinjection sectioning of resected tissue shows substitution of normal connective tissue and fat, with whorls of proliferative granulation tissue and fibroblasts interspersed with macrophages containing vacuoles of the injected material. Polymorphonuclear leukocytes, lymphocytes, and plasma cells are present, as well.16 Gillespie et al15 showed that soya alkyd resins produce greater inflammatory responses and are more caustic than mineral spirits, turpentine, xylol, and acrylic latex.
Inoculation of the tissue can occur during injection, leading to secondary infection that is facilitated by an ischemic environment and tissue necrosis.15,22 However, some authors have found wound infection to be rare, which they attribute to the fact that the injected material is an organic chemical that does not support bacterial growth.7 Although wound cultures have not been consistently obtained for injection injuries, infection rates have ranged widely, from 1.6% to 60%.5,8,20,23 In the literature review performed by Hogan and Ruland,18 wound cultures were reported for 126 of 435 patients, of which 53 were positive (42%). Most of the infections were polymicrobial. Infection is fostered by necrotic tissue, and the reluctance to aggressively débride these injection injuries early may allow infection to take hold.
Initially, only small punctate lesions may be seen in the skin, with minimal or no pain. Such innocuous presentation of wounds without pain can lead to the patient’s delaying medical evaluation. Some patients have seen as many as seven doctors before the significance of the injury was recognized.6 The average time to physician evaluation averages nearly 9 hours. However, as swelling develops, pain and paresthesias occur with loss of perfusion, and the urgency of the clinical presentation becomes obvious as the finger becomes bloated, edematous, tense, pale, and cold.6
The emergency department physician must have a high index of suspicion and recognize the severity of this injury. In the presence of radiopaque materials, radiographs can be effective and helpful in determining the spread of injected material; however, some material may be radiolucent24 (Figures 1, B and C, and 2). Lucent areas may represent injected materials or air.25 The laboratory evaluation includes a white blood cell count, which is expected to be elevated within a few hours after injury and which may be accompanied by lymphadenitis and lymphangitis.13
Initial management includes elevation of the limb, tetanus prophylaxis if needed, systemic prophylactic antibiotics, and analgesia. Digital blocks should be avoided because they may add to swelling and vasospasm in a digit that is already at risk. Wounds should be left open, with no attempt to obtain primary closure in the emergency department setting, and ice is discouraged due to the need to optimize perfusion of the injected hand.2
Nonsurgical treatment is reserved only for injections of air, water, or chicken vaccine; these injuries may be managed expectantly.26 High-pressure water injuries require surgical decompression only when there are signs of compartment syndrome.27,28
Early and aggressive surgical débridement has been advocated since the initial reports of injection injuries. 1 Wide débridement of all involved tissues, decompression of tissue compartments, exploration and incision of tendon sheaths, removal of injected material, and saline irrigation are critical in the management of high-pressure injection injuries to the hand (Figures 1, D through F, and 3). Surgeons have long recognized the importance of early decompression and the surgical removal of foreign material to avoid ischemic gangrene and reduce fibrosis and scarring.13,29 Delayed surgery has been associated with increased incidence of morbidity and amputation.3,13,24
Some authors have found that the destruction caused by this type of injury precludes restoration of function and have recommended amputation as the primary treatment.30 However, open wound packing, repeat débridement, and delayed closure were advocated by Pinto et al,5 who reported only 4 amputations in 25 patients (84% salvage rate). They described a wide exposure with Bruner palmar digital incisions and complete débridement of all devitalized tissue and injected material, while preserving the neurovascular structures. Repeat débridement was performed at 24 to 72 hours as necessary. Alternatively, a midaxial incision may be used to achieve full exposure of the zone of injury; in some cases, this may be preferable to palmar flaps, which might already be compromised (Figure 2). Following thorough débridement and excision of injected material where possible, irrigation with normal saline or lactated Ringer solution may be used. Organic solvents are contraindicated because their use will lead to further inflammation and tissue damage.
Steroids and Anti-inflammatory Agents
The use of steroids in high-pressure injection injuries was documented as early as 1962, when Bottoms31 advocated the use of dexamethasone, stating that its anti-inflammatory properties are of significant value. However, recent literature indicates that steroid use in the setting of high-pressure injection injuries is controversial. Some authors advocate the routine use of steroids in all patients, but others voice concern that steroid suppression of the leukocyte response will increase the risk of superinfections.11,32–34
In a study on the effects of dexamethasone on albino rabbits injected with subdermal paint, Gillespie et al15 found less inflammation but no difference in bacterial count. Waters et al11 injected saline, toluene, and turpentine into guinea pigs. On histologic sectioning an intense acute inflammatory reaction was noted, with vascular congestion and marked infiltration of polymorphonuclear leukocytes. In the same article, the authors include a clinical case report of steroid use which did not prevent tissue necrosis and may have contributed to the development of an infection. In contrast, Kaufman30 reported a benefit from the non-steroidal anti-inflammatory drug oxyphenbutazone, although its effects were not dramatic. This drug has been removed from the formulary because of other toxicities.
In a review of 127 case reports, Schoo et al8 found variable regimens of steroid use. Overall, however, the authors were impressed by the anti-inflammatory effects of steroids. Their own regimen consisted of routine use of hydrocortisone sodium succinate 100 mg intravenously every 6 hours until swelling and erythema improved, followed by oral prednisone 25 mg twice daily, with further intravenous doses as necessary and a tapered protocol thereafter.
The use of prophylactic empiric antibiotic coverage in high-pressure injection injuries was examined by Mirzayan et al,35 who found wound cultures to be positive at initial débridement in 15 of 35 patients; 58% of isolates were gram-negative bacteria. They recommended the routine use of prophylactic antibiotics to cover both gram-positive and gram-negative organisms.
Despite the antibacterial properties intrinsic to the injected substances, animal studies by Gillespie et al15 demonstrated a net decrease in the ability of the host to fight infection. Thus, they recommended antibiotic prophylaxis for all patients. Hogan and Ruland18 found no correlation between infection and the rate of amputation, but they recommended prophylactic broad-spectrum intravenous antibiotics to minimize the deleterious effects of bacterial contamination of the wound.
Postoperative care varies but has included early motion, twice daily hand soaks in povidone-iodine or sterile water whirlpools, and intensive physical therapy with active range of motion. Some authors advocate splinting the fingers in a resting position on a volar slab with the metacarpophalangeal joints flexed to 90° and the interphalangeal joints fully extended.8
Outcomes vary depending on the location of the injury, the type and amount of material, and the time from injury to débridement.5,13,23 Greater injection pressure, the presence of secondary infection, and more distal site of infection have also been correlated with prognosis.3
Location of Injury and Volume
Finger injuries are significantly more likely to require amputation than are injuries to the thumb and palm, with some authors reporting a sixfold greater likelihood of amputation of the finger.18 The increased rate of finger amputation may be indicative of the surgeon’s bias toward amputating fingers rather than thumbs. Loss of opposition is associated with greater morbidity. In addition, whereas a thumb may be usable even with no or lesser mobility in the metacarpophalangeal and interphalangeal joints, grasp is limited in a palmar digit with a stiff proximal interphalangeal joint. However, one possible anatomic rationale for this difference is the larger potential volume of the palm and thumb, which may tolerate greater swelling without increasing the pressure and limiting its devitalizing effects. This is consistent with the finding that higher volumes of injected material have been associated with worse outcomes.23 In a cadaver study, the final location of injected material was found to be dependent on the angle of entry, depth of penetration, and resistance of the anatomic structures encountered.12 Injuries over the thinner parts of the flexor sheaths overlying the joints of the digit allow entry into the tendon sheaths, further dispersing both the injected material and the force of injury over a greater zone.
In the thumb and small finger, where the tendon sheaths are in continuity with the radial and ulnar bursae, injected material may travel into the forearm, sometimes as far proximal as the mediastinum. Temple et al36 reported the case of a laborer who suffered a high-pressure injection injury to the hypothenar region from an air pressure hose, resulting in pneumomediastinum. During the injury, the patient felt an immediate sensation that proceeded from his hand to his face and trunk. The path of the air traveled from the ulnar artery up to the brachiocephalic artery, along the neck to the common carotid, then back down the thorax along the aortic arch to the posterior mediastinum. In contrast, injected material in the index, long, and ring fingers may be trapped in the tendon sheath, leading to increased pressures in a confined space.
In a case series of 28 patients, severity was found to be related to injected material, involvement of the tendon sheath, and proximal spread of the injected substance.7 The authors advocated early amputation in digits with poor perfusion on presentation, although they did not clearly define their criteria for poor perfusion. The differences in infection rate and sheath involvement were not significantly different between the 22 patients who required amputation and the 6 who did not.
In their meta-analysis of 127 cases of high-pressure injection injuries of the hand, Schoo et al8 concluded that the most important factor in determining outcome was the material injected. This study, which was published in 1980, reported an overall amputation rate of 48%, with an amputation rate of 80% for turpentine injections, 58% for paint injections, and 20% for grease injuries. A review of the literature from 1966 to 2003 by Hogan and Ruland18 also demonstrated that the material injected is a significant factor in determining the risk of amputation. Amputation was required in >40% of cases involving organic solvents, including paint thinner, paint, diesel fuel, gasoline, jet fuel, and oil. Mirzayan et al35 retrospectively reviewed the records of 35 patients and correlated amputation rate with type of paint. The rate of amputation was significantly higher following injuries involving oil-based paints than following injuries involving water-based paints (100% and 0%, respectively).
In comparison, high-pressure injection of water and air is likely much less toxic than injection of other materials.37 Veterinary vaccine injection injuries are sometimes classified as high-pressure injection injuries, but many authors believe that they should be a separate category because the amount injected is limited, the pressure and velocity are low, and nonsurgical treatment is usually adequate.26
Time to Débridement
Delay to surgical débridement and irrigation has long been thought to be a critical factor in the morbidity of high-pressure injection injury. However, the exact timing from injury to treatment in the operating room has not been well documented.
In a recent meta-analysis of 166 high-pressure injection injuries with adequate reporting of the interval between injury and surgery, the authors found no significant difference in amputation rate overall.18 However, the subgroup of patients injected with the most inflammatory organic solvents demonstrated a significantly higher rate of amputation when surgery was delayed >6 hours than in those treated within 6 hours (58% and 38%, respectively). In 1967, Stark et al13 found the interval from injury to treatment to be correlated with amputation rate, with delays of >10 hours leading to higher rates of amputation.
It is unclear whether the intensity of the pressure during the time of injury may reliably correlate with prognostic markers such as amputation rate. Whereas Ramos et al38 reported that higher pressures were important in the wider distribution of material, other authors have not found pressure to be a consistent independent prognostic factor for amputation. In one series with a small patient cohort, pressures of >7,000 psi were associated with a 100% amputation rate.8 In contrast, the subsequent meta-analysis by Hogan and Ruland18 included two patients with documented pressures of >7,000 psi, neither of whom required amputation. Their study revealed a greater risk of amputation for injuries >1,000 psi, although they stated that there is no pressure threshold above which amputation is inevitable.
Clinical Functional Outcomes
The clinical outcomes of high-pressure injection injuries have largely been inferred from presumed morbidity of amputation, with heterogeneous amputation rates ranging from 16% to 80%.2,8,20,32 Pinto et al5 reported an amputation rate of 16% (4 of 25 patients) and attributed their relatively improved results to their consistent and extensive surgical approach. In their series, 64% of patients had “essentially normal” hand function at last follow-up, with final flexion lag of <2.5 cm in 16 patients.
Rarely have studies reported subjective or objective functional outcomes such as patient-reported outcome measures, range of motion, or strength. Christodoulou et al19 assessed 15 patients and found a nearly 20% decrease in grip, a 23% reduction in lateral pinch, and a 25% reduction in three-point pinch strength compared with the contralateral uninjured side. Four patients were unable to return to their occupations, and all but one patient had abnormal peripheral nerve function with decreased two-point discrimination. Wieder et al6 followed 23 patients for a mean of 1 year and reported significant loss of grip and pinch strength compared with the contralateral side (12% and 35%, respectively). They also found significant loss of range of motion compared with the contralateral side, with 30% loss of distal interphalangeal joint motion, 24% of proximal interphalangeal joint motion, and 8% of metacarpophalangeal motion. In decreasing frequency, patients reported cold intolerance, hypersensitivity, paresthesias, constant pain, and impairment of activities of daily living. Despite the lack of urgency for surgical débridement and irrigation of high-pressure injection injuries due to injection of water and air, long-term peripheral neurologic dysfunction and infection may occur; thus, these injuries still warrant close observation and management.36,39
High-pressure injection injuries to the hand can have devastating sequelae, leading to eventual amputation and poor functional outcomes. Strong clinical suspicion and prompt wide surgical débridement as needed are critical to the long-term preservation and restoration of function. Empiric broad-spectrum antibiotic coverage is also reasonable to prevent infection. Although the use of steroids cannot be fully recommended based on current evidence, our understanding of the pathophysiology of these injuries has provided some insight into the potential determinants of prognosis with steroid use.
Evidence-based Medicine: Levels of evidence are described in the table of contents. In this article, references 1-13, 15-19, 21-24, 26-37, and 39 are level IV studies. References 14, 20, and 25 are level V expert opinion.
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