Hand High Pressure Injury

Etiology

Injection injuries of the hand commonly occur when the patient is cleaning the nozzle of a high pressured spray gun, and the gun misfires. This can also happen when the patient's skin comes in contact with a leak in the high pressured piping. The force generated by many of the modern high-pressure cleaning tools can reach up to 10000 psi and spray the contents at 400 mph.[1] The magnitude of the force is equivalent to 1000 kg falling 25 cm onto the affected digit.[2] The pressure is so great that when the fluid penetrates the skin, the contents of the container get rapidly expelled into the operator's hand. In an instant, the substance can traverse the fascial planes and enter the proximal hand and forearm. This scenario can happen even without direct nozzle-to-skin contact with the high pressures system.

Epidemiology

High-pressure injection injuries account for approximately 1 of every 600 hand traumas presenting to the emergency department. The average trauma center may see 1 to 4 cases per year.[3] This injury occurs most commonly in young men who are working as industrial laborers and working closely with chemicals such as paint, lubrication, and fueling. The most common location for these entrance points is the patient's nondominant index finger.[4] Other commonly injured areas include the thumb and palm. However, these injuries can occur anywhere in the upper or lower extremities. 

The infection rates of high-pressure injection injuries are inconsistently reported in the literature.  This may be because cultures are not routinely obtained except for when signs of infections are exhibited. A review by Hogan et al. found that only 126 of 435 patients obtained wound cultures and 53 of these cultures were positive.  Of the patients with positive cultures in this review, 31% of patients required amputation of the affected limb.[5]  The incidence of amputation after any high-pressure injection injury has been reported in 30% - 40% of cases.[3][5]  From the data reported by Hogan et al., we can see that the amputation rate is similar between all patients with high-pressure injection injuries and the subgroup with a concomitant bacterial infection. 

Pathophysiology

To fully understand the treatment and prognosis, one must separate this injury into three phases. The first phase includes the direct mechanical impact of injection: pressure-induced neurovascular compromise, edema, and possible compartment syndrome. As mentioned above, thousands of pounds of pressure can be transmitted through the nozzle and directly into the patient's hand and upper extremity. The high-pressure injection not only tears ligaments, tendons, and neurovascular structure but also causes osseous lesions in rare cases. The injected material or air rapidly flows around the neurovascular bundle, following the path of least resistance. The injection can reach as proximally as the mediastinum.[6] This infiltration can lead to vascular compromise, edema, and acute compartment syndrome, making it an orthopedic emergency.

The second phase of high-pressure injection injury is the inflammatory sequela and chemical interaction of injected media with biologic substrates. Grease, paint, fuel, plastic, cement, and hydraulic fluid are examples of substances that may get injected into the extremity. Some of these materials, such as turpentine and other organic solvents, are extremely cytotoxic to the tissues and offer an overall poor prognosis. Oil-based paints have been reported to be more inflammatory than water-soluble acrylic-based paints. Turpentine and other paint thinners generally function by dissolving fats and can cause liquefaction of the tissues.[7] Grease and wax, on the other hand, do not create a robust inflammatory response but instead are overtime engulfed by granulation tissue, lymphocytes, macrophages, and polymorphonuclear leukocytes to form chronic granulomas surrounding the substance.[8] Air and water injections have a minimally inflammatory response, are absorbed over time, and usually bypass this phase of the injury.

The third phase of high-pressure injection injury is the secondary microbial infection due to direct bacterial inoculation, potentially intensified necrosis precipitated by phases 1 and 2. This phase is relatively rare, ranging from 1.6% to 60% of cases reported in the literature, and is often polymicrobial.[9] Almost half of the cultures taken at the time of initial debridement will be positive, and 58% will show gram-negative bacteria.[10] The necrosis of local tissue creates a medium on which bacteria can feed. On the other hand, many of the substances injected into the tissue do not directly support microbial growth.[9][11] Empiric broad-spectrum antibiotics also have a role in preventing concurrent infections and have been advocated by many authors.[10][5]

History and Physical

Patients often present to the emergency department directly from an industrial job site with complaints of swelling, pain, and a small puncture wound on the affected hand. The physical exam may appear benign and initially deceive the practitioner. Weider et al. found that patients see several different physicians with an average of 9 hours before obtaining the correct diagnosis.[12] During this time, the patient can develop neurovascular compromises, edema, and compartment syndrome. The key to diagnosis is a thorough history including the time of the injury, how the injury occurred, the tools or machines involved, the chemical in the injector and the pressure magnitude of the injection tool if available.

The patient's history should help guide the evaluation of the affected extremity, but a full secondary exam is also necessary. Dedicated evaluation of the forearm, elbow, upper arm, and axilla is imperative to assess the proximal extent of the injury. Range of motion, skin discoloration, pulses, and a complete neurologic examination are prudent. Serial examinations of the compartments are also crucial as compartment syndrome can occur hours after the injury as the second injury phase leads to further inflammation and edema.[9] 

Evaluation

In the emergency department, there are several tools to help reveal the diagnosis and extent of the injury. An elevated white blood cell count is expected a few hours after the injury but can be useful in tracking the progression of the inflammatory phase or any secondary infection. Plain radiographs will clearly define the extent of penetration if the substance injected is radiopaque. Radiolucent material will not be visible on plain radiographs but may appear as subcutaneous emphysema. CT and MRI can be helpful with an assessment of soft tissue damage but are usually not necessary.[9]

Treatment / Management

Upon presentation for medical treatment, the patient should receive a tetanus booster if needed and a prophylactic third-generation cephalosporin antibiotic for coverage of both gram-negative and gram-positive bacteria.[11][5] The limb should be elevated and irrigated to remove large debris and the wound left open to further drain. Avoid compressive dressings or closing the wound at this time, as these injuries tend to swell. Ice and digital blocks can reduce blood flow to the affected area, so avoid these as well.[8] The patient needs to be promptly transferred to a trauma center if the facility does not have a surgeon on call or operating room capabilities.

Steroids have been historically used to reduce inflammation, but currently, their use in the acute setting is controversial because of the theoretical increased risk of bacterial super-infection.[13][14] One review article demonstrated effective anti-inflammatory effects of steroid use and advocated the use of intravenous hydrocortisone sodium succinate 100mg every 6 hours, followed by a tapered regimen when the swelling improves.[15] More evidence is needed to delineate the potential risk of super-infection, and if the risk outweighs the anti-inflammatory benefits of this medication.(B3)

Early surgical debridement is critical for controlling the inflammatory response, decompressing the compartments, and reducing the risk of long-term morbidity.[16] Delays in surgery have been reported by several authors to have a higher incidence of morbidity and amputation.[9][16] Surgical debridement includes removal of all injected material, copious saline lavage, decompression of compartment, and exploration of tendon sheaths.[9] Repeat debridements are usually necessary within 48 to 72 hours increments until achieving the removal of all devitalized tissue and injected material. Exposure to the digits is possible with a Bruner-type incision or a mid-axial incision based on the surgeon's preference. Some authors recommend primary amputation as the initial treatment with severe injection injuries, including paint and turpentine.[16]  The decision to amputate should be based on physician clinical discretion and discussions with the patient.

Injection injuries with air, water, or high pressured veterinarian vaccines can be treated non-surgically with close observation.[17] Surgical decompression and debridement will be reserved for resultant compartment syndrome or secondary infection.[18]  It is imperative to frequently check compartments and have close follow-up after discharge to ensure no concomitant infection develops. The treating physician must also be clear with the patient that surgical debridement may still be required if non-operative treatment fails.(B3)

Differential Diagnosis

In the acute setting, the patient will most likely disclose that his hand was normal before the injury. The differential diagnosis in this scenario includes a crush injury to the hand, fractures of the hand and digits, compartment syndrome of the hand, or just a localized benign laceration of the digit or palm. If the patient presents to the emergency department several days after the initial injury, then one must also be suspicious for flexor tenosynovitis or other infections of the digits and hand.

Prognosis

The prognosis is dependent on the following factors: time to debridement, the material injected, extent, and location of soft tissue injury, and the magnitude of pressure the device released.   These four factors should be the surgeon's focus when managing a patient with a high-pressure injection injury.

There is not a consensus on how urgently one must perform the initial debridement. However, there have been several studies that demonstrate increased morbidity with delays to the operating room. Hogan et al. found that patients injected with organic solvents showed a higher rate of amputation when initial debridement took place after 6 hours.[5] Another study demonstrated an increased amputation rate with delays to the operating room of over 10 hours. Overall, all studies have shown that the sooner is better when dealing with cytotoxic material or faced with extensive soft tissue damage.

The material injected is arguably the most important factor when managing these patients and determining overall prognosis. Organic solvents such as turpentine, diesel fuel, and some forms of paint have detrimental effects on the surrounding soft tissue.   One study demonstrated that amputation was necessary for 80% of patients with turpentine injections but only 20% of patients with grease injections.[15] On the other hand, injections of air and water have a much better prognosis due to their non-cytotoxic properties and will usually not require operative debridement.

The location of the injection injury has also been shown to affect the risk of amputation. Hogan demonstrated a sixfold higher risk of amputation of the fingers compared to the palm and thumb.[5] The reason for this higher risk may be multifactorial and include the surgeon bias to preserve thumb opposition and also that the thumb and palm can inherently accommodate more volume of material than the fingers. Furthermore, injections into the thumb and small finger are more likely to involve the forearm because of their connection with the radial and ulnar bursae.  Injections of the index, long, and ring fingers usually remain confined to the tendon sheath where there is limited space.[9]

It is unclear if there is a pressure threshold to determine the absolute indication for surgical amputation. However, multiple studies have reported an increased risk of amputation with higher pressured injuries.[5][15] The higher pressure leads to more severe soft tissue trauma and the distribution of material.[19]

Complications

Complications of this injury can be a loss of range of motion or function of the extremity, associated bacterial infections, chronic granulomas, necrosis, or loss of limb. There are reports that chronic pain, hypersensitivities, paresthesias, motor dysfunction, and contractures can ensue.[3]   Prompt diagnosis, early intervention, and aggressive postoperative physical therapy can help limit these complications.