High pressure injection injuries are rare, occurring in an average of 1 in 600 cases of hand trauma. Most are industry-related, and the preponderance are from grease guns, spray guns, and diesel injectors.  Other guns that reportedly cause such injuries include paint guns, concrete guns, and plastic injectors. Grease is the material most often injected, followed by paint.  Water, wax, paint thinner, cement, plastic, oil, and hydraulic fluid have also been reported.  Injection pressures are generally 2,000-10,000 psi. Because of these high pressures, the injected material may pass through gloves to cause the injury. Schoo et al reported that on average, patients were aged 35 years, with an age range of 16-65 years. 
The tamponade effect of the injected material results in ischemia. The ischemia and direct toxic effect of the injected substance appear to be responsible for the pathogenesis of the injury. Several factors determine the severity of the injury. The type and amount of injected material seem to be the most important factors determining the severity of the injury.  Other factors are the injection velocity (kinetic energy), time period between injection and treatment, and whether synovial sheaths have been penetrated. The flexor sheaths of the thumb and small finger extend into the radial and ulnar bursae, respectively, and may allow the injected material to reach the forearm. Paint thinner dissolves lipids even when not under high pressure, which causes tissue necrosis. Oil-based paints cause more injury than latex-based paints.
Other common injection sites are the long finger, thumb, and palm. The patient typically presents with an asymptomatic benign-appearing puncture wound at the injection site, and may delay seeking treatment. This may be accompanied by pallor, edema, and anesthesia, progressing to severe tenderness on palpation and gangrene if untreated, depending upon the chemical injected. Radiographic evaluation may reveal subcutaneous emphysema, paint, or both within the soft tissues.
Treatment & Management
Prompt recognition of the injury and aggressive early treatment are essential to avoid a poor outcome. [2, 3, 6] Tetanus toxoid should be administered if not up to date. The extensive amount of soft tissue necrosis resulting from the injury creates an environment that encourages the growth of bacteria. Prophylactic broad-spectrum antibiotics should therefore be administered. Pinto et al reported that 15 of 25 patients had infection confirmed by cultures, and growth of Staphylococcus epidermidis was noted in 10 of 25 patients.  Five injuries were polymicrobial.
All necrotic tissue and injected material should be debrided. Surgical treatment should ideally be carried out within 6-10 hours of the injury. The wound should be irrigated copiously with normal saline solution under general anesthesia or axillary block and then packed open. Preservation of vital structures such as nerves, vessels, and tendons that may be infiltrated can be conservative initially until they declare themselves. The packing can be removed in 24 hours, and the wound debrided again if necrotic tissue remains.
Fujitani et al described the case of a man with a dorsal hand wound caused by high-pressure oil injection who was successfully treated with negative-pressure wound therapy and application of a surgical glove. These were used to decrease swelling and manage wound exudate, with the investigators finding that swelling was reduced and that granulation tissue developed.  For more information on wound management, see Medscape's Wound Management Resource Center.
Despite an aggressive approach to treatment, amputation may be necessary in many patients. [2, 5] The incidence of amputation is higher in the digits than in the palm and is higher with paint and paint thinner injection injuries. Delay in treatment increases the risk of ankylosis and amputation. Amputation rates have been reported at 48%. 
The use of steroids in these injuries is controversial. Based on their own results, Lewis et al recommend the use of steroids with antibiotics in all patients except for those with grease gun injuries with minimal tissue extension.  Conversely, Jebson et al do not use steroids routinely,  whereas Pinto et al believe steroids are contraindicated because they depress the leukocyte response.  In a literature review of 435 cases over 37 years, Hogan and Ruland found that steroid administration did not impact the amputation rate or incidence of infection.  Range-of-motion exercises are begun early in the postoperative period to avoid a stiff digit or hand.
This aggressive approach can be modified for air and clean water injection injuries.  Air injection injuries may be treated by the administration of broad-spectrum intravenous antibiotics, splinting, and elevation.  Clean water injection injuries require superficial debridement (which can be performed under local anesthesia), broad-spectrum antibiotics, and elevation. In either situation, close observation is necessary, and modification to the aggressive surgical approach previously described is instituted if indicated. Reconstruction with skin grafts or local flaps may be necessary.
The final outcome must be guarded, especially when the injected material is a toxic chemical. Even if the digit survives, it usually results in a painful, stiff, atrophic digit. In a long-term follow-up prospective study, Wieder et al  found that the main complaints were cold intolerance, hypersensitivity, paresthesias, and constant pain. The stiff symptomatic digit may be more of a hindrance than of functional or aesthetic use. In such cases, amputation may be the best course of treatment. Patients with these injuries must be informed and prepared for a poor outcome, including eventual amputation of the involved digit.